Chapter 11: Problem 40
Do you think a heat pump system will be more cost-effective in New York or in Miami? Why?
Chapter 11: Problem 40
Do you think a heat pump system will be more cost-effective in New York or in Miami? Why?
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Get started for freeRefrigerant-134a enters the compressor of a refrigerator as superheated vapor at \(0.20 \mathrm{MPa}\) and \(-5^{\circ} \mathrm{C}\) at a rate of \(0.07 \mathrm{kg} / \mathrm{s},\) and it leaves at \(1.2 \mathrm{MPa}\) and \(70^{\circ} \mathrm{C}\). The refrigerant is cooled in the condenser to \(44^{\circ} \mathrm{C}\) and \(1.15 \mathrm{MPa}\), and it is throttled to 0.21 MPa. Disregarding any heat transfer and pressure drops in the connecting lines between the components, show the cycle on a \(T\) -s diagram with respect to saturation lines, and determine ( \(a\) ) the rate of heat removal from the refrigerated space and the power input to the compressor, \((b)\) the isentropic efficiency of the compressor, and \((c)\) the \(C O P\) of the refrigerator.
A refrigerator operating on the vapor-compression refrigeration cycle using refrigerant-134a as the refrigerant is considered. The temperature of the cooled space and the ambient air are at \(10^{\circ} \mathrm{F}\) and \(80^{\circ} \mathrm{F}\), respectively. \(\mathrm{R}-134\) anters the compressor at 20 psia as a saturated vapor and leaves at 140 psia and \(160^{\circ} \mathrm{F}\). The refrigerant leaves the condenser as a saturated liquid. The rate of cooling provided by the system is 45,000 Btu/h. Determine ( \(a\) ) the mass flow rate of \(R-134\) and the COP, \((b)\) the exergy destruction in each component of the cycle and the secondlaw efficiency of the compressor, and (c) the second-law efficiency of the cycle and the total exergy destruction in the cycle.
The COP of vapor-compression refrigeration cycles improves when the refrigerant is subcooled before it enters the throttling valve. Can the refrigerant be subcooled indefinitely to maximize this effect, or is there a lower limit? Explain
A heat pump water heater (HPWH) heats water by absorbing heat from the ambient air and transferring it to water. The heat pump has a COP of 3.4 and consumes \(6 \mathrm{kW}\) of electricity when running. Determine if this heat pump can be used to meet the cooling needs of a room most of the time for "free" by absorbing heat from the air in the room. The rate of heat gain of a room is usually less than \(45,000 \mathrm{kJ} / \mathrm{h}\).
Consider a heat pump that operates on the ideal vapor compression refrigeration cycle with \(\mathrm{R}-134 \mathrm{a}\) as the working fluid between the pressure limits of 0.32 and \(1.2 \mathrm{MPa}\). The coefficient of performance of this heat pump is \((a) 0.17\) \((b) 1.2\) \((c) 3.1\) \((d) 4.9\) \((e) 5.9\)
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