Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention concerns the design and t:he operation of hea-t-
ing installations, particularly hea-ting ins-tallations for
residences, and per-tains especially to the recovery of the
hea-t contained in -the flue gases of the heating furnace of
such heating installa-tions.
In -the conventional heating ins-tallations for dwellings
which are fired with oil or gas, during the normal heating
period up to 20% of the energy used escapes into the atmos-
phere with the flue gases. During the transitional periods
lo in the spring and fall, when such heating is not fully car-
ried out, because the heat requirement in the building is
lower, the efficiency is even fur-ther diminished.
It is a known prac-tice -to recover -to a greater or lesser
degree the heat contained in the flue gases. In addition
to the regenera-tive heat recovery which is used especially
in indus-trial furnaces, so-called recuperators are also
known in which the flue heat heats the air of combus-tion of
the furnace by means of heat exchange. Since the flue gas
contains harmful subs-tances in considerable amounts, es-
pecially sulfur compounds, the cooling of the flue gas is
problematic, because it can lead to the precipitation of
the harmful substances in the chimney and hereby to the
destruction of the chimney. The situation resulting from
the above-mentioned causes is especially unfavorable when
~5 only relatively small amounts of hea-t are required for the
heating of the building.
The main problem, then, of the invention is to better uti-
lize the fuel energy used, by means of the recovery of the
heat from the furnace flue gas, without endangering the
30 existence of the heating equipment and/or giving off noxious
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substances to a critical extent to the atmosphere.
According to one aspect of the inven~ion there is
provided metho~ for the recovery of heat from tile flue
gas of a furnace, especially of an oil or gas ~urnace,
as well as Eor tt~e puri~ication of these gases, with a
heating circuit connected with ~he ~urnace, charac~erized
by the fact that the Elue gases of the furnace are led to
the outside of the evaporator of a heat pump circulating a
refrigerant, cooled down in this to below the condensation
point of all noxious substances contained in the 1ue gas
and then given off into the atmosphere; and that the heat
absorbed by the eva~orator is given off directly into the
heating circuit via the heat pump condenser which is in a
heat exchange relationship with the heating circuit.
According to another aspect of the invention there is
provided heating installation with a heating circuit an~
a furnace located in it, which has an exhaust gas flue,
characterized by the fact that in the exhaust gas flue
the evaporator of a refrigerant-circulating heat pump
is installed for heat exchange, whose condenser is in a
heat exchange relationship with the heating circuit.
Thus the invention, at least in its preferred forms,
solves the problem referred to above in that the furnace
flue gases act upon the evaporator of a rerigerant-
circulating heat pump, located in the exhaust flue, so
that the flue gas heat is absorbed by the refrigerant
through heat exchange, with the flue gases being cooled
off essentially below the condensation point of all
noxious substances contained therein and therefore able
to be given off directly into the atmosphere. The heat
absorbed in the evaporator from the refrigerant is brought
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in the usual manner in heat pumps with the help of a com-
pessor to a higher temperature level and fed by renewed
heat exchange clirectly ,into the heating circuit of the
heating installation.
Throu~h this new application of a heat pump several
advantages are ohtained: The Elue gas is cooled oEf at
the heat pump evaporator to the point--as is obvious--
where the noxious substances carried along in the flue gas
are precipitated in a controlled manner and can be led
off. The remaining cooled gas is purified to the extent
that it no longer requires a c'nimney in the real sense
of the word. The heat energy obtained from the flue gas
can--as a result of the temperature increase through the
heat pump principle--be introduced directly into the
heating circuit.
Furthermore, the heat pump used Eor the flue gas heat
recovery can be used during the time when the heating
circuit has only a relatively low heating demand (transi-
tion period, cool days, etc.) as the sole heat source by
introducing the ambient outside air directly into the flue
and past the evaporator. In this operational state of the
heating installation based on the invention, the heat pump
works in the fashion of an ordinary heat pump.
A combination of these two operational states of
the heat pump makes it possible, according to a further
development
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of -t}-le inven-tion, -to rnix air into -the flue gas from the
furnace before the lat-ter is conduc-ted to the evapora-tor.
In this way, on the one hand, the high through~pu-t -that a
heat pump working in even pure air operation requires is
5 obtained, and on -the other, overhea-ting of the qvaporator
is avoided.
This me-thod of opera-tion can be developed further by re--
introducing, instead of fresh ou-tside air, -the cooled ex-
haust air which collects behind -the blower which forces
the necessary flue gas/air current -through -the evapora-tor.
This has the additional advan-tage tha-t -the condensation
poin-t drop tha-t occurs with fresh air admixing does no-t
take place and only a tempera-ture drop occurs.
Finally, the use of a heat pump as prescribed by the inven-
5 tion is especially advantageous because it makes possible
an especially simple basic control of the heating instal-
lation. Because the pressure ~and in like manner the tem-
perature) is a reliable indicator of -the s-ta-te of the re-
frigerant in -the heat pump and thus also of -the -temperature
~O in the evapor~-tor on the one hand, and of -the heat con-
veyance effected by the heat pump, on the o-ther, a simple
control device is sufficient, which, in dependence on the
pressllre or -the tempera-ture of -the refrigeran-t in the eva-
poratorregulates the opera-tion of -the furnace and the
25 blower in such a way that with continuous blowing and heat
exchange be-tween outside air and refrigerant the furnace
is turned on only when a predetermined lower limit value of
the pressure or of the temperature is exceeded, but that
the furnace is turned off when a predeterrnined upper limit
30 value of the pressure or of the temperature is exceeded.
On -the basis of the invention, this arrangement can be de-
veloped into a system with polyvalen-t heat utiliza-tion,
firs-t of all because additional heat energy sources can be
in-tegrated directly or indirectly in-to the heating circuit
35 in such a way tha-t without any greater control measures a
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"logical regulation" resu:L-ts from any given temperature
drop an~ new primary energy (wi-th the help of the furnace
burner) is used only when o-ther supplementary energies are
no-t sufficiently available.
S In par-ticular, a solar hea-t device is provided, which (to
the exten-t -that solar heat energy collects) warms up the
return of -the heating circui-t before it en-ters -the con-
denser and there absorbes -the heat of the refrigeran-t.
Only -then does the re-turn reach -the boiler, which, however, .
goes into opera-tion only when -the return temperature is be-
low the required forward flow -temperature. An advan-tageous
secondary effect of this arrangement lies in the fact -tha-t
the boiler is kept warm and no corrosion damage occurs as
a result of non-operation.
But more important than -this utilization of energy supplied
by a solar-heat device is the direct hea-ting of normal sup-
ply water ~ho-t wa-ter). If -the solar heat vehicle has an
adequate temperature, -then firs-t of all -the normal wa-ter
supply is heated and only if either enough solar heat is
available or the waterls temperature level is too low is
-the above-described heating of the hea-ting circuit return
undertaken.
If the solar heat is at a still lower temperature level,
so that it cannot be made available for either the normal
2S wa-ter supply heating or the return pre-heating, then its
u-tilization is provided through pre-heating of the air
which is fed either as fresh air or as returned cooled
flue gas/air mixture to the heat pump evaporator. Instead
of fresh air (or return air), the heated exhaust air of
3~ an air conditioner can also be used, which receives cold
fresh air through heat exchange wi-th at least a part of
the cold exhaust air leaving the heat pump evaporator (or
of the escaping cold flue gas/air mixture).
In a similar manner, the hea-t energy contained in the ex-
3S haust air from warm or heated areas, such as, e.g., swim-
ming pools or the like, can be made useful by mixing this
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clir directly wi-th -the air elowing -through -Lhe hea-t pump
evaporator (OI' with -the ~lue gas/air mix-l,ure).
On t:he o-ther hand, -the utilization of the hea-t energy
obtained can be :improved by having the peak hea-ting o~
5 -the normal wa-ter supply -take place in a heat exchanger
which on -the primary side has -the highly-heated re~rige-
rant of -the heat pump circui-t coming :~'rom the heat pu~p
compressor flowing -through it. Since here the re~rigeran-t
is cooled down from7 e.g., ~5C -to 80C and the required
peak heat -transferred to the normal water supply~ there
results at -the same tIme an improvement in the econom~ o~
the hea-t pump which is all the greater 7 -the lower the re~
frigerant condensa-tion -tempera-ture.
In order to take into consideration the di~erent condl~
t~ tions under summer and winter operation within the frame-
work of this arrangement, a cross oonnection can be pro~
vided between the normal water supply return and the heat~
ing circuit return, as well as a cross connec-tion in the
forward flow in such a way tha-t in -the summer OperatIon
2~ wi-th the heat shut o~ the hea-t exchangers serylng o-ther~
wise for the prehea-ting of the heating circuit return are
available to the normal water supply cirCuit~ Here all that
is needed, in addition to a thermostatically controlled
valve in the forward ~low cross connectl`on is two check
~5 valves, namely in -the return cross connection and between
this and the heating circult circulating pump, because the
la-tter is considerably stronger than the no~mal water su~-
ply circulatlon pumpO lf the heating ci~rcui-t pump turns
on, it opens with its pressure the check ~alve loca-ted be~ -
30 tween it and the cross C~nnectiQn and close$ the check
valye located in -the cross connec-tion, even when the ~
weaker--normal water supply pump opposes it, ~s SOQn~ how-
ever, as the heating circuit circula-tion pump shuts o~f,
the normal water supply pump can open the check yalye in
-the cross connection~ whereupon it simultaneously closes
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the other check valve and prevents -the incorpora-tion of
the rest of the heating circui-t into -the normal water
supply circuit.
A Eurther source of help for heat energy is the waste
water. According to a further developmen-t of the inven-
-tion, a branch is provided in -the heat pump circuit which
leads Wit}l i-ts own expansion valve to an evaporator
which is ins-talled in a was-te water reservoir and is in a
heat exchange rela-tionship with the waste wa-ter. Instead
of waste water, any other water (or any o-ther available
fluid) of appropria-te tempera-ture can be used.
A further u-ti]ization possibility of recovered heat energy
can be found in -the fact -that in the re-turn flow of the
refrigerant to the expansion valve and evaporator there is
15 located a heat exchanger by means of which the heat con-
tained in the still warm refrigerant condensate can be re-
leased to -the ambient air or---using a blower--for heating
the air. Such a utilization of the residual heat in the
refrigerant is more advantageous than a countercurrent heat
2~ exchange with the cold refrigerant flowing from -the eva-
porator to -the compressor~ because this leads to an in-
crease in -the compressor -tempera-ture.
This withdrawal of heat from -the heat pump circuit can also
be used in the summer, when the heat pump runs only for the
25 operation of an air conditioner (because normal water has
already been sufficien-tly heated), to carry off the heat
of condensation.
In order to prevent any heat being carried out of the
building via the heating circuit, it is advantageous -to
3~ provide a heat pump control in the heating circui-t in such
a way that the pump is shut off when the pressure or the
temperature in the condenser of the heat pump circuit goes
below a cer-tain value. If pressure or temperat~re again
go above this value, -the heat pump is again switched on.
3~ The drawings illustrate the invention on -the basis of the
embodiments.
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Fig. 1 shows a flue gas heat recovery ins-tallation
of a very simple -type in schematic represen-
ta-tion.
Fig. 2 shows likewise a schematic represen-tation of
the structure oE a compact apparatus with es-
sentially -the same characteris-tics, but with
an addi-tional control device.
~ig. 3 shows a representa-tion co-rresponding -to Fig. 2
of a an appara-tus equipped with further devices
~ for polyvalent hea-t utilization.
Fig. ~ shows a sh~meatic circuit diagram of
the installation shown in Fig. 3 for a better
clarification of the mode of operation.
Fig. 1 shows a boiler 1 with its furnace, which is not re-
t5 presented in detail. The heat-carrying vehicle heated in
-the boiler 1, usually water~ flows through the heating cir-
cuit 2, in which several radiators 3 are ineorporated;in
this case only 1 radiator is represented. A circulation
pump 4 provides for -the forced circulation of the heat ve-
2~ hicle.
The flue gases from the furnace escape into -the open air
vi,a the flue 6. Of the building in which the furnace is
installed, only the roof 7 is indicated.
An adjustable damper 8 in the exhaust flue 6 makes it pos-
25 sible to léad the flue gas into a branch 9 through the eva~porator 12 of a hea-t pump 13 described below, as well as a
further branch 10 back into the exhaust flue 6. Through
the connection 19, in which there is an adjusting damper
21, ambient air can be led in-to the branch 9 and mixed with
3~ the flue gas flowing,to the evaporator 12. A blower 22 is
in the branch 10 to provide the necessary flow of the'flue
gas or flue gas/air mixture,
It is advantageous if the speed of -the blower is adjustable
so that when air only is being blown it provides, e.g,~ 10
3~ times more -through-put than when flue gas/air is being
blown; further, a return line 29 branching off in back of
the blower 22 can be proYided in the connection 19 for cold
air ~or cold air/flue gas mix-ture); the adjustable damper 21
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is so designed and arrallged -that i-t opens either -the fresh
air or the cold air supply.
In addition to the evapora-tor 12, the heat purnp 13 also has
a compressor lL~, a condenser 15 and an expansion valve 16.
5 With their piping~ these componen-ts cons-ti-tute a secondary
circuit which is filled with a refrigerant that is circula-ted
by the compressor.
The refrigerant hea-ted in the evapora-tor 12 flows through the
piping 17 into the compressor 14. With the compression of
the refrigerant the tempera-ture rises sharply. In the con-
denser 15, which is in a heat exchange relationship with the
heat in circuit 2, the heat of the refrigerant is extensively
given off to the heat carrying medium being circulated in
the heating circuit 2. Upon the expansion of the refrigerant
1~ in the expansion valve 16, it cools off greatly so that the
refrigerant is ready -to absorb heat again. Generally the
temperatures in the evaporator are from o to +5C, in the
condenser, from 80 -to 90~.
The numeral 25 indicates a valve arrangement by means of
~o which a short circuit connection 26 of forward flow and re-
turn flow of the heating circuit 2 can be made when the heat-
ing of -the hea-ting circuit 2 is done only by such heat as
the heat pump 13 extracts ~rom the ambient air drawn in
through the connection 19 by the blower 22.
a 5 Fig. 2 shows--though only schematically--the design of a
hea-ting installa-tion with the features seen in Fig. 1. Like
par-ts bear like reference numerals and require no re-expla-
nation here. Deviations and additions are described below.
In the heating circuit 2 the forward flow is indicated by
3~ 5' and -the return flow by 5 " ; the dashed line 30 indicates
what belongs to a heating installation of simple design based
on the invention and can be set up as a compact unit in the
place of utilization.
At -the boiler 1 is shown the burner 38, which is under the
35 control of the control device 37; by way of an ins-trument lead
36 the pressure in hea-t pump 13 evaporator~ is measured,
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and wherl a predeterln;rled Ininimum pressure is passed the
control device 37 turns on the burner 38 via the indicator
lead 36'. Instead of -the pressure of the refrigerant in
the evaporator, i-ts -tempera-ture can also be used for the
S control of -the burner 38.
A base irame 33 res-ting on the floor 3L~ carries the boiler
1 as well as---par-tially by way of uprigh-ts 32 for an upper
frame 31--all other components of the heating ins-talla-tion.
The evapora-tor 12 of the heat pump 13 is suppor-ted on the
IV top frame 31. Underneath i-t is a drip pan 23 tha-t catches
the water of condensation and condensed noxious substances.
The exhaus-t fl~e is reduced -to an exhaus-t stack 6'. But
the exhaust flue con-tinues on in a connecting pipe 11 which
surrounds the exhaust flue stack 6' with an enlarged cross
sec-tion 11' in such a way that ambient air can enter the
connecting pipe as indicated by the arrows 18 and there-
~if the burner 38 is in operation--mix with the flue gas.
The air (or -the flue gas/air mixture) propelled by the
blower 22 leaves the building through the exhaus-t s-tack 2
in -the building wall 25, There is no need for a chimney 7
since -the escaping gas has been cooled off and cleaned up.
The hea-ting installation shown in Fig. 3 is, compared -to
that of Fig. 2, enlarged by numerous supplementary devices
for the purpose of polyvalent heat u-tilization. Again,
~5 like parts are designated with the same reference numerals
as in the preceding figures. This applies also to ~ig. 4,
which clarifies in terms of the circuitdiagram the design
of the heating installa-tion represen-ted in Fig, 3,
The blower 22 installed in the exhaust stack 2~ draws
3~ here, too 7 either air as per the arrows 18 or air and also
flue gas as per the arrows 18~ in the connecting flue ll and
through the evaporator 12 of the heat pump. In addition, an
inle-t 56 is provided, -through which ~the warm outside air
(e.g., ~rom a swimming pool) can be introduced. At the in-
3~ le-t for the ambient air a heat exchanger is provided which
is acted upon on the primary side via a llne 59 by a heat
carrying medium heated by solar energy (not shown in further
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de~ail here~. The air entering as indicated by -the ar-
rows 18 can -thus be prehea-ted. Further, a connecting pipe
(not shown here~ can lead from the exhaust stack 24 to the
inlet connection with the hea-t exchanger 48, so that the
cooled exhaust air is led back in-to the connecting pipe
11. The exhaust air escaping from the exhaust stack 24 as
per the arrows 24' can be further used for the air condi-
tioning (cooling) of rooms if necessary, in hea-t exchange
with fresh air. The air path represen-ted on -the left in
Fig. 4 illustrates this, with the heat exchanger 67 and
the air path 68 of an air conditioner.
By means of a swi-tching device 60 the heat exchanger 48
is activated only when a solar heat of low temperature is
available. In general, the solar heat is led direct:Ly to
the normal water supply (hot wa-ter~; this is not shown in
Fig. 3, but is indicated in Fig. 4. If there is sufficient
solar heat, or if this is not suitable for normal water
supply heating~ then the heat carrying medium in question
is conducted via -the line 41 to a hea-t exchanger 40 which
is acted on secondarily by the re-turn flow 5~ of the heat-
ing circui-t 2. The latter -then enters the heat pump conden-
ser 15 and leaves it at its connection with a hea-t exchanger
42 that is likewise located in the hea-t pump circuit and
which conducts normal supply water via the line 43 on the
secondary side.
The refrigerant circulated by the compressor 14 in the heat
pump circuit flows, after leaving the compressor 15, into
a collector 28, and from this into a heat exchanger 44,
which by means of a blower 46 heats the ambient air or--
3~ by means of a conduit that is not shown--the air in another
space. Before reaching the expansion valve 16 a branching
51 is provided which leads via an expansion valve 16' to an
eva~orator 12' shown only in Fig, 4 t The return circuit
bears -the reference numeral 52.
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The CirCUlatiOIl pUlllp 55 in -the hea-ting circuit 2 is con--
trolled by a pressure sw:i-tch 57 which measures the pres-
sure (or the tempera-ture) in the condenser 15 and turns
off -the circulation pump 55 when a minimum pressure in
5 the condenser lS is exceeded.
Fig. 4 supplemen-ts -the representation in Fig. 3 somewhat
further. Thus a line 41~ is provided which ex-tends -the
line 41 from the solar device 61 to a heat exchanger 62 9
which serves for the basic hea-ting of the normal wa-ter
supply. Furthermore, the circula-tion pump 63 for the
circulation of -the hea-t carrying medium -that heats the
normal water supply is marked. On the pressure side the
circulation pumps 63 and 65 are connected by a line 64.
In the line 64 there is a check valve 65, and an additional
check valYe 66 is located between circulation pump SS (in
the heating circuit 2) and the point where the line 64
branches off. The function of -the cross connection wi-th
the line 64 and the check valves 65, 66 has already been
explained above. The cross connection of the forward
~O flows consists of a line 69 with a valve 70, which is
opened by a thermoplastically controlled priority swi-tch
when the normal wa-ter supply requires heat.
In the case of-failure of the burner 38, the whole instal-
lation, above all the heat pump, is shut off by means of
an electrical in-terlocking switch.
