US20080034772A1

US20080034772A1 - Method and system for automatic capacity self-modulation in a comrpessor

Info

Publication number: US20080034772A1
Application number: US11/460,400
Authority: US
Inventors: Eugene K. Chumley; Joseph F. Loprete; David T. Monk; Scott G. Hix
Original assignee: Bristol Compressors Inc
Current assignee: Bristol Compressors Inc
Priority date: 2006-07-27
Filing date: 2006-07-27
Publication date: 2008-02-14

Abstract

An automatic self-modulation capacity compressor for an HVAC&R system is disclosed. The system includes a housing, a compressor, a motor, and a pressure sensitive control valve. The HVAC&R system further comprises an expander and a condenser. In the open position, the control valve permits a portion of the pressurized gasses from the compressor to escape, creating a partial capacity compressor within the system. Once a predetermined set point pressure differential is met, the control valve moves to the closed position, where all of the pressurized gasses within the compressor are provided to the system, thereby creating a full capacity compressor. Once the compressor is operating in full capacity, the compressor remains in full capacity mode until the demands of the system are met and the compressor shuts down. Upon restart, the compressor operates in partial capacity until the predetermined set point pressure is met once again and the compressor begins operating in full capacity.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to providing capacity modulation for compressors. More particularly, the present invention relates to automatic capacity modulation in a compressor without any need for external controls.
Frequently, compressors in heating, ventilation and air conditioning (HVAC) systems are limited to a single output capacity. One problem with the compressor being limited to a single output capacity is that the compressor, especially reciprocating compressors, can produce excess capacity at reduced outdoor ambient temperatures. The excess capacity produced by the compressor adversely affects any system incorporating the compressor during SEER (Seasonal Energy Efficiency Rating) testing and in subsequent operation of the system.
One attempt to solve the excess capacity problem in a compressor is discussed in U.S. Pat. No. 6,663,358, wherein an internal valve in the compressor is adjusted in response to operating conditions to effect a change in the capacity of the compressor. The output capacity of the compressor is controlled by a valve and biasing member within the motor cavity that responds to the pressure of the gasses. As the pressure builds in the compressor in response to an increasing outdoor temperature, the valve moves to the second position allowing the compressor to operate at the second, higher, output capacity. Once the demand subsides and the pressure drops, the valve then returns to the first position and operates at the first capacity. While this solution allows for the modulation of compressor capacity, the toggle effect between the two operational capacities during operation results in energy and efficiency losses and low reliability of the system.
Therefore, what is needed is a cost-effective, efficient and easily implemented system to provide for reduced compressor capacity at reduced outdoor ambient temperatures, but that can also provide full compressor capacity at higher outdoor ambient temperatures.

SUMMARY OF THE INVENTION

A method for modulating capacity in a compressor for a heating, ventilation, air conditioning and refrigeration (HVAC&R) system includes providing a control valve having a first position and a second position and configured and disposed to permit full compressor capacity in response to the control valve being in the second position and being configured to permit partial compressor capacity in response to the control valve being in the first position. The method also includes positioning the control valve in the first position upon start up of the compressor, operating the compressor at partial capacity in response to the control valve being in the first position and measuring a pressure differential in the compressor. In addition, the method includes comparing the measured pressure differential to a predetermined pressure differential set point switching the control valve to the second position to operate the compressor at full capacity in response to the measured pressure differential being equal to or greater than the predetermined pressure differential set point and operating the compressor at full capacity in response to the control valve being in the second position until a shut down of the compressor.
A compressor for an HVAC&R system includes a housing having an inlet and an outlet, a compression mechanism being configured to receive uncompressed fluid from the inlet at a first pressure and provide compressed fluid to the outlet at a second pressure higher than the first pressure and a pressure control valve having a first position and a second position and being configured to be in the first position on startup of the compressor. The pressure control valve is also configured to switch to the second position in response to the difference between the first pressure and the second pressure being greater than a predetermined pressure differential set point, and to remain at the second position until the compressor shuts down.
An HVAC&R system includes a compressor, a condenser and an evaporator connected in a closed refrigeration loop. The system also includes a temperature control system configured to receive a set point temperature and a corresponding measured temperature for an enclosed space; and the compressor is configured to receive a fluid at an inlet at a first pressure and discharge fluid at a second pressure higher than the first pressure. In addition, the compressor includes a pressure control valve having a first predetermined position and a second predetermined position. The pressure control valve is configured to be in the first position on startup of the compressor and to switch to the second position in response to the difference between the first pressure and the second pressure being greater than the predetermined set point pressure, and to remain at the second predetermined position until the compressor shuts down.
One advantage of the present invention is increased system performance, efficiency, and capacity control at reduced outdoor temperatures in both heating and cooling modes of operation.
Still another advantage of the present invention is increased reliability of the system.
Another advantage of the invention is that the system shuts down once a user-selected set point temperature is satisfied, thereby conserving energy.
Another advantage of the present invention is that the capacity modulation is automatic without need for external control.
A further advantage of the present invention is that the self-modulation from partial to full capacity occurs almost immediately, which allows the compressor to operate at partial capacity until the need arises for full capacity, which conserves energy and creates a more efficient compressor.
Accordingly, the present invention is directed to improved compressors for providing automatic capacity modulation. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate schematically a refrigeration system that can be used with the present invention.

FIG. 3 illustrates a flow chart of one embodiment of the capacity control process of the present invention.

FIG. 4 illustrates the control valve in the first position.

FIG. 5 illustrates the control valve in the second position.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, a heating, ventilation, air conditioning and refrigeration (HVAC&R) system 300 includes a compressor 302, a condenser arrangement 304, and an evaporator arrangement 306 (FIG. 1) or a compressor 302, a reversing valve arrangement 350, an indoor unit 354 and an outdoor unit 352 (FIG. 2). The system 300 can be operated as an air conditioning only system, where the evaporator arrangement 306 is preferably located indoors, i.e., as and indoor unit 354, to provide cooling to the indoor air and the condenser arrangement 304 is preferably located outdoors, i.e., as an outdoor unit 352, to discharge heat to the outdoor air. The system can also be operated as a heat pump system with the inclusion of the reversing valve arrangement 350 to control and direct the flow of refrigerant from the compressor 302. When the heat pump is operated in an air conditioning mode, the reversing valve arrangement 350 is controlled for refrigerant flow as described above for an air conditioning system. However, when the heat pump is operated in a heating mode, the flow of the refrigerant is in the opposite direction from the air conditioning mode, and the condenser arrangement 304 is preferably located indoors, i.e., as an indoor unit 354, to provide heating of the indoor air and the evaporator arrangement 306, i.e., as an outdoor unit 352, is preferably located outdoors to absorb heat from the outdoor air.
The compressor 302 compresses a refrigerant vapor and delivers the vapor to the condenser 304 through a discharge line (and the reversing valve arrangement 350 if operated as a heat pump). The compressor 302 is preferably a reciprocating compressor. However, it is to be understood that the compressor 302 can be any suitable type of compressor, e.g., scroll compressor, rotary compressor, screw compressor, swag link compressor, turbine compressor, or any other suitable compressor. The refrigerant vapor delivered by the compressor 302 to the condenser 304 enters into a heat exchange relationship with a fluid, e.g., air or water, but preferably air, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from condenser 304 flows through an expansion device (not shown) to the evaporator 306.
The condensed liquid refrigerant delivered to the evaporator 306 enters into a heat exchange relationship with a fluid, e.g., air or water, but preferably air, and undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the fluid. The vapor refrigerant in the evaporator 306 exits the evaporator 306 and returns to the compressor 302 by a suction line to complete the cycle (and the reversing valve arrangement 350 if operated as a heat pump). It is to be understood that any suitable configuration of condenser 304 and evaporator 306 can be used in the system 300, provided that the appropriate phase change of the refrigerant in the condenser 304 and evaporator 306 is obtained. The HVAC or refrigeration system 300 can include many other features that are not shown in FIGS. 1 and 2. These features have been purposely omitted to simplify the drawing for ease of illustration.
Referring now to FIG. 3, in a preferred embodiment of the invention, operation of the self-modulation compressor in the HVAC&R system 300 involves several steps. To begin, in Step 402, the temperature in an indoor space is measured. Next, the measured temperature is compared to a predetermined temperature set point in Step 404. If the measured temperature satisfies the predetermined temperature set point requirement, the control returns to Step 402. Otherwise, the measured temperature does not satisfy the predetermined temperature set point requirement in Step 404, i.e., the measured temperature is less than the predetermined temperature set point if this system is in a heating mode of operation or the measured temperature is greater than the predetermined temperature set point when the system is in a cooling mode of operation. In other words, for a cooling system, this occurs when the temperature of a space rises above the predetermined temperature set point. For a heating system, this occurs when the temperature of a space falls below the predetermined temperature set point.
If the temperature set point is not satisfied in Step 404, the control proceeds to Step 408, where the compressor is started (if necessary) and the control valve is in the open position to operate the compressor at partial or reduced capacity. Preferably, the partial capacity of the compressor can range from about 70% of full capacity to about 90% of full capacity. As the compressor operates, the pressure within the compressor housing builds if the heating or cooling demand is not being satisfied, thereby creating a need for higher capacity from the compressor. In Step 410, the pressure in the compressor is compared to a predetermined set point of pressure differential between the suction inlet and the discharge outlet of the compressor. In an alternate embodiment, the pressure in the compressor is compared to a predetermined pressure set point, e.g., suction pressure set point or discharge pressure set point, rather than the differential pressure of the suction inlet and discharge outlet of the compressor. If the pressure differential in the compressor is less than the predetermined pressure differential set point, the control returns to Step 408 to continue operating at partial capacity. Otherwise, the control proceeds to Step 412 to operate the compressor at full capacity.
In a preferred embodiment, the pressure control valve within the compressor housing is calibrated to perform the comparison Step 410 and to close from the open position to operate the compressor at full capacity when the pressure differential of the compressor reaches the predetermined pressure differential set point. When the pressure differential set point is reached, the control valve activates and closes, which generates full capacity in the compressor. The compressor operates at full capacity until the predetermined temperature set point is reached in Step 414. If the predetermined temperature set point is not satisfied in Step 414, the control returns to Step 412 to continue operating the compressor at full capacity. However, if the predetermined temperature set point has been satisfied in Step 414, the compressor is shut down at Step 406 and the process begins again at Step 402. Once the compressor is operating at full capacity, the control valve prevents any switching to the lower capacity until after the compressor has been shut down.
In an alternate embodiment of the invention, the control valve can be arranged to permit operation of the compressor in full capacity mode when the control valve is in the open position and in partial capacity mode when the control valve is in the closed position. In addition, the control valve can be located in any suitable location within the compressor to control the capacity during operation.
The control valve is activated only by pressure levels within the compressor regardless of the temperature levels within the compressor or surrounding the system. The transition between partial and full capacity occurs almost instantaneously with the control valve moving from the open to the closed position. The almost instantaneous switch from the open to the closed position essentially eliminates a transitional range where the valve is neither fully open nor fully closed.
FIGS. 4 and 5 illustrate one embodiment of the pressure control valve configuration of the present invention. FIG. 4 illustrates the pressure control valve 404 in the open position. The pressure control valve 404 is in the open position when the force exerted by the discharge pressure is less than the combined force of the biasing force of the biasing member 470 plus the force exerted by the suction pressure. A suction pressure channel 483 connects the suction side of the compressor to the low-pressure side of the valve 404. The valve member 464 being in the first, open, position permits flow through the opening 484 and the flow passage 454 to the suction channel 328. When the valve member 464 is in the first position opening the flow passage 454, the reciprocating compressor 416 operates in a reduced capacity mode. In this mode, the fluid in the compression chamber 332 flows back through the opening 484 into flow passage 454, and even into the suction channel 328 in the manifold. The opening 484 and flow passage 454 are in effect combined to provide a reexpansion area in fluid communication with the compression chamber 332. In effect, the fluid in the compression chamber 332 is not compressed beyond the suction pressure, until the reciprocating piston travels beyond the opening 484.
As illustrated in FIG. 5, when the discharge pressure reaches a predetermined level, the force exerted by the discharge pressure overcomes the combined force, i.e., the biasing force of the biasing member 470 plus the force exerted by the suction pressure channel 483, and moves the valve member 464 to the second position and the stem portion 465 prevents flow through the flow passage 454 (and possibly through suction pressure channel 483). When the valve member 464 is in the second position preventing flow through the flow passage 454, the reciprocating compressor 416 operates in a full capacity mode because no fluid exits the compression chamber 332 through the flow passage 454. In other words, the full stroke length of the reciprocating piston 336 is utilized to compress the fluid entering and exiting the compression chamber 332 through the inlet 340 and outlet 342.
Thus, by adjusting the location of the opening 484 relative to the bottom dead center position of the reciprocating piston 336, the reciprocating compressor 416 achieves a desired capacity modulation. Also, by adjusting the biasing force exerted by the biasing member 470, the reciprocating compressor 416 controls the discharge pressure at which valve member 464 prevents flow through the flow passage 454. Accordingly, the system efficiency of an air-conditioning or refrigeration system can be improved by optimizing the combination of the degree of capacity modulation and the pressure at which the valve member 464 prevents flow through the flow passage 454. Preferably, the location of the opening 484 is adjusted to obtain the desired reduced capacity percentage of full capacity. The valve member may be any suitable valve configuration or multiple valve configuration.
An alternate embodiment of the invention includes a system with no suction pressure channel 483 connected to the low-pressure side of the valve member 404. This embodiment allows for a transitional period between the open position and the closed position of the valve member 404. In one embodiment, the compressor pressure differential is at 0 psi on start-up and builds pressure in the compressor while operating in a reduced capacity mode. Once the compressor reaches the lower limit (e.g., 114 psi) of the predetermined differential pressure range, the control valve begins to close and reaches the fully closed position at the upper limit (e.g., 129 psi) of the predetermined differential pressure range. The pressure in the compressor continues to build until a full capacity steady state differential pressure (e.g., 145 psi) is obtained in the compressor. This transitional period exists during the time it takes the valve member to switch between the open position and the closed position.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method for modulating capacity in a compressor for an HVAC&R system comprising the steps of:

providing a control valve having a first position and a second position, the control valve being configured and disposed to permit full compressor capacity in response to the control valve being in the second position and being configured to permit partial compressor capacity in response to the control valve being in the first position;

positioning the control valve in the first position upon start up of the compressor;

operating the compressor at partial capacity in response to the control valve being in the first position;

measuring a pressure differential in the compressor;

comparing the measured pressure differential to a predetermined pressure differential set point;

switching the control valve to the second position to operate the compressor at full capacity in response to the measured pressure differential being equal to or greater than the predetermined pressure differential set point; and

operating the compressor at full capacity in response to the control valve being in the second position until a shut down of the compressor.

2. The method of claim 1 further comprising the steps of:

selecting a temperature set point for an enclosed space;

measuring an actual temperature of the enclosed space;

comparing the actual temperature and the temperature set point; and

initiating operation of the compressor in response to the temperature set point not being satisfied.

3. The method of claim 2 further comprising the step of deactivating the compressor in response to the actual temperature satisfying the temperature set point.

4. The method of claim 3 wherein the HVAC&R system is operated in a heating mode and the step of deactivating the compressor includes shutting down the compressor when the actual temperature is equal to or greater than the temperature set point.

5. The method of claim 3 wherein the HVAC&R system is operated in a cooling mode and the step of deactivating the compressor includes shutting down the compressor when the actual temperature is less than or equal to the temperature set point.

6. The method of claim 1 wherein the step of positioning the control valve includes positioning the control valve in an open position and the step of switching the control valve to the second position includes positioning the control valve in a closed position.

7. The method of claim 1 wherein the step of providing a control valve includes positioning the control valve in a closed position and the step of switching the control valve to the second position includes positioning the control valve in an open position.

8. The method of claim 1 wherein the step of switching the control valve to the second position occurs substantially instantaneously.

9. The method of claim 1 wherein the step of operating the compressor at full capacity includes continuing to operate the compressor at full capacity when the pressure differential is less than the predetermined pressure differential set point.

10. A compressor for an HVAC&R system comprising:

a housing, the housing having an inlet and an outlet;

a compression mechanism, the compression mechanism being configured to receive uncompressed fluid from the inlet at a first pressure and provide compressed fluid to the outlet at a second pressure higher than the first pressure; and

a pressure control valve having a first position and a second position, the pressure control valve being configured to be in the first position on startup of the compressor, to switch to the second position in response to the difference between the first pressure and the second pressure being greater than a predetermined pressure differential set point, and to remain at the second position until the compressor shuts down.

11. The compressor of claim 10 wherein the first position of the control valve is an open position and the second position of the control valve is a closed position.

12. The compressor of claim 11 wherein the open position of the control valve permits fluid to return to the inlet during operation of the compressor and the closed position of the control valve prevents fluid from returning to the inlet.

13. The compressor of claim 12 wherein the pressure control valve upon being in the closed position is configured to remain in the closed position when the pressure differential is less than the predetermined pressure differential set point.

14. The compressor of claim 10 wherein the first position of the control valve is a closed position and the second position of the control valve is an open position.

15. The compressor of claim 10 wherein the pressure control valve is in fluid communication with the inlet.

16. The compressor of claim 10 wherein the switch to the second position occurs substantially instantaneously.

17. An HVAC&R system comprising:

a compressor, a condenser and an evaporator connected in a closed refrigeration loop;

a temperature control system, the temperature control system being configured to receive a set point temperature and a corresponding measured temperature for an enclosed space;

the compressor being configured to receive a fluid at an inlet at a first pressure and discharge fluid at an outlet at a second pressure higher than the first pressure, the compressor comprising:

a pressure control valve having a first predetermined position and a second predetermined position; and

the pressure control valve being configured to be in the first position on startup of the compressor and to switch to the second position in response to the difference between the first pressure and the second pressure being greater than the predetermined set point pressure, and to remain at the second predetermined position until the compressor shuts down.

18. The system of claim 17 wherein the system is a cooling system and begins operation in response to the measured temperature being greater than the set point temperature and ends operation in response to the measured temperature being less than or equal to the set point temperature.

19. The system of claim 17 wherein the system is a heating system and begins operation in response to the measured temperature being less than the set point temperature and ends operation in response to the measured temperature being equal to or greater than the set point temperature.

20. The system of claim 17 wherein the first position is an open position and the second position is a closed position.

21. The system of claim 20 wherein the open position permits fluid to return to the inlet during operation of the compressor and the closed position prevents fluid from returning to the inlet.

22. The system of claim 21 wherein the pressure control valve is configured to transition from the open position to the closed position substantially instantaneously.

23. The system of claim 17 wherein the first position is a closed position and the second position is an open position.