EP0009145A1

EP0009145A1 - Refrigerant compressor capacity control apparatus

Info

Publication number: EP0009145A1
Application number: EP79103180A
Authority: EP
Inventors: Bruce A. Frazer; Jr. Curtis Holt
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1978-09-20
Filing date: 1979-08-28
Publication date: 1980-04-02
Also published as: JPS5551978A; AR221901A1; IN152999B; IL58116A; PH18397A; ZA794377B; NO793007L; NO146446C; EP0009145B1; NO146446B; DE2963419D1; AU5038479A; AU532017B2; ATE1396T1; ES484265A1; BR7905936A; IL58116A0; MX147475A; ES485139A1; DK361879A

Abstract

A capacity control for a multi-cylinder refrigeration compressor (20) includes a modulating valve (40) disposed between a suction manifold (34) and less than all of the cylinders (30) of the refrigeration compressor (20). The modulating valve (40) regulates the flow of refrigerant gas from the manifold (34) to the cylinders (30) in communication therewith, with the valve (40) functioning to increase the flow of refrigerant gas to the cylinders (30) as the load on the refrigeration unit (10) increases and to decrease the flow of refrigerant as the load on the refrigeration unit (10) decreases.

Description

This invention relates to capacity control of a refrigeration compressor, and in particular, to a capacity control device which decreases the power input requirements of the compressor motor as the load on the refrigeration unit decreases.
Mechanical refrigeration units, such as those employed in air conditioning systems, normally operate under varying load conditions. Typically, the units are designed to deliver conditioned air at a temperature of 25°C at high ambients, such as 40°C (hereinafter maximum load.) When the refrigeration unit is operating at less than maximum load conditions, it is desirable to reduce the refrigeration producing capacity thereof.
Numerous schemes have been proposed to reduce the capacity of a refrigeration unit operating at less than maximum load conditions to not only reduce the refrigeration producing capabilities of the unit to prevent undesired overcooling of a space being served by the unit, but also to reduce the input power required to operate the refrigeration unit. In effect, a refrigeration unit operating under conditions that require less than 100% capacity should ideally be designed to operate at reduced input power requirements to effectively conserve energy.
It has heretofore been known to employ a valve disposed between the suction manifold of the refrigeration compressor and one or more of the refrigerant compressor cylinders to unload one or more cylinders of a refrigeration compressor when reduced capacity is desired. When it is desired to unload the cylinders, to reduce the capacity of the compressor, the valve disposed within the manifold is placed in a position to terminate flow of the refrigerant gas from the manifold to the cylinders. While this method of achieving capacity control has proven somewhat effective, it has been found that further reductions in power input requirements at reduced loads may be obtained by modulating the valve as compared to operating the valve so it either is in an "open" position whereby full flow of refrigerant passes from the manifold to the cylinder or in a "closed" position whereby total flow of refrigerant gas is terminated.
Test results have indicated that a reduction of the input power requirements of approximately 10% may be achieved by modulating the valve to vary the flow of refrigerant to at least one of the cylinders of the compressor as compared to opening or closing a valve in the manner disclosed in the cited patent, particularly when it is desirable to reduce the capacity of the unit to 20% - 40% of its maximum load rating.
The above improved performance is attained in capacity control apparatus of a multi-cylinder refrigerant compressor employed in a mechanical refrigeration unit including a modulating valve disposed between a suction manifold, and less than all of the compressor's cylinders, the apparatus including control means for regulating the operation of the modulating valve directly in accordance with changes in the load on the refrigeration unit such that the valve increases the flow of refrigerant to the cylinders as the load increases and decreases the flow of refrigerant as the load decreases.
This invention will now be described by way of example, with reference to the accompanying drawing in which:

Figure 1 of the drawing schematically illustrates a mechanical refrigeration unit including a refrigeration compressor embodying the present invention; and
Figure 2 is an enlarged sectional view showing the details of the present invention.

Referring to the drawing, there is disclosed a preferred embodiment of the present invention. In referring to the various figures of the drawing, like numerals shall refer to like parts.
Referring particularly to Figure 1, there is disclosed a mechanical refrigeration unit 10 including an outdoor heat exchange coil 12, an indoor heat exchange coil 24, a compressor 20 and an expansion device 22. High pressure refrigerant gas compressed by operation of compressor 20 is discharged through conduit 16 and delivered to outdoor heat exchange coil 12 whereat fan 14 routes ambient air over the surface of the coil to condense the vaporous refrigerant flowing therethrough. The condensed refrigerant is delivered via conduit 18 through expansion device 22 to indoor heat exchange coil 24. The indoor coil has air or water to be cooled routed thereover by operation of fan 26. The air routed over the surface of coil 24 rejects heat to the refrigerant flowing therethrough causing the refrigerant to be vaporized. The vaporous refrigerant is returned to the suction side of the compressor via conduit 28. The aforedescribed mechanical refrigeration unit is conventional and is typical of units employed in mechanical air conditioning systems.
In many applications, multi-cylinder compressors are utilized. Generally multi-cylinder compressors are designed to function with all cylinders fully loaded when ambient temperatures are relatively high, as for example at 40°C. At such high ambient temperatures, the cooling load on the refrigeration unit is also large. At less than maximum load conditions, it is desirable to reduce the refrigeration capacity of the refrigeration unit to prevent overcooling of the space served by the unit and to reduce the power input requirements thereof. Many known compressor capacity control devices have been used on multi-cylinder compressors in attempts to achieve the aforegoing capacity reduction at reduced cooling loads. One such capacity control device includes the utilization of a valve disposed between the suction manifold and some of the cylinders of the compressor to terminate flow of refrigerant from the manifold to the cylinders when reduced capacity of the compressor is desired. While this form of capacity control has been found to be relatively efficient, it has been additionally determined that improvements in such arrangement can effectively reduce the power input requirements by a considerable amount.
Referring particularly to figure 2, there are disclosed the details of the present capacity control arrangement employed to reduce the cooling capabilities of the refrigeration unit at reduced cooling loads and simultaneously to decrease the input power requirements of the compressor to conserve energy.
The capacity control device of the present invention includes a housing 42 mounted within the cylinder head 46 of the compressor. The housing has an inlet 43 in communication with suction manifold 34 and includes an outlet preferably defined by one or more ports 58. Refrigerant gas flowing through ports 58 is delivered into a suction header 35 for an individual cylinder. Each cylinder or bank of cylinders will generally be associated with a separate suction header. The suction gas passing from header 35 flows through suction ports 36 into compressor cylinder 30. The refrigerant gas in cylinder 30 is compressed by reciprocal movement of piston 31 therein and is discharged therefrom through ports 38 into discharge chamber 32. The flow of refrigerant gas through ports 36 and 38 are controlled by suitable valves, as is well-known by those skilled in the art.
A piston type device 52 is movably disposed within bore 41 defined by housing 42. A retainer ring 48 maintains piston 52 within the bore. Springs 54 and 56, mounted on retainer 60, provide a force to move piston 52 upwardly within bore 41. A relatively constant magnitude force is developed in chamber 49 located above the top surface of piston 52 in opposition to the force acting on the bottom surface thereof generated by springs 54 and 56. The constant magnitude force may be generated by the pressure of the discharge gas passing through conduits 16 and 17. A constant pressure valve 44 is utilized to control the pressure of the gas flowing through conduit 17 to maintain the pressure in chamber 49 at a predetermined magnitude. An 0-ring 50 is provided to prevent leakage between the opposed surfaces of housing 42 and the cylinder block in which the valve 40 is mounted. A force developed by the suction pressure of the gas in manifold 34 operates in combination with the force developed by springs 54 and 56 on the bottom surface of piston 52 to move the piston upwardly within bore 41.
In operation, let us first assume that a maximum load condition exists on the refrigeration unit to require operation of all cylinders of the compressor to maintain the desired refrigeration capabilities of the unit. If the load on refrigeration unit 10 should diminish, the pressure of the refrigerant flowing through conduit 28 into manifold 34 will decrease. In essence, the suction pressure of the refrigerant gas flowing into manifold 34 varies directly with the load on the refrigeration unit; as the load decreases so will the pressure of refrigerant passing into manifold 34. The reduced pressure in manifold 34 will cause a concurrent reduction in the total force acting on the bottom surface of piston 52. As the pressure in chamber 49 is maintained at a constant level, the force acting on the top surface of piston 52 also remains at a constant magnitude. Thus, the force imbalance thus created results in piston 52 moving from the position shown in figure 2 (whereat a maximum flow of refrigerant passes to cylinder 30) downwardly within bore 41 towards manifold 34. The movement of piston 52 relative to port 58 resulting from a reduction in the refrigeration load tends to decrease the quantity of refrigerant passing from manifold 34 into suction chamber 35. In effect, piston 52 modulates the flow of refrigerant moving into header 35 in accordance with the changes in load on the refrigeration unit by changing the active flow area of port 58. As the load continues to decrease, thus reducing the force acting on the lower surface of piston 52, the piston will move within bore 41 to further reduce the active area of port 58 to further reduce the flow of refrigerant passing therethrough. Eventually, upon further decreases in the refrigeration load, piston 52 will move with respect to port 58 to completely terminate the flow of refrigerant therethrough. When this occurs, cylinder 30 is completely unloaded. The power input to the compressor is reduced generally in proportion to the movement of piston 52 with respect to port 58; as the piston reduces the flow of refrigerant through port 58 to cylinder 30, the power input to the compressor will likewise decrease since the compressor will require less energy to compress the refrigerant still flowing to its cylinders.
If the refrigeration load increases, the pressure of the refrigerant gas passing into manifold 34 increases to increase the force acting on the lower surface of piston 52 to thereby raise the piston within bore 41 to permit renewed flow of refrigerant gas through port 58. The quantity of refrigerant gas passing through the port will vary directly with the pressure of the refrigerant gas acting on the lower surface of piston 52. Thus, as the load continues to increase, the pressure acting on the lower surface of piston 52 will also increase to further move piston 52 with respect to port 58 to increase the flow passage opening defined thereby to permit a greater quantity of refrigerant gas to pass into suction header 35.
As may be readily recognized, the capacity control device of the present invention modulates the gas flowing to a bank of cylinders to improve the performance of the refrigeration unit by reducing the power consumption requirements of the unit at part-load conditions. The specific embodiment herein disclosed achieves the desired capacity control by regulating the movement of the capacity control device in response to changes in the difference in the pressure between suction pressure and a predetermined pressure-operating in a chamber provided above a piston of the capacity control device. While the capacity control device has been illustrated as employed with a compressor used in an air conditioning system, the invention may also readily be employed with refrigeration units employed to chill water. Generally in such units, the temperature of the water leaving the evaporator is monitored to sense changes of the refrigeration load on the unit.
While a preferred embodiment of the present invention has been described and illustrated, the present invention may be otherwise embodied within the scope of the following claims.

Claims

1. Apparatus for controlling the capacity of a multi-cylinder refrigerant compressor (20) employed in a mechanical refrigeration unit (10) characterized by means defining a manifold (34) for delivering refrigerant to be compressed to less than all of the cylinders of said compressor; a modulating valve (40, 52) disposed between said manifold and said cylinders (30) connected thereto for regulating the flow of refrigerant from said manifold (34) to said cylinders (30); and control means (44, 54, 56) for controlling the operation of said modulating valve (40) in accordance with changes in the load on the refrigeration unit (10) to increase the flow of refrigerant as the load increases and to decrease the flow of refrigerant as the load decreases.

2. Apparatus in accordance with claim 1 wherein said control means is further characterized by means for monitoring the pressure of the refrigerant delivered to said manifold and for developing a control signal directly related thereto for controlling the operation of said modulating valve to increase the flow of refrigerant to said cylinders as the monitored refrigerant pressure increases and to decrease the flow of refrigerant as the monitored refrigerant pressure decreases.

3. Apparatus in accordance with claims 1 or 2 wherein said modulating valve is further characterized by a housing (42) defining a fluid flow passage and having an inlet (43) in communication with said manifold (34) and an outlet (58) in communication with said cylinders; a piston (52) reciprocally disposed within the fluid flow passage to control the flow of refrigerant from said inlet to said outlet; constant force producing means (17, 44) for moving said piston to a first position whereat flow of refrigerant from said inlet to said outlet is terminated; and variable force producing means (54, 56, 28) acting in opposition to said constant force producing means for moving said piston from said first position to permit flow of refrigerant from said inlet to said outlet, the quantity of refrigerant flowing from said inlet to said outlet varying directly with the magnitude of the force produced by said variable force producing means.

4. Apparatus in accordance with claim 3 wherein said outlet is further characterized by means defining a plurality of ports (58) formed in said housing (42) and; said piston (52) is movably disposed with respect to said ports (58) to regulate the flow of refrigerant therethrough.

5. A method of controlling the flow of refrigerant into at least one cylinder (30) of a multi-cylinder refrigerant compressor (20) employed in a mechanical refrigeration unit (10) characterized by the step of modulating (40) the flow of refrigerant into the cylinder (30) in accordance with changes in load on the refrigeration unit to increase the flow of refrigerant as the load increases and to decrease the flow of refrigerant as the load decreases.

6. The method in accordance with claim 5 further characterized by monitoring (34, 52) the suction pressure of the refrigerant supplied to the compressor;. and the modulating step is accomplished in accordance with changes in refrigerant suction pressure to increase the flow of refrigerant as the suction pressure increases and to decrease the flow of refrigerant as the suction pressure decreases.