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Og base 3 of x in graphmatica1/5/2023 ![]() ![]() The load losses limit the max horsepower of the motor. The no load losses are constant, while the load losses go up with the square of the load. There is the load losses that result from copper losses and rotor slippage. There is two losses in an electric motor, the no load losses that occur as a result of magnetizing losses and copper losses. The higher you go in the range, the higher the motor load will be, and the higher the vapor density, and cooling effect of the vapor will be. That is limited by the maximum motor horsepower displacement and cooling. That will give you an idea why they categorize compressors as high temp, med temp, and low temp. So, at the bottom end of the graph the cooling effect of the returning vapor becomes really low for the displacement. The cooling effect of the refrigerant coming in goes down as the vapor density goes down. If you go to a lower evap temp than that then motor load goes down. IF you go to a higher evap temp than that then motor load goes down. Peak is about 30F to 40F for R12 and R22. (In addition to being a larger peak load.) So if the condensing point goes up, then the point of the peak load evaporating temp will go up by the same percentage. The peak point will always roughly be the same percentage of the condensing temp. Not on the ideal gas law with a fixed 120F gas temp. Or about 60F boiling point pressure based on pressure alone (ideal gas law) ignoring temperature induced changes.(Assuming gas temp to be 120F.)īoiling point temperatures on the graph are based on density listings from a pressure temperature chart. Peak is about 55F for R12 or R22 based on the vapor density chart.(Gas temp equal to evaporating temp) If we reference the condensing point (X=1) as 120F that will give you an idea of where the peak point lands. Second graph is a close-up of the normal operating range people deal with. But with the scale of this graph it is to little of a change to worry about.Īll in all, the graph is just something to get a general idea across so don’t nit pick it to death. Or basically the smaller the evap/condense temp split the higher the EER and COP.īoth lines are affected by volumetric efficiency which will push the figures a little. The higher you get the evaporating temp (closer to condensing) the lower the energy used to move every BTU of heat. That is the second line in the graph (green) Vapor density at the intake equals X so the efficiency of the compressor based on evap temp is roughly is. Since the vapor density roughly follows absolute pressure (ideal gas law) (ignoring temp induced shifts). ![]() but it is ignored to make the equation simpler. Refrigerant temperature will affect the density and push the peak a little bit one way or the other. X=0 when the evap pressure reaches pure vacuum and there is no vapor to compress (no load) X=1 when the evap pressure and condenser pressure are the same. It will give you a relative load graph for any compressor/ based on evaporator pressure with a fixed condensing pressure. ![]() The two on the front of the equation used in the graph is to scale it to make it fit in the 1 by 1 graph nicely. (pressure in the compressor case) which is X That makes it.īack pressure on the cylinder is the intake pressure. To graph it on a 1 by 1 Graph as 1 equal to the condensing pressure. MEP=(1+hyplog(no of exp)/(no of exp)-(BP) The initial pressure is the reference point (1) That is drawn from the “Audels engineers and mechanics guide 1” copyright 1921. (mean effective pressure) = (initial pressure abs)*(1+hyp.log(no of expansions)/(number of expansions) -(back pressure abs) The base equation for energy/force from/to a compression/expansion system is. ![]() The base point is motor loading based on evaporator temperature. I added the temps and labels with a paint program. Do a google search for it and you will find it. The program I used to make the graphs I attached to this post is graphmatica. And how you can use that information when applying that compressor to a job it isn’t listed for. Or basically how they classify compressors based on high temp, low temp, and medium temp operation. I thought I would bring up the subject of compressor motor load, and cooling based on the evaporator temp. ![]()
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