R410 heat pump info

I ran both of my heat pumps last night with the aux heat disabled to see how it would do. The house stayed at 70 degrees with the local low reported at 22 degrees. The actual low here was even less than that.

These units have programmable aux heat operation so I set it to stay off except for during the defrost cycle, approx 2 minutes every 30 minutes of unit run time.

These newer heat pump units that use R410 are awesome, these are some of the first ones made back in 2001. 3600 sf with a 3.5 ton and a 3 ton unit.

Wow, down to 22 degrees and lower.

We don’t use them up here, typically, so I’m not real familiar with those. How is the cost to run them?

Since electric costs heare are near 7 cents per kwh they are considered cheap to run, the outside units only draw around 12-13 actual measured amps each. I forgot to mention they have variable speed airhandlers too which helps a little bit.

Sizing a two stage unit for cooling load on first stage will get even lower outdoor temps on second stage than a single stage unit.

I’m surprised that either or both units weren’t defrosting more than heating. Humidity must have been very low. Are your systems operation based on calculated “balance set points” with outdoor thermostats, or did you just disable the strips at the main thermostats? I’m sure the compressors are “scroll type” and they are tough, but thats seems to be pushing even those units. I plan to use similar variable speed HP systems, but piggybacked with fossil fuel furnaces as my AHU’s. Good information though. Thanks

Heat pumps go into defrost mode based on sum total of run times not presence of ice.
They will go into defrost even when not needed but come back out quicker based on a sensor on the coil. The “run time until defrost” is based on jumper settings on most units. I changed mine to 30 minutes since the next choice was 45 minutes based on watching then closely the first few years. It is normal for a noticeable amount of frost to be present even for several minutes before a defrost cycle.

When it is really cold, heat pump compressors actually draw less power, they are just idling along since they can’t do much due to less heat available outside.

I have outdoor temp sensors that work in conjunction with the thermostats and their firmware that can be tweaked by entering a setup mode. This is where you can program the on/off or setpoints for the electric strips. The strips always come on during defrost though or the air would be <40 deg.

Some other brands or newer designs may have defrost modes that do not keep track of run time but use sensors to decide when to defrost, this would actually be better but may be hard to keep the outside temp from affecting the sensors and causing excess defrosting.