A house rises to 35°C on a hot summer day. When the owner comes home they turn on the air conditioning system to cool the house down. Within 30 minutes the house is cooled to 20°C.
The COP of the A/C unit (refrigerator) is 2.8. Assume the mass of the house to be cooled consists entirely of 800kg of air with a Cp of 1.0kJ/kg-K and a Cv of 0.72 kJ/kg-K. Determine the power required by the A/C unit if the house is well insulated.
Houses are usually not well insulated but leak a lot of heat ou to the surroundings. This heat leakage rate increases with T so as your home gets cooler the heat leaks increase and the overall efficiency of your a/c goes down. Assume the heat leakage of this home averages about 1.2kW while it being cooled from 35°C to 20°C. If the A/C work in is limited to the previously calculated value and the COP stays the same how long will it take to cool the home down now?