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Old 01-29-2014, 04:06 PM   #1
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Compressor time vs. Aux Heat


I have an ecobee smart si thermostat and I am trying to fine tune my settings for the most efficiency and comfort. As you know, this winter has been brutally cold on the east coast and my HP just isn't cutting it. With this thermostat I can run a report of run time, and on 1/27/14 my HP ran from 2am until 5pm.

On my settings I had comp to aux runtime disabled, meaning that it would never turn on the auxiliary heat no matter how long the HP had to run to reach the set point. I have since adjusted this to run HP for two hours and then engage aux if setpoint is not reached. But I have noticed that HP will run for two hours, engage aux until setpoint is reached, then the temp will drop and the two clock starts all over again....

My question is, am I causing damage to my HP system with these settings? My goal is to run the auxiliary the least amount possible, but also maintaining the set point inside and not damaging the heat pump.

I have the aux lock out team set at 20F degrees and compressor lock out set at 10F, so aux will not run if its warmer than 20F and compressor will run as long as its warmer than 10F. Should these be adjusted?

Please help! Thanks!

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Old 01-29-2014, 05:50 PM   #2
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Compressor time vs. Aux Heat


You are fine at those temps for the compressor but I have to wonder if it will cost more in the long run keeping the aux locked out so much. How big are your heat strips? Is your power high there?
I'm in a whole different climate than yours, Las vegas.
Somehow there has to be a way to figure if you might come out ahead cost wise by letting the strips kick in more often. I know the amp draw on a compressor drops real low in very cold weather but you may still be paying more in the long run, having it run constantly without some help.
We have some cold weather pros with heat pumps on this site, have to wait and see what they have to say.

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Old 01-30-2014, 06:39 AM   #3
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Compressor time vs. Aux Heat


Its not harming the heat pump. Depending how old the heat pump is. You can set the compressor lock out lower, and still get economical heat from it. How much does teh temp in your home drop in 2 hours. If less then 1/2 degree, set the timer to 2.5 or 3 hours. Its easier on a compressor to run 24/7, then to restart every 2 to 3 hours
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Old 01-31-2014, 02:06 PM   #4
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Compressor time vs. Aux Heat


Your heat pump is doing next to nothing at extreme low temps and you're asking your system to do the impossible - maintain efficiency AND comfort. This is simple, heat pumps are inefficient to useless at low temps and that is when your strips should take over, the time factor shouldn't be an issue. When the outdoor temp drops suddenly, like nightfall, it shouldn't take 2 hours for your heat pump to disengage. Heat pumps are for hybrid heating/cooling only and shouldn't be installed in northern climates at all, where 3-5 months of the year you need heat, not a/c, IMHO.
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Old 01-31-2014, 03:27 PM   #5
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Compressor time vs. Aux Heat


You haven't said what make/model heatpump you have or how old it is. If it's a reasonably recent one, you are probably fine (although I don't know why the system can't keep up as you have it set). If it's a an older system, it may be running inefficiently (eg low on charge) and you may be accelerating its demise.
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Old 01-31-2014, 07:37 PM   #6
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Compressor time vs. Aux Heat


Quote:
Originally Posted by IslandGuy View Post
Your heat pump is doing next to nothing at extreme low temps and you're asking your system to do the impossible - maintain efficiency AND comfort. This is simple, heat pumps are inefficient to useless at low temps and that is when your strips should take over, the time factor shouldn't be an issue. When the outdoor temp drops suddenly, like nightfall, it shouldn't take 2 hours for your heat pump to disengage. Heat pumps are for hybrid heating/cooling only and shouldn't be installed in northern climates at all, where 3-5 months of the year you need heat, not a/c, IMHO.
We have 7 to 8 moths of heating. We get to sub zero temps sometimes. heat pumps do fine. And are suppose to have long continuous run times.

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