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@
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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
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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&
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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~
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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
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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?
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=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~
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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§
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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-
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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~