Heat Pump Design

[behmin]

Anybody know of heat pumps working at low temperature wihtout having to go through defrost? By low temp I mean between 25-45 deg F.

[beenthere]

On an air to air unit. Only if you have no humidity in the outside air.

[beenthere]

I deleted your other thread, since its basically a duplicate of this thread.

If you don't want a defrost cycle.
Either set the heat pump to lock out before the outdoor temp gets cold enough.
Or, get a geothermol heat pump installed.

[behmin]

You know there is always some humidity. So, is there still a unit with no defrost at low temps 25-45F??

[beenthere]

Since I said only if there is NO humidity in the air.

The answer would be no. For air to air heat pumps.

[behmin]

What if using part of the discharge gas to run through an orifice and then attach it to the distributor intlet (after TXV, essentially putting hot gas back into the evaporator). This will raise the evaporator temperature and avoids less frost. Hav any body heard about this technique?

[beenthere]

Which would also mean you would get less heat from outside to put to the indoor coil. And have to run the more expensive aux heat to make up the difference.

[BaldLoonie]

Look for a unit with "demand" defrost. At least they will defrost only as needed. A timer, which most use, defrosts constantly even with no frost.

[Cold Feet]

You know there is always some humidity. So, is there still a unit with no defrost at low temps 25-45F??

What you're asking for is impossible for an air source heat pump. Defrost is required by the laws of physics.