AU2011253582A1 - Cooling system - Google Patents

Abstract

Abstract A cooling system including a primary fluid circuit about which a primary fluid is circulated. The primary fluid circuit includes a compressor to compress the primary fluid; a condenser in which the compressed fluid is condensed to release heat; a cooler to 5 cool the condensed fluid; an expansion device to expand the primary fluid; and an evaporator. The cooling system further includes an arrangement to thermally communicate the expanded primary fluid in the evaporator with an air stream to cool the air. The cooler may be configured to cool the primary fluid by heat exchange with a further fluid. a" -J \/V jjj~JjJJ r0.\/V z \/ r o' JJ\A/ < JJJ~j~\/V 0~zi0 C., V mz /V a \/V z \UJ 0A 0 \/V4

Description

P/00101 1 Regulatior 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Cooling system The following statement is a full description of this invention, including the best method of performing it known to us: 2 Cooling System Field of the invention The invention relates to cooling, e.g. to cooling an environment. The invention will be described with respect to air conditioning of a mine but has broader application. 5 Background of the invention In an existing cooling system a gaseous refrigerant is compressed and driven through a condenser in which the refrigerant condenses and heat is rejected to a heat sink, e.g. the atmosphere. Liquid refrigerant is conveyed from the condenser through an expansion valve and an evaporator in which the refrigerant evaporates and heat is 10 absorbed to provide cooling, e.g. to provide cooling to a flow of air. Gaseous refrigerant from the evaporator is returned to the compressor thus completing a fluid circuit. Another existing approach to cooling, referred to as evaporative cooling, involves bringing a stream of water into intimate contact with a stream of dry air so that a fraction of the water evaporates to produce respective streams of cooler water and warmer 15 moist air. Cooling can be energy intensive. It would be desirable to produce a more energy efficient cooling system. Water is scarce in some environments. It would be desirable to produce a cooling system which did not consume water. It is an object of the invention to provide an improved cooling system, or at least to 20 provide an alternative in the marketplace. Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a 25 person skilled in the art.

3 Summary of the invention One aspect of the invention provides a cooling system including a primary fluid circuit about which a primary fluid is circulated; the primary fluid circuit including 5 a compressor to compress the primary fluid; a condenser in which the compressed fluid is condensed to release heat; a cooler to cool the condensed fluid; an expansion device to expand the primary fluid; and an evaporator; 10 the cooling system further including an arrangement to thermally communicate the expanded primary fluid in the evaporator with an air stream to cool the air. The system may be employed to cool various fluids, but preferably the system includes an arrangement to thermally communicate the evaporator with air to cool the air. The evaporator could simply exposed the primary fluid to the air. 15 Preferably, the cooler is configured to cool the primary fluid by heat exchange with a further fluid and the further fluid may be cooled evaporatively. The cooler may thermally communicate with a heat exchange arrangement to cool the further fluid. The further fluid preferably communicates with an evaporative cooling device which evaporatively cools the second fluid and collects and circulates unevaporated second fluid to the 20 cooler. The arrangement to thermally communicate the expanded primary fluid with an air stream to be cooled may include the further fluid circuit in heat exchange arrangement with the expanded primary fluid at the evaporator, the further fluid circuit passing the further fluid to an air cooler which cools an air stream. The air cooler is preferably an 4 evaporative air cooler which directly contacts the further fluid with the air stream to provide a cooled air stream and condensate stream. In a further preferred form, a portion of the condensate stream communicates with the evaporative cooling device to maintain further fluid levels in the cooler. A condensate 5 collector may communicate with the portion of the condensate stream which then communicates with the evaporative cooling device to act as a buffer and maintain the fluid levels in the second fluid circuit. The condensate collector assists in maintaining the amount of fluid in the second fluid circuit is above a set volume. Preferably the second fluid is the same as the further fluid. 10 The condenser may be configured to reject heat to the atmosphere, in which case the condenser preferably cools the fluid to within 5-10 0 K of dry bulb temperature. The cooler preferably is configured to cool the fluid to within 5-10 K of wet bulb temperature. Brief description of the drawings / figures Figure 1 is a schematic diagram of a cooling system in accordance with a preferred 15 embodiment of the invention; and Figure 2 is a mollier diagram illustrating the operation of the cooling system of figure 1. Detailed description of the embodiments The cooling system 10 includes a principle fluid circuit 20 which is a closed circuit about which fluid is circulated. The circuit 20 includes a compressor 21, condenser 23, cooler 20 25, expansion valve 27 and an evaporator 28 connected in series by conduits 22, 24, 26 and 29. The compressor 21 receives gaseous refrigerant from conduit 29 (corresponding to point 1 in figure 2) and compresses and drives the gaseous refrigerant along conduit 22 (corresponding to point 2 in figure 2). As illustrated in figure 2 the compressor increases 25 both pressure and enthalpy of the refrigerant.

5 The condenser 23 receives the hot high pressure gaseous refrigerant from the conduit 22. The condenser 23 includes galleries of externally finned serpentine tubes. The refrigerant is carried within the tubes and atmospheric air is driven over the tubes to effect heat exchange between the refrigerant and the atmosphere. Ideally this heat 5 exchange occurs at constant (refrigerant) pressure as illustrated in figure 2. As heat is rejected to the atmosphere and the refrigerant cooled, it condenses (i.e. forms a liquid) thus releasing its latent heat to the atmosphere. The refrigerant exits the condenser via conduit 24 corresponding to point 3 in figure 2. Ideally the refrigerant is fully condensed and reduced close to dry bulb temperature. 10 According to the present invention the condensed, liquid, refrigerant is further cooled, or 'sub-cooled', by an additional cooling stage. In this embodiment the additional cooling stage takes the form of cooler 25 which includes an evaporative cooling tower 25B and is described in more detail below. The sub-cooled refrigerant exits the cooler 25A via conduit 26 (corresponding to point 4 15 in figure 2) before passing through an expansion valve 27 and an evaporator 28 to provide cooling to an additional fluid circuit 30 and ultimately a stream of air 40. The evaporator 28 includes a series of spaced thin plates defining an interleaved pair of multi-layered flow paths. The refrigerant is driven through one of the flow paths and water is driven through the other to effect heat exchange between the refrigerant and 20 the water of the circuit 30. The refrigerant absorbs heat from the water 30 as it evaporates to provide cooling to the water 30. The refrigerant preferably fully evaporates as it passes through the evaporator 28. The gaseous refrigerant is returned to the compressor 21 (corresponding to point 1 in figure 2) via the line 29 thus completing the principle fluid circuit 20. 25 The cooler 25 includes a cooling tower 25B along a secondary fluid circuit. This secondary fluid circuit is in heat exchange relation with the primary fluid circuit 20 at a heat exchanger in the form of liquid sub-cooler 25A.

6 The secondary fluid circuit 25 includes the liquid sub-cooler 25A and the cooling tower 25B, a conduit 25C defining a flow path for conveying water from the sub-cooler 25A to the tower 25B, and a return conduit 25D for conveying water from the cooling tower 25B to the sub-cooler 25A. A pump 25E is positioned along the conduit 25D to drive water 5 about the secondary fluid circuit. The sub-cooler 25A receives cool water from the conduit 25D which water is warmed as it cools the refrigerant so that the conduit 25C returns relatively warmer water to the tower 25B. The sub-cooler 25A includes a series of spaced thin plates defining an interleaved pair of multi-layered flow paths. The refrigerant is driven through one of the 10 flow paths and water is driven through the other The tower 25B includes structure to convey a flow of air and a fan to drive air therethrough. Water sprays receive warm water from the conduit 25C and spray the warm water into the conveyed air. Thus the air emerging from the cooling tower 25B is relatively warm and moist, and the water from the sprays which is not evaporated is 15 collected at the bottom of the tower 25B and is relatively cool. In this embodiment the condenser 23 serves to in substance reduce the refrigerant temperature close to dry bulb temperature and the cooler 25 serves to in substance reduce the refrigerant temperature close to wet bulb temperature. Of course, the condenser and the cooler 25 cannot fully reduce the refrigerant temperature to dry bulb 20 temperature and wet bulb temperature respectively - some temperature differential is required in order for heat transfer. A temperature differential of 100 or less is considered practical, whilst a temperature differential of 50 is highly desirable. The further fluid circuit 30 includes the evaporator 28 and a bulk air cooler 30A. A conduit 30C defines a flow path from the evaporator 28 to the bulk air cooler 30A. A 25 conduit 30D defines a flow path to convey water from the bulk air cooler 30A to the evaporator 28. A pump 30E is positioned along the conduit 30D to drive water about the circuit 30. The bulk air cooler 30A includes structure to convey air and a fan to drive air therethrough. The bulk air cooler 30A further includes sprays to spray chilled water from the conduit 30C into the conveyed air whereby the chilled water intimately contacts the 7 stream of air 40 to cool it. The further fluid circuit 30 is thus in heat exchange relation with the air 40 and the further fluid circuit 30 including the bulk air cooler 30A constitutes an arrangement to thermally communicate the evaporator 28 with the air 40. The bulk air cooler 30E includes a tray 30F to collect the sprayed water. The conduit 30D 5 connects to the tray 30F to receive the collected water. Within the bulk air cooler 30A as the stream of air 40 is cooled, any moisture carried thereby condenses. This condensate is also collected in the tray 30F whereby the tray 30F constitutes a collector to collect condensate. A condensate transfer system 50 transfers water from the fluid circuit 30, including a 10 portion of the condensate from the bulk air cooler 30E, to the cooler 25. In operation this condensate is evaporated within the tower 25B to cool the refrigerant at liquid sub cooler 25A. The condensate transfer system 50 includes a conduit 50A positioned to draw water from conduit 30D at a point downstream of the pump 30E and to convey the drawn 15 water to a storage tank 50B. A conduit 50C communicates the storage tank 50B with the cooler 25. In this embodiment the conduit 50C communicates directly with the tower 25B. A pump 50D is positioned along the conduit 50C to drive condensate from the tank 50B to the cooling tower 25B as required. The pump 50B is controlled to maintain a constant 20 volume of water in the cooling tower 25B. A controllable valve 50E along the conduit 50A regulates the flow of condensate along the conduit 50A so as to maintain a constant volume of water in the fluid circuit 30. It will be appreciated that the volume of condensate produced in the bulk air cooler 30A and the volume of water evaporated in the cooling tower 25B will vary depending on 25 environmental conditions so that the volume of condensate produced and water evaporated is rarely in unison. As such there is a mismatch between supply of and demand for condensate. The vessel 50B provides a buffer to allow for this mismatch.

8 Preferred forms of the invention lead to a reduction in specific energy consumption; i.e. a reduction in the amount of energy consumed for a given amount of cooling, compared to an otherwise similar refrigeration system without sub-cooling. With reference to figure 2 the amount of sub-cooling 3 to 4 can be projected down onto the line 5-1 and 5 represents an additional amount of cooling to the airstream 40 without additional work input from the compressor 21. This additional amount of cooling approaches the difference between wet bulb temperature and dry bulb temperature which on a sunny day in a temperate climate can be as much as 20 to 250 Kelvin. Moreover the described embodiment can operate in such an environment without an 10 external water supply because sufficient water is extracted from the atmosphere by the bulk air cooler 40. As such preferred forms of the invention are particularly suited to operation at remote mining sites wherein water is scarce. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features 15 mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims (9)

1. A cooling system including a primary fluid circuit about which a primary fluid is circulated; the primary fluid circuit including 5 a compressor to compress the primary fluid; a condenser in which the compressed fluid is condensed to release heat; a cooler to cool the condensed fluid; an expansion device to expand the primary fluid; and an evaporator; 10 the cooling system further including an arrangement to thermally communicate the expanded primary fluid in the evaporator with an air stream to cool the air.

2. The cooling system of claim 1 wherein the cooler is configured to cool the primary fluid by heat exchange with a second fluid in a second fluid circuit.

3. The cooling system of claim 2 wherein the second fluid being cooled 15 evaporatively.

4. The cooling device of claim 3 wherein the second fluid communicates with an evaporative cooling device which evaporatively cools the second fluid and collects and circulates unevaporated second fluid to the cooler.

5. The cooling device of anyone of the preceding claims wherein the arrangement 20 to thermally communicate the expanded primary fluid with the air stream to be cooled includes a further fluid circuit in heat exchange arrangement with the expanded primary 10 fluid at the evaporator, the further fluid circuit passing the further fluid to an air cooler which cools the air stream.

6. The cooling system of claim 5 wherein the air cooler is an evaporative air cooler which directly contacts the further fluid with the air stream to provide a cooled air stream 5 and condensate stream.

7. The cooling system of claim 6 wherein a portion of the condensate stream communicates with the evaporative cooling device to maintain fluid levels in the cooler.

8. The cooling system of claim 6 wherein a portion of the condensate stream communicates with a condensate collector which communicates with the evaporative 10 cooling device to maintain the fluid levels in the further fluid circuit.

9. The cooling system of claim 7 or 8 wherein the amount of fluid in the second fluid circuit is above a set volume.