Quote:
Originally Posted by Vlad
You are going wrong direction.
1. You lowered discharge pressure by oversizing condenser.
2. Because of #1 you feed less refrigerant through MD (and mass flow as well)
#2 is true because it is harder to push liquid refrigerant with less pressure.
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In the case of a fixed expansion device (orifice or cap tube) I agree with you completely.
A TXV or properly controlled EEV will open up further to maintain superheat thus increasing the mass flow in the system in line with the reduced condensing temperature. You move more heat from the evaporator. If you don't have the heat to move, then your SST drops until the system reaches an equilibrium.
Additionally, as the liquid entering the MD is cooler it has greater enthalpy and therefore you increase the evaporator capacity on a mass flow basis.
I'm not saying reducing condensing temperature is a good thing to do in isolation, but in my case where I'm designing the system cycle from scratch and have complete control over the metering device, it's a wickedly easy way to gain both capacity and efficiency.
My point is as a DIY'er, if you are aiming for super COP's it's something you should really consider. Now if you are heating water for a hydronic application, then oversizing the condenser is going to buy you nothing, but if you are trying to cool a space (like I am) it's like printing free money.
Based on the power savings converting from air to water condensed and going with a bigger HX, the water-side setup (pump, pipes, filter, HX) will pay for itself in less than 24 months. What's not to like?