Pulsed flow for capacity control

Step control in capacity modulation of a refrigeration or air conditioning circuit is achieved by rapidly cycling a solenoid valve in the suction line, economizer circuit or in a bypass with the percent of “open” time for the valve regulating the rate of flow therethrough. A common port in the compressor is used for economizer flow and for bypass.

BACKGROUND OF THE INVENTION

In a closed air conditioning or refrigeration system there are a number of methods of unloading that can be employed. Commonly assigned U.S. Pat. No. 4,938,666 discloses unloading one cylinder of a bank by gas bypass and unloading an entire bank by suction cutoff. Commonly assigned U.S. Pat. No. 4,938,029 discloses the unloading of an entire stage of a compressor and the use of an economizer. Commonly assigned U.S. Pat. No. 4,878,818 discloses the use of a valved common port to provide communication with suction for unloading or with discharge for Vicontrol, where Viis the discharge pressure to suction pressure ratio. In employing these various methods, the valve structure is normally fully open, fully closed, or the degree of valve opening is modulated so as to remain at a certain fixed position. One problem associated with these arrangements is that capacity can only be controlled in steps or expensive motor driven modulation valves must be employed to fix the valve opening at a certain position for capacity control.

SUMMARY OF THE INVENTION

Gradual compressor capacity can be achieved by rapidly cycling solenoid valve(s) between fully open and fully closed positions. The cycling solenoid valve(s) can be located in the compressor suction line, the compressor economizer line and/or the compressor bypass line which connects the economizer line to the suction line. The percentage of time that a valve is open determines the degree of modulation being achieved. However, because the cycling time is so much shorter than the response time of the system, it is as though the valve(s) are partially opened rather than being cycled between their open and closed positions.

It is an object of this invention to provide continuous capacity control.

It is another object of this invention to provide step control in capacity modulation.

It is a further object of this invention to provide a less expensive alternative to the use of variable speed compressors.

It is another object of this invention to provide a less expensive alternative to a modulation valve. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.

Basically, gradual or step control in capacity modulation of a refrigeration circuit is achieved by rapidly cycling a solenoid valve in the compressor suction line and/or the compressor economizer line and/or bypass line.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the FIGURE, the numeral12generally designates a hermetic compressor in a closed refrigeration or air conditioning system10. Starting with compressor12, the system10serially includes discharge line14, condenser16, line18, expansion device20, evaporator22, and suction line24completing the circuit. Line18-1branches off from line18and contains expansion device30and connects with compressor12via port12-1at a location corresponding to an intermediate point in the compression process. Economizer heat exchanger40is located such that line18-1, downstream of expansion device30, and line18, upstream of expansion device20, are in heat exchange relationship. The expansion devices20and30are labeled as electronic expansion devices, EEV, and are illustrated as connected to microprocessor100. In the case of expansion device20, at least, it need not be an EEV and might, for example, be a thermal expansion device, TEV. What has been described so far is generally conventional. The present invention provides bypass line50connecting lines18-1and24downstream of economizer heat exchanger40and evaporator22, respectively, and places solenoid valve52in line50, solenoid valve54in line24downstream of evaporator22and upstream of line50and solenoid valve56in line18-1downstream of economizer heat exchanger40and upstream of line50. Solenoid valves52,54, and56and EEV30are all controlled by microprocessor100responsive to zone inputs. Where expansion device20is, as illustrated, an EEV, it also is controlled by microprocessor100.

In “normal” operation of system10, valves52and56are closed and hot high pressure refrigerant gas from compressor12is supplied via line14to condenser16where the refrigerant gas condenses to a liquid which is supplied via line18and idle economizer heat exchanger40to EEV20. EEV20causes a pressure drop and partial flashing of the liquid refrigerant passing therethrough. The liquid-vapor mixture of refrigerant is supplied to evaporator22where the liquid refrigerant evaporates to cool the required space and the resultant gaseous refrigerant is supplied to compressor12via suction line24containing solenoid valve54to complete the cycle.

The operation described above is conventional and capacity is controlled through EEV20. Pursuant to the teachings of the present invention solenoid valve54can be rapidly pulsed to control the capacity of compressor12. Since the pulsing will be more rapid than the response time of the system10, the system10responds as though the valve54is partially open rather than being cycled between its open and closed positions. Modulation is achieved by controlling the percentage of the time that valve54is on and off. To prevent a vacuum pump operation, the “off” position of valve54may need to permit a limited flow.

To increase capacity of system10, economizer heat exchanger40is employed. In economizer heat exchanger40, lines18and18-1are in heat exchange relationship. Solenoid valve56is open and solenoid valve52closed and a portion of the liquid refrigerant in line18is directed into line18-1where EEV30causes a pressure drop and a partial flashing of the liquid refrigerant. The low pressure liquid refrigerant passes into economizer heat exchanger40where the refrigerant in line18-1extracts heat from the refrigerant in line18causing it to cool further and thereby provide an increased cooling effect in evaporator22. The refrigerant in line18-1passing through economizer heat exchanger40is supplied to compressor12via port12-1under the control of valve56which is, in turn, controlled by microprocessor100. Line18-1delivers refrigerant gas to a trapped volume at an intermediate stage of compression in the compressor12, as is conventional. However, according to the teachings of the present invention the economizer flow in line18-1and, as such, system capacity is controlled by rapidly cycling valve56to modulate the amount of economizer flow to an intermediate stage of compression in compressor12. To lower the capacity of system10, bypass line solenoid valve52is employed. In this arrangement, valve56is closed, and gas at intermediate pressure is bypassed from compressor12via port12-1, line18-1and line50into suction line24. The amount of bypassed gas and, as such, the system capacity is varied by rapidly cycling valve52. Thus port12-a is used as both an economizer port and a bypass or unloading port.

From the foregoing, it should be clear that the rapid cycling of valves52,54and56, individually, allows for various forms of capacity control with the amount of time a particular valve is on relative to the time that it is off determining the degree of modulation of capacity. The frequency of modulation for typical systems can range from 0.1 to 100 seconds.

Although preferred embodiments of the present invention have been illustrated and described, other changes will occur to those skilled in the art. It is therefore intended that the scope of the present invention is to be limited only by the scope of the appended claims.