# US 4,393,662 A · Control system for refrigeration or air conditioning installation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,393,662 A - Document ID: US4393662A - Status: Granted - Kind: A - Application number: 06/306,207 - Filed: 1981-09-28 - Granted: 1983-07-19 - Earliest claimed: 1981-09-28 - Inventors: George P. Dirth - Web page: https://patentgrep.com/patent/US4393662A ## CPC - F25B 49/02: for compression type machines, plants or systems - F25B 5/02: arranged in parallel - G05D 23/1917: {using digital means} - G05D 23/24: the sensing element having a resistance varying with temperature, e.g. a thermistor - F25B: REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS - G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES ## Abstract A method and apparatus for controlling principle power consuming components such as compressors and fans for a refrigeration or air conditioning system so it will operate automatically with minimal energy consumption despite changing environmental and system conditions. The apparatus comprises a series of sensors to provide input data including the temperature from selected conditioned zones, valves for controlling coolant and refrigerant flow; switching devices for on-off control of the power components; and computing elements for receiving input data and constantly recomputing operating instructions for the power components that control their operation. The method used with the apparatus comprises dividing the total running time for system components such as the compressor and zone fans into equal sampling time periods; modulating the compressor to operate at a relatively high load level for a first predetermined power-on portion of each time period and then at a relatively low load level for the remaining power regulation portion of the period; calculating the amount of compressor energy needed to be added or substracted to maintain temperature equilibrium in the control zone; controlling the compressor to increase or decrease its full power cycle in the next succeeding time period; thereafter continuously adjusting the power and regulation cycles for the compressor in each time period based on the calculations made using the most recent temperature input data. Fans in selected cooling zones are controlled in a like manner during each of a continuous series of sampling time periods of greater length and using a separate two-mode controller function, to further help maintain set point temperature in all zones of the system. ## Claims ### Claim 1 A method for increasing the efficiency and reducing the power consumption of a refrigeration system have a compressor driven by a motor, first heat exchanger means with evaporator means located in a control zone and one or more additional zones to be cooled, said first heat exchanger means being connected to the compressor inlet, fan means associated with said first heat exchanger means, a conduit for liquid refrigerant interconnecting an outlet from said compressor to a second heat exchanger means, means for varying the load on said compressor, a liquid coolant means connected to said second heat exchanger means, a receiver for cooled liquid refrigerant connected to said second heat exchanger means, conduit means connected from the outlet of said receiver to said evaporator means of said first heat exchanger means, and expansion valve means in said conduit means, said method comprising the steps of: establishing a desired set point temperature to be maintained in a predetermined one of said zones designated a control zone; constantly measuring the actual temperature in said control zone; establishing a continuous series of equal time sampling periods for said compressor; operating said compressor at a relatively high load for a predetermined first portion of each time sampling period responsive to said measured temperature and at a relatively low load for the remaining or second portion of the sampling period; during each time sampling period, determining the difference in the actual temperature from the set point temperature in the control zone; calculating any change in the length of time for the first portion of the next sampling period required to maintain the set point temperature in the control zone from said difference; controlling the compressor responsive to said calculation accordingly so that it is cycled from high load to low load during each time sampling period; establishing a continuous series of equal time sampling periods for each of said fans or valves; and controlling the length of time during the first parts of said time sampling periods for each of said fans or valves that each of said fans or valves are turned on for purposes of zone temperature control. ### Claim 2 (depends on 1) The method of claim 1 wherein the time sampling period for the compressor is between 10 and 15 minutes. ### Claim 3 (depends on 1) The method of claim 1 wherein the time sampling period for the compressor is approximately 12 minutes. ### Claim 4 (depends on 1) The method of claim 1 wherein any change in the length of time for the first portion of each time sampling period is calculated using a two-mode control function that takes into account both gain and delay. ### Claim 5 (depends on 1) The method of claim 1 wherein said two-mode control function for the compressor is defined by the expression: .DELTA.U.sub.k =Gain (e.sub.k -ae.sub.k-1) where: .DELTA.U.sub.k =Incremental change in time (minutes) to hold system in equilibrium Gain=Observed system gain in units of min/F..degree. e.sub.k =Error in target temperature minus actual measured temperature in F..degree. at end of sampling time interval a=Observed dimensionless constant that allows for system delay e.sub.k-1 =Error in target temperature minus actual measured temperature in F..degree. at end of last sampling time interval ### Claim 6 (depends on 5) The method of claim 5 wherein the Gain in the two-mode control function is obtained by: (1) turning the fan "on" at its steady state in the control zone; (2) stabilizing the compressor at a relatively no-load level; (3) introducing a step change in loading to a relatively high load level; (4) plotting the temperature change vs time in the control zone; (5) measuring the response time to stabilize the system; and (6) determining the value of G calculated by measuring E.sub.s, the step function change in zone temperature and T.sub.sr, the response time for step function change, using the expression: G.congruent.T.sub.sr /E.sub.s. ### Claim 7 (depends on 1) The method as described in claim 1 including the additional steps of: continuously running the fan in the control zone; continuously measuring the temperature in each of the additional zones; during each time sampling period for the fans, measuring any variation in the actual temperature in each additional zone from the set point temperature in the control zone; and for each additional zone, calculating any change in the length of time for the first portion of the next fan time sampling period required to maintain the set point temperature in that zone. ### Claim 8 (depends on 7) The method of claim 7 wherein the amount of "on" time for each fan in a said additional zone for a particular fan time sampling period is calculated by means of a two-mode control function using actual temperature input data from the same additional zone received during the immediately preceding fan time sampling period. ### Claim 9 (depends on 8) The method of claim 8 wherein said two-mode control function for determining the variation in "on" time of each fan during a time sampling period is defined by the expression: .DELTA.U.sub.k =Gain (e.sub.k -ae.sub.k-1) where: .DELTA.U.sub.k =Incremental change in time (minutes) to hold system in equilibrium Gain=Observed system gain in units of min/F..degree. e.sub.k =Error in target temperature minus actual measured temperature in F..degree. at end of sampling time interval a=Observed dimensionless constant that allows for system delay e.sub.k-1 =Error in target temperature minus actual measured temperature in F..degree. at end of last sampling time interval.