Useful control range of TXV
If you take (for example) a 2 ton system with a TXV, then slow down the compressor to half speed with a VFD, you essentially have a 1 ton compressor in an otherwise 2 ton system. Yet it can be made to work just fine.
Over what range do typical TXVs operate over? In other words, if you continued to lower the capacity of the compressor, about when would the TXV fail to operate properly? (Assume lubrication problems were solved in some other way.)
TXV are designed to regulate/ control with specific conditions, ie., evaporator TD., air on versus coil evaporation condition them regulate the suction super heat accordingly. By reducing evaporator duty the TXV will control superheat. The only mechanical TXV I have come across that will control down to 30% of select design is the sporlan ' O " series. Other than that electronic TXVs
Txv's also have a minimum pressure drop.
I agree, an electronic txv would likely be the best way to go, however if you're only running your speed down to 30% and your TXV goes down to 30 maybe you almost have a matched system?
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