Design a vapor compression heat pump that uses R134a as the working fluid that delivers a cooling duty of 3 tons (36,000 Btu/hr) for the cooling mode (summer) design conditions shown in the attached table. Design the system with evaporator and condenser approach ∆Ts (i.e., smallest ∆T between the air and the refrigerant) of 5oF. Also note that R134a exits the evaporator with 5oF superheat, while a reasonable condenser sub cooling is 3oF. The state points are identified as follows:

1. Evaporator inlet
2. Evaporator saturated vapor
3. Evaporator superheated outlet
4. Compressor actual outlet (assume 65% isentropic efficiency)
5. Compressor ideal outlet
6. Condenser saturated vapor
7. Condenser saturated liquid
8. Condenser subcooled outlet
9. Evaporator air inlet
10. Evaporator air outlet
11. Condenser air inlet
12. Condenser air outlet
As part of this design exercise, compute and report the following:
• Mass flow rate (lbm/hr), temperatures, pressures, qualities, enthalpies and entropies at each state of the eight state points of the working fluid, and also the relevant quantities for the air streams at the inlet and outlet (the array variables feature in EES will help ensure clarity in the reporting of these quantities).
• Condenser and evaporator UAs required to deliver this performance at the above A/C system rating condition
• System thermodynamic COP, and all component duties:
• Condenser: desuperheating load, condensation load, and subcooling load in Btu/hr
• Evaporator: evaporation load, superheating load, Btu/hr
• Compressor: Btu/hr, kW and Horsepower (report in all three units)
• Using local utility electricity rates, compute the operating cost of the heat pump per hour
of use at the rated capacity.

SYSTEM DESIGN CONDITIONS Cooling duty, Btu/hr 36000
Heating duty, Btu/hr Predict with designed system
Cooling Mode Heating Mode Indoor
Airflow,cfm 1350 Airinlet,oF 80
InletRelativeHumidity,%or51.1 Humidity Ratio, fraction
OutletRelativeHumidity,% 100 or Humidity Ratio, fraction
Cooling Mode Ambient Range Heating Mode Ambient Range
Outdoor Indoor Outdoor
5000 1350 5000 95 70 47 0.022 0.009 72.65
0.022 0.009 100
70-105oF 17-65oF

Answer rating: 100% (QA)

Vapor Compression Heat Pump Design with R134a Problem Design a vapor compression heat pump using R134a as the working fluid to deliver a cooling duty of 36000 Btuhr Given Cooling duty 36000 Btuhr Evap... View the full answer