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To meet the unique operating requirements of a supermarket, Foster-Miller designed and built a cogeneration system to use the waste heat from the compressor engine to provide additional cooling capacity. Four refrigeration compressors and an induction motor/generator are driven through a gearbox by a gas-fueled internal combustion engine. All components are mounted on two skids to facilitate installation in existing machine rooms and to reduce field installation costs.
A heavy duty, 110 hp gas engine is mounted on the engine skid. The skid itself is configured to accept gas engines of several manufacturers, depending upon buyer preference and availability of local service support. The engine's reject heat is recovered in the form of hot water circulated through the engine jacket cooling water and exhaust gas heat exchangers. The recovered hot water is used primarily to drive an absorption chiller (also mounted on the engine skid) that increases refrigeration capacity by subcooling the liquid refrigerant en route to the display cases. The remaining heat contained in the hot water leaving the absorption chiller can be employed for building space heating.
The four open-shaft type compressors are capable of providing refrigeration at any desired suction condition. All four compressors are connected to the gearbox through mechanical clutches. Also, on the compressor skid, connected to the gearbox, is the 125 hp induction motor/generator. The electric motor drives the compressors during periods of combustion engine maintenance. Refrigerant suction manifolds, oil separators, and suction filters have been arranged to provide easy access to the compressors, generator, and gearbox.
The cogeneration system described was constructed and successfully tested in the laboratory to verify system performance. The system was later installed in a supermarket in Los Angeles, CA, where it was operated for two years. Two supermarkets were instrumented for the field test. The first contained the cogeneration system, while the second employed electrically driven refrigeration compressors. Comparison of data from these two sites showed that the cogeneration system achieved annual savings of $11,040.
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