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Title:
AIR COOLING APPARATUS
Document Type and Number:
WIPO Patent Application WO/1995/033960
Kind Code:
A1
Abstract:
Air cooling apparatus has a casing (1) containing two air flow paths (12, 14) through one of which (14) cooled fresh air is supplied to a house, while the other (12) receives stale air from the house. An efficient heat exchanger (10) pre-cools the fresh air with heat extracted from the stale air. Further cooling is achieved by evaporative cooling of water from two honeycomb structures (15, 16) respectively spanning the two air flow paths. A pump (17) circulates cooled water to the upper end of one of the structures (15) from the lower end of the other structure (16) which receives, at its upper end, the water which has percolated down through the upper structure.

Inventors:
Urch
John
Francis
Application Number:
PCT/AU1995/000315
Publication Date:
December 14, 1995
Filing Date:
May 30, 1995
Export Citation:
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Assignee:
Urch
John
Francis
International Classes:
F24F12/00; F28C3/08; F24F1/00; (IPC1-7): F24F3/06; F28C3/08
Foreign References:
AU3305757A
AU5604165A
AU1868167A1969-09-11
AU1757088A1988-12-15
AU2200735A
US4380910A1983-04-26
Download PDF:
Claims:
CLAIMS
1. Apparatus for cooling a gas stream, comprising: an isolating heat exchanger providing two gas flow passages between which good heattransfer characteristics occur and each of which has an inlet end and outlet end; first means for circulating two gas streams respectively through the two passages each of which forms part of a different gas flow path through the apparatus; two honeycomb structures as herein defined, each spanning a respective gas flow path; second means for supplying an evaporative liquid to each of the structures to promote their cooling by the partial evaporation into the gas streams of the liquid flowing through the structures; and third means for collecting the liquid cooled by descent through one of the structures for supplying to the second means.
2. Apparatus as claimed in claim 1 , in which the two structures are arranged one above the other, and distributor means gravity feed liquid from the lower end of the upper structure to the upper end of the lower structure.
3. Apparatus as claimed in claim 1 or claim 2, in which one gas flow path (114, 137) is for fresh air and includes a cooling coil of a closed refrigeration circuit; drainage means are arranged to feed condensate collected beneath the coil to the upper end of the structure spanning the second gas flow path; and valve means are operated when the refrigeration circuit is energised, to transfer cold water from said third means from the upper end of the structure spanning said one gas flow path, to the upper end of the structure spanning the second gas flow path.
4. Apparatus as claimed in claim 1 , claim 2, or claim 3, in which the two structures comprise upper and lower portions of one common structure.
5. Apparatus as claimed in any one of the preceding claims, in which one of the flow paths includes a selectively operable burner for discharging hot products of combustion into the flow path downstream of the heat exchanger, and switching means for rendering the third means inoperable when the burner is in use.
6. Apparatus as claimed in claim 5, having two separate casings one which contains the honeycomb structures and the first, second and third means; and the other casing contains the burner.
7. Apparatus as claimed in claim 6, in which said one casing has a fan selectively movable between two outlets, means for selectively closing one of the outlets, and an opening in the second casing which is connected to receive the output from the fan when discharging into one of the two outlets.
8. Apparatus as claimed in any one of the preceding claims, it is constructed as an airconditioning unit for a dwelling house, one of the flow paths being arranged to supply fresh air to the house, and the other flow path being arranged to extract stale air from the house.
9. Apparatus as claimed in claim 8, constructed as a freestanding unit for siting against one wall of a room.
10. 1 0. Apparatus as claimed in claim 8, constructed to be mounted in the attic space of a house beneath its roof.
Description:
AiR COOLING APPARATUS

FIELD OF INVENTION

THIS INVENTION relates to apparatus for changing the temperature of a gas stream and is particularly, although not exclusively concerned with changing the temperature of an air stream flowing into a room.

STATE OF THE ART

Static evaporative panels of honeycomb structure have been developed for use in apparatus for cooling an air stream and are now commercially available. The panel occupies a static position in the apparatus and provides a multiplicity of through-passages extending between opposite faces of the panel and separated from one another by thin walls. The panel spans the flow path of a gas such as air passing through the apparatus and offers a low impedance to its flow. However it also offers a relatively large surface area contacted by the gas. The panel is normally arranged upright, and water or other evaporative liquid is trickled into the upper end of the panel so that it percolates and/or permeates down through the panel to wet substantially the entire surfaces of its walls exposed to the gas. The material of the panel may be fibrous to assist liquid permeation through it. If the material is not liquid-permeable, it may have its surface which is exposed to the gas coated with a hydrophilic layer. Either technique ensures that the gas contacts a very large area of the liquid during its passage through the honeycomb structure. As the gas passes through the panel, it evaporates some of the water. If the panel is being used as a cooler, the latent heat of evaporation of the water is extracted from the panel which is consequently cooled. The gas stream is thus cooled by its passage through the cooled panel.

Such a panel will hereinafter be referred to as a "honeycomb structure". Such structures are commercially availaole, for example, from the Swedish company AB Carl Munters, under various Trade Marks such as "CELdek" and "GLASdek" and are used in cooling panels, air humidifiers and droplet separators.

In the specification of my published International Patent Application No. PCT/AU93/00078, I have illustrated, in Figure 8, the use of an evaporative honeycomb structure in conjunction with apparatus for cooling an air stream flowing to and from a room. The stale air extracted from the room has water droplets sprayed into it immediately upstream f an evaporative honeycomb structure so that the water droplets

are carried by the air stream into the structure and into heat exchanger which follows it, to maintain its surface area wet. The evaporation of some of this water from the structure and the heat exchanger reduces the stale air temperature by extracting latent heat of evaporation from the structure and the heat exchanger. The stale air cooled by the evaporation of liquid water into it, is used to cool fresh air, passing in counterflow to the stale air, in the heat exchanger. This cooled fresh air is subsequently fed to the room.

OBJECT OF THE INVENTION

An object of this invention is to provide improved apparatus for cooling a stream of gas, such as air.

STATEMENT OF INVENTION

In accordance with the present invention, apparatus for cooling a gas stream comprising: an isolating heat exchanger providing two gas flow passages between which good heat- transfer characteristics occur and each of which has an inlet end and outlet end; first means for circulating two gas streams respectively through the two passages each of which forms part of a different gas flow path through the apparatus; two honeycomb structures as herein defined, each spanning a respective gas flow path; second means for supplying an evaporative liquid to each of the structures to promote their cooling by the partial evaporation into the gas streams of the liquid flowing through the structures; and third means for collecting the liquid cooled by descent through one of the structures and for supplying it to the second means.

SUBSIDIARY FEATURES OF THE INVENTION

The advantage of the invention is that cooling of the fresh air passing through the apparatus is achieved efficiently and without the use of a closed, refrigerant cooling circuit incorporating a motor-compressor circuit such as is used in a conventional house-cooling system. However such a circuit may be used to obtain additional cooling if desired.

INTRODUCTION TO THE DRAWINGS

The invention will now be described in more detail, by way of examples, with reference to the accompanying largely diagrammatic and schematic drawings, in which:-

IN THE DRAWINGS FIGURE 1 is a schematic vertical section through air cooling apparatus mounted in a loft space of a house and used to provide cooled air to the house;

FIGURE 2 shows to an enlarged scale a detail of figure 1 ;

FIGURE 3 shows a modification of the detail of figure 2;

FIGURE 4 shows apparatus for cooling fresh ambient air before it enters a room to be cooled, the apparatus being arranged as a free-standing unit positioned against one outside wall of the room;

FIGURE 5 is a schematic vertical section through a third embodiment of air cooling apparatus mounted in a loft space of a house and used to provide cooled air to the house when the ambient air is hot and relatively humid;

FIGURE 6 shows, to an enlarged scale, a detail of figure 5;

FIGURE 7 shows a modification of the detail of figure 6;

FIGURE 8 shows a floor-standing unit incorporating apparatus for cooling a hot and humid air stream, the unit being sited against one wall of a room which is to be supplied with cooled ambient air obtained from the unit by way of a wall opening located behind it;

FIGURE 9 shows apparatus for selectively providing a stream of cold air or hot air to a room;

FIGURE 10 shows a sixth embodiment of apparatus for providing, selectively, hot or cold air to a house;

FIGURE 1 1 is a cross-section through part of Figure 10 and taken on the line in the direction indicated by the arrows ∑i - XI in that figure; and,

FIGU RE 12 shows, in sectional elevation, a seventh embodiment of apparatus selectively for providing hot or cold air to a room.

DESCRIPTION OF FIRST EMBODIMENT

The apparatus shown in "igure 1 is located in a loft space of a house and is provided with an insulative metal or plastics casing 1 divided horizontally into upper and lower regions by a partition 2. Trunking 3 conveys fresh air to be cooled into the left-hand side of the casing, and further trunking 4 conveys the cooled air into the various rooms of the house. Stale warm air is sucked from the rooms by ducting 5 and, after passing through the apparatus, is expelled, by way of a fan 6, from a grill 7 in the upper left-hand side of the casing, into the loft space and /or outside the house. A second fan 8 on the right-hand side of the upper

region of the casing 1 draws the fresh air into the lower left-hand side of the casing 1 and has a slightly larger flow capacity than the fan 6 to maintain a slightly positive air pressure in the house. The two fans 6 and 8 are driven by a common motor.

A thermally-efficient heat exchanger 10 is located in the lower left-hand region of the casing and is of the design described in detail in my previously referred-to International Patent Application. The heat exchanger provides two mutually-isolated gas flow passages 11 , 13 in good heat-exchange relationship and virtually in counterflow. Each passage of the heat exchanger is arranged in series in a respective air-flow path through the casing. One of these gas flow paths, referenced 12 and shown by the broken arrowed line, conveys the stale air from the house to the fan 6. The other gas flow path, referenced 14 and shown by the arrowed full line, conveys the fresh air from the trunking 3 towards the upper region of the casing 1. A vertical baffle 9 separates stale air flow path 12 adjacent the fan 6, from the air travelling along the path 14.

Two evaporative honeycomb structures 15 and 16 respectively span across the upper and lower regions of the casing 1 towards its right-hand end. These structures provide a multiplicity of parallel gas passages extending at 30° - 60°, usually 45°, to the side faces of the structures. The walls of the passages are made of thin treated fibrous material resembling wood and have good water-absorbing characteristics. Such structures are commercially available under the trade mark CELdek referred to earlier. They offer a low resistance to air flow between opposite side faces of the structure, but a large area of contact between the air and liquid wetting the walls of the structure.

The underside of the lower structure 16 rests in a sump 19, and an adjustable pump 17 operates to circulate the cool sump water to a header 18 provided above the upper structure 15, at a rate determined by the amount of cooling of the fresh air desired. The water discharged from the header 18 percolates and/or permeates downwardly through the upper structure 15, and is collected by a funnel 20, shown more clearly in figure 2, at its lower end above an opening 21 in the partition 2. The funnel 20 prevents the flow of air through the opening 21 and acts to feed the water from the lower end of the upper structure 15, into the upper end of the lower structure 16. After percolating down through the lower structure 16 the water returns to the sump 19. A supply of make-up water is provided at 24 and is fed by a valve 25, controlled by a sump float 26, to the sump to maintain the sump water level sensibly constant.

OPERATION OF FIRST EMBODIMENT

The apparatus operates as follows:

Outside fresh air at an elevated temperature of, say 35°C. and with a wet-bulb temperature of 18°C, enters the casing 1 by way of the trunking 3 and immediately flows via the gas flow path 14 through the heat exchanger 10. Its temperature is rapidly cooled down to about 23°C. in the heat exchanger 10, by the cooler stale air from the room flowing through the heat exchanger 10 via the other path 12. The cooled fresh air from the heat exchanger 10 flows to the evaporative honeycomb structure 15. Water from the pump 17 at a temperature of about 16°C. - 17°C. is fed to the header 18 and percolates and/or permeates down by way of the thin walls of the structure 15. This water maintains the structure 15 cool. Also, some of this water is vaporised into the air flow path 14 so that the latent of heat evaporation is extracted from the structure 15 to cool it still further, by a degree or so, to about 14°C. - 15°C. The temperature of the fresh air leaving the structure 15 and flowing through the trunking 4 is reduced to about 15°C. Its water content per kilo is increased by about 2-3 grams during its flow through the structure 15, but the corresponding level of humidity of between 50% and 60% is quite acceptable.

The temperature of the water leaving the lower end of the structure 15 is at about 15°C. and this is fed by way of the funnel 20 to the upper end of the lower structure 16.

Stale air leaving the house by way of the duct 5 is at a temperature of about 29°C. This flows through the lower structure 16 which reduces the stale air temperature to approximately 16°C. There is a consequential slight increase in the temperature of the water flowing down through the structure 16. However some of this water vaporises into the stale air passing through the structure and the latent heat of evaporation it absorbs offsets, to some extent; the rise in temperature of the water which would otherwise be caused by the heating effect of the stale air passing through the structure. The temperature of the water in the sump 19 is at about 15°C. The loss of water by evaporation into the air streams flowing through both gas flow paths, is compensated for by the admission of make-up water from the inlet 24 by way of the valve 25 which opens when the float 26 signifies a loss of a desired water level in the sump 19.

The moist and cooled stale air from the structure 16 flows to the heat exchanger 10 where it cools the incoming fresh air to about 23°C. The stale air temperature is raised to about 27°C. when discharged by the fan 6 into the loft space. This is considerably beneath the temperature of a loft space when the ambient air temperature is about 35°C, so that the conduction of heat between the loft space and the house rooms beneath it, is reduced slightly.

MODIFICATION OF FIRST EMBODIMENT

In the modification shown in figure 3 the two structures 15 and 16 comprise, respectively, upper and lower portions of a single panel of CELdek material having its channels extending at about 45° to its side faces. The partition 2 is provided with vertical flanges 40 and 41 which lie against opposite faces of the panel to block-off those channels which communicate at their ends with the regions of the casing lying above and beneath the partition 2. In this way unwanted flow of air between the regions by way of the panel channels is prevented.

DESCRIPTION OF SECOND EMBODIMENT Figure 4 shows apparatus incorporated into a thermally insulated casing 30 which stands against an outside wall 31 of a room to be cooled. The room has a floor 32 and the casing is mounted inside the room. However the casing may readily be adapted for standing outside the room if preferred, so that useful floor space inside the room is not occupied.

The wall 31 is provided with two openings 33 the lower of which incorporates a grill 52 through which ambient air is admitted into the casing 30, and the upper opening 33 receives a blower outlet 35 through which stale air extracted from the room is discharged into the ambient air by a motor-driven fan 36.

The lower part of the casing 30 is occupied by a heat exchanger 39 of the type described in detail in my International Patent Application referred to earlier. It comprises two isolated air-flow passages 37, 38 in good heat-exchange relationship with one another and through which substantially counterflow streams of air are respectively passed at a relatively high rates of flow. These flows are denoted by arrows, the full arrow 37 denoting the fresh air flow and the broken arrow 38 denoting the stale air flow.

The casing 30 has three, vertically-spaced honeycomb structures 40,41 and 42 made of CELdek material which has previously been described. The centre and lower structures have water percolating down through them from the structure immediately above. The water leaving the lower structure 40 is collected at its lower end and pumped upwardly by a pump 44 to the upper end of the upper structure 42.

The room is supplied with cooled fresh air from a grill 45 at the upper end of the casing 30. A second fan 46, which provides a marginally higher rate of flow than the fan 36, ensures that a small positive pressure is maintained in the room by the apparatus. The fan 46 draws air through the upper structure 42, as shown by the arrowed line 37 where it is cooled by the water flowing down through the structure. The air enters the structure 42 after passage through the intermediate structure 41 which, in turn, is cooled by the

water discharging from the lower end of the upper structure 42. The fresh air is drawn into the structure 41 from the heat exchanger 39 as shown by the arrowed full line 37. A guide baffle 49 directs the fresh air flow from the heat exchanger 39 to the intermediate structure 41. The water leaving the lower end of the intermediate structure 41 passes into the upper end of the lower structure 40 which is located in the path of stale air leaving the room as shown by the broken-arrow path 38.

OPERATION OF SECOND EMBODIMENT The apparatus of figure 4 operates as follows:

Cool stale air from the room flows through the structure 40 to the heat exchanger 39 0 before discharging to atmosphere. It is cooled partially by the water percolating down through the structure 40 and partially by the extraction of the latent heat of vaporisation of the water which vaporises into the stale air stream. The stale air then passes through the heat exchanger 39 to lower the temperature of the incoming fresh air, from an outside temperature of, say 36°C, to a temperature of, say 23°C. - 24°C.

15 The cool water leaving the lower end of the structure 40 is pumped to the upper end of the structure 42 from which it cascades down, in turn, through the structures 41 and 40. This flow of water is in counterflow to the direction of the fresh air flowing through the structures 41 and 42. The temperature of the fresh air between the two structures 41 and 42 is at about 16°C. It enters the room through the grill 45 at a temperature of about

20 12°C.

The overall effect of the cooling produced by the apparatus of figure 4, is that very little energy is required to maintain the air temperature in the room, despite the relatively rapid replacement of the stale air drawn from it, with fresh air. Additionally the apparatus is quiet in operation and relatively inexpensive to purchase compared with 25 currently-available air-cooling equipment designed to produce the same degree of cooling.

In both embodiments of the invention illustrated in the drawings, the water pump may be automatically controlled by the temperature or the humidity of the fresh air passing through the casing before it reaches the honeycomb structure, or by a combination of the two, as the final cooled temperature of the fresh air admitted to the room varies with the 30 rate of flow of water percolating down through the structures. This rate may be reduced to zero or almost zero, if lesser cooling of the fresh air is required.

The apparatus described in both embodiments handles relatively large rates of flow of air and this is essential to achieve the cooling effect of the water flowing down through the

structures. In practice, the rate of flow of air through both embodiments may be varied between 300-1200 litres per second or even higher, depending on the size of the apparatus. The overall dimensions of the casing containing one embodiment of the apparatus of figure 4 are:

Width - 1 metre;

Height - 1.6 metres; Depth - 30 centimetres.

The static honeycomb structures through which water is percolated are CELdek structures in both of the embodiments of the invention described. However honeycomb structures of different constructions are equally usable. For example, the honeycomb structure may comprise a unit containing loose foraminous chips which allows water to percolate through it while offering negligible resistance to the flow of air between opposite sides by way of the air passageways provided through and between the chips. Although such passageways are not geometrically parallel they nevertheless extend effectively in parallel between opposite sides of the unit and offer a large surface area wetted with water and exposed to the flow of air passing between the opposite sides of the structure.

Although it is preferred that the solid material from which the structure is made is water- absorbent, this is not essential. It may be non-absorbent to water. One such structure currently available from the manufacturers of CELdek is GLASdek which utilises a glass structure which is largely inert to possible airborne pollutants which could adversely affect the correct operation of a CELdek structure. A GLASdek structure offers a large surface area exposed to air passing through it with the additional qualities of having a low resistance to airflow between its opposite sides and being capable of providing a large wetted area exposed to the air flow. It is to be understood that all such units fall within the term "honeycomb structure" as used in this patent specification.

In an un-iliustrated variation of the embodiments just described, the honeycomb structures are arranged to receive parallel flows of water from a common sump into which water, cooled by passage through both panels, is discharged. However such a parallel configuration of the water circuit is generally less effective than the series configuration used in the two embodiments described.

DESCRIPTION OF THIRD EM BODIMENT

The forms apparatus shown in figures 5, 6 and 7, and in figure 8, are basically of the same design as that shown in figures 1 to 3, and figure 4, respectively, and thus, to save needless repetition of description, corresponding parts have been given the same numerical references but in the one-hundred series. Thus the casing 1 of figure 1 is referenced 101 in figure 5. However parts of figures 5 to 8 which have no counterparts

in earlier figures are described in detail and are also referenced in the one-hundred series.

In figure 5 an evaporating unit, comprising a coil 129 of a closed refrigerant circuit diagrammatically represented at 160, is located upstream of the structure 115. The

5 circuit 160 has liquid refrigerant pumped around it by a motor-driven compressor (not shown). The closed circuit contains a condenser (also not shown) and is of reversible type so that the coil 129 can selectively be cooled or heated by the circuit 160, depending on whether the apparatus is to supply cold or warm air to the room. Reverse cycle refrigeration circuits of this type and used in air-conditioning equipment are well known

10 in the art, and will not be further described.

Moisture condensing on the coil 129 from the humid fresh air stream travelling along the arrowed path 114, collects at the underside of the coil and is drained downwards through an outlet pipe 128 to a distributor 165 above the lower structure 116 as shown in figure 7. The distributor 165 can also receive cooled water from the pump 117 by way of the 15 pipe 169 when a valve 170 is operated.

OPERATION OF THIRD EMBODIMENT The apparatus operates as follows:

Outside fresh air at an elevated temperature of, say 35°C. and with a wet-bulb temperature of 18°C, enters the casing 101 by way of the trunking 103 and immediately

20 flows through a screen 102 and into the gas flow path 113 of the heat exchanger 110. Its temperature is rapidly cooled down to about 23°C. in the heat exchanger 110, by the cooler stale air from the room flowing through the other path 111 of the heat exchanger 110. The fresh air from the heat exchanger follows the path indicated by the arrowed full line 114 and passes serially through the evaporation coil 129 and the honeycomb structure

25 115. Cool water from the sump 119 at a temperature of about 16°C. - 17°C. is fed by the pump 1 17 to the header 118 and percolates and/or permeates down by way of the thin walls of the structure 115. This water maintains the structure 115 cool. Also, some of this water is vaporised in the air travelling through the structure so that latent heat of evaporation is extracted from the water to cool the structure still further, by a degree or

^ so. to a temperature beneath 14°C. - 15°C. The temperature of the fresh air leaving the structure 115 and discharged through the trunking 104 by way of the fan 108, is consequently reduced to about 15°C. Its water content per kilo is increased by about 2-3 grams during its flow through the structure 115, but the corresponding level of humidity of between 50% and 60% is quite acceptable.

The temperature of the water leaving the lower end of the structure 115 and cooled by its passage through it is at a temperature of about 15°C. and this is fed by way of the funnel

120 (shown in figure 7) to the distributor 165 at the upper end of the lower structure

116 to cool it.

Stale air leaves the house being cooled by way of the duct 105 and is at a temperature of about 29°C. This flows through the lower structure 116 which, being cooled by the cold water descending through it, reduces the stale air temperature to beneath 16°C. Some of this water vaporises into the stale air and the latent heat of the evaporation it absorbs is extracted from the water in the structure. The temperature of the water collected from the structure in the sump 119, is beneath 15°C. Any loss of water by evaporation into the air streams flowing through both passages is compensated for, by the admission of make¬ up water from the inlet 124 by way of the valve 125 which opens when the float 126 signifies a loss of water level in the sump 119.

The moist stale air from the structure 1 16 follows the broken arrowed line 112 and passing through the heat exchanger 110, cools the incoming fresh air following the heat exchanger passage 114 to about 23°C. The temperature of the stale air rises to about 27°C. by the time it is discharged by the fan 106 through the grill 107. This is considerably beneath the temperature of the loft space when the ambient air temperature is about 35°C. , so that the loft space is cooled to some extent by the air discharged into it. This acts to reduce the conduction of heat between the loft space and the house rooms beneath it.

As long as the fresh air entering the trunking 103 is relatively hot and that its humidity is low, the closed refrigeration circuit 160 is not operated and the lower structure 116 receives cooling water only from the structure 115. The humidity of the air is sensed by a humidity-sensitive switch 180 located at a position in the fresh air path 1 14 immediately upstream of the evaporator coil 129. If the humidity of the fresh air at this position exceeds a preset value, a valve 170 at the outlet side of the pump 117 operates to divert the pumped cold water from the sump 119 to a second, lower header 168; and simultaneously the compressor of the refrigeration circuit 160 is activated to cool the evaporation coil 129, to provide further cooling of the fresh air stream. Condensate collected beneath the coil 129 is drained downwardly through the pipe 128 to the interior of the funnel 120, as shown in figure 7, and thus to the distributor 165 which supplies it to the upper end of the lower structure 115. The position of the humidity-sensing switch

180 may be changed to the location 161 shown in figure 5, to sense the humidity of the stale air leaving the room, if that is preferred.

DESCRIPTION OF FOURTH EMBODIMENT

The apparatus shown in figure 8 has a thermally-insulated casing 130 which stands against an outside wall 131 of a room to be cooled. The room has a floor 132.

The wall 131 is provided with a pair of vertically-spaced openings 133 the lower of which incorporates a grill 152 through which ambient fresh air is admitted into the casing 130. A fan 136 has an outlet 135 located in the lower opening 133 and which discharges stale air into the ambient air outside the room.

The lower part of the casing 130 is occupied by a heat exchanger 139 of the type described in detail in my PCT International Patent Application referred to earlier. It comprises two 0 isolated air-flow passages in good heat exchange relationship with one another and through which substantially counterflow streams of air are respectively passed at a relatively high rate of flow of anything between 300 litres per second and 1200 litres per second or higher, depending on the size and design of the apparatus. The flows of air through the heat-exchanger 139 are denoted by arrows, the full arrow 137 denoting the flow of fresh

j j air into the room and the broken arrow 138 denoting the flow of stale air from the room.

The casing 130 has two, vertically-spaced honeycomb structures 141 , 140 formed by the upper and lower portions of a single block of CELdek material. As long as the ambient air drawn into the casing 130 is hot and dry, ie., its humidity is low, each of the structures 140, 141 has water percolating down through it from above. The cold water leaving the 0 lower structure 140 is collects in a sump and is pumped upwardly by a pump 144 through a pipe 150 to the upper end of the upper structure 141 to cool it. A valve 190 is located in the pipe 150 and is operable to switch the pumped water from the upper end of the upper structure 141 , to the upper end of the lower structure 140 by way of a branch pipe 191 . The water leaving the lower end of the upper structure 141 passes into the upper 5 end of the lower structure 140 in a similar manner to that already described with reference to figure 6, and the pipe 191 corresponds to the outlet pipe 169 in that figure.

An evaporator unit, comprising a coil 142, forms part of a closed, reverse cycle, conventional refrigeration circuit 170 shown diagrammatically in figure 8. The circuit 170 has a compressor (not shown) and a condenser (also not shown) and is of a type well- 0 known in the air-conditioning art. It is of reverse cycle type so that it can optionally be used to cool or heat the air stream supplied to the room. When it is required to cool fresh air which is very humid, the evaporator coil 142 is in use, and water condensing on the outside of the coil 142 is drained by a pipe 151 which corresponds to the pipe 128 of figure 6, into the upper end of the lower structure 140. Simultaneously, the valve 190 is 5 operated so that the structure 140 is also cooled by the water delivered by the pump 144.

In this mode of operation, the upper structure 141 is not used. It is only used when the amount of cooling of the fresh air can be handled by the two structures 141 , 140 without the use of the refrigeration circuit 170. This occurs when the fresh air has a low or moderate humidity.

The room is supplied with cooled fresh air from a grill 145 at the upper end of the casing 130. A second fan 146 provides the air flow to the grill 145 at a marginally higher rate than the fan 135. This ensures that a small positive pressure is maintained in the room by the apparatus. A guide baffle 149 directs the fresh air flowing upwardly from the heat exchanger 139, to the upper structure 141. A humidity-sensitive switch, which may be located at position 166 or at position 167 in the casing, determines with its setting when the valve 190 and the closed refrigerant circuit 170 are to be operated. The refrigeration coil 142 is only used to cool the air if its sensed humidity is above a predetermined value.

OPERATION OF FOURTH EMBODIMENT The apparatus of figure 8 operates as follows:

Stale air from the room flows through the structure 140 before entering the heat exchanger 139. Water is evaporated into the stale air stream by the structure 140 and, by extracting the latent heat of evaporation from the structure 140, reduces the temperature of the water percolating down through it so that cool water collects at the lower end of the structure 140. The cooled stale air, which now has its moisture content increased, flows from the structure 140 to the heat exchanger 139 where it cools the warm ambient fresh air drawn through the grill 152 and following the path indicated by the arrowed full line 137.

As long as the humidity of the fresh air entering the apparatus is relatively low, the cool water leaving the lower end of the structure 140 is pumped by the pump 144 to the upper end of the upper structure 141. It then flows down, in turn, through the structures 141 and 140. The refrigeration circuit 170 is not then operating.

The cooled fresh air from the heat exchanger 139 passes upwardly through the structure 141 which cools it further. It is then discharged by the fan 146 into the room by way of the grill 145.

If the humidity-sensitive switch at either of the positions 166 or 167 senses the humidity as being above a threshold value, the valve 190 is operated and the compressor of the refrigeration circuit 170 is activated so that the evaporator coil 142 now cools the fresh air. Condensate from the coil 142 is fed by the pipe 151 to a position immediately above

the upper end of the structure 140 which receives at the same time the cold water output from the μump 144. so that the structure 140 is amply cooled by the downwardly- percolating cold water.

When the sensed humidity falls beneath a threshold value, the closed circuit compressor is switched off and the valve 190 is returned to its initial position at which the sump water is supplied to the upper structure 141 which then re-assumes the function of cooling the fresh air.

In both of the embodiments of figures 5 - 7 and figure 8, the use of a reverse cycle form of closed refrigeration circuit is optional. However it enables air supplied to the room to be 10 cooled or warmed, as required. If warm air is wanted, the water pump 144 is switched off so that the structures 140, 141 are not cooled. The reverse cycle operation causes the coil 142 to behave as a heater to warm the fresh air being fed by the fan 146 to the room.

DESCRIPTION OF FIFTH EMBODIMENT

Figure 9 shows apparatus 201 for heating or cooling fresh air, which comprises a casing 15 202 having a fresh air inlet 203, a fresh air supply outlet 204, a stale air extraction inlet 205, and a stale air outlet 206. The casing 202 has a low aspect profile and is designed to be accommodated in a roof space of a house so that it rests on the floor 207 of the house attic.

The casing is divided internally into a fresh air flow path 211 and a stale air flow path 20 212, by a partition 213. The fresh air flow path contains a secondary circuit 214 of a counterflow, isolating, gas heat exchanger 215 of the design described and claimed in my Australian Patent Application No. 36219/93 hereby inserted by way of reference. Such a heat exchanger has a thermal efficiency approaching 80% and can handle large air flows of the order of 500-1000 litres per second, upwards.

25 The secondary circuit 2 I4 is connected to the fresh air inlet 203 and supplies the fresh air to an upper structure 216 of two honeycomb structures 216 and 217 respectively, each of which is cooled by the evaporation of v/ater from it, as has previously been described with reference to earlier embodiments. The water is supplied by a pumping circuit 224 of the type already described in earlier embodiments and it is only partially

" 30 illustrated in figure 9.

After flowing through and being cooled in the structure 216 the fresh air travels past a temperature sensitive cut-out switch 218 to the position of a gas burner 220 which, when operated, is arranged to burn fluent fuel in the fresh air stream and has a capacity of

between twelve and twenty five kilowatts. The fresh air then flows through a fan 221 which discharges it through the air supply outlet 204 to the interior of the house.

Stale air from the interior of the house is withdrawn through the extraction inlet 205 by a second fan 226 which draws the stale air through the lower cooling structure 217 located 5 directly beneath the structure 216 and connected to receive cool water from the lower end of the upper structure 216. Water cooled by passage through the two structures collects in a sump 223 at the lower end of the lower structure and is recirculated by the pump 224 to the upper end of the upper structure 216.

The stale air leaving the lower structure 217 is sucked through a primary circuit 225 of 10 the heat exchanger 215 by the second fan 226 which discharges the stale air through the outlet 206.

OPERATION OF THE FIFTH EMBODIMENT The apparatus of figure 9 operates as follows:

When the unit is to be operated as an air heater, the pump 224 is not used. Stale air from 15 the building and at a temperature of about 22°C. is drawn through the inlet 205 by the fan 226 and passes through the structure 217 and the primary circuit 225 of the heat exchanger 215. As the heat exchanger is of counterflow type, it has a high efficiency and can transfer much of the useful heat of the stale air to the incoming fresh air flowing from the inlet 203 to the secondary circuit 214 of the heat exchanger. The stale air passes through the heat exchanger 215 at a high rate of flow which is normally of the order of 650 litres per second, and leaves the casing 202 by way of the fan 226 and the stale air outlet 206.

Cold fresh air at a temperature of between 0°C. and 10°C. enters the inlet 203 and is heated in the secondary circuit 214 of the heat exchanger to a temperature of about 18°C.

^ It then flows through the upper cooling structure 216 (which at this time is not operating) to the vicinity of the burner 220 which discharges directly into the fresh air stream its hot products of combustion. This raises the temperature of the air stream to between 35 C C. and 45 C C. and increases its water content so that, despite the rise in temperature from 18 0 C. -45°C. the humidity falls to only about 20%. This warm air is

30 then discharged into the building at a rate of about 500-700 litres per second by the fan 221 .

Should the fan 221 fail, the rise in temperature at the vicinity of the burner 220 is detected by the cut-out switch 218 which operates to switch off the burner. The heat

output of the burner is controlled by circuitry (not shown) to maintain the temperature of the warm air supplied to the building at the desired value. The low capacity of the burner is such that its noxious products of combustion are so diluted by the volume of fresh air flowing past it, that they are virtually unnoticeable and their percentage falls well within

^ the acceptable requirements of health regulations.

During summer, the unit is required to provide cool air to the building at a higher rate of flow of typically between 900-1000 litres per second. The burner is not then operated. Instead the pump 224 is activated to circulate water between the two structures 216 and 217. Obviously some of this water is lost through evaporation and this is compensated by a

10 supply of make-up water (not shown) as in previously described embodiments.

Cool stale air from the building is withdrawn through the extraction inlet 205 and supplied to the lower structure 217 so that it evaporates some of the water trickling down through it. This extracts the latent heat of evaporation from the structure so that the water is progressively cooled as it trickles down through it. The moist but still cool stale 15 air then passes through the primary circuit of the heat exchanger 215 where it cools the incoming warm fresh air drawn into the casing by the fan 221.

The cooled fresh air from the heat exchanger 215 flows next through the cooling structure 216 which has percolating down over its surfaces the cooled water pumped up from the lower end of the lower structure 217. The fresh air is thus cooled further and supplied to

20 the house by the fan 221 at a rate of about 1000 litres per second.

The above described heating and cooling unit has few parts, is small in size and cheap to construct. It is also cheap to run.

DESCRIPTION OF SIXTH EMBODIMENT

Figure 10 shows a further form of heating and cooling apparatus. It comprises a lower 25 casing 300 containing parts of the apparatus required to cool a fresh air stream, and an upper casing 301 containing parts required to heat the fresh air stream. The lower casing 300 can be provided separately from the upper casing 301 which, if required, can be buckled onto the upper surface of the lower casing 300 as shown in the figure.

The lower casing 300 has a heat exchanger 302 of the type described in earlier

30 embodiments. Stale air from a house enters the casing 300 through an inlet trunking 303 at a temperature beneath that of the ambient fresh air to be cooled and which is admitted to the casing 300 by way of a fresh air inlet trunk 304. The path of the fresh air through the

trunking is denoted by the full arrowed line 305, and that of the stale air denoted by the broken arrowed line 306.

The casing is divided horizontally by a first partition 307, and vertically by a second partition 308. Two honeycomb structures 310, 311 of similar type to those described in each of the earlier embodiments, are respectively arranged above and beneath the partition 307. The upper structure 310 spans the fresh air path 305 leading from the heat exchanger 302 to a fan 312, and the lower structure 311 spans the stale air path 306 leading from the trunking 303 to the heat exchanger 302. A sump 313 at the lower end of the lower structure 31 1 collects water cooled by downward passage through it, and a pump circuit, partially shown at 314, supplies the cold water from the sump 313, at a controlled rate, to the upper end of the upper structure 310. The cold water trickles down through both structures in turn, and is partially evaporated so that its latent heat of evaporation acts to assist the cooling effect on the structures 310 and 311.

The stale air is drawn through the arrowed broken-line path 306 by a second fan 385 and expelled to atmosphere or the roof space of the house, by way of exhaust trunking 386. Both fans are, as with earlier embodiments, driven by a common motor and have characteristics which ensure that a small positive air pressure exists in the house to be cooled.

The fan 312 is mounted so as to be rotatable through 90° from a first position, shown in broken outline, at which, it discharges through a first outlet 316 associated with trunking 315 through which cool fresh air is supplied to the house, to a second position, shown in full outline, at which it discharges the fresh air upwardly through a second outlet 317. The outlets 316, 317 are selectively useable in accordance with whether or not the casing 301 is mounted on the casing 300.

A blanking plate (not shown) is provided to close whichever of the outlets 316, 317 are not required.

The upper casing 301 is made of an insulated material and contains two fresh air inlets 320. 321 , shown in figure 11 , which each receive air directed upwardly by the fan 312 of the lower casing 300, by way of the outlet 317 and a cross connection duct 322. A removable filter screen 323 covers the upper end of the outlet 317.

Centrally mounted on top of the cross-connection duct 322 is a burner 325 of similar type to that described in the previous embodiment. As the burner 325 is mounted between the inlets 320, 321 it is out of the direct air flow path into the casing 301. It provides a

naked flame which directs its combustion products towards a cusp 326 which promotes good circulation of air within the casing 301. The warm air discharges from the casing

301 through two or mere of four outlets 327 which can be individually blanked off, as desired.

OPERATION OF THE SIXTH EMBODIMENT

The apparatus shown in full outline in figures 10 and 11 can be used to provide cool air in summer or warm air in winter, without the use of a reverse cycle refrigeration circuit.

During summer, the burner is not operated and the water pumping circuit 314 provides cooling of the fresh air flowing along the air path 305, by its flow through the upper structure 310. The structure 310 operates to cool the fresh air in the manner already described with reference to earlier figures, and is itself cooled by the cold sump water collecting at the underside of the lower structure 311.

During winter, the water pumping circuit 314 is switched off and the burner 325 is operated. Fresh air is drawn through the inlet trunking 304 and is pre-warmed by passage through the heat exchanger 302. The warm stale air is drawn from the house or building via the trunking 303 and, after flowing through the heat exchanger 302 to pre- warm the fresh air, is discharged into the roof space of the house through the outlet trunking 386.

The pre-warmed fresh air flows from the lower casing 300 into the upper casing 301 where it is further heated by the combustion products of the burner 325 before being discharged as warm fresh air into the house by way of the selected outlets 327.

The burner 325 has a low capacity, as it is only required to provide the make-up heat necessary to raise the temperature of the pre-warmed air from the heat exchanger 302, to the required temperature for the house. The rate of production of noxious combustion products it provides is therefore insignificant compared with the high rate of flow of fresh air through the casing 301 , and they are so diluted by the fresh air as not to pose a health hazard.

The advantage of the arrangement shown in figures 10 and 11 is that the upper and lower casings can be sold separately. If they are both to be used, all that is necessary is to rotate the fan 312 and close the outlet 316 while opening the outlet 317. At no time is the fan 312 required to receive hot air from the burner 325.

DESCRIPTION OF SEVENTH EMBODIMENT

Figure 12 shows a free-standing unit 400 sited outside a wall 401 of a room 402 which is to be supplied with warm fresh air in winter and cool fresh air in summer.

The unit has an insulated casing 403 which stands against the room wall 401 and has an upper fresh air outlet 404 for supplying air to the room, and a lower stale air inlet 405 for withdrawing stale air from the room. The wall is provided with openings 406 and 407 aligned with the inlet 405 and the outlet 404.

The casing 403 is provided on its side remote from the wall 401 with a stale air outlet 408, and a fresh air inlet 409.

Fresh air from the inlet 409 is drawn into the casing 403 by a fan 411 at its upper end, and passes first through a heat exchanger 412 having good heat transfer characteristics and of the type described in previous embodiments. The path of the fresh air is shown by the arrowed full line 413. After passage through the heat exchanger, the fresh air passes upwardly through an upper of two honeycomb structures 414, 415 and into a chamber 416 containing a burner 417. As with earlier embodiments, the burner heats the fresh air by discharging a naked flame into it, and is controlled by temperature sensitive equipment (not shown) which operates to maintain the temperature of the air supplied to the room 402 at a desired value.

Thorough mixing of the fresh air with the burner combustion products occurs in the chamber 416 and the so-warmed air is supplied by the fan 411 to the outlet 404 leading into the room 402.

Stale air is drawn from the room 402 by a second extraction fan 417 which is driven from the same drive as is used for the fan 411 . However, the extraction fan has a slightly lower rate of flow than the fresh air fan 411 so that a slightly positive air pressure is maintained in the room. A partition 418 separates the stale air flow path, indicated by the arrowed broken line 420, from the fresh air flow path 413.

A sump tray 421 is located beneath the lower structure 415 to collect cooled water from its lower end, and an associated water-pumping circuit, partially shown at 422, supplies cold water from the sump tray 422 to the upper end of the upper structure 414 when the apparatus is to provide cool air to the room 402 in summer. The rate of supply of water through the pumping circuit controls the amount of cooling of the fresh air. A distributor 423 at the lower end of the upper structure 414 supplies cold water leaving its underside io the upper end of the lower structure 415.

OPERATION OF SEVENTH EMBODIMENT

The embodiment of figure 12 operates as follows.

During summer cooled fresh air is to be provided to the room 402. The burner 417 is then not energised. The pumping circuit is activated to circulate water through the two structures 414 and 415.

Warm ambient fresh air is sucked into the casing 403 via the inlet 409, and flows first through the heat exchanger 412 where it is pre-cooled by the counterflow of cool stale air leaving the room 402 and following the broken arrowed path 420. The fresh air flows upwardly from the heat exchanger 412, through the upper structure 414 where it is cooled by evaporative cooling and by the cold water percolating downwardly through it. It then passes upwardly through the chamber 416 containing the non-operating burner 417, to the fan 41 1 which discharges it through the fresh air outlet 404 into the room 402.

Stale air from the room is drawn out by the fan 417 and passes first through the lower structure 415 to be cooled by the water flowing down through it, and then through the heat exchanger 412 to pre-cool the fresh air, before being discharged to atmosphere through the outlet 408.

During winter, the water pumping circuit 422 is de-energised and the burner 417 is ignited. The fan 411 draws the fresh ambient air first through the heat exchanger 412 in which it is pre-warmed by the stale air following the path 420. It then flows upwardly to the chamber 416 where it is further warmed by make-up heat from the burner 417 before being discharged at the desired temperature through the fresh air outlet 404.

The stale, but still warm air from the room 402 is drawn by the fan 417 through the heat exchanger 412 to pre-warm the fresh air, and is then discharged into the atmosphere outside the room by way of the outlet 408.

MODIFICATIONS OF DESCRIBED EMBODIMENTS

In the various embodiments of the invention which utilise a burner, it is convenient to provide two burners which are individually either off or on to determine the amount of heat they are to supply to the fresh air.