You do realize that these 2 statements conflict with each other - yes?
While true in a heat loss calculation, it may not be true in terms of dollars when it comes to heat pumps. Geothermal heat pumps are so efficient that you very well likely make up for greater heat loss (keeping the house warmer) by not having the resistance heat kick on to heat the house back up.
It depends on how the OP’s system is designed, including how the thermostat calls for resistance heat. If it’s designed for optimal efficiency, with a thermostat properly designed for a geothermal heat pump, then programming to turn the heat down at night may be optimal. If the thermostat turns on the resistance coils to heat the house back up, then keeping the temp stable will be cheaper.
The points made are correct.
The heat lost is dependent on the temperature differential between outside and inside. (65-32) loses more heat than (55-32) for example.
As others have pointed out - the energy you save by basically not running your heat pump 1/3 of the time (10PM-6AM?) you will have to recoup some of that by working much longer at 6AM to reheat the house; plus, if electricity is expensive, running several thousand watts of heating coil probably out-costs running just the pumps.
So it all boils down to an analysis of run times and costs. What percent of the time is your pump running during a cold spell of zero degrees?
How long does it take - pump runtime - to “re-heat” the house from 55 to 65 degrees? With electric heating coils? Without?
I’m guessing the pump runtime is a fixed value - so many hundred watts per hour.
Ditto for the heating coils - so many watts per hour.
If you know that the heating coils are unnecessary to re-heat the house in the morning, why not turn them off? (Install a switch and set them off). I assume they are only there because the manufacturer is allowing for the situation that it is so cold (or the house is so badly insulated) that the pump alone simply cannot heat the house to a steady state. If your pump can do so, turn off the coils, or mount a separate thermostat that says, for example, kick in when the temperature indoors hits 50F or something below typical nighttime cooling.
It may be that the system does not produce enough geothermal heat to re-heat the house in cold weather and NEEDS the electric heat. Only you can determine this.
If I make a wild-ass guess that the pump is, say 500 watts and the coils are 3,000 watts, then if you run the electric heat for an hour, it’s the same as running just the pump for 6 hours (7 actually, because the pump is also running during that time?) - so really, you wouldn’t save much money if you had to fall back on electric heat. My gut tells me falling back to electric heat negates any savings.
Plus, some places bill on peak use - but that’s typically for businesses, not residential.
But without electric heating, cooling at night is definitely cheaper.
Thanks everyone. I’m going to dig into how the system works so I can figure out how to eliminate the heating coils during normal operation.
After doing some research it looks like ‘set it and forget it’ is the only appropriate strategy for a GSHP system due to the inherent nature of its design. ‘Set Back’ and 'Set Up" strategies don’t work and force the system to use an auxiliary heating mechanism that is very inefficient and very expensive to run. Ignorance fought. This is my first GSHP system and old habits are sometimes hard to break.
Can you not put a switch on the heating coil power feed, turn it off manually, and try running without it for a while?
Worst case - the geothermal can’t keep up sometimes (which you’ll notice), or else it takes several hours to get back to 65F…
At the very least, turn off the system for a minute and manually disconnect the heating coils. Leave it like that for a day or two and decide if that does what you want.
The only time the supplementary heat should kick in is when the external unit intake air, or the intake water if it’s geothermal, is below a certain temperature. If the air/water the heat is being pumped from is too cold, the heat pump will not function very well. The rest of the time it should be off. This isn’t the standard configuratioN?
Not if you turn the thermostat up by more than a couple of degrees. If you turn the thermostat to, say, 5 or 10 degrees warmer than the room, that triggers the auxiliary/supplemental/emergency/resistance heating so the house warms up faster. To save money, a) leave the thermostat setting stable, b) move it up only a degree or two at a time, or c) find a programmable thermostat made for a heat pump system that slowly increases the temperature and doesn’t trigger the auxiliary heat.
Unlike a normal air-source heat pump, the great advantage of a geothermal system is that there should be plenty of heat to extract with the heat pump, even when the outside temp is below freezing. With reasonable insulation, the auxiliary heat should never have to come on, I would think.
With my geothermal the auto heat only comes on if it’s really cold and windy. Or as you said, if I move the heat setting more than a degree or so at a time. This morning it’s 12° and working fine.
And let’s not forget that the electric coils are also your emergency heat. If you physically cut them off and there’s a geo failure, it’s going to get mighty cold with no heat at all.
Sounds like the correct thing to do with a geothermal system is to just turn off the electric coil’s breaker, or disable it in software at the thermostat. Put a sticky note that if it is ever really cold in the house and/or a compressor failure, then take action <x> to restore electric coils to action.
So basically it’s a relatively dumb system, that assumes that a big difference between current and set value is either (a) due to the geothermal not keeping up with heat loss - needs supplement to remain stable - or maybe (b) the time to reach set-point would be too slow without supplemental heat.
For (a) the solution is to disconnect the coils unless you know there are times you will need them. For (b) it depends - is this correct? If you reach 55F by 6AM but it would take until 10AM to get back to 65F, then probably supplemental heat or more likely not setting the temperature down as low at night is the solution.
As I said, I would either put the supplemental coils on a manual switch and turn them off, or for safety put them on a thermostat switch set below 55F; obviously they are on a relay, add manual/thermostat override to that relay.
It’s also invalid because of the difference between temperatures (which is critical in heating/cooling). Your baking oven and the room are 300+ degrees different – there isn’t any habitation on earth with that big a temperature difference from outside the residence.
I use a small, electric, oil-filled heater by the bed and set it for about 65 - the thermostat is programmed to drop to 55 overnight, and back to 65 a few hours before I get up - which varies, so I don’t have it all the way up until I manually turn it up.
There is no reason to heat the entire (no so well insulated) house when I’m not moving.