GB2562674A

GB2562674A - Mechanical ventilation and heat recovery unit and system

Info

Publication number: GB2562674A
Application number: GB1813259.7A
Authority: GB
Inventors: James William Reaney Matthew
Original assignee: Polypipe Ltd
Current assignee: Polypipe Ltd
Priority date: 2013-02-08
Filing date: 2013-02-08
Publication date: 2018-11-21
Anticipated expiration: 2033-02-08
Also published as: GB2562674B; GB201813259D0

Abstract

A mechanical ventilation and heat recovery unit 100 comprises a housing with a plurality of inlets 112, 132, 114, 134 and outlets 122, 124 and a plurality of fluid passages extending between the inlets and outlets in the housing. The housing provides a volume for receiving a heat exchanger 155. A first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the heat exchanger volume from a second inlet to a second outlet. A warming plate 170, positioned adjacent to the heat exchanger volume, provides trace heating to the heat exchanger 155. A cover 175 may enclose the heat exchanger and warming plate. The warming plate 170 may be warmed by power resistors (172, Fig. 10) attached to the warming plate. The warming plate 170 may prevent condensate cooled in the heat exchanger from freezing.

Description

(54) Title of the Invention: Mechanical ventilation and heat recovery unit and system Abstract Title: Mechanical ventilation and heat recovery unit with warming plate (57) A mechanical ventilation and heat recovery unit 100 comprises a housing with a plurality of inlets 112, 132, 114, 134 and outlets 122, 124 and a plurality of fluid passages extending between the inlets and outlets in the housing. The housing provides a volume for receiving a heat exchanger 155. A first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the heat exchanger volume from a second inlet to a second outlet. A warming plate 170, positioned adjacent to the heat exchanger volume, provides trace heating to the heat exchanger 155. A cover 175 may enclose the heat exchanger and warming plate. The warming plate 170 may be warmed by power resistors (172, Fig. 10) attached to the warming plate. The warming plate 170 may prevent condensate cooled in the heat exchanger from freezing.

Mechanical Ventilation and Heat Recovery Unit and System

Background of the Invention

The present invention relates to a mechanical ventilation with heat recovery (MVHR) unit and a system incorporating such a unit.

Mechanical Ventilation with Heat Recovery (MVHR) units are known. Such units are used to provide fresh air ventilation, for example into rooms of a building, and removal of warm damp air from said rooms. The MVHR unit is normally provided with a heat exchanger. The heat exchanger can be used to exchange heat between the warm damp air being removed from the building and the fresh air being provided to the building. In this way, heating costs normally associated with heating the building can be reduced, as heat which would otherwise be wasted is used to preheat fresh, typically colder, air being provided to the building.

The warm air which is removed from the building may be damp, particularly where air is removed from so-called wet rooms such as kitchens and bathrooms. Damp air can result in condensation build up and the formation of mould. MVHR units serve to remove damp air from the building and avoid the build-up of condensation and associated problems, e.g. structural damage to the building and/or health problems.

Typically the MVHR unit is located in a roof space or utility room of a building. The MVHR unit has a fresh air inlet connected to fresh air externally of the building. The MVHR has a fresh air outlet which is connected to fresh air inlets in rooms in the building. The MVHR unit includes a warm air outlet, which is connected externally of the building. The MVHR unit includes a warm air inlet which is connected to warm air outlets in rooms of the building. The MVHR unit is sized and specified with an appropriate heat exchanger for the ventilation requirements of the building.

The present invention seeks to overcome at least one of the problems associated with the prior art.

Summary of the Invention

Described herein is a mechanical ventilation and heat recovery unit, comprising a housing, a plurality of inlets into the housing and outlets out of the housing, a plurality of fluid passages in the housing, the housing comprising a volume for receiving a heat exchanger, wherein a first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the heat exchanger volume from a second inlet to a second outlet, further comprising a third inlet in the first fluid passage, on the first outlet side of the heat exchanger in the fluid path, and a fourth inlet in the second fluid passage on the second outlet the heat exchanger, the third and fourth inlets being closable and individually openable.

The unit comprises a heat exchanger contained within the heat exchanger volume, the heat exchanger having first and second separate flow channels provided therein to transfer heat between fluids in the respective channels, the first and second fluid passages being fluidly connected through the first and second flow channels in said heat exchanger respectively.

The third and fourth inlets may be formed as removable closures in the housing, being closed on manufacture, and are openable by removing a respective closure in the housing. This provides a convenient way to provide an alternate inlet into the first/second fluid passages, only if necessary, while maintaining a defined fluid path if the third and fourth inlets remain closed.

In some examples, the first inlet and second outlet are on one side of the unit, and the second inlet and first outlet are on the other side of the unit. This is beneficial as one side of the unit (eg left hand side in Figure 1) relates to an inlet and outlet for the internal side of the unit, ie the side of the unit from which the ventilation pipes will travel to the internal volume of the building, while the other side (eg right hand side in Figure 1) relates to an inlet and outlet for the external side of the unit, ie the side of the unit from which ventilation pipes will travel to the outside of the building. Thus it becomes easy for an installer to ensure that the ventilation pipes are coupled to the unit correctly. It is possible to install the unit with either of the sides being connected to the external pipes, and the other being connected to the internal pipes. Once the pipes are connected, a small drainage hole may be placed into the fluid passage which receives the stale air to be expelled. The drainage hole may be placed on the opposite side of the unit to the side in which the inlets and outlets are mounted in the present example.

Preferably, the hole is placed in the in use lower side of the unit. This allows condensation from the warm humid air exiting the building to drain away from the unit as it condenses as it cools by travelling through the heat exchanger, as it loses heat to the cold external fresh air entering the other fluid passage.

Also described herein is a system comprising a unit according to the first aspect and a bypass, for diverting fluid from a position upstream of the first inlet to the third inlet to provide a third flow path to the first outlet bypassing the heat exchanger volume, or from a position upstream of the second inlet to the fourth inlet to provide a fourth flow path to the second outlet bypassing the heat exchanger volume. In this way, when the bypass is fitted to the unit between the first inlet and the third inlet, and the third inlet is opened, it forms a bypass passage, which forms part of a third fluid passage. This fluid passage joins with the first fluid passage downstream of the heat exchanger volume, and thus provides a convenient bypass for the heat exchanger. Similarly, the bypass may instead extend between the second inlet and the fourth inlet for the same reason, to bypass the heat exchanger volume in the second fluid passage. Only the inlet that is connected to the bypass is opened. The other of the third and fourth inlets remains closed. In this way, it is possible to make the unit and bypass “handed” in order that it is much easier to install into a confined space, for example in an attic space of a house. Generally, the bypass is fitted to the outgoing air and is used during the summer months. The fresh air is brought in through the heat exchanger, but, as the exhaust, stale air is not passed through the heat exchanger, the outgoing air does not heat the incoming air, and cool, fresh air is delivered into the building. Alternatively, the fresh air may be bypassed from the heat exchanger, and the exhaust air passed through the other side of the heat exchanger. Again, however, as the cool air is not passed through the heat exchanger, it is not warmed by the exhaust air, and cool, fresh air is delivered into the building. Depending on which side of the unit is connected to the inside of the building, the bypass can be installed in either of the two ways, as is convenient. Further, as the third inlet is on the opposite side to the first inlet and second outlet, and the fourth inlet is on the opposite side to the second inlet and first outlet, and the distances between the first/second inlet and third/fourth inlet are different from the distances between any other pair of inlets/outlets, there is only one way that the bypass can be fitted for each of the two configurations, so avoiding installation error.

The bypass may comprise a valve to control fluid flow along the first/third, or second/fourth fluid passages. This valve may control whether the bypass is active or not, so increasing ease of use. This is particularly true when the valve is remotely controlled to activate and deactivate the bypass.

The third inlet may be in the first fluid passage, downstream of the heat exchanger volume. Similarly, the fourth inlet may be in the second fluid passage, downstream of the heat exchanger volume. This conveniently provides the bypass with a fluid flow that bypasses the heat exchanger, without the need for separate further fluid passages within the unit.

A first fan may be provided in the first fluid passage, downstream of the heat exchanger volume. Similarly, a second fan may be provided in the second fluid passage, downstream of the heat exchanger volume. These provide an efficient way of moving air through the unit.

The outlets may all be positioned on a first side of the unit. This provides convenience during installation, as well as a compact and easy to manufacture unit.

According to a first aspect of the invention, a mechanical ventilation and heat recovery unit is provided, comprising a housing, a plurality of inlets and outlets into the housing, a plurality of fluid passages extending between outlets in the housing, the housing providing a volume for receiving a heat exchanger, wherein a first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the other side of the heat exchanger volume from a second inlet to a second outlet, further comprising a warming plate, positioned adjacent to the heat exchanger volume, configured to provide trace heating to the heat exchanger. This can help to prevent damage to the heat exchanger caused by freezing of condensate from the moist stale air leaving the building, as it is cooled by the incoming air. This is particularly likely when the cool incoming air is extremely cold, as it could be in winter, or in certain climates. The warming plate provides a trace heating effect, which is small in power input/output, but, because it may be directly attached to the heat exchanger, effectively heats condensate inside the heat exchanger and prevents it from freezing and cracking the heat exchanger. Conveniently, the warming plate may be formed from aluminium. One or more power resistors may be attached to the warming plate, acting as heating elements, to warm the warming plate, and, thus, the heat exchanger.

Detailed Description of Embodiments of the Invention

Exemplary products and embodiments of aspects of the present invention will now be described, purely by way of example, with reference to the Figures, in which:

Figure 1 is a view of an exemplary ventilation unit;

Figure 2 shows a plan view of the unit of Figure 1;

Figure 3 shows the unit of Figures 1 and 2, with the side removed and with the flow paths of fluid passing through the unit;

Figure 4 shows a system comprising the unit of Figures 1 to 3 and a bypass attached to the unit;

Figure 5a shows a valve of the bypass of Figure 4 connected to the unit, and Figure 5b shows the system including the unit and a bypass including the valve of Figure 5a;

Figure 6 shows an alternate system comprising the unit of Figures 1 to 3 and a bypass, mounted on the unit in a different configuration to that of Figures 4 and 5a,b;

Figures 7 and 8 show a valve of the bypass of Figures 4 and 5a,b in different configurations;

Figure 9 shows a unit according to the present invention; and

Figure 10 shows a portion of the unit of Figure 9.

As shown generally in Figures 1 to 3, there is described a first exemplary mechanical ventilation and heat recovery unit 1, comprising a housing 10 a plurality of inlets 12, 14, 32, 34 into the housing and outlets 22, 24 out of the housing. A plurality of fluid passages 42, 44 is formed in the housing 10, the housing 10 comprising a volume 50 for receiving a heat exchanger 55, wherein a first fluid passage 42 extends through the heat exchanger volume 50 from a first inlet 12 to a first outlet 22, and a second fluid passage 44 extends through the heat exchanger volume 50 from a second inlet 14 to a second outlet 24. The first example further comprises a third inlet 32 in the first fluid passage 42, on the first outlet 22 side of the heat exchanger volume 50 in the fluid path, and a fourth inlet 34 in the second fluid passage 44 on the second outlet 24 side of the heat exchanger volume in the fluid path, the third and fourth inlets 32, 34 being selectively closable and individually openable. In the figures, a “tick” shown against an inlet or outlet denotes that it is open, whereas a “cross” denotes that the inlet/outlet is blocked.

The unit 1 of the present example comprises a heat exchanger 55 formed in the heat exchanger volume 50. However, it will be understood that the unit 1 could be fabricated without such a heat exchanger 55, which could be inserted into the unit 1 prior to installation. Alternatively, the heat exchanger may be integral with the unit. The heat exchanger 55 fits within the volume 50 in such a way as to form a seal with the housing 10 so that fluid flowing in the first and second flow passages 42, 44 can only flow through the heat exchanger and sealed first and second flow passages are formed, extending between the first inlet and first outlet and second inlet and second outlet respectively. The heat exchanger 55 has first and second separate flow channels provided therein for transferring heat between fluids in the respective channels, the first and second fluid passages being fluidly connected through the first and second flow channels in said heat exchanger respectively.

In the present example unit 1, the third inlet 32 is provided to open into in the first fluid passage 42, downstream of the heat exchanger 55. Similarly, the fourth inlet 44 is provided to open into the second fluid passage, downstream of the heat exchanger 55. A first fan 52 is provided in the first fluid passage 42, downstream of the heat exchanger 55. Similarly, a second fan 54 is provided in the second fluid passage 44, downstream of the heat exchanger 55.

In the present example unit 1, the third and fourth inlets 32, 34 are formed blind, and, on manufacture of the housing, comprise removable closures formed in the housing 10. After manufacture, the third and fourth inlets 32, 34 are therefore closed, and can be subsequently opened independently, if desired, by removal of a separate blank or closure in each inlet. Alternatively, the housing 10 could be formed with six openings and removable blind closures could be fitted to the third and fourth inlets 32, 34 subsequent to manufacture.

As shown in Figure 4, there is a system provided with an example unit 1 as described above, and further comprising a bypass 60, for diverting fluid from a position upstream of the first inlet 12 of the unit 1 to the third inlet 32 to provide a third fluid passage to the first outlet 22 bypassing the heat exchanger 55. The bypass 60 comprises a valve 62, and a coupling 64 connecting the valve to the third inlet 32 to form part of the third fluid passage 52. The remainder of the third fluid passage 46, from the third inlet 32 to the first outlet 22 corresponds to the part of the first fluid passage 42 downstream of the third inlet 32. This is placed downstream of the heat exchanger 55, but upstream of the first fan 52. The second fluid passage 44 remains unchanged, and fluid therefore flows from the second inlet 14 to the second outlet 24.

Figure 5a shows the blind third inlet 32 having been opened into the first fluid passage 42 and the valve 62 mounted to the first inlet 12. In Figure 5b, the coupling 64 is mounted between the valve 62 and the third inlet 32. The valve 62 prevents fluid flow into the first inlet 12, and, instead, diverts fluid flow along the coupling to the third inlet

32.

As shown in Figure 6, in an alternative configuration, the bypass 60 is instead mounted on the unit 1 between the second inlet 24 and the fourth inlet 34, from a position upstream of the second inlet 24 to the fourth inlet 34, to provide a fourth fluid passage to the second outlet 24 bypassing the heat exchanger 55. Similarly as described above in relation to Figures 4 and 5a,b, a fluid path, this time the second fluid path 44, is partially bypassed, to a position downstream of the heat exchanger 55, while maintaining the second fan 54 in the fourth fluid passage 48. The fourth fluid passage, downstream of the fourth inlet corresponds to the same portion of the second fluid passage 44.

Figure 7 shows the valve in a first configuration in which fluid entering the valve 62 is directed into the coupling 64, and thus diverted from the first/second flow path into the third/fourth flow path, thus bypassing the heat exchanger. Figure 8 shows the valve in a position in which the fluid flow is not diverted from the first/second fluid passage, and thus the heat exchanger 55 is not bypassed.

As stated above, the unit is manufactured with the third and fourth inlets 32, 34 closed. The unit 1 can be installed in this way. The unit 1 can be configured with either the first inlet or the second inlet receiving fresh external air, which travels through the corresponding fluid passage, being sucked into that inlet 12 and through the heat exchanger 55, before being pumped out of the corresponding outlet, by the fan in that fluid passage. Similarly, the other of the first and second inlet is coupled to stale air exiting a building in which the MVHR is installed, the stale air is sucked into the other of the first and second inlets of the unit, along the other of the first and second fluid passages, and through the other side of the heat exchanger 55 by the other fan, before being blown out of the second outlet to the outside of the building.

The configuration shown in the Figures, with the first inlet and second outlet on one side of the unit, and the second inlet and first outlet being on the other side of the unit, is beneficial as one side of the unit (eg left hand side in Figure 1) relates to an inlet and outlet for the internal side of the unit, ie the side of the unit from which the ventilation pipes will travel to the internal volume of the building, while the other side (eg right hand side in Figure 1) relates to an inlet and outlet for the external side of the unit, ie the side of the unit from which ventilation pipes will travel to the outside of the building. Thus is becomes easy for an installer to ensure that the ventilation pipes are coupled to the unit correctly. It is possible to install the unit with either of the sides being connected to the external pipes, and the other being connected to the internal pipes. Once the pipes are connected, a small drainage hole is placed into the fluid passage which receives the stale air to be expelled. The drainage hole is placed on the opposite side of the unit to the side in which the inlets and outlets are mounted in the present example. Preferably, the hole is placed in the in use lower side of the unit. This allowed condensation from the warm humid air exiting the building to drain away from the unit as it condenses as it coils by travelling through the heat exchanger, as it loses heat to the cold external fresh air entering the other fluid passage.

Figure 4 shows the fluid flow in the fluid passages when the bypass is fitted between the first inlet 12 and the third inlet 32. The bypass 60 therefore creates a third fluid passage, which extends from adjacent the first inlet 12 (i.e. at a point upstream of the first inlet) to the third inlet. The third inlet is opened by removal of the closing blank formed in the inlet during manufacture. As explained previously, the third inlet is positioned at a point downstream in the first fluid path of the heat exchanger. Thus, when the bypass is fitted, stale air entering the system from the building enters the bypass valve 62 and is diverted along the coupling 64 in the third fluid passage to the third inlet 32. The air then enters the unit 1 in the first fluid passage 42 downstream of the heat exchanger 55, and from this point, the third fluid passage and first fluid passage coincide. The air does not back flow up the first fluid passage 42, as the air takes the path of least resistance, by being pushed out of the first outlet by the first fan 52. Further, the valve 62 closes the first inlet 12 so back flow out of the first inlet 12 is not possible. The second fluid passage 44 is unaffected by the presence of the bypass 60, and fluid flows in the same way as described above in relation to the second fluid passage 44. In the present example, the bypass 60 is fitted to the incoming fresh air side of the MVHR system. It would be possible to connect the bypass 60 to the exiting stale air instead.

Figure 6 shows the bypass 60 fitted to the unit the other way, ie to produce an oppositely “handed” system. In this case, the valve 62 is connected upstream of the second inlet 14, rather than the first 12. The coupling creates the fourth fluid passage 48 from the valve 62 to the fourth inlet 42, which provides a bypass for the other side of the heat exchanger 55, the fourth and second fluid passages combining to be coincident downstream of the fourth inlet 48. The first fluid passage 42 is unaffected by the addition of the bypass 60 in this example. Similarly to what is described above, the bypass 60 is fitted to the air exhaust side of the system. However, it would also be possible to connect it to the fresh air inlet side. The ability to connect the bypass 60 either between the first and third inlets 12, 32 to bypass 60 on one side of the unit, or between the second and fourth inlets 14, 34 to bypass 60 on the other side of the unit, allows the system to be “handed” to connect the bypass 60 and the fresh air side of the MVHR system to which ever physical side of the unit 1 is most convenient.

Figure 9 shows a first embodiment of the invention. The features of this embodiment are each and individually interchangeable with those of the preceding examples.

Features of the previous examples may be omitted or changed from this embodiment.

Figure 9 shows a partially cut out and partially exploded view of an MVHR unit 100 of an embodiment of the invention, including inlets 112, 132, 114, 134 and outlets 122, 124 for fresh and stale air respectively (i.e. that entering a building/other enclosed space and leaving respectively). Although six openings are shown, a different number may be provided. The unit 100 contains a heat exchanger 155 for exchanging heat between the stale air and fresh incoming air. A fan 152, 154 is provided on each side of the heat exchanger 155 in the respective fluid flows. A warming plate 170 is provided. The warming plate 170 is fixed directly to the side of the heat exchanger 155, to efficiently conduct heat from the warming plate 170 to the heat exchanger 155. A lower cover 175 is then added to enclose the heat exchanger 155 and the warming plate 170 of the unit 100.

Figure 10 shows the warming plate 170, and also two power resistors 172 attached directly thereto. The power resistors 172 are not particularly high power, in the present embodiment, between 20-100W. The power resistors 172 act as heating elements, and heat the warming plate 170 to which they are attached. The warming plate 170 then, in turn, heats the heat exchanger 155. An air preheater, placed in the air stream of the incoming air, might have a power consumption of around 1kW, which is much higher than that of the power resistors 172. Their purpose is not to preheat the fresh air entering the building or other enclosed space, but to warm the heat exchanger 155 directly and prevent condensate from the stale air, as it is cooled in the heat exchanger 155 by the incoming fresh air, from freezing and thus damaging the heat exchanger 155. In this way, the unit can continue to operate when the incoming air is cold, whereas a bypass might otherwise be activated to protect the heat exchanger 155 from the adverse conditions.

The present invention has been described above purely by way of example. Unless the context clearly requires otherwise, the terms “comprise, comprises, comprising” and the like are to be interpreted in the inclusive rather than exhaustive sense, i.e. in the sense of “including, but not limited to”.

Description of the reference numerals

Mechanical ventilation and heat recovery unit 1, 100

Housing 10

Inlets: first 12, 112, second 14, 114, third 32, 132, fourth 34, 134

Outlets: first 22, 122, second 24, 124 fluid passages: first 42, second 44 heat exchanger volume 50 heat exchanger 55, 155 third fluid passage 46 fourth fluid passage 48 first fan 52, 152 second fan 54, 154 bypass 60 valve 62 coupling 64 warming plate 170 power resistors 172 lower cover 175

Claims

Claims:

1. A mechanical ventilation and heat recovery unit, comprising:

a housing;

a plurality of inlets and outlets into the housing;

a plurality of fluid passages extending between outlets in the housing;

the housing providing a volume for receiving a heat exchanger;

wherein a first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the other side of the heat exchanger volume from a second inlet to a second outlet, further comprising a warming plate, positioned adjacent to the heat exchanger volume, configured to provide trace heating to the heat exchanger.

2. A unit according to claim 1, further comprising a heat exchanger contained within the heat exchanger volume, the heat exchanger having first and second separate flow channels provided therein to transfer heat between fluids in the respective flow channels, the first and second fluid passages being fluidly connected through the first and second flow channels in said heat exchanger respectively.

3. A unit according to claim 1 or claim 2, wherein the warming plate is formed from aluminium.

4. A unit according to any one of the preceding claims, wherein the warming plate is fixable directly to the side of the heat exchanger to efficiently conduct heat from the warming plate to the heat exchanger.

5. A unit according to any one of the preceding claims, further comprising a lower cover configured to enclose a or the heat exchanger and the warming plate of the unit.

6. A unit according to any one of the preceding claims, wherein power resistors are attached to the warming plate to warm the warming plate.

7. A unit according to claim 6, wherein the one or more power resistors are in the power range of 20W to 100W.

8. A unit according to any one of the preceding claims, wherein the warming plate is for warming condensate in a heat exchanger mounted in the heat exchanger volume.

9. A unit according to any one of the preceding claims, further comprising a heat exchanger contained within the heat exchanger volume, the heat exchanger having first and second separate flow channels provided therein to transfer heat between fluids in the respective flow channels, the first and second fluid passages being fluidly 5 connected through the first and second flow channels in said heat exchanger respectively.

Application No: GB1813259.7

9. A unit according to any one of the preceding claims, wherein the heating plate 5 is configured to warm a heat exchanger directly and prevent condensate from the stale air from freezing as it is cooled in the heat exchanger by the incoming fresh air.

15 10 18

Amendments to the claims have been filed as follows

Claims:

1. A mechanical ventilation and heat recovery unit, comprising:

a housing;

5 a plurality of inlets and outlets into the housing;

a plurality of fluid passages extending between outlets in the housing;

the housing providing a volume for receiving a heat exchanger;

wherein a first fluid passage extends through the heat exchanger volume from a first inlet to a first outlet, and a second fluid passage extends through the heat 10 exchanger volume from a second inlet to a second outlet, further comprising a warming plate, positioned adjacent to the heat exchanger volume, configured to provide trace heating to a heat exchanger.

2. A unit according to claim 1 , wherein the warming plate is formed from 15 aluminium.

3. A unit according to any one of the preceding claims, wherein the warming plate is fixable directly to the side of a heat exchanger to efficiently conduct heat from the warming plate to the heat exchanger.

4. A unit according to any one of the preceding claims, further comprising a lower cover configured to enclose a heat exchanger and the warming plate of the unit.

5. A unit according to any one of the preceding claims, wherein power resistors 25 are attached to the warming plate to warm the warming plate.

6. A unit according to claim 5, wherein the one or more power resistors are in the power range of 20W to 100W.

30 7. A unit according to any one of the preceding claims, wherein the warming plate is for warming condensate in a heat exchanger mounted in the heat exchanger volume.

8. A unit according to any one of the preceding claims, wherein the warming plate is configured to warm a heat exchanger directly and prevent condensate from stale air 35 from freezing as it is cooled in the heat exchanger by incoming fresh air.