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Carbon dioxide savings in the commercial building sector
Energy Policy. Vol. 26, No. 8, pp. 615 — 624, 1998 ( 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0301-4215/98 $ 19.00#0.00
PII: S0301-4215(98)00019-6
Carbon dioxide savings in the commercial building sector N D Mortimer, A Ashley, C A C Moody and J H R Rix Resources Research Unit, Sheffield Hallam University, School of Urban & Regional Studies City Campus, Sheffield SI IWB, UK
S A Moss Environment Group, Building Research Establishment ¸td
This paper summarises the results of an initial assessment of the potential to reduce carbon dioxide emissions from the commercial building sector of the United Kingdom. The assessment relies on information provided by the non-domestic building stock database which is currently being developed with funding from the Global Atmosphere Division of the United Kingdom Department of the Environment, Transport and the Regions. Results are presented in the form of carbon dioxide abatement curves which rank energy efficiency measures capable of reducing carbon dioxide emissions in order of decreasing cost effectiveness. Preliminary conclusions are drawn from this work both of the relative importance of the abatement measures considered and of the need to identify additional energy efficiency measures which would be particularly suitable for the commercial building sector. ( 1998 Elsevier Science Ltd. All rights reserved
Introduction
The economic evaluation of measures for reducing carbon dioxide emissions is assisted by the derivation of carbon dioxide abatement curves. Such curves illustrate graphically the potential savings and cost effectiveness of measures for reducing carbon dioxide emissions. A schematic example of a carbon dioxide abatement curve is given in Figure 1 which plots the potential carbon dioxide savings of each measure horizontally and their respective net cost vertically (the quantities of carbon dioxide have been converted here to their equivalent in terms of tonnes of carbon: tC). It can be seen from Figure 1 that the measures are ranked, from left to right, in increasing order of net cost. In this paper, the net cost of a measure is defined as the discounted total (investment and operating) financial costs less the financial savings that accrue from use of the chosen measure per unit of carbon dioxide emissions saved. As will be seen later, this will be used to represent the private investor cost of each energy efficiency measure. Initial carbon dioxide abatement curves were produced for the United Kingdom (UK) in 1989 (Jackson, 1991). This work considered a broad range of possible measures for saving carbon dioxide emissions based on currently available data. The costs and potential savings of energy efficiency measures were derived from published information on energy use in the UK industrial, domestic
Global climate change is now generally regarded as one of the most important environmental challenges facing humankind. Various solutions have been proposed for reducing the carbon dioxide emissions that result from the combustion of fossil fuels and which have been implicated in global warming. Most of these solutions involve fundamental changes in either human behaviour and/or changes in the activities which provide the diverse products and services required to meet the complete range of human needs. It is widely recognised that choices have to be made between competing options and that economic considerations will play a key role in the selection process. Given the uncertain consequences of global climate change and the relative efficacy of proposed solutions, a prudent approach is often advocated for carbon dioxide abatement strategies. The basis of this approach involves proposing the adoption and implementation of measures which not only reduce carbon dioxide emissions but also result in other benefits of known and worthwhile value. Hence, cost effective energy efficiency improvements which produce carbon dioxide savings, while providing a net benefit financially, can be regarded as a prominent component of a measured response to global climate change. 615
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Carbon dioxide savings in the commercial building sector: N D Mortimer et al
Figure 1 Schematic example of a carbon dioxide abatement curve
and commercial sectors (Energy Efficiency Office, 1984; Evans and Herring, 1989; Herring et al, 1988). There are extensive differences in the various processing and manufacturing activities undertaken by industry. However, following work by the Energy Technology Support Unit (ETSU), there is now an improved understanding of the patterns of energy use and prospects for energy efficiency improvements in this sector (Fletcher, 1994). Similarly, as a result of the efforts of the Building Research Establishment Ltd. (BRE), the details of energy use in the UK domestic building sector and the potential for savings from relevant energy efficiency measures in this sector are well documented (Shorrock and Henderson, 1990;1992). In contrast, there is much less reliable published information on energy consumption in the UK commercial building sector. This is because, until recently, only limited basic research has been conducted on energy use in this sector which contains a very wide range of building forms within which extremely diverse activities occur. Hence, as a consequence of this diversity and the limited data available, it has only been possible in the past to derive approximate estimates of energy use and energy efficiency potential in the UK commercial building sector. However, due to work funded by the Global Atmosphere Division of the Department of the Environment, Transport and the Regions (DETR) to develop a nondomestic building stock (NDBS) database, extensive and detailed information is now being assembled which allows more reliable estimates of UK commercial building sector energy use to be derived and which enables numerous important studies to be performed, including the formulation of the carbon dioxide abatement curves presented here.
NDBS database development Work on development of the NDBS database began in 1991 with the aim of collecting and presenting detailed
information related to energy use within the stock to inform policy decisions concerning the so-called ‘greenhouse gas’ emissions. Four main areas of work contribute to the development of the database. The first consists of establishing the national composition of the NDBS in terms of numbers of premises, floor area and types of building. The principal sources of this information are the Rating and Valuation Office (RVO) Rating List and the Valuation Support Application (VSA) database. These provide details of the number of hereditaments (which are rateable properties recognised by the RVO) and their defined floor areas, for building types specified by their RVO Primary Description (PD). Such information is only available for England and Wales and, hence, extrapolation is necessary to obtain a full representation of the UK. Additional sources of information, chiefly for non-rateable properties, are needed to achieve a complete summary of the national NDBS. The second contribution to the development of the NDBS database consists of providing a description of the physical characteristics of the buildings which comprise the stock. This has involved collecting detailed descriptive information, by means of external surveys, on the built form of 3350 addresses in 4 locations chosen as representative of the UK stock; Bury St. Edmunds, Central Manchester, Swindon and Tamworth. This information on built form is being related to the RVO data in order to characterise the entire NDBS. This work on summarising and characterising the NDBS is being conducted by the Centre for Configurational Studies at the Open University (Steadman et al, 1994). The third component of the database development consists of collecting detailed information on energy use within the NDBS. This work, which mainly involves internal surveys of buildings to record details of energyconsuming equipment, is being undertaken by the Resources Research Unit of Sheffield Hallam University. It
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
is currently planned to conduct about 800 energy surveys and to combine subsequent results with bulk data, collected from ongoing monitoring and targeting systems by Building Energy Solutions, to derive representative descriptions of energy use in the NDBS. The internal surveys are designed to obtain extensive data on important aspects of the building and its use which influence energy consumption. The specific energy data collected during internal surveys include fuel records for relevant periods of time and a complete listing, wherever possible, of all energy- consuming equipment and appliances along with information on their energy consumption ratings and usage times. Additionally, the floor area of each internal space within the building is measured during the survey and other appropriate information is collected, such as details of building fabric, energy system control settings, etc. By combining such data together during subsequent analysis, performed on a specially formulated spreadsheet package, it is possible to determine the total delivered or primary energy consumption per unit floor area per year (GJ/m2/yr), the total carbon dioxide emissions per unit floor area per year (tC/m2/yr) and a breakdown of energy use by fuel type and application. Additionally, since all relevant internal survey data are recorded in machine readable form, the retrieval and subsequent analysis of information related to the evaluation of suitable energy efficiency measures is possible and comparatively easy for relatively large number of buildings. The BRE oversees the fourth component of database development which consists of developing a model of energy use in the NDBS and generating suitable results to inform policy making on potential means of reducing carbon dioxide emissions from the UK NDBS. The BRE will conduct studies for the DETR relevant to UK policy needs. As users, the BRE have a co-ordinating role in the development of the database. The database is an extremely important element of the Non-Domestic Buildings Energy and Emissions Model (N-DEEM) which the BRE is formulating to address questions about past, current and possible future trends in carbon dioxide emissions, as well as the potential for reducing these emissions by various means including energy efficiency improvements. Since policy issues in this area are the principal concern of the Global Atmosphere Division, funding and overall responsibility for the development of both the NDBS database and NDEEM are undertaken by this part of the DETR. It was decided in July 1994 that preliminary illustrative results, in the form of carbon dioxide abatement curves, should be produced for the UK NDBS. The preparation of these curves was performed by the BRE with assistance from the Resources Research Unit. At that time, analysed data from internal surveys of 175 buildings were available. Despite this comparatively small sample size, this was considered adequate for producing indicative carbon dioxide abatement curves for a limited number of energy efficiency measures.
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Energy efficiency measures The commercial building sector, which is the subject of this assessment of energy efficiency measures, was defined by reference to the Standard Industrial Classification (SIC). Using the 1980 version of the SIC (Central Statistical Office, 1979), the commercial building sector was assumed to consist of all activities within Classes 61—67, 71—79, 81—85, 92, 94, 963, 966, 969, 97 and 98. A description of the composition of these Classes is provided in Table 1. SIC codes are included in the information held in the NDBS database. Using the above SIC Classes to define the commercial building sector, it was established that data for 146 buildings from the sample available at the time were relevant for this assessment. The agreed list of energy efficiency measures to be investigated by this assessment is presented in Table 2. The selected energy efficiency measures fall into one of three general categories: fabric energy efficiency measures, building service energy efficiency measures and other energy efficiency measures. The fabric energy efficiency measures consisted of loft and cavity wall insulation, and double glazing. Building service energy efficiency measures relate to the plant and equipment which create and maintain suitable environmental conditions within buildings. The selected measures presented in Table 2 refer to the use of plant and equipment which provide space heating, water heating, air conditioning and lighting. Energy efficiency measures include the replacement of one type of appliance with another and improvements in the control of such plant and equipment (such as the installation of programmable timers Table 1 Definition of the commercial sector SIC 1980 Class 61 62 63 64 & 65 66 67 71 72 74 75 76 77 79 81 82 83 84 85 92 94 963 966 969 97 98
Description Wholesale distribution (except dealing in scrap and waste materials) Dealing in scrap and waste materials Commission agents Retail distribution Hotels and catering Repair of consumer goods and vehicles Railways Other inland transport Sea transport Air transport Supporting services to transport Miscellaneous transport services and storage not elsewhere specified Postal services and telecommunications Banking and finance Insurance (except for compulsory Social Security) Business services Renting of movables Owning and dealing in real estate Sanitary services Research and development Trade unions, business and professional associations Religious organisations and similar associations Tourist offices and other community services Recreational services and other cultural services Personal services
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Table 2 Selected energy efficiency measures Category
Description
Fabric energy Installation of 250 mm of loft insulation. efficiency measures Installation of cavity wall insulation. Replacement of single glazing with double glazing. Building service energy efficiency measures
Replacement of existing natural gas boilers with condensing natural gas boilers. Fuel switching by replacing electric room heaters with natural gas room heaters (for premises with an existing gas supply). Installation of 7 day programmable timers in space heating systems. Installation of thermostatically controlled radiator valves. Installation of hot water tank and pipe insulation. Improved design and control of airconditioning systems. Replacement of tungsten filament lamps with compact fluorescent lamps. Replacement of 38 mm diameter fluorescent tubes with 26 mm diameter fluorescent tubes. Replacement of tungsten filament display lights with tungsten halogen lamps.
Other energy Replacement of existing computing equipment efficiency measures and accessories with low energy alternatives. Use of night blinds in commercial refrigeration. Use of electric motor controllers in commercial refrigeration.
and thermostatically controlled radiator valves). Specific process energy efficiency measures were not considered in this initial assessment because of the diversity of activities within the commercial building sector. Apart from covering a range of energy efficiency measures which may be appropriate for commercial sector buildings, the options summarised in Table 2 were also chosen because suitable information was accessible in the NDBS database to evaluate the costs and carbon dioxide saving potential of these selected measures. Essential built form and fabric data, necessary for calculations involving fabric energy efficiency measures, are available from both external and internal surveys. Specific information relevant for such calculations include floor area measurements, wall and glazing area measurements which can be derived from building photographs, and details of building fabric composition derived from inspections and interviews with building occupiers. The information required to perform calculations on building service and other energy efficiency measures was chiefly derived from internal surveys, which enabled lists of all energy-consuming equipment, ratings of their energy consumption and probable usage times to be compiled and incorporated into the NDBS database. Such lists provided important information on the occurrence of particular appliances, such as conventional natural gas boilers, electric room heaters, hot water tanks and air conditioning systems, and the numbers of specific items of equipment, such as space heating radiators, light fittings, computers and accessories, and commercial refrigeration units. Relevant data on control systems, current
settings and hours of use, provided by the internal surveys, also gave insight into improvement and refurbishment options.
Basis of calculations Two types of calculation had to be performed to derive the carbon dioxide abatement curves. These consisted of calculations to obtain estimates of the cost effectiveness of each measure and calculations to evaluate the amount of carbon dioxide emissions likely to be saved nationally as a result of the application of such measures throughout the UK commercial building sector. The following expressions were used to derive the cost effectiveness of any given efficiency measure: A!SP E" SC
(1)
where E is the cost effectiveness of a given energy efficiency measure (£/tC), A the discounted annual cost of a given energy efficiency measure (£/yr), S the annual energy saved by a given energy efficiency measure (GJ/yr), P the price of energy saved by the given energy efficiency measure (£/GJ) and C the carbon dioxide emission coefficient of the energy saved by the given energy efficiency measure (tC/GJ) and IR A" (2) 1 100 1! (1# R )T 100 where A is the discounted annual cost of a given energy efficiency measure (£/yr), I the total investment in a given energy efficiency measure (£), R the real discount rate (%) and ¹ the lifetime of a given energy efficiency measure (yr). As expressed by Equations (1) and (2), the use of cost effectiveness here reflects the perspective and particular concerns of the investor in energy efficiency measures within the commercial building sector. Consequently, other costs and benefits, which may have been considered in other studies, are not taken into account. Environmental benefits and social costs are not evaluated. More specifically, the avoided costs of marginal capacity within fuel and electricity supply systems, which could be displaced by subsequent savings from energy efficiency measures, are not incorporated into these calculations of cost effectiveness. Also excluded are any resulting reductions in fuel and electricity prices which might arise from such savings in the long-term. Instead, the nature of Equations (1) and (2) means that cost effectiveness, as applied here, indicates the current financial implications, in terms of a comparison between initial expenditure in an energy efficiency measure and accumulated reductions in annual expenditure on fuels or electricity, for individuals, companies or organisations which occupy
C
D
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
commercial sector buildings. Although related carbon dioxide savings can be regarded in broader social terms, this interpretation of cost effectiveness is specifically relevant to those making current decisions on energy efficiency investments. As can be seen from Equations (1) and (2), a variety of different information is required to calculate the cost effectiveness of each energy efficiency measure. Prevailing energy prices for the period of the assessment were based on published information (Department of Trade and Industry, 1994) and quoted utility tariffs and charges for commercial consumers. In subsequent calculations, electricity prices were further reduced by 9% to take account of future removal of the fossil fuel levy. Subsequent prices are summarised in Table 3. The carbon dioxide emission Table 3 Energy Prices for 1993/94 Source of Energy
Price (£/GJ)
Oil Natural gas Electricity, low tariff Electricity, normal tariff
3.33 4.04 7.78 16.49
Table 4 Carbon dioxide emission coefficients Source of energy
Oil Natural gas Electricity from CCGT power plant Electricity from coal-fired power plant
Carbon dioxide emission coefficient (tC/GJ) 0.021 0.014 0.034 0.080
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coefficients adopted in the calculations are presented in Table 4. It can be seen that different carbon dioxide emission coefficients are given for electricity depending whether it is generated by coal-fired or combined cycle gas turbine (CCGT) power plant. This distinction enabled carbon dioxide savings to be evaluated making different assumptions concerning the source of the electricity displaced by the energy efficiency measures. The investment costs of specific energy efficiency measures were derived from quotations of the prices of materials, equipment and, where appropriate, installation. Table 5 gives the assumed values of percentage savings and the lifetime of the chosen energy efficiency measures. In this context the lifetime of an energy efficiency measure is taken to be the period of time for which the measure is fully operational or effective. It should be noted that, for an individual occupier, the actual energy and carbon dioxide savings, investment costs and cost effectiveness of specific energy measures depend on the particular circumstances in which they are implemented. For example, the potential benefits of replacing a tungsten filament lamp with a compact fluorescent lamp will depend on the hours of use of that lamp which, in turn, are influenced by many considerations including, principally, the usage of the room in which it is fitted. For this reason, the cost effectiveness and amount of carbon dioxide saved by each energy efficiency measure can vary. In particular, any given measure can either be cost effective or non-cost effective. It can be seen from Equation (1) that the cost savings from an energy efficiency measure can exceed its discounted annual cost, resulting in a negative value which indicates that the measure is cost effective. Alternatively, if the cost savings do not cover the initial investment of the measure over its
Table 5 Potential energy savings and lifetimes of selected energy efficiency measures Energy efficiency measure
Installation of 250 mm loft insulation Installation of cavity wall insulation Replacement of single glazing with double glazing Replacement of existing natural gas boilers with condensing natural gas boilers Fuel switching by replacing electric room heaters by natural gas room heaters Installation of 7 day programmable timers in space heating systems Installation of thermostatically- controlled radiator valves Installation of hot water tank and pipe insulation Improved design and control of air conditioning systems Replacement of tungsten filament lamps with compact fluorescent lamps Replacement of 38 mm diameter fluorescent tubes with 26 mm diameter fluorescent tubes Replacement of tungsten filament display lights with tungsten halogen lamps Replacement of existing computing equipment and accessories with low energy alternatives Use of night blinds in commercial refrigeration Use of electric motor controllers in commercial refrigeration
Potential energy saving! (%)
Lifetime" (yrs)
75# 44—57$ 39—53% 15 & 14—29 10 25 20 75 10 25 25 5—10 5—15
30 40 20 15 10 20 25 20 15 3' 3' 3' 10 5 10
! Saving relative to energy specifically lost through particular fabric component or consumed by previous type or operation of a given appliance or item of equipment. " Duration time for potential effectiveness of the measure. # Assuming U-value reduced from 1.40 to 0.35 W/m2K. $ Assuming U-values reduced from 0.90—0.93 to 0.50—0.40 W/m2K. % Assuming U-values reduced from 3.80—4.30 to 2.30—2.00 W/m2K. & No energy saving assumed. ' Actual operating lifeline of 8000 h.
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expected lifetime, represented by its annual discounted cost, then a positive value is derived which demonstrates that the measure is non-cost effective. It must be emphasised that cost effectiveness is used here as an indicator of the financial viability of an energy efficiency measure. All the measures considered must be technically effective means of saving energy and associated carbon dioxide emissions. However, they may, in some circumstances, be uneconomic as an investment because annual savings in fuel or electricity expenditure do not exceed the discounted annual cost of the energy efficiency measure which is, therefore, non-cost effective. Although each energy efficiency measure can be designated specifically as either cost effective or non-cost effective under all conditions, it is possible for any measure to display differing cost effectiveness when implemented in different situations. Hence, some energy efficiency measures may be divided into applications which are cost effective and those which are non-cost effective. Additionally, the amount of carbon dioxide saved and the cost effectiveness of an energy efficiency measure can vary with general conditions, such as the source of the electricity used in the commercial building sector, as discussed previously, and the chosen discount rate, respectively. In this initial assessment, discount rates of 8% and 15% were adopted in subsequent calculations. The calculation of national carbon dioxide savings, depends not only on the effect of the individual application of an energy efficiency measure but also on its potential penetration throughout the entire UK commercial building sector. Two general methods of extrapolation were used to achieve this; one was applied to fabric energy efficiency measures and the other to the remaining, essentially equipment-related energy efficiency measures. The method for fabric energy efficiency measures was based on the built form classifications derived by the Centre for Configurational Studies from the external surveys in the 4 survey locations (Steadman et al, 1994). Built form characteristics have a direct influence on heat loss and potential savings by loft insulation, cavity wall insulation and double glazing. Preliminary investigation established that the two most numerous built forms were ‘cellular sidelit buildings with 4 or fewer storeys’ (referred to by the code CS4) and buildings described as ‘cellular sidelit around open plan artificially lit’ (known by the code CD0). In terms of gross external floor area in the 4 survey locations, the CS4 and CD0 built forms account for approximately 56% and 27%, respectively, of the total commercial building sector floor space. Hence, these two particular built forms, taken together, cover 82% of the gross external floor area, whilst the remaining 18% comprises as many as 14 other built form classifications. For practical purposes, subsequent assessment of fabric energy efficiency measures was concentrated on these two most prominent built forms. Within the sample of 146 commercial buildings for which detailed energy survey data were available, the
built forms of 86 buildings were identified as CS4 and 14 as CD0 classifications. Treating these two built forms separately, the useful space heating energy consumption per unit gross external floor area was estimated for each type. This involved adopting assumptions concerning the thermal efficiency of the existing space heating system within each building. Additionally, it had to be assumed that acceptable levels of thermal comfort were maintained within these buildings. Frequency distributions of the useful space heating energy consumption per unit gross external floor area were then prepared for each built form and the respective mean values were established. Actual buildings within the sample were then identified which displayed energy performances which coincided approximately with these observed mean values. Representative buildings were selected from these specific groups to form the basis for subsequent modelling of the costs and savings of fabric energy efficiency measures. Simple modelling procedures were used, involving static heat flow calculations based on assumed values of thermal conductivity for roofs, walls and windows. Dynamic thermal modelling was not attempted in this initial assessment. Additionally, heat flow interactions, especially involving existing heat gains, could not be taken into account. The simple modelling procedures adopted enabled both the cost effectiveness of each fabric energy efficiency measure and resulting carbon dioxide savings to be estimated. These estimated savings for individual representative buildings were then extrapolated to the UK stock of commercial buildings on a pro rata basis using gross external floor area data for these buildings, the proportion of CS4 and CD0 buildings in the 4 survey locations and the total floor space of commercial buildings recorded in the VSA database. A simple ratio was used to adjust the statistics of the VSA database, which represents England and Wales only, to obtain estimates for the UK commercial sector building stock. A much less complex method of extrapolation was needed for equipment-related energy efficiency measures. This involved evaluating the costs and savings of implementing such measures in all appropriate instances within the sample of 146 buildings. Such data were essential to this type of evaluation because information is required on the occurrence and use of relevant plant, equipment and appliances within the sample. In some cases it was necessary to separate instances where the application of the same type of energy efficiency measure proved to be either cost effective or non-cost effective. For example, the proportion of time a compact fluorescent lamp is used during a year determines its cost effectiveness as a result of the discounting procedure introduced by Equation (2) into Equation (1). Estimates of the percentage energy and carbon dioxide savings for the sample of 146 buildings were derived for each energy efficiency measure. These were then taken to be representative of the potential for such energy efficiency measures within the entire UK commercial building sector. National
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
savings were calculated by applying these derived percentages to estimates, produced previously by the BRE, of UK commercial building sector delivered energy consumption by application, such as space heating, water heating, lighting, etc. For certain energy efficiency measures, such as those associated with air conditioning systems and commercial refrigeration, additional published data were used in this assessment (Department of the Environment, 1991).
Carbon dioxide abatement curves Results of this initial assessment of carbon dioxide savings in the UK commercial building sector are shown, in the form of carbon dioxide abatement curves, in Figures 2—5. A discount rates of 8% is assumed in Figures 2 and 3, and 15% in Figures 4 and 5. The distinction between these two assumptions is that the 8% discount rate can be generally regarded as relevant for public sector and large private sector investments, whereas the 15% discount rate is more applicable to small- to medium-sized enterprises and private individuals. In Figures 2 and 4, carbon dioxide savings from energy efficiency measures which reduce or displace electricity consumption are based on the generation of electricity from coal-fired power plants. This can be taken as representative of the
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current situation where savings might primarily affect the use of existing coal-fired power plants. The assumption incorporated into Figures 3 and 5 is that certain energy efficiency measures reduce or displace electricity generated from new CCGT power plants. Such power stations are accounting for an increasing proportion of electricity generation in the UK. Hence, the savings illustrated in Figures 3 and 5 are relevant to energy efficiency measures which result in the deferral of the need to provide new power plant capacity or, alternatively, to the assessment of the future impact of these measures. This combination of assumptions about discount rates and the source of electricity generation was selected to cover a wide range of possible interpretations of results from this assessment. Under these circumstances, Figures 2 to 5 demonstrate that the total annual carbon dioxide savings which could be achieved by the application of all the energy efficiency measures considered here range from 2.8 million tonnes of carbon, when electricity from coal-fired power plant is displaced, to 1.5 million tonnes of carbon when electricity from CCGT power plant is displaced. In the former situation savings of 2.5 million tonnes of carbon are cost effective, whilst in the latter case savings of 1.3 million tonnes of carbon are cost effective. Such savings can be compared with estimated total annual emissions from the UK commercial building sector of 15.5 million tonnes of
Figure 2 Carbon dioxide abatement curve for the UK commercial sector: 8% discount rate and electricity from coal-fired power plant
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Carbon dioxide savings in the commercial building sector: N D Mortimer et al
Figure 3 Carbon dioxide abatement curve for the UK commercial sector: 8% discount rate and electricity from CCGT power plant
carbon. (Building Research Establishment, 1994). Hence, total potential savings from these selected measures range from 10% and 18% of total emissions, and total cost effective savings amount to between 8% and 16% of total emissions. It is important to note that the majority of savings from the energy efficiency measures considered here are, in fact, cost effective. Additionally, it can be seen that the main effects of varying the applied discount rate are, obviously, to change the magnitude, but not the sign, of the cost effectiveness of all the energy efficiency measures and, more importantly, to alter the relative ranking of specific energy efficiency measures. This is also affected by the choice of the assumed source of electricity generation. A number of important points can be noted from Figures 2—5. In particular, when electricity is generated from a coal-fired power plant, the largest cost effective carbon dioxide savings come from: f The replacement of tungsten filament lamps with compact fluorescent lamps f The replacement of existing computing equipment and accessories with low-energy alternatives f Fuel switching by replacing electric room heaters with natural gas room heaters
f Improved design and control of air conditioning systems f The replacement of existing natural gas boilers with condensing natural gas boilers f The installation of thermostatically controlled radiator valves Assuming that electricity is generated by CCGT power plants, the order of the prominent cost effective energy measures changes to: f f f f f f
Condensing natural gas boilers Compact fluorescent lamps Low energy computing-equipment and accessories Thermostatically controlled radiator values Improved air conditioning systems Fuel switching
The most prominent energy efficiency measure found not to be cost effective as a retrofit option is double glazing. However, it should be noted that decisions over the installation of such a measure are often not based on energy efficiency and energy cost saving considerations, but on other factors such as the need to replace old window fittings, the avoidance of painting and maintenance, and the reduction of noise. Similarly, other nonenergy concerns affect the implementation of certain cost
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
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Figure 4 Carbon dioxide abatement curve for the UK commercial sector: 15% discount rate and electricity from coal-fired power plant
effective energy efficiency measures including, for example, low energy features which are gradually being adopted as standard in all new computing equipment and accessories. Finally, a specifically notable feature of Figures 2—5 is the comparative insignificance of loft and cavity wall insulation as a means of reducing carbon dioxide emissions in the UK commercial building sector. The reason for the relative unimportance of loft insulation is that few opportunities for installation arise in the prominent built forms which occur in the UK commercial building sector. Indeed, flat roofs are considerably more commonplace and hence, with the benefit of hindsight, it would have been more appropriate to assess flat roof insulation techniques as relevant energy efficiency measures. There are two main reasons why the estimated carbon dioxide savings from the installation of cavity wall insulation are so low. Firstly, it appears that a large proportion of the UK commercial building stock, typified by the CS4 built form, has no cavity walls. Secondly, glazed curtain walls feature extensively in the CD0 build form which characterises much of the remainder of this building stock. Hence, external wall insulation may be a more appropriate measure for the former building types and a suitable form of double or secondary glazing may be more relevant for the latter building types.
Conclusions This assessment has demonstrated that initial results from the NDBS database development can be used to derive preliminary versions of carbon dioxide abatement curves for the UK commercial building sector. The curves are incomplete, but they indicate that there are realistic opportunities for achieving substantial reductions in carbon dioxide emission by means of cost effective energy efficiency measures. It has been found that these measures are chiefly equipment-related, involving the installation and operation of energy saving building services plant and appliances, and low-energy equipment, such as computers and accessories. Only minor contributions to carbon dioxide savings seem to be achievable from the application of cost effective fabric energy efficiency measures such as loft and cavity wall insulation. Although such measures are commonly regarded as significant in the domestic sector, they do not appear to be wholly relevant to the built forms of most commercial buildings. Hence, there is a need to identify fabric energy efficiency measures which are specifically appropriate for the built forms found in the commercial sector. It is possible to extend this conclusion to other energy efficiency measures. Due to the considerable diversity of
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Carbon dioxide savings in the commercial building sector: N D Mortimer et al
Figure 5 Carbon dioxide abatement curve for the UK commercial sector: 15% discount rate and electricity from CCGT power plant
the commercial sector, it will be necessary to identify measures which are specially designed to improve the energy efficiency of particular activities. The wide range of activities which occur within the commercial sector may mean that a large number of measures must be evaluated. The application of each special measure to the entire commercial building stock may only result in modest energy efficiency improvements. However, collectively, such measures may make a substantial contribution to national carbon dioxide savings. Further investigation is planned, involving more detailed information for a larger, more representative sample of commercial buildings. Such information is becoming available as work progresses with the development of the NDBS database.
References Central Statistical Office, (1979) Standard Industrial Classification, Revised 1980, HMSO, London. Department of Trade and Industry, (1994) Digest of ºnited Kingdom Energy Statistics 1994, HMSO, London. Department of the Environment, (1991) Energy Consumption Guide 19: Energy Efficiency in Offices. Building Research Establishment Energy Conservation Support Unit, Watford.
Department of the Environment, Good Practice Case Study 223: Night Blinds on Refrigerated Cabinets. Energy Technology Support Unit, Harwell. Department of the Environment, Good Practice Case Study 27: Compressor Motor Controllers on Refrigeration Plant. Energy Technology Support Unit, Harwell. Building Research Establishment (1994) Energy Consumption in Public and Commercial Buildings, IP16/94, Watford. Energy Efficiency Office (1984) Energy ºse and Energy Efficiency in ºK Manufacturing Industry up to the ½ear 2000, Energy Efficiency Office, HMSO, London, October 1984. Evans, R D and Herring, H P J (1989) Energy ºse and Energy Efficiency in the ºK Domestic Sector up to the ½ear 2010. Energy Efficiency Office, HMSO, London, September 1989. Fletcher, K (1994) An Appraisal of ºK Energy Research, Development, Demonstration and Dissemination, Energy Technology Support Unit, HMSO, London. Jackson, T (1991) ¸east-cost Greenhouse Planning; Supply Curves for Global ¼arming Abatement, Energy Policy, 19(19), pp 35—46. Herring, H P J, Hardcastle, R and Phillipson, R (1988) Energy ºse and Energy Efficiency in ºK Commercial and Public Buildings up to the ½ear 2000, Energy Efficiency Office, HMSO, London. Shorrock, L D and Henderson, G (1990) Energy ºse in Buildings and Carbon Dioxide Emissions. Building Research Establishment, Watford. Shorrock, L D, Henderson, G and Brown, J H F (1992) Domestic Energy Fact File. Building Research Establishment, HMSO, London. Steadman, P, Bruhns, H and Rickaby, P (1994) Classification of Building ¹ypes in the National Non-domestic Building Stock Database: An Overview. Centre for Configurational Studies, The Open University, June 1994.
PII: S0301-4215(98)00019-6
Carbon dioxide savings in the commercial building sector N D Mortimer, A Ashley, C A C Moody and J H R Rix Resources Research Unit, Sheffield Hallam University, School of Urban & Regional Studies City Campus, Sheffield SI IWB, UK
S A Moss Environment Group, Building Research Establishment ¸td
This paper summarises the results of an initial assessment of the potential to reduce carbon dioxide emissions from the commercial building sector of the United Kingdom. The assessment relies on information provided by the non-domestic building stock database which is currently being developed with funding from the Global Atmosphere Division of the United Kingdom Department of the Environment, Transport and the Regions. Results are presented in the form of carbon dioxide abatement curves which rank energy efficiency measures capable of reducing carbon dioxide emissions in order of decreasing cost effectiveness. Preliminary conclusions are drawn from this work both of the relative importance of the abatement measures considered and of the need to identify additional energy efficiency measures which would be particularly suitable for the commercial building sector. ( 1998 Elsevier Science Ltd. All rights reserved
Introduction
The economic evaluation of measures for reducing carbon dioxide emissions is assisted by the derivation of carbon dioxide abatement curves. Such curves illustrate graphically the potential savings and cost effectiveness of measures for reducing carbon dioxide emissions. A schematic example of a carbon dioxide abatement curve is given in Figure 1 which plots the potential carbon dioxide savings of each measure horizontally and their respective net cost vertically (the quantities of carbon dioxide have been converted here to their equivalent in terms of tonnes of carbon: tC). It can be seen from Figure 1 that the measures are ranked, from left to right, in increasing order of net cost. In this paper, the net cost of a measure is defined as the discounted total (investment and operating) financial costs less the financial savings that accrue from use of the chosen measure per unit of carbon dioxide emissions saved. As will be seen later, this will be used to represent the private investor cost of each energy efficiency measure. Initial carbon dioxide abatement curves were produced for the United Kingdom (UK) in 1989 (Jackson, 1991). This work considered a broad range of possible measures for saving carbon dioxide emissions based on currently available data. The costs and potential savings of energy efficiency measures were derived from published information on energy use in the UK industrial, domestic
Global climate change is now generally regarded as one of the most important environmental challenges facing humankind. Various solutions have been proposed for reducing the carbon dioxide emissions that result from the combustion of fossil fuels and which have been implicated in global warming. Most of these solutions involve fundamental changes in either human behaviour and/or changes in the activities which provide the diverse products and services required to meet the complete range of human needs. It is widely recognised that choices have to be made between competing options and that economic considerations will play a key role in the selection process. Given the uncertain consequences of global climate change and the relative efficacy of proposed solutions, a prudent approach is often advocated for carbon dioxide abatement strategies. The basis of this approach involves proposing the adoption and implementation of measures which not only reduce carbon dioxide emissions but also result in other benefits of known and worthwhile value. Hence, cost effective energy efficiency improvements which produce carbon dioxide savings, while providing a net benefit financially, can be regarded as a prominent component of a measured response to global climate change. 615
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Figure 1 Schematic example of a carbon dioxide abatement curve
and commercial sectors (Energy Efficiency Office, 1984; Evans and Herring, 1989; Herring et al, 1988). There are extensive differences in the various processing and manufacturing activities undertaken by industry. However, following work by the Energy Technology Support Unit (ETSU), there is now an improved understanding of the patterns of energy use and prospects for energy efficiency improvements in this sector (Fletcher, 1994). Similarly, as a result of the efforts of the Building Research Establishment Ltd. (BRE), the details of energy use in the UK domestic building sector and the potential for savings from relevant energy efficiency measures in this sector are well documented (Shorrock and Henderson, 1990;1992). In contrast, there is much less reliable published information on energy consumption in the UK commercial building sector. This is because, until recently, only limited basic research has been conducted on energy use in this sector which contains a very wide range of building forms within which extremely diverse activities occur. Hence, as a consequence of this diversity and the limited data available, it has only been possible in the past to derive approximate estimates of energy use and energy efficiency potential in the UK commercial building sector. However, due to work funded by the Global Atmosphere Division of the Department of the Environment, Transport and the Regions (DETR) to develop a nondomestic building stock (NDBS) database, extensive and detailed information is now being assembled which allows more reliable estimates of UK commercial building sector energy use to be derived and which enables numerous important studies to be performed, including the formulation of the carbon dioxide abatement curves presented here.
NDBS database development Work on development of the NDBS database began in 1991 with the aim of collecting and presenting detailed
information related to energy use within the stock to inform policy decisions concerning the so-called ‘greenhouse gas’ emissions. Four main areas of work contribute to the development of the database. The first consists of establishing the national composition of the NDBS in terms of numbers of premises, floor area and types of building. The principal sources of this information are the Rating and Valuation Office (RVO) Rating List and the Valuation Support Application (VSA) database. These provide details of the number of hereditaments (which are rateable properties recognised by the RVO) and their defined floor areas, for building types specified by their RVO Primary Description (PD). Such information is only available for England and Wales and, hence, extrapolation is necessary to obtain a full representation of the UK. Additional sources of information, chiefly for non-rateable properties, are needed to achieve a complete summary of the national NDBS. The second contribution to the development of the NDBS database consists of providing a description of the physical characteristics of the buildings which comprise the stock. This has involved collecting detailed descriptive information, by means of external surveys, on the built form of 3350 addresses in 4 locations chosen as representative of the UK stock; Bury St. Edmunds, Central Manchester, Swindon and Tamworth. This information on built form is being related to the RVO data in order to characterise the entire NDBS. This work on summarising and characterising the NDBS is being conducted by the Centre for Configurational Studies at the Open University (Steadman et al, 1994). The third component of the database development consists of collecting detailed information on energy use within the NDBS. This work, which mainly involves internal surveys of buildings to record details of energyconsuming equipment, is being undertaken by the Resources Research Unit of Sheffield Hallam University. It
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
is currently planned to conduct about 800 energy surveys and to combine subsequent results with bulk data, collected from ongoing monitoring and targeting systems by Building Energy Solutions, to derive representative descriptions of energy use in the NDBS. The internal surveys are designed to obtain extensive data on important aspects of the building and its use which influence energy consumption. The specific energy data collected during internal surveys include fuel records for relevant periods of time and a complete listing, wherever possible, of all energy- consuming equipment and appliances along with information on their energy consumption ratings and usage times. Additionally, the floor area of each internal space within the building is measured during the survey and other appropriate information is collected, such as details of building fabric, energy system control settings, etc. By combining such data together during subsequent analysis, performed on a specially formulated spreadsheet package, it is possible to determine the total delivered or primary energy consumption per unit floor area per year (GJ/m2/yr), the total carbon dioxide emissions per unit floor area per year (tC/m2/yr) and a breakdown of energy use by fuel type and application. Additionally, since all relevant internal survey data are recorded in machine readable form, the retrieval and subsequent analysis of information related to the evaluation of suitable energy efficiency measures is possible and comparatively easy for relatively large number of buildings. The BRE oversees the fourth component of database development which consists of developing a model of energy use in the NDBS and generating suitable results to inform policy making on potential means of reducing carbon dioxide emissions from the UK NDBS. The BRE will conduct studies for the DETR relevant to UK policy needs. As users, the BRE have a co-ordinating role in the development of the database. The database is an extremely important element of the Non-Domestic Buildings Energy and Emissions Model (N-DEEM) which the BRE is formulating to address questions about past, current and possible future trends in carbon dioxide emissions, as well as the potential for reducing these emissions by various means including energy efficiency improvements. Since policy issues in this area are the principal concern of the Global Atmosphere Division, funding and overall responsibility for the development of both the NDBS database and NDEEM are undertaken by this part of the DETR. It was decided in July 1994 that preliminary illustrative results, in the form of carbon dioxide abatement curves, should be produced for the UK NDBS. The preparation of these curves was performed by the BRE with assistance from the Resources Research Unit. At that time, analysed data from internal surveys of 175 buildings were available. Despite this comparatively small sample size, this was considered adequate for producing indicative carbon dioxide abatement curves for a limited number of energy efficiency measures.
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Energy efficiency measures The commercial building sector, which is the subject of this assessment of energy efficiency measures, was defined by reference to the Standard Industrial Classification (SIC). Using the 1980 version of the SIC (Central Statistical Office, 1979), the commercial building sector was assumed to consist of all activities within Classes 61—67, 71—79, 81—85, 92, 94, 963, 966, 969, 97 and 98. A description of the composition of these Classes is provided in Table 1. SIC codes are included in the information held in the NDBS database. Using the above SIC Classes to define the commercial building sector, it was established that data for 146 buildings from the sample available at the time were relevant for this assessment. The agreed list of energy efficiency measures to be investigated by this assessment is presented in Table 2. The selected energy efficiency measures fall into one of three general categories: fabric energy efficiency measures, building service energy efficiency measures and other energy efficiency measures. The fabric energy efficiency measures consisted of loft and cavity wall insulation, and double glazing. Building service energy efficiency measures relate to the plant and equipment which create and maintain suitable environmental conditions within buildings. The selected measures presented in Table 2 refer to the use of plant and equipment which provide space heating, water heating, air conditioning and lighting. Energy efficiency measures include the replacement of one type of appliance with another and improvements in the control of such plant and equipment (such as the installation of programmable timers Table 1 Definition of the commercial sector SIC 1980 Class 61 62 63 64 & 65 66 67 71 72 74 75 76 77 79 81 82 83 84 85 92 94 963 966 969 97 98
Description Wholesale distribution (except dealing in scrap and waste materials) Dealing in scrap and waste materials Commission agents Retail distribution Hotels and catering Repair of consumer goods and vehicles Railways Other inland transport Sea transport Air transport Supporting services to transport Miscellaneous transport services and storage not elsewhere specified Postal services and telecommunications Banking and finance Insurance (except for compulsory Social Security) Business services Renting of movables Owning and dealing in real estate Sanitary services Research and development Trade unions, business and professional associations Religious organisations and similar associations Tourist offices and other community services Recreational services and other cultural services Personal services
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Table 2 Selected energy efficiency measures Category
Description
Fabric energy Installation of 250 mm of loft insulation. efficiency measures Installation of cavity wall insulation. Replacement of single glazing with double glazing. Building service energy efficiency measures
Replacement of existing natural gas boilers with condensing natural gas boilers. Fuel switching by replacing electric room heaters with natural gas room heaters (for premises with an existing gas supply). Installation of 7 day programmable timers in space heating systems. Installation of thermostatically controlled radiator valves. Installation of hot water tank and pipe insulation. Improved design and control of airconditioning systems. Replacement of tungsten filament lamps with compact fluorescent lamps. Replacement of 38 mm diameter fluorescent tubes with 26 mm diameter fluorescent tubes. Replacement of tungsten filament display lights with tungsten halogen lamps.
Other energy Replacement of existing computing equipment efficiency measures and accessories with low energy alternatives. Use of night blinds in commercial refrigeration. Use of electric motor controllers in commercial refrigeration.
and thermostatically controlled radiator valves). Specific process energy efficiency measures were not considered in this initial assessment because of the diversity of activities within the commercial building sector. Apart from covering a range of energy efficiency measures which may be appropriate for commercial sector buildings, the options summarised in Table 2 were also chosen because suitable information was accessible in the NDBS database to evaluate the costs and carbon dioxide saving potential of these selected measures. Essential built form and fabric data, necessary for calculations involving fabric energy efficiency measures, are available from both external and internal surveys. Specific information relevant for such calculations include floor area measurements, wall and glazing area measurements which can be derived from building photographs, and details of building fabric composition derived from inspections and interviews with building occupiers. The information required to perform calculations on building service and other energy efficiency measures was chiefly derived from internal surveys, which enabled lists of all energy-consuming equipment, ratings of their energy consumption and probable usage times to be compiled and incorporated into the NDBS database. Such lists provided important information on the occurrence of particular appliances, such as conventional natural gas boilers, electric room heaters, hot water tanks and air conditioning systems, and the numbers of specific items of equipment, such as space heating radiators, light fittings, computers and accessories, and commercial refrigeration units. Relevant data on control systems, current
settings and hours of use, provided by the internal surveys, also gave insight into improvement and refurbishment options.
Basis of calculations Two types of calculation had to be performed to derive the carbon dioxide abatement curves. These consisted of calculations to obtain estimates of the cost effectiveness of each measure and calculations to evaluate the amount of carbon dioxide emissions likely to be saved nationally as a result of the application of such measures throughout the UK commercial building sector. The following expressions were used to derive the cost effectiveness of any given efficiency measure: A!SP E" SC
(1)
where E is the cost effectiveness of a given energy efficiency measure (£/tC), A the discounted annual cost of a given energy efficiency measure (£/yr), S the annual energy saved by a given energy efficiency measure (GJ/yr), P the price of energy saved by the given energy efficiency measure (£/GJ) and C the carbon dioxide emission coefficient of the energy saved by the given energy efficiency measure (tC/GJ) and IR A" (2) 1 100 1! (1# R )T 100 where A is the discounted annual cost of a given energy efficiency measure (£/yr), I the total investment in a given energy efficiency measure (£), R the real discount rate (%) and ¹ the lifetime of a given energy efficiency measure (yr). As expressed by Equations (1) and (2), the use of cost effectiveness here reflects the perspective and particular concerns of the investor in energy efficiency measures within the commercial building sector. Consequently, other costs and benefits, which may have been considered in other studies, are not taken into account. Environmental benefits and social costs are not evaluated. More specifically, the avoided costs of marginal capacity within fuel and electricity supply systems, which could be displaced by subsequent savings from energy efficiency measures, are not incorporated into these calculations of cost effectiveness. Also excluded are any resulting reductions in fuel and electricity prices which might arise from such savings in the long-term. Instead, the nature of Equations (1) and (2) means that cost effectiveness, as applied here, indicates the current financial implications, in terms of a comparison between initial expenditure in an energy efficiency measure and accumulated reductions in annual expenditure on fuels or electricity, for individuals, companies or organisations which occupy
C
D
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
commercial sector buildings. Although related carbon dioxide savings can be regarded in broader social terms, this interpretation of cost effectiveness is specifically relevant to those making current decisions on energy efficiency investments. As can be seen from Equations (1) and (2), a variety of different information is required to calculate the cost effectiveness of each energy efficiency measure. Prevailing energy prices for the period of the assessment were based on published information (Department of Trade and Industry, 1994) and quoted utility tariffs and charges for commercial consumers. In subsequent calculations, electricity prices were further reduced by 9% to take account of future removal of the fossil fuel levy. Subsequent prices are summarised in Table 3. The carbon dioxide emission Table 3 Energy Prices for 1993/94 Source of Energy
Price (£/GJ)
Oil Natural gas Electricity, low tariff Electricity, normal tariff
3.33 4.04 7.78 16.49
Table 4 Carbon dioxide emission coefficients Source of energy
Oil Natural gas Electricity from CCGT power plant Electricity from coal-fired power plant
Carbon dioxide emission coefficient (tC/GJ) 0.021 0.014 0.034 0.080
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coefficients adopted in the calculations are presented in Table 4. It can be seen that different carbon dioxide emission coefficients are given for electricity depending whether it is generated by coal-fired or combined cycle gas turbine (CCGT) power plant. This distinction enabled carbon dioxide savings to be evaluated making different assumptions concerning the source of the electricity displaced by the energy efficiency measures. The investment costs of specific energy efficiency measures were derived from quotations of the prices of materials, equipment and, where appropriate, installation. Table 5 gives the assumed values of percentage savings and the lifetime of the chosen energy efficiency measures. In this context the lifetime of an energy efficiency measure is taken to be the period of time for which the measure is fully operational or effective. It should be noted that, for an individual occupier, the actual energy and carbon dioxide savings, investment costs and cost effectiveness of specific energy measures depend on the particular circumstances in which they are implemented. For example, the potential benefits of replacing a tungsten filament lamp with a compact fluorescent lamp will depend on the hours of use of that lamp which, in turn, are influenced by many considerations including, principally, the usage of the room in which it is fitted. For this reason, the cost effectiveness and amount of carbon dioxide saved by each energy efficiency measure can vary. In particular, any given measure can either be cost effective or non-cost effective. It can be seen from Equation (1) that the cost savings from an energy efficiency measure can exceed its discounted annual cost, resulting in a negative value which indicates that the measure is cost effective. Alternatively, if the cost savings do not cover the initial investment of the measure over its
Table 5 Potential energy savings and lifetimes of selected energy efficiency measures Energy efficiency measure
Installation of 250 mm loft insulation Installation of cavity wall insulation Replacement of single glazing with double glazing Replacement of existing natural gas boilers with condensing natural gas boilers Fuel switching by replacing electric room heaters by natural gas room heaters Installation of 7 day programmable timers in space heating systems Installation of thermostatically- controlled radiator valves Installation of hot water tank and pipe insulation Improved design and control of air conditioning systems Replacement of tungsten filament lamps with compact fluorescent lamps Replacement of 38 mm diameter fluorescent tubes with 26 mm diameter fluorescent tubes Replacement of tungsten filament display lights with tungsten halogen lamps Replacement of existing computing equipment and accessories with low energy alternatives Use of night blinds in commercial refrigeration Use of electric motor controllers in commercial refrigeration
Potential energy saving! (%)
Lifetime" (yrs)
75# 44—57$ 39—53% 15 & 14—29 10 25 20 75 10 25 25 5—10 5—15
30 40 20 15 10 20 25 20 15 3' 3' 3' 10 5 10
! Saving relative to energy specifically lost through particular fabric component or consumed by previous type or operation of a given appliance or item of equipment. " Duration time for potential effectiveness of the measure. # Assuming U-value reduced from 1.40 to 0.35 W/m2K. $ Assuming U-values reduced from 0.90—0.93 to 0.50—0.40 W/m2K. % Assuming U-values reduced from 3.80—4.30 to 2.30—2.00 W/m2K. & No energy saving assumed. ' Actual operating lifeline of 8000 h.
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expected lifetime, represented by its annual discounted cost, then a positive value is derived which demonstrates that the measure is non-cost effective. It must be emphasised that cost effectiveness is used here as an indicator of the financial viability of an energy efficiency measure. All the measures considered must be technically effective means of saving energy and associated carbon dioxide emissions. However, they may, in some circumstances, be uneconomic as an investment because annual savings in fuel or electricity expenditure do not exceed the discounted annual cost of the energy efficiency measure which is, therefore, non-cost effective. Although each energy efficiency measure can be designated specifically as either cost effective or non-cost effective under all conditions, it is possible for any measure to display differing cost effectiveness when implemented in different situations. Hence, some energy efficiency measures may be divided into applications which are cost effective and those which are non-cost effective. Additionally, the amount of carbon dioxide saved and the cost effectiveness of an energy efficiency measure can vary with general conditions, such as the source of the electricity used in the commercial building sector, as discussed previously, and the chosen discount rate, respectively. In this initial assessment, discount rates of 8% and 15% were adopted in subsequent calculations. The calculation of national carbon dioxide savings, depends not only on the effect of the individual application of an energy efficiency measure but also on its potential penetration throughout the entire UK commercial building sector. Two general methods of extrapolation were used to achieve this; one was applied to fabric energy efficiency measures and the other to the remaining, essentially equipment-related energy efficiency measures. The method for fabric energy efficiency measures was based on the built form classifications derived by the Centre for Configurational Studies from the external surveys in the 4 survey locations (Steadman et al, 1994). Built form characteristics have a direct influence on heat loss and potential savings by loft insulation, cavity wall insulation and double glazing. Preliminary investigation established that the two most numerous built forms were ‘cellular sidelit buildings with 4 or fewer storeys’ (referred to by the code CS4) and buildings described as ‘cellular sidelit around open plan artificially lit’ (known by the code CD0). In terms of gross external floor area in the 4 survey locations, the CS4 and CD0 built forms account for approximately 56% and 27%, respectively, of the total commercial building sector floor space. Hence, these two particular built forms, taken together, cover 82% of the gross external floor area, whilst the remaining 18% comprises as many as 14 other built form classifications. For practical purposes, subsequent assessment of fabric energy efficiency measures was concentrated on these two most prominent built forms. Within the sample of 146 commercial buildings for which detailed energy survey data were available, the
built forms of 86 buildings were identified as CS4 and 14 as CD0 classifications. Treating these two built forms separately, the useful space heating energy consumption per unit gross external floor area was estimated for each type. This involved adopting assumptions concerning the thermal efficiency of the existing space heating system within each building. Additionally, it had to be assumed that acceptable levels of thermal comfort were maintained within these buildings. Frequency distributions of the useful space heating energy consumption per unit gross external floor area were then prepared for each built form and the respective mean values were established. Actual buildings within the sample were then identified which displayed energy performances which coincided approximately with these observed mean values. Representative buildings were selected from these specific groups to form the basis for subsequent modelling of the costs and savings of fabric energy efficiency measures. Simple modelling procedures were used, involving static heat flow calculations based on assumed values of thermal conductivity for roofs, walls and windows. Dynamic thermal modelling was not attempted in this initial assessment. Additionally, heat flow interactions, especially involving existing heat gains, could not be taken into account. The simple modelling procedures adopted enabled both the cost effectiveness of each fabric energy efficiency measure and resulting carbon dioxide savings to be estimated. These estimated savings for individual representative buildings were then extrapolated to the UK stock of commercial buildings on a pro rata basis using gross external floor area data for these buildings, the proportion of CS4 and CD0 buildings in the 4 survey locations and the total floor space of commercial buildings recorded in the VSA database. A simple ratio was used to adjust the statistics of the VSA database, which represents England and Wales only, to obtain estimates for the UK commercial sector building stock. A much less complex method of extrapolation was needed for equipment-related energy efficiency measures. This involved evaluating the costs and savings of implementing such measures in all appropriate instances within the sample of 146 buildings. Such data were essential to this type of evaluation because information is required on the occurrence and use of relevant plant, equipment and appliances within the sample. In some cases it was necessary to separate instances where the application of the same type of energy efficiency measure proved to be either cost effective or non-cost effective. For example, the proportion of time a compact fluorescent lamp is used during a year determines its cost effectiveness as a result of the discounting procedure introduced by Equation (2) into Equation (1). Estimates of the percentage energy and carbon dioxide savings for the sample of 146 buildings were derived for each energy efficiency measure. These were then taken to be representative of the potential for such energy efficiency measures within the entire UK commercial building sector. National
Carbon dioxide savings in the commercial building sector: N D Mortimer et al
savings were calculated by applying these derived percentages to estimates, produced previously by the BRE, of UK commercial building sector delivered energy consumption by application, such as space heating, water heating, lighting, etc. For certain energy efficiency measures, such as those associated with air conditioning systems and commercial refrigeration, additional published data were used in this assessment (Department of the Environment, 1991).
Carbon dioxide abatement curves Results of this initial assessment of carbon dioxide savings in the UK commercial building sector are shown, in the form of carbon dioxide abatement curves, in Figures 2—5. A discount rates of 8% is assumed in Figures 2 and 3, and 15% in Figures 4 and 5. The distinction between these two assumptions is that the 8% discount rate can be generally regarded as relevant for public sector and large private sector investments, whereas the 15% discount rate is more applicable to small- to medium-sized enterprises and private individuals. In Figures 2 and 4, carbon dioxide savings from energy efficiency measures which reduce or displace electricity consumption are based on the generation of electricity from coal-fired power plants. This can be taken as representative of the
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current situation where savings might primarily affect the use of existing coal-fired power plants. The assumption incorporated into Figures 3 and 5 is that certain energy efficiency measures reduce or displace electricity generated from new CCGT power plants. Such power stations are accounting for an increasing proportion of electricity generation in the UK. Hence, the savings illustrated in Figures 3 and 5 are relevant to energy efficiency measures which result in the deferral of the need to provide new power plant capacity or, alternatively, to the assessment of the future impact of these measures. This combination of assumptions about discount rates and the source of electricity generation was selected to cover a wide range of possible interpretations of results from this assessment. Under these circumstances, Figures 2 to 5 demonstrate that the total annual carbon dioxide savings which could be achieved by the application of all the energy efficiency measures considered here range from 2.8 million tonnes of carbon, when electricity from coal-fired power plant is displaced, to 1.5 million tonnes of carbon when electricity from CCGT power plant is displaced. In the former situation savings of 2.5 million tonnes of carbon are cost effective, whilst in the latter case savings of 1.3 million tonnes of carbon are cost effective. Such savings can be compared with estimated total annual emissions from the UK commercial building sector of 15.5 million tonnes of
Figure 2 Carbon dioxide abatement curve for the UK commercial sector: 8% discount rate and electricity from coal-fired power plant
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Figure 3 Carbon dioxide abatement curve for the UK commercial sector: 8% discount rate and electricity from CCGT power plant
carbon. (Building Research Establishment, 1994). Hence, total potential savings from these selected measures range from 10% and 18% of total emissions, and total cost effective savings amount to between 8% and 16% of total emissions. It is important to note that the majority of savings from the energy efficiency measures considered here are, in fact, cost effective. Additionally, it can be seen that the main effects of varying the applied discount rate are, obviously, to change the magnitude, but not the sign, of the cost effectiveness of all the energy efficiency measures and, more importantly, to alter the relative ranking of specific energy efficiency measures. This is also affected by the choice of the assumed source of electricity generation. A number of important points can be noted from Figures 2—5. In particular, when electricity is generated from a coal-fired power plant, the largest cost effective carbon dioxide savings come from: f The replacement of tungsten filament lamps with compact fluorescent lamps f The replacement of existing computing equipment and accessories with low-energy alternatives f Fuel switching by replacing electric room heaters with natural gas room heaters
f Improved design and control of air conditioning systems f The replacement of existing natural gas boilers with condensing natural gas boilers f The installation of thermostatically controlled radiator valves Assuming that electricity is generated by CCGT power plants, the order of the prominent cost effective energy measures changes to: f f f f f f
Condensing natural gas boilers Compact fluorescent lamps Low energy computing-equipment and accessories Thermostatically controlled radiator values Improved air conditioning systems Fuel switching
The most prominent energy efficiency measure found not to be cost effective as a retrofit option is double glazing. However, it should be noted that decisions over the installation of such a measure are often not based on energy efficiency and energy cost saving considerations, but on other factors such as the need to replace old window fittings, the avoidance of painting and maintenance, and the reduction of noise. Similarly, other nonenergy concerns affect the implementation of certain cost
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Figure 4 Carbon dioxide abatement curve for the UK commercial sector: 15% discount rate and electricity from coal-fired power plant
effective energy efficiency measures including, for example, low energy features which are gradually being adopted as standard in all new computing equipment and accessories. Finally, a specifically notable feature of Figures 2—5 is the comparative insignificance of loft and cavity wall insulation as a means of reducing carbon dioxide emissions in the UK commercial building sector. The reason for the relative unimportance of loft insulation is that few opportunities for installation arise in the prominent built forms which occur in the UK commercial building sector. Indeed, flat roofs are considerably more commonplace and hence, with the benefit of hindsight, it would have been more appropriate to assess flat roof insulation techniques as relevant energy efficiency measures. There are two main reasons why the estimated carbon dioxide savings from the installation of cavity wall insulation are so low. Firstly, it appears that a large proportion of the UK commercial building stock, typified by the CS4 built form, has no cavity walls. Secondly, glazed curtain walls feature extensively in the CD0 build form which characterises much of the remainder of this building stock. Hence, external wall insulation may be a more appropriate measure for the former building types and a suitable form of double or secondary glazing may be more relevant for the latter building types.
Conclusions This assessment has demonstrated that initial results from the NDBS database development can be used to derive preliminary versions of carbon dioxide abatement curves for the UK commercial building sector. The curves are incomplete, but they indicate that there are realistic opportunities for achieving substantial reductions in carbon dioxide emission by means of cost effective energy efficiency measures. It has been found that these measures are chiefly equipment-related, involving the installation and operation of energy saving building services plant and appliances, and low-energy equipment, such as computers and accessories. Only minor contributions to carbon dioxide savings seem to be achievable from the application of cost effective fabric energy efficiency measures such as loft and cavity wall insulation. Although such measures are commonly regarded as significant in the domestic sector, they do not appear to be wholly relevant to the built forms of most commercial buildings. Hence, there is a need to identify fabric energy efficiency measures which are specifically appropriate for the built forms found in the commercial sector. It is possible to extend this conclusion to other energy efficiency measures. Due to the considerable diversity of
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Figure 5 Carbon dioxide abatement curve for the UK commercial sector: 15% discount rate and electricity from CCGT power plant
the commercial sector, it will be necessary to identify measures which are specially designed to improve the energy efficiency of particular activities. The wide range of activities which occur within the commercial sector may mean that a large number of measures must be evaluated. The application of each special measure to the entire commercial building stock may only result in modest energy efficiency improvements. However, collectively, such measures may make a substantial contribution to national carbon dioxide savings. Further investigation is planned, involving more detailed information for a larger, more representative sample of commercial buildings. Such information is becoming available as work progresses with the development of the NDBS database.
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Department of the Environment, Good Practice Case Study 223: Night Blinds on Refrigerated Cabinets. Energy Technology Support Unit, Harwell. Department of the Environment, Good Practice Case Study 27: Compressor Motor Controllers on Refrigeration Plant. Energy Technology Support Unit, Harwell. Building Research Establishment (1994) Energy Consumption in Public and Commercial Buildings, IP16/94, Watford. Energy Efficiency Office (1984) Energy ºse and Energy Efficiency in ºK Manufacturing Industry up to the ½ear 2000, Energy Efficiency Office, HMSO, London, October 1984. Evans, R D and Herring, H P J (1989) Energy ºse and Energy Efficiency in the ºK Domestic Sector up to the ½ear 2010. Energy Efficiency Office, HMSO, London, September 1989. Fletcher, K (1994) An Appraisal of ºK Energy Research, Development, Demonstration and Dissemination, Energy Technology Support Unit, HMSO, London. Jackson, T (1991) ¸east-cost Greenhouse Planning; Supply Curves for Global ¼arming Abatement, Energy Policy, 19(19), pp 35—46. Herring, H P J, Hardcastle, R and Phillipson, R (1988) Energy ºse and Energy Efficiency in ºK Commercial and Public Buildings up to the ½ear 2000, Energy Efficiency Office, HMSO, London. Shorrock, L D and Henderson, G (1990) Energy ºse in Buildings and Carbon Dioxide Emissions. Building Research Establishment, Watford. Shorrock, L D, Henderson, G and Brown, J H F (1992) Domestic Energy Fact File. Building Research Establishment, HMSO, London. Steadman, P, Bruhns, H and Rickaby, P (1994) Classification of Building ¹ypes in the National Non-domestic Building Stock Database: An Overview. Centre for Configurational Studies, The Open University, June 1994.