Chapter 5, Problem 5.41P

At steady state, a heat pump provides energy by heat transfer at the rate of 25,000 Btu/h to maintain a dwelling at 70°F on a day when the outside temperature is 30°F. The power input to the heat pump is 4.5 hp.Determine:(a) the coefficient of performance of the heat pump.(b) the coefficient of performance of a reversible heat pump operating between hot and cold reservoirs at 70°F and 30°F, respectively, and the corresponding rate at which energy would be provided by heat transfer to the dwelling for a power input of 4.5 hp.

An inventor claims to have devised a refrigeration cycle operating between hot and cold reservoirs at 308 K and 278 K, respectively, that removes an amount of energy QC by heat transfer from the cold reservoir that is a multiple of the net work input—that is, QC = NWcycle, where all quantities are positive. Determine the maximum theoretical value of the number N for any such cycle.

To maintain a dwelling steadily at 68°F on a day when the outside temperature is 30°F, heating must be provided at an average rate of 300 Btu/min. Determine the electrical power required, in kW, to deliver the heating using: (a) electrical-resistance heating, (b) a heat pump whose coefficient of performance is 3.5, (c) a reversible heat pump operating between hot and cold reservoirs at 68°F and 30°F, respectively.

To maintain a dwelling steadily at 68°F on a day when the outside temperature is 30°F, heating must be provided at an average rate of 300 Btu/min. Determine the electrical power required, in kW, to deliver the heating using: (a) electrical-resistance heating, (b) a heat pump whose coefficient of performance is 3.5, (c) a reversible heat pump operating between hot and cold reservoirs at 68°F and 30°F, respectively. Part A Determine the electrical power required, in kW, to deliver the heating using electrical-resistance heating. Wa i Save for Later kW Attempts: 0 of 4 used Submit Answer

A heat pump cycle is used to maintain the interior of a building at 25°C. At steady state, the heat pump receives energy by heat transfer from well water at 9°C and discharges energy by heat transfer to the building at a rate of 120,000 kJ/h. Over a period of 14 days, an electric meter records that 1500 kW · h of electricity is provided to the heat pump.Determine:(a) the amount of energy that the heat pump receives over the 14-day period from the well water by heat transfer, in kJ.(b) the heat pump’s coefficient of performance.(c) the coefficient of performance of a reversible heat pump cycle operating between hot and cold reservoirs at 25°C and 9°C.

A heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 3 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min. (a) Determine the coefficient of performance. (b) Evaluating electricity at $0.18 per kW · h, determine the cost of electricity in a month when the heat pump operates for 300 hours.

Kelvin-Planck statement defines the Second law of thermodynamics as a. It is impossible to construct a machine that will operate in a cycle, extract heat from a reservoir, and do an equivalent amount of work on the surroundings. b. It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. c. It is possible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. d. It is possible to construct a machine that will operate in a cycle, extract heat from a reservoir, and do an equivalent amount of work on the surroundings.

An air conditioner is a device used to cool the inside of a home. It is, in essence, a refrigerator in which mechanical work is done and heat removed from the (cooler) inside and rejected to the (warmer) outside. A home air conditioner operating on a reversible Carnot cycle between the inside, absolute temperature T2, and the outside, absolute tempera- ture T1 > T2, consumes P joules/sec from the power lines when operating continuously. (a) In one second, the air conditioner absorbs Q2 joules from the house and rejects Q1 joules outdoors. Develop a formula for the efficiency ratio Q2/P in terms of T1 and T2. (b) Heat leakage into the house follows Newton's law Q = A(T, – T2). Develop a formula for T, in terms of T1, P, and A for continuous operation of the air conditioner under constant outside temperature T and uniform (in space) inside temperature T2. (c) The air conditioner is controlled by the usual on-off thermostat and it is observed that when the thermostat set at 20°C and an…

The thermal efficiency of a reversible power cycle operating between hot and cold reservoirs is 50%. Evaluate the coefficient of performance of: (a) a reversible refrigeration cycle operating between the same two reservoirs. (b) a reversible heat pump cycle operating between the same two reservoirs.