# This is a HVAC / Thermodynamics question I am trying to draw a pressure/ enthalpy diagram for a chiller system I wish to build . I already have a...

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This is a HVAC / Thermodynamics question

I am trying to draw a pressure/ enthalpy diagram for a chiller system I wish to build . I already have a condensing unit and have A BPHE. I want to run the BPHE at -12 with 5 degrees of superheat and at that temperature the cooling capacity of condensing unit is around 650 watts at ambient of 25 degrees, from the documentation. The calculated mass flow rate is around 0.006 Kgs-1(r404a) . To complete my diagram I need to know how much the pressure increase will be form the compressor. The only other info I have about the condensing unit compressor is the electrical power consumption at cooling capacity 650 watts which is useless because I do not know its efficiency. I also have that at a cooling capacity of 1192 watts, the inlet pressure is 0.83 Mpa and the outlet pressure is 2.8 Mpa. I am asking whether the ratio of inlet pressure to outlet pressure for a isentropic process such as the compressor(ideal I know) is always constant. In this way I may use the ratio 2.8/8.3 to calculate the ouput pressure from my input pressure which at -12 degrees is around 4 bar. Alternatively it could be that the pressure difference is always the same, so instead of using a ratio I subtract 0.83 from 2.83 and simply add the difference to the pressure at -12.Other than these two options I fail to see how supplied info will allow me to complete the diagram and derive head pressure. Thank you Paul

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