GB2539912A

GB2539912A - Heat recovery device

Info

Publication number: GB2539912A
Application number: GB1511465.5A
Authority: GB
Inventors: Callaghan Nicholas; Hulston Wayne
Original assignee: IMPROVAIR THERMAL RECOVERY SYSTEMS Ltd
Current assignee: IMPROVAIR THERMAL RECOVERY SYSTEMS Ltd
Priority date: 2015-06-30
Filing date: 2015-06-30
Publication date: 2017-01-04
Also published as: GB201511465D0

Abstract

A heat recovery device comprises a sheet of heat conductive material 12, such as copper, with a plurality of fluid tight compartments 14 connected by fluid conduits 16, which may be pipes in series. The compartments may be shallow, rectangular enclosures formed from plates 18 fixed to the sheet, and may include baffles (e.g. 514, fig 5). The device can be used in an air extraction system (100, fig 2), and form a top sheet or back sheet of an extractor canopy (102) for cooking appliances. A second heat recovery means may be located adjacent an extraction duct (104) by surrounding a section (104a) of the duct, with a third heat recovery means adjacent a terminal end of the duct. The device can be used to heat water in a stratified tank (120) for a hot water supply (130) or heating system (136). The tank may comprise a coil (126) connected to a solar collector (132).

Description

Heat recovery device

TECHNICAL FIELD

This invention relates to a heat recovery device, more specifically to a heat recovery device for use in an air extraction system.

BACKGROUND

Most commercial buildings, whether schools, hospitals, restaurants, hotels, food processing plants or other industrial processing plants have areas, such as kitchens and other processing areas where heat and combustion gases or other hot gases are generated, that are provided with heat and vapour extraction systems. These systems typically vent heated air along with any other contaminating vapours and gases to atmosphere. In kitchens the heat and combustion gases generated during cooking operations are typically vented through an extraction canopy and associated ductwork. At the same time, the relevant buildings all have a supply of hot water for various uses throughout the building. Typically, a direct hot water cylinder is provided to store water and heated to temperatures in the region of 70° C. When a portion of the hot water is run off for use in an appliance or for hand washing etc., this water is replaced in the tank by cold water, often mains cold water, which is generally at around 10° C. Energy is always needed to keep the temperature of the water in the tank at around 70° C. Consequently, such a hot water/heating system consumes a large amount of heat energy and is expensive to operate, as well as being inefficient.

It is recognised as generally desirable to provide an energy recovery system in conjunction with a heated air and vapour extraction system in order to collect and reuse waste heat energy, which is otherwise vented to atmosphere. Various proposals for recovery of waste energy have, accordingly, been proposed.

It is an object of the present invention is to provide heat exchanger apparatus of improved efficiency, which is suitable for energy recovery in an air extraction system of the aforesaid type.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a heat recovery device comprising a sheet of heat conductive material provided with a plurality of fluid tight compartments, these compartments being in communication with each other by way of fluid conduits so that a fluid can flow through each of the compartments in turn, absorbing heat energy from the sheet. This arrangement advantageously provides an efficient means of heat transfer from the sheet into the fluid flowing through the heat recovery device.

In preferred embodiments, each of the plurality of fluid tight compartments is formed from a respective plate affixed to a first major surface of the sheet of heat conductive material. This arrangement constitutes a practical means of constructing a heat recovery device. Each plate may be bonded to the sheet of heat conductive material by an adhesive substance or a solder.

The plurality of fluid tight compartments may be in the form of shallow, blister-like enclosures. Moreover, the plurality of fluid tight compartments may be in the form of substantially rectangular enclosures.

Preferably, the fluid conduits are in the form of pipes extending between adjacent compartments. Further, it is optional that one or more of the plurality of fluid tight compartments includes at least one baffle to guide the flow of fluid flowing therethrough.

The sheet of heat conductive material may consist of or include copper.

In certain embodiments, the sheet of heat conductive material serves as a top sheet of an extractor canopy of an air extraction system. In certain embodiments, the sheet of heat conductive material may serve as a back sheet below an extractor canopy of an air extraction system. In certain embodiments, the sheet of heat conductive material may serve as a side wall of a heat exchange outlet chamber of an air extraction duct. In certain embodiments, the sheet of heat conductive material may serve as a side wall, or be mounted to a side wall, of an air extraction duct.

According to a further aspect of the invention, there is provided an air extraction system incorporating a heat recovery device as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:

Figure 1 is a perspective view of a practical embodiment of a heat recovery device in accordance with the invention;

Figure 2 is a schematic diagram of a combined air extraction and heat recovery system incorporating the heat recovery device of Figure 1;

Figure 3 is a part sectional front view of an apparatus incorporating the heat recovery device of Figure 1;

Figure 4 is a part sectional side view of the apparatus of Figure 3;

Figure 5 is an internal view of a practical embodiment of a component part of a heat recovery device in accordance with the invention; and

Figure 6 is an internal view of a further practical embodiment of a component part of a heat recovery device in accordance with the invention;

DETAILED DESCRIPTION

Figure 1 illustrates a practical embodiment of a heat recovery device 10 according to the invention for incorporation in a combined air extraction and heat recovery system. The device 10 includes a substantially rectangular sheet of heat conductive material 12 having a major surface 12a and an upturned edge margin 13 extending around the perimeter thereof. In the illustrated embodiment, the sheet 12 is formed from copper, as copper is known for its excellent heat transfer properties by conduction and radiation. Flowever, it will be understood that in alterative embodiments the sheet 12 may be formed from any other suitable heat conductive material. The sheet 12 is provided with a plurality of fluid tight compartments 14 connected in series by fluid conduits 16. The fluid tight compartments 14 are formed as shallow, blister-like enclosures on the major surface 12a of the sheet 12, provided within the confines of the upturned edge 13. As illustrated in the accompanying drawings, the compartments 14 may be substantially rectangular enclosures arranged in an evenly spaced grid-like array over of the surface 12a of the sheet 12.

The compartments 14 may be formed from plates 18 pressed out of a heat conductive material, e.g. copper, and subsequently affixed to the sheet 12. Thus, each plate 18 may be configured as a shallow tray with downturned side walls having edges affixed to the sheet 12. The plates 18, at their edges, may be bonded to the sheet 12 by an adhesive substance, for example an epoxy or polyurethane adhesive bonding compound. Alternatively, the plates 18, around their edges, may be soldered or welded to the sheet 12. The fluid conduits 16 are in the form of pipes extending between adjacent compartments 14. Each compartment 12 has a fluid inlet and a respective fluid outlet. The outlet of one compartment 14 may be connected to the inlet of an adjacent compartment 14 by a respective conduit 16. However, the inlet of one compartment 14 and the outlet of another compartment 14 are connected to a wider fluid circulation system for supplying and removing fluid to/from the device 10. In use, a fluid flows through the compartments 14 in turn absorbing heat energy from the sheet 14.

Figure 2 shows a practical embodiment of a combined air extraction and heat recovery system, denoted generally at 100. The system 100 includes an extractor canopy 102 providing a plenum there below and an extraction duct 104 leading upwards from the side of the canopy 102. Note that the canopy 102 is shown first in plan view and again, beneath the plan view, in side view. An exhaust fan (not shown) is provided within the extraction duct 104 which propels exhaust air, fumes, etc. to atmosphere. The canopy 102 is fabricated, as is conventional, of a number of panels, typically side panels 106, which may be substantially vertical or may be sloping and which define the outer extent of the plenum, and one or more top panels 108, 110. In the illustrated embodiment, a front portion of the top of the canopy 100 is provided by a stainless steel top sheet 108 and a rear portion of the top of the canopy 100 is provided by multiple copper top sheets 110. Each of the top sheets 110 is provided as the heat recovery device 10 described above with reference to and as illustrated in Figure 1. The sheets 110 provide a first heat recovery means of the system 100. An inlet 112 for a ventilation duct 114 is formed in the stainless steel top sheet 108.

The sheets 110 are fluidly connected in series and further connected by way of valves 116a, 116b to pipes of a fluid circulation system, designated generally by reference 118, which is typically a water circulation system providing part of the hot water supply and heating system of a building premises in which the extractor canopy is installed. The sheets 110 are overlaid by insulation, such as a conventional high density foam layer, e.g. polyurethane foam layer with a foil outer facing, to minimise loss of heat in an upward direction and maximise heat recovery by transfer to the fluid flowing in the sheets 110.

The hot water supply and heating system 118 also includes a thermal storage device in the form of a stratified thermal store cylinder 120. A coiled section of pipework 122 of the circulation system 118 provides a heating coil within the cylinder 120. This coil 122 is preferably of copper for optimum heat transfer to the water in the cylinder 120. In this embodiment, it is shown as the central one of three stacked coils 122, 124, 126. The upper coil 124, typically of copper, is for heat transfer from water in the cylinder 120 to a hot water supply, namely for receiving cold mains water at a lower inlet 128 and supplying heated water at an upper outlet 130. The lower coil 126, also typically of copper, is for additional heat transfer to the water in the cylinder 120 from water circulated through the coil 126 from a solar thermal collector 132. This optional solar heating circuit is controlled by a pump and control box 134.

The cylinder 120 is also typically and conventionally connected to a heating system for the building premises, namely pipework connecting to radiators 136, only one of which is shown, through which hot water circulates in known manner. The cylinder 120 may also be provided with an emersion heater 138 and will typically have an air vent 140. Various expansion vessels and valves 142a, 142b, 142c are provided at appropriate locations in the pipework of all the circulation systems to control flow of liquid therein.

The heat recovery system 100 also includes second heat recovery means adjacent the extraction duct 104. More specifically, the second heat extraction means surrounds a section 104a of the extraction duct 104. The second heat recovery means comprises sheets of a heat conductive material 212 provided with fluid tight compartments 214 connected in series by fluid conduits 216. Moreover, the sheets 212 may form an integral part of the extraction duct section 104a itself. The compartments 214 connect into the same fluid circulation system 118 by way of further valves 144a, 144b, as is apparent in Figure 2. It will be understood that further features of the second heat recovery means are analogous to those of the heat recovery device 10.

The heat recovery system 100 also includes third heat recovery means adjacent the terminal end of the extraction duct 104, i.e. where the duct 104 leads to the external environment (e.g. outside the building). The terminal end of the extraction duct 104 is provided with an outlet chamber 105. The chamber 105 is fabricated of a number of panels 107 which comprise sheets of a heat conductive material 312 provided with fluid tight compartments 314 connected in series by fluid conduits 316. Once again, the compartments 314 connect into the same fluid circulation system 118, although this arrangement is not shown in Figure 2. It will be understood that further features of the third heat recovery means are analogous to those of the heat recovery device 10.

The operation of this exemplary system in recovery of heat will be readily apparent from the accompanying figures. It has been verified that an extractor canopy top sheet, which is conventionally fabricated of stainless steel, often reaches (and maintains for a significant period of time thereafter) a temperature of over 150° C when cooking or other combustion is taking place there below, as by a cooking appliance (not shown), and the exhaust fan is operating to exhaust air and other gases via the extraction duct 104. By using heat recovery means in accordance with the invention to provide the top panels 110 of the canopy 102 and at least part of the extraction duct 104 and/or the terminal end of the extraction duct 104, a significant amount of heat can be recovered and reused. Of course, it will be understood that recovery means in accordance with the invention may be provided at other locations of a heat recovery system. For example, in alternative embodiments, a heat recovery device in accordance with the invention may form part of substantially vertical surface adjacent a combustion source. Specifically, Figures 3 and 4 show a supporting wall 400 of a canopy 402. The wall 400 incorporates sheets of a heat conductive material 412 provided with fluid tight compartments 414 connected in series by fluid conduits 416.

Use of copper as material of the sheets 110, at least in part, and as material of the exhaust duct 104 and the outlet chamber 105 improves the heat transfer and the amount of heat recovered. The exemplary system uses series of shallow compartments 14, 214, 314 linked to a hot water and heating system 118 with flow of water (or strictly an aqueous solution as additives and contaminants may be present) therethrough to a hot water tank, i.e. stratified cylinder 120, which is then used to heat radiators 136 and hot water supply in an indirect system 126, 128, 130. It is envisaged that by using the exemplary heat recovery system as outlined, a temperature in the range of 40 to 65 °C may be achieved in the cylinder 118, depending upon the available heat. A useful additional option is controlled additional use of solar heating, as indicated.

The top sheets 110 need not be a horizontally aligned. Rather the sheets 110, may be inclined, partially inclined, or otherwise non-planar. In all embodiments it is preferable that heat recovery takes place in inherently safe and non-obstructive locations. The interior of the canopy 102 and duct 104 are to be free of obstacles so no additional surfaces or niches for build-up of grease (a fire hazard) and dirt, no impediment to cleaning of the interior surfaces (important in kitchens for hygiene), no unnecessary hindrances to flow of exhaust gases, and no additional heat sinks are created, thereby maximising heat recovery possibilities.

Any of the compartments 14, 214, 314, 414 of the heat recovery means described may include one or more baffles to guide the flow of the fluid flowing therethrough. Figures 5 shows the inside of an exemplary compartment 512 which includes a single baffle 514. Figure 6 shows the inside of a further exemplary compartment 612 which includes two baffles 614, 616. In alternative embodiments, further baffles may be provided. The baffles may be straight, as illustrated in the accompanying figures, or curved or bent in order to direct the flow as desired.

The air extraction/heat recovery system of the invention may advantageously also include a ventilation system, designated generally by reference 146. A preferred version is shown in the illustrated embodiment. In this preferred version, as shown in Figure 2, a ventilation duct 114 leads from the external environment (e.g. outside the building) to the inlet in the steel top sheet 108 providing the front section of the canopy upper wall. Fresh air (as opposed to the exhaust air which flow up into the exhaust duct and is removed via extraction duct 104 by operation of the extraction fan) is supplied to the room below and around the canopy 102 via air grills 150 in a front wall 152 of the canopy 102.

To demonstrate the efficiency of a heat recovery device according to the invention, the heat transferred into a heat recovery system comprising a canopy with a surface area of 1.28 m^ fitted with known coil arrangement, i.e. a copper pipe bent into a serpentine configuration mounted above a top panel of the canopy, was compared to the same system in which the coil arrangement and panel was replaced with a heat recovery device according to the invention. Heat added to the system, 0, is calculated as the product of the specific heat capacity of the fluid in the system, c, the mass of the fluid in the system, m, and the change in temperature over time, ΔΤ. EXAMPLE 1

Canopy with known coil arrangement

Flow rate of the system: 240 l/hour

Mains cold water average temperature: 14.8 °C

Heated/raised water temperature: 18.8 °C (increase of 4.0 °C)

Q = cmAT = 4.186x240x4.0 = 4019 kJ = 1.12 kWh EXAMPLE 2

Canopy with heat recovery device according to the invention

Flow rate of the system: 360 l/hour

Mains cold water average temperature: 8.1 °C

Heated/raised water temperature: 13.3 °C (increase of 5.2 °C)

0 = cmAT = 4.186x360x5.2 = 7836 kJ = 2.18 kWh

With the canopy provided with the heat recovery device according to the invention the system exhibited increased flow rates and increased heat energy transfer when compared the system when the same canopy was provided with the known coil arrangement.

The invention is not restricted to the details of the forgoing embodiments. Many variations in detail of the practical design are possible in other embodiments, as will be apparent to a person skilled in the technical field. For example, while only first, second and third heat recovery means are shown in the illustrated embodiment it will be understood that multiple heat recovery means, each comprising a device according to the invention, may be incorporated as part of a suitable heat recovery system.

In alternative embodiments, the compartments may be shapes other than rectangular, e.g. the compartments may be triangular or circular.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other components. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

All of the features disclosed in this specification (including any accompanying claims and drawings) may be combined in any combination, except combinations where at least some of such features are mutually exclusive.

Claims

1. A heat recovery device comprising a sheet of heat conductive material provided with a plurality of fluid tight compartments, these compartments being in communication with each other by way of fluid conduits so that a fluid can flow through each of the compartments in turn, absorbing heat energy from the sheet.

2. A heat recovery device according to claim 1, wherein each of the plurality of fluid tight compartments is formed from one of a plurality of respective plates affixed to a first major surface of the sheet of heat conductive material.

3. A heat recovery device according to claim 2, wherein the plates are bonded to the sheet of heat conductive material by an adhesive substance or a solder.

4. A heat recovery device according to any preceding claim, wherein the plurality of fluid tight compartments are in the form of shallow enclosures.

5. A heat recovery device according to any preceding claim, wherein the plurality of fluid tight compartments are in the form of substantially rectangular enclosures.

6. A heat recovery device according to any preceding claim, wherein the fluid conduits are in the form of pipes extending between adjacent compartments.

7. A heat recovery device according to any preceding claim, wherein one or more of the plurality of fluid tight compartments includes at least one baffle to guide the flow of fluid flowing therethrough.

8. A heat recovery device according to any preceding claim, wherein the sheet of heat conductive material consists of or includes copper.

9. A heat recovery device according to any preceding claim, wherein the sheet of heat conductive material serves as a top sheet of an extractor canopy of an air extraction system.

10. A heat recovery device according to any of claims 1 to 8, wherein the sheet of heat conductive material serves as a back sheet below an extractor canopy of an air extraction system.

11 .A heat recovery device according to any of claims 1 to 8, wherein the sheet of heat conductive material serves as a side wall of a heat exchange outlet chamber of an air extraction duct.

12. A heat recovery device according to any of claims 1 to 8, wherein the sheet of heat conductive material serves as a side wall, or is mounted to a side wall, of an air extraction duct.

13. An air extraction system incorporating a heat recovery device according to any of claims 1 to 8.

14. A heat recovery device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.