It is often stated that the refrigerator door should be openedas few times as possible for the shortest duration of time to saveenergy. Consider a household refrigerator that have an averageinternal temperature of 4o C. Assume that one-third of therefrigerated space is occupied by food items, and the remaining isfilled with air. Given that the moisture contents of the air in thekitchen and the refrigerator are 0.010 and 0.004 kg per kg of air,respectively, and thus 0.006 kg of water vapor is condensed andremoved for each kg of air that enters. The refrigerator door isopened an average of 30 times a day, and each time half of the airvolume in the refrigerator is replaced by the warmer kitchen air.The refrigerator has a coefficient of performance of 1.5 and thecost of electricity is RM0.218/kWh in Malaysia.
Design the interior volume of the refrigerator and assume theaverage temperature and pressure in the kitchen. From your design,assumptions and the information given above, determine the cost ofthe energy wasted per year as a result of opening the refrigeratordoor.
Explain the changes on your results if the kitchen air were verydry and thus a negligible amount of water vapor condensed in therefrigerator.
