GB1559607A - Heat exchanger - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO A HEAT EXCHANGER (71) We, ISOVEL LIMITE, a British Company, of 76 East Street, Epsom, Surrey KT17 IEQ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- The present invention relates to a heat exchanger, and more particularly to a heat exchanger for use in air-conditioning apparatus such as, for example, air-conditioning apparatus suitable for maintaining the temperature, humidity and cleanliness of air in a room in which computers or like equipment are utilise.

Computers and like equipment can only be operated satisfactorily within a narrow temperature range and if the temperature rises or falls by a large amount various components of a computer may not function, and thus the computer may not operate satisfactorily.

Many computers utilise magnetic tape as a memory and it has been found that such magnetic tape may become brittle and break if the ambient air conditions are too dry. Also, if the ambient air is too dry static electricity may become present on the tape which may deleteriously effect the data stored on the tape. However, on the other hand, if the relative humidity is too high moisture and dust present in the atmosphere may combine to create problems in the electrical system of the computer.

Thus it has been proposed to provide airconditioning apparatus to maintain the air within a room containing computers or the like within a predetermined range of tem perature and humidity.

It has been proposed to provide such airconditioning apparatus with a heat exchanger comprising cooling coils to cool the air, if necessary, and the present invention rclates to a heat exchanger which can be used in the cooling of air in an air-conditioning apparatus.

In a prior proposed air-conditioning apparatus, when the relative humidity of the air is too high the cooling coils are operated at a very low temperature, so that all air extracted from the space that is to be air conditioned and passing the cooling coils is cooled, leading to the condensation of water onto the cooling coils and reducing the overall humidity of the air. However, this led to the air being cooled to a very low temperature, and thus the air had to be heated before being returned to the space being air conditioned. This consumed. a large quantity of power.

According to one aspect of this invention there is provided a heat exchanger arrangement for an air-conditioning apparatus, said heat exchanger comprising at least one cooling element comprising two element parts for cooling air passing past the element and means for causing an air stream to flow past the element so that every portion of the air stream which contacts one element part does not subsequently contact the other element part, the element being provided with a control valve arrangement, and means for operating the control valve arrangement so that coolant may be caused to cool the entire element or may be caused to cool one of the said element parts to cool and simultaneously de-humidify a stream of air flowing past the element, the control valve arrangement caus ing the flow rate of coolant through said one element part to be greater when refrigerant is supplied only to said one element part than the flow rate of coolant through said one element part when coolant is sup- plied to the entire element.

In order that the invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawing which is a schematic diagram of part of an air-conditioning apparatus incorporating a heat exchanger in accordance with the invention.

Referring to the drawing one cooling element of a heat exchanger of an air conditioning apparatus is shown, this element comprising a coil formed of two separate parts, the parts, in this embodiment each comprising precisely one half of the coil 1, 2. Of course, the two parts could be of different sizes if desired. The half coils 1, 2 are connecte in parallel and are located within a passage which is traversed by air flowing through an air-conditioning apparatus. The arrangement is such that the air which contacts one of the half coils does not subsequently contact the other half coil.

The half coils are supplied with a refrigerant which is initially compressed in a compressor 3 to provide high pressure refrigerant vapour and is subsequently condensed in a condensor 4 to reduce the temperature thereof. The resultant liquid high pressure refrigerant is fed to a liquid receiver tank 5 from which it is supplied through two thermostatic expansion valves 6,7 to the half coils 1, 2 which together form the cooling element or coil. The thermostatic expansion valves are thermostatically controlled by sensors which sense the temperature of the coolant leaving the respective half coils. The supply of coolant to one of the half coils 2 is controlled additionally by a solenoid controlled valve 8 which is operated in response to signals generated by a humidistat 9 which is in the space which is being air conditioned~ A humidistat is a device adapted to sense the humidity of the air.

Each half coil is manufactured from 0 625 inches outside diameter copper tube provided with aluminium plate fins which are spaced at a spring of 12 fins per inch of tube length.

Under normal operating conditions, the air cooling half coils are both supplied with the liquid refrigerant at a low temperature, the liquid refrigerant expanding through the thermostatic expansion valves and causing the half coils to achieve a low temperature so that air passing over the half coils is cooled. During this cooling process, a small proportion of the total cooling achieved may manifest itself in the form of moisture condensation but the greatest proportion of the cooling effect is manifested as useful cooling of air.

However, under special circumstances, where the air which is brought into contact with the coil halves is of a high moisture content, the air, after it has been in contact with the coil halves may still have excessive moisture therein, as a result of the high original moisture content, and thus the reauired conditions will not be maintained within the air conditioned space, particu larly in respect of relative humidity. If this situation is detected by the humidistat 9 the solenoid controlled valve 8, which is controlled by the humidistat 9, will be closed so that all the refrigerant will then pass through one single half 1 of the coil. Consequently there is then a greater flow rate of coolant through this half coil than when coolant was flowing through both half coils, and thus the temperature of this half 1 of the coil falls to a lower level than previously and the temperature of this half of the coil is such that air flowing past the respective half coil is dehumidified at a substantially increased rate, greater quantities of the water then condensing on the half coil, then condensed on the whole coil during operation of both coil halves. The air flowing past the operative half of the coil is cooled to a very low temperature, and is subsequently remixed with the air flowing past the other half of the coil which is not cooled at all. Thus the remixed air has a satisfactory temperature.

The end result is that the combined stream of air that flows past the two coil halves air is cooled by a similar amount overall as when the two half coils are both supplied with refrigerant simultaneously, but the overall humidity of the combined stream of air is reduced By choosing a suitable coil temperature for normal operation, namely operation when both coil halves are operative, virtually all the cooling effect derived from the refrigerant may be achieved in a useful form for the purposes of"dry bulb"temperature controlled within the conditioned space. Thus the cooling effect of the coil halves is solely used to cool the air, and there is virtually no condensation on the coil halves. Thus the energy supplied to the compressor is utilise in an optimum manner.

In the second mode of operation described above the dehumidification and cooling process is performed by part of the coil only and it has been found that greatly accelerated condensation rates may be achieved. It is to be appreciated that in the previously mentioned prior proposed air conditioning apparatus when it has been necessary to dehumidify the air it has been equally necessary to reduce all the cooling coil to a low temperature to achieve the necessary condensation of water, and conse quently the air that passes the very cold coil is too cold to be returned directly to the space being air conditioned. Subsequent re-heating of the air has thus been necessitated which has caused substantial quantities of energy to be wasted. It is to be appreciated that in utilising the present invention energy consumption may be minimised.

Whilst the invention has been described with reference to the provision of a coolant in the form of a compressed refrigerant which is supplied to a cooling coil through a thermostatic expansion valve it is to be appreciated that the invention may be utilised in connection with alternative types of refrigerant and the important feature of the invention is that the refrigerant may either be provided to one part or half of the coil to bring one said half of the coil to a very low temperature or the refrigerant may be provided to both halves of the coil to bring the whole of the coil to a somewhat higher temperature.

Claims (9)

1. WHAT WE CLAIM IS :- 1. A heat exchanger arrangement for an air-conditioning apparatus, said heat exchanger comprising at least one cooling element comprising two element parts for cooling air passing past the element and means for causing an air stream to flow past the element so that every portion of the air stream which contacts one element part does not subsequently contact the other element part, the element being provided with a control valve arrangement, and means for operating the control valve arrangement so that coolant may be caused to cool the entire element or may be caused to cool one of the said element parts to cool and simultaneously de-humidify a stream of air flowing past the element, the control valve arrangement causing the flow rate of coolant through said one element part to be greater when refrigerant is supplied only to said one element part than the flow rate of coolant through said one element part when coolant is supplied to the entire element.
2. 2. A heat exchanger arrangement for an air conditioning apparatus according to claim 1, wherein each element comprises two parts for the flow of refrigerant which are connected in parallel, the control valve arrangement including a valve adapted to permit the flow of coolant through both said parts or to permit the now of coolant only through said one part.
3. 3. A heat exchanger arrangement for an air-conditioning apparatus according to claim 2, wherein the said valve comprising a solenoid controlled valve which is controllable in response to a humidistat.
4. 4. A heat exchanger arrangement for an air-conditioning apparatus according to claim 2 or 3 wherein the control valve arrangement includes thermostatic control valve means to control the flow of coolant through said element parts.
5. 5. An air conditioning apparatus including a heat exchanger according to any one of the preceding claims.
6. 6. An air conditioning apparatus according to claim 5 including means for supplying a high pressure liquid refrigerant to said cooling element, the arrangement being such that the refrigerant is expanded and vapourised within the cooling element.
7. 7. An air conditioning apparatus according to claim 6 as dependant upon claim 4 wherein said thermostatic valve means comprise thermostatic expansion valves.
8. 8. A heat exchanger for an air condi tioning apparatus substantially as herein described with reference to and as illustrated in the accompanying drawing.
9. 9. An air conditioning apparatus including a heat exchanger according to claim 8.