GB2122335A

GB2122335A - Air conditioning system

Info

Publication number: GB2122335A
Application number: GB08316079A
Authority: GB
Inventors: George Peter Wright
Original assignee: WRIGHT AIR CONDITIONING LIMITE
Current assignee: WRIGHT AIR CONDITIONING LIMITE
Priority date: 1982-06-15
Filing date: 1983-06-13
Publication date: 1984-01-11
Also published as: GB2122335B; GB8316079D0

Abstract

Air from a room 10 to be conditioned is passed through respective channels in a module 11 as a plurality of mutually parallel streams. In each channel, the respective air stream passes sequentially over a cooling coil 24 and also over an expansion coil 15 of a compression refrigeration system which also includes a condenser 16. The coils 15 and 24 in each channel are selectively operable so that the respective air stream is either cooled by the refrigerant in the coil 15 with the heated refrigerant subsequently being cooled by a water/glycol mixture in the condenser 16, or is cooled by the same water/glycol mixture flowing through the coil 24. In both cases, the heated water/glycol mixture is passed to dry coolers 18 where it is cooled by the ambient external atmosphere. A sensor 25 is responsive to the temperature in the room 10 and operates to bring the coils 15 and 24 selectively into operation from channel to channel in accordance with that temperature. <IMAGE>

Description

SPECIFICATION Air conditioning system This invention relates to apparatus, such as an air conditioning system, for cooling a fluid.

Conventional air conditioning systems typically comprise a refrigeration system having an expan sion coil where a refrigerant absorbs heat from air drawn off from the space to be conditioned, the refrigerant itself then being cooled by heat exchange with a coolant, such as water or a water/glycol mixture. The heat thus absorbed from the refrigerant is dissipated by passing the coolant through a cooling tower, dry cooler or other heat rejection device which is in contact with the surrounding atmosphere.

During periods (such as in winter) when the surrounding atmosphere is at a low temperature, the coolant is cooled sufficiently that it is capable of cooling the air in the space to be conditioned without the need to operate the refrigeration system. By making use of this effect, a saving can be made in the cost of operating the air conditioning system.

The normal manner of implementing this effect is to provide a cooling coil where the coolant can absorb heat from the air, the cooling coil being disposed upstream of the expansion coil of the refrigeration system with respect to the direction of air flow. It then becomes possible to control the operation of the air conditioning system in accordance with the ambient conditions.

When the surrounding atmosphere is at a temperature which is not sufficiently low for the cooling coil to be operated alone but which is nevertheless still cold, in principle it is possible to bring the expansion coil and the cooling coil into operation at the same time, so that the cooling coil removes some of the loading from the refrigeration system. In practice, however, problems are encountered here because the cooling coil depresses the temperature of the air before the latter reaches the expansion coil causing the refrigerant to evaporate at a lower temperature than the refrigeration system has been designed for.

This not only reduces the efficiency of the expansion coil, but also produces unwanted dehumidification of the air. Accordingly, it is not possible to take full advantage of the economies which could be obtained by using the coolant to cool the air.

It is an object of the present invention to obviate or mitigate this disadvantage.

According to a first aspect of the present invention, apparatus for cooling a fluid comprises a plurality of channels through which respective streams of said fluid flow in parallel with one another, each channel including first heat exchange means composed of a heat exchanger wherein a first coolant can be placed in heat-exchange relation with the respective fluid stream to absorb heat therefrom and heat transfer means wherein the thus heated first coolant can be cooled, each channel also including second heat exchange means wherein a second coolant can be placed in heat-exchange relation with the respective fluid stream to absorb heat therefrom, the first and second heat exchange means in each channel being selectively operable, the apparatus further comprising cooling means wherein the second coolant is cooled by heat exchange with the external ambient atmosphere and a control whereby the first and second heat ex change means can be brought into operation selec tively from channel to channel.

Preferably, the fluid to be cooled is circulated from a reservoir through said channels and back into the reservoir, and the control includes a sensor which is operative to sense the temperature of the fluid in said reservoir and which is arranged to bring the first and second heat exchange means selectively into operation in dependence upon the temperature thus sensed. Where the apparatus is in air conditioning system, the reservoir will be constituted by the space (e.g. a room in a building) which is to be conditioned.

A detector may be provided to detect when the temperature of the cooled second coolant exceeds a predetermined value, the first heat exchange means of all said channels being brought into operation in response to such detection.

Advantageously, the apparatus further comprises control means which controls operation of the cooling means such that the cooled second coolant is prevented from falling below a preset temperature. This will prevent the fluid flowing through the channels from being cooled excessively when the second heat exchange means of all said channels are operational, an effect which will be most pronounced in periods such as during winter when the external ambient atmosphere is rather cold.

Desirably, the heated first coolant is cooled by the second coolant in the heat transfer means.

Conveniently, the first heat exchange means of each channel is in the form of a compression refrigeration system with said heat exchanger and said heat transfer means being constituted respectively by an expansion coil and a condenser of said system.

The first and second heat exchange means are preferably sequentially disposed in each channel with respect to the direction of fluid flow.

According to a second aspect of the invention, an air conditioning system comprises a plurality of channels arranged in parallel with one another and through which air from a space to be conditioned is passed, each channel including first heat exchange means composed of a heat exchanger wherein a first coolant can be placed in heat-exchange relation with said airto absorb heat therefrom and heat transfer means wherein the thus heated first coolant can be cooled, each channel also comprising second heat exchange means wherein a second coolant can be placed in heat-exchange relation with said air to absorb heat therefrom, the first and second heat exchange means in each channel being selectively operable, the air conditioning system further comprising a cooling means wherein the second coolant is cooled by heat-exchange with the ambient atmosphere externally of said space, and a sensor which is responsive to the temperature of the air in said space and which is operative to bring the first and second heat exchange means selectively into operation from channel to channel in accordance with said temperature.

The invention will now be further described, by way of example only, with reference to the-accompanying drawings, in which: Figure 1 is a schematic diagram of a first embodiment of apparatus according to the invention, in the form of an air conditioning system; Figure 2 is an enlarged view of part of the system shown in Figure 1; and Figure 3 is a schematic diagram of a second embodiment of apparatus according to the invention, also in the form of an air conditioning system.

Referring first to Figures 1 and 2, the system illustrated therein is designed to condition the air in an enclosed space 10, such as a room in a building.

Disposed in the room 10 is a module 11 through which air is drawn for cooling, the-cooled air being recirculated through vents 12 or the like in a floor 13 of the room. Arrows 14 indicate the direction of circulation of the air.

Air entering the module 11 forms two mutually parallel streams which flow through respective channels. Provided within each channel is an expansion coil 15 of a respective compression refrigeration sytem, which system also includes a condenser 16.

When the refrigeration system is operational, a refrigerant is expanded in the coil 15 to absorb heat from the air entering the module 11, and the heated refrigerant is subsequently passed to the condenser where it is cooled by a suitable coolant, such as water or a water/glycol mixture. From the condenser 16, the coolant from both channels is passed by way of a common pump unit 17 (see Figure 1) to a series of dry coolers 18 or other heat rejection devices which are in contact with the external atmosphere, such that the coolant is thereby cooled. The coolant then flows from the dry coolers 18 back to the condensers 16 by way of control valves 19 and 20 in each channel.Reference numeral 21 denotes a header/expansion tank for the coolant, while reference numeral 22 designates a control device which operates fans (not shown) of the dry coolers 18 in dependence upon signals received from a sensor 23 which monitors the temperature of the coolant flowing from the coolers 18.

In each channel within the module 11, a cooling coil 24 is disposed upstream of the expansion coil 15 with respect to the direction of air flow through the channel. By suitable operation of the respective control valve 19, coolant flowing from the dry coolers 18 can be passed through the coil 24 to cool the air flowing through the respective channel.

Operation of the two valves 19 is controlled by signals from a sensor 25 monitoring the temperature of the air in the room 10. The valves 19 are also responsive to signals from a thermostat detector 26 which detects when the temperature of the coolant flowing from the dry coolers 18 exceeds a predetermined value.

The above-described air conditioning system has four different modes of operation. In a first mode, both refrigeration systems are inoperative and the valves 19 and 20 are operated so that the coolant flows through one only of the coils 24 and by-passes the respective condenser 16. In a second mode, both refrigeration systems remain inoperative, but the valves 19 and 20 are now operated so that the coolant flows through both of the coils 24 and again by-passes the condensers 16. In both of these modes, therefore, the air passing through the module 11 is cooled by the coolant in one or both of the coils 24 alone. In the third mode of operation, the refrigeration system associated with one of the channels is in operation, and the valves 19 and 20 of that channel are operated so that the coolant now by-passes the respective coil 24 and flows through the respective condenser 16.Air passing through one channel is now cooled by the refrigerant in the expansion coil 15 alone, while air in the other channel is still cooled solely by the coolant in the coil 24. In the fourth mode of operation, both refrigeration systems are in operation and the valves 19 and 20 are operated so that the coolant by-passes the coils 24 and flows through the condensers 16 of both channels. Air flowing through the channels is now cooled solely by the refrigerant in the expansion coils 15.

Switching of the air conditioning system between these four modes of operation is performed automatically in order to maintain the air temperature in the room 10 at the desired level. The particular mode in which the system operates at any given time will be dependent upon two main factors, namely the amount of heat beinggenerated in the room 10 and the temperature of the external atmosphere. Dealing with the first of these factors, when the amount of heat generated causes the air temperature in the room to rise beyond a certain level, the sensor 25 switches the mode of operation of the system to increase its cooling effect. Similarly, if the air temperature in the room should fall below a certain level, then the sensor 25 will switch the mode of operation of the system to decrease its cooling effect.

With reference to the second of the abovementioned factors, during periods (such as in winter) when the external atmosphere is at a low temperature, the coolant will be cooled in the dry coolers 18 to such a degree that it is capable of performing the required cooling effect without the need to operate the refrigeration system. Accordingly, the aircondi- tioning system will operate in either its first or its second mode depending upon just how cold the external atmosphere is (unless of course the air temperature in the room rises excessively in the manner explained above). Under these conditions, there is a danger that the coolant may cause undue cooling of the air in the room 10 in the event that the external atmosphere becomes very cold: to prevent this from happening, the control device 22 limits operation of the fans in the dry coolers 18 so that the temperature of the coolant does not fall below a pre-set value1 chosen in accordance with the desired operating conditions. For example, where the air entering the module 11 is at a temperature of 72"F (22.2"C) and it must be cooled to a temperature of 60 F (15.5 C) to maintain the desired conditions in the room 10, the control device 22 can be arranged to maintain the coolant at a minimum temperature of 50 F (10.0 C).

In periods when the external atmosphere is at higher temperatures (such as in spring and autumn), the temperature of the coolant flowing from the dry coolers 18 will rise so that the air issuing from the module 11 becomes warmer. This causes a rise in temperture of the air in the room 10 sufficient to cause the sensor 25 to switch the air conditioning system to its third mode of operation. In other words, the coolant is not now cooled sufficiently that it can perform the required cooling effect on its own, and it becomes necessary to bring into operation the refrigeration system of one of the channels. By way of example, suppose that air entering the module 11 at a temperature of 72"F (22.2 C) must be cooled to substantially 60"F (1 5.5"C) as before.Assuming that equal volumes of airflow through both channels in the module 11, then the output temperature of the mixed air from both channels issuing from the module can be taken to be the average of the two temperatures to which the individual air streams are cooled. Thus, if the expansion-coil 15 in one channel operates at 56"F (13.3 C), then the required effect will be obtained if the air in the other channel is cooled to, say, 65"F (18.3 C) by the coil 24. Typically, the air conditioning system will operate in this mode for coolant temperatures of between 50"F (1 O.00C) and 68F (20C).

When (for example in the summer) the temperature of the external atmosphere exceeds a certain value, it will not be possible for the coolant to be cooled sufficiently in the dry coolers 18 for the above-described effect to be maintained. Under these conditions, it becomes necessary to bring the refrigeration system of the other channel into operation, and accordingly the air conditioning system is now operated in its fourth mode.

Normally, the air conditioning system seeks to operate in the most economical manner possible, having regard to the heat being generated in the room 10 and the temperature of the external atmosphere. Thus, at least one of the refrigeration systems will be turned off whenever possible. When however the coolant flowing from the dry coolers 18 exceeds a predetermined temperature, for example 68"F (20"C), the system will be able to operate effectively only with both refrigeration systems turned on. To prevent the system from being switched unnecessarily from mode to mode in this situation, the detector 26 commands the system to operate in its fourth mode in the event that the coolant exceeds the said predetermined temperature.Such a situation may arise not only at times when the external atmosphere is at a high temperature, but also during cooler periods in the event of a malfunction in the fans of any one of the dry coolers 18.

From the above description, it will be manifest that considerable economies can be made in the operating costs of the air conditioning system by relying on the coolant to perform at least part of the desired cooling effect, so that for a certain period of the year one or both of the refrigeration systems can be inoperative.

Of course, it would still be possible to operate the air conditioning system at reduced power simply by turning off one of the refrigeration systems even if the cooling coils 24 were not provided. However, the cooling effect produced by one refrigeration system operating alone would be rather less than that produced by the refrigeration system operating in conjunction with one of the cooling coils 24 in the manner described above. Accordingly, the provision of the coils 24 not only increases the period of the year for which one of the refrigeration systems can be shut down, but also reduces the loading on the refrigeration system which remains working.

Moreover, because the air entering the module 11 is effectively divided into two channels, when the air conditioning system is operating in its second mode the operational cooling coil 24 will produce some form of cooling effect as long as the temperature of the coolant is at least a few degrees below that of the air entering the module. Consequently, as compared with the conventional arrangement described previouslywherein an expansion coil and a cooling coil are operated together, the system can remain in operation in its third mode at higher coolant temperatures and can therefore remain in this economy mode for a longer period of the year. Furthermore, even greater economies can be obtained by providing more than two channels for cooling the air, thereby increasing the number of economy modes in which the system can be operated.

In the air conditioning system described above, the cooling coil 24 in each channel is disposed upstream of the respective expansion coil 15 with respect to the direction of air flow. With such an arrangement, dehumidification of the air passing through the module 11 will occur for the reasons stated previously if, for example, either one of the valves 19 jams so that both of the coils 24 and 15 in the respective channel operate together. Where such dehumidification is likely to be a problem, the positioning of the coils can be reversed, i.e. so that each cooling coil 24 is disposed downstream of the respective expansion coil 15.

A second embodiment of the air conditioning system is shown in Figure 3, and is generally similar to the arrangement described above with reference to Figures 1 and 2, similar parts being accorded the same reference numerals. In the system of Figure 3, however, the coolant is no longer employed to cool the refrigerant flowing through the expansion coils 15. Instead, the condensers 16 of the refrigeration systems are air-cooled and are disposed outside the module 11, being connected to the expansion coils 15 by way of direct expansion pipework 27. This enables the control valves 20 to be omitted, thereby simplifying the construction and reducing the installation cost of the air conditioning system. In addition, improved cooling capacity can be obtained from the refrigeration sytems.

Also in this embodiment, the thermostat detector 26 is no longer responsive to the temperature of the coolant flowing from the dry coolers 18, but rather is sensitive to the temperature of the external ambient atmosphere. When this temperature exceeds a predetermined value, such as 60 F(1 5.5 C), at which the cooling coils 24 can no longer be effectively operated, the detector 26 operates the valves 19 to switch to both of the expansion coils 15.

Although in the air conditioning system described above air is drawn from the room 10 into the upper part of the module 11 and the cooled air issues through the vents 12 in the floor 13, the direction of air flow could be reversed so that warm air is drawn through the vents 12 and cooled air issues from the top of the module 11. In this case, the cooling coils 24 and the expansion coils 15 are preferably reversed from their illustrated positions so that the former are still upstream of the latter.

In the above description, reference has been made to the module 11 comprising channels through which respective air streams flow. It is to be appreciated, however, that these channels may be notional, i.e. they need not be positively divided off from one another. For example, where the cooling coils 24 are disposed immediately upstream of the coils 15, the air flowing over each coil 24 will immediately thereafter flow over the respective coil 15, and there will be no need for the two air streams to be physically separated.

Although the invention has been described above in relation to an air conditioning system, it will be manifest that it has many other applications. For example, the invention could be used in a refrigeration unit with the room 10 being replaced by a space which is to be refrigerated. In addition, the invention can be utilized to cool fluids other than air: for example, it could be applied to a water cooling system.

Claims

1. Apparatus for cooling a fluid, comprising a plurality of channels through which respective streams of said fluid flow in parallel with one another, each channel including first heat exchange means composed of a heat exchangerwherein a first coolant can be placed in heat-exchange relation with the respective fluid stream to absorb heat therefrom and heat transfer means wherein the thus heated first coolant can be cooled, each channel also including second heat exchange means wherein a second coolant can be placed in heat-exchange relation with the respective fluid stream to absorb heat therefrom, the first and second heat exchange means in each channel being selectively operable, the apparatus further comprising cooling means wherein the second coolant is cooled by heat- exchange with the external ambient atmosphere and a control whereby the first and second heat exchange means can be brought into operation selectively from channel to channel.

2. Apparatus as claimed in claim 1, wherein the fluid is circulated from a reservoir through said channels and back into the reservoir, and the control includes a sensor which is arranged to bring the first and second heat exchange means selectively into operation in dependence upon the temperature thus sensed.

3. Apparatus as claimed in claim 2 in the form of an air conditioning system, wherein said reservoir is constituted by a space to be conditioned.

4. Apparatus as claimed in claim 1,2 or 3, further comprising a detector which detects when the temperature of the cooled second coolant exceeds a predetermined value and which brings the first heat exchange means of all said channels into operation in response to such direction.

5. Apparatus as claimed in any preceding claim, further comprising control means which controls operation of the cooling means such that the cooled second coolant is prevented from falling below a preset temperature.

6. Apparatus as claimed in any preceding claim, wherein the heated first coolant is cooled by the second coolant in the heat transfer means.

7. Apparatus as claimed in any preceding claim, wherein the first heat exchange means of each channel is in the form of a compression refrigeration system with said heat exchanger and said heat transfer means being constituted respectively by an expansion coil and a condenser of said system.

8. Apparatus as claimed in any preceding claim, wherein the first and second heat exchange means are sequentially disposed in each channel with respect to the direction of fluid flow.

9. An air conditioning system comprising a plurality of channels arranged in parallel with one another and through which air from a space to be conditioned is passed, each channel including first heat exchange means composed of a heat exchanger wherein a first coolant can be placed in heatexchange relation with said air to absorb heat therefrom and heat transfer means wherein the thus heated first coolant can be cooled, each channel also comprising second heat exchange means wherein a second coolant can be placed in heat-exchange relation with said air to absorb heat therefrom, the first and second heat exchange means in each channel being selectively operable, the air conditioning system further comprising a cooling means wherein the second coolant is cooled by heatexchange with the ambient atmosphere externally of said space, and a sensor which is responsive to the temperature of the air in said space and which is operative to bring the first and second heat exchange means selectively into operation from channel to channel in accordance with said temperature.

10. Apparatus for cooling a fluid, substatially as hereinbefore described with reference to the accompanying drawings.