New Build in 2018: Geothermal vs NG/conventional AC

[buckeyefarmer]

20 yrs ago i put in oil because it was $.69 gallon. When it went over $4 gallon i put in geo. Now, nat gas and propane has lowered in cost, and electric has gone up. You never know where the prices will go.

 

[KYErik]

Your bills do seem a bit high for what you described. What are your loop temps at the peak times. You may not have good coupling to the soil (air pockets, etc)

I have a 2800 sq ft house, 4" walls, all electric, 4 adults, etc. My bills are an average of $ 100/mo over a year ($ 1200/yr). For sure your summer cooling should be much lower.

paul

I honestly don't know that the water temps were- I never measured them. I would have guessed that the soil would have settled nicely onto the pipes over the 10 years that I used the unit before I sold the house. It sounds like your unit is very efficient. I wish my unit would have performed that well.

 

[japody]

Geo units are still more efficient overall. You must compare EER or COP as a comparison. Most heat pumps offer their SEER rating, which is a seasonal average performance and does not give a clear indication of overall efficiency. Note that Geo units do not give SEER ratings, only EER or COP for that reason.

Look at: Seasonal energy efficiency ratio - Wikipedia

Note the statement that for residential cooling systems: "EER for residential central cooling units = 0.875 ﾗ SEER"

paul

EER on my Bosch unit is 28, COP is 4.6.

 

[Larry Caldwell]

20 yrs ago i put in oil because it was $.69 gallon. When it went over $4 gallon i put in geo. Now, nat gas and propane has lowered in cost, and electric has gone up. You never know where the prices will go.

That's exactly the reason that you should put your money into insulation. Just about every energy utility will do a free energy audit on your house, which includes a blower door to test for air infiltration. Sliders are notorious leakers, and it can be an advantage to replace them. A blower door will tell you how many air changes per hour your house has, but of course it varies if the wind is blowing. A drafty house is an expensive house. Blown cellulose in the attic cuts air infiltration. Subfloor insulation, if you have a crawl space, is surprisingly effective at preventing cold feet.

Windows are rated by U value, which is the reciprocal (1/R) of the R value. A U.34 window is equivalent to about R-3 insulation. Low -E glass will reduce heat penetration in the summer, and honeycomb blinds will reduce nighttime heat loss. I highly recommend them. Once you eliminate air infiltration, cellular blinds will double the energy efficiency of glass.

It makes no sense to gain a few percent of efficiency on an expensive HVAC system that will have to eventually be replaced anyway, when you could get better savings from insulation that never has to be replaced.

 

[rScotty]

That's exactly the reason that you should put your money into insulation. Just about every energy utility will do a free energy audit on your house, which includes a blower door to test for air infiltration. Sliders are notorious leakers, and it can be an advantage to replace them. A blower door will tell you how many air changes per hour your house has, but of course it varies if the wind is blowing. A drafty house is an expensive house. Blown cellulose in the attic cuts air infiltration. Subfloor insulation, if you have a crawl space, is surprisingly effective at preventing cold feet.

Windows are rated by U value, which is the reciprocal (1/R) of the R value. A U.34 window is equivalent to about R-3 insulation. Low -E glass will reduce heat penetration in the summer, and honeycomb blinds will reduce nighttime heat loss. I highly recommend them. Once you eliminate air infiltration, cellular blinds will double the energy efficiency of glass.

It makes no sense to gain a few percent of efficiency on an expensive HVAC system that will have to eventually be replaced anyway, when you could get better savings from insulation that never has to be replaced.

I agree with that completely. If the house is well insulated, it simply doesn't make much difference what kind of heat source is used. The energy cost is negligible.
Insulation is cheap, easy to install, & lasts a lifetime. It's simple to do - maybe that's why it isn't more popular.
rScotty

 

[MacLawn]

Ebb = electric baseboard heaters
Dhw = domestic hot water
CW = cold water
HW = hot water
GT = geothermal
FA = forced air heat
NG = natural gas

Thanks a lot Erik. But right above is a new one on me. VRF, all that mess. It's hopeless. I reckon a bunch of whippersnaps here.

 

[rScotty]

Thanks a lot Erik. But right above is a new one on me. VRF, all that mess. It's hopeless. I reckon a bunch of whippersnaps here.

I had to look that one up VRF = variable refrigerant flow.

Variable refrigerant flow - Wikipedia

Reading through the article made me realize how far out of time I am with this subject. I thought that all the systems were VRF 20+ years ago. Apparently not.
yes, I am a whippersnapper.
rScotty

 

[rngrrymd]

New member here. I'm a manager at a HVAC wholesale supply and I would suggest NG backup furnace with a high efficiency heat pump as primary heat/ac vs the Geothermal and let me explain why.
1. Generator Capability. What is your electrical power situation? If u lose power - how long are u out until it is fixed? In NEPA, some customers have now gone 8 days without power because of winter storm Riley. And that is in sub-freezing weather as well. A lot of people are asking about whole house generators, wishing they had them installed before the storm. The problem with GT and standard HP systems is they require electric backup heat (1kw is about 3400 btu's). Most new construction homes typically take 10kw up to 15kw to heat with insulation levels at the current code levels. Sometimes a larger home may take up to 20kw or more. The power needed for 10kw and an air handler is 60A. 15kw is 85A. 20kw (68,000 btu's) is 110A. A 20kw Kohler whole house generator puts out about 83A and can go up to 100A before the 100A breaker protection trips. Electric Backup Heat Strips hog too much of that power and are impractical for generator backup power. A gas furnace, however, only needs a 15A breaker to run on and u can get a high-efficiency 2-stage or modulating gas furnace up to 120k btu's to cover your house heat load. Combined with a high-efficiency 2-stage or inverter HP u get cost savings with the HP but backup protection that a whole house generator can handle with the NG furnace.
2. Geothermal installations are top-heavy priced and not worth it unless building brand new like the OP. You will probably never recover the extra dollars incurred to drill the wells, run the pipe and manifolds, etc unless u do some of that work yourself. (In my area almost all GT contractors are installing closed loop wells. South and West of me they are installing pump and dumps. I can't speak for slinky systems. ) When the Feds were offering 30% rebates on taxes for GT, Wind and Solar equipment installs then it was more worth it because the rebate helped u possibly realize recovery of the extra expense. Unless u are paying cash, u also have to factor in amortization rates on a 30 year loan if rolling into the cost of building the home. My credit union is offering 4.38% for 30 years fixed right now. If the GT costs $10,000 more to install than a HP/NG hybrid system the interest in 30 years is $7,974 equaling an extra cost of $17,974. If the cost is $20,000 more the interest is $15,949 equaling an extra cost of $35,949. U will never recover that extra cost.

High Efficiency NG Furnace with High Efficiency HP hybrid system. Best option.

 

[LD1]

The problem with GT and standard HP systems is they require electric backup heat

Not true at all.

If a GT is sized properly....ideally....backup is never used.

And in the event of an extended power outage....simply turn OFF the strips if you are running a generator and have strips. Geo will still be making heat, even if you let a contractor convince you to undersize and you would normally be using backup heat.

I have a Geo with NO backup.

But one can easily be equipped with propane or natural gas for backup.

Heat pump with propane is common around here as nat gas isn't widely available.

 

[LD1]

Oh, and there still is the federal tax credit. It was reinstated.

And check local utilities companies. They offer credits too. I got another $1000 from the power company for Geo....and another $400 from the power company for the hot water heater I used for my buffer tank setup