This invention relates to a cooling apparatus and, more particularly but not exclusively, relates to a cooling apparatus for cooling residential and commercial buildings including factories. The invention also relates to a method of cooling and to an air conditioning apparatus.

It is well known that warm, dry air can be cooled by being passed through water. As the water evaporates the energy absorbed by the water turning to vapor causes the temperatures of the air to drop by several degrees.

The problem is that the warm dry air becomes humid and the moisture content of the cooled air can be uncomfortable if the humid air is released directly into the room being cooled.

US-A-4 827 733A, which is the closest prior art known to the applicants, addresses this problem by using the humid air to cool one end of a heat pipe and rejecting the humid air to atmosphere.

The other end of the heat pipe is then used to cool a room without the burden of the moisture.

Although there are undoubted benefits to be gained by using evaporative cooling, either separate from or in conjunction with conventional compressor driven air conditioning the benefits have been marginal.

The present invention seeks to improve the viability of evaporative cooling by addressing the construction and operation of the evaporator and/or the heat pipe.

According to one aspect of the present invention there is provided a cooling apparatus which comprises:

(a) a fan rotatable to create a stream of air;

(b) a spray header capable of generating a downwardly flowing curtain of water through which said stream of air can pass;

(c) a reservoir in which water from said downwardly flowing curtain of water can collect; and (d) an air permeable hydrophilic membrane capable of transferring water into the path of said stream of air which has passed through said downwardly flowing curtain of water.

Preferably, the reservoir is arranged to provide water to wet said air permeable hydrophilic membrane.

The size of the fan will vary according to the application. However, for cooling, for example a bedroom, it is envisaged that a variable speed in-line fan with a maximum throughput of from 150 m ³ /h to 600 m ³ /h will be acceptable. A power consumption of about 60W will be more than adequate.

The fan is preferably disposed upstream of the spray header and the air permeable hydrophilic membrane although it could conceivably be located downstream of the air permeable hydrophilic membrane or between the spray header and the air permeable hydrophilic membrane

The spray header preferably comprises one or more spray nozzles capable of producing a generally planar curtain of water comprising a myriad of water droplets. The droplets may all be of a similar size, for example from 2mm to 6mm in diameter to a wider spectrum of sizes, for example from 1 mm to 15 mm in diameter. An Uxexcel ½ BSP Male Thread 180-degree garden irrigation flat spray is currently preferred.

It would also be possible to replace the spray nozzles with a spray header having a multiplicity of holes to achieve a similar effect. Such holes would preferably be arranged in a straight line although they could be offset from one another so that the curtain would be wavy.

The primary aim is to create a curtain of water droplets through which the air must pass.

If desired the cooling apparatus could incorporate two or more spray headers arranged to create a number of curtains through which the stream of air could pass sequentially. However, our present experiments indicate that one spray header should suffice. The reservoir can conveniently comprise a plastic vessel positioned to collect the water from the film and having a sloped lower section to direct the water into a reservoir which accommodates one end of the air permeable hydrophilic membrane.

The air permeable hydrophilic membrane is preferably disposed in a vertical plane although it could be inclined to the vertical or even arranged horizontal. All that matters is that the stream of air which has passed through the curtain of water can pass through the air permeable hydrophilic membrane.

The choice of air permeable hydrophilic membrane is important. In particular it is important that the air permeable hydrophilic membrane can transfer sufficient water across its surface to be effective. We have found that an air permeable hydrophilic membrane with a contact angle (as defined in Applied Colloid and Surface Chemistry by Richard M Pasley, Marlyn E Karman Oct 2004) of 90° or less is desirable with 35 to 70 degrees being acceptable. Our presently preferred membrane comprises a mixture of 25% (by weight) Viscose and 75% Polyester (by weight) with a weight of 40g/m ² , and a thickness of approximately 0.57 mm. Such material is sold by Euroslu Nonwoven Group

(Eng) with a current catalogue number of ERU 257500000.

The cooling apparatus preferably comprises a pump to provide water to the spray header although this may not be necessary if a suitable supply of water is available.

The present invention also provides a method of cooling air, which method comprises:

(a) generating a stream of air;

(b) passing said air through a curtain of water;

(c) collecting water from said curtain of water in a reservoir; and

(d) using an air permeable hydrophilic membrane to transfer water into the path of air which has passed through said curtain.

Preferably, the method including the step of using water from said reservoir to wet said air permeable hydrophilic membrane.

The efficiency of the method will vary according to the condition of the ambient air. Satisfactory performance can be obtained where the ambient temperature is from 26 degrees C to 28 degrees C and the relative humidity is from 15% to 20%. Very good performance can be obtained when the ambient temperature is from 28 degrees C to 31 degrees C and the relative humidity is from 15% to 24%. Excellent performance can be obtained where the ambient temperature is about 32 degrees C and a humidity of 20%. Such conditions are often found in places such as California in the summer.

Because of hydrodynamic considerations the curtain will not be of uniform thickness. However, it should preferably be between 1 and 8 mm in thickness and more preferably between 2 mm and 5 mm in thickness.

The reservoir preferably has a lower surface which is inclined downwardly at a angle of from 2 degrees to 10 degrees, preferably 5 degrees to encourage water to flow into a reservoir into which one end of the air permeable hydrophilic membrane extends.

Although it would be possible to supplement the wetting of the air permeable hydrophilic membrane by supplementary sprays it is intended that no additional wetting should be used thereby reducing overall energy consumption.

Turning now to heat pipe considerations the present invention also provides: a cooling apparatus for cooling a room, which cooling apparatus comprises:

(a) a fan rotatable to create a stream of air;

(b) an evaporator for cooling said stream of air; and

(c) a heat pipe for, in use, transferring thermal energy from the room to be cooled to said stream of air leaving said evaporator;

wherein said heat pipe comprises:

(d) an upper section for thermal contact with air from said evaporator;

(e) a lower section for thermal contact with said room; and

wherein said upper section of said heat pipe is provided with a multiplicity of plates in thermal contact therewith;

and

baffles to direct said air back and forth across said heat pipe.

Preferably, the lower section of said heat pipe is provided with a multiplicity of plates in thermal contact therewith;

and baffles to direct air to be cooled back and forth across said heat pipe.

Advantageously, the heat pipe comprises a multiplicity of heat pipes.

The present invention also provides an air conditioning apparatus which combines the improved evaporation and heat pipe features described herein.

Such an air conditioning apparatus may additionally be provided with a refrigeration unit which may be a mechanical arrangement including a compressor, a condenser, a thermal expansion valve, for example a Joule Thompson valve and an evaporator.

The refrigeration unit might also comprise a thermoelectric device using, for example the Peltier Effect.

In the former case the condenser of the refrigeration unit is preferably arranged downstream of the heat pipe(s) with the evaporator preferably positioned upstream of the heat pipe(s)..

Advantageously, the upper section(s) of a second heat pipe/bank of heat pipes is located between the evaporator and the condenser with the lower section(s), in use, being in the room to be cooled. In such an arrangement the evaporator of the refrigeration unit can conveniently be arranged between the first and second heat pipe/bank of heat pipes.

The lower section(s) of the heat pipe(s) upstream and downstream of the evaporator may be spaced apart but are conveniently arranged side by side in parallel or in series. Both arrangements have the advantage that only a relatively compact, unit need be placed in the room to be cooled and that only a single fan is needed.

Preferably, the lower section(s) of the heat pipe(s) upstream and downstream of the evaporator are arranged side by side in a common enclosure.

Advantageously, the common enclosure is provided with an inlet for, in use, transporting air from a room to be cooled into said enclosure, an outlet for, in use, allowing cooled air to reenter said room, and a single fan to, in use, blow relatively warm air from the room to be cooled over the lower section(s) of the heat pipe(s) and the relatively cool air thus produced back into the room. The fan may be positioned upstream, downstream or within the enclosure and is preferably a variable speed fan. Alternatively several fans may be used which can each be of variable speed or switched on and off as required.

In the context of a thermoelectric device the condenser become the hot junction and the evaporator the cold junction.

For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings in which:

Fig. 1 is a simplified view of known cooling apparatus being used to cool a bedroom;

Fig. 2 is a simplified side view of part of one embodiment of a cooling apparatus in accordance with the present invention;

Fig. 3 is a photograph, to an enlarged scale, of part of a preferred air permeable hydrophilic membrane used in the cooling apparatus shown in Figure 2;

Fig. 4 is a simplified side view of heat pipes being used to transfer refrigeration from cool moist air to a room below;

Figure 5 is a simplified vertical cross end through one of the heat pipes shown in Figure 4;

Figure 6 is a simplified side view of an air conditioning apparatus in accordance with the present invention; and

Figure 7 is a view similar to Figure 6 but showing a more compact arrangement of the components in the room to be cooled.

Referring to Figure 1 a fan 100 sucks warm, dry air through a duct 102.

The air passes through a pad 104 which is kept moist by a stream of water which is pumped onto the top of the pad 104 through pipe 106 by a pump 108.

As the warm, dry air passes through the pad 104 part of the water is vaporized and the air cools down by a few degrees. At the same time the relative humidity of the air increases.

The moist air then passes across the upper section 110 of a heat pipe 112 where it condenses the vapor therein. The moist air then passes through the fan 100 and is rejected to atmosphere.

In the meantime, the condensate in the heat pipe 112 flows downwardly through the insulated ceiling 114 of the bedroom 116 below.

A fan 118 blows air from the bedroom 116 across the lower section 120 of the heat pipe 112. This cools the air whilst causing the condensate to boil and return upwardly in the heat pipe 112. It will be appreciated that the temperature and humidity of the air in the bedroom 116 will initially be similar to ambient conditions and consequently the cooled air will have a lower humidity than the moist air leaving via the fan 100.

Until now the benefits achievable using the cooling apparatus described have not been sufficient to make such cooling apparatus commercially acceptable.

The present invention looks at improving the performance of the evaporation and and/or the performance of the heat pipe.

Turning firstly to evaporation Figure 2 shows a fan 200 which blows 151 m ³ /h warm, dry ambient air at 30 degrees C and 20% relative humidity through a duct 202 which is 200 mm in diameter. The duct 202 leads into a rectangular end 203 which is 23 cm wide, 19 cm deep and 90 cm long before reverting back into a duct 204 similar to duct 202.

The warm dry ambient air first passes through a curtain 205 of water which emerges from a spray header 207 which comprises an Uxexcel ½ BSP Male Thread 180 degree garden irrigation flat spray with a current catalogue number of ERU 257500000.

The water is supplied to the spray header 207 at a rate of 75.66 L/h through a pipe 206 which is fed by a pump 208. Because of the hydrodynamic conditions the exact thickness of the curtain 205 is difficult to determine but (with no air flow present) appears to be between 2 mm and 8 mm.

The unevaporated water from the curtain 205 drops into a reservoir 209 which has a lower section which is inclined downwardly at an angle 211 of about 5 degrees into a reservoir 213.

The curtain 205 of water cools the air by 4 degrees C so that it leaves at 26 degrees C whilst the relative humidity increases to 40%.

An air permeable hydrophilic membrane 214 is suspended across the rectangular end 203. The air permeable hydrophilic membrane 214 is 19cm wide and 23 cm high. It is supplied by Eruslu Nonwoven Group (Eng) and comprises a mixture of 25% (by weight) viscose and 75% (by weight) polyester. It is approximately 0.57 mm thick and has a contact angle of 90 degrees and a weight of 40g/m ² . An idea of the structure of the air permeable hydrophilic membrane 214 may be gathered by looking at Figure 3 - particular attention being drawn to the scale superimposed on the Figure.

A water supply line 215 is provided with a valve 216 which is controllable to maintain the level of water in the reservoir 209 substantially constant. The water temperature was 18 degrees C.

In our most promising experiment to date the water was admitted through valve 216 at a rate of 0.66 L/h.

The air left the rectangular end 203 at a temperature of 18.6 degrees C and a relative humidity of 72%.

It should be noted that we recommend that the maximum relative humidity should not exceed 95% to try and minimize condensation in the vicinity of the upper section of the heat pipe as will be explained in more detail hereinafter.

The overall power consumption (two fans plus pump 208) was 0.35kWh. We were not able to achieve the desired result using either the spray header 207 or the air permeable hydrophilic membrane 214 alone.

As shown in Figure 4, the duct 204 leads into rectangular enclosure 217 which is 19 cm wide, 23 cm high and 30 cm long.

The rectangular enclosure 217 houses the top end of a multiplicity of heat pipes 212 each of which is of similar construction.

As shown in Figure 5, heat pipe 212 comprises a tube 218 which is made of copper and has an outer diameter of 12.7 mm and a wall thickness of 1.5 mm.

The tube 218 is sealed at both ends and has an overall length of 85cm.

The lower (evaporative) section of the heat pipe 212, ie the section within the enclosure 231 in Figure 4, is filled to the uppermost plate 232 with R134 refrigerant at a pressure which is equivalent to 564kPa at a temperature of 25°C.

In other embodiments 10% to 100% of the evaporative section of the heat pipe could be filled with a working fluid which could be R134 or other working fluids such as acetone or ammonia. In use, the heat from the bedroom 216 vaporizes the refrigerant in the lower section of the heat pipe 212.

The vapor rises and collects in the upper section of the heat pipe 212 where it is condensed by the cool moist air from the duct 204.

As the outer wall of the tube 218 is in contact with the moist cool air the vapor adjacent the inner wall of the tube 218 condenses first so that liquid flows down the inner wall of the tube 218. After a few minutes there is a steady flow of vapor up the heat pipe 212 and a flow of liquid down the inner wall of the tube 218.

Referring back to Figure 4, the enclosure 217 contains the upper sections of 24 heat pipes 212 which are arranged in a 6 x 4 grid.

The heat pipes 212 each pass through a plurality of plates 223 (thirty nine in this embodiment although only a token number are shown in the drawing) which are 0.1 mm thick. Each plate is provided with a plurality of holes which are of a diameter marginally smaller than the outer diameter of the tube 218 so that the tube 218 is in good thermal contact therewith.

The plates 223 are spaced apart by approximately 5 mm.

The enclosure 217 is divided into three sections by baffles 224 which ensure that the cool moist air coming from duct 204 passes back and forth across the heat pipes 212 in the direction of the arrows 227. This movement increases the path of the cool moist air with the upper section of the heat pipes 212 and increases the amount of heat transferred by increasing the heat transfer coefficient.

If desired the number of sections can be varied by changing the number of baffles.

In a manner similar to that shown in Figure 1 the heat pipes 212 pass through an insulated ceiling 225 into the bedroom 226 where the lower section of the heat pipes 212 is brought into contact with air being recirculated by a fan 228.

The fan 228 blows 151 m ³ /h through duct 229 which is 200 mm in diameter.

The heat exchanger surrounding the lower sections of the heat pipes 212 is a mirror image of the arrangement at the top although this is not essential.

In particular, the fan 228 blows 69 m ³ /h air through duct 229 which is 200 mm in diameter. The duct 229 enters a enclosure 231 which contains the lower sections of the 24 heat pipes 212.

The heat pipes 212 each pass through a stack of thirty nine plates 232 each of which is 0.1 mm thick. Each plate 232 is provided with a plurality of holes which are of a diameter marginally smaller than the outer diameter of the tube 218 so that the tube 218 is in good thermal contact therewith.

The plates 232 are spaced apart by approximately 5 mm.

The enclosure 217 is divided into three sections by baffles 234 which ensure that the warm, dry air coming from duct 229 passes back and forth across the lower section end of the heat pipes 212 in the direction of the arrows 233. This movement increases the path of the cool moist air with the upper section of the heat pipes 212 and increases the amount of heat transferred by increasing the heat transfer coefficient.

Ambient air from the bedroom, which is initially at 30 degrees C and 20% relative humidity is passed back and forth over the lower section of the heat pipes 212. This vaporizes the refrigerant in the lower section of the heat pipes 212 whilst simultaneously cooling the air. The air is passed into the bedroom 226 initially at a temperature of 30° C and at a relative humidity of 22% (the relative humidity having increased because of the lowering of the temperature).

A drain 230 is provided to accept any condensate which may form, for example as a result of the use of a shower in the bedroom.

The total power consumed was 0.35kWh which is significantly less than a conventional compressor operated air conditioning system - typically 1.5 to 2 kW/h.

Various modifications to the process described are envisaged. For example, the cooling could be supplemented by a conventional air conditioning system.

In addition, the reservoir (209) shown in Figure 2 could be replaced by two separate and distinct reservoirs, one adapted to provide water for the curtain (205) and the other to provide water for wetting the air permeable hydrophilic membrane (214). In such an embodiment the water for wetting the air permeable hydrophilic membrane might be deionized water to enhance the working life of the air permeable hydrophilic membrane. (214). In contrast the water for the curtain could be tap water or, although not recommended, well water or brackish water.

Referring now to Figure 6, there is shown an air conditioning apparatus which is generally identified by the reference numeral 300.

The air conditioning apparatus 300 comprises the heat pipes shown in Figure 4 mounted downstream of the cooling apparatus shown in Figure 2.

The reference numerals used in Figures 2 and 4 have been retained for simplicity.

In addition, the air conditioning apparatus 300 includes a mechanical refrigeration unit 302 which comprises a compressor 304, a condenser 306, a J-T. expansion valve 308 and an evaporator 310.

The mechanical refrigeration unit 302 contains R410A as a working fluid.

The compressor is 304 is connected to a 700W electric motor (not shown). Whilst the compressor operates, it increases the refrigerant’s pressure to approximately 2800 kPa and drives the refrigerant around the system. As the refrigerant goes through the J- T expansion valve 308, its pressure is reduced to approximately 1000 kPa. The temperature of the high pressure fluid can reach between 40 and 70 degrees Celsius and the low pressure fluid can reach a temperature between 0 and 10 degrees Celsius.

The evaporator 310 is mounted in the duct 229 downstream of the heat pipes 212 and the condenser 306 is mounted in the duct 229 downstream of the evaporator 310.

Another set of heat pipes 212’ similar to the heat pipes 212 are disposed in the duct 229 downstream of the evaporator 310 and upstream of the condenser 306. The features of the heat pipes are similar to those of the heat pipe 212 and these similar features have been identified by the same reference numerals with the addition of an apostrophe.

The provision of the mechanical refrigeration unit 302 and the second set of het pipes 212’ gives the air conditioning unit 300 considerable versatility.

In particular, if it is desired to keep the bedroom 116 particularly cool, or to cool it down rapidly, the mechanical refrigeration unit 302 can be started. Cold working fluid in the evaporator 310 will cool the air leaving the heat pipes 212 and the cool air will cool the upper sections of the heat pipes 212’ which in turn will cool the lower sections of the heat pipes 212’ and the bedroom 216. By using both sets of heat pipes 212 and 212’ and both fans 228 and 228’, which are arranged in parallel, the bedroom 116 can be relatively rapidly cooled.

In another scenario, if the ambient air is extremely humid (greater than 60% relative humidity) then the temperature drop by evaporative cooling as the air passes through the curtain 205 of water and the air permeable hydrophilic membrane 214 and hence any cooling via the hear pipes 212 may be minimal. In this case actuation of the mechanical refrigeration unit 302 will result in the evaporator 310 cooling the saturated air during which time some water will condense out. This can be drained through a drain pipe (not shown). Provided there is sufficient cooling the temperature of the air will fall and this will cool the upper section of heat pipes 212’ which, in turn, will cool the lower section of the heat pipes 212’ and hence the bedroom 116. In certain situations it is envisaged that it may be beneficial to shut down the pump 208 and lower the air permeable hydrophilic membrane 214 into the reservoir 204

Although the lower sections of the heat pipes 212,212’ are disposed alongside one another each is preferably proved with its own fan 228, 228’ which are independently controllable. However, the fans 228 and 228’ could be replaced by a common fan. In addition, whilst the fans 228, 228’ are preferably arranged so that their outputs enter the bedroom in parallel they could be operated in series. In such an arrangement the output from the lower section of heat pipes 212 would preferably be directed to the input of the lower section of heat pipes 212’.

Although the upper sections of the heat pipes 212 and 212’ are separated by the evaporator 310 and the lower sections are similarly separated the lower section(s) can be housed in a common enclosure as shown in Figure 7.

Figure 7 differs from Figure 6 only in the details in the bedroom 226.

In particular, the lower sections of the heat pipes 212, 212’ are disposed in a common enclosure 231”

The lower sections of the heat pipes 212, 212’ each pass through a stack of thirty nine plates 232” each of which is 0.1 mm thick. Each plate 232” is provided with a plurality of holes which are of a diameter marginally smaller than the outer diameter of the tube 218 so that the tube 218 is in good thermal contact therewith.

The plates 232” are spaced apart by approximately 5 mm.

The enclosure 231” is divided into three sections by baffles 234” which ensure that the warm, dry air coming from duct 204” from the bedroom 226 passes back and forth across the lower sections of the heat pipes 212, 212’ in the direction of the arrows 233”. This movement increases the path of the air with the lower sections of the heat pipes 212, 212’ and increases the amount of heat transferred by increasing the heat transfer coefficient.

The cooled air is released back into the bedroom 226 through outlet 312 which is in the form of a grille.

The fan 228” blows 69 m ³ /h air through duct 204” which is 200 mm in diameter.

100 fan

102 duct

104 pad

106 pipe

108 pump

110 top

112 heat pipe

114 insulated ceiling

116 bedroom

118 fan

120 lower section end

200 fan

202 duct

203 rectangular end

204 duct

204’ duct

205 curtain

206 pipe

207 spray header

208 pump

209 reservoir

211 angle

212 heat pipes

212’ heat pipes

213 reservoir

214 air permeable hydrophilic membrane

215 water supply line

216 valve

217 enclosure

217’ enclosure

218 tube

223 plates

223’ plates

224 baffles

224’ baffles

225 insulated ceiling

226 bedroom 227 arrows

227’ arrows

228 fan

228’ fan

229 duct

229’ duct

230 drain

231 enclosure

231’ enclosure

231”

232 plates

232’ plates

233 arrows

233’ arrows

234 baffles

234’ baffles

300 air conditioning apparatus

302 mechanical refrigeration unit

304 compressor

306 condenser

308 J-T expansion valve

310 evaporator

312 outlet