State-of-the-Art Geothermal Efficiency
ohioandy
| Posted in Mechanicals on
I’m on the periphery of managing a 6,000 sq.ft. medical office built in the 1980s. HVAC has been a single well serving four air handlers, with return water dumped to storm sewer. Now equipment updates are needed and well is showing signs of less water available, what is state-of-the-art in 2021 in terms of geothermal efficiency? I sense HVAC contractors in this rural area are not at the front of the envelope; they want to abandon geothermal, add electric heat pumps and trench in a gas line to avoid heat strips. Curious what else might be possible.
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Open-loop geothermal is generally frowned on, even in areas with plentiful water. Some areas do allow for reinjection wells, so you would only need one more. Even so, geothermal is having a hard time competing with high efficiency air-air heat pumps these days. Even in zone 5, you should be able to meet the heating demand with cold climate heat pumps. I wouldn't even consider gas for backup if it's not there already. We need to get away from fossil fuels and that's going in the wrong direction. Properly size the heat pumps and add heat strips to make everyone feel better. They will probably never come on.
> Properly size the heat pumps and add heat strips...
But avoid heat pumps that turn off when it gets to record lows. This would cause occasional massive grid load. Geo heat pumps don't suffer from this.
You can purchase units rated COP > 5, but be careful to adjust for differences to air source (like well pump energy used).
https://www.energystar.gov/products/energy_star_most_efficient_2020/geothermal_heat_pumps
When it comes to water use, I'd trust local regulations more than a blanket "it's wasteful". With that broad stroke, natural springs are even worse.
Geothermal is, unfortunately, not normally economical. I've always thought is a very interesting way to heat and cool, but the cost for the wells or underground loop is usually so much that such systems aren't considered. Air source heat pumps are much more commonly installed, can usually handle the load just find, and are much cheaper to install since they don't require any of the underground work.
I absolutely agree with Peter that open source geothermal systems aren't a good idea -- they are very wasteful. You MIGHT be able to adapt your existing well to house a closed loop system, you'd need someone familiar with these systems to come look at what you have and see what can be done as a retrofit.
I would use natural gas as a backup heat source instead of electric resistance though. Electric resistance heating in most areas will be using electricity that is generated in large part from natural gas fired generators, so the overal system efficiency of electric resistance heat is much lower -- you end up burning less gas by using it directly in your building for heating than you would using electricity generated by burning gas somewhere else. I do agree that with modern heat pumps, you'll only very rarely need your backup heat source.
BTW, with a 1980s building, there is probably room for improvement in insulation too. Keep that in mind with maintenance work, and add in insulation when you can during other projects. A reinsulating project is usually pretty expensive done on it's own, but when it's done along with other maintenance work (especially replacing any type of exterior siding) it can be much more cost effective.
Bill
> improvement in insulation
Start with better ROI air sealing.
>Start with better ROI air sealing.
In commercial buildings that require high ventilation rates, such as "...a 6,000 sq.ft. medical office..." air sealing won't have anywhere near the ROI that it would in a residential structure. The same can be said for going high-R /low-U on insulation & windows. If it doesn't already have it, balanced HRV ventilation may have a better ROI.
To be sure, air sealing is a pre-condition for being able to control the indoor environment and indoor air quality even at lower ventilation rates. It's still worth fixing any low-hanging fruit on both air tightness and insulation.
As Zephyr7 points out, IF the existing well(s) has/have sufficient capacity to be retrofitted with a closed system it's probably going to be reasonably economic and possibly even cheaper than air source heat pumps to replace it with a right-sized fully modulating system such as a WaterFurnace Series 7 (or a simpler multi-stage, like the Series 5). There are others. But this requires more analysis and experience than your local contractors may be up for. It's worth paying for that analysis (or even a complete design) from a competent contractor to make that call, even if the contractor is 1000 miles away. (What is your ZIP/postal code?)
> won't have anywhere near the ROI
Unless they are reducing powered ventilation to account for natural ventilation (an unreliable practice without complicated sensors and zoning), I disagree - the ROI is independent. Agreed, there might be even better ROIs on other things.
His name says Zone 5 NW Ohio.
If the question is whether new technology will allow you to get more heat out of less water than 35 years ago I'm afraid the answer is no, the limit is really the physics.
I read contractors are using trenchless boring machines now, so I contacted a Iowa local who said $1800 per 1 ton well including grouted piping.. I'm not sure what the total price would be, but for a well I can use over and over.. That doesn't sound to bad..
That actually sounds excellent.
Here in CT prices are $50-70K. Perfect ROI for the next owner of my home.
Since the geothermal doesn't add anything to the price of the house, for the second and subsequent owners the ROI is indeed excellent.
Mike when you say “trenchless boring” what sounds like a horizontal loop then you say “well included” sounds like a vertical loop. Sounds like they have baffled you with bull stuff. Seem to me that is the only way to sell a ground source system as the math says most every buyer will be dead long before the system can recover its cost.
The way I understand it when the pipe in a geo well is grouted in place so when the pipe fails the well must be abandoned. Yes the well is likely to out live the heat exchangers in the heat pump a few time over.
Walta
Sorry.. I added "well" when I should have said horizontal loop..
Here's the email from [email protected]
"For the horizontal loop system you are looking at $1800.00 per loop which includes the pipe. Each loop is 1 ton so you can figure out how many ton system you need and multiply by 1800 and then add $2000.00 for boring the feeder lines in the utility room."
That sounds great. I've been wondering when people will start using that type of equipment to do it cheaper. I would want to ask them how deep below ground the loops will be. If they can be 20 feet deep or more for most of the length, that's a lot better than 6 feet deep.
Also, at that price, I'd definitely oversize the loop to get better performance.
Do they say how long a one-ton loop is?
Presumably you'd have to keep it on your own property so you'd need a fair bit of land.
No he didn't say how long, but Im pretty sure 20' deep wouldn't be a problem.. One red flag is that trenchlesssolutionsiowa.com isn't a HVAC contractor..