R134A Pressure Temperature Chart
Learn the R134A pressure temperature relation to use PT chart to maximum advantage.Its a shame that it is rarely used.
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The pressure temperature relationship as shown in pt chart is simply a chart listing the Boiling temperature of refrigerant.By convention, pressure is listed on left hand side of chart and the coreesponding boiling temp for the refrigerant on the right.Refrigerant at these conditions are refrred to as saturated.
If we measure the Pressure of the refrigerant,we can easily determine its saturation temperature.This is true for every part of system.At the points of system where only vapor is present.The actual vapor temperature will be at or above the temperature indicated in the pt chart.
Baiscs of R134A Pressure temperature chart
- Vapor will only be present in the suction or discharge lines.
- Where only liquid is present,the actual liquid temperature will be at par or below the pt chart.
- Liquid refrigerant will be present in the liquid line which connects the evaporator and condenser coils.
Now We understand the basics of pt chart.Let us analyse the system for Superheated,refrigerants.
Let us say that the measured pressure at Evaporator coil outlet is 18 psig and Assume Minimal pressure drop.So the pressure inside the evaporator coil will be 18 psig and it corresponds to a temperature of 19 degree farenhite in PT Chart.Liquid and vapor must be present in evaporator coil.The refrigerant must be at 19 degree farenhite in evaporator coil.So if you measure the temperature at Evaporator coil outlet as 19 farenhite,you know that refrigerant is saturated and a mixture of liquid and vapor will enter the suction line.
If the actual measured temperature is 27 farenhite at evaporator coil outlet than we know the refrigerant is superheated vapor as this temperature is higher than saturated temperature.To determine the amount of superheat,consult the pt chart.Take the difference between measured temperature and saturated temperature in pt chart.So the superheat is 27-19=8 degree farenhite.
R134a is placement of r12 because of lower GWP.It needs higher operating pressure than r12 and hence r22 can not be used in existing r12 systems.