Heat Pump pressure variations

[Fridge in Focus]

Hi Gents,

I know there is a simple anwser to my question.

IE why is the suction pressure different during the heating cycle as it is to the cooling cycle? I know it's more efficient during the heating cycle, is this anything to do with the variation in pressures?

Thanks FIF

[The Viking]

FiF,
The pressures will differ depending on various factors, design and surrounding temperatures being the main ones.
You don't tell us what type of system you are thinking of so I will assume it is a single split for simplicity.

When the system is in cooling mode the outdoor temperature, ambient for the condensor, is likely to be around 20-25ºC (here in UK) and the indoor temperature, ambient for the evaporator, around the same 20-25ºC.
Now, when the system is used as a heat pump it is likely that the outdoor temperature has dropped significally. The indoor temperature, now ambient for the condensor is likely to still be in the region of 20-25ºC but the outdoor temperature where the evaporator now is are likely to be lower.

Most manufacturers will have compensated for this in their designs, utilising "oversized" coils in the outdoor unit.

But the big question is, why do you think the units are more efficient during the heating cycle???


.

[frank]

Where are you measuring the 'suction' pressure?

When the system is in heating mode, the true suction pressure can be measured between the accumulator and the compressor, not at the service valve. At this point, you would be measuring discharge pressure.