Question

Statement:
Selection of compressor and refrigerant for HVAC system that is operating on Vapor Compression Refrigeration System. The heat load is 120,000 BTU/hr and temperature is to be maintained at space is 50C.
Step 1:
Select ambient and environmental conditions
Step 2:
Select refrigerant, preliminary calculations, use of property charts, suction discharge pressure of compressor to achieve required cooling, compressor capacity etc.
Step 3:
Select compressor (Stage, rpm, displacement, size etc)

need detailed solution

Answer 1

1 room temperature 50c

condenser coil temperature = 60c

outside temperature = -10c

ambient pressure 1bar

2 refrigerant   - R134a

heat load = 120,000btu/hr or 35.16kJ

condenser pressure P2 = 16.18bar(discharge of compressor )

t2 = 70

specific energy lost bby condenser = h2-h3 = 438-288 = 150kJ/kg

mass flow rate of refrigerant m = 35.16/150 = 0.23kg/sec

no subcooling

evaporator temperature -10deg c assuming isentropic expansion

specific energy gained by the evaporator = h1-h4 = 394-288 = 106kJ/kg

specific workdone by compressor = 150-106 = 44kJ/kg

suction pressure of compressor = 2.006bar

3

single stage compressor

specific volume at stage1 v1 = 0.09959m^3/kg

volume flow at suction Qc = m*v1 = 0.023m^3/sec

p1 = 2.006 bar

p2= 16.18 bar

compression ratio = 16.18/2.006 = 8.065

stroke of cylinder = 0.2m

bore of cylinder = 0.1m

swept volume of cylinder V = .2*(.1^2*0.785)m^3 = 1.57*10^-3m^3

hence the size of compressor = 1.57Lt

speed of rotation  = N rpm

volume flowrate = V*N/(2*60)m^3/sec

which is equal to v1 = 0.023 = 1.57*10^-3*N/(2*60)

hence the speed of compressor N = 1757.96RPM