Liquid receiver on a reverse cycle VRV system

[BradC]

Also the outdoor unit may record SST and SCT but if subcooling to fan coils is different then for a fixed EEV opening more or less rerigerant will be needed for the same amount of cooling. Some have a thermistor mid coil also for this reason.

That makes sense.

All the bolt-on EXV controllers I've seen take the temp and pressure at the outlet of the coil (as per convention) to determine superheat. Could you reliably determine superheat by simply measuring both ends of the coil? (with suitable qualifications about limited application to unrestrictive coils with low pressure drops)

Hope that helps.

Heaps. Cheers for that Andy.

[aramis]

That makes sense.

All the bolt-on EXV controllers I've seen take the temp and pressure at the outlet of the coil (as per convention) to determine superheat. Could you reliably determine superheat by simply measuring both ends of the coil? (with suitable qualifications about limited application to unrestrictive coils with low pressure drops)
Heaps. Cheers for that Andy.

Yes, in general for azeotropes (or near): you can measure superheat more reliably with 2 temperature sensors than temperature/pressure unless you compensate for the different time constants the transducers have.

Usually system pressure time constant + pressure transducer time constant are shorter than temperature TC, but you also have to consider the time it takes to look up saturation tables for the controller.

For non azeotropes you must calibrate/compensate.

(with suitable qualifications about limited application to unrestrictive coils with low pressure drops)

All designs should keep pressure drop in the coils low for all types of refrigerants or you have to measure the coil’s pressure differential too, and compensate.

--- o ---

You must follow the controller’s manufacturer manual as to where, how and number of sensors must be installed, for it's control logic success depends on it.

[BradC]

You must follow the controller’s manufacturer manual as to where, how and number of sensors must be installed, for it's control logic success depends on it.

Which is all well and good if the controller *has* a manufacturer.