The coefficient of performance K = H/P is a dimensionless quantity. Its value is independent of the units used for H and P, as long as the same units, such as watts, are used for both quantities. However, it is common practice to express H in Btu/h and P in watts. When these mixed units are used, the ratio H/P is called the ?energy efficiency ratio? (EER). If a room air conditioner has K = 3.0, what is its EER?
Solution 8E Step 1 of 4: The refrigerator or air conditioner operation can be consider as the reverse operating heat engine. As heat engine takes heat from the hot body and transfers the heat into colder object. Whereas a refrigerator does the reverse process; that is, it takes heat from the cooler place(inside refrigerator) and gives it off to a warmer place(outside the refrigerator). That is, a heat engine will do a net output mechanical work whereas the refrigerator or air conditioner requires a net input mechanical work. Step 2 of 4: The coefficient of performance of refrigerator or air conditioner which is dimensionless as both H and P are expressed in watts is given by, Q c Ht H(watts) K= |W |= Pt = P(watts)…….1 Where H is the heat current and P is power output. Similarly if the heat current is expressed in Btu/h and Power in watts, the ratio is know as energy efficiency ratio(EER), that is H(Btu/h) EER = P(watts)………..2 Where H is the heat current and P is power output.