Thermodynamics

Chapter 6 | 313Steel shellSteel or plastic linerThermal Insulation6%Externalheater6%Fanmotor6%Defrostheater52%Wallinsulation30%DoorgasketregionFIGURE 6–55The cross section of a refrigeratorshowing the relative magnitudes ofvarious effects that constitute thepredictable heat load.Plastic breaker stripsPlastic door linerFrom ASHRAE Handbook of Refrigeration, Chap.48, Fig. 2.consumed by the refrigerator can be minimized by practicing good conservationmeasures as discussed below.1. Open the refrigerator door the fewest times possible for the shortestduration possible. Each time the refrigerator door is opened, the cool airinside is replaced by the warmer air outside, which needs to be cooled.Keeping the refrigerator or freezer full will save energy by reducing theamount of cold air that can escape each time the door is opened.2. Cool the hot foods to room temperature first before putting them into therefrigerator. Moving a hot pan from the oven directly into therefrigerator not only wastes energy by making the refrigerator worklonger, but it also causes the nearby perishable foods to spoil by creatinga warm environment in its immediate surroundings (Fig. 6–56).3. Clean the condenser coils located behind or beneath the refrigerator. Thedust and grime that collect on the coils act as insulation that slows downheat dissipation through them. Cleaning the coils a couple of times a yearwith a damp cloth or a vacuum cleaner will improve cooling ability of therefrigerator while cutting down the power consumption by a few percent.Sometimes a fan is used to force-cool the condensers of large or built-inrefrigerators, and the strong air motion keeps the coils clean.4. Check the door gasket for air leaks. This can be done by placing aflashlight into the refrigerator, turning off the kitchen lights, and lookingfor light leaks. Heat transfer through the door gasket region accounts foralmost one-third of the regular heat load of the refrigerators, and thusany defective door gaskets must be repaired immediately.5. Avoid unnecessarily low temperature settings. The recommendedtemperatures for freezers and refrigerators are 18°C (0°F) and 3°C(37°F), respectively. Setting the freezer temperature below 18°Cadds significantly to the energy consumption but does not add much tothe storage life of frozen foods. Keeping temperatures 6°C (or 10°F)Warmair30°C6°CHotfood80°C5°CFIGURE 6–56Putting hot foods into the refrigeratorwithout cooling them first not onlywastes energy but also could spoil thefoods nearby.