Energy performance of low charge NH3 refrigeration systems in practice.

This paper describes the measured energy performances of five medium sized refrigerated distribution centres with storage volumes from approximately 10,000 m³ to 50,000 m³. The comparison is based on the electrical energy consumed over one calendar year as measured either by the electrical energy provider or by means of kWh meters integrated into the SCADA system for the plant. Four facilities are serviced by state of the art low charge, dual stage, central type, NH3 refrigeration systems with VFD controlled reciprocating compressors, evaporative condensers and hot gas defrost. One warehouse is serviced by an NH3 based screw compressor plant with gravity flooded evaporators. Several systems employ refrigerant injection into the evaporators controlled by the refrigerant quality as measured at the evaporator exits. In the case of one plant, the contribution of photovoltaic (PV) panels to the total amount of electrical energy consumed by the facility as a whole is shown on a month by month basis. An energy performance comparison is also made between two refrigerated distribution centres each with a volume of approximately 10,000 m³, but serviced by two different types of NH3 refrigeration systems. In one case the system is a single stage, economized screw compressor based plant with gravity flooded refrigerant feed. The other facility is serviced by speed controlled reciprocating compressors in dual compression stage configuration. Other features of the two facilities including warehouse layout are more or less identical. The facilities are approximately 300 km apart and the electricity tariffs are identical. All facilities have a common owner. The differences in the modes of operation and the products stored are therefore minimal between the plants compared. There are minor differences in the climatic conditions between the various sites.