Hi, Folks, calmed down yet?
What I was going to say, or more to the point explain was my post saying that the refrigerant leaving an evaporator of a LPR system is most likily slightly superheated. This statement is general and comes from the fact that most liquid metering devices used to feed the evaporator in an LPR system use a pulse width modulation. This is basically open/shut with the evaporator over-feed during the on pulse and slightly under-fed during the off pulse. The liquid seen in the LPR sight-glass builds up from the on pulses, creating the subcooling. As energy can neither be created or destroyed, any energy given up to the cold liquid in the LPR ends up in the suction vapour, hence Marcs interpretation that subcooling does not increase COP, but subcooling does have advantages in delivering a full head off liquid to the evaporator. With an LPR the idea is to add subcooling without superheating the suction vapour too much. The increased COP comes from the fully or nearly flooded evaporator which increases the evaporation pressure, reducing the compression ratio and the lower head pressures from a condenser which can be allowed to run to a lower condener sett point. Another advantage that is gained from the LPR being employed is a better draining of the condenser, again given a decrease compression ratio, although this can be a dis-advantage if taken too far as the heat rejected in a condenser from the trapped liquid is rejected outside the system increasing COP, a proper balance is required to acheive the best results.
Anybody fancy posting a PH diagram to explain?(I am still playing with my Iscool program)
Regards. Andy.