GB2463004A

GB2463004A - Heat exchanger in a heat recovery ventilation system

Info

Publication number: GB2463004A
Application number: GB0815455A
Authority: GB
Inventors: Daniel Carl Lane
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-08-26
Filing date: 2008-08-26
Publication date: 2010-03-03
Also published as: GB0815455D0

Abstract

A heat exchanger 1 when used in a heat recovery ventilation system 5 comprises a plurality of heat conducting barriers (3 fig 1) within a conduit 2 thereby defining two sets of adjacent flow channels (4, 4A) along the conduit 2 permitting heat to be transferred through the heat conducting barriers (3). The first set of channels (4A) are open to a first end 7 of the conduit 2 and open through a hole 14 in a side wall of the conduit 2 adjacent a second end 6 of the conduit 2. The second set of channels (4) are open to the second end 6 (fig 3) of the conduit 2 and open through a hole 14 in the side wall of the conduit 2 adjacent the first end 7 of the conduit 2. A sleeve (22, figs 10 — 12) surrounding the conduit 2 may be provided whereby the openings 14 in the side wall communicate with a gap (23) between the sleeve (22) and the conduit 2. The sleeve (22) may be circular in cross section and the conduit 2 may be rectangular in cross section. The barriers (3) may be non-planar (figs 6) and orientated substantially vertical. Centrifugal fans 8, 9 driven by a single motor 13 and mounted on a common shaft 12 may be located at each end 6, 7 of the conduit 2 and configured to draw in air from opposite directions creating a counter current flow.

Description

Heat Recovery Apparatus

Field of the Invention

The invention relates to heat exchangers for the recovery of heat from air streams in ventilation systems. The invention also relates to ventilation systems embodying such heat exchangers.

Background and Prior Art Known to the Applicant

As a result of an ever-increasing desire to conserve energy, buildings have become significantly more air-tight over the years, preventing drafts and associated energy loss.

However, there is also a conflicting need to provide ventilation for buildings, to remove "stale" air from within, and replace it with "fresh" air. The need to provide such ventilation is particularly acute in areas of high moisture generation, or areas in which odours are produced, such as kitchens and bathrooms. Simply venting stale or moist air to the outside results in a loss of energy from the building, costing money in additional space heating requirements and causing damage to the environment.

As a result, a number of systems have been developed over the years to recover heat from air that is vented from a building. Typically, extracted air is actively replaced with fresh air from outside of the building, and the inlet and outlet streams of air are passed through a heat exchanger in order to transfer heat from the outgoing, warm stale air to the incoming cooler fresh air. Crossflow heat exchangers are typically used, being of relatively low cost construction. However, such units are bulky, often noisy, and require two motor-driven fans: one to extract the stale air to pass through one side of the cross-flow heat exchanger, and a second fan to draw fresh air in through the other side of the cross-flow heat exchanger. As the demand for heat recovery in domestic premises increases, driven -at least in part in the UK -by more stringent Building Regulations, the need for compact, efficient, and lower cost heat recovery ventilation systems continues to increase. There is a particular need to be able to readily upgrade existing unidirectional extractor fan installations with heat recovery ventilation systems with minimal alteration to the fabric of the building in which they are installed.

It is among the objects of the present invention to provide a solution to these and other problems.

Summary of the Invention

Accordingly, in a first aspect, the invention provides a heat exchanger for a heat recovery ventilation system comprising: a conduit; a plurality of heat-conducting barriers arranged within the conduit defining two sets of flow channels running along the conduit; the first set of channels arranged to open to the end of the conduit at the first end of the conduit and to open through a side wall of the conduit adjacent the second end of the conduit; and the second set of channels arranged to open to the end of the conduit at the second end of the conduit and to open through a side wall of the conduit adjacent the first end of the conduit; said flow channels being arranged such that channels in the first set are adjacent channels in the second set, thereby allowing heat to be transferred from gas in channels in the first set to gas in channels in the second set, via said heat-conducting barriers.

In a second aspect, the invention provides a heat exchanger for a heat recovery ventilation system comprising: a conduit; a plurality of heat-conducting barriers arranged within the conduit defining two sets of flow channels running along the conduit; the first set of channels arranged to open to a central region of the end of the conduit at the first end of the conduit and to open only to a peripheral region of the conduit adjacent the second end of the conduit; and the second set of channels arranged to open to a central region of the end of the conduit at the second end of the conduit and to open only to a peripheral region of the conduit adjacent the first end of the conduit; said flow channels being arranged such that channels in the first set are adjacent channels in the second set, thereby allowing heat to be transferred from gas in channels in the first set to gas in channels in the second set, via said heat-conducting barriers.

In any aspect, the heat exchanger preferably comprises a sleeve surrounding said conduit and wherein openings in the side wall of the conduit are in communication with a gap between the sleeve and the conduit. More preferably, said sleeve has a circular cross-section and said conduit has a rectangular cross-section.

In any aspect, it is preferred that the heat-conducting barriers have a non-planar profile.

Also included within the scope of the invention is a heat exchanger substantially as described herein, with reference to and as illustrated by, any appropriate combination of the accompanying drawings.

The invention also provides a heat recovery ventilation system comprising: a heat exchanger described herein; an impeller mounted at each end of said conduit, said impellers configured to draw air in opposite directions through respective sets of channels, thereby creating a counter-current flow through said heat exchanger.

Preferably, in such a ventilation system, said impellers comprise centrifugal fans.

Also preferably, in such a ventilation system, said impellers are configured to be driven by a single motor. More preferably, said impellers are mounted for rotation on a common shaft.

In any such ventilation system, the system is configured such that, on installation, said heat conducting barriers are oriented substantially vertically. In this way, any condensation within the channels can readily be discharged from the bottom of the channels.

Also included within the scope of the invention is a ventilation system substantially as described herein, with reference to and as illustrated by, any appropriate combination of the accompanying drawings.

Brief Description of the Drawings

The invention will be described by reference to the accompanying drawings, in which: Figure 1 is an end view of an embodiment of a heat exchanger of the invention; Figures 2-4 are schematic cross-sections of heat recovery ventilation systems of the invention; Figures 5 and 6 are schematic cross-sections of a heat exchanger of the invention, showing arrangements of heat-conducting barriers; Figure 7 is an end view of an embodiment of a heat exchanger of the invention; Figures 8 and 9 are schematic cross-sections of heat recovery ventilation systems of the invention; Figure 10 is an end view of an embodiment of a heat exchanger of the invention; and Figures 11 and 12 are schematic cross-sections of heat recovery ventilation systems of the invention;

Description of Preferred Embodiments

Figure 1 illustrates an end view of a heat exchanger of the present invention, generally indicated by 1. The heat exchanger comprises a conduit 2 in the form of a circular cr0 ss-section tube and a number of heat-conducting barriers 3 arranged within the tube in a spaced-apart fashion, and extending along the length of the tube. In this embodiment, the barriers are in the form of flat copper plates. The barriers define adjacent channels 4 within the conduit, also running along the length of the conduit, substantially from one end to the other.

In preferred embodiments, the heat-conducting barriers 3 may be formed by folding a sheet of copper around a former, in a zig-zag fashion, the spaces between adjacent folds constituting the channels, as illustrated in Figure 5. Other materials are also envisaged for the heat-conducting barriers, including aluminium, other metals and their alloys, and plastics. In order to increase the area for heat transfer, the heat conducting barriers 3 may be formed to be non-planar, e.g. having a corrugated profile, such as that illustrated in cross-section in Figure 6.

The channels so formed comprise, ftinctionally, two sets of channels: one to carry the stale or damp air extracted from a building (or room) and a second set to bring in fresh air from outside. Channels from the two sets of channels are arranged adjacent each other, most preferably alternately, to provide a maximum heat transfer from one set of channels to the other, via the heat-conducting barrier. At one end of the heat exchanger, alternate openings are blocked, to resist the flow of air, as indicated by the hatched lines on Figure 1, in channels 4A. The openings of the other set of channels (unhatched in Figure 1) are left unblocked. At the other end of the heat exchanger, those channels blocked at the first end are left open, and those channels left open at the first end are blocked. At each end of the heat exchanger, those channels that are blocked at the end face are opened through a hole in the side wall of the conduit 2, as will be illustrated more clearly in Figures 2-4.

Figure 2 is a schematic cross-section of a heat recovery ventilation system generally indicated by 5 incorporating the heat exchanger 1 of Figure 1, taken through the line B-B' of the heat exchanger a, and including additionally some further components to be described below. Figure 2 illustrates the conduit 1 and a closed end 6 of a channel 4A in a first set of channels, with a corresponding open end 7at the other end of the conduit.

Holes 14 in the side wall of the conduit 2 adjacent the closed end of the channel communicate with the interior of the channel.

Also illustrated in Figure 2 are two impellers 8, 9 mounted at each end of the heat exchanger. In this embodiment, the impellers comprise centrifugal fan impellers having blades 10 mounted on a backing plate 11 in a conventional manner. The impellers 8,9 are mounted on a single, common shaft 12, driven by a motor 13 at one end of the assembly.

The shaft passes through a support 14 at the end plates of the heat exchanger. As illustrated, the centrifugal impellers are mounted such that, when rotated, each impeller acts to draw air through a respective set of channels, in opposite directions, thereby creating a counter-current flow. The use of centrifugal fan arrangements allows identical fans to be used at each end, driven by a common motor, without the need to provide "mirror image" fan blades to provide air propulsion in different directions. Centrifugal fans also provide considerable air movement in a compact unit.

Figure 2 illustrates a cross-section through a notional "outflow" channel, with air being drawn into the channel through the hole 14, along the channel, and expelled by the centrifugal fan 9 at the other end. Arrows in Figure 2 indicate the airflow.

Figure 3 illustrates a similar schematic cross-section through a heat recovery ventilation system 5 incorporating the heat exchanger of Figure 1, but this time along line A-A'. For clarity, the motor and shaft are not illustrated. This section is though a notional "inflow" channel, with air being drawn in through the holes 14 at the corresponding other end of the heat exchanger to the channel illustrated in Figure 2, along the channel, and expelled (e.g. into a room) by the centrifugal fan 8 at the other end of the heat exchanger.

Figure 4 illustrates a similar schematic cross-section, this time along line C-C' of Figure 1, illustrating then use of cowls 15, 16 at each end of the heat exchanger 1, to redirect the incoming and outgoing air flow at each end of the heat exchanger. The inner cowl 15 is arranged to redirect the radial flow of air from each centrifugal fan 8,9 50 that it is ejected approximately along the axis of the conduit 2. The outer cowl 16 serves to draw air into the heat exchanger's channels, again from a direction approximately along the axis of the conduit; this can have the benefit of reducing staining of walls through which system passes that might otherwise result from dust entrainment in the radial flow. If the outer cowl 16, is omitted, however, there is less mixing between the incoming and outgoing streams of air, and the heat-transfer efficiency of the device is improved.

Figure 7 illustrates an end view of a further embodiment of a heat exchanger according to the present invention, generally indicated by 1. The heat exchanger has a conduit 2 in the form of a circular cross-section tube within which are a number of spaced apart heat-conducting barriers 3, extending substantially along the length of the conduit 2. Again, the barriers 3 define two sets of channels 4, extending along the conduit. The channels are defined as inflow or outflow channels by the partial closure of the channels at the end of the heat exchanger 1. A first set of channels 4A are open to a central region of the end of the conduit 2. Other portions of these channels 4A are closed at a peripheral region of the conduit, as indicated by the hatching in Figure 7. The second set of channels 4B are open only to a peripheral region of the end of the conduit 2, again illustrated in Figure 7, where the hatching indicates closure of the channel. On the other end of the heat exchanger, corresponding opposite ends if the channel are blocked as illustrated in Figures 8 and 9.

Channels from the two sets of channels are arranged adjacent each other, most preferably alternately, to provide maximum heat transfer from gas in one set of the channels to gas in the other set of channels.

Figure 8 is a schematic cross-section of a heat recovery ventilation system generally indicated by 5, incorporating the heat exchanger 1 of Figure 7. Additionally illustrated are impellers 8, 9 which in this embodiment are of propeller form the impellers are preferably driven by a single motor, and more preferably mounted for rotation on a single common shaft (not illustrated for clarity). The propellers are configured such that they move air in opposite directions. Figure 8 is a cross-section through line D-D' of Figure 7, and illustrates the action of impeller 9 in drawing air through the end holes 14 in the peripheral region of the left-hand (as illustrated) end of the heat exchanger, and out through the central region of the end of the heat exchanger at the right-hand end as illustrated by the arrows in Figure 8.

Figure 9 is a similar schematic cross-section to Figure 8, but taken through the line E-E' of Figure 7. In this channel, air is drawn through the holes 14 in the peripheral region at the right hand end of the heat exchanger (as illustrated) by the action of impeller 8, and expelled through the central region at the left-hand end, as illustrated by the flow arrows.

The impellers are arranged to act only on the central region illustrated by the circle 20 in Figure 7, by means e.g. of a cowl arrangement 21 illustrated in Figures 8 and 9 at each end of the heat exchanger 1.

Figure 10 illustrates a yet further embodiment of a heat exchanger of the present invention comprising a rectangular conduit 2 mounted within a sleeve 22. Heat-conducting barriers 3 are located within the conduit, again in a spaced-apart fashion, along the length of the conduit. The two sets of channels are defined by closing one or another end of the channels at the end face of the heat exchanger. In the end of the channels having a closed end, an opening in the conduit 2 communicates with a gap 23 between the conduit 2 and the sleeve 22 close to the end face of the heat exchanger, as illustrated in the schematic cross-sections of Figures 11 and 12.

Figure 11 shows a schematic cross-section through line F-F' of a heat recovery ventilation system incorporating the heat exchanger of Figure 10. Centrifugal fans 8 and 9 are position to act on the central region of the face of the heat exchanger indicated by circle of Figure 10. A cowl arrangement similar to that illustrated in Figures 4, 8 and 9 may be used to direct the air flows. Fan 9 acts to draw air into the gap 23 (which is blocked part way down the conduit by a barrier 24), through a hole 14, into the channel 4 to be expelled at the opposite end.

Figure 12 is a schematic cross-section though line G-G' of the system of Figure 10. Fan 8 acts to draw air in an opposite direction, though the gap 23 and into the channel 4, via the hole 14, to be expelled at the other end of the channel.

Particular features of the invention provide distinct advantages over the known prior art: The arrangement of the heat exchanger allows the to impellers of the unit to be driven by a single motor, for example through a common shaft. This allows for a very compact unit that can be readily fitted within a standard nominal 4 inch (100mm) ventilation extract duct. Furthermore, having only a single motor, the unit can be arranged with the motor on the inside of an external wall of a house, thereby keeping the electrical parts of the apparatus protected from the outside weather.

Claims

CLAIMS1. A heat exchanger for a heat recovery ventilation system comprising: a conduit; a plurality of heat-conducting barriers arranged within the conduit defining two sets of flow channels running along the conduit; the first set of channels arranged to open to the end of the conduit at the first end of the conduit and to open through a side wall of the conduit adjacent the second end of the conduit; and the second set of channels arranged to open to the end of the conduit at the second end of the conduit and to open through a side wall of the conduit adjacent the first end of the conduit; said flow channels being arranged such that channels in the first set are adjacent channels in the second set, thereby allowing heat to be transferred from gas in channels in the first set to gas in channels in the second set, via said heat-conducting barriers.
2. A heat exchanger for a heat recovery ventilation system comprising: a conduit; a plurality of heat-conducting barriers arranged within the conduit defining two sets of flow channels running along the conduit; the first set of channels arranged to open to a central region of the end of the conduit at the first end of the conduit and to open only to a peripheral region of the conduit adjacent the second end of the conduit; and the second set of channels arranged to open to a central region of the end of the conduit at the second end of the conduit and to open only to a peripheral region of the conduit adjacent the first end of the conduit; said flow channels being arranged such that channels in the first set are adjacent channels in the second set, thereby allowing heat to be transferred from gas in channels in the first set to gas in channels in the second set, via said heat-conducting barriers.
3. A heat exchanger according to claim 1 or claim 2 further comprising a sleeve surrounding said conduit and wherein openings in the side wall of the conduit are in communication with a gap between the sleeve and the conduit.
4. A heat exchanger according to claim 3 wherein said sleeve has a circular cross-section and said conduit has a rectangular cross-section.
5. A heat exchanger according to any preceding claim comprising heat-conducting barriers having a non-planar profile.
6. A heat exchanger substantially as described herein, with reference to and as illustrated by, any appropriate combination of the accompanying drawings.
7. A heat recovery ventilation system comprising: a heat exchanger according to any preceding claim; an impeller mounted at each end of said conduit, said impellers configured to draw air in opposite directions through respective sets of channels, thereby creating a counter-current flow through said heat exchanger.
8. A ventilation system according to claim 7 wherein said impellers comprise centrifugal fans.
9. A ventilation system according to either claim 7 or claim 8 wherein said impellers are configured to be driven by a single motor.
10. A ventilation system according to claim 9 wherein said impellers are mounted for rotation on a common shaft.
11. A ventilation system according to any of claims 7 to 10 configured such that, on installation, said heat conducting barriers are oriented substantially vertically.
12. A ventilation system substantially as described herein, with reference to and as illustrated by, any appropriate combination of the accompanying drawings.