STOY HEAT PUMPS AND HEAT RECOVERY IN BUILDINGS OF THE FEDERAL REPUBLIC OF GERMANY Bernd Stay Rheinisch-Westfalisches Elektrizitatswerk AG INTRODUCTION In 1972~ the author has made the statement that the energy consumption per head of the of the population must not increase with the nation's wealth - at that time still a criterion for the economic power and the prosperity of a country - but that, in the future, a nation will have an advantage, if there is a lowest possible specific energy consumption per application combined with a relatively high energy consumption per heado This resulted in the idea of the so-called "decoupling" of economic growth and increased energy consumption~ That this decoupling is possible in reality within certain limits, which are surprisingly broad, was confirmed by the past years which were characterized by two oil price crisis~ Here, the current application played an important - and especially posi ve role@ At least in the Federal Republic of Germany, it was above all the electrical engineering industry which stood up for a rational use of energy, for the development of regenerative energies, and also for a reasonable use of electricity this far more than the producers and suppliers of coal, oil or natural gas did~ Yet, the electricity portion of the final energy demand was not on the decrease~ The reason was that, on the one hand, electric energy was used more economically and more effecti ; on the other hand, electric energy could replace expensive fossil energy sources - above all mineral oil - in more and more fields0 After the rst oil price crisis, it was the key task of the International Energy Agency to take care that its member countries made great progress in the substitution of oil in any possible field of application~ The fact that the International Energy Agency then did very well was proved by the past years0 Recently, the International Energy Agency also pointed out that, among all of its member states~ the Federal Repulic of Germany is the one which - relatively seen - has made the in the substitution of oil$ With great delight, the ce the International Energy Agency ions and lectures of its former director, idea of decQupling@ ~I~~nwni ~ the problem is no longer restricted to the mere supply of energy; an active, responsible and intelligent use of energy plays an ever increasing role for a large number of people and, above all, for the responsible politicians@ Today, this consciousness has become the norm. The necessity which became obvious as a result of the so-called oil crisis in autumn 1973 - to economize fossil energy sources by domestic ones, was 'an impetus in all of the highly developed 'industrial states to develop appropriate techniques@ J-145 STOY To which extent in particular the German electric engineering industry contributed to the development and use of heat pumps and heat recovery systems in buildings will be illustrated by the author in the following considering the premises I substitution of import-dependent energy sources I optimum utilization of primary enery and I the lowest possible environmental load0 by domestic ones, However, these goals can be achieved only by an appropriate interplay of very different measures~ With regard to the subject of this paper, these include , heat insulation for a lowest possible use of energy, @ heat recovery for a multiple utilization of the energy used and I the heat pump technique for utilizing regenerative energies or waste heat0 HEAT INSULATION TodaY9 there are approximately 24 million dwellings in the Federal Republic of Germany; approximately 85 % of them were built before the so-called rst oil cr!sis in October 19730 For the heating of these llings alone~ more energy is used up than is, for example, required by the entire industry~ On the other hand, the energy used for space heating is an especially low-grade one, whereas in industry mostly high-grade is used0 In addition, about 50 %of all dwellings are heated with minera oil which must be imported~ The wastage of imported energy, which will exhausted in the long run, as a result of an obsolete minimum thermal protection can be reduced mainly by the modern possibilities of heat insulation0 And the energy savings are not connected with reduced convenience~ On the contrary: by less draught, higher surface temperatures room-enclosing surfaces in winter and cooler rooms in summer, convenience and thus comfort even increase0 In the 1 Republic of Germany, the trend for highly heat-insu1 buildings is running more and more towards air heating systems, since in the Federal Rupublic - different from the United States - even today almost exclusively hot water systems are used for the heat distribuon in dwelling houses~ At the same time, air heating provides for a constant reliable ventilation of all rooms In addition, the heat contained in the spent air can be recovered. & Our company, the Rheinisch-We~tf~lisches Elektriztit~tswerk,. and here especially the department of energy application technology, developed a prefabricated house, the so-called low-energy prefabricated house~ for one of the largest prefabricated house manufactures in the Federal Republic of Germany~ Without exaggerating, it can be stated that the heat insulation but also the possibilities of heat recovery and of passive solar energy utilization of this prefabricated house have set new standards (see figure 1)0 J-146 STOY kWh/a Utilized inner heat Utilized solar energy 3130.0 ~!:i!!i!!!!!~!!(j3500 ~!;~:i~\!~!:i:~i }\~:9::::5:::0:::0:<~~t ..... .... ". .... ......... :- - ---. ._ - _ . ••••• - . --. -.-- --. - - --- .-- .. · a-· • • • ~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~ Utilized inner heat Utilized solar energy Heat recovery Required heat for heating Required heat for heating Low energy prefabricated house Conventional massive house Figure 1: Useful energy balance of the low energy prefabricated house as compared with a conventional massive house (same ground plan and same window surface) heat loss of many components of the low-energy prefabricated house ( ) is two and a half times smaller than the standards of the new heat insulation regulations which are legally prescribed in the Federal Repuic of Germany since January. 1, 1984. To sum it up, the author therefore would like to point out that the present energy consumption for heating purposes can be considerably reduced by heat insulation". For example, a broad application of heat insulation in buildings in the Federal Republic of Germany alone would result in annual energy savings which correspond approximately to the estimAted overall add i t ion a 1 energy demand of the next five years& J"'147 STOY HEAT RECOVERY Heat Recovery l.!! Large Buildings A further possibility of saving energy is offered in the case of buildings with forced ventilation where the air is directed through air ducts. Here, the heat content of the exhaust air can be transferred to the fresh air at a central point by recuperative or regenerative heat exchangers or heat pumpse This has the advantage that the various interior heat gains by the lighting, solar radiation, running machines and persons do not get lost for the space heating e So to speak, the building is then heated largely "by itselfll~ This technology was "imported" from the United States to the Federal Republic of Germany in the seventies and has been generally accepted in building construction for administration buildings, hospitals, schools and supermarketse Combined with an improved heat insulation, energy savings up to 75 % as compared to cenvontional techniques could be achieved0 Another system of heat recovery was developed out of the consideration that it is a foolish action to cool the sunny side of an air-conditioned building on many days of the year with electric energy while at the same time the shady side is heated with fuels~ By a system of small heat pumps in form of a cabinet, which are disbuted decentrally in the building and. are supplied via a double-pipe water system, it is possible of directly compensating the heat differences in the building0 So, for example~ the sunny side can be cooled while the withdrawn heat is used for heating the shady side~ Since these systems do not allow a recovery of the heat contained in the vent air, the small heat pump system can be adequately combined th recuperative or regenerative heat exchangers, if a defined air routing via air duct~ is provided0 Only then all of the heat fluxes in the building can be controlled~ Heat Recovery l.!! Indoor Swimmi Is field of application for heat recovery systems are the lie indoor S0 Here, the warm room air reaches a high moisture contents as a result of evaporating pool water0 In order to avoid damages of building and to create conditions, which are comfortable for the user~ the air moisture must therefore be reduced~ In the past, this was done in the case of conventional, mostly oil-fired systems by dischargi the moist and warm room air with six hourly air changes to the open air~ 0e~~ the entire air volume of the swimming-pool was renewed six times hour by hour and then again heated up with fuel oil to the relativehigh room temperature level - regardless whether the swimming-pool was used or not0 This striking wastage of energy was only terminated by the use of heat pumps@ Since the sixties, compact systems for heating and dehumidifying indoor swimming-pools have been used in the Federal Republic of Germany@ These systems cool the warm and moist exhaust air of the swimming-pool and return it as a IIdried" and warm supply air~ J-148 STOY The heat recovered by the condensation of the water vapor largely covers the heat losses of the pool water, the heat losses of the indoor pool and the heat requirement of the fresh air which still must be fed by hygienic reasons, however, meanwhile only during the opening hourso These examples show that the realization of adequate heat recovery systems requires an early cooperation between builder-owner architect, sanitary engineer and experts of the energy supply industrY0 t Heat Recovery ~ Livestock Stables Aside from the already mentioned heat sources ambient air, water and soil, stable air is available in many agricultural enterprises as a useful heat source@ Stable air has the advantage that its temperature is usually between 10 and 20°C, and this also on cold dayse Therefore, it is a very suitable heat source0 In practice, the stable air is to be brought to an optimum of a certain temperature, a certain relative air moisture and without dangerous gas concentrations via a ventilation system~ Since the animals emit depending on their weight - more or less heat, water vapor and pollution gases to the air, it must be constantly renewed by fresh air supplY0 The largest part of the heat is emitted to the ambient temperature which is increased by this (sensible heat) as well as by the conversion of discharged moisture quantity into water vapor (latent heat)~ By the stable ventilation, the excess air moisture is removed from the stable~ Of this ventilation heat, large heat quantities get irretrievably lost~ This is the starting point for a well-aimed utilization of the heat contents of the vent air for recovering useful heat~ If, for example, heat from the stable1s vent air is transferred to the stable's fresh air supply by means of heat exchangers, this results in a heat exchange from one to another medium, provided there is a temperature gradient between these air flows& If is is not the case, the heat can still be recovered and trans. ferred by means of the heat pump~ By heat recovery, the required elecc work for .the ventilation heat demand in winter can be reduced and consi es energy can saved0 Heat in Trade Aside from agriculture, heat recovery has also taken its place in since here, too, the reduction of the specific energy use is an aI prerequisite for an economical operation0 Heat recovery systems are used, for example, in the catering trade where the waste heat from cooling and ventilating systems is utilized@ In bakeries and confectioneries, where the hot water gained from the waste heat of refrigerating systems is used for washing~ Or in butcher's shops where water heating by utilizing waste heat is possible, t000 J-149 STOY In addition, heat pumps (see next chapter) are also used in hairdresser1s shops, especially in those for women. This heat pump allows for an adequate and economical connection between the cooling of the room air on the one hand while utilizing the thus gained heat for water heating on the other hand~ Here t it is an advantage that the heat is produced almost at the same time as the hot water is required. HEAT PUMPS "Cold" Energy Sources When using heat pumps, seldom waste heat but mostly ambient heat, i~e~ the energy contents coming from solar energy in the soil, in ground and surface water and in the outer air, is used. Heat extraction from the soil shows good operational results in practice@ Unfortunately, the use of this heat source is restricted to areas of a low density of development since, due to the unfavorable thermal conductivity of the soil, approximately twice the housing area to be heated must be available as a land area for bringing in the heat exchangersG Restrictions, however, also result from the necessity of installing the heat exchangers at a depth of approximately 1~2 to 1@5 m in order to prevent a freezing in winter0 Ground water represents an ideal heat source, provided it is availab at a developable depth and in sufficient quantity and quality: to tap ground water as a heat source directly at the house and in any quantity, sufficient heat supply at any time, no area limitations as in the case of soil heat pumps, no limitations by outside temperature drops these are ideal circumstances but also very rare ones@ In addition, in practice there were often problems regarding the service life of the supplying Is espacially that of percolation wells0 water is also a ucold energy source" for the use of heat is true that a river is a great heat supplier; the installation pump systems is, however, often handicapped by the regulathe extraction and return of surface water as well as by the tal ture intake and outlet workse surface water are and will therefore remain restrictin areas and locations~ As a heat source in all other cases, lize what is always around us: the ambient air~ It is a natusource - always renewing itself - of solar energy and also of conversions caused by menQ is only medium which, as a solar energy carrier, is always available free of charge, at any quantity and anywhere0 Heat pumps uti lizi . the energy contents of' the outside air could therefore - at first 5i - represent the ideal heating source~ On closer examination, however, thermodynamics turn out to be a handicape The operating value of the heat pump, i@ e0 the relation between supplied heating energy and required dri ng energy, is the more unfavorable the lower the temperature difference between the medium to be heated and the medium to be cooled@ In summer during the transition period, heating can be well done by the heat pump utili ng the outside air0 STOY At an outside temperature of e*g~ 15 °C and a then sufficient heating water temperature of 45 °C, the performance number is approximately 304. However, only approximately half this value is achieved, if the outside temperature is -10 °C and the heating water temperature shall be 55 °c. Therefore, it would be logical to operate the universally employable ambient air heat pump not on very cold days. But who will then take over the heat supply, who will be the "stopgap" for extremely cold days? valent Heat Pump Heating By the end of 1982, 12 million out of approximately 24 million dwellings in the Federal Republic of Germany were still heated with fuel oil, and 9.6 million of these with a central oil heating3 This should answer the question for, if one tries to find a compromise between the existing heating technology and an adequate energy application by indirectly using solar energy, many considerations result in a combination of heat pump and oil heating~ so to speak in a IImarriage of convenience between oil and current This means that this so-called bivalent heating consists of the oil heating, which is operated only on extremely cold days) and the heat pump, which is connected to the heating systems and takes over the heat supply during the transition period~ ll & But what are the advantages of this umarriage of convenience between oil and current U ? The operator of a bivalent heat pump has a system which, on the one hand, can cover the entire heating capacity only with oil and~ on the other hand, can also cover appproximately half the heating capacity by means of the heat pump~ The energy suppliers, i~e0 the power industry and the oil companies, of course have different interests@ The power industry is interested in being able to supply additional heating customers aside from night storage heating thout the necessity for additional special generation and distributing capacities~ Since in the case of bivalent heating the heat pump is disconnectable by the electricity supply company) current is on requi at times where power plant and mains reserves are still avail e~ In to Ie to answer the disputed question as to which heatsystem needs more energy, whi would be reli e, so-called energy balances of the different charts may be used~ In these, the are ill ical can easier compared0 In an example, energy flow chart of the I heating of a single residence will be explained as well as, in comparison, the energy flow chart the valent heat pump heating of the same house (see figures 2 3) @ At rst, the primary energy consumption of the oil heating and of the electric heat pump heating is compared~ Critics state that the heat pump would only shift energy consumption0 On the one hand, it saved fuel oil and, on the other hand, it consumes ~urrent; and for the curre~t producers, so much primary energy is needed that the heat pump in the end requires as much primary energy as would be the case with fuel oil~ Well, what is to be thought of this statement? J-151 STOY =une ~edutCh :-----'2:> :2 If'ft~ 2 Ve!1US1e C@9 O@r S8~ung 16 : ~1)OlMl' 17 ~ng Ra~.und 3 ~1Il1e Figure 1: Energy flow chart oil heating& Figure 2: Energy flow chart bivalent heat pump0 1 8 2 3 4 5 Heat for heating losses by regulation and distribution in the house Boiler losses Secondary energy to purchased Refinery and transport losses 6 oi I 7 neral oi 1 9 10 11 12 13 14 10 Ambient heat Heat for heating Losses by regulation and heat distribution in the house Boiler losses Fuel oil Current Secondary energy to be chased 15 Coal losses during current mission 17 Waste heat during current generating 18 Refinery and transport losses 19 Mineral oil 16 is true, that for the supply of e.g. 33 kWh current to the customer, about 100 kWh primary energy (e.g coal) are required in the power station. When generating steam for the power station turbines, when converting turbine rotation into current, when transporting the current, when converting high voltage into low voltage for the domestic current, in most cases energy in the form of nonusable waste heat gets lost. this is not a result of sloppy work or technical inability but of laws~ J-152 1 STOY For the electric heat pump one has to buy 33 units current - for most of the ambient air heat pumps, however, often 40 units current as a result of faulty planning - for 100 units heate In the case of oil heating, however, 140 to 180 units$ Thus, the relation is approximately 1 : 4! In addition to this, a comparison of energy costs: Each liter of fuel oil has an energy contents of approximately 1.0 kWh~ At the present price of Oe75 OM per liter the cost per kWh is 0.075 OM + VeAoT. In the case of heat pump heating, one has to calculate about 0015 OM per kWh + V.AoT. This means that the energy cost relation between current and oil is approximately 2 : 1. However, as compared to oil heating only about one Quarter of the energy quantity to be purchased is required for heat pump heatinge Thus, the energy costs of the electric heat pump are already today half those of the oil heatingo t With increasing energy prices, this advantage will become even greater in the futureG The reason is that the heat pump extracts about two thirds of the heat produced from the surroundings~ This stored solar heat will remain free of charge also in the future~ Only the current portion, i0e@ 33 to 40 % of the heat supply, will increase in price0 On the contrarYt in the case of oil heating the entire heat supply becomes more expensive in the same relation as the oil price! So~ in many cases the calculation of the heat pump operator has proved ght already today~ It is true that the costs of acquisition are much more higher for heat pumps, but one can save a lot of money each year by lower heating costs~ In additlon, the acquisition costs for heat pumps in exi ng buildings can be written off immediately or during a period of two to five years as maintaining expenses and in the case of new bUildings at 10 %per year for ten years ide from these economical aspects, there are the following overrideconomic aspects: the heat pump operator actively contributes towards a careful use of the energy resources and a reduction of foreign-exchange costs for the purchase of mineral oil~ Heat Pumps for Hot Water Supply cally yen pumps are not only excellently suited for ing operation but also for an energy-saving hot water supplY0 The si energy costs as well as the increasing energy consciousness here, too, ed to the search for possibilities of improving the utilization of energy for hot water supplY0 In the case of conventional hot water supply, energy utilization is uenced by the kind of water heating or storing and by the distribution0 When distributing hot water, energy can be saved by a decentral and thus consumer-close electric hot. water supply~ Regarding "the heating of fuel oil or natural gas can be replaced by devices utilizing regenerative energies or waste heat0 Here, there are two possibilities: solar i STOY collectors in connection with hot water storages and hot water heat pumpso The first possibility is hardly used in the Federal Republic of Germany by climatic reasons and because of the high installation costs; the latter has become a bestseller as to the utilization of regenerative energies during the last few greater discussions~ By the end of 1983, about 110,000 units were installed in different plug-in designs throughout the country~ As to the principle of hot water heat pump, it can be shortly stated that it functions like the heating heat pump@ It extracts energy from its environs, for example~ waste heat at its location (mostly the heating basement), and pumps it by means of current to a higher temperature level0 Depending on the ambient~ temperature, the hot water heat pump together with the corresponding hot water storage achieves operationg values between 1.7 and 208~ Again and again critics state that hot water heat pumps don't produce a gain from environmental energy since they only extract heat from the room of location and those next to it. This statement must be contradicted since the largest part of the heat quantity utilized by the hot water heat pump would be lost heat anyway This means that the use of this heat pump leads directly to the substitution of fuel oil~ & Here, a large energy-saving potential is offered in the Federal Republic of Germany since hot water is heated by the oil heating in still approximately 7 million households@ Regarding the fact that the share of hot water heati is about 10 % of the final energy requirement in an average household in the Federal Republic of Germany, it would be desirable that the oil burners of these households remain out of operation at least in summer and that the water is heated by such heat pumps@ Heati of Industrial Buildi Also in industrial production, the bivalent supply in connection with line-dependent energy sources is gaining more and more importance0 Whereas in the high-temperature sectors - melting, heating, heat treatment - often product quality, emissions or coupled production are in the fore, aspects as waste he~t utilization, improvement of the plantUs efficiency rate or an optimized rate of utilization of energy supply possibilities are the decisive factors in the low-temperature sector~ incorporation of the waste heat as useful heat in the heating system requires a heat pump0 From the technical point of view, three solutions are offered for optimizing the bivalent supply system: 1~ The heat pump is connected to the boiler and thus can reach a supply temperature of 80 °C required also in the case of partial supply@ The cooling water circuit is equipped with a circulation control for raising the outlet temperature§ J-154 STOY 2~ The heat pump operates to an additional heat distribution system, the supply temperature is limited to maX0 60°C, the cooling water control is installed, the operating value of the heat pump increases considerablYa 3~ The heat pump operates only at supply temperatures up to 60°C (heat capacity control via sliding supply temperatures), in the case of higher temperature requirements~ it is bypassed~ The cooling water control is also installed~ The State of Engineering of Devices and Systems of el.e"Cfrfcally drt ven Heat Pumps For the electric heat pumps of the first generation, mainly components from the refrigeration and air conditioning technology were used6 Meanwhile, components were developed which are adapted to modern heat pump operation so that the state of engineering of heat pumps has reached high technical standards@ In addition, it was possible to considerably reduce the manufacturing costs and to increase the gain of environmental heat~ Moreover, the connection technique was simplified and thus the incorporation in already existing central heating systems has become easier~ In addi on, the necessary control equipment was ful integrated in the device in order to achieve a problem-free parallel operation with supplementary heat generators And last but not least) almost maintenance-free components guarantee a 1 probl operation~ 0 to the use of electriC31ly driven heat pumps in single residences state of engineering can be described as follows: Elecor duplexes, cally driven heat pumps are used almost exclusively in hot water central heating systems Here, the service water supply can also be taken the favorab operation costs and the over by the heat pump~ Because of covering the entire heat requirement of the building withpossi Ii out by heat pump alone, at first mainly heat pumps using water as a source were installede However, the limited availability of ground and surface water on the one hand, and the increasing number of ties on the other hand have led to the lations by the water heat source water is more and more replaced by the alway avail source the of r-water heat pumps is more all 0 Devel Trends single residences and duplexes as well as for smaller apartment with a heat requirement of up to approximately 50 kW, today mainly compact c heat pumps operating in different ways are used which are produced in series~ heat requirement range between 50 and approximately 400 kW, i@c0-engine-driven heat pumps are available0 Here, single and °mul p ce systems are offered which supply, for example, larger apartment houses or commercial buildings (e@g~ hotels)~ There are also application possibilities in the public sector (e~g~ in swimming-pools, schools, gymnasiums and administration buildings)& 11- STOY In large buildings with a heat requirement of more than 300 to 400 kW, the heat pump systems consisting of standard components are installed directly in the building. This method is applied in large apartment blocks and large objects of the public and industrial sector (e.ge in sports centers, hospitals, slaughterhouses, universities and recreation centers.) Regarding the electric heat pumps for single residences and.duplexes, a trend towards plug-in devices of a low capacity (3 t 4 kW heat capacity) can be observed, in order to reduce the absolute investment costs of the system~ The installation expenditure is simplified by the development of components which are harmonized by the manufacturer (boiler/heat pump)~ At the site, these prefabricated components can then be connected qUickly and at low costs& In the Federal Republic of Germany, there are also efforts to create a market for the so-called ventilation heat pump which utilizes the vent air from ventilation systems in housing areas as a heat sourceo Here~ also the compact small heat pumps are included which can be used decentrally and independent of the heating system for heating and ventilation individual rooms~ The further development heat pumps of a lower capacity main aims at simpli ing and cheapening the peripheral system components (e~g~ installation~ l)~ on ses why it was the electric engineering industry which this especial the oil sis in October 1 and application of heat pumps so forcefully? Was it the on wi other energy sources as a result of the fact that heat ire considerably less energy for generation heat than convening systems? Was is perhaps a concealed current sales promoutilizing the popular solar energy? n_~~~n'~n~ Or was it a sense of responsibility for power economy? All of these ions are more or less correct0 When looking into the future, however, regardi the regenerative energy sources as that what they will ~ namely the greatest alternative energy low-temperature heat, then becomes c Since in the Federal Rereal reason lic ~ entire energy demand ist required for low-temn households, public buildings, agriculture and industry, this half again more than half is covered by imported fuel oil, ion an alternative energy arises automatically~ And this is ar energy, i0 e~ ambient heat combined with electricitYe The ion of this energy source, with electricity as a supplementary can substitute large quantities of fuel oil~ In other words: with sun litte current, a lot of oil can be saved~
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