WO1994021919A1

WO1994021919A1 - Equalization of load across a compressor upon shutdown

Info

Publication number: WO1994021919A1
Application number: PCT/AU1994/000140
Authority: WO
Inventors: Robert Arden Higginbottom
Original assignee: Robert Arden Higginbottom
Priority date: 1993-03-25
Filing date: 1994-03-23
Publication date: 1994-09-29
Also published as: IN181812B; TW234166B

Abstract

A refrigeration, air-conditioning, or like system including a compressor (1, 15) having an inlet (29) and an outlet (28), the inlet (29) and the outlet (28) having an operative connection (27) with a valve (30) therein; the valve (30) being open when the compressor (1, 15) is off, and closed when the compressor (1, 15) is on.

Description

EQUALIZATION OF LOAD ACROSS A COMPRESSOR UPON SHUTDOWN

This invention relates to the equalization of loads in apparatus and refers particularly, though not exclusively, to such equalization for pumps, compressors, and motors or generators for use in refrigeration, air-conditioning, or like systems.

Throughout this specification reference to "refrigeration" includes reference to air-conditioning or any other system where a compressor, pump, generator or motor is used in which unequal starting loads on the motor, compressor, generator, pump or the like is a problem.

With refrigeration systems, the compressor (which is, basically, a pump) normally has twin pistons. One is on the suction side and one is on the delivery side. When the compressor is switched off there can be great inequality in the pressures. The extent of the inequality would depend upon the extent of the system itself. Due to this inequality in pressures, the motor which drives the compressor has to be of sufficient size, and starting torque, to be able to overcome that pressure differential. As a result, the motor is larger that would otherwise be necessary. This means that the current drawn during the starting of the motor is high and the use of current during the running of the motor is higher than otherwise would be required.

It is therefore the principal object of the present invention to provide a refrigeration system (as hereinbefore defined) wherein, when not operating, pressure equalization between inlet and outlet can take place.

With the above and other objects in mind the present invention provides a refrigeration system (as hereinbefore defined) including a compressor, said compressor having an inlet and an oudet, there being provided an operative connection from said inlet to said outlet, and a valve in said operative connection, said valve being adapted to be open when said compressor is off and closed when said compressor is in a normal running condition. In order that the invention may be fully understood there shall now be described by way of non-limitative example only a preferred construction of a refrigeration system (as hereinbefore defined). The description will be with reference to the accompanying illustrative drawings in which:- Figure 1 is a schematic presentation of a cascade refrigeration system;

Figure 2 is a schematic representation of a basic refrigeration system;

Figure 3 is a plan view of a system such as that of Figure 2 fitted in a portable drink cooler; and

Figure 4 is a graph illustrating current drawn vs time for the system of Figure 2.

Figure 1 shows a schematic view of a cascade refrigeration system. The drawing is illustrative of that form of refrigeration circuit but the invention is not to be limited to this form. In a cascade refrigeration system, one circuit of the refrigeration system is used to cool the other.

In this particular embodiment, there is a compressor generally designated as 1 which has a dual pressure control 2 and an oil separator 3. The condensing unit 4, valve 5, dryer 6, hand valve

7, capillary tube 8 and heat exchanger 9 are very much standard for a cascade form of refrigeration system.

The cascade condenser 10 is connected back to the compressor 1 via hand valve 11, dryer 12, hand valve 13, and pressure regulator 14.

On the other side of the cascade system, there is a compressor 15 with dual pressure controls 16, oil separator 17, hand valve 18, dryer 19, valve 20, and heat exchanger 21. This naturally then passes through the cascade condenser 10 and back through the evaporating unit 22, hand valve 23, dryer 24, valve 25 and pressure regulator 26.

With this form of system, a line 27 can pass between the inlet and outlet lines 28 and 29. In the line 27 is a valve 30. The purpose of line 27, and valve 30, is that when the compressor 15 switches off, valve 30 opens so that there is pressure equalization between the inlet and outlet lines 28,29. Immediately upon the compressor 15 starting, and being up to full speed and pressure, the valve 30 is closed, to close the line 27, to thus allow the inlet and outlet pressures to achieve normality.

The valve 30 is closed and opened by a solenoid or the like (not shown). Therefore, during a normal operating cycle, the valve 30 would be held open by the solenoid when the compressor 15 was off and held closed by the solenoid when the compressor was on. The valve 30 may be biased to the open position so that when the entire system is turned off it opens to equalize the pressure automatically; or biased to the closed position for those installations rarely turned off so that it will only be open when the power is on and the compressor off. By having the inlet and outlet lines 28 and 29 under equal pressure when off, upon the compressors 1,15 starting, there is not the load upon the compressor motor and, therefore, the current being drawn to start the motor is significantly reduced. This means that the motor itself can be smaller, and the energy consumed less. Naturally, with the system illustrated in Figure 1, under normal operation the compressors 1,15 would cycle on and off over a period of time. It is during that cycle, when the compressor is on, that the valves 30 are closed. When the system is still operating, but the compressors 1,15 turn off, is when the valves 30 open to equalize the pressure on the compressors 1,15 at the inlet and outlet lines

28,29. When power to the entire system was withdrawn - as in the refrigeration system being turned totally off - the compressors 1,15 would stop and the valves 30 opened to equalize the pressure between the lines 28 and 29. The valve may then remain open until the power is restored and the system commenced operation again.

Preferably, and although not shown, a valve would be provided on the inlet lines 29 between line 27 and the compressor 1,15 and which would be on when the valve 30 was off, and off when the valve 30 was on. The purpose of such a valve is that the refrigerant would tend to migrate to the coolest part of the system, particularly in air-conditioning systems, with centrifugal compressors. When a shut-down on the cycle occurs, there may be liquid refrigerant in the line and thus by the valve 30 opening and this extra valve (not shown) closing, the liquid refrigerant would by-pass the compressor 1,15 and pass along the line 27 and into the outlet line 28. There would therefore not be liquid refrigerant in the compressor 1,15 when starting up again and thus damage to the compressor may be avoided.

Furthermore, by virtue of this system, and with appropriate controlling being used (in accordance with normal techniques), the chances of burn-out of the motor are far, far less.

It is advantageous that the compressors 15,1 would have an oil which was not picked-up by the refrigerant during normal operation. In this way, oil in the system would not be blown into the compressor when equalization took place and then start-up occurred. A synthetic oil such as that available from Mobil Oil Australia Limited under the trade mark "ERG 1000" is an example of such a suitable oil.

Figure 2 shows a basic circuit which has a compressor 115 with inlet and outlet lines 128 and 129. A line 127 passes therebetween and which has a solenoid controlled valve 130 in that line. The valve is controlled by a general control unit (not shown).

Naturally, there is a condenser 104 as well as a liquid receiver 131, sight glass 132, and thermal expansion (TX) valve 133. An evaporator 134 is also provided in the normal way.

The valve 130 is normally closed during the operation of the compressor 115. As soon as the compressor 115 stops, the valve 130 is operated and opened and is kept open until the compressor 115 starts again, provided power to the compressor is maintained. Once the compressor 115 has started again and is at normal operating speed, the valve 130 is closed. This is in accordance with the previous description.

In tests it has been shown that the current drawn during the operation of a compressor installed in a refrigeration system in accordance with the above description is far less. Figure 4 is illustrative of a print-out obtained in accordance with normal means during such cycling. Curve 401 is the normal operating curve for the system of Figure 2. Curve 402 is the curve for a similar system but without the equalization of load. The gap between the two represents the power saving for that part of the cycle. The initial surge in current for curve 402 is the current required to start compressor 115 when under load. With no load (i.e. equal pressures) there is no start-up surge in the current, and thus the curve 401 is substantially flat.

It must be realized that the graph of Figure 4 illustrates the start-up situation only. Naturally, for both the curve 401 and curve

402, when the compressor turned off there would be a sharp fall back to a zero current. The current would remain, essentially, at zero until next start-up. The curves of Figure 4 would then be repeated. With a system which cycles infrequently (such as a domestic refrigerator or freezer) the peaks would be relatively well spaced and thus the savings in power, although substantial, would not be significant. However, with a commercial refrigeration system or air- conditioning system, particularly for a drink cooler with remote dispensing apparatus or the like, the cycling time is very rapid and it is not unusual to have the compressor turning on and off many times per hour. It can therefore be seen that in that situation, with the graph of Figure 4 being repeated many times an hour, the savings in power can be quite substantial. Figure 3 shows a system of Figure 2 installed to provide a drink cooler. There is a container 310, preferably an insulated container having an insulating layer 312, with a hollow interior 314. Within interior 314 is located a coil 316 having an inlet 318 and an outlet 320, both passing through end wall 322 of container 310. Interior 314 is substantially filled with a cooling medium such as, for example, water or glycol. The cooling medium is preferably a mixture of water with glycerine in the ratio of three parts glycerine to one hundred parts water. Advantageously, the glycerine is food grade. An anti-algae solution should be added at an appropriate concentration.

The refrigeration system, generally designated as 324, is enclosed in a side box 326. The system comprises a compressor 328, condenser 330, TX valve 332 and valve 334. These are all connected and operate as per Figure 2. The refrigeration system 324 is connected by lines (not shown) to two dimple plates 336 recessed into walls 338 and 340 of container 310. The dimple plates 336 cool the cooling medium in the interior 314.

With this system of Figure 3, it has been shown that the refrigeration system 324, by using that as illustrated in Figure 2, can be substantially smaller than hitherto realized even using standard componentry and thus the refrigeration system can be used to cool a dispenser for beverages such as, for example, "Coca-Cola" or any other suitable beverage from relatively high room temperatures to normal drinking temperatures very quickly and in constant operation.

Whilst there has been described in the foregoing description a preferred construction of a refrigeration circuit (as hereinbefore defined) incorporating the principal features of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the essential features of the present invention.

Claims

1. A refrigeration system (as hereinbefore defined) including a compressor, said compressor having an inlet and an outlet, there being provided an operative connection from said inlet to said outlet, and a valve in said operative connection; said valve being adapted to be open when said compressor is off, and closed when said compressor is on.

2. A refrigeration system as claimed in claim 1, wherein there is provided a further valve in said inlet between said compressor and said operative connection; said further valve being open when said valve is closed, and closed when said valve is open.

3. A refrigeration system as claimed in claim 1 or claim 2, wherein said valve is solenoid operated.

4. A refrigeration system as claimed in any one of claims 1 to 3, wherein said refrigeration system is fitted liquid cooler; said liquid cooler comprising a container of an insulating material, said container having a hollow interior in which is located a coil having a liquid inlet and a liquid outlet, said liquid inlet and said liquid outlet being located outside said container, said interior being substantially filled with a cooling medium, said cooling medium being adapted to be cooled by at least one dimple plate immersed in said cooling medium; said dimple plate being operatively connected to said refrigeration system.

5. A refrigeration system as claimed in any one of claims 1 to 3, wherein said refrigeration system is duplicated in a cascade refrigeration system.

6. A refrigeration system (as hereinbefore defined) substantially as hereinbefore described with reference to the accompanying drawings.