Floating head pressure can save lots of energy and money. Many people have heard this before but are hesitant to implement technology they may not understand. If you need a basic understanding of how refrigeration systems and floating head pressure work, then read on.
The Refrigeration Cycle: Refrigeration is really all about removing heat and sending it elsewhere. One or more compressors create pressure (and suction) which causes refrigerant to flow through a closed loop. After leaving the compressor the refrigerant reaches a condenser coil (often on your roof) where it transforms from a gas to a liquid as it releases heat into the air. The cooled liquid refrigerant then travels to the evaporator coils (in display cases and walk-ins) where it transforms from a liquid to a hot gas as it picks up heat and travels back to the compressor.
Controlling Local Temperatures: When a local case or walk-in temperature rises above a specified threshold, a local expansion valve “opens” allowing refrigerant to flow through a local heat absorbing evaporator coil causing the local temperature to drop to the desired level. Each case or walk-in can have a specific target temperature (not just medium or low temperature) to accommodate the grouping of products requiring similar storage temperatures as defined on their packaging. Products having similar tolerances to defrost duration and frequency should also be grouped in cases.
How Much Pressure Is Needed: If all of your display cases and walk-ins were cold enough none of the expansion valves would be open. Pressure in the closed loop system would quickly build up and the compressor motors would shut off after exceeding the specified “shut off head pressure”. There needs to be enough pressure in the loop so that when one or more expansion valves open refrigerant flows. There also needs to be enough pressure (and suction) to cause refrigerant to pass through the condenser coils at a flow rate which allows adequate release of heat into the air. As outdoor temperatures decrease, each condenser coil’s ability to release heat into the air increases. Colder outdoor temperatures also result in cooler refrigerant returning to the compressor. This cooler refrigerant can absorb and carry more heat as it passes by evaporator coils. As expansion valves open and close and outdoor temperatures rise and fall, the amount of (head) pressure required for correct refrigeration system operation goes up and down.
Change System Pressure Based On Changing Needs: Some refrigeration systems have you select fixed high and low (head) pressures which will determine when compressors start and stop enabling the refrigeration system to function properly, even under the most challenging conditions (all expansion valves open and the outdoor temperature is 112 degrees). But what about when the conditions aren’t so challenging which is most of the time. Maintaining high system pressure at times when it isn’t really needed means your compressor is running when is doesn’t have to. Refrigeration system controllers can be added which change the shut off head pressure as outdoor temperatures go up and down. This is floating head pressure.
Saving Energy And Money: Floating head pressure saves energy by reducing the average amperage draw (motors perform less work when they maintain lower pressures) and compressor run time (cooler refrigerant allows target temperatures to be achieved sooner).
