This RTF Standard Protocol (Protocol) establishes methods for estimating the energy savings due to floating head pressure control and floating suction pressure control retrofits to commercial refrigeration systems.
Commercial refrigeration systems rely on a vapor compression cycle to absorb heat from a cooling load (for example, a refrigerated case or walk-in cooler) and reject heat to the atmosphere. Reductions to the pressure on the high-pressure, or “head” side of the cycle, and increases to the pressure on the low-pressure, or “suction” side of the cycle can reduce the energy consumed by the compressor. These modifications are the focus of this Standard Protocol.
The pressure of the refrigerant on the high-pressure, or “head” side of the refrigeration cycle is maintained sufficiently high to allow for the necessary heat rejection to the atmosphere in the condenser. The minimum condensing temperature (corresponding to a minimum head pressure) is commonly set to temperature that will suffice for most outdoor air temperatures. However, when outdoor air temperatures are relatively low, this minimum condensing temperature is higher than necessary for sufficient heat rejection and to achieve a condensed refrigerant. Floating head pressure is a control strategy that lowers the minimum condensing temperature setpoint and allows the condensing temperature to “float” higher when outdoor air temperature necessitates it.
The pressure of the refrigerant on the low-pressure, or “suction” side of the refrigeration cycle is maintained sufficiently low to allow for the necessary heat absorption from the cooling load. The saturated suction temperature (and corresponding pressure) are commonly maintained at a single specified temperature. However, during times of relatively low cooling load (e.g., hours when refrigerated cases remain closed), the suction temperature can be increased and still support the necessary amount of heat transfer. Floating suction pressure is a control strategy that adjust the suction temperature higher when excess cooling capacity is sensed are referred to as floating suction pressure controls.
The baseline for this measure is a refrigeration system without floating head and/or floating suction pressure controls. The measure is to implement one or both of these control strategies where they were not previously implemented.