Question

A heat pump that operates on the ideal vapor-compression cycle with refrigerant-134a is used to heat a house. The mass flow rate of the refrigerant is 0.2 kg/s. The condenser and evaporator pressures are 1 MPa and 400 kPa, respectively.
Required:
a. Determine the rate of heat supply to the house.
b. The rate of heat supply to the house is ___________ kW.

Answer 1

(a)  

Use “saturated refrigerant-134a pressure tableâ€, to find $ , h ,           and of refrigerant-134a, at 320kPa (P) .

     $h_{1} h_{g}$ = 251.93kJ/kg

    $s_{1} (s_g}$) =0.93026 kJ/kg-K

    $v_{1}(v_{g})$ =0.063681 m/kg

we solve $h_{6}$ ,

$h_{6}$ = 282.62 kj/kg

$h_{3} (h_{f)}$ = 127.25 kJ/kg

We use this formula for finding $Q_{n}$

$Q_n} =( h_{2} - h_{3} )$

      = 38.8 kw

(b)

Find the COP of the heat pump ($COP_{R}$) .

($COP_{R}$)  = $q_{L} /w_{in}$

$COP_{R}$ = (282.62 -127.25) / (282.62-251.93)

          = 5.06

What is evaporator pressures ?

Valves for regulating evaporator pressure

Although the compressor suction pressure may be lower, evaporator pressure regulation (EPR) valves can be employed in the suction line to prevent the evaporator pressure from dropping below a set or controlled value.

An EPR valve is used for the following tasks:

1. Prevent potential damage to a liquid chilling evaporator from the liquid freezing.

2. Prevent frost from accumulating on an air-cooling evaporator when it is near freezing point or when operation cannot be interrupted by a brief failure.

3. Permit the operation of two or more evaporators with the same compressor at various load temperatures.

4. Vary the evaporator pressure in accordance with a fluctuating load that is managed by the load temperature.

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