9.C-2 The purpose of this problem is to determine the performance of residential vapor compression heat...

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9.C-2 The purpose of this problem is to determine the performance of residential vapor compression heat pump operating in the heating mode using refrigerant R134a. The heat pump system has a fixed speed reciprocating compressor that provides a constant displacement rate (Vdisp) when it is operating. The volumetric flow rate of the refrigerant entering the compressor is given by: V = V disp [1-(-1)] where V disp = 0.0055 m/s is the compressor displacement rate, C = 0.025 is the clearance volume ratio, and v and v3 are the specific volumes of the refrigerant at the compressor inlet and outlet, respectively. The compressor isentropic efficiency can be expressed approximately as: ne 0.84-0.0075 (Tcond - Tevap) where Tcond and Tevap are the saturation temperatures (in C) in the condenser and evaporator, respectively. The heat exchange rates in the condenser and evaporator can both be modeled with effectiveness relations of the form: Q=&min ATmax where = 1-exp(-NTU) is the effectiveness, NTU is the number of transfer units, Cmin is the minimum capacitance rate, and ATmax is the maximum temper- ature difference between the entering air and the saturation temperature of the refrigerant. Air is supplied to the condenser at Tonda -25 C and macond = 1 kg/s. The outdoor evaporator coil sees an air supply at the outdoor temperature and maevap 1 kg/s. The overall heat transfer coefficients for the condenser and evap- orator are both U= 40 W/m-K. Assume that the evaporator outlet is saturated vapor and the condenser outlet is saturated liquid. Pressure drops in the heat exchangers can be neglected. a) Assume the outdoor air temperature is Taout = -5C and the heat transfer surface area of condenser and evaporator are each A = 35 m. Calculate the heating capacity (kW) and COP at this condition and plot the cycle on a pressure-specific enthalpy diagram. b) Calculate and plot the heating capacity and COP as a function of the outdoor temperature for values between -30C < Taout < 20C. Explain the behavior you observe in the plot. 9.C-2 The purpose of this problem is to determine the performance of residential vapor compression heat pump operating in the heating mode using refrigerant R134a. The heat pump system has a fixed speed reciprocating compressor that provides a constant displacement rate (Vdisp) when it is operating. The volumetric flow rate of the refrigerant entering the compressor is given by: V = V disp [1-(-1)] where V disp = 0.0055 m/s is the compressor displacement rate, C = 0.025 is the clearance volume ratio, and v and v3 are the specific volumes of the refrigerant at the compressor inlet and outlet, respectively. The compressor isentropic efficiency can be expressed approximately as: ne 0.84-0.0075 (Tcond - Tevap) where Tcond and Tevap are the saturation temperatures (in C) in the condenser and evaporator, respectively. The heat exchange rates in the condenser and evaporator can both be modeled with effectiveness relations of the form: Q=&min ATmax where = 1-exp(-NTU) is the effectiveness, NTU is the number of transfer units, Cmin is the minimum capacitance rate, and ATmax is the maximum temper- ature difference between the entering air and the saturation temperature of the refrigerant. Air is supplied to the condenser at Tonda -25 C and macond = 1 kg/s. The outdoor evaporator coil sees an air supply at the outdoor temperature and maevap 1 kg/s. The overall heat transfer coefficients for the condenser and evap- orator are both U= 40 W/m-K. Assume that the evaporator outlet is saturated vapor and the condenser outlet is saturated liquid. Pressure drops in the heat exchangers can be neglected. a) Assume the outdoor air temperature is Taout = -5C and the heat transfer surface area of condenser and evaporator are each A = 35 m. Calculate the heating capacity (kW) and COP at this condition and plot the cycle on a pressure-specific enthalpy diagram. b) Calculate and plot the heating capacity and COP as a function of the outdoor temperature for values between -30C < Taout < 20C. Explain the behavior you observe in the plot.