Note: Descriptions are shown in the official language in which they were submitted.
' CA 02240~2~ 1998-06-12
17~35PC I .PO I
A HEAT E~G~3,NGER DEVICE FOR AN AIR CONDITIONI ~G SYSTEM
The present invention relates to a heat e.~changer device ~or
an air conditioning system, especially ~or conditioninc ~'~e
air in cabins o~ cars or other vehicles.
Air conditioning systems ~or cars comprising thermoelectric
cooling units are disclosed in US Patent Mo. 3.236.056 and in
the published Swedish Patent Application No. ~70d395. The air
conditioning systems disclosed in these documents comprise
one or more thermoelectric units which are sandwiched ketw2en
straight wate~ conduits having a rectangula~ c~oss-section
and ~orming part cf heat transfer circuits.
The known air conditioning systems have a relatively small
coolins capacity and this may be the reason why the documents
are sil~nt about the source o~ the electric energy which has
to be supplied to the thermoelectric units o~ the system.
This energy source is apparently supposed to be the standard
battery and electricity supply system already available in an
existing standard car in which the air conditioning sys~em is
to be installeâ.
The object of the present invention is to provide a hea,
exchanger device ~or an air conditioning system cf the a ove
type by means cf which the capacity and/or e~iciency of the
air conditioning system may be substantially increased.
The heat exchanger device according to the present inventicn
comprises ~irst and second heat exchanger elements de~ining
separate ~irst and second ~low passages therein lor heat
transporting medium, and a thermoelectric unit, such as a so-
called Peltier element, arranged between and having opposite
heating and cooling sur~aces in heat conductive contact with
the ~irst and second he~t exchanger element, respectively,
and the heat exchanger device according to the invention is
characterised in that a plurality o~ thermoelectric units
arranged in side-by-side relationship are sandwiched between
A~E~IOEo 9HEET
b CA 02240525 1998-06-12
- L7~3~PCI.POI
] 1~1
the heat exchanger elements, and in that each hea, e~changer :=
element de~ines a tortuous fiow passage therein hav~ng a
length being several
,4M~ND~D S~EET
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WO 97/22486 PCT/DK96/00~;31
times the maximum dimension of the heat exchanger element or
a plurality of coextending separate flow passages each having
a small cross-sectional area.
The heat exchanger device according to the invention may
secure an efficient cooling of the warm sides of the
thermoelectric units and an efficient heating of the cold
sides of these units, whereby the overall thermal efficiency
of the air conditioning system may be increased. Furthermore,
the capacity of the air conditioning system may be adapted to
that desired by using a suitable number of thermoelectric
units and by dimensioning the heat exchanger device corre-
spondingly.
The flow passages formed in any of the heat exchanger
elements may comprise two or more tortuous coextending flow
15 passages or a plurality of substantially straight flow pas-
sages extending in the longit~ n~ l direction of the heat
exchanger. As an example, each heat exchanger element may
define one or a few separate tortuous flow passages covering
substantially the area contacting the thermoelectric units,
2 0 or a plurality of separate adjacent flow passages extending
in the longitudinal direction of the heat exchanger element.
In order to obtain substantially the same effect, the total
cross-sectional area or areas of the flow passage or passages
should be substantially the same in either case.
25 The thermoelectric units may, for example, be of the type
marketed by Marlow Industries Inc., such as Model SP1996.
In principle, the heat exchanger device may have any suitable
shape allowing the selected number of thermoelectric units to
become sandwiched between the heat exchanger elements. In the
preferred embodiment, however, the heat exchanger element has
a flat, block-like shape, so as to allow a m~; mllm number of
thermoelectric units to be included in the heat exchanger
device in relation to the total volume of this device.
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WO 97/22486 PCT/DK96/00531
The heat exchanger elements may have any suitable shape in
plan view. However, each heat exchanger element is pre~erably
elongated and may, for example, be rectangular. It has been
found that the e~iciency o~ the heat exchanger is improved
when the maximum longitudinal dimension o~ each element and,
consequently, of the heat exchanger device substantially
exceeds the maximum transverse dimension o~ the element or
device. Thus, the length or longitudinal dimension may be
about twice the transverse dimension or width, or more.
The best e~iciency or coe~ficient of per~ormance o~ the heat
exchanger device is obtained when the cross-sectional area o~
the flow passage or passages (when each heat exchanger
element de~ines two or more separate, coextending pas6ages)
and the area o~ the element contacting the thermoelectric
units or Peltier elements is between 0.4 x 10-3 and 0.2 and
pre~erably between 1 x 10-3 and 40 x 10-3. In the presently
prei~erred embodiment the said ratio is between 2.5 x 10-3 and
7.5 x 10-3.
The tortuous ~low passage may/, for example, be made in a
block-shaped metal sample by drilling and by plugging some o~
the open ends o~ the passages drilled. Pre~erably, however,
the ~low passage in at least one o~ said ~irst and second
heat exchanger elements is a channel or groove ~ormed in a
side sur~ace of the element. The side sur~ace in which the
channel or groove is ~ormed may then be covered or closed in
any suitable manner, for example by a ~ilm or a ~oil, so as
to ~orm the tortuous ~low passage. Straight ~low passages may
be made in the same way or by extrusion o~ the heat exchanger
element.
In a pre~erred embodiment the ~irst as well as the second
~low passage are channels or grooves ~ormed in opposite,
adjacent side sur~aces o~ the ~irst and second heat exchanger
elements. The channel or groove in each heat exchanger
element may then be covered by a cover plate or foil sealed
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to the element at least along the contour o~ the element. The
plate-like thermoelectric unit or Peltier element may then be
arranged between the cover plates of the first and second
heat exchanger elements, ~or example by means of thermo con-
ductive paste or adhesive. Alternatively or additionally, theheat exchanger elements may be clamped together by releasable
mechanical clamping means, such as screws or bolts, whereby
an optimum specific contact pressure between the heat
exchanger elements and the thermoelectric units sandwiched
therebetween may be adjusted.
The tortuous flow passages de~ined in the heat exchanger
elements may have any desired shape securing a good heat
transfer between the heat transporting medium, usually water
or an aqueous liquid, flowing through the flow passages and
the ad~acent side surfaces of the thermoelectric units.
However, preferably at least one of the ~irst and second ~low
passages defines one or more m~An~e~-shaped patterns which
have been ~ound to be especially efficient.
Each o~ the flow passages defined by the heat exchanger
elements has an inlet and an outlet which may be located at
any suitable position o~ the element. Pre~erably, each o~ the
heat exchanger elements has the inlet as well as the outlet
arranged at the same end. Thus, the first heat exchanger
element may have its inlet and outlet positioned at one end
while the ~irst element may have its inlet and outlet posi-
tioned at the opposite end of the heat exchanger device. In
such case each of the circuits of the air conditioning system
for heat transporting medium has to be connected to only one
end of the heat exchanger device.
Each of the heat exchanger elements may have a substantially
rectangular outline, and the flow passage defined in each
element may then comprise a transversely extending meander-
shaped flow passage section at each end of the heat exchanger
element interconnected by a longitudinally extending m~n~er-
CA 02240~2~ 1998-06-12
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shaped flow passage section. This flow passage pattern has
proved to be especially efficient.
The heat exchanger device according to the invention may be
given any desired size and shape so that any desired number
of thermoelectric units or Peltier elements may be sandwiched
between the heat ~ch~nger elements. Conse~uently, any
desired cooling capacity of an air conditioning system inclu-
ding the heat exchanger may be obtained.
When the heat exchanger device comprises a plurality of
thermoelectric units or Peltier elements these thermoelectric
units are preferably divided into a number of groups, the
thermoelectric units of each group being electrically con-
nected in series and the groups of thermoelectrlc units being
mutually electrically connected in parallel. This arrangement
has the advantage that in case a thermoelectric unit belong-
ing to one of the groups breaks down only that group to which
it belongs becomes ine~ficient.
Even though the thermal efficiency of an air conditioning
system including the heat ~rh~nger device according to the
invention is rather high, the standard electrical supply
system in a standard car is usually not sufficient to supply
electric energy also to the thermoelectric units of the heat
exchanger device in cases where a good cooling capacity is
required. Therefore, electric energy may be supplied to the
thermoelectric units of the heat exchanger device from a
separate electric supply system including a current generator
driven by the engine of the vehicle being air conditioned.
In order to obtain maximum performance of the thermoelectric
units the heat transporting capacity of the ~1uid flowing in
the flow passage adjacent to the warm sides of the
thermoelectric units should substantially exceed the heat
transporting capacity of the medium flowing in the flow
passage adjacent to the cold side of the thermoelectric
units. This may, for example, be obtained by a heat exchanger
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device being formed by three superposed heat exchanger
elements, the flow passages formed in the outer elements
being interconnected. Thermoelectric units may then be
arranged between the inner heat exchanger element and any of
the outer elements so that the warm sides of the thermoelect-
ric units are in contact with the outer elements while the
cold sides are in contact with the inner heat ~xch~nger
element. In the preferred embodiment, however, the heat
~h~nger device comprises only a pair of heat exchanger
elements, and the length of the flow passage adjacent to the
warm sides of the thermoelectric units may then be longer
than that of the other flow pas~age adjacent to the cold side
of the thermoelectric units.
The heat exchanger elements should be made from a material
with good heat conductive characteristics. Thus, the first
and second heat exchanger elements are pre~erably made ~rom
aluminum, copper and/or from alloys thereo~.
The present invention further provides a system for condi-
tioning air in a room, such as a cabin of a vehicle, such
system comprising a heat exchanger device according to the
invention as described above, the first and second passages
of the heat exchanger device being included into first and
second closed liquid circuits, respectively, each liquid
circuit including a radiator and means for circulating liquid
therethrough. One of these radiators may be arranged inside
and one being arranged outside the room in which the air is
to be conditioned. When the air conditioning system is used
for conditioning the air of a vehicle cabin, one of the
liquid circuits may include part of the liquid cooling system
of a combustion engine for driving the vehicle. The radiator
in the cabin may then selectively be provided with hot water
from the driving engine or with cold water from the heat
exchanger device.
The invention will now be further described with reference to
the drawings, wherein
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Fig. 1 diagrammatically illustrates an air conditioning
system according to the invention for use in a car,
Fig. 2 is a top plan view of a heat exchanger device shown in
an enlarged scale,
Fig. 3 is a longitll~in~l sectional view along the line III-
III shown in Fig. 2,
Fig. 4 i6 a transverse sectional view along the line IV-IV in
Fig. 2,
Figs. 5 and 6 are plan views showing liquid passages ~ormed
in elements o~ the heat exchanger device shown in Figs. 2-4,
and
Fig. 7 diagrammatically illustrates a modi~ied embodiment o~
the system shown in Fig. 1.
Fig. 1 diagrammatically illustrates an air conditioning
system which has been installed in a standard automobile
having a driving combustion engine 10. The engine 10 drives
an extra current generator 11 which is supplying current to
an el~ct~ic circuit 12 which comprises an on-o~ switch 13, a
pair o~ relays 14, a pair o~ fuses 15, and an ignition lock
16. The cabin heating system o~ the automobile or car com-
prises a closed cooling water circuit 17 including the cool-
ing jacket o~ the engine 10 and a radiator 18, which is
arranged within the cabin o~ the car and which is associated
with a blower or ~an 19. The air within the car cabin may be
heated in a conventional manner by controlling the ~an 19 and
the ~low o~ hot cooling water circulating through the radi-
ator 18.
A second water circuit 20 ~or cooled water including a water
pump 21 and a solenoid valve 22 is connected to part o~ the
water circuit 17 so as to include the cabin radiator 18. The
second water circuit 20 also includes a cold ~low passage o~
a heat ~ch~nger device 23 illustrated i~ Figs. 2-6 and
~urther described below.
The air conditioning system shown in Fig. 1 ~urther comprises
a third closed liquid circuit 24 comprising a hot ~low pas-
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sage o~ the heat exchanger device 23, a circulating pump 25,
a radiator 26 arranged outside the car cabin and having an
associated blower or ~an 27, and a liquid expansion tank 28.
The cabin radiator 18 may be disconnected ~rom the water
jacket o~ the engine lO by means o~ solenoid valves 29.
The heat exchanger device 23 will now be described in more
detail. The device 23 comprises a pair o~ plate-like elements
30 and 31 made ~rom metal, such as aluminum. A tortuous
channel or groove 32 and 33, respectively, is formed in a
side sur~ace o~ each o~ the elements 30 and 31. The channel
32 ~ormed in the element 30 comprises a me~n~ shaped chan-
nel section 34 arranged at one end o~ the substantially
rectangular element 30, a corresponding meander-shaped chan-
nel section 35 arranged at the opposite end o~ the element,
15 and an interconnecting, longitudinally extending, meander-
shaped channel section 36. The end channel section 35 is
connected to a li~uid inlet 37, and the end channel section
34 is connected to a liquid outlet 38 via a longitudinally
extending straight ch~nn~l segment 39. Through holes 40 are
positioned along the periphery o~ the element 30 and through
holes 41 are positioned along the central line o~ the
element. A circum~erential groove 42 ~or receiving a sealing
ring or gasket is ~ormed outside the ch~nn~l sections 34-36
and 39.
25 Apart ~rom the ~act that the total length o~ the channel 33
in the plate-like element 31 is substantially greater than
the total length o~ the channel 32 in the element 30, the
elements 30 and 31 are alike. There~ore, the re~erence
numerals used in Fig. 6 are the same as those o~ Fig. 5.
30 However, in Fig. 6 a mark has been added to the re~erence
numerals.
The channels or grooves 32 and 33 in each of the plate-like
elements 30 and 31, respectively are covered by a thin, heat
conductive cover plate 43 and 44, respectively, and each of
35 the cover plates are in sealing engagement with a gasket or a
CA 02240~2~ l998-06-l2
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sealing ring positioned in the gasket grooves 42 and 42 ',
respectively. As shown in Figs. 3 and 4 an arrangement of a
plurality of plate-like Peltier elements 45 are sandwiched
between the cover plates 43 and 44 sO as to cover substan-
5 tially the total area inside the gasket groove 42. Theelements 30 and 31 with their cover plates 43 and 44 and with
the Peltier elements 45 arranged therebetween are clamped
together by means of bolts 46 or similar releasable fastening
means extending through the aligned holes or bores 40, 40'
and 41, 41~.
The Peltier elements are preferably of the type marketed by
Marlow Industries Inc., Model SP1996. The heat exchanger
device may, for example include twelve Peltier elements which
may be divided into six groups each including a pair of
15 elements connected in series. Each of the six groups of
Peltier elements may be connected mutually in parallel into
the current supply circuit 12 sO that the plate-like element
30 is positioned on the cooling side of the Peltier elements
45 while the plate-like element 31 is positioned on the
20 heating side of the Peltier elements.
The meander-shaped ch~nn~ls or grooves 3 2 and 33 shown in
Figs. 5 and 6 may be replaced by a plurality of straight,
substantially parallel, separate channels or grooves extend-
ing in the longitll~;n~l direction of each of the elements. In
25 such case, the cross-sectional area of each channel or groove
as shown in Fig. 4 would be substantially smaller. When the
channels or grooves are straight, each element 30 and 31 and
the corresponding cover plate 43 or 44 may be formed by
extrusion as a coherent part.
30 The heat exchanger device 23 is preferably heat insulated and
supported by shock absorbing means. The heat insulating means
may, for example, be foamed plastic which also functions as a
shock absorber.
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The air conditioning system illustrated in Fig. 1 operates as
follows. When the on-off switch 13 is in its of~ position the
solenoid valves 29 are open while the valve 22 is closed. In
this state the cabin radiator 18 and the blower 19 may heat
the air in the car cabin in a conventional m~nn~r
When the switch 13 is moved to its on position the valves 29
are closed while the valve 22 i9 opened and electric current
is supplied to the Peltier elements 45 of the heat exchanger
device 23, to the pumps 21 and 25 and to the fan 27. Water in
the second water circuit 20 will now be circulated through
the flow passage de~ined by the channel 32 in the heat
exchanger device 23 whereby the water will be e~iciently
cooled by the Peltier elements 45 in a m~nn~ known per se.
The cold water ~lowing through the cabin radiator 18 will now
15 cool the cabin air being circulated in the cabin by means of
the blower 19. At the same time the warm side of the Peltier
elements 45 will be cooled by water or another liquid being
circulated in the third water circuit 24 which includes the
channel 33 of the heat exchanger device 23, by means of the
pump 25. The heat removed from the heat exchanger device 23
will be given of~ to the outside air via the outside radiator
26.
In the air conditioning system shown in Fig. 7 the parts
similar to those shown in Fig. 1 has been indicated by the
same reference numerals.
In the embodiment shown in Fig. 7 the second water circuit
has been made independent of the cooling water circuit 17 and
comprise a separate radiator 47 arranged opposite to the
blower 19 and a liquid expansion tank 48. Furthermore, the
operation of the various electrical devices of the system i8
controlled by an electric control unit 49. It is appreciated
that the air conditioning system shown in Fig. 7 may be
installed in a car without interfering with the existing
electrical and cooling systems of the car.
CA 02240~2~ l998-06-l2
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11
EXAMPLE
A heat exchanger device as that illustrated in Figs. 2-6 has
a length of 330 mm, a width of 152 mm and a total thickness
o~ 51 mm. The cross-sectional dimensions o~ the channel 32 in
the plate-like element 30 is 9 x 14 mm, while the cross-sec-
tional dimensions o~ the channel 33 in the plate-like member
31 is 6 x 14 mm. The heat exchanger device contains twelve
Peltier elements Model SP1996 ~rom Marlow Industries Inc.
These elements are divided into six pairs which are mutually
connected in parallel while each pair i8 connected in series.
During cooling down ~rom a temperature in the cabin o~ a car
substantially above ambient temperature, the device is ope-
rating at an electric direct current o~ 42.1 ampere at a
voltage o~ 27.2 volts is supplied to the Peltier elements.
Thus, the power consumption i8 1145 W/h. Water or water
containing glycol is circulated in the circuits 20 and 24 and
through the associated channels or grooves 32, 33 o~ the heat
exchanger device. The ~low rate through the ~h~nn~ls 32 at
the cold side o~ the Peltier elements is 6 l/min at a pres-
sure of 0.6-0.8 bar. The cooling rate o~ the cabin by means
o~ the radiator 18 corresponds to lOOO W/h.
The liquid is ~orced through the liquid circuit 24 including
the channel~ 33 by means o~ the pump 25 at a rate o~ 6 l/min
at a pressure o~ 0.6-0.8 bar.
The coe~icient o~ per~ormance o~ the system may be calcula-
ted as ~ollows:
1000 W x 100
= 87,4~.
1145 W
