New construction heating/cooling

Sal Santamaura

There's been discussion in the Politics of Heating category about how geothermal is not being supported in Congress. This thread is to ask those with relevant knowledge/experience how the numbers pencil out for geothermal on its own, i.e. without government incentives.

Last evening, I watched the latest episode of This Old House. Richard Trethewey has presented such systems before, but for some reason I was more interested this time. Please share your analysis of the following situation.

I own land in Bartlett, New Hampshire. If we build a home on it, the size will be anywhere from 1,700 square feet (minimum permitted by covenants) to around 2,500 square feet (what my wife thinks we "need"). It'll not meet Passivhaus standards, but I'd ensure a very high level of envelope performance, with closed-cell foam insulation and many other design/material features to minimize heat loss.

There's no natural gas available, but every year our homeowners association negotiates with the major local supplier to establish a propane price for anyone in this subdivision who opts to purchase from them. Right now it's $1.64/gallon (last August through the end of July). In addition to a fixed monthly charge of $28.93, electricity costs $0.15/KWH in winter and $0.12/KWH in summer.

What multiple of the upfront cost for hydronic heating with a boiler (either atmospheric and mod/con type - please specify which, but I'd appreciate estimates for both) would you expect for a geothermal system? Assume the drilling would need to penetrate substantial ledge; we're talking about the Granite State, after all. It's typical in this location to have both central hydronic heat (propane- or, more rarely, oil-fired) and a separate central A/C system. What percentage of the initial A/C system cost might be eliminated if a reversible geothermal source were available? For both heating alone and combined heating/cooling, given today's fuel costs, how many years do you think payback might take, ignoring the cost of money?

Thanks in advance for your replies. I hope that structuring the question this way, i.e. in terms of multiples/percentages, means it hasn't violated the rule against pricing discussions. If it has, Erin, please delete the whole thread.

SWEI

Assuming that $0.15 per kWH number is fully loaded, here's a quick shot at your energy costs for heating:

A 95% efficient appliance burning $1.64 per LPG gallon will cost you $18.90 per million BTUs produced.

A heat pump with an average annual heating COP of 3 (a modern VRF ASHP can do this) would cost you $14.65 per million BTUs. Bump the COP to 4 for a quality GSHP and that cost falls to $10.99 per million BTUs.

Assuming you're talking about forced air heating, a heat pump (air source or water) will include air conditioning essentially for free, meaning no real net increase in system cost. Non-reversible heat pumps are not commonly offered in residential sizes.

Sal Santamaura

SWEI said:

Assuming that $0.15 per kWH number is fully loaded, here's a quick shot at your energy costs for heating:

A 95% efficient appliance burning $1.64 per LPG gallon will cost you $18.90 per million BTUs produced.

A heat pump with an average annual heating COP of 3 (a modern VRF ASHP can do this) would cost you $14.65 per million BTUs. Bump the COP to 4 for a quality GSHP and that cost falls to $10.99 per million BTUs.

Assuming you're talking about forced air heating, a heat pump (air source or water) will include air conditioning essentially for free, meaning no real net increase in system cost. Non-reversible heat pumps are not commonly offered in residential sizes.

Thanks for your reply.

I'm interested in knowing about hydronic heating, with appropriate emitters for the low-temperature water one would reap from a ground-source, water-to-water heat pump. A/C would be a separate system driven, I assume, by water from the same heat pump reversed into cooling mode and fed to one or more air handlers.

The information you've posted does not address initial system costs, which are probably the most important factors in determining payback time. If anyone can address that entire balancing act, I'd be most appreciative.

SWEI

If your hydronic heating uses large area emitters (generally floors, walls, or ceilings) you can use the same emitters to provide sensible cooling. This will allow you to use smaller ducts sized to handle the latent load plus any conditioned fresh air.

Total system costs depends so much on the loop field that it's essentially impossible to estimate without knowing both the soil conditions and the pricing range of drilling contractors who work in the area. It's not cheap. In colder climates you might even consider something like http://www.thermalbatterysystems.com/

SWEI

Based on the energy cost figures you provided, and assuming the LPG boiler was a condensing model as I did, you could start with a rough straight-line approximation something like this:

Annual LPG cost for boiler = X
Annual electrical cost for an ASHP = X - 22.5%
Annual electrical cost for GSHP = X - 41.9%

Looking at the difference in capital cost between an ASHP and a GSHP, and assuming the same COP's I used above: If the initial cost of the GSHP was 33% higher than the ASHP, the simple payback period would be the same for both. I doubt you can have a ground loop installed for anywhere that kind of adder over the cost of an ASHP.

Throw in changing fuel and electricity prices and things get murky fast.

Sal Santamaura

SWEI said:

...assuming the LPG boiler was a condensing model...the difference in capital cost between an ASHP and a GSHP...If the initial cost of the GSHP was 33% higher than the ASHP, the simple payback period would be the same for both. I doubt you can have a ground loop installed for anywhere that kind of adder over the cost of an ASHP...

The problem is one needs to know capital cost of a ground source water-to-water heat pump system and compare that to the condensing boiler. Only then can all the other factors be considered in determining even a rough estimate of payback, even assuming today's energy costs remain valid into the future.

Thus, I hope someone familiar with both the geology in northern New Hampshire and geothermal technology can roll everything into approximately how many times the boiler-based initial outlay I'd be looking at as well as how many years it might take to break even. Without government incentives.

Sal Santamaura

Sal Santamaura said:

...Thus, I hope someone familiar with both the geology in northern New Hampshire and geothermal technology can roll everything into approximately how many times the boiler-based initial outlay I'd be looking at as well as how many years it might take to break even. Without government incentives.

Anyone?

njtommy

I'm beginning to think Geothermal may not be worth the high cost of install with all the newer HPs being able to give you full btu out put at -5 and even down to -15. Especially now everyone is using VRF systems or compressors. You can run that and propane furnace or boiler for back up in extreme low temps.

margsuarez

Another perspective - as a homeowner whose contractor attempted and failed the installation of a closed-loop geothermal system, I'll say that there is great variability in cost of installation not just specific to your region but your specific parcel of land. In my case it was not possible/economically feasible to drill even one of six required 80-foot wells due to sandy and rocky conditions in a limited area. In my case the contractor assumed the risk of that variability and had to back out after a week of trying, at a considerable loss to him. If he hadn't assumed the risk I'm sure the quoted price would have been much higher. Make sure you do your research.

As quoted, ROI was claimed to be 8-10 years. But I can't verify that because the system was not installed.

kcopp

I am in The seacoast of NH.... a couple hours south but not NY or PA.
I really feel that GEO is a huge waste of money.
Its not simple and a lot of parts to coordinate.
You bet bang for your buck is to Take care of the envelope. You dont need to go all Passive Haus but shoot to get as low a possible ACH/ hr as you can. Thick walls and ceiling.
I am thinking that spray foam is less of a good thing long term. Tapes on the outside will do a better job sealing than the foam.
This simpler the design the easier it will be to do this.
Lots of resources to help in this.

http://buildingscience.com/documents/insights/bsi-001-the-perfect-wall

https://foursevenfive.com/

A good small LP gas condensing boiler and an indirect w/ some panel rads or you can add a Hyper heat ductless minisplit. For cooling or redundancy.
(not that you will need much cooling there at all. (I think they had snow up there today!)

Sal Santamaura

Thanks very much Kevin. After doing additional research I'm starting to agree with your conclusion.

kcopp said:

...I am thinking that spray foam is less of a good thing long term. Tapes on the outside will do a better job sealing than the foam...

Is there any reason other than cost not to do both? I shouldn't think adding the tape would be too expensive.

kcopp

There are some thoughts that the foam will start to pull away from the sides. The whole air quality issue just has not gone away w/ foam. Most of the time its ok but the training to do it right is lacking in many installers.

http://www.finehomebuilding.com/2013/04/25/makers-of-spray-foam-insulation-named-in-lawsuits

kcopp

Thinking about the walls in a house if I were to do it...

Double 2x4 walls w/ off set studs to keep the thermal bridging to nil.
Dense pack Blown in cellulose.
Intello interior wrap on the inside. Make the inside air tight but Vapor permeable.
Same on the outside. Seal and tape every seam, crack and crevice.

JUGHNE

What type do you have now and are you used to the comfort it provides.....(good or fair)?

I have installed just about all types of heating systems. My wife and I have been in this house about 22 years, we are in our 60's. Had I put heat pumps in this house she would have left me 10 years ago.....(women age different than men if you get my drift ). We keep the master bath at 74 and the bedroom at 65, sometimes less. My office is 74, basement is 70 (heated floor).
We have infloor/inwall heat and if we visit anyone else, especially with a heat pump, we wish we were wearing thermo's.
It is called a comfort system after all. Something to consider if this house is the last one to build. For resale do people consider the super efficiency of GSHP when purchasing? more likely the granite tops and car wash showers.