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Energy recycling system for urban waste heat
Energy and Buildings, 15 - 16 (1990191) 553 - 560
553
Energy Recycling System for Urban Waste Heat KATSUHIKO NARITA and TETSUYA MAEKAWA
Urban Energy System Project Team, The Tokyo Electric Power Company Inc. (TEPCO), 1-3, Uchisaiwai-cho, 1-chome, Chiyoda.ku, Tokyo 100 (Japan)
ABSTRACT
Today, energy is indispensable to daily life all over the globe. Nevertheless, it is clear that energy cannot be consumed without limit given the finite nature of resources and environments. The consumption of abundant amounts of energy today unavoidably releases huge amounts of waste energy to the surrounding environment from houses, offices, shops, factories, subways and other facilities. Heat pumps can raise the temperature of waste heat to a usable temperature range with the use of a small quantity of driving energy. In this way heat pumps act like water pumps, which can lift river water to a higher elevation by using a small amount of driving energy. Thus if a piping network for gathering and transporting waste heat is available, heat pumps can efficiently supply useful heat to customers by recovering energy from waste heat. If the waste heat of cities can be recovered, a kind of energy recycling system can be constructed using heat pump technology. This will result in the efficient use of energy and the conservation of our precious natural environment. For individual use, a heat source network might be too expensive. But waterworks and sewer systems in cities can be used for this purpose with slight modifications. In many cities, maintaining a sufficient water supply is becoming a real problem, leading to the promotion of water recycling and separate networks for the provision of drinking and non-drinking water. Sewers are one of the main repositories of waste heat, and sometimes waste heat is then diffused to rivers and lakes which are water supply sources. A heat source network would distribute waste heat and protect the environment at the same time. 0378-7788]91]$3.50
A heat distribution network using heat pumps also has advantages over conventional district heating systems: little heat loss, economical district piping, easy expandibility, and the ability to make use of a variety of waste heat sources. Such a system can efficiently meet the complex needs of modern cities where heating and cooling demands coexist in a variety of areas. A heat pump can heat and cool both simultaneously and alternatively, and works best in balancing heating and cooling demands. In this way energy recycling systems using heat pumps can play an important role in daily life through energy and environmental conservation. Consequently, energy recycling systems should be introduced as part of our social system from the viewpoint of urban planning, energy policy and environmental protection. A model project will be introduced with actual operational experiences.
1. INTRODUCTION
People's desire for a more convenient, comfortable living environment combines, with the recent brisk economic activities to develop a basic trend toward increased energy consumption for nonindustrial uses. In addition, amid the rapidly advancing information age, private corporations in larger numbers than ever have set up their offices in major cities to benefit from economies of concentration, and this has led to unusual overgrowth of urban areas both in size and population density. Thus it has come about that as cities rely more heavily on artificial environments, their energy consumption grows in volume and density. Apparently such overgrowth of cities is now bringing about two serious problems © Elsevier Sequoia]Printed in The Netherlands
554 w h i c h m u s t be solved u r g e n t l y . One is envir o n m e n t a l d a m a g e , i n c l u d i n g air a n d w a t e r pollution, p a r t i c u l a r l y in u r b a n areas, a n d the o t h e r is the need to m a i n t a i n a s t a b l e s u p p l y of energy. It is m o r e likely t h a n ever t h a t d i s r u p t i o n of e n e r g y s u p p l y will c a u s e incalculable c o n f u s i o n a n d d i s a s t e r s in cities. As is a p p a r e n t f r o m the last two oil crises w h i c h a r e p e r h a p s a m o n g the g r a v e s t e v e n t s in the 20th c e n t u r y , we h a v e to c o n s i d e r limited energy resources, their distribution among w o r l d n a t i o n s , s h a r p i n c r e a s e s in e n e r g y prices due to a d e s p e r a t e s t r u g g l e to s e c u r e a s t a b l e s u p p l y of t h e s e r e s o u r c e s , a n d t h e g r e a t adv e r s e effects of s u c h price h i k e s on t h e t r a d e b a l a n c e s of e n e r g y i m p o r t i n g c o u n t r i e s . Bec a u s e of limited n a t u r a l r e s o u r c e s , the everg r o w i n g w o r l d p o p u l a t i o n is p o s i n g a g r a v e p r o b l e m n o t o n l y to d e v e l o p i n g c o u n t r i e s w h e r e the n u m b e r of i n h a b i t a n t s is i n c r e a s i n g v e r y r a p i d l y b u t also to all o t h e r peoples on this earth. S o m e global m e a s u r e s h a v e to be t a k e n u r g e n t l y to cope w i t h serious world-wide energy and environmental problems arising f r o m a n u p s u r g e in e n e r g y c o n s u m p t i o n due to the c o n t i n u e d g r o w t h of w o r l d p o p u l a t i o n a n d the g e n e r a l i m p r o v e m e n t of living s t a n d a r d s .
INPUT
HARDWARE SYSTEM
OUTPUT
Work Eo Energy Source Ei
/ Loss(Waste Heat)
Contaminants
Fig. 1. Concept of energy consumption. Energy efficiency ratio ~/= Eo/Ei < 1. v a r i e t y of w o r k p e r f o r m e d t h r o u g h e n e r g y c o n s u m p t i o n . In a n y a s p e c t of o u r a c t i v i t i e s f r o m p r o d u c t i o n to c o n s u m p t i o n , i n c l u d i n g the i n d u s t r i a l , m a r k e t i n g , c u l t u r a l a n d recrea t i o n a l sectors, we t h i n k we m a y say t h e r e is no h u m a n a c t i o n t h a t does n o t i n v o l v e a n y e n e r g y c o n s u m p t i o n . T h u s we rely h e a v i l y on e n e r g y in o u r daily lives.
2.2. Energy consumption pattern F i g u r e 1 gives a s c h e m a t i c d e s c r i p t i o n of energy consumption patterns. It s h o u l d be n o t e d h e r e t h a t the performance of work using energy involves the production of wastes and a loss of energy. T h e e n e r g y loss e v e n t u a l l y r e s u l t s in w a s t e h e a t which, a l o n g w i t h o t h e r wastes, is d i s c h a r g e d into o u r living e n v i r o n m e n t .
2. USE OF ENERGY To s u c c e s s f u l l y a p p r o a c h t h e s e p r o b l e m s , we m u s t go b a c k to b a s i c c o n s i d e r a t i o n s on the use of energy. First, we s h o u l d s t u d y h o w a n d for w h a t p u r p o s e s e n e r g y is used.
2.1. Purposes of energy use T o d a y a d i v e r s i t y of e n e r g y s o u r c e s a r e used for different p u r p o s e s ( T a b l e 1). N e e d l e s s to say, o u r a i m of u s i n g t h e s e e n e r g y s o u r c e s is n o t to simply c o n s u m e t h e m b u t to get a
3. USE OF ENERGY IN CITIES E n e r g y c o n s u m p t i o n in cities, w h e r e a div e r s i t y of h u m a n a c t i v i t i e s are c o n c e n t r a t e d , s h o w s m a n y different w a y s in w h i c h we use energy.
3.1. Purposes and ways of energy use in cities In cities, e n e r g y is n e e d e d a n d used for different p u r p o s e s in all p h a s e s of o u r
TABLE 1 Energy utilization and efficiency Equipment
Energy conversion
Efficiency (%)
Automobile Small electric motor Small boiler Fluorescent lamp Electric bulb Power generation plant Solar cell
Chemical- Mechanical Electric - Mechanical Chemical- Thermal Electric- Light Electric - Light Chemical - Electric Light - Electric
20 65 - 80 65- 70 18 10 36 10
555 Electricity ~ - - " ~ - - - ~
48.9 TWh/y
IT.ky.I ~
Oil
CO= 35,800 kTon/y
- SOx
8.8 kTon/y
147.1 TWh/y Fig. 3. Waste substances and waste heat from T o k y o area
(FY 1986).
Fig. 2. Energy consumption in Tokyo.
activities from production to distribution and consumption, including commercial operations, services, recreation, restaurants, hotels and housing, cultural and educational sectors, environmental preservation, and waste disposal. A series of studies is well under way on each of these consumption processes, but this Section deals with a macroscopic study on how energy is used in Tokyo, one of the world major cities. First, an attempt was made to find the current state of energy consumption in each of the 500-meter meshes into which Tokyo is divided. The findings are summarized in Fig. 2. The total energy consumption in Tokyo is more than 229.8 TWh/y with the consumption density in the central part reaching 778.4 kWh per square meter. This is equivalent to the amount of electricity needed to keep a 26.2 MW heater operating for a year.
3.2. Consequences of large energy consumption Now let us consider how urban environment is affected by such huge energy consumption. Before going into the details of
this problem, we should take a look at Fig. 3 which shows the results of a survey on how much waste heat and other wastes are discarded in Tokyo. Undoubtedly waste heat and other wastes resulting from such an enormous amount and density of energy consumption worsen the city environment in many ways. Some trends of air environmental indexes are given in Fig. 4. As is apparent from these indexes, despite increased heat and other wastes from energy consumption, the atmospheric concentration of such visible pollutants as soot and sulfur oxides tends to be lowered through the implementation of emission regulations and the installation of decontamination devices, while the concentration of nitrogen oxides which are invisible and difficult to control is still above the permissible level. However we have to keep the closest watch on such gradual, invisible environmental deterioration because in general we fail to readily perceive its graveness, and therefore cannot control it immediately. Figure 5 shows mean lowest temperature values in February, the coldest season in Tokyo, over the years. Obviously the temperature began to rise in 1950 when J a p a n entered a period of high economic growth. As a variety of environmental damage came to the fore during the period of rapid economic growth, the Japanese government took stricter environmental control measures for industrial production activities, taking into consideration the general trend of public opinion. Meanwhile little attention has been given until quite recently to the wastes from energy consumption for air-conditioning in commercial buildings because the quantity of such wastes is insignificant, their sources are not concentrated in any particular region, and there are complicated relations between victims and polluters. But these days, when air-conditioning systems are used widely not only in production facilities but also in
556
--'-- c e n t r a l
.....
area
suburbs average
NOx PP=
004 [
,..I"-'~'~-'-~, _.
~"
0.03
!
"~ .. '~%,°, ,%
,
"..,..o-,,.,.~~-
=f
. . . . . . . .
i
i
1965
0.02
. . . . . ,..._
. ..............
i
1970
c0L~ "
0.03
0.01 |
1975
1980
i
1985
19'65
(FY)
1970
Oxidant
1675
1680
Afloat
ppm
19'85
(FY)
Particle
mglm3 030 0.~
o.od
0,0~
%,
"" "'~:........
......
OOZ2
0.~
0.02 o.ot
0.07
1965
1970
1975
19'80
19'85 (FY)
1 9'6 5
i9'70
19'75
1680
19'85
(FY)
Fig. 4. Trend of air pollution index in Tokyo. 4. THREE-POINT PRINCIPLE FOR FUTURE ENERGY USE
(~) 4 2 0 -2 ~ ' . , , -... ,..,',..,',: -4
-6 r
I
r
-8 1880 1900 1920 19t40 19~6019180 Fig. 5. Average (Tokyo).
minimum
temperature
in
January
commercial buildings and private houses, emissions from energy consumption for nonindustrial uses are becoming very significant both in quantity and environmental impact. It is expected that the ongoing shift of relative importance in industrial economy from hardware to software will lead to further increases in energy consumption for nonindustrial uses. We fear this may cause serious environmental problems particularly in cities, and what is worse, it is difficult to control them.
Energy requirements for nonindustrial uses have thus increased rapidly and are expected to continue growing in the years to come. Since nonindustrial energy is mainly consumed in cities, it is essential that this energy should be used in accordance with the following three-point principle: (1) good economical efficiency; (2) contribution to energy conservation; and (3) satisfactory environmental control. Under the free economy society, economical efficiency is a primary consideration in distribution and consumption as well as in industrial production. It is one of the essential factors in getting any method or technique accepted widely. Energy-saving effects play an important role in conserving limited, valuable energy resources of the earth, achieving satisfactory economical performance and precluding environmental pollution. In other words, the
557 second element of the principle encourages efficient utilization of energy for each purpose. Satisfactory environmental control has often been neglected in nonindustrial uses of energy. Until recently, we could usually rely on the self-cleansing function of a na t ur al environment for purifying u n t r e a t e d wastes from energy consumption for nonindustrial uses. With a remarkable increase in energy consumption due to the growth of population and cities, we can no longer rely on such n a t u ral purification. These days, for instance, our living environment is contaminated and made less comfortable to live in by emissions from the combustion of coal or oil for space heating systems which were originally intended to improve our living environment.
Heat Output
Contaminants
J
Energy
Input
Waste
() WasteHeat
Heat
V
(~
Fig. 6. Concept of urban waste heat network.
5. PROPOSED ENERGY USE UNDER THE THREE-POINT PRINCIPLE
using electricity, the most suitable energy carrier for cities.
5.1. Use of e l e c t r i c i t y - the optimum energy carrier for cities
5.2. Development of electric heat pump
Of all energy sources, electricity is best prepared and available for all uses while involving little environmental pollution in places of consumption. In addition, it can be produced not only by hydro, thermal and nuclear power facilities but also from such natural resources as solar energy, wind power and tidal power. The problem is the low efficiency of electricity generation which is only about 40% at the best. From the economical performance of different energy sources and the total energy efficiency, including the production of electricity, it has been argued t h a t the use of electricity should be avoided for certain purposes, p ar ticu lar l y the generation of heat, wherever alternative energy sources are available. For this reason, some have recently contended t h a t efforts should be made to facilitate the development of cogeneration. However small decentralized cogeneration units are not suitable energy supply systems for cities because they have such drawbacks as inadequate reliability and the emission of h eat and other wastes from their operation. In addition, the use of these installations should be limited to those places which are covered by the service network of the local gasworks. Efforts are needed therefore to develop a new technique for economically and efficiently
The heat pump can move heat from a colder place to a h o t t e r one in the same m a n n e r as the water pump draws up the liquid from a lower place to a higher one. The heat pump has a very high energy efficiency; it can produce an amount of thermal energy several times as large as the energy used for its operation. Figure 6 shows a flowchart of energy in a heat pump system. This installation has satisfactory economical performance and great energy-saving effects, because the amount of energy required for its operation is only a fraction of the effective thermal out put it offers. This is equivalent to the reduction of energy cost to a fraction of its c u r r e n t level. An electric heat pump can make high-temperat ure thermal output corresponding to several times as much energy as it spends in gathering low-temperature heat. This econom-
ical, efficient, non-polluting device enables better energy utilization exactly in accordance with the three-point principle noted earlier in this report. A scheme has been proposed to form a social system using the heat pump technology for recycling a large am ount of waste heat from the enormous energy consumption in cities. The following Section briefly describes this system, known as the "energy recycling system with electric heat pump technology".
558 THERMAL ENERGY
buildings 7C
25C
~nc|neratton
plant
?C
power
47C U
Fig. 8. System diagram of Hikarigaoka Park Town district heating and cooling system.
HC PLANT
J
6.1. System construction The energy recycling system (Fig. 7) consists of several processes, including energy consumption in the city for various purposes, the emission of waste heat from such energy consumption, the recovery and storage of waste heat, the heating of stored thermal energy to the desired temperature by the heat pump and its distribution, and the use of thermal energy thus supplied. 6.2. Examples of energy recycling system installation The heat-pump-based energy recycling system can be used for communities or districts of various sizes. Some examples of the system installation are given in Figs. 8- 10. 6.3. Major considerations in promoting energy recycling systems From the three-point principle for future energy use and the performance records of the installed systems shown above, the energy recycling system using the electric heat pump technology looks very promising as a new energy system for cities. In a closely built-up area like Tokyo, however, installation of the system may often face many difficulties, especially in building the waste heat gathering and transmission subsystems, and thus incur a huge construction cost. To solve this problem,
ldlng
30C used hot water
Fig. 7. Energy recycling system.
6. ENERGY RECYCLING SYSTEM WITH ELECTRIC HEAT PUMP TECHNOLOGY
pubJ,~c b a ~ h
47¢
Fig. 9. System diagram of Ginza district heating and cooling system.
s.ewage treat,ent plant
Fig. 10. System diagram of Makuhari district heating and cooling system.
an arrangement will have to be made to include waste heat gathering and heat service pipelines, along with nonpotable water supply and dust collecting systems, as the essential elements of infrastructure in all future city planning. Efforts are also needed to help the general public fully understand the serious problems arising from tremendous energy consumption in our daily lives and the favorable social and economic effects of the energy recycling system.
6.4. Economic and social effects of the energy recycling system Thus the heat pump technology is expected to play an important role in preserving natural resources and a sound living environment which is among the hardest tasks we have to carry out from now on. With this in mind, we established the Heat Pump Technology Center of Japan in 1987 to accelerate the further development of this technology. With the participation of scientists, researchers and engineers from academic and industrial circles,
559 TABLE 2 Energy saving with heat pumps in the year 2000 in Tokyo Case
Category
Saved energy (megalitres o.e.)
Percentage of total energy demand
Percentage of thermal energy demand
Maximum
Residential Commercial Total
521 675 1196
10.9 10.1 10.5
16.6 17.6 17.1
Minimum
Residential Commercial Total
368 447 815
7.7 6.7 7.1
11.7 11.7 11.7
1988
Residential Commercial Total
70 156 227
1.8 4.1 3.0
2.8 7.1 4.8
TABLE 3 Environmental effect of heat pumps in the year 2000 in Tokyo Case
Category
SOx reduction
NOx reduction
(ton/year)
(%)
(ton/year)
(%)
Maximum
Residential Commercial Total
909 46 955
53 46 53
644 2392 3036
54 48 49
Minimum
Residential Commercial Total
472 35 506
28 35 28
334 1461 1794
28 29 29
a two-year research project was conducted on the social and economic effects of the diffusion of the heat pump technology. Under this project, our efforts were focused on finding what changes the spread of heat pumps would bring about in Japan's energy consumption and the resultant emissions. A report on the project says that by the year 2000 the spread of the heat pump technology will reduce energy consumption and the resultant emissions in Tokyo Metropolitan Area as follows:
• amount of energy saved: 11 - 17% (Table 2); • decrease in NOx emission: 29- 49% (Table 3). The projected amount of energy saving will amount to as much as 1196 megaliters in oil equivalent.
7. CONCLUSIONS
Energy resource and environmental problems have grown so grave and extensive that they are now beyond the scope of national control measures; the international community, including developing nations, will have to take an urgent global approach to these problems. Before the current favorable economic climate and relatively stable oil prices turn for the worse, we have to study in earnest what remedies to take for these problems and how to solve them. J a p a n experienced lots of environmental pollution during the period of rapid economic growth and has since then made continuous efforts to cope with these environmental problems. Without such experience, we probably could not have developed the
560 energy recycling system with the heat pump technology described earlier in this report. W e h o p e t h e s y s t e m w i l l be of s o m e h e l p to the s o l u t i o n of global e n e r g y r e s o u r c e a n d environmental problems.
BIBLIOGRAPHY Research on the utilization of low grade waste heat in
urban area. Century Research Center, National Institute for Research Advancement, 1985. Chronological Tables of Science, Tokyo Meteorological Institute, 1988. Social and Economic Effects of Diffusion of Heat Pump Technology in Japan, Heat Pump Technology Center of Japan, 1988. White Paper on Environment, Environment Agency, Japanese Government, 1988. General Statistics of Energy of Japan, Ministry of International Trade and Industry, Japanese Government, 1988.
553
Energy Recycling System for Urban Waste Heat KATSUHIKO NARITA and TETSUYA MAEKAWA
Urban Energy System Project Team, The Tokyo Electric Power Company Inc. (TEPCO), 1-3, Uchisaiwai-cho, 1-chome, Chiyoda.ku, Tokyo 100 (Japan)
ABSTRACT
Today, energy is indispensable to daily life all over the globe. Nevertheless, it is clear that energy cannot be consumed without limit given the finite nature of resources and environments. The consumption of abundant amounts of energy today unavoidably releases huge amounts of waste energy to the surrounding environment from houses, offices, shops, factories, subways and other facilities. Heat pumps can raise the temperature of waste heat to a usable temperature range with the use of a small quantity of driving energy. In this way heat pumps act like water pumps, which can lift river water to a higher elevation by using a small amount of driving energy. Thus if a piping network for gathering and transporting waste heat is available, heat pumps can efficiently supply useful heat to customers by recovering energy from waste heat. If the waste heat of cities can be recovered, a kind of energy recycling system can be constructed using heat pump technology. This will result in the efficient use of energy and the conservation of our precious natural environment. For individual use, a heat source network might be too expensive. But waterworks and sewer systems in cities can be used for this purpose with slight modifications. In many cities, maintaining a sufficient water supply is becoming a real problem, leading to the promotion of water recycling and separate networks for the provision of drinking and non-drinking water. Sewers are one of the main repositories of waste heat, and sometimes waste heat is then diffused to rivers and lakes which are water supply sources. A heat source network would distribute waste heat and protect the environment at the same time. 0378-7788]91]$3.50
A heat distribution network using heat pumps also has advantages over conventional district heating systems: little heat loss, economical district piping, easy expandibility, and the ability to make use of a variety of waste heat sources. Such a system can efficiently meet the complex needs of modern cities where heating and cooling demands coexist in a variety of areas. A heat pump can heat and cool both simultaneously and alternatively, and works best in balancing heating and cooling demands. In this way energy recycling systems using heat pumps can play an important role in daily life through energy and environmental conservation. Consequently, energy recycling systems should be introduced as part of our social system from the viewpoint of urban planning, energy policy and environmental protection. A model project will be introduced with actual operational experiences.
1. INTRODUCTION
People's desire for a more convenient, comfortable living environment combines, with the recent brisk economic activities to develop a basic trend toward increased energy consumption for nonindustrial uses. In addition, amid the rapidly advancing information age, private corporations in larger numbers than ever have set up their offices in major cities to benefit from economies of concentration, and this has led to unusual overgrowth of urban areas both in size and population density. Thus it has come about that as cities rely more heavily on artificial environments, their energy consumption grows in volume and density. Apparently such overgrowth of cities is now bringing about two serious problems © Elsevier Sequoia]Printed in The Netherlands
554 w h i c h m u s t be solved u r g e n t l y . One is envir o n m e n t a l d a m a g e , i n c l u d i n g air a n d w a t e r pollution, p a r t i c u l a r l y in u r b a n areas, a n d the o t h e r is the need to m a i n t a i n a s t a b l e s u p p l y of energy. It is m o r e likely t h a n ever t h a t d i s r u p t i o n of e n e r g y s u p p l y will c a u s e incalculable c o n f u s i o n a n d d i s a s t e r s in cities. As is a p p a r e n t f r o m the last two oil crises w h i c h a r e p e r h a p s a m o n g the g r a v e s t e v e n t s in the 20th c e n t u r y , we h a v e to c o n s i d e r limited energy resources, their distribution among w o r l d n a t i o n s , s h a r p i n c r e a s e s in e n e r g y prices due to a d e s p e r a t e s t r u g g l e to s e c u r e a s t a b l e s u p p l y of t h e s e r e s o u r c e s , a n d t h e g r e a t adv e r s e effects of s u c h price h i k e s on t h e t r a d e b a l a n c e s of e n e r g y i m p o r t i n g c o u n t r i e s . Bec a u s e of limited n a t u r a l r e s o u r c e s , the everg r o w i n g w o r l d p o p u l a t i o n is p o s i n g a g r a v e p r o b l e m n o t o n l y to d e v e l o p i n g c o u n t r i e s w h e r e the n u m b e r of i n h a b i t a n t s is i n c r e a s i n g v e r y r a p i d l y b u t also to all o t h e r peoples on this earth. S o m e global m e a s u r e s h a v e to be t a k e n u r g e n t l y to cope w i t h serious world-wide energy and environmental problems arising f r o m a n u p s u r g e in e n e r g y c o n s u m p t i o n due to the c o n t i n u e d g r o w t h of w o r l d p o p u l a t i o n a n d the g e n e r a l i m p r o v e m e n t of living s t a n d a r d s .
INPUT
HARDWARE SYSTEM
OUTPUT
Work Eo Energy Source Ei
/ Loss(Waste Heat)
Contaminants
Fig. 1. Concept of energy consumption. Energy efficiency ratio ~/= Eo/Ei < 1. v a r i e t y of w o r k p e r f o r m e d t h r o u g h e n e r g y c o n s u m p t i o n . In a n y a s p e c t of o u r a c t i v i t i e s f r o m p r o d u c t i o n to c o n s u m p t i o n , i n c l u d i n g the i n d u s t r i a l , m a r k e t i n g , c u l t u r a l a n d recrea t i o n a l sectors, we t h i n k we m a y say t h e r e is no h u m a n a c t i o n t h a t does n o t i n v o l v e a n y e n e r g y c o n s u m p t i o n . T h u s we rely h e a v i l y on e n e r g y in o u r daily lives.
2.2. Energy consumption pattern F i g u r e 1 gives a s c h e m a t i c d e s c r i p t i o n of energy consumption patterns. It s h o u l d be n o t e d h e r e t h a t the performance of work using energy involves the production of wastes and a loss of energy. T h e e n e r g y loss e v e n t u a l l y r e s u l t s in w a s t e h e a t which, a l o n g w i t h o t h e r wastes, is d i s c h a r g e d into o u r living e n v i r o n m e n t .
2. USE OF ENERGY To s u c c e s s f u l l y a p p r o a c h t h e s e p r o b l e m s , we m u s t go b a c k to b a s i c c o n s i d e r a t i o n s on the use of energy. First, we s h o u l d s t u d y h o w a n d for w h a t p u r p o s e s e n e r g y is used.
2.1. Purposes of energy use T o d a y a d i v e r s i t y of e n e r g y s o u r c e s a r e used for different p u r p o s e s ( T a b l e 1). N e e d l e s s to say, o u r a i m of u s i n g t h e s e e n e r g y s o u r c e s is n o t to simply c o n s u m e t h e m b u t to get a
3. USE OF ENERGY IN CITIES E n e r g y c o n s u m p t i o n in cities, w h e r e a div e r s i t y of h u m a n a c t i v i t i e s are c o n c e n t r a t e d , s h o w s m a n y different w a y s in w h i c h we use energy.
3.1. Purposes and ways of energy use in cities In cities, e n e r g y is n e e d e d a n d used for different p u r p o s e s in all p h a s e s of o u r
TABLE 1 Energy utilization and efficiency Equipment
Energy conversion
Efficiency (%)
Automobile Small electric motor Small boiler Fluorescent lamp Electric bulb Power generation plant Solar cell
Chemical- Mechanical Electric - Mechanical Chemical- Thermal Electric- Light Electric - Light Chemical - Electric Light - Electric
20 65 - 80 65- 70 18 10 36 10
555 Electricity ~ - - " ~ - - - ~
48.9 TWh/y
IT.ky.I ~
Oil
CO= 35,800 kTon/y
- SOx
8.8 kTon/y
147.1 TWh/y Fig. 3. Waste substances and waste heat from T o k y o area
(FY 1986).
Fig. 2. Energy consumption in Tokyo.
activities from production to distribution and consumption, including commercial operations, services, recreation, restaurants, hotels and housing, cultural and educational sectors, environmental preservation, and waste disposal. A series of studies is well under way on each of these consumption processes, but this Section deals with a macroscopic study on how energy is used in Tokyo, one of the world major cities. First, an attempt was made to find the current state of energy consumption in each of the 500-meter meshes into which Tokyo is divided. The findings are summarized in Fig. 2. The total energy consumption in Tokyo is more than 229.8 TWh/y with the consumption density in the central part reaching 778.4 kWh per square meter. This is equivalent to the amount of electricity needed to keep a 26.2 MW heater operating for a year.
3.2. Consequences of large energy consumption Now let us consider how urban environment is affected by such huge energy consumption. Before going into the details of
this problem, we should take a look at Fig. 3 which shows the results of a survey on how much waste heat and other wastes are discarded in Tokyo. Undoubtedly waste heat and other wastes resulting from such an enormous amount and density of energy consumption worsen the city environment in many ways. Some trends of air environmental indexes are given in Fig. 4. As is apparent from these indexes, despite increased heat and other wastes from energy consumption, the atmospheric concentration of such visible pollutants as soot and sulfur oxides tends to be lowered through the implementation of emission regulations and the installation of decontamination devices, while the concentration of nitrogen oxides which are invisible and difficult to control is still above the permissible level. However we have to keep the closest watch on such gradual, invisible environmental deterioration because in general we fail to readily perceive its graveness, and therefore cannot control it immediately. Figure 5 shows mean lowest temperature values in February, the coldest season in Tokyo, over the years. Obviously the temperature began to rise in 1950 when J a p a n entered a period of high economic growth. As a variety of environmental damage came to the fore during the period of rapid economic growth, the Japanese government took stricter environmental control measures for industrial production activities, taking into consideration the general trend of public opinion. Meanwhile little attention has been given until quite recently to the wastes from energy consumption for air-conditioning in commercial buildings because the quantity of such wastes is insignificant, their sources are not concentrated in any particular region, and there are complicated relations between victims and polluters. But these days, when air-conditioning systems are used widely not only in production facilities but also in
556
--'-- c e n t r a l
.....
area
suburbs average
NOx PP=
004 [
,..I"-'~'~-'-~, _.
~"
0.03
!
"~ .. '~%,°, ,%
,
"..,..o-,,.,.~~-
=f
. . . . . . . .
i
i
1965
0.02
. . . . . ,..._
. ..............
i
1970
c0L~ "
0.03
0.01 |
1975
1980
i
1985
19'65
(FY)
1970
Oxidant
1675
1680
Afloat
ppm
19'85
(FY)
Particle
mglm3 030 0.~
o.od
0,0~
%,
"" "'~:........
......
OOZ2
0.~
0.02 o.ot
0.07
1965
1970
1975
19'80
19'85 (FY)
1 9'6 5
i9'70
19'75
1680
19'85
(FY)
Fig. 4. Trend of air pollution index in Tokyo. 4. THREE-POINT PRINCIPLE FOR FUTURE ENERGY USE
(~) 4 2 0 -2 ~ ' . , , -... ,..,',..,',: -4
-6 r
I
r
-8 1880 1900 1920 19t40 19~6019180 Fig. 5. Average (Tokyo).
minimum
temperature
in
January
commercial buildings and private houses, emissions from energy consumption for nonindustrial uses are becoming very significant both in quantity and environmental impact. It is expected that the ongoing shift of relative importance in industrial economy from hardware to software will lead to further increases in energy consumption for nonindustrial uses. We fear this may cause serious environmental problems particularly in cities, and what is worse, it is difficult to control them.
Energy requirements for nonindustrial uses have thus increased rapidly and are expected to continue growing in the years to come. Since nonindustrial energy is mainly consumed in cities, it is essential that this energy should be used in accordance with the following three-point principle: (1) good economical efficiency; (2) contribution to energy conservation; and (3) satisfactory environmental control. Under the free economy society, economical efficiency is a primary consideration in distribution and consumption as well as in industrial production. It is one of the essential factors in getting any method or technique accepted widely. Energy-saving effects play an important role in conserving limited, valuable energy resources of the earth, achieving satisfactory economical performance and precluding environmental pollution. In other words, the
557 second element of the principle encourages efficient utilization of energy for each purpose. Satisfactory environmental control has often been neglected in nonindustrial uses of energy. Until recently, we could usually rely on the self-cleansing function of a na t ur al environment for purifying u n t r e a t e d wastes from energy consumption for nonindustrial uses. With a remarkable increase in energy consumption due to the growth of population and cities, we can no longer rely on such n a t u ral purification. These days, for instance, our living environment is contaminated and made less comfortable to live in by emissions from the combustion of coal or oil for space heating systems which were originally intended to improve our living environment.
Heat Output
Contaminants
J
Energy
Input
Waste
() WasteHeat
Heat
V
(~
Fig. 6. Concept of urban waste heat network.
5. PROPOSED ENERGY USE UNDER THE THREE-POINT PRINCIPLE
using electricity, the most suitable energy carrier for cities.
5.1. Use of e l e c t r i c i t y - the optimum energy carrier for cities
5.2. Development of electric heat pump
Of all energy sources, electricity is best prepared and available for all uses while involving little environmental pollution in places of consumption. In addition, it can be produced not only by hydro, thermal and nuclear power facilities but also from such natural resources as solar energy, wind power and tidal power. The problem is the low efficiency of electricity generation which is only about 40% at the best. From the economical performance of different energy sources and the total energy efficiency, including the production of electricity, it has been argued t h a t the use of electricity should be avoided for certain purposes, p ar ticu lar l y the generation of heat, wherever alternative energy sources are available. For this reason, some have recently contended t h a t efforts should be made to facilitate the development of cogeneration. However small decentralized cogeneration units are not suitable energy supply systems for cities because they have such drawbacks as inadequate reliability and the emission of h eat and other wastes from their operation. In addition, the use of these installations should be limited to those places which are covered by the service network of the local gasworks. Efforts are needed therefore to develop a new technique for economically and efficiently
The heat pump can move heat from a colder place to a h o t t e r one in the same m a n n e r as the water pump draws up the liquid from a lower place to a higher one. The heat pump has a very high energy efficiency; it can produce an amount of thermal energy several times as large as the energy used for its operation. Figure 6 shows a flowchart of energy in a heat pump system. This installation has satisfactory economical performance and great energy-saving effects, because the amount of energy required for its operation is only a fraction of the effective thermal out put it offers. This is equivalent to the reduction of energy cost to a fraction of its c u r r e n t level. An electric heat pump can make high-temperat ure thermal output corresponding to several times as much energy as it spends in gathering low-temperature heat. This econom-
ical, efficient, non-polluting device enables better energy utilization exactly in accordance with the three-point principle noted earlier in this report. A scheme has been proposed to form a social system using the heat pump technology for recycling a large am ount of waste heat from the enormous energy consumption in cities. The following Section briefly describes this system, known as the "energy recycling system with electric heat pump technology".
558 THERMAL ENERGY
buildings 7C
25C
~nc|neratton
plant
?C
power
47C U
Fig. 8. System diagram of Hikarigaoka Park Town district heating and cooling system.
HC PLANT
J
6.1. System construction The energy recycling system (Fig. 7) consists of several processes, including energy consumption in the city for various purposes, the emission of waste heat from such energy consumption, the recovery and storage of waste heat, the heating of stored thermal energy to the desired temperature by the heat pump and its distribution, and the use of thermal energy thus supplied. 6.2. Examples of energy recycling system installation The heat-pump-based energy recycling system can be used for communities or districts of various sizes. Some examples of the system installation are given in Figs. 8- 10. 6.3. Major considerations in promoting energy recycling systems From the three-point principle for future energy use and the performance records of the installed systems shown above, the energy recycling system using the electric heat pump technology looks very promising as a new energy system for cities. In a closely built-up area like Tokyo, however, installation of the system may often face many difficulties, especially in building the waste heat gathering and transmission subsystems, and thus incur a huge construction cost. To solve this problem,
ldlng
30C used hot water
Fig. 7. Energy recycling system.
6. ENERGY RECYCLING SYSTEM WITH ELECTRIC HEAT PUMP TECHNOLOGY
pubJ,~c b a ~ h
47¢
Fig. 9. System diagram of Ginza district heating and cooling system.
s.ewage treat,ent plant
Fig. 10. System diagram of Makuhari district heating and cooling system.
an arrangement will have to be made to include waste heat gathering and heat service pipelines, along with nonpotable water supply and dust collecting systems, as the essential elements of infrastructure in all future city planning. Efforts are also needed to help the general public fully understand the serious problems arising from tremendous energy consumption in our daily lives and the favorable social and economic effects of the energy recycling system.
6.4. Economic and social effects of the energy recycling system Thus the heat pump technology is expected to play an important role in preserving natural resources and a sound living environment which is among the hardest tasks we have to carry out from now on. With this in mind, we established the Heat Pump Technology Center of Japan in 1987 to accelerate the further development of this technology. With the participation of scientists, researchers and engineers from academic and industrial circles,
559 TABLE 2 Energy saving with heat pumps in the year 2000 in Tokyo Case
Category
Saved energy (megalitres o.e.)
Percentage of total energy demand
Percentage of thermal energy demand
Maximum
Residential Commercial Total
521 675 1196
10.9 10.1 10.5
16.6 17.6 17.1
Minimum
Residential Commercial Total
368 447 815
7.7 6.7 7.1
11.7 11.7 11.7
1988
Residential Commercial Total
70 156 227
1.8 4.1 3.0
2.8 7.1 4.8
TABLE 3 Environmental effect of heat pumps in the year 2000 in Tokyo Case
Category
SOx reduction
NOx reduction
(ton/year)
(%)
(ton/year)
(%)
Maximum
Residential Commercial Total
909 46 955
53 46 53
644 2392 3036
54 48 49
Minimum
Residential Commercial Total
472 35 506
28 35 28
334 1461 1794
28 29 29
a two-year research project was conducted on the social and economic effects of the diffusion of the heat pump technology. Under this project, our efforts were focused on finding what changes the spread of heat pumps would bring about in Japan's energy consumption and the resultant emissions. A report on the project says that by the year 2000 the spread of the heat pump technology will reduce energy consumption and the resultant emissions in Tokyo Metropolitan Area as follows:
• amount of energy saved: 11 - 17% (Table 2); • decrease in NOx emission: 29- 49% (Table 3). The projected amount of energy saving will amount to as much as 1196 megaliters in oil equivalent.
7. CONCLUSIONS
Energy resource and environmental problems have grown so grave and extensive that they are now beyond the scope of national control measures; the international community, including developing nations, will have to take an urgent global approach to these problems. Before the current favorable economic climate and relatively stable oil prices turn for the worse, we have to study in earnest what remedies to take for these problems and how to solve them. J a p a n experienced lots of environmental pollution during the period of rapid economic growth and has since then made continuous efforts to cope with these environmental problems. Without such experience, we probably could not have developed the
560 energy recycling system with the heat pump technology described earlier in this report. W e h o p e t h e s y s t e m w i l l be of s o m e h e l p to the s o l u t i o n of global e n e r g y r e s o u r c e a n d environmental problems.
BIBLIOGRAPHY Research on the utilization of low grade waste heat in
urban area. Century Research Center, National Institute for Research Advancement, 1985. Chronological Tables of Science, Tokyo Meteorological Institute, 1988. Social and Economic Effects of Diffusion of Heat Pump Technology in Japan, Heat Pump Technology Center of Japan, 1988. White Paper on Environment, Environment Agency, Japanese Government, 1988. General Statistics of Energy of Japan, Ministry of International Trade and Industry, Japanese Government, 1988.