GB2361991A

GB2361991A - A Heat Recovery Unit

Info

Publication number: GB2361991A
Application number: GB0105310A
Authority: GB
Inventors: Robert Donald Aldo Spearman
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 2000-03-10
Filing date: 2001-03-05
Publication date: 2001-11-07
Also published as: GB0105309D0; GB0105310D0; GB2361993A

Abstract

A heat recovery unit has a stack 42 of aluminium plates 43 arranged so that warm air flows between adjacent pairs of plates in one direction and cool air flows in an orthogonal direction between other pairs of plates taking up heat from that conducted through the plates. The plates 43 are spaced one above the other by clips 65 at the edges of the plates. The plates 43 have dimples 64 one or both surfaces to promote transfer of heat between the air and the plates. The dimples are preferably about 3mm deep and 4mm wide with a spacing between dimples of preferably 15mm and no more than 25mm. The heat recovery unit 41 can form part of a room ventilation system with an extract vent and filter to cool and filter air and return it to the same room.

Description

2361 R91 VENTILATION SYSTEMS AND HEAT RECOVERY This invention relates to

ventilation systems and heat recovery.

In various building spaces there can be regions where there is excessive heat or pollution and different regions where maximum supply of fresh air is needed. For example, in pubs and clubs body heat in the centre of the room can raise the temperature above a comfortable level and there may also be excessive levels of smoke or alcohol fumes. It is preferable, however, that any fresh air supplied to such a room be delivered preferentially to the region behind the bar where staff work since they are exposed to the environment for prolonged periods. In conventional situations of this kind, extractor fans are provided in the main part of the room to vent the smoke and excessive heat, and air inlets open in the bar region so that fresh air is supplied to the bar region. The problem with such an arrangement is that the heat in the air vented externally is lost and that energy has to be consumed to warm the inlet fresh air.

Heat recovery units are commonly used to transfer some of the heat in air exhausted from a room to fresh air. Such heat recovery units can have a high efficiency of heat transfer but usually have a relatively high resistance to flow, which can make them unsuitable for some applications.

It is an object of the present invention to provide an alternative heat recovery unit.

2 According to the present invention there is provided a heat recovery unit including a stack of a plurality of thermally-conductive plate members spaced above one another and providing two separate air flow paths between pairs of adjacent plate members whereby heat in air flowing along one path is conducted through the plate members to warm air flowing along the other path, the plate members being formed at least on one surface with an array of dimples arranged to promote transfer of heat between the air and the plate members.

The dimples are preferably formed on both surface of the plate members. The plate members are preferably of metal, such as aluminium and may be substantially 0.25mm thick. The stack preferably has four sides, each side providing an inlet or outlet of one of the flow paths. The dimples may be substantially 3mrn deep and 4mm wide, and the spacing between adjacent dimples is preferably no more than about 25mm and is preferably substantially 15nun. The plate members may be retained at their edges by clips, each clip preferably having two channels that resiliently engage the edges of adjacent plate members.

A ventilation system and heat recovery unit according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of the ventilation system installed in a room; Figure 2 is an enlarged perspective view of a part of the system of Figure 1; Figure 3 is a schematic perspective view of the heat recovery unit; and 3 Figure 4 is a more detailed perspective view of the heat recovery unit.

With reference first to Figures 1 and 2, the ventilation system is indicated generally by the numeral 1 and is installed in a room 2 of a building having an outside wall 3. The room 2 has a first region 20, in which smoke or other contaminants and excess heat is generated and a different region 21 where the enviromnent must be kept as unpolluted as possible for the comfort and health of workers in this region. The ventilation system 1 is installed within the ceiling 4 of the room or may be fastened beneath the ceiling.

The ventilation system 1 has an extract vent 30 located in the warm, polluted region 20, which includes a smoke filter 3 1, such as an electrostatic filter. Alternative air treatment means could be used, such as humidifiers or dehumidifiers, electrostatic particle removers, ionizers or the like. The vent 30 forms the lower wall of a box-like casing 32 containing a conventional fan or other air mover 33. The casing 32 opens on one side 34, the fan 33 being arranged to draw air in through the vent 30 and filter 31 and to expel it through the open side. The open, downstream side 34 connects with one side 40 of a heat exchange or heat recovery unit 41 having a square shape in section.

The heat recovery unit 41 may contain any conventional heat recovery element of the kind having two separate air flow paths by which heat in air flowing along one path is transferred in part to air flowing along the other path. Preferably, however, the heat recovery element 42 is of the kind shown in Figures 3 and 4, the construction of which will be described later.

4 Air supplied to the inlet side 40 of the heat recovery unit 41 flows through and out of its opposite, outlet side 44, after having given up a part of its heat to the heat recovery element 42. The outlet side 44 of the heat recovery unit 41 connects with a short diverter 45 having a curved upper wall and opening at its lower surface through the ceiling 3 via an inlet vent 46. Warm, smoke-laden air is, therefore, drawn from the region 20 through the extract vent 30, it is filtered by the filter 3 1, cooled by the heat recovery unit 41 and is returned to the room 1 via the inlet vent 46 close to the extract vent and in the same region.

1 The system also includes a duct 50 extending at right angles to the air flow path between the extract and inlet vents 3 0 and 46. The duct 5 0 opens at one end 5 1, externally of the room 1, through a hole 52 in the wall 3. A fan 53 is mounted at some position along the duct 50, so as to draw external air into and along the duct. The opposite end 54 of the duct 50 opens through an inlet vent 55 located in the second region 21. Between its two ends 51 and 54, the duct 50 is connected in series with the heat recovery unit 41 so that all the air passing along the duct flows through the heat recovery unit along a path separate from the path of air extracted from within the room. The relatively cold air from outside the room 1 is, therefore, warmed by passage through the heat recovery unit 4 1. The air delivered at the vent 5 5 to the region 21 is, therefore, fresh external air but is warmed above the outside temperature.

Referring now to Figures 3 and 4, the construction of the heat recovery unit 41 will be described in more detail. The heat recovery unit 41 has a recovery element 42 comprising a stack of several thin plates 43 of aluminium, about 0.25nim. thick. Alternatively, some other heat conducting material could be used. The plates 43 are each formed with dimples 64 over one or, preferably, both surfaces, such as by CNC machining. The dimples 64 are preferably about 3mm deep and 4mrn wide and the spacing between adjacent dimples is preferably about l5mm and no more than about 25mm. The plates 43 are retained spaced above one another in a stack by means of edge clips 65.

The clips 65 are extruded or formed from a spring metal or plastics and have two parallel channels 66 spaced from one another across the width of the clip by a spacer section 67. The dimensions of the channels 66 are such that they engage resiliently the edges of the plates 43, the width of the spacer section 67 being selected to produce the desired spacing between the plates. The stack of plates has four sides A, B, C and D, two clips 65 are used to retain the lowest pair of two plates 43 in the stack with one another, the clips being fastened to opposite edges of the adjacent plates on sides A and C. A further pair of clips 65 is fastened to the other two edges of the second and third plates 43 in the stack on sides B and D. A third pair of clips is fastened to the third and fourth plate 43 on sides A and C and so on. The ends of the clips 65 are mitred at 45' so that clips engaging adjacent edges of the same plate can fit together. The complete stack of plates 43 provides, therefore, two isolated, orthogonal air flow paths through it parallel to the planes of the plates. Each air flow path comprises a number of parallel paths between adjacent pairs of plates 43 and opening at those edges not blocked by clips 65. The dimples 64 on the plates 43 have been found to disturb air flow sufficiently to produce efficient transfer of heat between the air and the plates without significantly increasing resistance to flow. Heat given up to the plates 43 by air flowing along one path is readily conducted through the thickness of the plates to their opposite surface where heat is given up to air flowing along the other path. The efficiency of heat transfer between the two different air flow paths can be increased by reducing the spacing between 6 the plates 43 but with the penalty of an increased resistance to flow. In the present application it is more important for the heat recovery unit 41 to provide a low resistance to flow so that the maximum volume of air can be filtered.

The ventilation system of the present invention provides air cleaning and cooling in regions of maximum contamination and excess heat, and also enables the heat extracted from the contaminated air to be used to warm fresh air supplied to a different region.

It will be appreciated that the,heat recovery unit of the present invention could be used in other systems and is not confined to use in the system of the present invention.

7

Claims

CLAIMS 1. A heat recovery unit including a stack of a plurality of thermallyconductive plate members spaced above one another and providing two separate air flow paths between pairs of adjacent plate members whereby heat in air flowing along one path is conducted through the plate members to warm air flowing along the other path, wherein the plate members are formed at least on one surface with an array of dimples arranged to promote transfer of heat between the air and the plate members.

1

2. A unit according to Claim 1, wherein the dimples are formed on both surfaces of said plate members.

3. A unit according to Claim 1 or 2, wherein the plate members are of metal.

4. A unit according to Claim 3, wherein the plate members are of aluminium.

5. A unit according to any one of the preceding claims, wherein the plate members are each substantially 0.25mrn thick.

6. A unit according to any one of the preceding claims, wherein the stack has four sides, and wherein each said side provides an inlet or outlet of one of said flow paths.

7. A unit according to any one of the preceding claims, wherein the dimples are substantially 3nim deep.

8 8. A unit according to any one of the preceding claims, wherein the dimples are substantially 4ram wide.

9. A unit according to any one of the preceding claims, wherein the spacing between adjacent dimples is no more than about 25mm.

10. A unit according to Claim 9, wherein the spacing between adjacent dimples is substantially 15mm. 1

11. A unit according to any one of the preceding claims, wherein the plate members are retained at their edges by clips.

12. A unit according to Claim 11, wherein each said clip has two channels that resiliently engage the edges of adjacent plate members.