An architect wants to use an electrical work input to keep the temperature inside a building at 20° C when the outside temperature is –20° C. Determine the maximum heat-transfer rate (kW) that can be supplied to the building (per kW of electrical input) by 

(a) A resistance heater; 

(b) A vapor-compression cycle using R-134a with T_evap = –20° C and T_cond = 20° C, saturated vapor leaving the evaporator, and saturated liquid leaving the condenser; 

(c) The best possible method.