ENERGY PERFORMANCES OF LOW CHARGE NH3 SYSTEMS IN PRACTICE

The paper describes the measured energy performances of two medium sized refrigerated distribution centres with respective storage volumes of approximately 10,000 and 40,000 m(3). The performance evaluations are based on the electrical energy consumption as measured by the electrical energy provider over one calendar year. Both systems are serviced by state of the art low charge, dual stage NH3 refrigeration systems with VFD controlled reciprocating compressors; evaporative condensers and hot gas defrost. In the case of one plant the contribution of the photovoltaic panels to the energy requirement of 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 m(3), but serviced by two different types of ammonia refrigeration systems. In one case the plant is a single stage economized dual screw compressor based system with gravity flooded refrigerant feed. In the other case the plant is a low charge NH3 dual stage system with speed controlled semi-industrial reciprocating compressors. Other features of the two facilities including general warehouse design are more or less identical. The energy performance comparisons are again based on the electrical energy consumption as recorded by the electrical energy provider over one calendar year. 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 climatic conditions between the three sites.