Yeah, up here where we rarely see under 25 they rock. We see about 2 weeks of the year under 25 degrees and I heat with wood in winter anyway so its purely supplemental at that point anyway.

 

 




 

At about 25-30 it goes to emergency heat mode.  Upstairs gets cold as there's less insulation up there, but nobody sleeps up there.

I just run a couple of small space heaters downstairs when it drops into the teens and we're all comfortable.

The Mitsubishi that I have will supposedly provide heat to -13F.  I can testify that it works great to about 15F which is the coldest temp I have seen here in the Hill country since I installed it.

They are virtually silent and work great in cooling mode also.  Installation is not hard but is less forgiving than R22 since they use R410a.

I don't want to beat a dead horse with you, but I will assure you the basis of the design and calculations used for the length and quantity of loops has zero to do with any type of "banking" or heat storage. Nor is there any kind of recovery of heated rejected into the ground to be used for cold conditions.



I'm sure you won't believe me but there are numerous articles available and the NGWA is a good place to start on your research endeavors.





 

Keith is talking about how AC just moves heat. In the winter it pulls it from the ground and brings it into the house. In the summer it pulls it out of the house and deposits it into the ground.

Fine, but you are not storing rejected heat into the ground to be recovered later when the temps drop.



 

Neither Keith nor I were under the impression that you could. He is a mechanical engineer by trade and I used to sell building automations.

Nope, Kieth clearly was saying you recover the heat you put in the ground.  I was simply trying to clarify that the real benefit is the reduced delta in temps from heating or cooling based upon an average 65 degree constant.



 

Ground loops are installed below the area's isothermal depth.  That is the depth where soil temperature is nearly constant.  This is a situation where the soil insulation above the isothermal line SLOWS heat transfer so seasonal changes aren't seen.  

 

Soils are typically poor thermal conductors meaning they are insulators.  Meaning a thermal flux WILL change the temperature below the isotherm.  Meaning there WILL be heat added during months where heat from air conditioning is dumped.  It IS significant since both rejected heat AND all the electrical energy moving that heat is dumped to the ground sink.


In the winter, the electrical energy used to move heat from the ground to the house also heats the house.


I realize heat transfer is invisible alchemy to most as it requires some math that is normally reserved for upper division math/science types.  I hope I explained why dumping heat below soil isothermal depth is banking.  Because a few raised hackles..there are a few exceptions like when there is significant water movement below the isotherm.  Or when you are in a volcanic area. Like hot springs.  These are trivially simple cases.

Worthless?

Our house is a constant 68° despite it being in the single digits at night, and in the 20's during the day with 10-30mph winds all day long.  

Our electric bill is less than half of what it was before we had the heat pumps installed (house had electric ceiling heat and no A/C before June '15).

Which means your system uses a different refrigerant than old R22 and has higher working pressures which mean it can absorb heat from lower temperatures.  

 
The only caveat on such systems is evaporator ice deposition.  This is controlled with microprocessor logic, frost point sensing and reversal valve defrost.

A "HEAT PUMP" is just a very expensive version of Electric Heat.

not really.

It extracts heat from colder outside, pumping it inside.  Heat is work is energy.  All the electrical energy consumed is converted to heat and combined with heat extracted from outside.

 

It is an air conditioner turned around.  An a.c. pulls heat from inside, pumping it to outside.  Likewise, the hot discharged air is all the electrical energy plus the heat pulled from inside.

Thermodynamics.  GD has less understanding of it than they know of relationships

I'm sure if I kept my house a little warmer the temp would be warmer also.  It dropped down to 1* over night.  The emergency heat actually never kicked on (I want to say the first stage emergency kicks on at a 5* differential).  Such a worthless piece of crap that doesn't work at all when it's below 30*.  

Heat pumps - at what point does yours become worthless?

South Florida, any further north and they are worthless.

Yea.  Okay.

Can't you just have a contractor cut a round hole in the wall and blow insulation in between the joists?  Seems like it would be cheaper than demo'ing all the plaster walls out to replac with dry wall.

After being in the trade for 20yrs with a degree in this business.

My personal thoughts are a heat pump with electric back up is great for a one element home...all electric and no gas.  They are fairly efficency however somewhat discomforting when Temps drop in the mid 20s and below.

Geothermal heatpumps are much better as we utilize 55 ground temp vs 20*and lower ambient air temps, but cost is much higher upfront for the ground loop wells

I like heat pumps with a hydronic coil for aux and emergency heat fed via water heater.  Many companies are making on demand tankless water heaters with dual domestic and process heat exchangers.

I am also big on dual fuel gas furnace and heat pump.

I also live in a area where power outages happen.  I do not need a big generator to heat my home with the hybrid dual fuel systems like hydronic aux or gas furnace.

I personally feel anything N of NC  VA line and higher elevations on NC say W of Raleigh should have a hybrid system.

Now add in new home design with spray foam insulation and that changes everything.

How so?