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ABSTRACT
In a typical supermarket, open, multi-deck, medium-- temperature display cases could account for up to 50% of the total refrigerated display case line-ups (EPRI 1992). The major contributor to the total cooling load ofthis type of fixture is infiltration, which comprises approximately 70% to 80% of the total cooling load (Faramarzi 1999). The infiltration load ofthe display case refers to the entrainment of warm and moist air from the room, across the case air curtain, into the refrigerated space. This makes open multi-deck display cases vulnerable to indoor dry-bulb (DB) temperature and relative humidity (RH) variations. Installing glass doors on open vertical display cases can reduce the infiltration load, hence, the power consumption of the refrigeration system.
This paper presents the laboratory test results, which evaluated the performance and energy impact of installing conventional glass doors on an open five-deck refrigerated dairy/deli display case. Retrofitting the fixture with glass doors reduced the entrainment of warm and moist air from the room into the refrigerated space. This reduction caused the total cooling load of the case to decrease by 68%. Installing glass doors on the display case reduced the refrigerant mass flow rate by 71 %, resulting in the reduction of compressor power demand by 87%.
INTRODUCTION
A Southern California utility conducted this test at its Refrigeration and Thermal Test Center (RTTC), located in Irwindale, California. The controlled environment chamber was maintained at a constant DB temperature of 75 deg F and a constant RH of 55% for all tests. The refrigeration system was charged with a hydroflurocarbon (HFC) refrigerant (R-404A). Throughout the test, the refrigeration systems' controller maintained a fixed saturated condensing temperature (SCT) of 95 deg F (+/-0.5 deg F). The test rack controller was programmed to run at the manufacturer's specified suction pressure of 59 psig, corresponding to saturated evaporator temperature of 23 deg F.
The performance of an open five-deck dairy/deli fixture, commonly found in supermarkets, was evaluated under fixed conditions to develop the baseline characteristics. The display case was then retrofitted with glass doors. Under the same indoor and operational conditions as the baseline, the performance of the retrofitted case was evaluated. The project then closely compared the key performance attributes of the fixture under both scenarios. The following...