Improved efficiency in domestic electricity use

Improved efficiency in domestic electricity use

Improved efficiency in domestic electricity use JCrgen S. NCrgard This paper describes how domestic appliances (excluding water and space heaters) an...

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Improved efficiency in domestic electricity use

JCrgen S. NCrgard This paper describes how domestic appliances (excluding water and space heaters) and lighting devices can be redesigned to use electricity more efficiently. Three levels of conservation strategy are analysed: 'moderate', "strong" and "radical'. These result in the reduction of electricity consumption to 80%, 5 0 % and 3 5 % respectively, w i t h o u t affecting the service and comfort obtained. T h e calculations are based on Danish behaviour patterns and appliances sold in Denmark, but the results can be transferred to other countries. T h e savings reported are shown to be economically attractive as well as technologically possible.

&brgen S. N~rgard is with Physics Laboratory III, Technical University of Denmark, DK 2800 Lyngby, Denmark.

Whenever shortages occur in industrial societies, it is usual to look for ways of increasing supply rather than to consider possibilities for reducing demand. This is so in the case of energy shortage. The term 'energy planning' is, for example, often taken as synonymous with 'energy supply planning'. This attitude helps to explain why little attention is given to ways of making do with less energy. The search for savings in the use of the highest quality energy - electricity - is particularly neglected. It is only in very recent years that investigations of electricity conservation in private households have been initiated. The lack of interest in domestic electricity savings is often explained by the following arguments - to which I have added selected counter arguments: •







Niels I. Meyer et al, A l t e r n a t i v e D a n i s h energy d e v e l o p m e n t s - d y n a m i c analysis, Report No 9, DEMO-project, Physics Lab Ill, Technical University of Denmark, Lyngby, Denmark, forthcoming.

The daily electricity consumption of each household appliance is insignificant and not worth considering. A counter argument is that the domestic sector accounts for 40% of Denmark's electricity consumption. Consumers are not asking for appliances which save electricity, and, more importantly, they are not willing to pay a higher price for them. A counter argument is that the payback time for electricity saving design changes is usually only a few years, and in many cases is negligible. Only by offering consumers an opportunity to choose the improved goods, combined with proper declarations and information, can we decide whether people are interested in buying the energy-economic equipment. Waste heat from electricity consumption contributes to space heating, and a reduction in electricity usage would require a corresponding increase in the use of oil and other fuels for heating purposes. This is only partly true. In the Danish climate only about 35% o f the waste heat from electrical appliances contributes to space heating. The future is 'electric' and more electricity means a higher standard of living. This argument has roots in the past when electricity replaced gas- and oil-lighting and hard manual work, but can never be a good argument for not improving the energy efficiency in achieving those and other services.

The present study, carried out as part of the ' D E M O ' project on energy options for Denmark, 1 thus deals with possibilities for reducing electricity consumption and was motivated by the lack of data on domestic energy conservation strategies.

0301-4215/79/010043-14 $02.00 © 1979 IPC Business Press

43

Improved efficiency in domestic electricity use Table 1. Summary of results of conservation measures for various types of domestic appliance Appliance

'Normal 'a electricity consumption

Moderate measures ~ consumpOon Cost

Strong measures Beclzicityconsumption Cost

Radical measures ~consumptJon

Cost

(kWh/year)

(kWh/year)

(kWh/year)

(19755)

(kWh/year)

(%of 'normal')

Payback (19755) time (years)

Payback (%of (19755) time 'normal') (years)

(%of

'normal')

Payback time (years)

Electric cooker Refrigerator Freezer Washing machine Clothes dryer Dishwasher TV, black and

950 550 800

845 345 480

89 63 60

0 8 13

0 2 2

540 200 270

57 36 34

60 20 38

6 5 4

440 90 145

46 16 18

95 100 120

7 8 8

575 625 650

460 440 480

80 70 74

0 35 0

0 4 0

200 260 285

35 42 44

27 115 30

6 11 5

71 130 95

13 21 15

27 155 30

6 9 8

white TV, colour Hi-fi, etc

165 275 45

120 130 45

73 47 100

0 0 0

0 0 0

120 130 45

73 47 100

0 0

0 0

0 0

0

73 47 100

0 0

0

120 130 45

0

0

480

100

0

0

190

40

40

4

140

29

40

4

115 270

100 90

0 0

0 0

100 210

85 70

0 0

0 0

100 140

85 47

0 0

0 0

Domestic heat distribution 480 Small appliancesb 115 Lightingc 300

a 'Normal' refers to average models, sold in Denmark in 1975.

b Consumption figures for small appliances are per household. c Consumption figures for lighting are per capita.

Only technological savings are considered. These are defined as energy savings achieved through changes in the design of new appliances which do not, in so far as can be judged, affect the basic service or comfort for which those goods are purchased. Savings involving changes in lifestyle and material living standards are no! examined here, z which means that the present analysis does not reflect the full potential for reducing domestic electricity consumption. Even the measures described in the present study as 'radical' do not involve any new technology and should thus be without unforeseen drawbacks. Furthermore, the measures are not at all extreme. It is therefore very likely that even greater technological savings are possible than those reported here. This is partly confirmed by the fact that some of the newer models of domestic appliance are already close to achieving what are here described as 'moderate' savings but by measures not fully included here. Summary of savings

2 These aspects are however considered in t h e D E M O project. See Meyer, op cit, Ref 1, J ~ r g e n S. N C r g a r d , Husholdninger og Energi (Possible future energy consumption patterns in the D a n i s h household sector), Report N o 4, D E M O project, Physics Lab III, Technical University of Denmark, Lyngby, D e n m a r k , 1 9 7 8 and Niels I. M e y e r and J~brgen S. N~rgard, 'Ecology and energy policy', planned for publication in J. G a l t u n g , ed,

The Global Household: Perspectives on Ecology, EDA Foundation. 3 N ~ r g a r d ; op cit, R e f 2. average 35% of every kWh of electricity supplied t o an appliance is converted into useful space heating (this allows for seasonal variations in heating requirements, wastage etc). T h u s to compensate for the loss of space heating 4On

caused

by

electricity

a

one

kWh

reduction

in

an additional 0 . 3 5 k W h o f h e a t m u s t be purchased. T h u s if electricity costs 5 c / k W h and h e a t costs 1.7c/kWh, reducing electricity consumption by one kWh saves not 55 but ( 5 - 1.7 x 0 . 3 5 ) ¢ = 4 . 4 5 .

44

consumption

Table 1 summarizes the possible electricity savings for various types of domestic appliance. The basis for the calculations is the 'typical' annual electricity consumption for each appliance, defined as the consumption of an average 1975 model when used in the manner of a typical Danish household in 1975. 3 The same appliance usage patterns are assumed throughout, since the paper deals with technological measures only. Table 1 illustrates the effects of three different levels of conservation measures: 'moderate', 'strong' and 'radical'. For each of the three levels, the resulting electricity consumption is presented both in kWh/year and as a percentage of the 'normal' 1975 level. The extra investment necessary to obtain the savings is shown together with the payback time. Calculation of the payback time - ratio of extra investment to annual saving - is based on a price for electricity of 4.4 c/kWh. 4 The payback time shown is the marginal payback time, ie it is calculated for the least paying change in the group of measures. For a mix of appliances like those used in Denmark in 1975 the potential savings from the three design strategies are illustrated in Figure 1. Total savings for each level of conservation are about 20%, 50% and 65% respectively. Assuming one of each appliance the corresponding figures would be about 25%, 55% and 70%. Note that

E N E R G Y P O L I C Y March 1 9 7 9

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1500

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zg

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1300

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Figure 1. Effects of three degrees of conservation measure on Danish domestic electricity consumption and estimated costs of the measures. The mix of appliances assumed is that i n Denmark in 1975.

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the extra investment for the most radical measures is estimated to result in an average increase in purchase price of only about 11% for the Danish mix of appliances, corresponding to $120 per capita. Furthermore this would be distributed over an average appliance lifetime of 10-15 years. We now examine electricity saving possibilities for each type of appliance.

Cooking

Cooking consists of heating food t o a particular temperature and - in a few cases - m a i n t a i n i n g this temperature. Usually the temperature required for cooking is below 100°C. Potatoes, for instance, can be cooked at 8 0 ° C , j u s t as meat often needs to be heated to only 70 ° or 8 0 ° C . T h u s , in p r i n c i p l e , h i g h quality energy, like electricity or high temperature gas flames, is not necessary. For the sake of cooking speed and culinary display (grilling, frying, etc), however, a temperature higher t h a n 1 0 0 ° C is needed in some cases.

'Cooking' refers only to the heating of food, 5 and not to mixing, chopping etc. Currently in Denmark more than half the domestic cookers are electric, while almost all the rest use gas in one form or another. The present average electricity consumption for cooking in Denmark is about 950 kWh/year per household (2.5 persons). As Figure 2 shows, however, the energy which actually goes into heating the food is less than 15% of the total input. 3 More than 55% of the energy used is attributable to heat losses during cooking. This points to thermal insulation as a way of improving the energy efficiency of cooking. Most obviously ovens could be better insulated. Another possibility would be to improve the insulation of the sides and lids of saucepans by, for instance, using double walls. An extreme case of using insulation is to use the hay-box principle (leaving a heated pan containing food in a well insulated box) instead of simmering. This extends the cooking time, but needs no supervision. Figure 2 also indicates that a large portion of the electricity is used to heat equipment such as pans, hotplates, the oven-casing, and the insulation material. Some reduction in the heat capacity of these

E N E R G Y P O L I C Y March 1 9 7 9

45

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950 900

800 o

700

600 540

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F i g u r e 2. T h e p o t e n t i a l f o r e l e c t r i c i t y c o n s e r v a t i o n in c o o k i n g , f o r a t y p i c a l D a n i s h h o u s e h o l d (2.5 p e r s o n s ) . M o d e r a t e measures: Insulation thickness

in oven is increased from 2 cm to 5 cm, w i n d o w in oven is double glazed, and heat losses through the metal support of the inner oven case are halved. This reduces heat losses during oven cooking by 40% Better insulation under the hotplaves saves 10% of heat losses. Total electricity savings amount to 105 kWh per year and do not increase production costs, if incorporated in new models. Strong measures: Insulation of oven with 10 cm of hard mineral wool (4 cm thick in door) can support the oven case, and partly replace h e a t conducting metal supports. Area of double glazed w i n d o w is halved. Heat capacity of oven case reduced by 25%. Savings are 75 kWh per year and cost estimated to be $6. For

hotplate cooking strong measures involve insulated sauce pans, lids, and kettles (double walls), use of hay-box principle, and heating of water for tea, coffee etc by immersion heaters. Annual electricity consumption for hotplate cooking is 3 6 5 kWh lower than normal. Total savings are 4 1 0 k W h per year and the extra cost about $ 6 0 per household. Radical measures: Oven is used once a day compared to the usual rate of three times a week. About 90% of the oven cooking is done in a small (8 litre) well insulated oven unit inserted into the standard oven, which is used for the remaining 10%. Electricity consumption by the small oven is 0.5 kWh per use compared to the usual 1.3kWh and the extra cost is $35. Radical measures assume no further improvement in hotplate cooking, except that some of the more energy intensive processes, like frying, are transferred to the small oven.

items can be achieved. For instance, a small, highly insulated oven unit (about 8 litres in volume) can be inserted into the normal large oven (50 litres) and used for everyday cooking. The large oven will still be available whenever it is needed (for baking bread, roasting turkey etc). The electric hotplate, on which pans are placed, is to some extent reminiscent of the gas cooker or the old kitchen stove. The contact

46

;ENERGY POLICY March 1 9 7 9

Improved efficiency in domestic electricity use

between the plate and the pans requires that both contact surfaces are plane and stable. This requires the use of a large amount of metal which must be heated up whenever the cooker is used. One obvious improvement is to generate heat directly in the saucepans, or kettle. An inexpensive and very effective way to achieve this is to use an immersion heater (possibly thermostatically controlled) for heating water for tea, coffee and the like. Electricity consumption drops to about half of that required for heating a kettle on a hotplate. The wide range of cooking practice makes it difficult to generalize about potential savings and those illustrated in Figure 2 should only be taken as examples. Additional savings could also be achieved by: • • •

using immersion heaters for cooking vegetables, such as potatoes, possibly in combination with some kind of hay-box; using pans with built-in electric heater units; 6 using pressure cookers, which both conserve energy and reduce cooking time.

It should also be noted that cooking does not, in fact, require electricity at all, and gastronomes often prefer an open flame heat source like gas.

Refrigerators

Report CPA-74-4, The Center for Policy Alternatives, Massachusetts Institute of Technology, Cambridge, Mass.

About 15% of the electricity used for lighting and appliances in Danish households is used by refrigerators, and typically the electricity bill for running a refrigerator over an eight year lberiod equals the cost of purchasing the appliance. The main role of refrigerators and freezers is similar to that of houses themselves - to maintain a temperature difference between the exterior and the interior. Thermal insulation is therefore an obvious measure to consider, when the goal is to reduce energy consumption. 7 Maintenance of tlae temperature difference requires a refrigeration system capable of removing the heat - the thermal load - which is continuously admitted into the interior of the cabinet. The calculations presented here (Figure 3) are for a system using an electric compressor, which is the most common form of refrigeration system. The refrigerator, typical of those sold in Denmark in 1975, is assumed to have an inside volume of 0.22 m 3. It has a small freezer compartment and automatic defroster. The temperature of the interior is maintained at 5°C while the temperature in the kitchen is assumed to be 20°C. Forty door openings per day are assumed, each resulting in the replacement of half the air volume in the cabinet. It is further assumed that 30 kg of food is put into the refrigerator per week. Figure 3 shows that the greater part of the thermal load is heat transmitted through the insulation in the door and walls. Warm air admitted when the door is opened and through leaks at the door seals adds to the thermal load, and so does heat from food put into the refrigerator. Some types of refrigerators have a defrosting system based on heating the evaporator electrically. Part of this heat is removed with the melt water, which is usually carried outside, but the remainder (roughly half) contributes to the thermal load. The total thermal load thus amounts to 475 kWh heat per year, and this must be removed by the refrigeration system. The efficiency of a refrigeration system is expressed by the coefficient of performance (COP), defined as the ratio of the removed

ENERGY POLICY March 1979

47

This is a somewhat elaborate and expensive means of avoiding the use of hotplates, but the principle is used in tea and coffee machines. Microwave ovens also save electricity but are presently too expensive to be considered as a viable energy conservation measure. 7 Current US refrigerators consume more than twice as much electricity per unit storage volume as did the 1925-35 models, mainly because of a decline in insulation quality. See The productivity of

servicing

consumer

durable

products,

Improved efficiency in domestic electricity use 600 550 I

500

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Heat tr0nsmission through walls and-door

v

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300

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200 8 '~

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Pleat odmifled by door opening - Leeks ot door seals-Heatfrom food lead--

As well as considering possibilities for reducing the electricity consumption of domestic refrigerators, it is also instructive to look at possibilities for i n c r e a s e d consumption. The potential for greater electricity consumption - and hence for greater savings is illustrated by data for US models, which consume about 5 0 0 kWh more than Danish ones according to data in R.A. Hoskins and E. Hirst, E n e r g y and Cost Analysis of Residential Refrigerators, ORNL/CON-6, Oak Ridge National Laboratory, Oak Ridge, Tennessee, January 1977. This increased consumption is due to larger interior volume (which may be double that assumed here) and extra accessories (automatic icemaker, electrical defroster, electrically heated butter compartment).

8

48

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~

oo o m zE

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conservation

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measures: Insulation (polyurethane) thickness increased by 50%, ie in the walls from 3 cm to 4.5 cm, saving 135 kWh/year at a cost of about $8. Improved compressor (already available) increases COP from 0.9 to 1.1, and reduces electricity consumption t o 3 4 5 kWh/year at no extra cost. Strong measures: Insulation thickness increased to between 6 and 9 cm, which brings electricity consumption d o w n to 2 7 5 kWh/year at an extra cost of $ 1 2 per appliance. Automatic defrosting by

Moderate

\\

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-8

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Electricity for a

200

COP#`

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Figure 3. possibilities ( 0 . 2 2 mS).

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stopping compressor (already possible) saves 4 0 kWh/year and costs nothing. COP increased to 1.3 by doubling condenser surface, bringing electricity consumption d o w n to 2 0 0 kWh/year at an estimated cost of $ 8 per appliance. R a d i c a l m e a s u r e s : Insulation thickness is 15cm in walls and l O c m in door, bringing electricity consumption down to about 135 kWh/year and costs about $ 3 5 extra. Condenser and evaporator surfaces are both tripled which costs about $ 3 5 per uriit. This brings COP up to about 1.95 and electricity consumption d o w n to 9 0 kWh/year. Extra floor space in the kitchen (0.4 m 2) for this refrigerator is estimated to cost $30.

neat energy to the energy (usually electricity) consumed by the system. The COP depends on the design of the motor, the compressor, and the heat exchangers (condenser and evaporator), and on the temperature and ventilation conditions of the surroundings. For a 1975 refrigerator, the COP is typically found to be about 0.9. In addition to the electricity required to run the refrigeration system, a small amount is also used for automatic defrosting. The total electricity consumption is thus 550 kWh per year (as shown in Figure 3). The measures to reduce electricity consumption 8 are concentrated around improving the thermal insulation and the COP. Some improvement in COP is obtained through more efficient compressor units, but the major part is achieved by enlarging the two heat exchangers, the evaporator (refrigeration unit) and the condenser. An enlarged evaporator could serve as part of the inner cabinet and shelves. Insulation is improved by increasing the thickness of the material (usually polyurethane foam). With unchanged interior volume this will require larger outside dimensions. In the most radical case - with an electricity consumption of only 16% of normal - the extra space required for insulation and condenser amounts to less than 0.8 m 3, corresponding to about 0.4 m 2 of floor space. With a built-

E N E R G Y P O L I C Y March 1 9 7 9

Improved efficiency in domestic electricity use

in refrigerator cabinet the heavy insulation will not be visible and is assumed to be acceptable. Savings beyond those included in the 'radical' measures of Figure 3 could be achieved by even larger heat exchangers and by using different types of refrigerant. It is also likely (but n o t assumed in the calculations) that the improved models on which our calculations are based, could be manufactured even more cheaply than present models, provided much smaller compressor units become available. The whole refrigerator system, including the heat exchangers, can be smaller when insulation is improved. Like cooking, refrigeration does not necessarily require energy in the form of electricity. Gas-driven refrigerators have long been available and solar-powered refrigerator plants are being constructed. 9 However, when low quality energy, like heat from gas or solar collectors, is used for refrigerators, the amount of energy needed is much greater than for electrical systems.

Freezers Domestic deep freezers have become widely adopted and presently more than half of the homes in Denmark have one. About two thirds of the freezers are the horizontal chest type with a lid and the vest are vertical cabinet types. For the purposes of the present calculations both types are considered together as one average type of freezer, with a storage volume of 0.25 m 3 at a temperature o f - 2 0 ° C . Most of what is said about refrigerators applies to freezers too, except that automatic defrosting is not used in freezers. Figure 4 illustrates the annual electricity consumption for a freezer with the efficiency of a typical 1975 model, and the effects of each of the three strategies for improving the efficiency. While insulation has always been thicker in freezers than in refrigerators, increased insulation is still the major possibility for electricity saving. In some types of freezers (mainly American) the outer steel case and the seals are kept dry by electrical heating. This could be replaced by a system using heat from the hot refrigerant, as already introduced in most European freezers. Heavy insulation of the walls and door, however, eliminates the need for heating of the case to prevent condensation. A further benefit of improved insulation and seals~ besides savings in electricity, is a much slower rise in temperature when the electricity supply is accidently interrupted. The temperature in a standard freezer, with a full food load, will typically rise from - 1 8 ° C to - 1 0 ° C in 24 hours. The same temperature rise in the freezer with 'strong measures' adopted will take between two and three days, and in the radically improved version, four to five days. Improved compressors and enlarged heat exchangers are used to increase the COP for freezers just as for refrigerators, but, due to the lower temperature required in the freezer, its maximum COP is only 1.6.

9 p. WorsCe-Schmidt, A Solar-powered

Sofid-absorption Refrigeration System,

Washing machines

Report F 30 - 77.02, Refrigeration Laboratory, Technical University of Denmark, Lyngby, Denmark, 1977.

Washing machines belong to a group of appliances (including dishwashers and clothes dryers) in which most of the electricity consumed is used to produce low temperature heat (below IO0°C), by

ENERGY POLICY March 1979

49

Improved efficiency in domestic electricity use

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600

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measures: Increase insulation thickness by 50% to 7-9 cm. Annual saving is 160 kWh with a standard compressor (COP = 0.80) and extra cost is $13. Improved compressor raises COP to 1.0 at no extra cost and electricity consumption is reduced to 520 kWh per year. Electric heating of seals in some models is replaced by heating from the hot refrigerant circuit, Total saving is 320 kWh per year. S t r o n g measures: Insulation thickness increased to 12 cm which itself saves 285 kWh per year. In addition, the exterior casing no longer needs to be heated to prevent condensation. This saves another 35 kWh per year. The cost Moderate

of the extra insulation is about $16. Improved door seals and/or more extensive use of the horizontal chest type of freezer eliminates half of the heat introduced by leakage and saves about 55 kWh per year for a cost of about $10. The improved compressor, combined with 30% larger evaporator and condenser surfaces, increases COP to 1.15 at a cost of $12. Electricity consumption for the improved freezer is 2 7 0 kWh per year and total extra cost is $38. Radical measures: Insulation in walls increased to 25 cm and in lid to 20 cm. With the improved seals and horizontal lid, electricity consumption is reduced to 145 kWh per year, if COP is 1.6. The latter requires a tripling of the surface area of both the evaporator and the condenser. The extra cost of this freezer, which is assumed placed in a cool or well ventilated room, is $120.

means of resistance heating elements. Only about 10-15% of the electricity is used to run the motor which eliminates the hard manual work. It is the elimination of this work and, in the case of automatic models, of time consuming manual control, which are the major benefits of the washing machine. Neither of these benefits requires the water to be heated electrically - as long as another hot water source is available. In the estimates presented in Figure 5 we distinguish between three washing programs, namely: @

50

'hot-wash', which requires a temperature of around 90°C and is used for roughly half of the Danish laundry;

E N E R G Y P O L I C Y March 1 9 7 9

Improved eJficiency in domestic electricity u s e 600

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5. Electricity c o n s e r v a t i o n possibilities for a washing machine. Moderate measures." Reducing the amount of water in pre-wash and main wash by 25% and 40% respectively saves 115 kWh/year and involves no extra cost. Strong measures: These omit pre-wash a n d use 40% less water for the main wash. This brings electricity cor-sumption down to 3 1 5 kWh/year at no extra cost. Efficiency of the electrical motor is improved by 15%, saving about 15 kWh/year, at a cost of less than $2. Intake of both hot and cold water saves 100 kWh electricity per year (which is replaced by hot water), and costs about $25, including $ 2 0 for installation. Radical measures: Electrical heating of water is completely omitted which reduces electricity consumption to only 70 kWh/year (which is required for t h e motor and automatic control). The extra cost for thermal insulation of the wash tub is estimated to be more than offset by savings in the heating element etc. Figure

5OO - Heating

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E N E R G Y POLICY March 1 9 7 9

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to It is a question of reducing the d e a d volume between the stationary outer drum and the moving washing drum. ~ The average water consumption for pre-wash for 23 types of washing machine tested in Denmark was 6.7 litres per kg of washing (dry weight) with a range of 4-9.3 litres. See Raad og Resultater, No 3, 1971; No 1, 1973; No 5, 1974; No 1, 1975; No 6, 1975; and No 5, 1976 (Statens Husholdningsraad (The Danish Home Economics Council), Copenhagen, Denmark). For the main wash the average consumption was 3.9 iitres/kg with a range of 2.3-5 litres/kg. Nothing in these tests and in Swedish experiments indicates any tendency for increased water consumption to improve washing quality. See Optimering av tv&ttprocessen mad h#nsyn till energifSrbrukningen, Tekniska byran, Report 1976:2, Konsumentverket (Swedish Government Home Economic Council), rack 162 10 V~illingby, Sweden, 1976 and Hushallens energikonsumtion, Rapport til handelsdepartementet, Konsumentverket, rack 162 10 V~illingby, Sweden, 1976. lZSee Konsumventverket, Report 1976:2, op cit, Ref 11.

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'warm-wash', which requires a temperature of about 60°C and is used for about a quarter of the laundry; 'gentle-wash', which requires a temperature of 40°C or below and accounts for the remainder.

The electricity consumption estimates in Figure 5 are based on this distribution of washing programs. The annual electricity consumption estimates assume about 20 uses of the machine per month, which seems to be typical in Denmark today? Reducing water consumption, but not the level of water in the tub, ~° appears to be a feasible means of saving electricity, since no decline in washing standards occurs, and water as well as electricity is conserved, l] Furthermore, eliminating the pre-wash does not seem to affect the quality of the washing, lz especially if the heating time for the main-wash is extended, and if all the detergent is used for the main-wash. Allowing the intake of both hot and cold water could save a considerable amount of electricity, especially if an inlet temperature of 50-60°C is assumed sufficient for washing, as in the 'radical case' of Figure 5. Thermal insulation of the washing tub might be necessary in the latter case, in order to maintain a reasonably high temperature during the washing process. Technological progress over recent decades in the field of detergents has partly eliminated the need for hot water. Instead of choosing the highest temperature which the textiles can stand, one could choose the lowest temperature necessary to achieve clean laundry. This would further add to the savings. Clothes dryers The type of clothes dryer considered here is the electric tumbler dryer which is used in about 5% of Danish households and which is practically the only energy consuming clothes drying equipment in

51

Improved efficiency in domestic electricity u s e 625 Figure 6. Electricity c o n s e r v a t i o n p o s s i b i l i t i e s for a clothes dryer.

60C

\

Moderate savings: In this case 50% of the

air is recirculated, saving 30% of electricity requirements for heating of air. Automatic humidity controlled cut-out is estimated to save 30 kWh per year. Total savings are 185 kWh per year, while the extra cost is estimated to be $35 per dryer. Strong measures; Efficiency of motors and ventilator is improved, reducing their electricity consumption by 1 5% (17 kWh per year) for an estimated cost of $5. Heat recovery is achieved through a heat exchanger with a thermal efficiency of 50%, saving 1 55 kWh per year. The extra cost is high, an estimated $75, Total electricity saving is 365 kWh per year for a total cost of $11 5. Radical measures: Hot water from the space heating system is used to heat the

air. 50% more heat energy is used compared to the electrical heating, due to lower temperature" Drying time and hence ventilator running time is extended by 35%, also because of lower temperature. The cost of this radical step is estimated to be $40, making this dryer $155 more expensive than the normal version.

~a Commercial clothes dryers have been thoroughly investigated from an energy conservation point of view, see Per Jess Jorgensen, Genvinding af varme fra torretumblere, Kemiteknik, The Technological Institute, Taastrup, Denmark, April 1977. The measures considered here are partly based on this research, but the payback time for improvements in domestic dryers is several times longer than for commercial dryers, for which payback time is often a matter of a few months because of their intensive utilization. 14 In this study we do not consider the 'hidden' energy consumption by a clothes dryer - due to the drawing in of warm indoor air and its discharge outside.

52

\

\ \

500 -8 ~, 400 = O ~. =E ~, 300

\

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Heating air - -

440

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260

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o ~' ~

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2001--

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\ \ £a

t

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_ Hot water for i heating air

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\1

-- 250--

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O~ n~ E

domestic use.13 The benefits provided by a clothes dryer, as compared to drying in the open air or in special drying rooms, are the saving of labour and time and also independence of weather conditions. The purpose of heating the air in the clothes dryer is mainly to speed up the process. Figure 6, which assumes four uses of the dryer per week, shows that more than 80% of the electricity is used for heating the incoming air. ~4 The simplest way to save energy is thus to recirculate the air. In a typical 1975 model the heated air is circulated through the drum only once, but by recirculating part of the air (which requires installation of a fluff filter) it is possible to further raise the humidity of the warm air before discharging it. The result is that less warm air, and hence less energy, is needed to dry the clothes. Heat recovery units could also be installed to make use of the heat from the outflowing air to preheat the incoming air. The heat exchanger needed for this is, however, rather expensive for use in the domestic sector. The use of heat sources other than electricity is an obvious possibility for saving electricity. Commercial dryers use gas, steam and hot water as well as electricity, and by 1973 about 30% of domestic dryers in the U S A were heated by gas. As a radical measure to conserve electricity the hot water from a central heating system (which may be oil-fired, gas-fired, coal-fired, solar-heated or wind-heated) is used in a closed circuit, as in the space-heating system. Through a water-to-air heat exchanger, heat at about 55°C can be delivered to the air at 40-45°C. The drying time is estimated to be extended by about 30% at this temperature, compared to the drying times obtained in the usual 40-80°C range. The amount of energy required, in the form of low-temperature heat, is also

E N E R G Y P O L I C Y March 1 9 7 9

Improved efficiency in domestic electricity use 65O \

600

\ k \

.~

5oo

\

\

\,

480 \

F i o u r e 7 . Electricity c o n s e r v a t i o n possibilities for a d i s h w a s h e r . Moderate m e a s u r e s : Reduction of the a m o u n t of water for washing by 30% water for hot rinse by 50%. This saves 170 kWh per year, and costs nothing. Strong m e a s u r e s : Efficiency of pump motor increased by 15%. saving about 15 kWh per year at a cost o f about $2. Intake of both cold and warm water (55°C), leads to the replacement of 180 kWh electricity per year by the same a m o u n t of heat. Extra cost for the changes, including installation, is estimated to be $30. Radical measures: Extra heating of hot water (already at 5 5 ° C or more) is eliminated. The interior container is insulated in order to reduce temperature drop. Electricity consumption is reduced to about 95 kWh per year. Extra cost for insulation is assumed to be o u t w e i g h e d by saVing the cost of a heating system in the dishwasher.

400 R cm

\\

Heating water for hot rinse - -

', \

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-~

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increased - it is about 50% more than the electrical energy consumed in electric drying) 5 Dishwashers

~SAnother possibility for drying clothes indoors is to hang t h e m in a drying closet. The closet is heated and well ventilated. If electricity is used for heating, the energy consumption seems to be as high, or higher than, that of the tumbler dryer.

E N E R G Y P O L I C Y March 1 9 7 9

The advantage of using a dishwasher, compared to manual dishwashing, is that it saves both labour and time. About 12% of Danish households had a dishwater in 1975, and an estimated 90% of those were connected to the cold water suppl~,, as assumed in this study. Figure 7 illustrates the electricity consumption for four versions of dishwasher. It is assumed that the dishwasher is used five times per week. Dishwashers are in many respects very similar to washing machines, and thus many of the conservation measures are similar. The amount of water contained in the dishwasher during the washing process can be reduced from 12 to 8 litres, and during rinsing from 12 to 6 litres. Connection to the hot as well as the cold water supply would save electricity, as in the washing machine case, especially i f as implied by the 'radical' measures - the temperature of the standard hot water supply is considered sufficient for washing dishes (as it is for manual dishwashing). The energy consumed by the pump motor will supply some heat to the water, but in order to avoid a drop in temperature, the inner container should have a low heat capacity and be well insulated. Adoption of the 'radical' measures reduces electricity consumption to less than 15% of 'normal', although part of this saved electricity must be replaced by hot water. R a d i o , t e l e v i s i o n a n d hi-fi Electronic equipment has undergone rapid development during the

53

Improved efficiency in domestic electricity use

last 10-20 years, mainly through the introduction of semiconductor technology. This has reduced energy consumption considerably and, typically, the power rating of a colour TV has declined from more than 500 W to nearly 100 W. Most of the electricity consumed by this type of appliance is used to supply the output stages (cathode ray tube, loudspeaker, etc) and these parts of electronic devices still have very low energy efficiencies. In the case of a loudspeaker, for example, only a few percent of the electrical energy supplied is converted to sound. No technology capable of improving this efficiency is, however, currently imminent. The figures presented in Table 1 for the annual consumption are based on average usage times of three hours per day for the TV, two h o u r s per day for the radio and ten hours per week for the hi-fi system. The latter term covers all kinds of electronic music systems (record player, tape recorder etc). Only moderate electricity savings are possible with present technology, as can be seen in Table 1. Most of these improvements are already available at no extra cost, in fact some have already occurred, as a means of lowering production costs.

Domestic heat distribution systems

,6 Air duct systems are very seldom used in Denmark.

54

The vast majority of heating systems in Danish dwellings are central heating systems in which the heat is distributed via the flow of hot water from a furnace (usually oil-fired) or from a district heating supply. The electricity consumption considered here includes only the electricity used for distribution, ie for operating ventilators, oil pumps and water pumps 16rather than for the space or water heating itself. A typical 1975 heating system is equipped with a 65 W circulation pump for space heating. This runs constantly during the 220 day heating season, and consumes about 350 kWh of electricity per year, as shown in Figure 8. Use of the furnace, however, depends on the need for space heating and for hot water. It is estimated to be in use for an average of only 1 500 hours per year, including the supply of hot water during the summer. As indicated in Figure 8, the introduction of an additional circulation pump for the hot water supply can make the heat distribution system one of the largest users of electricity in the home. Even though such pumps, which must run all y e a r , are used in many new systems, they are not considered 'normal' for the present calculations. The fact that 25 years ago domestic central heating systems were usually not connected to the electricity supply at all, suggests an infinite potential for electricity saving. If the heat source (furnace or district heat connection) is placed in a basement, the natural convection due to temperature differences can circulate the water in both the hot water supply and space heating circuit. When the heat source is on the same level as the rooms to be heated, a pump may be necessary for the space heating system. Rough calculations show, however, that the pumping power required in a typical house is only 1-2 W. The pumps used for this purpose usually have a power requirement of 65 W and a total efficiency of about 0.35, thus delivering about 25 W pumping power. The pumps are accordingly much too large. A smaller pump might have a lower efficiency but,

E N E R G Y P O L I C Y March 1 9 7 9

I m p r o v e d e f f i c i e n c y in d o m e s t i c electricity use

F . . . .

9OO

I I

I I t I I I

800 "C

600

v

Figure 8. Electricity c o n s e r v a t i o n possibilities f o r a typical d o m e s t i c oil fired central h e a t i n g system. Moderate measures: Hot water circulation pump is not introduced. Natural temperature convection is used, or faucets are placed not too far from hot water tank. Strong measures: A smaller pump (13 W) is developed to circulate water in the space heating system. Efficiency of pump plus motor is assumed to be reduced from 0.35 to around 0.15. Extra cost for this pump is estimated to be $ 4 0 , and the saving is 2 9 0 kWh per year. R a d i c a l m e a s u r e s : Savings are achieved by the simultaneous introduction of heat conservation measures (insulation etc). Heating season is reduced by 15% and so is the running time for the circulation pump. Furnace is in use for 35% less time, reducing its electricity consumption correspondingly. No extra costs are associated with this step.

700 Circulationpump for hot water supply

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even with an efficiency as low as 0.15, the necessary electrical power requirement would be less than 13 W - 20% of present requirements.

Small appliances Modern households possess a vast number of small electrical appliances in addition to those described so far. These include toasters, irons, hand-tools, mixers, shavers, vacuum cleaners, battery chargers, and hairdryers. These are grouped together in the category 'small appliances' in Table 1. Small appliances are responsible for only a few percent of the total electricity used for appliances and lighting in Danish households. Some of these appliances, eg toasters and irons, have a very high electricity consumption when in use but are used relatively rarely, and thus have very small annual requirements. 'Moderate' conservation measures are not considered for small appliances but a 15% saving is obtained when 'strong' measures are adopted (see Table 1). These measures involve improving the efficiency of motors, ~7 but modest savings may also be possible for appliances which use electricity for heating. It seems very likely that more thorough investigation would reveal much better conservation potential for small appliances than indicated here. 7 Technical Summary of Wanlass Controlled Torque Electrical Motors and other information from the Cravens Wanlass Corporation, California, June 1977.

ENERGY

POLICY

March 1 9 7 9

Lighting In Danish homes lighting accounts for about a quarter of electricity consumption, and incandescent lamps - with an efficiency of only

55

Improved efficiency m domestic eleeirieity use

18The starting flicker of the fluorescent lamp is still a drawback. Hence, the quality of the light from the two sources is not completely equal. It is questionable, therefore, whether replacement of all incandescent lamps with fluorescent lamps c a n be considered a purely technological conservation measure, as it does affect the service and Comfort provided, in this study, fluorescent lamps are assumed acceptable for certain uses. 19 Litek Lamp Optimization Study, Final Report, Executive Summary, Contract E(04-3)-1166, The Energy Research and Development Administration (ERDA), Washington, DC, April 1977.

56

about 5% - predominate. Even though fluorescent tubes are about 2.5 to 3 times as efficient in producing light from electricity, they have not been able to oust the incandescent type. One reason is the latter's pleasant colour spectrum. This can now, however, be copied very closely by fluorescent lamps. TM The 'moderate' measures to reduce electricity consumption in lighting, referred to in Table 1, involve changing the efficiency of the light bulbs and lampshades. Incandescent light bulbs can be made with a built-in reflector (already available), which directs the light in the required direction. Little is known about the efficiency of lampshades, but there is no doubt that often more than half of the light is absorbed by the shade. A modest 10% saving is assumed possible by redesigning lampshades and light bulbs. Other possible measures to achieve this 10% saving is to include the use of crypton-filled bulbs, allowing a higher temperature and thus a higher efficiency. The development of small screw-in fluorescent lamps for standard light sockets might facilitate the introduction of energy efficient fluorescent light sources for the domestic market. Such lamps are expected to be available within a few years? 9 Whether this occurs or not, the 'strong' measures in this study are assumed to include the use of fluorescent lamps (mainly in kitchens, bathrooms, garages etc) for 40% of domestic lighting. These measures reduce electricity consumption for lighting from 300 kWh/year to 210 kWh/year per capita. The 'radical' measure requires that only 20% of domestic light is obtained from incandescent lamps (mainly in living rooms etc) and reduces electricity consumption for lighting to 140 kWh/year per capita (or 47% of'normal'). Changes in lighting systems are not assumed to entail extra costs, thus the expensive screw-in fluorescent lamps, for instance, are expected t ° balance their higher cost w~h their longer lifetimes.

Conclusions It has been demonstrated that considerable potential exists for saving electricity in the domestic sector and that these savings can be achieved at reasonable expense and without affecting the benefits obtained from the appliances considered. It is also shown that most of these improvements, even the most 'radical', are feasible with present technology.

E N E R G Y P O L I C Y March 1 9 7 9