or cooling

Applied Energy 25 (1986) 97-163

The Total Energy Approach: Evolution of Combined Heat and Power for District Heating and/or Cooling R. F. B a b u s ' H a q , S. D. P r o b e r t a n d M. J. Shilston School of Mechanical Engineering, Cranfield Institute of Technology, Bedford MK43 0AL (Great Britain)

S UMMA R Y Combined heat and power (CHP) generation is not a new concept, but it provides an elegant solution to some of our present fuel problems, offering, as it does, 80% or greater efficiency. However, Great Britain lags behind other European countries with respect to the rate of introduction of CHP together with district heating and/or cooling (DHC) systems. Reviews of(i) the historical development of the designs of DHC pipelines, from insulated pipes m air-filled ducts to the modern preinsulated pipes buried in the ground, and (ii) sources of energy as well as developments in metering and control, for CHP-DHC systems, are presented. The cost effectiveness of each CHP-DHC system is highly sensitive to unit fuel prices, current discount rate, as well as the capital cost incurred. In the best interests of Britain, major governmental investments are non, needed urgently in order to encourage the wider adoption of these systems.

ABBREVIATIONS British Gas Corporation Central Electricity Generating Board Combined heat and power District cooling District heating District heating and/or cooling Electricity Supply Industry 97 Applied Energy 0306-2619/86/$03"50 ~ Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain

BGC CEGB CHP DC DH DHC ESI

R. F. iBabus'Haq, S. D. Probert, M. J. Shilston

98

GLC hp IDHA lEA ITOC

lfg MEB NCB OAP RoR SNG

Greater London Council Horse power (1 hp = 745.7W) International District Heating Association International Energy Agency Intermediate take-off condensing turbines Land-fill gas Midlands Electricity Board National Coal Board Old age pensioner Rate of return (on capital invested) Synthetic natural gas

GLOSSARY Cogeneration:

Condensing boiler:

Culm: Discount rate:

Fuel cell: Heliostat:

Land-fill gas:

Implies the production of shaft power plus heat, both of which are usefully employed. The shaft power is usually transformed into electricity, i.e. production in parallel with that for the national grid supply. A boiler with the ability to condense water vapour from the combustion products by reducing the flue-gas temperature to below the dew point. Coal dust, especially of anthracite. The rate of interest used in discounting costs and benefits with respect to assessing proposed and actual investments. A galvanic cell in which oxidation of a fuel is utilised to produce electricity. A device consisting of a mirror which turns, so as to always reflect the insolation from the Sun, in a fixed preselected direction. A combustible mixture of gases ( ~ 50%-60% CH4; 35%-40% CO2; < 5 % - 1 0 % N 2 and 0 2 < 0.2%) resulting from the decomposition of buried domestic, municipal and/or industrial refuse. Its gross calorific value is usually 20 ___2 MJ/m 3.

Combined heat and power

Load factor: Martin grate: Operational pay-back period:

Premium fuel:

Rate of return: Syncrude: VKW grate:

99

The average load divided by the designed m a x i m u m capacity of the installed system. Oscillating-step grate facilitating the downward discharge of the combustible material. Capital cost of the system divided by the average savings achieved per hour by the installation of that system. It depends upon the number of operating hours per year as well as the relative cost of the rival fuels (natural gas or electricity). A high-quality primary fossil fuel: electricity can be considered as the premium fuel because it has an exergy of unity. Annual percentage financial return on the capital invested. Synthetic crude oil derived from coal or oil shale. In this grate, the downward movement of the combustible material is encouraged by the use of rollers.

D I S T R I C T H E A T I N G A N D / O R C O O L I N G SYSTEMS In these, a heated or cooled fluid (usually water) is distributed from a central source to residential, commercial or industrial consumers, usually in high intensity of d e m a n d areas, such as well-occupied buildings in which comfortable conditions need to be maintained. The central source may be either a chiller, 1 a boiler, 2 a refuse incinerator, 3 a geothermal source, 4 solar energy, 5 or waste-heat, e.g. as a by-product of electricity generation, 6 This latter approach is known generally as the combined heat andpower (CHP), or cogeneration, procedure (see Fig. 1): it usually represents a much more effective use of fuel as well as a low-risk option (both with respect to accidents and financial returns) for the heating of cities. The world's worst nuclear-power accident at Chernobyl (USSR) in April, 1986, will probably accelerate the more rapid and widespread adoption of CHP. The extent of the delivery zone alone should not be regarded as the sole criterion for assessing the economic feasibilities of prospective

100

R. F. Babus'Haq, S. D. Probert, M. J. Shilston SEPARATEHEATAND POWEROENERATION FUEL IN

FUELIN

I TRADITIONALL

ELEETRIC WER

THERMAL POWER

W ' ASTE POWER (IN THEFORMOFA HEATCURRENT)

WASTE POWER (IN THE FORMOFA HEATCURRENT)

COMBINEDHEATAND POWERPRODUCTION FUELIN

ELECTRIC POWER

THERMAL POWER

WASTE POWER (IN THEFORMOFHEAT CURRENT)

Fig. I.

Alternative methods of producing electricity and thermal power: for the numbers given as typical percentages, it can be seen that the CHP option, from an energy-thrift viewpoint, is likely to be the preferred method.

district-heating or district-cooling schemes. The most important factor dictating the demand for heat (or 'cold') is the ambient environmental temperature. C H P - D H C is least attractive economically for a greenfield site despite the many claims by 'experts' to the contrary. It should be ~ealised that, before starting on an ambitious C H P - D H C scheme, one needs a large assured heat load ( > 2 0 M W / k m 2) from already committed customers. Nevertheless, it is the ratio of the price paid for satisfying the annual thermal load to the cost of laying the DHC pipelines which primarily dictates the feasibility of such a scheme. However, a small project can be attractive financially if a sufficiently large heating or cooling demand exists, whereas it will probably be uneconomic to serve a large area having only low demands. 7

Combined heat and power

101

Relatively small-scale CHP systems have been installed for hotels, hospitals, group-residential accommodation, prisons, swimming pools as well as leisure centres, with pay-back periods of ~ 3 years being achieved (e.g. at the White Hart Hotel, Exeter, and the Royal Infirmary, Bristol, Great Britain). Such CHP systems are usually far more cost effective and less troublesome than heat pumps. Guidelines with respect to the installation of CHP systems have been issued by the Electricity Council (Document G 59) and the BGC (Document IM 17).

The history of C H P - D H C A sufficient supply of heat is a basic human necessity. The Romans employed piped heating systems for dwellings as well as baths, whereas mediaeval castles had vast chimney-less fireplaces, in which piles of logs were burned. 8 Sir William Cook, in 1745, used pipes for conveying steam to heat his home in Manchester, Great Britain: he also attempted to warm a group of buildings in this same way from a single source of heat. 9 During 1748, Benjamin Franklin installed an underground ironstove furnace to heat a row of houses, via a small thermo-syphon DH scheme, in Philadelphia, USA. 1° Throughout the eighteenth century, in many places, men were applying their wits, skills and hands to devise and improve heating services. For instance, Thomas Newcomen, a British mechanic, in 1712, took what, in retrospect, has been called 'one of the longest steps in history' when he improved significantly the primitive, steam-driven, water-lifting device invented by Thomas Savery. 1° James Watt, in 1774, heated his upstairs workroom with heat derived from a basement boiler. Subsequently, in 1791, Hoyle of Halifax, Great Britain, obtained a patent for a system involving pipes filled with steam to heat a building. In 1816, Jacob Perkins and the Marquis de Chambonne employed hot water as the heat-distribution medium for a system they introduced in England. 1° However, Birdsill Holly, in 1877, deserves the credit for being the first person to put district heating on a successful commercial basis. 9 By 1879, Holly's Corporation had nearly three miles of mains heating pipelines in service, and, by 1880, the steam service had been extended to include several factories. ~ In 1879, Wallace D. Andrews founded the Steam Heating and Power

102

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

Co. in New York, USA, and, by 1882, this DH system had been expanded to be the world's largest and remained so for many years. A DH scheme supplying hot water was installed in Toledo, Ohio, USA, in 1896.12 That at Dresden, in Germany, became operational in 1900 and was the first DH system worthy of that name in Europe, although it was not a commercial project. However, there are many examples, from around the turn of the century, whereby buildings were heated from a single central boiler or where one building received heat distributed via a pipe buried in the ground--the Sabbatsberg Hospital in Stockholm, Sweden, in 1878; the Technical University of Berlin, Germany, in 1884; the town hall in Hamburg, Germany, which was connected to the Poststi'asse electrical station, in 1893; the Shoreditch refuse-incineration plant in London, Great Britain, in 1896, which had been initiated by Lord Kelvin; the Sahlgrenska Hospital in Gothenburg, Sweden, in 1898; and a hospital in Fredriksberg (a suburb of Copenhagen), Denmark, supplied by heat from a refuse-incineration plant in 1903. These systems are not normally considered as ordinary DH systems because the activities were not handled by a company whose main interest was district heating. 12 Simultaneously, the opportunities for CHP were also evolving: many small electric companies were set up to satisfy the eager appetite for electric supplies, following Edison's pioneering efforts at the end of the 1870s. Electric generators, driven by reciprocating steam-engines, were employed in plants sited in high population-density urban areas. The waste steam was not always exhausted to the atmosphere but used profitably. However, as significant economies of scale began to be achieved in the generation of electricity during the early part of the twentieth century, this 'total-energy' approach was abandoned, and so, at that time, district heating failed to gain in popularity. By 1909, only about 150 district-heating systems existed in the United States, and many of these operated on low profit-margins.~ ~ In Europe, the Hamburg system was followed by those for the Fernheizanlage Humboldstrasse in Kiel in 1922, Barman in 1922, Braunschweig in 1924, Leipzig in 1925, and Charlottenburg (Berlin) in 1927. Outside Germany, DH systems were started at Copenhagen, Denmark, in 1925; Utrecht, the Netherlands, in 1927; Paris, France, in 1930; and Zurich, Switzerland, in 1933. In the USSR the general implementation of cogeneration was recommended in Lenin's 1920 (i.e. the GOELRO) plan for electrification.

103

Combined heat and power

The first heat supplied from the Leningrad DH system was delivered during 1924 to a house on the embankment of the river Fontanka. In Moscow, DH distribution started in 1928" the Teploset Mosenergo was organised in 1931 and is today (1986) responsible for the world's largest DH system.12 Significant numbers of district-heating installations were not installed in Europe until after World War Two. Since then, mainly in Northern European countries, the USSR (the largest user of district heating in the world) and the other communist bloc, centralisedplanning countries, DH systems have become common. This was feasible and economic there because of the building of large (but compact) housing blocks: a policy which is favoured in many of these countries. For instance, in East Germany, DH networks supply hot water to 1.3 x l 0 6 residential flats (i.e. for about one-third of the total population). ~3 District heating in the other European countries has grown in popularity less rapidly because of low unit fuel costs, or the abundance of available fossil fuels. The chief inhibitions to the introduction of a DH system are the disruptions (e.g. of streets) that ensue during installation, and the associated high costs. Thus it was far sighted of the burghers of Rotterdam, The Netherlands (whose city centre was destroyed in 1940) to install an extensive DH system soon after the end of the 1939/45 war. Since then, in the USA, DH has been adopted frequently for college/university campuses, and for commercial multipurpose buildings. 14 Due to the 1973/1974 and 1979/1980 oil crises, and the political reluctance in the U K to permit nuclear power to be substituted, in a large way, for fossil fuels, the problem of energy thrift has, intermittently during the last decade, been regarded as urgent. Thus the concepts of DH, DC and CHP have become increasingly advocated as desirable in energy-thrift written communications and speeches by many planners, architects, engineers and even some politicians.15- 28 For instance, DH is included in the US Government's energy-conservation programme, and is now regularly commended in the British Parliament as an important means of reducing the national rate of fuel consumption. 29 32 Yet too few of the good intentions have been translated into positive actions in the UK. However, in France, laws have been adopted to encourage the use of CHP systems. 33 The Czechoslovakian State has published, in 1986, a plan for the modification of fourteen power stations, twelve of which are in Bohemia and Moravia, and two in Slovakia. It is predicted that this programme will cost £794 x l 0 6, but -

104

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

will save about 12.5 x 10 6 tonnes of lignite annually, i.e. one-fifth of the present rate of consumption. In the USA, new systems (e.g. C H P / D H C systems in Trenton, New Jersey and St. Paul, Minnesota) have recently been brought into service as a direct consequence of the US Department of Energy and US Department of Housing and Urban Development grants and technical support. 34-37 DC is not so widely implemented as DH, but it is being advocated and adopted slowly as a financially attractive process. One of the biggest systems in the world, outside Japan, is located in Hartford, Connecticut, USA: it was, in 1962, the first utility-operated district plant to market both chilled water and steam. Nevertheless, fewer than sixty urban systems are in current use in the USA. ~4 Japan has been somewhat of a pioneer in the field of DC: even in 1981, it was estimated that about ninety different systems were in operation there. However, DC systems are already operating, or are being installed, in several cities of Europe and the USSR. In the UK, DC is employed at the Heathrow International Airport complex, London, and also at a major shopping precinct in Chatham, Kent. 3a'39

TECHNICAL CONSIDERATIONS Basic features

D H C systems usually consist of three major components. 1~ The first is the production plant (i.e. the energy-release system) which provides either steam, hot water or chilled water. CHP is the production of heat as well as useful shaft power. However, it should be noted that CHP does not necessarily result in the generation of electricity (see Fig. 1): for instance, the shaft power released can be used directly to drive machinery. In a swimming pool, the water could be heated via the CHP system which could also simultaneously drive the pumps for circulating the water through the filters. The direct-drive option is used for running the air compressor in the Bird's Eye frozen-pea factory at Grimsby, Great Britain, as well as for computer suites, in the chemical industry, and for drying materials. Recent: thermodynamic-availability studies, 4° applied to the processes involved in CHP plant, consider the optimal amounts of mechanical power and heat current as end-products. CHP can involve topping

Combined heat and power

105

cycles or bottoming cycles. In the more commonly employed topping cycle, the generation of electricity is the prime aim, the exhaust-stream heat being made available at various pressures and temperatures. In the bottoming cycle, heat is produced for process use, and relatively high temperature and high pressure waste heat is then recovered and used to generate electricity. 41'42 It must be remembered that, for CHP systems, it is the output temperature which primarily dictates the cost of the heat. Also, if the water returns via the DH system to the CHP plant at too high a temperature to achieve the necessary cooling of the engine, then the efficiency of the system deteriorates significantly. Usually it is possible to use all the electricity generated profitably, but not so all the heat output. Therefore, it is preferable to size the CHP plant to satisfy the minimum demand for electricity, which will probably occur during the summer. Then it is likely to be commercially viable to have additional boilers available in order to supplement the heat supply from the CHP system during periods of very cold weather. The second component in a C H P - D H C system is the transmission (i.e. the distribution) network of pipes, which convey the heated or cooled fluid from the production plant to the consumers. Frequently nowadays, high-pressure water (not steam) at --~ 120°C is sent out through the DH mains pipelines, and is subsequently returned to the power station at ,~ 70°C. However, for DC systems, the chilled water is initially at ,-~4°C and returns at ,~ 13°C. DHC well-insulated linenetworks are expensive: they constitute at least 50% of the total capital costs of the D H C supply systems. The use of flexible pre-insulated pipelines (e.g. Flexalen from C M R Systems, London, Great Britain), simplified fittings and small, easily installed measuring instruments can reduce the costs of distribution systems significantly. 43 -45 Several design studies, as well as behavioural tests, have been undertaken, and computer program packages for predicting the performances of proposed C H P DHC distribution networks have been devised. 46- 91 Much time, effort and money have been devoted to producing reliable, cheap, well thermally insulated underground pipelines, but, unfortunately, to date, these endeavours have not been completely s u c c e s s f u l . 62 However, the pre-insulated pipe manufacturers would contest this assertion. C H P - D H C pipeline networks are usually either buried or laid in trenches beneath ground level. Nevertheless, in some cases, they are installed above the ground. 64- 66.80 Some of the available DH configurations are shown schematically in Figs 2 to 12. Historically the most

106

R. F. Babus'Haq, S. D. Probert, M, J. Shilston

EARTH-------,

CONCRETE LID

°

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AIR-FILLED - - CAVITY

INSULANT

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Fig. 2. Schematic cross-section through a concrete trench housing the supply and return pipelines. 62 Great care is necessary in sealing the top of a duct to prevent the ingress of water.

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Fig. 3.

Schematic cross-section through a half-round clay-tile system for the supply and return pipelines. 62

Combined heat and power

107

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Fig. 4. Schematic cross-section through an insulating-concrete encasement for the supply and return pipelines. 62 This arrangement originated in Denmark, but is now only rarely installed.

EARTH

- -

CONCRETE COVER METAL LATH STEAM Pt CONDENSA RETURN PIPE

STEAM SUPPLY PIPE

RE-INFORC CONCRETE SUPPORT FOR PIPE. c

CONCRETE BASE

Fig. 5.

DRAINAGE HOLE (>1 IN ~,0 SLOPE

Schematic cross-section through a concrete conduit system for the supply and return pipelines. 62

108

R. F. .Babus'Haq, S. D. Probert, M. J. Shilston

~IYLENE OUTER

~ER PIPE

Fig. 6. Schematic cross-section through a sealed pre-insulated pipeline (with a corrosive resistant outer casing) for a DH system. 62 Such prefabricated pipes can be welded together on site. The polyurethane can be joined effectively in situ relatively easily, so the possibility of the ingress of water is almost negligible.

frequently recommended and widely adopted design (e.g. in the U K and East Germany) was that of two thermally insulated pipelines, located side-by-side in an atmospheric-pressure, air-filled, rectangular trench-see Fig. 13.13'37°92 (It is much more difficult to thermally insulate a pipe in situ than it would be before it is put in the trench.) In the event of such a trench becoming flooded (which occurs intermittently in Britain, because of its maritime climate, relative high humidities, water dribbling down the pipe hangers during heavy rainstorms, and often high watertable levels), drainage and evaporation from around the pipelines can then ensue. Otherwise, if the insulant is allowed to remain in intimate physical contact with damp ground, the moisture will reduce the insularft's effectiveness and mechanical strength (sometimes permanently), as well as promote corrosion of the underlying steel pipelines, which are supposedly being protected by the insulant. However, recent design studies recommended that it is preferable to place the two pipelines one-above-the-other in the air-filled trench, the hotter pipe being the upper member. By employing such a configuration, an increase

POLYUI FOAM INSULI

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Fig. 7.

Schematic representations of pre-insulated supply and return pipelines, in a concrete duct, for a DH system. 6a

I VERTICALLY i ~ YURETHANE~

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COOLER-WATER

[/

~ " ~

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Fig. 8. Schematic representation of a 'hot-aboveocooler' pipe arrangement contained in a foamed-insulant cylinder for a DH system. 64 (The same configuration could be used for a DC network, the warmer pipe again being uppermost.)

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

110

VERICALLY UPWARDS

\\\\ STEELORCOPPERWATER-PP I E . . . . . . . . . -" AIR" SPACE . . . . . . . . . . . . . . . . . . . . . . . . . STEEL CONDUIT . . . . . . . . . . . . . . . . . . . . . . . . . .

\x ~

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COATING TO STEEL CONDUIT . . . . . . . . . . . . . . . . . . . . . . .

Fig. 9.

Schematic cross-section through an air-filled steel conduit with hot-abovecooler pre-insulated pipelines.65

S WATER RETURN7

PIPE

/

/

/

~

CASING

FOAMEDINSULANT

WATER SUPPLY/

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I I VERTICALLY UPWARDS Fig. IO. Schematiccross-secUon through supply and return pipelinescontained in a Foamed-insulant filled duct.66

Combined heat and power

,••v•

FOAMED POLYURETHANE INSULANT WATER RETURN PIPE

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z / V /

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Fig. 11.

Schematic cross-section through a roof-top assembly of pre-insulated supply and return pipelines. 65

of ,--3% in the overall thermal insulation of the system was achieved compared with that for the side-by-side arrangement of the same pipelines. Moreover, this design permits the use of narrower (and hence cheaper to excavate) trenches. 46-51'55 The hotter-above-cooler configuration (which should be adopted for both DH and DC systems) is now employed in several DH systems in Europe, e.g. the cities of Rotterdam, the Netherlands, and Rostock, East Germany; as well as for the Byker wall housing development in Newcastle; the Royal hospital in Shrewsbury; and a housing estate in Oldham, Great Britain. Current practice increasingly favours the use of steel mains pipes (preinsulated with polyurethane foam)--see Fig. 6---buried directly in the ground (rather than in air-filled trenches as shown in Figs 2, 3, 7 and 9). These pre-insulated buried systems have an expected minimum lifetime of 30 years for service at up to 120°C. Such pipes have been used extensively in West Germany, Sweden, Finland and the USA. The associated smaller excavations are cheaper. Sometimes such preinsulated pipes are surrounded by pebbles rather than earth, so achieving

112

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

WATER RETURN~

jf ~

'

/

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POLYURETHANE~ i ~ - ' ~ : ~ - - ' ~ ~

WA I

,,~JLANT

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Fig. 12. Schematic cross-section through an above-ground arrangement of pre-insulated supply and return pipelines with other facilities.6~ some degree of drainage, but an optimal design for this system (e.g. optimal pebble size, and most suitable location of the warmer pipe above the cooler pipe) has not been achieved as yet. The use of powders or loose-fill water transmitting materials for thermally insulating pipes which are to be used below ground level should be avoided because of the likelihood of water penetration. Figures 2 to 5 are drawn with the supply and return pipes of different bores. This is because s t e a m is supplied, whereas condensate water is returned. However, in the case of hot water being distributed and returned, the bores of these pipes would be identical because approximately the same volumes would be conveyed per second in both. The use of steam for heat distribution is becoming less popular because of

Combined heat and power

113

Fig. 13. Traditional practice, i.e. the side-by-side arrangement of the supply and return thermally insulated DH pipelines in an air-filled rectangular trench in the UK as sccn during repair in 1985.

114

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

the large pressure drops necessary along the pipelines, condensate problems, and the frequent maintenance of 'steam' traps incurred, as well as the difficulties ensuing from the inferior quality of the water employed. Therefore, for large DH systems in Europe, the heat distribution is now usually accomplished via hot water. The third component of a C H P - D H C system is the 'in-building' equipment. If steam is supplied by the DH system, it may be (i) employed directly for heating; (ii) conveyed through a pressure-reducing station for use in either a low-pressure steam space-heating system, a domestic water-heating system or an absorption-.cycle refrigerating system; or (iii) passed through a steam-to-water heat exchanger in buildings employing hot-water heating systems, l~ However, in most hot-water systems, water-to-water heat exchangers a r e u s e d . 93 Heat-distribution systems, developed in conjunction with CHP, will differ from existing group-heating schemes in both technical and marketing features. C H P - D H will serve existing properties, which already have their own heating systems and will probably be of different suitabilities for connection to a DH network. On the other hand, CHPDH schemes will be installed progressively and on a larger scale than existing group-heating systems--potentially these could be city-wide. Moreover, the cost of CHP heat depends upon the temperature at which it is produced, and its unit fuel cost is relatively low. However, the capital costs of C H P - D H C are high compared with the present alternative heating systems. Thus government inducements would appear to be desirable.

Types of CHP-DHC systems DHC systems may be classified according to the heat-transfer medium employed:l i

(a) Steam types (1) Heat-only systems, for which the boiler supplies only steam at the required design pressure to the distribution network. 37 (2) CHP, cogeneration, or dual-energy use systems, in which the available steam is a by-product of the electricity-generation process. Back-pressure steam turbines, intermediate take-off condensing (ITOC) turbines, gas-turbines and diesel-engine driven generators are employed in such systems. 42'94- ~oo

Combined heat and power

1! 5

(3) Purcfiase systems, where steam surplus to the supply demands imposed on other boiler plants, including refuse-incineration systems, is bought for district-heating distribution. 1°1'1°2

(b) Hot-water types (1) Hot water supplied from boilers at central locations in the system. 1o3 (2) Hybrid systems, where there is a basic steam system which develops on-site hot water for a localised hot-water network.~°4 (3) CHP, cogeneration, or dual-energy use, where hot water is produced as part of an electricity-generation process. 1°5 (4) Hot water obtained from geothermal sources. 1°6- los (5) Preheated water arising from refuse-burning operations; hot water extracted from an industrial waste-heat system (e.g. cooling water from a power station or a heating system return-pipe); or sea or lake water upgraded with respect to temperature, by means of heat pumps. ~°9-116 (c) Chilled-water types (1) Chilled water produced at a central plant by steam-driven equipment. ~1 (2) Electrically-driven equipment producing chilled water at a central plant. 1is (3) Absorption refrigerators (e.g. operating on a lithium bromide/ water mixture). 11.119 (4) Natural cold-water direct-cooling systems, using fresh water sources such as lakes, reservoirs, rivers, ice ponds and groundwater.a2.~20

SOURCES OF E N E R G Y FOR C H P - D H C SCHEMES Wood Wood has a relatively low calorific value compared with those for bituminous coal and oil. Because cellulose (wood being its chief source) is the most abundant natural material on Earth (as well as the most abundant chemical species in municipal refuse), and we are not dependent upon it for food supplies, it is the logical material choice for conversion

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to fuels. Thus several different economic procedures have been proposed in order to maximise the efficiency of the conversion of wood to oil (which should have improved physical properties as a fuel compared with those of wood). 121'122 Until the latter part of the nineteenth century, when it was replaced by coal, wood was the principal fuel used in the world for providing heat. However (except for a few regions, e.g. in Finland, where wood wastes still represent a large contribution), it is no longer a major fuel source due to (i) forest depletion and (ii) the increasing demand for wood as lumber and for the production of paper, plywood, rayon and other products. Forest lands now comprise some 9.6 x 10 9 acres, which is equivalent to about 27% of the world's land area. The productive forest area is estimated to be 6.4 x 10 9 acres, some 4.0 x 109 acres of which being accessible economically.ll Peat It is desirable to avoid polluting the environment, and so one major advantage of peat as a fuel is its low sulphur content. However, the combustion of peat involves many difficulties and risks. The problems of operating peat-fuelled DH systems are due mainly to the impurities which occur in the peat, variations of its calorific value, and corrosion of the combustion system's components. Ligneous matter, stones, pieces of metal, large lumps of peat and (even ice in winter), hamper the peat's reception and handling. Their removal at the bog would reduce the combustion plant construction costs and raise the unit price of peat appropriately, but would probably be the preferred option. Mechanical handling and transportation of the peat is difficult: when used in silos, it is liable to arching, thereby possibly obstructing the feed mechanisms. The sand in the peat causes wear of the conveyors, and of the combustion and ash-removal equipment. Dry peat is extremely dusty, and so the risks of explosion (and fires) when using it in this state are high. For peat-fuelled DH schemes to be feasible commercially, peat must be cheap. However, investment costs in the combuster equipment required are higher when peat, rather than when oil or coal, is used as the fuel because the calorific value of peat per unit volume is lower and its handling problems are greater. The unit price of peat must therefore be correspondingly smaller for it to be a commercial proposition as a fuel for DH systems. The competitiveness of peat is being improved

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continuously by technological development and standardisation of the DH plants using it. Finland now (in 1985) has some fifty peat-fuelled heat-supply stations, with a total capability of delivering 230 MW, as well as three peatfuelled CHP plants: the combined thermal-power output of these three plants is 259 MW, together with 256 MW of electricity. In addition, a few peat-burning industrial plants also supply DH alone. 123'124 Coal Although the price of coal (in £ per kWh which is capable of being released) is generally lower than those for the other fossil fuels, and the UK national reserves of coal are substantially greater, coal consumption in the UK is unlikely to increase significantly during the next decade because of several technological reasons, as well as some political ones. For direct-combustion applications, coal is usually less convenient (and dirtier) to use, particularly with regard to storage and handling, than oil or natural gas. Also, combustion equipment, fired by coal, is often significantly more expensive than commensurate systems using premium fuels, and this offsets the unit-fuel price advantage of coal. In the case of electric-power generation, coal is facing increasing competition from non-fossil energy sources; namely, nuclear and the 'alternative' (e.g. hydro, wind, solar, tidal and even wave) powers. Furthermore, environmental protection standards are becoming increasingly more stringent: coal-fired power stations being under attack due to the generation of acid-rain. Hence the unit cost of coal divided by the retail price index will inevitably rise. Technological improvements are required if coal is to make a significantly greater contribution to future UK annual energy supplies. Many of the traditional demands for coal (e.g. railways or domestic open-fires) have almost completely declined and are unlikely to be reinstated. Therefore, it is desirable to develop new markets, such as those in CHP-DHC, where the economies of scale favour the use of coal. The adoption of pneumatic coal-and-ash handling in a coal-fired CHP station at the Boots Co. Plc., Beeston, England, has resulted in a system that is both relatively clean in operation and low in manpower requirements. 125.126 Nevertheless, in Great Britain, political leadership and incentives are overdue with respect to CHP-DH. The government provides financial grants to private industries to convert their plants

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from oil-firing to coal-firing systems, but the take-up of the scheme has been disappointing. Whereas in France and West Germany, coal-fired C H P - D H C plants benefit specifically from government sponsored fiscal advantages and inducements arising out of national desires to substitute the use of coal for that of oil, because the coal reserves are so much greater than those of oil. aa'127 In the USA, more and more industries that produce their own power will be relying on solid fuel, such as coal (which is readily available), instead of oil or gas. 128

Coal-derived synthetic fuels The conversion of most types of coal (except anthracite) is directed primarily at producing synthetic low-sulphur, low-ash, liquid or solid fuels. Coal liquefaction shows promise for making commercially syncrude (which is suitable for use as a refinery feedstock) as well as petrochemicals. A wide range of liquid products, especially heavy fuels, distillate fuel oil, and gasoline, can be derived from coal by varying the operating conditions. The Bergius single-stage process for direct liquefaction and hydrogenation of coal was developed in the 1920s and proved to be viable, under the conditions of World War II, in Germany. In the USA, there are three second-generation progenies of this process, none of which is predicted to be commercially successful before 1990. However, the chief means for indirect liquefaction of coal are the Sasol process and the Mobil-M process. Sasol-I, developed in the Republic of South Africa, but based in part on German techniques used during the 1939/45 war, was, in 1955, the only commercially operating coal-liquefaction plant in the world. Sasol-II went into operation in the early part of 1980, and a site has been prepared for Sasol III. Both are modified and enlarged versions of Sasol-I. Notable improvements claimed for the Mobil-M process over Sasol-I are that it is much more selective in making gasoline, and its end-product has a higher octane number. 129 Coal gasification requires a higher chemical transformation (with gasification temperatures of about 1000°C) than liquefaction, and achieves only a 60%-70% energy conversion efficiency versus 78% for liquefaction. However, gasification is arguably the most versatile of the presently available coal-conversion processes, having applications in almost every sector of energy demand (e.g. industrial installations and power-generation systems). In most gasification processes, which are

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available for use or under development, the reactions are endothermic, air or oxygen being supplied to the gasifier. From the industrial user's viewpoint, the net result is a low or medium calorific-value gas. However, the medium calorific-value gas can be upgraded to a high calorific-value gas--called synthetic natural gas (SNG)--by removing the sulphur compounds and carbon dioxide, and then passing the resulting gas to a catalytic methanation unit.129'130 However, this is often uneconomic. Fluidised beds have been developed, during the last 30 years, for achieving higher combustion efficiencies. The fuel (which, for instance, can be a mixture of anthracite coal and culm) is fed-in above the bed's material, which is usually crushed limestone, sand, or crushed dolomite. Air is blown uniformly through the mix at a controlled rate: the resulting bubbling fluidised mixture acquires the free-flowing characteristics of a liquid and permits stable combustion to ensue throughout the whole bed. Moreover, the fluid-bed boiler is environmentally beneficial: it can satisfy existing air-pollution control regulations pertaining to SO 2 and particulate emissions. 131,132 Development studies on coal-water mixtures began during the 1970s. The main incentive is that the overall costs of using coal-water mixtures are expected to be substantially less than for employing coal-oil mixtures. because they avoid using the relatively expensive fuel oil component. Coal-water mixtures consist of a suspension of finely ground coal particles in water, such that the resulting mixture may be pumped and generally regarded as a fluid fuel. The prospectively attractive economics of coal-water mixtures have encouraged the establishment of development programmes in several countries, the leads being taken by Sweden and the USA.130 Refuse-derived energy

With land-fill sites for burying refuse becoming scarcer, and environmental controls more costly to satisfy, some cities have built plants to recover artefacts and materials from refuse as well as to produce marketable energy from the residual domestic municipal and industrial solid wastes. For example, Luxembourg uses 76% of its refuse for producing energy, while Denmark, Sweden and West Germany use 75%, 50% and 25%, respectively, for this purpose. In Japan, where refuse and sewage are increasingly burnt to generate electricity, there are sixty-three energy-from-waste plants. In the USA, the practice of

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energy recovery from trash has also been given a higher priority over the last 15 years. However, although some components of refuse are reclaimed and their valuable constituents recycled, vast tonnages per annum are still discarded, thereby incurring significant disposal costs. 133-136

Four tonnes of typical British refuse can provide approximately the same amount of energy as one tonne of coal: lay three tonnes of pulverised waste a year could produce one tonne of waste-derived fuel pellets, with a specific calorific value about two-thirds that of coal.laa At present, the U K produces about 30 million tonnes of household rubbish annually 138 and about 40% of this is combustible. It is reckoned that waste-derived fuels from refuse have the potential to contribute 1214 million tonnes of coal equivalent per year to the British economy. 139 A British city with approximately 5 x l05 inhabitants, producing 150 kilo-tonnes of rubbish annually, spends about £1.5 x l 0 6 each year on waste disposal. The calorific content of that rubbish is currently worth about £2.5 × 106: the energy saving alone would amount to that derivable from approximately 3 x l04 tonnes of oil.13a However, the harnessing problem is complicated by the fluctuating amount, variations of the constituents of the refuse and the changing unit prices paid for energy. Nevertheless, with the growing need to develop alternative sources of energy, municipal, commercial and industrial wastes are being actively explored as potentially useful sources of both materials and fuels. 14o- 142 DH from refuse incinerators is common in Europe, but it is only during the last twenty years that it has even been contemplated or installed in Britain. Such schemes are now (1986) in service in Coventry (heat recovery), Sheffield (to be CHP), Nottingham (with its two 12 tonnes per hour Martin grates, being the largest CHP plant at present in the UK) and Edmonton in London (with five 14 tonnes per hour VKW grates, being the largest British plant producing electricity from refuse). Nevertheless, the plant being developed at Corby, arising from the feasibility study undertaken by Orchard Partners, reflects the first serious development of a large CHP plant of this type, employing grates to accommodate 18 to 27 tonnes per hour. 119'1av'14a- 145 Refuse incineration, linked with CHP, can be a cost-effective exercise for both the public and private sectors. The overall financial account depends on five major factors: 144 the rates of income from (i) the refuse to be disposed of; (ii) the electricity generated; and (iii) the heat sold; as well as on (iv) the operating and maintenance costs incurred during

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the considered period; and (v) the pay-back period required on the capital invested: the latter will depend on whether the enterprise is public-sector or private-sector led and funded. A range of fluidised bed hot-gas generators and boilers have been designed by Babcock and Worsley in collaboration with the U K National Coal Board. Although the systems were intended for coal firing, they have been operated satisfactorily with refuse-derived fuels. 146 Also, refuse has been burnt successfully as a supplementary fuel in coal-fired boilers; for example, in the 100 MW unit at the Meramec station of the Union Electric Company in the city of St. Louis, USA.119 Land-fill gas (lfg), is formed by the biological degradation of the organic components of refuse. Its commercial importance has only recently been recognised because the unit prices of other fuels have risen, and because it is now much more abundant as the percentage organic component of refuse has become greater in recent years. The typical recovery cost of lfg from a large site is ~ 0"3 p/m 3 at atmospheric pressure, whereas lfg can be sold for > 3 p/m 3, i.e. ~ 12p/therm. Lfg can be burnt successfully either on its own or in conjunction with either natural gas or heavy fuel oil. It has proved to be a safe and reliable source of energy and its potential for the U K has been estimated as 106 tonnes of coal equivalent. Currently, a number of schemes are operational in the UK, mainly on using lfg directly as a fuel in boilers, kilns and furnaces. Some power-generation investigations and projects are under way, but not at the scale of those in Europe and the U S A . 147-149 Oil

Before the 1973/1974 oil crisis, oil-fired DHC plants were cheaper to run than coal-fired systems. Also, coal has a much lower calorific value than oil, and it cannot be transported and stored as easily, compactly and cleanly. The plant required for the conveyance, storage and combustion of oil is simpler, requires less maintenance and can be operated with less difficulty than the commensurate coal plant. On the other hand, proven indigenous oil reserves are much smaller ( ~ 5% if compared in tonnes of reserves) than those of indigenous coal in Britain, and there is an enormous competing demand for oil to provide petrol, paraffin, plastics .... etc. In consequence, the current price of oil per unit of heat content is likely to remain higher than that of coal, and this disparity will inevitably increase during the next 30 years. Oil is used to

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great advantage in transport systems. However, it is still sometimes financially advantageous to use the cheapest grade (i.e. the viscous heavy fuel) oils in C H P - D H C systems rather than coal. In this financial assessment, due allowance must be made for the expense of heating the oil to an optimal temperature (~60°C), and maintaining it at such a temperature, in order to reduce its viscosity, so permitting it subsequently to be pumped at the least total financial cost (i.e. for pumping-power expenditures and heat losses), as'Is° Oil shale

Oil shale deposits are widely distributed throughout the world, with the largest reserves being in the US and Canada.11 The production of oil from oil shale has not progressed rapidly, mainly because conventionally obtained oil per gallon is usually still cheaper than that extracted from shale. Natural gas

This (i.e. predominantly methane) frequently occurs in the same geographic regions as petroleum is found naturally. Due to its lower density, natural gas usually is located above the petroleum, trapped by a layer of non-porous rock. Such conditions create the high pressures which cause the gas to be discharged readily from a well.:1 The use of natural gas for stimulating C H P - D H C schemes is a relatively simple operation: the associated boiler plants can be simple and compact. The number of chimneys required can be deduced in order to comply with the requirements of the UK Clean Air Acts of 1956 and 1968: their heights are usually kept to a minimum, subject to satisfying standard codes, as Natural gas has captured major shares in each of the main energy markets in the UK excluding transport. Sales are expected to increase significantly during the late 1980s and then continue at approximately the same level at least to the end of the century. By employing gas-fired condensing boilers, significant improvements in the efficiency of combustion and performance are being made. Such boilers are now being designed to withstand the corrosive effects of condensation: they are capable of attaining practical efficiencies exceed-

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ing 90%. The condensing boiler is now widely used throughout the European Continent and increasing numbers are being specified in Britain. 15 By 1984, over thirty gas-engine heat pumps had been, or were being, installed in the UK: their use achieves significant energy thrift. However, design improvements and technological innovations for mass production are still required before the domestic heat pump becomes a more efficient alternative and a commercial competitor to conventional or condensinggas boilers. Since the passing of the 1983 Energy Act, ~mall-scale CHP sets (each producing < 200 kWe) based on gas-fired internal combustion engines, have become increasingly attractive in many circumstances, and more than 200 such units are now installed and running in the UK. The growing availability of lean-burn gas engines, with their high efficiencies and low rates of pollution, should accelerate this trend. However, it has been found that their operational pay-back periods are ,-,2 × l04 operating hours, which may ensue during 3-7 years, according to their frequencies of use.~5~- ~54 Also, the BGC allege that it is usually more cost effective to distribute natural gas to blocks of houses than to distribute hot water (via a DH scheme). Hence more and more mini natural-gas driven CHP units are being introduced in the UK. Geothermal energy As a drill penetrates downwards through the Earth's crust, the temperature of the layer encountered generally increases: the magnitudes of these temperature gradients depend upon the thermal conductivities of the rocks. Scientists now believe that heat is being produced continuously inside the Earth by radioactive disintegration; the interior of the Earth, like that of the Sun, being a continuously operating nuclear furnace. The internal molten core of the Earth comprises an almost inexhaustible energy source (with respect to the normal human-life span). Usually, when this released energy reaches the surface layers of the Earth, it is highly diffuse. However, in some regions it accumulates: from these, it can be exploited more easily for direct (e.g. non-electric) uses or for the generation of electricity.~l Extensive pertinent observations have been obtained in Iceland, New Zealand, Hungary, the Soviet Union (where the largest harnessed geothermal heat source for DH exists) and elsewhere. 3s, ~55

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Several schemes are established in France for using subterranean hotwater for DH purposes. One such successful scheme is at Carrieres sur Seine near Paris, which is not a volcanic region. The heat contained in this hot water has been taken, for over 10 years, to satisfy part of the heating load of a group-heating scheme for 800 dwellings, as The Paris Basin DH system delivers hot water (at --, 70°C) for communities at Melun, Creil and Villeneuve la Garenne. ~29 Another geothermal DH scheme is at Creteil: this supplies a total of 5660 dwellings (including shops, offices .... etc.).~°6 However, the Beauvais geothermal DH installation was the first in France to be designed for gas-engine driven heat pumps. The DH network there supplies floor heating for a development of over 100 flats and commercial premises, in 15 buildings, with a total design load of 6-5 MW. 1°7 Parts of Great Britain have a similar geological structure to Northern France. Yet, there has been no direct commercial exploitation of geothermal resources in Britain since the Romans utilised such heat in the city of Bath, almost 2000 years ago. Experience from other countries suggests that the use of geothermal (including hot dry rock) resources has only a negligible adverse environmental impact. 156 Research is under way in the U K (e.g. at the Camborne School of Mines, Cornwall) on the use of hot dry rocks and aquifers. Recent studies in the city of Ely, Minnesota, USA, led to the conclusion that the use of water-filled abandoned mines could be a potential heat source for district heating. The water so heated will be pumped from one of the shafts through a heat exchanger where the temperature is reduced by approximately 5°C, after which it is either returned to the mine or discharged into an adjacent lake. 157 For many years, heat has been used to produce cooling.l~ However, geothermal energy is rarely employed for this purpose. Nevertheless, space cooling is achieved by this means in Rotorua, New Zealand: a lithium bromide/water absorption unit (involving evaporation and condensation) produces the cooling. Highly corrosive contaminated water ht about 150°C from the geothermally hot strata is passed through a heat exchanger to raise the temperature of the water in a piping circuit to 120°C. This heated water is employed later to drive the absorption unit. Recently, because of the growing interest in the use of solar energy and recovered waste-heat, there have been efforts to employ these energies to produce cooling. Achieving space cooling (via absorption

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units) of, say, a warehouse from the same geothermal resource that is used simultaneously for space heating of other buildings has the potential to improve the overall efficiency of use of the geothermal energy. The potential for improvement is due primarily to a potentially increased load factor. Nevertheless, whether or not the provision of space cooling will actually increase the load factor depends on the temperature of the geothermal resource and the ratio of the cooling load to the heating load. It is expected that large-scale DHC systems will require geothermal resources with temperatures exceeding 90°C, and that the systems to be used will be designed to achieve a relatively large temperature drop from the geothermal fluid. The first large geothermal space-cooling application is at present (1986) in the design phase: the city of El Centro, California, is planning to use 115°C fluid from the Heber resource area to provide about 230 kW of cooling via absorption units.1 Solar insolation

Heat from the Sun is potentially a major source of energy for stimulating DH systems. At present, only a small part of the solar insolation potential is being realised: the annual amount of solar energy which reaches the Earth is approximately 22 500 times as great as the present world-wide total energy usage during a year. 11 Although the rising unit energy costs of the more conventional sources have offset some of the barriers to the more widespread use of solar energy, other obstacles still remain. The principal ones include: the relatively low heat intensity of solar insolation; its daily intermittency and seasonal fluctations, as well as it being subject to unpredictable interruptions due to clouds, rain, snow .... etc.; and the still relatively high cost of large solar collectors. Many of the obstacles associated with central-station huge solar facilities are surmountable. For example, the Electric-Power Research Institute, USA, already has plans for large-scale solar electrical generation. These include the use of a big receiver, filled with helium, placed on an 80-storey high tower surrounded by 320 acres of reflectors. These reflectors will track the Sun, and be able to concentrate the radiant energy onto the receiver. Heated to 810°C, the helium in the receiver will drive a turbine to produce electricity and then be passed through a cooling tower and reused.ll

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As part of the Sunshine Project, the National Energy Development Organisation of Japan completed two thermal electric-power generation plants, each with a capacity of 1 MW, in the Nio-cho, Kanagawa Prefecture. Although these installations have been used experimentally with success, the Organisation decided recently (1985) that, because the commercial viability of these plants was contentious, they would henceforth be operated on a reduced budget. However, even though this particular project failed to attain fully the expectations of it, a significant step forward in the history of solar-stimulated power generation has been achieved and it attracted worldwide attention. Each central receiver's pilot plant has an output of 1 MW. Numerous heliostats, with plane mirrors, were installed around a 69-m high solar-energy collection tower housing the pilot plant. The insolation reflected by these mirrors is concentrated at the top of the tower. There the solar-heat receiver consists of numerous pipes coated with black paint. The water in these pipes is heated and vaporised (attaining a temperature of approximately 250°C) and temporarily stored in a steam drum at the uppermost part of the tower. From this, the steam is piped to five heat storage tanks (i.e. accumulators) on the ground, where the steam is compressed and stored in the form of hot pressurised water. These storage tanks have a combined capacity for storing heat equivalent to 3 000 kWh of energy. The necessary amount for power generation is then piped, as saturated steam, to drive a turbine (of rated output 1 MW for a steam temperature of 187°C) and so generate electricity. The steam used for power generation is subsequently sent to a condenser, reverts to water and is recycled to the heat receiver at the top of the tower. 158 For Japan, the theoretical availability of solar energy, which is capable of being converted into electric power, is estimated to be in the vicinity of 1.6 x 1014kWh per annum. Of this, the practically usable amount has been predicted to be 6 x 1012 kWh. However, further efforts must be made to ensure a stable power supply by developing more efficient methods for collecting the solar power harnessed over vast sites. With present systems, only about 10% of the collected solar energy is converted into electricity, whereas the optimal conversion rate is expected to be about 20%. Technologies need to be developed to operate several such installations as one system through a commercial power network. Lof and Tybout ~59'~6° have developed a mathematical model for predicting the costs of delivered solar energy for houses. This model has been validated by showing that the predictions agree with observations

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for two sizes of houses in eight US locations experiencing significantly different climates. Several system design parameters were varied, in addition to collector area, in order to determine the range of optimal values, including collector inclination, number of 'transparent' covers on the collectors, and the heat storage capacity per unit collector area. During 1977, a research and development programme was supported in Corsica, France, concerning the conceptual design of a solar thermalelectrical power plant for producing continuously, during daylight hours, 50 to 1000kW of electricity. 16~ The design involved: linear-focusing collectors (operating at design temperatures ranging from 180°C to 250°C); a heat store using stratification of the heat-transfer fluid itself; and a Rankine-cycle conversion loop, with a turbine expanding a heavy organic fluid (namely, Fluorinert). The construction of an experimental prototype plant started at the beginning of 1980, and it is now connected to the local grid, i.e. it is one of the first major solar plants, in operation in the world, using this kind of collector and such high-efficiency turbines. Since October, 1983, a solar-energy laboratory was associated with this power plant. The tests carried out there indicate that the plan can provide medium-temperature heat (at 150-300°C), as well as mechanical and electrical power simultaneously. A conceptual renewable-energy conversion system, suitable for industrial applications in the UK, has been investigated. 162 A computer program was developed to simulate the performances of the solar, wind and thermal storage sub-systems, either individually or in combination. The renewable heat and electricity system showed considerable advantages in performance over the equivalent single-source energy-conversion systems (i.e. a solar or wind only system). For instance, a more nearly constant rate of heat output was achieved. However, extensive further experimental studies are needed in order to test the predictions from the computer model for various system configurations with a range of specified costs and investment conditions. Nuclear power

Improving our financial standard of living will depend upon the availability of adequate amounts of nuclear energy. This appears, in the short term, to be the only large-scale realistic alternative to fossil fuels, even though solar energy will make an increasing contribution. It is alleged that it permits the generation of electricity at lower unit costs than those achieved using fossil fuels, unless the latter are used via a

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C H P system. 16a'164 However, the economics depend upon the rate of return (RoR) expected on finance invested (see Energy Paper 35165). If all the influential factors are taken into account (e.g. the cost of dealing with nuclear pollution), nuclear power investments, even with as low as a 5% RoR, will probably not be regarded as cost effective. However, nuclear power in France, with a zero RoR, has been seen to be a justifiable economic investment. 144 Nevertheless, there are other advantages in the use of nuclear power: in Switzerland, for example, reduced oil consumption and avoidance of air pollution due to the combustion of oil were the main driving forces behind the nuclear C H P movement.166'167 In general, to be commercially viable, a DH system fed from a nuclear-power station, which has been designed deliberately to provide CHP, should have a load exceeding 1000 MW, and so must usually supply many consumers; e.g. in West Germany, a DH grid network which covers the entire country is being constructed whereas, in Switzerland, nuclear power networks are intended to supply space heating to about 65% of the population, as'16s'169 For the operation of such DH systems, it is necessary to be able to vary the heat output significantly, yet keep the plant running at a constant rate. Hence, nuclear stations should not be used solely for supplying heat: it is desirable that the heat and power generation should be combined using intermediate take-off condensing (ITOC) turbines to adjust the heat supply to that demanded. 3a. 1vo Although the capital investment required to develop and construct a nuclear-based DH system is relatively high, the associated operating costs are usually low. This occurs partly because the cost of nuclear heat is affected only to a minor extent by the price of the uranium fuel. The single most uncertain variable is likely to be the democratic opposition, which all types of nuclear plant now engender. Also in some cases, e m o t i o n a l i s m associated with such opposition may make the nuclear approach unfeasible politically.11,171.1 ~2 For instance, in the USA, no new orders for nuclear reactors have occurred since the ThreeMile Island disaster in 1979. However, even in Japan, there is only a slow growth of nuclear power output, and this is mainly to reduce the dependence on the shifting politics of the oil-producing countries. Nevertheless, there are rational anti-nuclear arguments, e.g. the substantial risks incurred in this aspect of high technology due to human fallibility.

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Electricity Using electricity to provide heat is relatively expensive per k w h . This occurs because, when electricity is produced from fossil fuels, only about one-third of the energy in the fuel is converted into electric power, and it requires a high capital investment plant to achieve this. Hence, even if domestic electric-heating appliances are taken as running at 100% efficiency, the overall thermal efficiency is usually less than 33%, i.e. much lower than the efficiencies that can be achieved by burning the fossil fuels where and when required in the home. aa However, to achieve high conversion-to-electricity efficiencies (even though still only ~ 37%) with nuclear generating plant, the waste heat is discarded at too low a temperature for most commercial applications of it. In normal parlance, CHP is taken to imply cogeneration where commercial use can be made of both the electricity as well as the heat that would otherwise be rejected. It is also employed by industries who sell their excess electricity and/or heat to neighbouring facilities. 11 Industrial CHP schemes are well established in most developed countries, including the UK, France, West Germany and Spain. There are (in 1986) more than 150 relatively small (,~ 6 MW) industrial CHP schemes operating in the UK. However, they are mostly privately owned, having grown as an integral part of the industry concerned, particularly in the paper, food and chemical industries: many have a cheap source of fuel (e.g. refinery by-products). 1v3,174. Fuel-cell power plants are novel electrochemical devices which offer numerous benefits, including high efficiencies and freedom from pollution. Existing cells, with phosphoric acid as the electrolyte, operate at over 40% conversion efficiency from a hydrocarbon fuel to electricity, plus approximately a further 40% of the released energy is recoverable as heat. Several pertinent major development and demonstration programmes are in progress, mainly in the USA and Japan. Two consortia, consisting of Hitachi and Toshiba, and Mitsubishi and Fuji, are each constructing 1 MW demonstration plants under the Moonlight Programme: these should be operational during 1987. A second phase, leading to commercialisation, is planned for the five years subsequent to 1987. All of these companies, together with Sanyo, have developed 30-50 kW fuel-cell systems independently, and studies are progressing rapidly for CHP generators for on-site installation. In the longer term,

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it is expected that cells operating at temperatures of up to I O00°C will be developed, and these will offer conversion efficiencies approaching 55% together with high-grade heat recovery. 175

D E V E L O P M E N T S IN THE M E T E R I N G A N D CONTROL OF C H P - D H C SYSTEMS Metering provides a means of indication, so that consumers can measure the effects of modifying their behaviour and hence consumption patterns. Obtaining revenue in the commercial operation of a DH and/or DC business usually occurs with less irritation to the consumer via the aid of meter readings that record the amount of the product he or she actually used. A meter is regarded, and generally accepted, as an impartial arbitrator between the supplier and the consumer. Thus meters should be sturdy, reliable, tamper-proof and preferably cheap. These systems must be capable of sustained operation at a prescribed accuracy level to qualify as a measuring device in commercial service.IV6 It is interesting to note that Birdsill Holly's meter patent in 1880 preceded the first Edison electric meter by three years. Gas meters, however, were well-established devices, having been manufactured in the USA since 1832. The rate of progress in steam, and hot, as well as chilled, water measuring systems and practices during the past decade has been disappointing. If DHC is implemented rapidly, it will be a major challenge for the instrument designers and manufacturers to keep pace. 11.177 Current U K practice in the metering and control of heat-distribution systems is based largely on the experience obtained with group-heating schemes in local-authority housing and at various sites, particularly military, within government estates. The nature of these market sectors has been significant, particularly in determining the adopted control philosophy, which generally is a desire to limit the capital cost of group heating. ~78 The metering and 'fiddle-proof' control arrangements for a proposed C H P - D H system will usually form an integral part of the design. The standard of service desired by consumers in each market sector should be provided as cost effectively as possible, so as to achieve the maximum competitive advantage of C H P - D H over other heating systems. However, the cost of metering can amount to as much as 10% of the cost

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of heat supplied per year. Nevertheless, it is alleged that not employing meters for the individual customers can lead to energy profligacy.* 79 It would be more economic to install collective metering, e.g. a simple meter for a block of flats. In 1980, reliable electronic heat meters were introduced and proved to be acceptable. Currently, in the UK, only about 300 000 dwellings, or 7% of the total DH market, have any form of individual metering device. *so A novel design has recently been proposed 1a i for a heat meter: it (i) provides a direct connection across the consumer/heat network interface; (ii) controls the pressure in the consumer's system independently of that in the distribution system; (iii) measures accurately the water flow-rate taken by the consumer (and controls its maximum value); (iv) measures the temperatures of the water at the inlet and the outlet of the consumer's system; and (v) detects any leakage from, or failure of, the system. Nevertheless, the system should be controlled, on the consumer's side, entirely by two-way valves in order to enable (i) the minimum volume of water to be taken and (ii) the lowest water-return temperature to be achieved. So a combination of the facilities offered by the normal direct system and by the heat exchanger system was developed. The requirements to measure the water flow accurately, and control the m a x i m u m volume rate, suggested the use of positive-displacement devices, such as rotary-vane meters or piston meters. Arrangements have to be devised to deal with wear and the turn-down of the equipment. However, the performance of the proposed system ~al in the field has yet to be determined. For a C H P - D H C system, both the cost-effectiveness and acceptability of the chosen meter will vary between markets, and possibly even between individual consumers within the same sector. It is therefore likely that metering will be observed in some sectors, but not in others, and that different forms of metering, associated with different charging arrangements and tariff structures, will be applied in different sectors. For instance, as regards cost-effectiveness alone, the heat-metering of individual dwellings is unlikely, in many situations, to be cost-effective with CHP, because of the low marginal cost of the C H P heat which would be saved. ~a2 However, recent studies ~79 suggest that metering would influence consumers and so result in a reduced peak heat demand, as well as a a smaller annual consumption, thereby allowing other savings to be made in the installed heating-plant capacity. Nevertheless, this would not be the case for large consumers of heat, such as

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R. F. Babus'Haq, S. D. Probert, M. J. Shilston

institutional buildings, because of their proportionally lower costs of metering. Alternatively, simpler and cheaper forms of metering could be adopted which would not measure heat consumption directly. An example would be flow-metering alone, which has the additional advantage of encouraging low flow rates and low return-water temperatures, x7s At present it is the policy of many local authorities not to charge customers (on their group-heating schemes) according to metered consumptions. Sometimes the heating charge, often paid as part of the rent, is based on dwelling-design rate of heat loss or floor area, or number of bedrooms, and is set so as to recover the annual operating cost of the scheme (or a proportional part of all the authority's scheme if it operates a 'pooled' system of charges). This does not encourage, or result in, energy thrift by the individual customer. In some market sectors, the attractiveness of C H P - D H C to consumers may well be enhanced by the provision of pre-payment facilities. Modern electronic pre-payments, coded onto magnetic cards, are flexible and can be programmed to take account of special requirements, such as charging OAPs at a lower rate, or providing a certain a m o u n t of free heat to protect the building structure, or to reduce the likelihood of deaths from hypothermia, l a 3 - is ~ Recently, an average saving of approximately 28 % has been claimed for the Billingham DH scheme in which a package of metering, pre-payment, and time-clock, thermostatic controls had been installed. ~86 Metering cannot be divorced from the question of financial charging arrangements, and of the tariff structure adopted for the C H P heat supply. The tariff devised for each market sector should be such as to indicate to the consumers that they should use heat in such a way as to minimise the unit cost of its supply: the adopted charging procedure must also be perceived by consumers to be equitable. In the early years of C H P - D H C development, tariff structures should also be designed to encourage the rapid take-up of such schemes by additional customers so that the true unit cost of supplied heat gets less and the whole scheme becomes more commercially viable. One problem with the development of C H P - D H C is that these requirements might sometimes be in conflict. ~78 The UK 1983 Energy Act placed a duty on the Electricity Boards to (i) publish tariffs for the purchase of electricity from private generators, (ii) state the principles upon which these tariffs are established and (iii)

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support viable C H P projects. Tariffs have been published but principles have not, other than as informal statements. 1a ~.18a There is no statutory assurance that the varying values involved in the Area Board tariffs are consistent with the principles that have been set down and discussed. 189 The principles, as can be deduced from informal statements by the Electricity Council, should be related quantitatively to the Area Board tariffs. However, there are still significant variations which can affect adversely the introduction of small C H P generation systems in particular locations. Tariffs based on these principles should always be reasonable and result in fair levels (i.e. allowing for some profit) of remuneration for selling electricity privately generated by effective organisations, to the CEGB. At present, for most areas the Electricity Boards will purchase electricity at about 80% of the price per unit at which they will supply it. Although the ESI states that fully harmonised tariffs will be made available equally to consumers, whether or not they are private electricity generators, these have still to appear in some c a s e s . 1 4 9 , 1 8 8 . 1 9 0 - 192

T H E D E V E L O P M E N T OF C H P - D H IN G R E A T B R I T A I N In Western Europe, more than three-quarters of the currently existing DH load ( ~ 100GW) has been built since the end of the Second World War. Those countries in which DH supplies a significant proportion of the heat used for achieving warm comfortable environments are West Germany (35% of the total load), France (20%) and Sweden (18°,/0). 193 But the prospects for C H P - D H in the UK contrast poorly with those in such countries, as well as in many Eastern European countries. At present, only the Nottingham system approaches the scope of even the smallest European ones. Essential extensive post-war reconstruction in Europe provided an excellent opportunity for introducing district heating. Other contributory factors resulting in the relative lack of interest in DH in Britain include the major role of gas in the domestic sector, and the different traditions in the supply of services (water, natural gas and electricity) between Britain and the rest of Europe.al,lsT,194-196 In Britain, the control over each of the water, gas, electricity and telephone services remained in the hands of separate nationalised industries, each with its own bureaucracy, often in unnecessary and wasteful competition one with another. This makes it excessively

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R. F. Babus'Haq, S. D. Probert, M. J. Shilston

frustrating even to try to get accepted the techniques for laying se~icedistribution mains effectively in a c o m m o n d u c t as adopted in many other countries. 3s It would also appear wise to have a co-ordinated Energy Supply Board, to avoid unnecessary repetition (e.g. different employees reading meters for natural gas and electricity used in the same house) when it is contrary to the best interests of the state. At present, about two-thirds of the total energy used in electricityproducing power stations is dissipated wastefully as heat via cooling towers, rivers and/or the sea. The average 'person in the street' may wonder why he has to pay to heat the air or the sea in this way. This 'wild heat'--Britain's largest untapped energy source--it needs to be reemphasised, time and time again, is equivalent to more than twice the amount of the electricity now generated. Annually (in 1985) it was equivalent to more than the total amount of natural gas brought ashore from the British sector of the North Sea and was enough to heat every home in Britain for that year. Yet much of this wild heat could be harnessed via CHP schemes. As a result, electricity could be generated via CHP schemes at about half the price that it can at present be purchased from the local Electricity Board. Denmark (one of the pioneers in CHP technology) satisfies 40% of its community heating needs via CHP. This is primarily because Denmark has relatively little in the way of indigenous fossil fuels, so that a more efficient use of energy there is regarded as essential. For Finland, the figure is 30%, whereas, for Sweden, the proportion is 25%. However, the vast reserves of natural gas belonging to Norway and the relatively cheap hydroelectric power available have discouraged the implementation of C H P DH systems in that country. Nevertheless, Europe has approximately 3000 C H P - D H schemes. Many incorporate a refuse-incineration heat station, so satisfying the dual purpose of providing heat and/or electricity, as well as reducing the volume of refuse needed to be transported to the declining number of suitable land-fill sites.197- 199 The first industrial CHP installation in the U K was at the Singer Factory on Clydebank in 1898. Early C H P - D H schemes soon followed. In 1911, a small power station was modified in Bloom Street, Manchester, to supply steam to neighbouring shops, offices and factories. In 1920 and 1922, respectively, DH schemes were started at Dundee (the Logic scheme) and at Stirling. Via the Dundee scheme, four blocks of buildings, divided into fiats, were supplied with hot water. Since then, with the exception of a few housing blocks supplied with district heat on a small

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scale, there have been only a few notable developments. However, one is the Whitehall scheme which supplies all the government buildings in that area. Another was the Pimlico DH undertaking in London, which was commissioned in 1950 to serve a community of about 11 000 people using waste heat from Battersea power station (which was closed down in 1983). In 1960, a scheme was introduced based on the Spondon power station, near Derby, to supply steam to the adjoining Courtaulds Factory. Another municipal scheme (the largest U K coal-fired groupheating scheme) was introduced in 1965 at Billingham using a centralboiler plant and circulating hot water, s'174,2oo-202 There are now more than ten large CHP systems ( > 4 0 0 k W e ) operating in the UK (e.g. at the Harrods Store and the National Westminster House, London; the General Infirmary, Leeds, England; and the P.O. Telecommunications Centre, Cardiff, Wales). DH has not been popular in the UK, partly because of the difficulties encountered, as might be expected with any new large-scale technological venture. In the early stages some schemes proved to be financially disastrous because of inexperience in the operation of this new form of public-utility service. Latterly there have been some failures due to the use of unproven designs and installation methods for the transmission network. However, despite setbacks of this kind, interest in DH has grown steadily. 8 The oil-price shock in November, 1973, and the subsequent fluctuations of the unit price of crude oil have encouraged UK interest in alternative energy systems, including CHP. A well-attended Institute of Fuel (now Energy) conference in December, 1971, was devoted to 'Total Energy' (subsequently called CHP). 2°3 On investigating such a scheme in detail, it became clear that there were grave disadvantages in Total Energy schemes as then practised. 204 By the end of 1974, the Government established the CHP Group, under the aegis of the Secretary of State for Energy's Advisory Council on Research and Development, to consider the economic role of CHP in the UK and to identify technological, institutional, planning, legal and other obstacles to the fulfilment of that role, and to make recommendations. Their report was published in 1977 as Energy Paper No. 20205 by the Department of Energy in the form of a discussion document. It resulted in extensive debate and has been accepted as one of the most comprehensive assessments attempted in the area of C H P - D H . The medium-term analysis of the prospects for CHP assumed that both natural gas and oil would be available as

136

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

fuels for heating for ~ 15 years. However, it was assumed that reserves of these fuels would, in the longer term ( > 50 years), be severely depleted and so would not be available for space-heating purposes: by then the energy economy would be primarily nuclear and coal based. In July, 1979, the CHP Group produced the Marshall Report, which appeared as Energy Paper No. 35.165 Relatively little use to that date had been made of CHP for domestic or commercial space and waterheating purposes in the UK, by contrast to the situations in countries such as Sweden, Denmark and West Germany. The major reason for this was the availability of a convenient and highly competitive alternative; namely, the use of natural gas, for which an elaborate distribution network already existed in the UK. Heat from CHP stations could be competitive with heat derived from burning natural gas only in densely populated cities, where the heat loads are highly concentrated. However, in these areas, natural gas is already supplied to consumers as an established cheap and convenient fuel. Nevertheless, in the longer term, large CHP plant is likely to become an attractive, economic and energy-thrift option compared with the other developed forms of heating. The Group reported that energy savings, achieved by the adoption of C H P - D H economically viable schemes, ~65 might amount to as much as 30 million tonnes of coal equivalent per year, a figure representing between 5% and 10% of the probable U K annual primary-energy demand beyond the year AD 2000. The comparative economics of the alternatives at 5%, 10% and 15% discount rates, in 1976 money values, were presented for the long term. The economics of CHP investments are very sensitive to the discount rate and the choice of the appropriate figure is a key issue. CHP has a clear advantage over other options at a 5% discount rate, when the unit fuel prices double in real terms. However, at a 10% discount rate, CHP has only a small advantage even for high densities of dwellings. At a 15% discount rate, gas-fired central heating generally is financially more attractive than CHP. The standard U K Treasury discount rate is at present 5%: it stood for a long time at 10%. This is the rate used for public-sector appraisals of proposed investments in projects. 2°6 Figure 14 shows that nuclear electricity for heating would cost at least twice as much as CHP heat (whether from coal or nuclear plants), and even more compared with the heat from large refuse-incinerators. However, it has been alleged, ~44 that nuclear electricity cannot provide cheap heating. It may well be cheaper per unit of electricity produced than that from coal in conventional power

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stations, but it is not as cheap a way of producing heat as is generally alleged if capital and running costs are properly accounted for. The public and industrial responses to contemplated CHP schemes were regarded as probably the most important consideration to be settled before initiating a lead-city project for the implementation of CHP. Financial assistance from the Government appeared to the Marshall Group to be highly desirable in order to help CHP schemes to 'get off-the-ground'. The Marshall Report included the results of a

138

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

survey of actual and potential CHP users. Of the fifty-six companies which had considered the use of a CHP scheme, twenty-six rejected it: the most frequently stated reasons being unattractive overall economics and available-capital shortages. The tariffs for the supply, as well as purchase, of electricity then offered to CHP operators by Electricity Boards were also quoted as obstacles. It was also clear that a high plant load-factor was a necessity for CHP to be commercially viable. 187 One reason for the apparent lack of interest in industrial CHP is the decline of British manufacturing industry relative to those of our competitors. U K industrial energy demand peaked in 1973, and, by 1980, had declined by 25%, and a further 5% by 1981. This undoubtedly has greatly lessened the scope for development and modernisation. 2°4 In 1983, for the first time and ever since then, an adverse balance-oftrade in manufactured goods occurred for the UK, which now relies on indigenous oil and 'invisibles' (i.e. earnings from investments abroad, banking, insurance, etc.) to keep its current account in surplus. 2°7 This adverse trend with respect to manufactured goods appears unlikely to change in the immediate future. In April, 1981, a further report, produced by Members of the Building Research Establishment and the Atomic Energy Research Establishment, was published by the Department of Energy.la2 It deduced that for the conversion of an existing city to C H P - D H , where the cost of the mains network is important, estimates were around 30% less than those given in Energy Paper No. 20. The reduction in the estimates resulted mainly from an examination of the cost of a real network serving commercial and institutional properties as well as housing. The study concluded, somewhat surprisingly, that the overall cost-effectiveness of converting an existing city to C H P - D H would not be greatly affected by: (i) the size and location of the CHP station, (ii) the cost-effective improvements necessary to the thermal insulation of dwellings, and (iii) whether or not the supplies of heat to domestic customers were metered. 31 In response to the Marshall Report, the Government announced that it proposed to initiate investigations concerning the feasibility of C H P DH schemes in particular locations in the UK. The first stage, which was undertaken by consultants, indentified possible locations where C H P - D H might be an economic proposition. The second stage involved a detailed examination of these locations with a view to using them as lead-city schemes. The Government took the view that a National Heat Board, as proposed by the majority of the Marshall Group, was

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unnecessary, at least at present, because during the early stages of any development programme, the investigations and analyses would be carried out mainly by consultants paid by local government and local interests.2° 1 The first stage was carried out by the consultants W. S. Atkins and Partners, whose report was published in August, 1982 (and as Energy Paper No. 53 in 1984). 2°s The report indicated that nine cities showed promise with respect to the economic feasibility of installing a major C H P - D H scheme: these were Belfast, Edinburgh, Glasgow, Leicester, Liverpool, London, Manchester, Sheffield and Tyneside. In these cities, high-density heat load demand areas of 20 MW per square kilometre or

140

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

more were identified, with a peak heat requirement of 100MW per square kilometre or more. 2°1 Domestic central-heating costs for four representative years are presented for Great Britain (i.e. excluding Northern Ireland) in Fig. 15. A separate assessment has been undertaken for Northern Ireland, where unit fuel prices are higher than in the rest of the UK. In April, 1984, the Government's Department of Energy announced that it was initiating the second stage of the investigation and would contribute a total of £750 000 towards further detailed studies, including engineering-design, financial and marketing plans for large-scale C H P DH schemes in up to three of the chosen cities. It invited applications from local consortia involving both the public and private sectors to bid for these grants in order to prepare prospectuses for the implementation of C H P - D H systems. 2°1 Since the publication of the report, much has happened. Sheffield's City Council has refined its plans, and formed a consortium to implement them. 2°9 In Tyneside, a detailed programme of work was proposed to be undertaken by the consortium members, the CEGB and the financial advisers: the end-product is intended to be a practical CHP scheme, funded by the private sector. The first phase of the development-representing about 20% of the final scheme--was based on refuse incineration as the heat source. 21° In London, the Borough of Southwark has (i) examined the prospects for C H P - D H within its boundaries, (ii) considered the potential impacts of installing DH mains in an existing built-up area, and (iii) investigated the possibility of interconnecting its major existing DH schemes. 2t~'2 ~2 A GLC-sponsored study, undertaken by Orchard Partners, has concluded that a coal-fired C H P - D H development could ultimately meet half the heating requirements of London's Inner Boroughs. 2t i - 214 The study also concluded that the proposed development would (i) benefit electricity consumers to about the same extent as the introduction of a new nuclear-power station and (ii) make a real return of 5% per annum on its DH operation, which is the same as that required for the natural gas and electricity-supply industries. Moreover, it would provide heat to customers at 20% less cost than otherwise would be incurred. The development, as envisaged, would, by the year AD2012, encompass a total connected heat load of 2895 MW. However, this would be satisfied by a staged (in time) construction of six separate CHP sets, all located on the CEGB's Barking site. The scheme is three times the size envisaged

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in the Atkins Report. Nevertheless, the Outer London Boroughs were also found to be suitable for DH. There was a worry for the towns involved in the C H P - D H studies that, by involving suppliers of equipment or services as members of the consortia, i.e. at the planning stage, they would be allowing these companies to be in a very strong position for bidding with respect to the supply of equipment or services. 212 214 In January, 1985, the Government announced the winners of the grants, of up to £250,000 (per city) to fund research study groups concerning their city's prospects for implementing a C H P - D H scheme. The three British cities chosen were Belfast, Edinburgh and Leicester. This reflected the Department of Energy's aim to incorporate one city from each of Northern Ireland, Scotland and England in the overall investigation. Substantial private-sector funding has provided additional capital to finance extensive analyses of C H P - D H prospects in all the three cities chosen. 215 For Belfast, whose award of £250 000 was a foregone conclusion, the Northern Ireland Electricity Service network is not large, and the size of the C H P - D H plant to supply heat to its high-density heat load is commensurate with that of a new power station for their system. Their next major development, for commissioning in the mid-1990s, could be an extension at Kilroot (where civil works are already in place) or a lignite (soft brown coal) fired station at Crumlin. The location decision is linked with plans for the use of the Province's lignite resources, but the present feasibility study may not be completed by the time that such a decision has to be taken. On the basis that one of the two locations will be developed, the Belfast C H P study is concerned with predictions of the incremental costs of installing C H P - D H plants relative to conventional plants at each site. It may be that those increments are similar, even allowing for transmission COSTS.216 Members of the Edinburgh consortium, while undertaking an 18month feasibility study, concentrated on developing the engineering procedures and economics for a C H P scheme, for an area containing the highest proportion of offices and public buildings and the lowest proportion of industrial floor space of any of the nine cities short-listed as suitable in the Atkins Report. 2°s The two sites available for the C H P station are Cockenzie (selected in the proposed programme, but its claims are not conclusive) and Seafield. If the detailed study confirms the viability of using the Cockenzie Power Station as the prime source -

142

R. F. Babus'Haq, S. D. Probert, M. J. Shilston

of heat, alterations will be made to the generating plant and to the operating regime there to divert some of the heat produced through the district-heating system. Two additional sources of fuel have been considered in the design of a system for the city; namely, refuse incineration and a coal-fired boiler station at Dalry. As the peak highdensity heat load reaches 500 MW, the Cockenzie station will satisfy about 85% of the heat consumption. It leaves a significant fraction of heat to be supplied by heat-only boilers and, given the complex interplay of economics and load factors, together with the need for flexibility with respect to changes in heat-consumption habits, Seafield remains a possibility. Pass-out sets can increase electrical generation at peak times: these are superficially attractive for Seafield, but, given the characteristics of the Scottish network, this flexibility may be of little v a l u e . 2 1 6 - 2 1 8 A consortium of varied interests has come together in Leicester. The proposed CHP plant would produce a high proportion of district heat relative to electricity. The plant is therefore treated primarily as a heat producer, with electricity as a by-product. This would increase the efficiency of the fuel used from 35% to 70% approximately. If the generation of electricity was to be regarded as the prime objective, then different rules would apply concerning cost allocation. From such considerations, the consortium decided to evaluate the finances of the following options: either (i) small coal-fired CHP stations; (ii) gasturbine plants based on retrofits of existing machines; or (iii) heat extraction via a pipeline from the Ratcliffe 2000 MW electricity-generating power station. Within these options, further evaluations were made on the optimal configurations for boilers and steam turbines. It was also thought that a single solution may not apply, and that a combination of the options might eventually be s e l e c t e d . 219-221 Despite only three cities, out of the original list of nine, having been chosen to feature in the government prospectus, it is probable that CHP assessments will continue in the other cities. For instance, the consortium of business and local authorities, which submitted a plan to build a multi-million pound CHP plant on Tyneside, has decided to press ahead. They were anxious not to waste the efforts expended on the preparatory investigations that had already been completed, and which have led to considerable interest from potential customers for the 'cheap' heat to be produced, and from other firms working in this area, who are not at present involved in the Tyneside s c h e m e . 222 Given that London has consistently come out on top in the Depart-

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ment of Energy's recommendations for suitable venues for CHP, the GLC-led consortium is now funding independently further studies concerning CHP for London, with approval and encouragement from the Department of the Environment. The Council has commissioned two engineering consultants; namely, Orchard Partners and W. S. Atkins, for the Boroughs of Southwark and Tower Hamlets, respectively, to undertake detailed studies and to investigate the potential for a core scheme or schemes. In March, 1986, each consultant submitted a report and the Joint Advisory Committee of the GLC of the London Boroughs of Southwark and Tower Hamlets produced a summary report including the institutional study and a people's plan for CHP. They are intended to encourage the early development of CHP in L o n d o n . 215'223-225 A research project into small-scale CHP, covering parts of South London, was launched officially during December, 1985: the scheme uses equipment producing as little as 15 kW of electricity and 40 kW of heat. It was organised by London's South Bank Polytechnic with the help of the Inner City Partnership. Efficiencies of up to 85% are being attained. 190 However, the city which has probably achieved most progress towards realising its own CHP scheme is Sheffield: already it has received a grant from the EEC towards the cost of its study. The scheme has been designed to be implemented in two stages. The first stage will be based on an existing refuse incinerator and a new heat-station using fluidisedbed technology, with in-bed desulphurisation, to provide 75 MW of heat and 10MW of electricity. The second stage will be based on a new CHP station, using coal-gasification combined-cycle technology with desulphurisation. Many institutional and commercial buildings, with firm heating requirements, will be supplied, together with two large existing residential group-heating schemes. 2°1"225 -228 Superficially this would appear to be a time of hope for advocates of CHP in the UK. However, in practice, apathy is prevalent: pessimism prevails because of the Government's requirement that approval for city-wide CHP will depend on the availability of private finance. However, because of the high degree of bureaucracy that will inevitably be encountered in getting C H P - D H systems implemented, it is unlikely to be sufficiently attractive for private finance alone without subsidies. Also, there is a conflict of interests between CHP and the existing power utilities: the widespread introduction of CHP in the UK would contribute significantly to fuel thrift by reducing the demands for natural gas.

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electricity and coal, whose suppliers each still compete to sell customers more of their type of fuel (see Fig. 16).229 Investment in a public utility, like a nuclear power station (having a payback period > 14 years), is essentially long t e r m and therefore is fundamentally less attractive to private investors. It is difficult to compare on a like-by-like basis the private and state sectors with respect to financial investments in CHP. For instance, in the private sector, debts are not underwritten by the consumer. Equally, there is no absolute guarantee that electricity produced in the private sector will be purchased by the nationalised system for a sufficiently financially attractive rate of return for the private investor. Also, the expected payback periods for investments differ significantly between the two sectors. This is despite the 1983 Energy Act, which was heralded as paving the way for competition from the private sector37"2°l"23°--the opportunity for this may be appreciated from Fig. 17. A private sector industry, which is linked to the national electricity grid and also generates its own electricity, is obliged to inform the local Electricity Board. They will need to ensure that any surplus electricity exported to the grid is 'clean' (e.g. at the right frequency). Currently, the CEGB produces electricity at an average rate of 25 GW e

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Fig. 17. A prediction of how the total output of all existing electrical-generating power plant in the U K would decline if no new stations are built. T M

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R. F. Babus'Haq, S. D. Probert, M. J. Shilston

throughout the year (but can satisfy a peak demand of 45 GW e in winter). The MEB has only two small C H P - D H schemes operating in Hereford and Fort Dunlop, near Birmingham, England. That at Hereford uses two 7.5MW, 11 kV alternators driven by 104hp diesel engines burning heavy residual-fuel oil. The scheme at Fort Dunlop, which is under development, is similar but somewhat larger with 24 MW of electricity-generating capability. 2°1'232 However, some of the older coal-fired DH schemes have been modernised with respect to the introduction of simplified (but more comprehensive) controls, which can be monitored individually by the user. This has resulted in lower overall costs, and significantly smaller running costs. The range of options for refurbishment, which an authority may wish to consider, can be very broad. Apart from fuel switching and/or a change of heat source, they include (i) installing controls for consumers, heat emitters and heat meters, as well as improving the thermal insulation of the dwellings served, (ii) installing hydraulic controls and increasing the hot-water storage in the local plant rooms and (iii) improving the system's efficiency by 'tuning' the existing boiler plant. It is also important to be satisfied as to the exact cause of any failure in the heat mains before contemplating replacement. For instance, Fig. 18 indicates the effects of a range of alternatives which can be adopted with respect to a DH scheme in the UK. Nevertheless, it is assumed that the heat mains have an average service life of 25 years, and that the mains repairs will increase at 0.085 repairs/km/annum. Conversion of firing from oil to coal is also assumed. CHP linked to DH may yet become highly competitive. More than 200 small CHP systems (producing only about 0.2% of Britain's total electricity supply at present) have been installed (compared with ,-~600 in the Netherlands), often driven by modified automobile engines (e.g. the Totem system). 2°4'233-242 The latter, with a 15kWe and 2.6:1 thermal-to-electric power output, achieves an overall efficiency of 88%. Corresponding figures for the 18 kW e output Holec unit are 2.4:1 and 900/0. 243 The machine at the headquarters of the Devon and Cornwall police force in Exeter is at present the largest plant (in Britain) that generates CHP for a single building. 244 However, there is a vast prospective market for mini-CHP units in the domestic housing area, where one unit could provide enough heat and power for up to 50 houses. Such units are smaller and quieter than conventional power stations. It has been alleged 242'24'* that a national CHP generation

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A - FAULTCORRECTION: ecj. DEALING 9/131-1VALVES, STRAINERS THAT ARE BLOCKED B- MAINS REPAIRS E " MAINS REFURBISHMENT D " DWELLINU-'~THERMAL I MPROVEHENTS E - BOILER CONVERSION (OIL ~ COAL)

18 16

12 ~o10

1985

1990

1995

2000

2005

2010

2015

YEAR F i g . 18.

Projected costs of upgrading and refurbishment of an older type heat mains DH

system since 1980. t a6

programme based on gas-fired mini-CHP units would incur about onethird the capital cost of the equivalent energy-output nuclear power programme. At present, a CEGB nuclear power station costs about £1500 per kW e o f capacity to build compared with about £500 per kW for a mini-CHP system to be installed in a building. Nevertheless, unless the ESI is forced to invest in this new cheap power source, the amount of power so generated will grow more slowly than it should, and the consumer will be denied the benefit o f low risk, low cost and low pollution power. If all the heat so released can be used, then the production cost o f electricity is about 0.3-0.5 p/kWh including capital and maintenance costs over a 25-year life. Nuclear power costs about 1-2 p/kWh. However, in national macroeconomic policy terms, there is a serious disadvantage in biasing CHP developments towards the use of smaller schemes. Such schemes will generally be based on oil or gas,

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and so cannot offer the long-term balance-of-payments benefits that would accrue from large city-wide schemes using coal, refuse-derived fuels or, eventually, nuclear power. 2°1 Because of government policies, DH will frequently have to struggle at present to compete with 'off-peak' electricity and domestic or imported natural gas. However, it would appear that 'off-peak' electricity is artificially cheap and so may not be a long-term competitor. SNG produced from coal is estimated to be two to three times the price of today's natural gas per resulting therm obtained via their combustion, even given the availability of secure and relatively cheap coal supplies. Both coal and nuclear power, which provide the most immediate and substantial options for diversifying the energy economy, are the subjects of deep divisions of opinion within British society. The miners' strike revealed significant dilemmas about the future role of indigenous coal in the U K energy economy, and over the modernisation of the methods of coal excavation. 31'2°7'245 The present Government's policy of allowing free market forces to dictate decisions is often ignored for sociopolitical reasons: e.g. even when it is cheaper to import coal than to use that from the NCB. Also, it is quite natural that the NCB (and the other competing energy-supplying industries) would be far more interested in selling fuel directly to the public, rather in supplying it for C H P - D H schemes and thereby possibly reducing their overall market. The introduction of CHP would probably reduce the rate of demand for coal in the UK. However, it would increase the overall percentage of coal in the UK's total annual energy consumption. Clearly this would not be universally welcomed, and there are those whose cynicism is such that they believe that the conditions attached to the funding of the leadcity schemes have been contrived to prevent such an outcome. Even if this depressing view is rejected, it is still hard to believe that the situation is fair, or even remotely likely to provide a proper basis for the assessment of the potential benefits of CHP. Without such an assessment, there is the distinct possibility that British society will be poorer because of the failure to implement C H P - D H schemes on a vast scale and, for some, this will mean being very much colder. 2°1 The Government appears to have no energy policy. It prefers to involve itself as little as possible, allegedly letting market forces (with significant Government interference via taxation) control the development of the electricity, gas and coal industries. But this may not be the wisest approach to see us into the next century. T M -246. In 1982, Nigel Lawson, the then Energy

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Secretary, explained that, 'in his view, the future, even the 20-year future, was unguessable in relation to U K energy consumption'. 247 Nevertheless, the present Energy Secretary, Peter Walker, has claimed 19s that he can make Britain the most energy-efficient country in Europe. To achieve this will require further Government leads and significant investments with respect to C H P - D H and a more reasonable (i.e. what is in the best interest of Britain) approach from the Electricity Boards!

CONCLUSIONS DH and DC are means of distributing a heated or cooled fluid, respectively, from a central source to highly occupied areas. C H P or cogeneration is the production of heat as well as useful shaft power. This safe, proven technology is a worthwhile, but relatively neglected, option in Britain. With fossil-fuel prices tending to rise once again, it appears inevitable that for groups of more than 5000 houses, C H P DH systems will be installed as financially attractive investments. Unfortunately, there are many practical difficulties concerning its implementation, e.g. the tearing up of streets required for the laying heat mains. Also, there are numerous vested interests (e.g. BGC and CEGB) who are unenthusiastic or opposed to the implementation of CHP, maintaining it is much more logical to distribute natural gas or electricity rather than heat. The available sources of energy for C H P - D H C schemes have been discussed. With greater incentives to employ new sources of fuel, municipal, commercial and industrial wastes are being explored actively as potentially useful sources of both materials and fuels. Of the non-conventional fuels, nuclear energy, solar energy and coal-derived synthetic fuels show promise as large-scale realistic alternatives for CHP-DHC. In order for C H P - D H to be economic overall, tariffs must be so structured as to make it financially attractive for as many individual prospective consumers in the served region as possible. The selection of metering and control arrangements for C H P - D H C systems should form an integral part of any design. Yet, the rate of progress in this field has been disappointing. Avoiding the use of meters can lead to the energy profligacy. However, at present, it is the policy of many local authorities not to charge customers according to metered

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heating consumptions. Nevertheless, modern electronic pre-payment magnetic cards are flexible and can be programmed to take account of special requirements. Is the UK 1983 Energy Act being interpreted as it was intended? It has been alleged that the CEGB view CHP as a threat, a competitor and doubt its economic viability.19° However, the ESI emphasises that fully harmonised tariffs will be made available equally to consumers whether they are electricity generators or not. Many small CHP schemes, driven by modifiedautomobile engines, are being installed in the UK. They usually should be sized to supply a waste-heat recovery base load (e.g. for summer operation in the UK) and be operated for at least 6000 h per year, with options (i) to export excess electricity generated, and (ii) to provide additional means to satisfy peak-heating demands. The future development of the C H P - D H in Great Britain is uncertain. Decisions are now needed urgently, because it appears that large-scale C H P - D H schemes will not be developed, in the near future, without significant government financial inducements. Unfortunately, the forecasting and consequent planning that have occurred during the last decade give little confidence that this can be done effectively for decisions that will have their economic impacts more than a few years ahead. Even decisions that have turned out to be fortuitous retrospectively were often made for other reasons. For example, the use made in the 1984/85 coal-miners' strike of the excess capacity of oil-burning electricity-generating plant in frustrating the wishes of the strikers' leaders. This plant had been installed more than a decade previously, when it was believed that the unit prices for oil would be far less than they are today, and that the demand for electricity in Britain would continue to rise: neither assumption proved to be correct. However, relatively recently, the Government has offered to contribute towards the cost of planning (but not implementing the introduction of) C H P DH supplies for three cities; namely, Belfast, Edinburgh and Leicester. More encouragingly, the Electricity Supply Industry is now working closely with the municipal authorities in the cities of London, Newcastle and Sheffield to develop CHP schemes. However, to date (1986), with the exception of the MEB, the track records of the Electricity Boards in fostering CHP in the UK are not impressive. An investigation should be undertaken of the investment-appraisal criteria which are used when assessing possible alternative investments

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in energy-producing projects (e.g. the various power supplies--nuclear energy; natural gas; coal; solar energy; w i n d and/or waves; geothermal heat; etc.). It appears that there is a prima facie case that, in the UK, various energy projects are not judged on a like-by-like basis. (This also applies with respect to comparing the worth-whileness of investments in CHP, nuclear power stations, the proposed Severn barrage (with a roadway across its top) for harnessing tidal power, or the fixed-link English-channel tunnel). It would appear that a consistent and coherent national energy policy is now long overdue!

ACKNOWLEDGEMENTS The authors wish to thank the University of Technology, Baghdad, Iraq, for the award o f a Research Fellowship to R. F. Babus'Haq to permit this survey to be undertaken. We are also indebted to William Orchard of Orchard Partners, S o u t h a m p t o n Row, London, England, who advised on several aspects of the project.

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APPENDIX

Political leadership Following the circulation of a prepublication copy of the main body of the paper to interested organisations, several comments and suggestions for a bibliographical extension to the reference list have been received. These are now presented for completeness. The dilatory approaches of successive governments to the development of C H P in the U K have squandered opportunities to revitalise our inner cities, combat cold homes and hypothermia, boost energy efficiency and create jobs, as well as stimulate the power-engineering industry. British citizens are being deprived of what is readily available in many other parts of Europe--namely relatively cheap heat from electricitygenerating power stations. The World Health Organisation recently rated Britain as the worst offender, with respect to sickness and death arising from underheating, among all the industrialised developed nations. The potential for C H P is good, despite its prospects of rapid implementation nationwide being so relatively poor that many enthusiasts even suspect a political conspiracy in favour of nuclear power. However, it is more probable that political misjudgement, bureaucratic inertia and institutional resistance to change have all ensued, leading to excessive procrastination and contributing to inhibiting progress. The Government's internal wrangle between the Treasury and the Department of Energy concerning investments in the energy infrastructure of Britain has produced frustrations and delays. Now it is urgent to have a C H P - D H strategy as part of Government policy, for social and economic as well as energy reasons.

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