Mitsubishi heat pump - advice for use in heating mode

Hi,

I am in the filed of BMS and controls and so my knowledge of heat pumps is limited. I'd be very greatful if anyone could assist with my query.

Background info:
A site I am working on currently has a number of AHUs which serve different areas. Each of these has a Mistubishi PR-20YC heat pump (currently used for cooling only but capable of heating according to Mistu literature). There is also an LPHW coil on the AHUs to provide heating when required. The supply air setpoint is 20degC. The LPHW heating is disabled when the outside air temp exceeds 17degC.

The question:
This heat pump is capable of being used in a heating mode. At what conditions will the heat pump be more efficient for use in heating mode than using the LPHW coil?

My idea:
I am considering setting up some kind of control whereby the LPHW coil will be used in cold weather up until the outside air temp reaches say, 15degC (as a rough estimate). The LPHW will then be disabled and the heat pump will then take over to provide heating until the outside air temperature reaches 17degC at which point all heating will be disabled. Does this sound like a sensible routine to implement?

Cheers

Rob

Mitsubishi Electric PR-20YC

I think this unit is about 10 years old
Refrigerant R22
Single package roof top unit
Cooling only
20 HP about 50kw cooling

If it was a heat pump it would have been PRH-20YA or PRH-20YA-L

H = heat pump

There you go, fair idea let down by having the wrong kit. ;)

Aha, very interesting. Thanks very much for the info and despite being a bit disappointing this has saved me a lot of potential aggro!

Appreciate the prompt response.

Many thanks,

Rob