AWHP superheat & sub-cooling

[desA]

The storage vessels are usually fairly large, for the larger heat-pumps. Some could be in the region of 4000L or so. There would be a fair amount of thermal lag there.

A sensor signal from the tank can be input into the heat-pump controller & action taken to shut back the pump, fan etc. Typically the water temp is used to shut the heat-pump off, when the pre-set temp has been reached.

Hi/low pressure trips are also installed. If the water flow drops too low & SCT rises above the critical value, the hi/low should catch it, if correctly set - to protect the compresor.

Basically, since the hot water is generally blended with cold water by the end user, the terminal tank temperature can undershoot, or even overshoot a little, without much problem - in general.