matching evaporator to compressor on walk in cooler

[mosher1983]

got a copeland cs10k6epfv277 10100 btu/hr compressor. the customer needs a new one but wants to use one from different room. old evap. is 7600 btu/hr new one is 6200 btu/hr. pretty self explainatory that they dont match but question is why is the evap 7600 btu/hr and the compressor 10100btu/hr working fine no problems??? i thought we always matched close without going over compressor. dont know size of cooler, evap is original so it was sized for cooler at 7600btu/hr but condensing unit may be newer.

[Magoo]

Hi Mosher.
short answer is, compressors, evaporators and condensers perform at specific conditions. To mix and match is a disaster waiting to happen.
More factual condition comparisons would help, refrigerant, SST/ SDT ambient temps and control temp conditions. being an international forum the majority work in SI metric.

[Gary]

got a copeland cs10k6epfv277 10100 btu/hr compressor. the customer needs a new one but wants to use one from different room. old evap. is 7600 btu/hr new one is 6200 btu/hr. pretty self explainatory that they dont match but question is why is the evap 7600 btu/hr and the compressor 10100btu/hr working fine no problems??? i thought we always matched close without going over compressor. dont know size of cooler, evap is original so it was sized for cooler at 7600btu/hr but condensing unit may be newer.

Components are rated under specific conditions. Of particular importance is the saturated suction temperature (SST). If we increase the SST (larger evap) the compressor capacity increases to balance against the evap output and there is a danger of overloading the compressor during pulldown. If we decrease the SST (smaller evap) the compressor capacity decreases to balance against the evap output and the run time is extended.

Perhaps more important is the humidity. Lower SST (undersized evap) means the evap is running colder and a colder evap removes more humidity from the air, resulting in dryer products. If the products being refrigerated are sold by weight, then a dryer product is a less valuable product.

Also keep in mind that it takes energy to remove moisture, so this adds to the running costs.

The proper "match" depends upon the conditions (both temperature and humidity) you are trying to achieve. The ratings are a handy guideline and starting point. Factor in the desired conditions and adjust accordingly.