Note: Descriptions are shown in the official language in which they were submitted.
CA 02214409 1997-09-02
WO 96~27767 PCT/F196/00123
Arrangement in connection with an air conditioning unit
comprising heat recovery means and means for introducing
additional heating and cooling.
The present invention relates to an arrangement
in connection with an air conditioning unit, comprising
means for conveying exhaust and supply air through the
air conditioning unit, a heat recovery unit having at
least two stages and means for introducing additional
heat or cooling power into the supply air.
Arrangements of this kind are nowadays ~r ~ 1l in
air conditioning solutions for buildings. Energy is
transferred from air to air mainly indirectly through
heat exchangers. Ventilating installations are today
almost without exception provided with heat recovery
units. Also indirect evaporative cooling has increas-
ingly been introduced into the market. In such cooling,exhaust air is cooled by humidification, whereafter the
temperature effect will be transferred through a heat
recovery stage to the supply air, which is cooled. The
heat recovery unit may be a plate heat ~ch~nger, a
rotor, a radiator combination operating with a fluid, or
a heat pump, depending on the reguirements on hygiene,
technical requirements and space solutions.
Despite the good efficiency of heat recovery
units, additional heat is normally ~eeded in ventilation
installations in order for the temperature of the supply
air not to be too low, in particular if the amount of
energy transmitted from the exhaust air must be limited
on account of frosting of the exhaust air. The
additional heat has conventionally been introduced into
the supply air after the heat recovery unit with a water
radiator or an electric heater. The use of electricity
for heating of air is, however, questionable, and this
will be a growing trend in the future. The exhaust air
side of heat recovery units becomes frosted when the
humidity in the exhaust air is condensed onto the
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surface of the heat recovery unit if the surface
temperature of the heat recovery unit is below zero.
Depending on the relative humidity of the exhaust air,
this will take place when the outdoor temperature is -
15~C or lower. The defrosting of a plate heat exchanger,for example, takes place in such a way that part of the
supply air is conveyed past the plate heat exchanger, or
the entry of supply air to various sections of the heat
exchanger in turn is prevented, which will make the warm
exhaust air defrost the frosted areas. During the
defrosting step, the efficiency of heat recovery will be
impaired. The operation of the frosting step and anti-
freezing of the additional heating radiator requires
special automatics and also electro-mech~nical devices
in order that the operation may be realized.
It is an object of the invention to provide an
arrangement wherewith the drawbacks of the prior art can
be ~l;m;nated. This has been achieved with the arrange-
ment of the invention, which is characterized in that
the means for introducing additional heat or cooling
power into the supply air comprise at least one heating
device or/and cooling device disposed between the stages
of the heat recovery unit in the exhaust air flow or
separate air flow or a combined heating-cooling device
adapted to change the temperature of the exhaust air and
thereby to influence the temperature of the supply air
indirectly through the heat recovery unit.
An advantage of the invention is first of all
its good basic heat recovery efficiency and very high
community thermal energy efficiency in the heating
and/or cooling stage. Furthermore, the overall solution
is inexpensive and easy and reliable in operation and
has a low consumption of electricity. The good thermal
energy efficiency in the heating stage is based on the
possibility to use low-grade thermal energy, such as
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waste heat or condensation heat, which may even be free
o~ cost if it is not reclaimable in any other ~nne~.
The low consumption of electricity is based on the fact
that the radiator surfaces are effectively utilized in
all stages, and thus the air flow includes no components
causing extra air resistance. The plate heat exchanger
is not provided with a liquid pump consuming elec-
tricity. The conventional components provided in the
supply and exhaust air flows can advantageously
supplement the outcome. In winter, the supply air flow
passes through the first stage of the heat exchanger and
is heated by the exhaust air, whereafter it is trans-
ferred to the following stages of heat recovery, in
which the temperature reaches a basic level that may be
sufficient as such. If this is not enough in the case of
air heating, for example, the supply air passes through
an additional heating radiator. Since the additional
heating radiator is connected in series with the exhaust
air heating radiator, these may have a control circuit
in ~o,-l,nu-~.
In summer, the supply air flow may by-pass heat
exchangers through a by-pass route, for example, if no
change of state is desired. If the sy~ is provided
with humidifying cooling of the exhaust air, the supply
air is cooled stepwise in passing through the heat
recovery stages. If the temperature is not low enough,
it is possible to provide the supply air flow with a
cooling radiator.
In winter, the exhaust air flow first passes
through the last heat recovery stage on the supply air
side, which will decrease the temperature of the exhaust
air. Thereafter the radiatûr in the exhaust air flow
will heat the exhaust air before it is passed to the
next heat recovery stage, delivering its additional
thermal energy and possibly the thermal energy re~in;ng
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from the preceding stage or part of it to the supply air
through the heat recovery unit.
In summer, it is possible to cool the exhaust
air flow by humidifying either in one stage in connec-
tion with the heat recovery stages or in separatehumidifiers in the flow direction of the exhaust air
prior to the heat recovery stages. If this is not suf-
ficient, the heating radiator provided in the exhaust
air flow can be used as a cooling radiator. Additional
power can be achieved by furnishing the supply air flow
either with a separate cooling radiator or a combined
heating and cooling radiator connected in series with
the radiator in the exhaust air flow.
The essential difference to conventional oper-
ation is that the temperature of the additional energymay be at a lower level, since in normal operation there
is no risk of freezing, while the temperature difference
of the heated medium and the heat-delivering medium can
still be advantageous. With the conventional arrange-
ment, the temperature of the heating medium in the inletpipe cannot be lower than 30-40~C, which is the normal
temperature of water when ventilation is stopped. As a
rule, the design temperature for normal use is +60~ in
and +40~ out. With the invention, an energy source may
well be used having a temperature of +25~C, for example,
in which case the corresponding temperatures may be
+25~C in and +20~C out, since the purpose is to heat
exhaust air having a temperature above 0~C, yet lower
than the temperature of the air exiting the room. At the
same time, the automatics can be simplified as regards
anti-freezing, anti-frosting and possibly temperature
control. Also varying water flows can be passed through
the additional heating radiator(s) without any risk of
the water becoming frozen.
In the following the invention will be explained
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in greater detail by means of preferred embodiments
shown in the accompanying drawing, in which
Figure 1 is a schematic side view of a preferred
embodiment of an arrangement of the invention,
Figure 2 is a schematic side view of a second
embodiment of the arrangement of the invention,
Figure 3 is a schematic side view of a third
embodiment of the arrangement of the invention,
Figure 4 is a schematic side view of a fourth
embodiment of the arrangement of the invention,
Figure 5 is a schematic side view of a fifth em-
bodiment of the arrangement of the invention,
Figure 6 is a schematic side view of a sixth em-
bodiment of the arrangement of the invention,
Figure 7 is a schematic side view of a seventh
emboA;~nt of the arrangement of the invention,
Figure 8 is a schematic side view of an eighth
embodiment of the arrangement of the invention,
Figure 9 is a schematic side view of an altern-
ative implementation of the embodiment of Figure 8,
Figure 10 is a schematic side view of a secondalternative implementation of the embodiment of Figure
8, and
Figure 11 is a schematic side view of an altern-
ative implementation of a detail of the arrangement ofthe invention.
In Figure 1, reference numeral 1 denotes the
first stage and reference 2 the second stage of a heat
recovery arrangement in the flow direction of supply
air. These stages are plate heat exchangers. Reference
3 denotes an additional heating device located between
the heat recovery stages, e.g. an additional heating
~ radiator, operating if desired at a low temperature
level, for example with waste heat or ~onA~n~ation heat
that is supplied to the radiator through service pipes
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8. It is to be noted that Figure 1 is simplified over
against the actual construction, wherefore the figure is
to be understood only as a symbolic representation.
Reference 14 in Figure 1 denotes the jacket of
an air conditioning unit, reference 15 a supply air fan
and reference 16 an exhaust air fan or separate air fan.
In this context, separate air denotes other air than
exhaust air from the ventilation, which delivers energy
to the supply air or in which a change of state
indirectly affects the state of the supply air. An
example of separate air could be outdoor air or a
mixture of outdoor air and indoor air. Reference 17
denotes a possible supply air filter and reference 18 a
possible exhaust air filter, respectively. Reference 19
denotes a possible damper for supply air and reference
20 a possible damper for exhaust air. In addition to
these details, the apparatus can be provided with
conventional components, such as an air mixing unit,
electrical outfit, etc.
Figure 1 clearly shows the main idea of the
invention, i.e. that the means for introducing addi-
tional heat or cooling power into the supply air com-
prise at least one heating device or cooling device 3
disposed between the stages 1, 2 of the heat recovery
unit in the exhaust air flow or separate air flow,
adapted to change the temperature of the exhaust air and
thereby to influence the temperature of the supply air
indirectly through the heat recovery unit.
Figure 1 additionally shows one possible embodi-
ment. Reference 27 denotes a device consuming thermal
energy and reference 28 a heat-delivering device,
respectively. The device 27 consuming thermal energy
or/and the heat-delivering device 28 is/are preferably
connected to the same liquid circuit in series with the
heating or cooling device 3, and further at a point up-
CA 02214409 1997-09-02
WO 96127767 P'CT~96/OOlZ3
stream of the heating or cooling device 3 in the li~uid
flow direction.
The embodiment of Figure 2 shows a heat recovery
arrangement in which references 1 and 2 denote the
stages of the heat recovery unit, reference 3 an addi-
tional heating radiator and reference 8 service pipes.
Reference 13 denotes an air flow by-pass duct system
wherein damper 12 controls the air flow. The damper 12
can be used in summer conditions, for instance, when it
is not desired to transfer thermal energy to the supply
air.
Figure 3 illustrates by references 1 and 2 the
stages of the heat recovery unit and by means of
reference 3 a heating air radiator that is located
between the heat recovery stages in the exhaust air
flow. Reference 4 denotes a heating radiator in the
supply air flow; the piping of the liquid side of this
radiator is connected in series with the heating radi-
ator 3 indirectly affecting the temperature of the
supply air. soth radiators can be controlled with a
single common automatic control circuit, for instance.
In this embodiment, the radiator 3 indirectly affects
the supply air flow through the heat recovery unit, and
radiator 4 affects it directly on account of being
located in the supply air flow.
Figure 4 shows an arrangement in accordance with
Figure 1, to which an exhaust air humidifier denoted by
reference 5 has been incorporated. This humidifier may
be a separate humidifier, a humidifying nozzle or a heat
recovery unit provided with a humidification arrange-
ment. It is possible to duplicate the solution in
connection with each stage of the heat recovery unit, or
upstream of the heat recovery unit in the flow direction
of the exhaust air.
It is evident that devices 27 and 28 can also be
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incorporated into the embodiments of Figures 2-4 as
shown in Figure 1.
Figure 5 shows an arrangement in accordance with
Figure 4, in which the additional heating radiator 6 has
two functions, i.e. heating and cooling. These functions
can be performed with the same radiator 6.
Figure 6 shows two stages 1 and 2 of the heat
recovery unit and a humidifier 5. A combined radiator 6
enabling heating and cooling is operationally - i.e. on
the liquid side - connected with pipes 11 in series with
a second combined radiator 7 provided in the supply air
flow. By this arrangement, it is possible to ~nh~nc~ the
effect of the heating and cooling stages. In this
embodiment, radiator 6 indirectly affects the supply air
flow through the heat recovery unit, and radiator 7
affects it directly on account of being located in the
supply air flow.
Figure 7 shows the basic idea of the solution of
Figure 1 implemented with rotary recovery cells illus-
trated by references 21 and 22. Other operationalalternatives can be implemented in a corresponding way.
Radiator 3 is located in the exhaust air flow.
Figure 8 correspondingly shows the basic idea of
the solution of Figure 1 implemented with a radiator
solution employing some medium. Radiators provided in
the supply air flow are denoted by references 23 and 24
and radiators provided in the exhaust air flow by
references 25 and 26, respectively.
With regard to the solution of Figure 8, it can
be stated that a particularly preferred embodiment is
achieved by connecting radiators 23-26 in series in the
same flow circuit on the counter-current principle, as
shown in Figure 9. Furthermore, for example radiators 23
and 24 can be combined into radiator 234 and radiators
25 and 26 can be separate, as shown in Figure 10. It is
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WO 96/27767 PCT~F~96~00~23
naturally also possible to implement this constructional
alternative vice versa.
The heating device and/or cooling device 3 can
also be fitted in a by-pass duct 110 as shown in Figure
11. Figure 11 is based on Figure 8. Figure 11 shows only
the radiators 25, 26 on the exhaust air side, in other
respects the embodiment of Figure 11 corresponds to the
embodiment of Figure 8. In this embo~i~ent, the air flow
can be directed with baffle 111 to pass via by-pass duct
110 through the heating device 3, or alternatively
directly in such a way that the air does not flow into
by-pass duct 110, but past the heating device 3. It is
also possible to make the construction such that one of
the radiators of the heat recovery unit can be by-
passed. Also this detail is shown in Figure 11, wherein
reference 112 denotes a second baffle that can be turned
into the positions shown in the figure, thus enabling
the air flow to be directed in the desired manner.
Figure 11 shows various possibilities for air flow by
means of arrows.
Devices 27 and 28 in accordance with Figure 1
can also be incorporated into the embodiments of Figures
5-8, as has been explained in connection with Figure 1.
The above exemplary embodiments are not to be
construed as limiting the invention, but the invention
can be modified with complete freedom within the purview
of the claims. It will be appreciated that the
arrangement of the invention or its details need not
necessarily be exactly as shown in the figures, but
other kinds of solutions are possible as well. It is to
be noted, for example, that even though the figures
present solutions in which one radiator located between
, the heat recovery stages and one radiator fitted in the
supply air flow, this is not the only possibility, but
it is possible to use more radiators at these points,
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etc. Even though the figures primarily illustrate
embodiments with a plate heat exchanger, the invention
is well suitable for other equipment stated above, or
combinations of such equipment.
