AWHP superheat & sub-cooling

[Gary]

What are your thoughts on COP,hp optimisation?

How to force the heat-pump system to operate on maximum COP,hp throughout the heating cycle?

Now that we are maximizing the heat absorption on the low side, what remains is to transfer that heat to the water flowing through the condenser.

As heat is transferred from the refrigerant to the water, the refrigerant temp drops, having lost heat, and the leaving water temp rises, having gained heat.

The two temperatures "approach" each other. Thus the difference between the SCT temp and the leaving water temp is called the approach temp.

By installing a water regulating valve at the condenser outlet (which senses and controls SCT) we can regulate the flow to give us a steady SCT of 75C, which is the upper limit of the compressor.

Since the SCT is thereby fixed at 75C, the variable in our approach becomes the water leaving temp. The better the heat transfer, the higher the leaving water temp.

We need to have a condenser large enough to give us 65C leaving water temp, giving us an approach temp of 75-65=10K approach.

By increasing the condenser size beyond this minimum we can increase water temp and reduce the approach, but this again involves a point of diminishing returns.

I'm thinking a reasonable approach target would be about 5K (75-70=5K).