US 4,621,502 A · Electronic temperature control for refrigeration system · patentgrep

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Abstract

A refrigeration system for a display case including electronic means for controlling an expansion valve and a refrigerant compressor used in the system. The expansion valve is cycled between open and close positions to modulate refrigerant flow into an evaporator coil. A microprocessor controls the operation of the expansion valve in response to: (a) the relationship of the temperature of air that has passed over the evaporator coil to multiple upper and lower limits (b) time integrated temperature deviations beyond preselected limits (c) upward or downward trend of the differential in temperature in the refrigerant during its flow through the evaporator coil, and (d) extreme deviation of the temperature of air that has passed over the evaporator coil. Compressor cut-in and cut-out pressures are also adjusted by the control in response to these air and refrigerant temperatures. In addition, the various limits may be adjusted according to a night setback schedule, and an alarm is provided to warn of relatively long-term deviation of the controlled temperature.

Claims60

Dependent claims

A refrigeration system comprising:

A refrigerated display case with a primary air conduit having air inlet and outlet openings and an evaporator coil arranged therein for refrigerating air passing therethrough;
An expansion valve coupled to said evaporator coil for providing refrigerant thereto;
Electronic means for controlling the rate of refrigerant flow through said expansion valve;
A refrigeration control system including:
Temperature sensing means for sensing the temperature (T.sub.case) of air that has passed over said evaporator coil;
means for storing sensed time related temperature parameters;
means for setting preselected temperature control parameters including temperature differential limits and time related temperature parameters;
means for comparing temperature T.sub.case with said limits;
electronic signals indicative of the flow rate of said valve;
means for comparing the sensed temperature and the stored time related temperature parameters with said set limits and set time related temperature parameters;
and means for controlling the flow rate of said valve as a function of the differentials of T.sub.case and said stored time related temperature parameters and set time related temperature parameters and the flow rate of said valve as indicated by said electronic signal.

8 more elements

A refrigeration system comprising:

A refrigerated display case with a primary air conduit having air inlet and outlet openings and an evaporator coil arranged therein for refrigerating air passing therethrough;
An expansion valve coupled to said evaporator coil for providing refrigerant thereto;
Electronic means for controlling the rate of refrigerant flow through said expansion valve;
A refrigeration control system including:
Temperature sensing means for sensing the temperature (T.sub.case) of air that has passed over said evaporator coil;
means for setting multiple preselected temperature control parameters including a set temperature for T.sub.case and positive and negative temperature differential limits therefrom;
means for comparing temperature T.sub.case with said limits;
electronic control signals indicative of the flow rate of said valve;
and means for controlling the flow rate of said valve as a first function of the differentials of T.sub.case and one set of said limits and as a second function of the differentials of T.sub.case and a second set of limits wherein said second function is dependent upon the flow rate of said valve as indicated by said electronic signal.

6 more elements

A refrigeration system comprising:

A refrigerated display case with a primary air conduit having air inlet and outlet openings and an evaporator coil arranged therein for refrigerating air passing therethrough;
Electronic means for controlling the rate of refrigerant flow through said expansion valve;
A refrigeration control system including:
Temperature sensing means for sensing the temperature (T.sub.case) of air that has passed over said evaporator coil;
Means for setting a preselected level of T.sub.case (T.sub.set) and multiple plus or minus limits of T.sub.case deviation therefrom, T.sub.set +K.sub.1, T.sub.set +K.sub.2, T.sub.set -K.sub.1, T.sub.set -K.sub.2 ;
Comparator means for comparing temperature T.sub.case with said limits of deviation and producing an output comparison signal;
and
Control means receiving the output comparison signal and providing an output control signal for controlling operation of the valve so that the flow rate of refrigerant through the valve is adjusted in accordance with the following:
If T.sub.case >T.sub.set +K.sub.2 the valve flow rate is increased by a predetermined amount;
If T.sub.case <T.sub.set +K.sub.2 but >T.sub.set the valve flow rate is increased by an amount which is a function of its preadjustment setting;
If T.sub.case <T.sub.set -K.sub.2 the valve flow rate is decreased by a predetermined amount;
If T.sub.case >T.sub.set -K.sub.2 but <T.sub.set the flow rate is decreased by an amount which is a function of its preadjustment setting;
Said control means further responding to the value of T.sub.case relative to T.sub.set .+-.K.sub.1 over time in controlling the valve.

10 more elements

A refrigeration system comprising:

A refrigerated display case with a primary air conduit having air inlet and outlet openings and an evaporator coil arranged therein for refrigerating air passing therethrough;
An expansion valve coupled to said evaporator coil for providing refrigerant thereto;
Electronic means for controlling the rate of refrigerant flow through said expansion valve;
A refrigeration control system including:
Temperature sensing means for sensing the rise in temperature of the refrigerant in its passage through the evaporator coil (DELTA T.sub.sh);
Means for scanning DELTA T.sub.sh at cyclic intervals;
Storage means for storing scanned values of DELTA T.sub.sh in a cycle sequence DELTA T.sub.sh1, DELTA T.sub.sh2, DELTA T.sub.sh3, DELTA T.sub.shx ;
Comparator means for comparing a recent value of DELTA T.sub.shx with an earlier value of DELTA T.sub.sh1 to determine an upward or downward trend in DELTA T.sub.sh during the comparison time period;
Means for setting a trigger temperature differential for an upward trend in DELTA T.sub.sh (upward DELTA T.sub.set) and for setting a different trigger temperature differential for a downward trend in DELTA T.sub.sh (downward DELTA T.sub.set);
Comparator means for comparing DELTA T.sub.sh selectively with upward DELTA T.sub.set during an upward trend and with downward DELTA T.sub.set during a downward trend;
and
Control means for receiving the output comparison signal and providing an output control signal for controlling operation of the valve so that the flow rate of refrigerant through the valve is adjusted downwardly when the comparison signal is less than the appropriate trigger differential in effect.

9 more elements

A refrigeration system comprising:

A refrigerated display case with a primary air conduit having air inlet and outlet openings and an evaporator coil arranged therein for refrigerating air passing therethrough;
An expansion valve coupled to said evaporator coil for providing refrigerant thereto;
Compressor means for compressing gaseous refrigerant received by said compressor from said evaporator coil at a compressor suction pressure;
Means for actuating said compressor means at a preselected cut-in suction pressure P.sub.ci ;
Means for deactuating said compressor means at a preselected cut-out suction pressure P.sub.co ;
Electronic means for controlling the rate of refrigerant flow through said expansion valve;
A refrigeration control system including:
Temperature sensing means for sensing the rise in temperature of the refrigerant in its passage through the evaporator coil (T.sub.sh);
means providing an electronic signal representative of said rate of refrigerant flow through said expansion valve;
comparator means for determining when said rate of refrigerant flow has exceeded a preselected value for a preselected period of time AND when said T.sub.sh has exceeded a preselected value for a preselected period of time;
and means responsive to said conditions determined by said comparator means for raising the cut-out suction pressure P.sub.co by a preselected amount in response thereto.

8 more elements

Dependencies are inferred from the claim text.