GB2296968A

GB2296968A - Heat exchange ventilator

Info

Publication number: GB2296968A
Application number: GB9424362A
Authority: GB
Inventors: David Applegate
Original assignee: THERMAL TECHNOLOGY
Current assignee: THERMAL TECHNOLOGY
Priority date: 1994-12-02
Filing date: 1994-12-02
Publication date: 1996-07-17
Also published as: GB9424362D0

Abstract

A ventilation apparatus comprises a box having an inlet 142 and an outlet 146 for fresh air, an inlet 150 and an outlet 154 for vitiated air, and at least two heat exchangers 102, 104 in series. Fresh air 160 is drawn in (by fan 148) through inlet 142, heat exchanger 102, heat exchanger 104 and outlet 146 to the space to be ventilated. Vitiated air 162 is drawn out (by fan 156) through inlet 150, heat exchanger 104, heat exchanger 102 and outlet 154 to atmosphere. The heat exchangers are of the aluminium plate type with corrugated spacers (Fig 2). The heat exchangers may be stacked one above the other to save space (Fig 6).

Description

IMPROVEMENTS IN OR RELATING TO VENTILATION This invention relates to improvements in or relating to ventilation, and in particular concerns ventilation apparatus incorporating heat exchangers.

Air conditioning units or apparatus are commonly used in many buildings, both industrial and domestic, to replace warm vitiated air with cool fresh air. An important disadvantage of many air conditioning units is that they uses CFCs, or chlorofluorocarbons, which are now considered to be unacceptable in the environment.

However, in temperate climates it is often possible to use mechanical ventilation without recourse to the use of air conditioning units. Modern mechanical ventilation systems will use balanced ventilation/heat recovery units which are designed to ventilate buildings efficiently by positive control of both the supply and exhaust air streams. This in itself is a notable advance over the traditional practice of ventilation by fitting a fan in a window or wall, which does little more than to draw air from one room to another, at the same time transferring smells, fumes and moisture. The modern mechanical ventilation systems will extract vitiated air and replace it with clean air directly from the external atmosphere.

This introduction of 100% fresh air, equal to the amount of exhaust air, helps to overcome the "building sickness" syndrome, which is believed to be associated, at least in part, with an inadequate supply of fresh air. The modern mechanical ventilation systems furthermore incorporate heat exchangers to extract heat energy from the outgoing exhaust air and transfer it to the incoming clean air supply, thereby enabling an optimum temperature to be maintained within the building.

It will be convenient to discuss first the technology of a known mechanical air ventilation unit incorporating a heat exchanger (alternatively known as a "recuperator"), which will now be described with reference to Figures 1-3 ofJthe accompanying diagrammatic non-scale drawings.

Figure 1 is a plan view of a known mechanical air ventilation unit.

Figure 2 is a perspective view of a known heat exchanger incorporated in the unit of Figure 1.

Figure 3 is a thermal efficiency nomogram associated with the unit of Figure 1.

Referring to Figure 1 there is shown in plan view a ventilation apparatus comprising a rectangular box 10 divided into four compartments 12, 14, 16, 18 by vertical divider plates 20, 22, 24, 26 extending inwardly from mid-lines on respective walls 28, 30, 32, 34 of the box to meet respective corner edges 36, 38, 40, 42 of a plate recuperator heat exchanger 44, which will be described in more detail with reference to Figure 2. The heat exchanger 44 is cuboid and is positioned diagonally within the box 10 so that vertical sides of the heat exchanger face generally towards the corners of the box.

The divider plates 20-26 are arranged to ensure that the compartments 12-18 are isolated from each other so that interchange of gases (i.e. fresh air or vitiated air, as the case may be) between the compartments is possible only by means of the heat exchanger 44. Thus, as will be explained with reference to Figure 2, gas may flow via the heat exchanger 44 between the compartments 12 and 16, and between compartments 14 and 18, but not between compartments 12 and 14 or between compartments 16 and 18.

Compartment 12 is provided with a supply of fresh air by means of an inlet supply air duct 46 in wall 28. A filter 48 is provided immediately downstream of the inlet duct 46 to filter the incoming supply air. The air in compartment 12 is able to pass through the heat exchanger 44 into compartment 16 to exit therefrom into a building through an exit supply air duct 50 in wall 32. The passage of supply air through the system is ensured by an extraction fan 52 immediately upstream of the exit supply air duct 50. The entire passage of supply air through the system is indicated by arrows 54.

Similarly, exhaust, or vitiated, air enters compartment 18 from the building through a duct 56 and filter 58 in wall 32 and passes through the heat exchanger 44 (the passage of the exhaust air being indicated by arrows 60) into compartment 14 which it leaves via an exhaust duct 62 into the outside atmosphere. As with the supply air, the passage of the exhaust air through the system is ensured by an exhaust extraction fan 64 upstream of the exhaust duct 62.

Referring now to Figure 2, there is shown the heat exchanger 44 which comprises a stack of corrugated aluminium laminates 66, 68, 70, 72, only four of which are shown, although as many as is necessary may be provided in practice. Each laminate consists of a pair of parallel plates of heat conductive material (e.g. aluminium) separated by a corrugated member which in cooperation with the plates provides channels through the laminate. Clearly, when the laminates are stacked it may be arranged that adjacent laminates share a plate. The laminates are stacked so that the channels in one laminate are at right angles to the channels in immediately adjacent laminates.

As will be understood from Figure 2, the stream of gas 54 travels through the channels of laminates 66 and 70, but not through the channels of laminates 68 and 72, while the stream of gas 60 travels through the channels of laminates 68 and 72, but not through those of 66 and 70. Heat exchange between the gas streams 54 and 60 is thus achieved.

In a typical prior art example using a ventilation unit similar to that described above, together with the thermal efficiency nomogram of Figure 3, the efficiency of the system is calculated as follows.

Assume the following measured values for the inlet air at duct 46 and the exhaust air at duct 56: (a) supply air volume = 300 l/s (Qa) (b) supply air temperature = -1 C (Ta) (c) exhaust air volume = 300 l/s (Qc) (d) exhaust air temperature and humidity = 21"C (Tc), at 50% saturation then, (1) Calculate temperature difference between the supply and exhaust air streams: Tc-Ta = 21-(-1) = 220C (2) Calculate air mass imbalance ratio: Qa/Qc = 300/300 = 1 (3) Find efficiency ("n") from Figure 3, starting at the bottom left hand side: n = 55% (4) Calculate supply air temperature (Tr) at duct 50: Tr = Ta+n(Tc-Ta) = -1+0.55x(21-(-1)) = 11.1"C (5) Estimate amount of heat saved (Qs): Qs = 300/1000 x 1.23 x (Tr-Ta) = 4.46kW It will be understood that in some circumstances a supply air temperature of 11.1"C at duct 50 may be considered to be too low and that it accordingly will be necessary to heat the supply air further at this point.

It is an objective of the present invention to provide an improved air ventilation apparatus that achieves a very high level of energy efficiency, is very suitable for low energy use, and avoids the need for further heating of the supply air on its introduction to the building.

According to the present invention there is provided a ventilation apparatus comprising a box having an inlet and an outlet for fresh air, an inlet and an outlet for vitiated air, and at least two heat exchangers within the box, each heat exchanger having first and second regions for the passage there through of fresh air and vitiated air respectively, the arrangement of the regions within a said heat exchanger being such that heat exchange between the vitiated air and the fresh air is able to take place, characterised in that the fresh air and vitiated air regions of a first said heat exchanger are in series communication with the respective fresh air and vitiated air regions of a second said heat exchanger.

Preferably, fans are provided to drive fresh air and vitiated air respectively through the apparatus.

The invention will now be described by way of non-limiting examples only with reference to Figures 2 and 4-6 of the accompanying diagrammatic non-scale drawings of which, Figure 4 is a plan view of a first embodiment of an air ventilation apparatus according to the invention; Figure 5 is a thermal efficiency nomogram associated with the ventilation apparatus of the invention; and Figure 6 is a perspective view of a second embodiment of an air ventilation apparatus according to the invention.

Referring now to the embodiment of Figure 4 there is shown in plan view a ventilation apparatus according to the invention comprising a rectangular box or casing 100 in which there are provided two heat exchangers 102, 104, each of which is of similar cuboid shape, construction and mode of operation to the heat exchanger 44 described above with reference to Figure 2, and so have similar provision for distinct streams of gas to pass through in different directions and exchange their heat content.

Within the box 100 the heat exchangers 102, 104 are positioned horizontally and diagonally such that, (a) a corner edge 106 of heat exchanger 102 makes sealing contact with a middle region of a first end wall 108 of the box 100, (b) a corner edge 110 of heat exchanger 104 likewise makes sealing contact with a middle region of a second end wall 112 of the box opposed to the first end wall, (c) corner edges 114, 116 of the heat exchangers, diagonally opposed to respective corner edges 106 and 110, make sealing contact together in the middle of the box, and (d) the remaining corner edges 118 and 120 of heat exchanger 102 and corner edges 122 and 124 of heat exchanger 104 make sealing contact with opposed side walls 126 and 128 of the box.

Heat exchanger 102 in cooperation with box end wall 108 and side walls 126, 128 therefore defines compartments 130, 132 respectively at one end of the box. Likewise, heat exchanger 104 in cooperation with box end wall 112 and side walls 126, 128 defines compartments 138, 140 respectively at the other end of the box. Both heat exchangers in cooperation with box side walls 126, 128 define side compartments 134, 136 respectively of the box.

The heat exchangers 102, 104 are arranged so that compartments 130, 136 and 138 are interlinked for the flow of one stream of gas therethrough, and compartments 140, 134 and 132 are likewise interlinked for a second stream of gas to flow there through.

An inlet duct 142 and filter 144 for clean supply air are provided in box end wall 108 leading into compartment 130.

An exit duct 146 and fan 148 in box end wall 112 leading from compartment 138 enable clean supply air to be brought into a room or building from the ambient atmosphere.

A duct 150 and filter 152 for vitiated air are provided in box end wall 112 leading into compartment 140. An exit duct 154 and fan 156 in box end wall 106 leading from compartment 132 enable vitiated air from the room or building to be ejected into the ambient atmosphere, preferably into a location where the ejected vitiated air is not likely to be drawn into the inlet duct 142.

Hence, the two heat exchangers 102, 104 are provided in series, and clean inlet air and vitiated exhaust air pass through them in contraflow via the compartments 130-140. The sealing between the compartments 130-140 is such that a communication between them is solely by means of the heat exchangers 102, 104. Arrows 160 and 162 indicate the pathways through the apparatus taken by the clean inlet air and vitiated exhaust air respectively.

Drain plugs 158 provided with air break pipe traps are located in one or more of the exhaust air compartments 132, 134, 140 to allow condensate to drain away.

The efficiency of the ventilation unit of the invention described above with reference to Figures 2 and 4 is calculated as follows with reference to the thermal efficiency nomogram of Figure 5.

Assume the following measured volume values for the inlet air at duct 142 and the exhaust air at duct 150: (a) supply air volume = 1000 l/s (Qa) (b) supply air temperature = -1 C (Ta) (c) exhaust air volume = 1000 l/s (Qc) (d) exhaust air temperature and humidity = 21"C (Tc), at 50% saturation then, (1) Calculate temperature difference between the supply and exhaust air streams: Tc-Ta = 21-(-1) = 22"C (2) Calculate air mass imbalance ratio: Qa/Qc = 1000/1000 = 1 (3) Find efficiency ("n") from Figure 5, starting at the bottom left hand side: n=80% (4) Calculate supply air temperature (Tr) at duct 146: Tr = Ta+n(Tc-Ta) = -1+0.80x(21-(-1)) = 16.6"C (5) Estimate amount of heat saved (Qs): Qs = 1000/1000 x 1.23 x (Tr-Ta) = 21.7kW These calculations show that the ventilation apparatus of the invention achieves a very high level of energy efficiency and is ideal for low energy use systems. Efficiencies of up to 90% are obtainable under the right conditions. The invention is especially suitable for use with positive displacement ventilation systems because the recovered supply air temperature is at an ideal level and does not require further heating before being re-introduced into the building.

Figure 6 shows a second embodiment of the invention which operates in the same manner as the first embodiment of Figure 4, features the same as or similar to those of Figure 4 being given the same numbers as in Figure 4. The main difference between the first and second embodiments is that the heat exchangers 102 and 104 are now not positioned in the same plane but are placed one on top of the other. This positioning gives a more compact arrangement in the second embodiment which may be more appropriate in some working installations.

In the second embodiment, as in the first embodiment, the air flows in both directions pass through the heat exchangers 102, 104 in series, and the sealing arrangements between the heat exchangers and the external casing 100 are again such that mixing of the incoming supply air and the outgoing exhaust air cannot take place.

Claims

1. A ventilation apparatus comprising a box having an inlet and an outlet for vitiated air, and at least two heat exchangers within the box, each heat exchanger having first and second regions for the passage therethrough of fresh air and vitiated air respectively, the arrangement of the regions within a said heat exchanger being such that heat exchange between the vitiated air and fresh air is able to take place, characterised in that the fresh air and vitiated air regions of a first said heat exchanger are in series communication with the respective fresh air and vitiated air regions of a second said heat exchanger.

2. An apparatus as claimed in claim 1 wherein there are provided fans to drive fresh air and vitiated air respectively through the apparatus.

3. An apparatus as claimed in any preceding claim wherein the heat exchangers are arranged within the box so as to provide at least one first compartment within the box but external of the heat exchangers for the passage of fresh air, and at least one second compartment within the box but external of the heat exchangers for the passage of vitiated air, there being no communication between a said at least one first compartment and a said at least one second compartment, the arrangement being that communication between one first compartment and another first compartment is solely by means of one or more said heat exchangers, and communication between one second compartment and another second compartment is solely by means of one or more said heat exchangers.

4. An apparatus as claimed in claim 3 wherein each said first or second compartment is defined by one or more walls of the box, the walls of one or more said heat exchangers, and seals between one or more said heat exchangers and the wall of the box.

5. An apparatus as claimed in claim 3 or 4 wherein at least one second compartment is provided with drain means to permit the drainage of condensed water.

6. An apparatus as claimed in claim 5 wherein the drain means is provided with a trap to permit the drainage of condensate only.

7. An apparatus as claimed in any preceding claim wherein one said heat exchanger is located above another said heat exchanger so as to provide a compact arrangement.

8. A ventilation apparatus substantially as hereinbefore described with reference to Figures 4 and 6 of the accompanying drawings.