www.bls.gov/ro1/cpibosap.pdf Is 1 kW.hr power or energy and why? Show your analy

Question

www.bls.gov/ro1/cpibosap.pdf

Is 1 kW.hr power or energy and why? Show your analysis. A refrigerator operates reversibly with a COP equal to beta max = 7.45. The refrigerator transfers heat to a kitchen at 70 degree F. Find the temperature of the food compartment in degree F. Find the temperature expression symbolically first before you plug and chug! How much on a rate basis in kW is the refrigerator capable of transferring heat from the food compartment if 5 kW is transferred from the working refrigerant to the kitchen? What is the yearly electrical bill in Massachusetts if the refrigerator runs an average of 7 hours per day? Use the average price for the Boston-Brockton area: www.bls.gov/rol/cpibosap.pdf

Explanation / Answer

1kWh is energy. since it has the dimensions of energy analysis (power*time) (J/s)*(s) =J COP of refrigerator = 7.45 let the temp of Kitchen be T1 food compartment be T2 given T1 = 70 F = 294.261 K COP = T2/(T1-T2) solving, T2 = 259.44 K = 7.322 F let the heat transferred to Kitchen be Q1 from food compartment be Q2 given, Q1 = 5 kW COP = Q2/(Q1-Q2) solving, Q2 = 4.41 kW work input to refrigerator = 5-4.41 = 0.59 kW energy used per year = 0.59*365*24 = 5168.4 kWh price per kWh = $0.151 electricity bill = $ 780.43

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