IEA common study on advanced heat pump systems, technology survey. Part 1: Research and development trends

lEA common study on advanced heat pump systems, technology survey. Part 1: Research and development trends D. L. Hodgett and G. Oelert Key words: heat pump, sorption, compression

Etude commune de I'AIE sur les systCmes de pointe de pompe & chaleur. Revue de la technologie. le partie: tendances de la recherche et du d6veloppement

Ce rapport r#sume /'#va/uation des tendances de la recherche et du d#ve/oppement dans /e domaine de /a pompe J cha/eur qui on[ #t# rda/is#s dans le cadre du pro/el commun de I'Agence /nternadonale de I'Energie auque/ treize pays ont particip#. On d#crit /e pro/e[ e[ sa portde et /'on ana/yse /es tendances actuelles du ddve/oppement des pompes chaleur sous les rubriques de syst#mes ~ sorption et ~ compression.

The paper summarizes the evaluation of heat pump research and development trends which was carried out as part of the International Energy Agency collaborative project organization in which 13 countries

participated. The project and scope is described and the current trends in the development of heat pumps are analysed under the broad headings of sorption and compression systems.

Project organization and scope

study, performing the technology survey and assessment.

The common study of advanced heat pump systems was initiated in October 1978 by the Committee on Energy Research and Development of the International Energy Agency (lEA), Paris, as Annex 1 of an 'Implementing agreement for a programme of research and development on advanced heat pump systems'. The participating countries were Austria, Belgium, Canada, Denmark, Federal Republic of Germany, Italy, Japan, Netherlands, Spain, Sweden, Switzerland, UK and the USA. The project was completed in July 1980. KFA JQlich, as representative of the Federal Republic of Germany, was appointed to act as operating agent with Battelle-lnstitut e.V., Frankfurt as its assistant, responsible for co-ordinating the The authors are from the Plant and Process Engineering Department, Battelle-lnstitut e.V., 6000 Frankfurt am Main 90, FRG. Volume 1 of the project final report (Res.ults and Conclusions) has been published by Verlag TUV-Rheinland, K61n, copyright for which is the property of KFA JQlich Paper received 25 August 1981.

The market study part of the programme was assigned to the USA, which nominated Resource Planning Associates Inc. as its assistant, responsible for the market study. The overall objectives of the study were to collect and collate data on advanced heat pumps, to produce an evaluation of selected systems, to identify desirable developments and thereafter to propose an international research and development programme. The project consisted of the initial phase of the identification of the basic types of heat pumps and their classification, the market analysis and the determination of the state of heat pump development in each country. Thereafter the basic types of heat pumps of interest to the participating countries were identified and detailed technical and cost profiles prepared on each system of interest. These "case studies' were then used in the market study to estimate the potential market in each

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The major performance criteria are the coefficient of performance (COP) and seasonal performance factor (SPF). There are many possible definitions of these, depending on what the system boundaries are considered to be. Thus there is the performance of the heat pump subsystem, that including the drive subsystem, and that of the system including the electricity and fuel producing subsystems.

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Fig. 1 Principles of major advanced heat pump systems. a - electric motor- Rankine (thermally generated electricity); b - single stage absorption: c - internal combustion engine: d - Rankine-Rankine (single fluid) Fig. I Principes des principaux syst~mes de p o i n t e de p o m p e chaleur, a - M o t e u r #lectrique - #lectricit# p r o d u i t e t h e r m i q u e m e n t p a r cycle Rankine; b - absorption m o n o - # t a g # e , c - m o t e u r ~ c o m b u s t i o n interne," d - cycle R a n k i n e - R a n k i n e (un seul fluide)

country for the chosen systems to year 2000, comparing them to the conventional systems prevailing in that country.

The research and development trends were considered under the classifications of heat pump, ie sorption, compression and other systems, with the drive as a subclassification.

Sorption systems The research and development trends concerning sorption systems have been in two major areas, firstly fossil fuelled liquid/vapour systems (absorption, resorption etc) for space and water heating and secondly the solar energy driven systems to provide heating, cooling, refrigeration and air conditioning, using all sorption techniques. Market

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Fig. 1 shows the principles of the electric heat pump and three of the major advanced systems. Each heat pump system consists of a heat pump cycle (or subsystem) and a drive cycle (or subsystem). In the case of mechanical systems, the subsystems are usually separate units connected by a mechanical linkage or shaft to the heat pump compressor, while in absorption systems, the drive cycle is that part of the thermodynamic cycle which by absorption and desorption provides compression and expansion of the volatile work fluid. Fig. 2 shows the range of applications covered in the study with the approximate range of heat pump power outputs required for each application.

Volume 5 Number 3 May 1982

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Fig. 3 illustrates the research and development trends in sorption systems. The selection of system type and working pair is primarily governed by the temperature levels required for the absorber, evaporator, condenser and generator. The latter is determined by the available source of high level heat, whether solar, waste heat or fossil fuel, while the evaporating and condensing temperature are fixed by the source and sink temperatures, which are functions of the application. The two classical working pairs NH3/H20 and H20/LiBr are still strongly favoured in many countries for most applications, and most system developments are based on one or the other. The search for new working pairs is only a result of the well known weaknesses of both pairs, which limit them to particular applications. It is quite clear that it is extremely unlikely that new working pairs will be found which will be applicable, with better performance, over the complete range of conditions covered by refrigeration, cooling and heating. The research and development trends in sorption systems were analysed with reference to the energy source used for generator heating, with further discussion based on the application and working pairs. The major factor in solar driven systems is the low level of heat to the generator, which would generally have a temperature less than 90°C. This low temperature requirement of the generator has focused attention on the H~O/LiBr single stage absorption system except where the evaporating temperature is likely to be lower than 0°C. Thus for

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solar powered space coolers, air-conditioning, and combined heating and cooling, H20/LiBr shows superior performance than the alternative absorption cycle working pairs, and systems are under development in many countries. 27-32 Single stage H20/LiBr absorption systems are also being developed with an open generator, 3334 or adding other salts to increase performance or to broaden the region of operation without crystallization, allowing air cooled condenser and absorber operation. Other developments are based on the use of methanol (CH3OH) as the working fluid 35 or lithium chloride (LiCI) as solvent. 36 Other solar driven systems are based on the adsorption of a vapour or gas by a solid. The favoured refrigerants are hydrogen with metal hydrides such as lanthanum pentanickel (LaNis) alloy as sorbent, 37'38water with zeolites, 39 or sodium sulphide 4° or potassium thiocynate (KCNS) 41 as sorbent. All these systems and some of the NH3/H20 systems 42 are periodic in operation, ie they require flow reversal and heat storage rather than continuous unidirectional flow. The main group of sorption systems, which are of interest in Northern Europe and the USA, are those which are suitable for both space heating and cooling or for space heating only, using fossil fuel to heat the generator. The two classical working pairs, NH3/H20 and H20/LiBr, have been the focus of development for this purpose although their disadvantages (toxicity of NH 3, freezing and crystallization with H20/LiBr ) have resulted in efforts to find alternatives.

Revue Internationale du Froid

NH3/H20 systems are currently being developed for the single family house application for space and water heating using single stage absorption 37 (and also at British Gas Corporation, London) or by resorption. 43 However, the toxicity of NH 3 makes it unattractive for this application (indeed it is prohibited in Japan for this purpose) and since space heating under European and US conditions with air as heat source requires evaporating temperatures in the range + 1 0 ° to -10°C, and perhaps to -20°C, the H20/LiBr system cannot be used. Thus, it is for this area of application that a major trend has developed to find and use alternative working pairs. One such pair, R 22/E 181, has been chosen for a system currently under development. 44'45 Many studies are underway to find better working pairs 46-51 (Columbia Gas System, USA), particularly for this application for solar cooling or for vehicle cooling 52.~3(which has similar operating conditions). Several approaches are being attempted: One, improvement of the performance of H20/LiBr systems by reducing the temperature at which crystallization occurs through the addition of other salts. 46 Two, using NH 3 as refrigerant, but with alternatives to H20 as absorbent (such as NaSCN, 46 LiNO3, 47 or KSCN 41) to avoid use of a rectifier. Three, using H20 as refrigerant, but with alternatives to LiBr as absorbent (such as LiCI or other metal salts 54) to avoid crystallization problems. Four, replacement of NH 3 as refrigerant by other fluids, such as CH3NH 2 (methylamine) or C2HsNH2 (ethylamine) with H20 as absorbent, to reduce the problems due to toxicity and explosivity. Five, search for organic working pairs such as R 22/E 1 81 46-50,52,53to avoid the safety and rectification problems of NH3/H20 and the crystallization problems of H20/LiBr. So far little has been published to show that a suitable working pair has been found, though the fact that Allied Chemical 5~ and Columbia Gas Systems are developing systems based on unnamed organic working pairs is hopeful. Waste heat driven systems are generally for industrial use, or use industrial waste heat for applications such as district heating. The waste heat sources can be used solely for heating the generator or for heating both the generator and as source for the evaporator. Under these circumstances the traditional working pairs NH3/H20 and H20/LiBr can be used to good effect, since large units can be multi-staged. Where low pressure steam or low pressure water can be made available, eg from burning waste gas, or by heat recovery from flues or from iron and steel furnaces etc, the NH3/H20 system can be used to

Volume 5 Num~ro 3 Mai 1982

provide district heating. A two stage system (two stage evaporation and absorption) is currently under development. ~6A single stage H20/LiBr unit is also under development for the same purpose, 57 and also with a heat transformer variant using a large quantity of medium temperature water (at about 60°C) to provide a smaller amount of heat at a higher temperature (80°C), and rejecting heat to the environment. A similar system to the latter but based on NH3/H20, has also been proposed. 58 These systems are, in effect, thermodynamically equivalent to heat engines rather than heat pumps since they operate with the condenser rejecting heat at a low temperature and the evaporator absorbing heat at high temperature. Nevertheless, the effect is to provide high grade heat from a low grade source using the same technology as absorption heat pumps and refrigeration systems. A further development has been in the use of absorptionresorption and two stage absorption systems, eg using NH3/H20, 59 which are being evaluated for incorporation in chemical engineering processes such as the production of styrene and cyclohexane.

Compression systems The research and development trends in compression heat pump systems are summarized in Fig. 4. The initial trends were in the development of the well established electric motor driven Rankine cycle heat pump. Later came the development, particularly in Germany, Denmark and Holland, of internal combustion engine driven Rankine systems using Diesel and Otto engines, while in the US and several other countries research and development has concentrated on external combustion engine driven Rankine cycle systems. Drive cycles under development include organic Rankine, steam Rankine, Stirling and Brayton (or Joule). In the US a further development is the combined Ericsson drive, Ericsson heat pump unit. The different trends can be attributed to the requirement in the US for summer cooling as well as winter heating and thus the preferred use of air as the distribution medium, the availability of solar radiation as drive energy in a large proportion of the US, and the spin-off from aerospace technology. In Germany and other European countries the requirement is for heating only, using hot water as distribution medium for multi-family houses. The heat load for this application could easily be matched by that of available technology, such as industrial refrigeration compressors and engines. E/ectric systems. Major developments in electric heat pumps have occurred in the US, where there has been a strong demand for air conditioning in many parts of the country since the 1 950's. Thus the initial developments were towards reversible air-toair, and for larger applications air-to-water, systems capable of providing summer space cooling and a proportion of the winter space heating. The trends in the 1 970's were firstly to improve reliability, the lack of which has previously been a factor limiting sales of equipment. Studies of the modes of failure

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of existing equipment indicated major deficiencies in the compressor design, controls and associated electrical equipment. 8° As a consequence of this, improvements were made to compressor design, suction accumulators and sump heaters were added, simpler controls were developed, manufacturing techniques were improved and better outside coil design and defrost control were developed. Later an improved performance standard (ASHRAE Standard 90-75) was introduced, 61 which set higher standards for both heating and cooling performance. To achieve these standards manufacturers have introduced larger heat exchangers, speed modulated compressors and more efficient fans. 6~,62Subsequent developments in the US have been towards the production of systems for use in northern climates, where cooling is unnecessary and external winter conditions are more severe. Such system use either air or ground water as source and have electric resistance heaters, oil or gas fired furnaces as backup. 62,63In Germany, the same trend towards fossil fuel fired back-up systems has also been strong.64 These 'bivalent systems', usually consisting of an electric air-to-water heat pump with oil or gas fired boiler back-up, have been extensively promoted by the electric utilities and heat pump manufacturers as the use of a fossil fuelled back-up avoids the maximum demand period of the whole electricity system. However, the increased capital cost and complexity makes them unattractive to the user with current energy costs.

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In countries with a high proportion of hydroelectricity direct electrical back-up systems are common, and with the high standards of thermal insulation which are obligatory in countries such as Sweden. the heat pump can be incorporated into the ventilation system (which is often necessary to ensure controlled air changes). Alternatively, air-towater systems are used with direct electric heating incorporated in the flow system after the heat pump. One such system uses a so-called regenerative cycle involving by-passing the expansion devices for about 15% of the operating time. so increasing the system capacity by about 30% without increased power consumption. 6~ In the UK the trend has been towards the development of small air-to-air systems suitable for a single room, 86 and small (or well insulated) single family house heating, z67'88 Recent trends in electric heat pump systems have been towards alternatives to ambient air as the source. 7 One such trend is towards ground source systems, and although previous work (eg by ERA in England in the 1950's) had not been successful, the reawakened interest in the ground as heat source697° lies in its high heat capacity and low amplitude and frequency of temperature oscillation, which makes it particularly attractive in countries such as Sweden and Canada which have winter minimum air temperatures of less than -20°C. Current efforts are directed towards low cost optimized systems, using both horizontal pipes 7172 and vertical pipes. 71"73'74Another source being

International Journal of Refrigeration

extensively investigated is solar radiation, either using conventional solar panels 75-79or specially developed solar roofs. 8° Other sources currently being examined are geothermal, 8~ surface water 1 and sea water. 8 Another trend has been towards better compressors, both from the efficiency and reliability aspects. Improvements to the designs of hermetic and semihermetic reciprocating compressors which predominate in the size range <50 kW (electrical power input), are being made which should yield benefits at little increase in cost. These include better motor and compressor design, 82 use of speed control 83 and recovery of the compressor waste heat by simple means. 84 Meanwhile advanced small rotary compressors are being developed by Fedders, Prestcold and others 85 which have the advantages of small size, less complex construction, insensitivity to liquid flooding, and the potential for improved efficiency. A novel development is a free piston electrodynamic compressor 86 driven by a linear motor, which has the potential of being easily capacity controlled. Finally, the use of non-azeotropic mixtures as working fluids has been shown to give increased performance, 87-89though they require larger heat transfer surfaces than single systems.

/nterna/ combusdon engine systems. Internal combustion (ie Otto and Diesel) engine driven heat pumps were first used in the 1950's for large building heating, and in the last decade for swimming pool and leisure centre heating, 9° an application for which electric motor driven systems have also been used. Often combined heating and cooling is necessary in this application (eg in air conditioning or combined skating ring-swimming pool-sports hall complexes) making a heat pump system the natural choice. The advantages of using engine driven systems are that a substantially higher coefficient of performance can be achieved. 9°-92 than with electrical heat pumps, and higher output temperatures can be obtained while still using R 12 or R 22 as working fluids. These commercial heat pump installations generally use medium to high speed (1000-2000 Hz), four stroke, gas (ie Otto) engines of the type used for stand-by generators, with shaft powers in the range 1 50-750 kW. 93 Although Diesel engines have generally higher efficiencies than Otto engines, the general preference has been for gas engine driven systems, because of the lower fuel cost, the lower dew point of the acidic components in the exhaust and sooting problems with Diesel exhaust. Later developments have used high speed automotive Otto engines 21 and Diesel engines 22.94with shaft powers from 50 to 250 kW, while for district heating systems large medium speed Diesels (>1 MW) have been employed. 95 A particularly interesting development has been the use of Wankel engines for this purpose. 96

Volume 5 Number 3 May 1982

For small systems (thermal output in the range 10-100 kW) both Otto 97 and DieseP T M systems are under development in West Germany. Current developments also include an Otto engine driven, higher temperature machine for industrial purposes, 99 and the development of systems using other prime energy sources. Examples include Otto engine systems using colliery gas (and mine cooling as the heat source) and wood gasifier produced biogas as fuel for Otto engine district heating schemes. The major trends are therefore towards large systems, to capitalise on the higher efficiency obtainable from the use of large engines and waste heat sources, or towards medium-sized systems, using low-cost series produced automotive engines. The development of small systems (less than 100 kW output) has been hindered by the relatively high specific cost and lower efficiency of small engines, and the anticipated problems with lifetime and service.

Externa/ combustion engine systems. At present no external combustion engine heat pumps are commercially available. Research and development has concentrated on Rankine and Stirling drive cycles, each of which shows particular advantages for this purpose. Rankine drive cycles have been selected because systems can be developed with a combined expander and compressor unit giving a mechanically simple unit suitable for either fossil fuel or solar power. The Stirling cycle has been chosen by others because of its possible high efficiency, low noise and reliability. Rankine-Rankine systems can have either a single working fluid or two separate working fluids for the drive and heat pump cycles. The advantage of the latter is simplicity, having a single condenser for both cycles and no problem with sealing between the expander and the compressor. The use of a single working fluid results in an inability to optimize both the power and heat pump cycles, giving either an excessively low heat pump evaporator pressure or an excessively high feed heat pressure, and poor part load performance. For large systems, turbo-expanders and compressors have been selected, since these have high efficiencies and are compact, with water 1°° or a low pressure organic fluid TM for the drive cycle working fluid and with a normal halogenated hydrocarbon refrigerant for the heat pump fluid. For small systems many developments are also based on turbomachinery through these, for the sake of simplicity, use a single work fluid. 2°.1°2-1°4Alternative approaches for small systems are to use a combined free piston expander and compressor, ~°5.~°6a combined rotary-vane expander-compressor 107with a single fluid (usually R 11 or R 114), or a rotary expander with a normal reciprocating compressor with R 11 as the power cycle fluid and either R 12 or R 22 as the heat pump fluid, T M Because of its superior performance, R 1 1 is favoured for solar powered single fluid applications, while R 1 14 is

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favoured for fossil fuelled systems because of its higher thermal stability. Stirling engine systems are at a very early stage of development, whether these are driven by the so called kinematic, ie mechanically coupled, piston engines or by the more novel free piston systems. The kinematic engine developments are generally based on earlier work in the Netherlands by Philips. Philips are still active in developing their engine, ]6 while United Stirling in Sweden 1°9 are at an advanced stage of development of a series of medium-sized engines for automotive use which could be used for this application. In the UK, a machine has been patented which could be used for both drive and heat pump cycles. 1]° Research is also being conducted on the practical applications of kinematic Stirling engines to drive conventional Rankine cycle heat pumps, TM and also at the Technical University of Denmark into a StirlingStirling heat pump unit to produce both heat and power. Free piston Stirling-Rankine systems are also being developed with both the Stirling engine and Rankine compressor being in a single hermetic unit. Major development efforts are in the USA. rTJg,5~ Both systems are air-to-air units, for both cooling and heating, and are suitable for single family house use. A gas turbine, (or Brayton cycle), is being developed by Air Research in the USA as a heat pump drive unit. 17.18This uses a sub-atmospheric pressure, regenerative gas turbine with heat recovery to drive the turbo-compressor of an air-to-air Rankine cycle heat pump through a magnetic coupling. This is intended for commercial building heating and cooling, The air (or Joule) cycle has also been considered for use for the heat pump subsystem, TM particularly for applications when hot (and dry) air is required, such as industrial drying. The Joule cycle, though having a high theoretical efficiency, suffers from a high sensitivity to irreversibilities and the properties of the work fluid, and so efforts are aimed at improving its performance by injecting water ~12 or another condensible vapour ~13,~14to reduce compression power.

achieve the heat pump effect. These use an ejector, 24 or a heat pipe. ~ The former is suitable for industrial applications where high pressure steam is available and the unit is used to recover waste heat. The latter is suitable for the generation of cold using solar generated heat. The thermoelectric heat pump, using the Peltier effect, continues to be developed for heat pump applications though the intractability of finding pairs of conductors which show a high Peltier effect (high conversion efficiency from electricity to heat and cold) with low thermal conductivity has resulted in no practical use for this technique in the thermal output range of interest. However, recent developments suggest that the effect combined with semiconductor photoelectric devices could be used for solar cooling applications. 11~

Comments

The review of research and developments trends shows that there is a large and extremely wide range of activities covering most of the possible heat pump systems. It is clear that heat pump technology is emerging from many years of neglect, and that systems are being developed for all possible applications, though emphasis lies in the development of small systems for residential heating and cooling. Part 2 of the paper describes the comparison of selected systems for a range of applications and the conclusions and recommendations of the project.

References

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4 5

6 Benson 19 selected the free piston Ericsson-Ericsson system as having the highest potential of all the free piston systems and this is being developed by ERG. This machine can be either fossil fuel or solar powered, and has the potential of near optimum performance from both cycles. This, combined with a self-modulating capacity and possible provision of heating, cooling and electricity generation, is the motive for its development. Other systems

Two developments are based on using nonmechanical compression of a gas or vapour to

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Rumpf, H. G. Space heating pumps using running water as a heat source Paper No 70/D2, UNIPEDE, Warsaw Congress, June 11-15 (1 979) Heap, R. D. Heat pumps for domestic use. Proc 2nd Int CIB Symp on Energy Conservation in the Built Environment, Copenhagen, 28 May-1 June (1979) Gilli, P. V. et al. Verringerung des Energieaufwandesmit Hilfe yon W~rmpumpen (Reduction of energy consumption using heat pumps) dbv Verlag Graz, 1. Auflage 1978, tSBN 3 7041-0007 2 Soil temperature data (1 958-1972), Environment Canada (1973) Waterkotte, K. Erdreich-Wasser Warmepumpe for ein Einfamilienhaus (Groundwater heat pump for a single family house) E/ektrowbrme International 30 (Jan 1972) Researchand development on extended range water source heat pumps. Report to DBC/NRC by Hydro Quebec Research Institute, Canada (March 1978) Yon Cube, H. L. Warmequellen fQr W~rmepumpen (Heat sources for heat pumps) W~rmepumpentechnotogie, Band I, Vulkan-Verlag ISBN 3-8027-2340 6 (1 978) Lorentzen, G., Haukas, H. T. The effect of climate on the economy of heat pumps. Paper E1-56, IIR XVth Congress, Venice (Sept 1979) A new and novel form of district heating using thermal effluents from electricity generating plants Energy, Mines and Resources, Canada (Dec 1977) HeatPumps 1978. Report by the Ad Hoc Committee on Heat Pumps, World Energy Conference, London (July 1979) Altenkirch, E. Absorptionsk~ltemaschinen, VEB Verlag Technik, Berlin (1954) Plank, R. Ed Sorptionsk~ltemaschinen, Handbuch der Kgltetechnik, Teit 7, Springer-Verlag, Berlin (1 959)

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Lotz, H. Behaviour of single- and manifold-medium heat pumps, W~rmepumpentechnologie. Band I, Vulkan-Verlag, Essen, ISBN 3-8027-2340-6 (1978) Ellington, R. T. et al. The absorption cooling process Inst Gas Techn Res Bull 14 (1957) Wurm, J. An assessment of selected heat pump systems, Institute of Gas Technology, February (1977) Hermans, M. L., Asselman, G. A. A. A Stifling Engine heat pump system, Paper 789274, Proc 13th intersociety Energy Conversion Conference, (IECEC), 3 San Diego (August 20-25, 1978). SAE P-75 Society of Automotive Engineers Inc, US Sarkes, L. A. at al. Gas fired heat pumps: An energy technology ,4SHRAE Journal 9 (March 1977) 36-41 Friedmann, D. Light commercial Brayton/Rankine space conditioning system, Energy use management, Ed Fazzolare, R. A , Pergamon Press (1977) 243-250 Benson, Go M. Free piston heat pumps, Proc 12th/ECEC (August 1977), American Nuclear Society Strong, D. T. G. Directly fired domestic heat pump development, W~rmepumpentechnologie, Band II, VulkanVerlag, Essen (1979), ISBN 3-8027-2341-4 Pegley, A. C., Rieke, A. Small gas engines as prime movers for heat pumps in domestic heating, ibid Struck, W. Antrieb von W~rmepumpen mittels Dieselmotor, ibid Steimle, F. Absorptionsw~rmepumpen, W~rmepumpentechnologie, Band IV. Vulkan-Verlag. Essen (1980), ISBN 3-8027-2346-5 Mostofizadeh, Ch. Thermische W~rmepumpe, Elektrow~rme im Technischen Ausbau, Elektrow#rme Interna#ona/EdA, 35 (January 1977) DIN 8900 (Draft), Part 3, Deutsches Institut for Normung e V. (1979) ASHRAE Standard 90-75, American Society of Heating, Refrigeration and Air Conditioning Engineers, New York (1975) Lazzarin, R. at al. Performance predictions of a LiBr absorption air conditioner utilising solar energy, in Sun: Mankind's Future Source of Energy, Ed. de Winter, F., Cox. M, Pergamon Press, Vol 3, ISBN 0-08-022725-2, New York (1978) 1572-1580 McChesney, R. M. Solar heated and cooled financial building, ibid Naito, S. Absorption refrigerator of natural recirculation type, US Patent 3978683 (Sept 1976) Ward, Do S. Solar absorption cooling feasibility Solar Energy 22 (1979) 259-268 Boldrun, B., Lazzarin, R. How to control a solar powered absorption chiller, Paper E1-45, XV International Congress of Refrigeration, Venezia, 23-29 Sept (1979) Grallert, K. K. H. Entwicklungsaspekte fQr solare K0hlanlagen Sanit#r- und He/zungstechnik 3 (1979) 293-297 Schelpuk, B. C., Hooker, D. W. Development programmes in solar desiccant cooling for residential buildings I m J Refrigeration 2 5 (1979) 173-179 Bolzan, M., Lazzarin, R. Open cycle absorption cooling devices with spray chamber regenerator and air solar collector. Paper E1-46, XV Int.Congress of Refrigeration, Venezia. 23-29 Sept (1979) Birnbreier, H. Absorptionsw~rmepumpen, Rationelle Energieverwendung, Status-bericht (1978), BMFT, ISBN 3-88135-069-1 (1979) 528-531 Kremnyor, O. A. at al. Study and development of absorption-type solar-cooling units, Paper B2-54, XV Int Congress of Refrigeration, Venezia, 23-29 Sept (1979) Wolf, So Hydrogen sponge heat pump, Paper 759196, lOth IECEC, ASME, NY (August 1974) Gruen, D. M. at al. Lanthanum nickel aluminium alloy, US Patent 4 142 300 (March 6, 1979) G u i l l e m i n o t , J. J. at al. Utilisation d'un cycle intermittent Zeolithe 13X-H20 pour la refrigeration solaire, Paper E1-88, XV Congress of Refrigeration, Venezia, 23-29 Sept (1979) SystemTepidus, US PatentAppl 865 214 TepidusAB, Box 5607, 11486 Stockholm Kinsella, E. Development of an absorption heat pump of improved COP, Paper B3.2 to Co-ordination Meeting of

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Contractors, E.C. Solar Energy R+ D Programme. Brussels (8 Dec, 1978) Blakeley, R. E. at al. The design and development of an absorption cycle heat pump optimised for the achievement of maximum coefficient of performance, E.C. Meeting on Heat Pumps Research, Development and Application, Brussels (27-28 September, 1978) Gelesic, A., Kampfenkel, O. Sorption heat pumps, UK Patent Application GB 2 002 505A (10 August, 1978) Janssen, H. A., Oelert, G. Development of a primary energy driven absorption heat pump for domestic heating, E.C. Meeting on Heat Pumps Research, Development and Application, Brussels (27-28 September, 1978) Janssen, H. A. et al, Heizverfahren mit einer Absorptionsw~rmepumpenanlage, German Patent Application DE 2803118A1 Macriss, R. A. Selecting refrigerant-absorbent fluid systems for solar energy utilisation ASHRAE Trans 82 1 (1976) 975-988 Ranz, M. Suitability of solvent/refrigerant agents in absorption heat pumps, W~rmepumpentechnologie, Band I, Vulkan-Verlag, ISBN 3-8027-2340-6, Essen (1978) Stephan, K., Seher, D. Arbeitsgemische for Sorptionsw~rmepumpen, K/ima-K#lte-Heizung (January 1980) 21-32 Biermann, W° J., Offenhartz, P. O. D. Absorption cooling systems, ISES, 3rd Conf Use of solar energy for cooling of buildings, San Francisco (Feb 15-17, 1978) 23 Jelinek, M. at al. Enthalpy-concentration diagram of the system R 22-dimethyl-formamide and performance characteristics of refrigeration cycle operating with this system ASHRAE Trans 84 2 (1978) Colosimo, D. D. On-site heat activated heat pumps, Paper presented at the Conference for Technical Opportunities for Energy Conservation in Appliance, ERDA, Boston, Mass, USA (11 May, 1976) Akerman, Jo R. Automotive air conditioning systems with absorption refrigeration, Paper 710037, SAE Automotive Engineering Congress, Detroit (Jan 11-15, 1971) Wallner, R. Fuel saving future alternatives for automotive A/C plants, Paper E1-57, XV Int Congress of Refrigeration, Venezia. (23-29 Sept 1979) Felli, M., M u t t u c c i , F. p-T-x experimental data on working mixtures for absorption refrigeration, evaluation of their performance with low generator temperatures, Paper B1-83, XV Int Congress of Refrigeration, ibid. Allan, R. A., Murphy, K. P. Development of a new gas fired absorption heat pump. paper presented at ASHRAE Semiannual Meeting, Los Angeles (3-7 Feb 1980) M a l e w s k i , W. Heat pump system according to the absorption principle for performance feed into district heating systems, W~irmepumpentechnologie, Band II, Vulkan-Verlag, Essen, ISBN 3-8027-2341-4 (1979) Absorption heat pump for waste heat, geothermal and solar energy, Sanyo Electric Air Conditioning Equipment Co Ltd, 3-10-15, Hongo, Bunkyo-Ku, Japan A heat transformer that upgrades waste heat to higher temperatures Chemical Engineering (Sept 24, 1979) 67 Cohen, G. at al. Valorisation de colones ~ bas niveau au moyen de cycles trithermes Entropie 84 (Nov-Dec, 1978) 31-37 Ambrose, E. R., Ed. Proceedings on the Symposium, Heat Pumps- Improved Design and Performance, San Francisco (19-22 January, 1970) ASHRAE, NY Comly et al. Heat pumps - limitations and potential, GEC Report No 75CRD185 (September, 1975), Schenectady, NY Kirschbaum, H. S., Veyo, S. E. An investigation of methods to improve heat pump performance and reliability in a northern climate, Vol. I-Ill, EPRI Report EM-319 (January 1977) Groff, G. C. at al. Recent investigations of air-source heat pump performance in cold climates, Paper E1-25, XV Int Congress of Refrigeration, Venezia (23-29 Sept, 1979) Operating experiences with electric, dual source (hybrid) heat pumps, W~rmepumpentechnologie, Band I, VulkanVerlag, Essen (1978) ISBN 3-8027-2340-6 Granryd, E. Experiences from a domestic heat pump installation, field measurements, Winter 1979, Scandinavian Refrigeration (April, 1979)

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Freund, P. Domestic applications of small heat pump units, Paper E1-12, XV Int Congress of Refrigeration, Venezia (23-29 September, 1979) 67 O'Connor, T. C., Kyne, H. F. The performance of air source heat pumps in Northern European climatic conditions, Presented at Meeting on E.C. Heat Pumps Research, Development and Application, Brussels (27-28 Sept, 1978) 68 M c M u l l i n , J. T., Morgan, R. The development of domestic heat pumps, ibid 69 Burgess, A. S. et al. Ground source heat pumps, Report No HP-5, solar energy project, by Acres Consulting Services Ltd for Division of Building Research, National Research Council of Canada (June, 1978) 70 Jacobson, L. Ed. Nordic Symposium on earth heat pumps, Chalmers University of Technology, G6teborg, Sweden (15-16 October, 1979) 71 Mogensen, H. P. The ground as a heat source for heat pumps, performance and reactions, Paper E1-27, XV Int Congress of Refrigeration, Venezia (23-29 September, 1979) 72 Granryd, E. G. Ground source heat pump systems in a northern climate, Paper E1-82. ibid 73 Gouldburn, J. R., Fearon, J. Deep ground evaporators for heat pumps App/ied Energy 4 (1978) 293-313 74 Schlosser, K. A mathematical analysis of the earth system for heat pumps Scandinavian Refrigeration 4 (1979) 267272 75 V a n der Kooi et al. A solar assisted heat pump system for residential heating, Paper E1-62. XV Int Congress of Refrigeration (23-29 Sept. 1979) 76 Bougard, J., Pilatte, A. Performance des installation solaire ~ pompe ~ chaleur, Paper E1-38, ibid 77 Lorenz, F. Simulation d'une chauffage residentiel par pompe de chaleur utilisant des capteurs solaires nus commesourcedu froid Paper E1-81, ibid 78 Speidel, K. Dornier/RWE solar house in Essen. FRG Proc. CCMS/ISES, Int Solar Energy conference on Performance of Solar Heating and Cooling Systems, DUsseldorf (19-20 April, 1978) 79 Bruno, et al. The Philips' experimental house: a system's performance study, ibid 80 S c h i m m e l p f e n n i g , K. Energy roof for utilisation of environmental energy for space heating, Warmepumpentechnologie. Band III, Vulkan-Verlag, Essen (1979), ISBN 3-8027-2345-7 81 Kremnyov, O. A. et al. Geothermal air conditioning with heat pumps, Paper E1-22, XV Int Congress of Refrigeration, Venezia (23-29 September, 1979) 82 Kruse, K., Wrede, F. Possibilities of energy saving in compressors for refrigeration systems, Paper B2-37, ibid 83 Paul, J., Steimle, F. Speed controlled compressors effects on the performance of domestic heat pumps, Paper E1-68, ibid 84 Vester, P. Heat pump compressor, 220 V. Danfoss energy view, KF O0.V1.02 (1979) 85 Wurm, T., Lassota, M. J. New rotary refrigeration compressor - its development and potential. Paper B7-42, XV Int Congress of Refrigeration, Venezia (23-29 September, 1979) 86 Polman, J. et al. A capacity controlled free piston electrodynamic compressor, Paper B2-12, ibid 87 Cooper, W. D., Borchardt, H. J. The use of refrigerant mixtures in air-to-air heat pumps, Paper E1-60. ibid 88 Kraus, W. E., V o l l m e r , D. Thermodynamic diagrams for non-azeotropic refrigerant mixtures, Paper B1-48, ibid 89 Saluja, S. N. et al. Operating characteristics of a mixed refrigerant vapour compression system Refrigeration and Air Conditioning (March 1978) 83-86, 11 3 90 Paul, J, Ed. Gasw~rmepumpenpraxis, W~rmepumpentechnologie, Band IV, Vulkan-Verlag, Essen (1980), ISBN 3-8027-2345-5 91 Fox, U., Broer, F. Zur Auslegung von GasmotorW~rmepumpen, HLH 30 8 (August 1979)

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