Heat pumps

[davesl708]

Back to the OP's numbers. If he using 3900kwh a month, in my area a KWH is about $0.12, that would be about $468. Is the price of electricity less where you live? I'm not sure of my exact numbers but I think we are using about half that much electricity a month with a 1900 sf house with a new geothermal system.

My rate is 1.7 cents per KW. my 1500 sq ft. uses around 1100kw per month in winter and half that in summer.

 

[LD1]

So your monthly bill is $19 or so?

 

[grsthegreat]

I was just told by our HVAC guy that we cant do this.

if you have a gas indoor unit, you cannot just add the strips. If you have an electric indoor unit, you can add strips up to the units listed make. no more than 20KW allowed on a 200 amp system per NEC though.

 

[RalphVa]

The refrigerant in the newer systems allow heat pumps to work down to lower temperatures. We've our bigger unit with such a new system. I can turn the auxilliary heat coil off on it and still get heat down to about 20 F. Below that, I put the thermostat on "system control". There's also a setting for "emergency heat only", which is just the electric coil. Because we get such ups and down during our winters, I just keep it on "system control".

Geothermal will work down to any temperature because it gets the system heat from the ground, which is typically about 50 F. You need a place to drill another water well or two or some ground where they can put the heat pump refrigerant piping in ground trenches. In my case, they'd have to go trenching back down the hill and into my trees. Geothermal also puts the compressor inside your house. Some of those can get pretty noisy.

Ralph

 

[kcflhrc]

You have a coil that is mounted at the air outlet of the furnace. In that case they use the blower from the furnace, and as you stated you do not have an air handler. Also with this setup the heat pump and the furnace can NOT run at the same time. Hot furnace air blown across the heat pump coil, with the heat pump running, would result in very high, and potentially destructive pressure in the heat pump refrigerant.

paul

You are correct Paul. I have a coil above the furnace. Didn't really understand what I had. I thought all heat pumps were the same with an air handler, not so. I basically have a propane furnace with a heat pump. I have the lockout set at 32 degrees. Thanks for explaining, from one Paul to another.

Thanks

Paul

 

[buickanddeere]

Yep, dual fuel heat pump with a lockout is a completely different animal than an air handler with electric strips. Can you change over a dual fuel system with propane backup to an all electric with heat strips easily? Or is it a completely different inside unit?

Just cut a hole in the side of the hot air plenium as close as possible to direct flow from the fan. Install an electric heater of your choice. 10Kw are common.

 

[buickanddeere]

Own

The back up better be on or you'll freeze to death.. At 0* ambient, you aren't going to get much heat from the HP alone. On top of that, it's going to go into defrost mode a lot more

I agree. A super dupper heat pump or not with 410A an over sized outdoors coil . The avaliable btu's from the great outdoors and the condensor temp will both be dropping Exponentialy on a steep curve from 40F and down. Also putting 1KW of energy into a heat pump to obtain 1Kw of heat into the furnace plenium makes no sense.

 

[Country Geek]

Geothermal will work down to any temperature because it gets the system heat from the ground, which is typically about 50 F.

This is true but the geothermal, like any heat pump, is blowing air that is not as hot as furnace air. When it gets really cold out it can get overwhelmed by the amount of heating required. My geothermal heat pump lost 3 degrees off the 70* set point temperature during the 8* morning today. The air coming out of the ducts felt just as warm as usual, but there was just too much heating required. It was the first time since installation that the outside temp has gotten that cold and the first time (not counting power outages) I had to turn on the backup gas furnace (mine is manually controlled). It took a 30 minute shot with the backup furnace to get the temp back up, then back to heat pump and it's held the temp all day so far, outdoor high temp in the 20's.

Geothermal also puts the compressor inside your house. Some of those can get pretty noisy.

Yes and no. My previous air source heat pump had the compressor outside but the rest of the system was still inside (in the crawl space). The geo system is no louder inside than the previous split system was. And of course outside is much quieter. No more having that outdoor compressor and fan kick in and break the peace while BBQing and listening to the crickets!

 

[kenmac]

Own

I agree. A super dupper heat pump or not with 410A an over sized outdoors coil . The avaliable btu's from the great outdoors and the condensor temp will both be dropping Exponentialy on a steep curve from 40F and down. Also putting 1KW of energy into a heat pump to obtain 1Kw of heat into the furnace plenium makes no sense.

Yep,I live where it don't get really cold..Sometimes it does get cold ( too cold for me) right now 28*... AT around 30* ambient, I can get about 70* air out of the registers on HP only. without back up, most people won't feel comfortable .On top of that I'm going into defrost xxxx# of times, which in turn,, Turns the HP in to an A/C.. Now, I the elec, etc, back up heat has to come on to offset the A/C.. Which is a waste of $$..SO, in my opinion, when it gets down this cold (or colder) It's best just to switch over to back up heat

 

[Coyote machine]

I live in wicked cold zone here in VT. Last week we had -27* in the area. I run two Fujitsu mini-splits that are rated to be able to produce heat to -15*. Our state's electric Co., GMP, was incentivizing these units for heat and AC, via a lease or own program subsidized by them. I had to get 2 outdoor wall bracket units, one for 1st floor bedroom and one for 2nd floor. They did not/ have not yet figured out how to combine 2 cold climate heat pumps into one outside unit, UNLESS one opts for a unit that is only capable to 0*, not -15*
These are all electric, run on 240V, have inside distribution ductless, remote control wall mount/ hand held thermostats. I use them to supplement an existing propane condensing boiler, a Buderus GB 142.
They are very quiet inside, and provide excellent AC output and steady/smooth supplemental heat when it is extremely cold outside.
Note, I have done as much tightening of the exterior/interior envelope as possible with rigid foam board, foil faced on both sides, blown in cellulose to R-50 in attic, etc. The blocking of air infiltration has made the most difference in comfort level in the entire house, especially at the sill plate/rim joist area where the heat loss is often the most evident. My propane boiler serves the entire first floor with radiant, and the pre-existing hydronic baseboard throughout the rest of the house, basement and 2 heated garage bays.

I mention all of the above because mini-splits for those running electric households may be a good way to heat and cool their homes going forward. This 'cold climate' mini-split tech is widely used in Europe as well as becoming the latest efficient technology for many parts of the US.