Most efficient way to run my heat pump?

Posted By nola mike, Dec 13, 2013 at 5:11 AM

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1. #1

nola mike Minister of Fire 2. ```NULL ```

Sep 13, 2010
547
76
Loc:
Richmond/Montross, Virginia
This is for my river place. It has a heat pump, which I rarely use in the winter (that's what the stove is for). I got an internet t-stat that lets me program from afar. In the winter, I keep the house at 42' when I'm not there. If I'm coming in, especially at night or with the wife/kids, 42' on arrival doesn't cut it, so I turn on the heat remotely to at least get it to 55' or so (it takes a LONG time for the stove to heat the place from 42' if it's cold outside!). The heat pump of course sucks in the cold weather, but will eventually warm the house (also takes a LONG time, but I can turn it on 12 hours or whatever before I'm arriving). The problem is/was that with that much of a differential between actual/set temp, and with the suckiness of the heat pump in the cold, the system wants to turn on the electric emergency strip heat until it gets up to temp. This it does far quicker than just using the pump, which basically will run constantly. I disabled the strip element, so now it only will use the heat pump.

The question is:
Am I better off running the strip heaters for a shorter period of time (at much higher energy consumption), or the heat pump using less energy/hour, but taking a much longer time?

2. #2

woodgeek Minister of Fire 2. ```NULL ```

Jan 27, 2008
3,559
618
Loc:
SE PA
Your first thought is right. Disable the strip when you leave, turn on the stat to run the HP before you arrive. If it reaches setpoint, the stat will maintain. Re-engage strip if needed upon arrival.

If your intuition is that at some point (what if it took a week for the HP to reach setpoint, but the strip could do it in 1 hour) it WOULD make sense to use the strip (rather than heat the house for days) then, yes, you are mathematically correct. So there is warming time where it might cross over. I would guess (having solved similar problems) that timescale is the natural cooling time of the structure. IOW, if it takes 24 hours to cool down most of the way to exterior temps after you leave, then any warmup time less than 24 hours prob makes sense with the HP. Make sense?

3. #3

maverick06 Minister of Fire 2. ```NULL ```

Sep 27, 2008
765
40
Loc:
media, pa
agreed
use the heat pump, it takes a while, but its cheap to operate compared to resistance heat. My thermostat i have increase the temp in the morning slowly slow as not to call for oil heat. Of course wood does most of the heat. I try only to use the heat pump when its above 45F here... but thats not always an option since i do lings like work and have a life

4. #4

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,056
465
Loc:
SW Virginia
Interesting question. There would seem to be a "cross-over" point where it makes sense to use the resistance strip rather than the HP. I suspect that woodgeek's 24 estimate is about right.
If it were me I'd rather not use the resistance element at all for this regardless of energy use just because of the risk of fire, especially in a vacation home.
Detritus tends to accumulate on the resistance strips over time. I could easily see mice building a nest there in a vacation place.
Whatever is there burns off when they are engaged.