Rooftop AC in Cold Weather

[randynavarro]

This situation was a first for me:

Cold day; 40-50 degrees.

I inspected a poochy-fanooli condo on the top floor of a multi-floor building.

In the condo is an air handler with a roof mounted heat pump / ac unit with electric back up heat. There is no access to the roof (for me at least).

The inside temp of the condo was about 72 deg and climbing as the sun continued to hit the building. I could easily see the need to need the a/c later in the day.

So, running the A/C when its chilly outside runs counter to the notion of NOT running them when temps are low.

So, I'm confused. Are there units designed to operate in cold temperatures or is the whole idea of running them in the cold just more inspector folklore?

[hausdok]

I'd tell them to open the normal Seattle air conditioner or get some blinds to reduce solar gain.

OT - OF!!!

M.

[inspector57]

Different manufacturers have different cut-off points for running the A/C, but in GENERAL, heat pumps are better equiped to handle lower temperatures even in the cooling mode. 55-60 degrees comes to mind, but don't quote me on that.

Jim

[Jim Katen]

Originally posted by randynavarro

. . . So, I'm confused. Are there units designed to operate in cold temperatures or is the whole idea of running them in the cold just more inspector folklore?

1. You don't want to run an AC compressor when it's cold out unless you know it has a crankcase heater. The compressor might be full of liquid refrigerant. If it's a piston-type compressor, you can kill the compressor this way. If it's a scroll compressor, you won't kill the compressor, but it won't be happy either. In either case, the system won't behave properly unless it was designed (or converted) for use in low temperatures.

2. You can run a heat pump in the air conditioning mode during cold weather because it was designed to be able to do this during it's defrost cycles. However, just as with an air conditioner, the system won't behave properly unless it was designed for low temperature use. With a heat pump, there's really no reason to run it in more than one mode. If it works properly in heating, it'll almost certainly work properly in cooling. The only exception would be if there were a problem with the reversing valve -- such a problem is exceedingly rare.

3. High rise buildings often have cooling systems that are designed to be used in the middle of the winter. There's probably no way for you to tell this though. The safest course is to tell the customer that it's too cold out for you to make a safe and meaninful test of the AC system.

- Jim Katen, Oregon