Well contamination from geothermal system
Carfar96
| Posted in Green Building Techniques on
We are in Michigan and planned to install a horizontal closed loop geothermal system. Due to township restrictions and setbacks, our system will not be less than 50 feet from our well. There will be a methyl alcohol (20%) solution added to the system as an antifreeze. I am very concerned about possible contamination of our well if there is a leak in the system. Can anyone give me any experience or recommendations? I don’t know what to do. Thank you!
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Carolyn; I have no experience with leaks from ground-source heat pump loops. But in my law practice, I did have many cases involving leaks of toxic substances into the ground. Every case was different, but all were insanely expensive to fix. Alcohols tend to biodegrade, though.
As I'm sure you know, methyl alcohol is toxic. Right there, you may want to rethink your plan. Should anyone run several hundred feet of plastic tube filled with poison in the ground around a home? I don't know how common leaks are, but any leak would be expensive to fix.
If a leak arises, will it contaminate your well? That depends on soil conditions, ground water location and flow and a host of other factors. Is the well cased? How far down is the water column in the well? If it flows toward the well, could it get in the water? You'll not get an answer to that question other than "maybe, maybe not." If it gets in the well, will it hurt you? Again, you probably won't get an answer.
Would a leak contaminate the ground water and get into someone else's well? How about a nearby stream?
I'd either use a non-toxic anti-freeze, like propylene glycol, or rethink the whole geothermal idea. Most people around this forum think such systems are too expensive and too complicated.
Another less-toxic option for antifreeze is ethyl alcohol.
Good practice includes pressure testing of the loop (with air) prior to filling it; in some cases this is legally required. But it's unlikely there will be an official there enforcing that requirement, so I'd ask to witness the test, and perhaps even do an extended test.
If you do have a leak, you'll know, because it will quit running if the fluid level gets low. I would guess that you'd therefore know about it before enough leaked to cause a problem, given that there's opportunity for it to biodegrade or evaporate before it reaches your well. But that's just a guess on my part.
Do you have any links to why the geothermal systems are too expensive and complicated? We are really starting to question our decision. It is going to be close to $35,000 for our 2200 square foot new build and run about $900 a year to operate.
You just answered your own question. :-) $35k is a huge amount of money, and you can achieve a projected cost of $900/yr with a substantially cheaper system and more insulation or solar panels (or both). A couple of ductless mini-splits should cost less than $15k at most. You could install a chiller system for $25k or less, and it might even beat the geothermal system for efficiency. If you don't need air conditioning, you can probably use electric resistance heat panels and buy enough solar PV to run them for free year-round. And then there's the issue that geothermal systems are custom-engineered per job, which increases the risk over a more standardized "system in a box" that can go through QA at a factory assembly line.
Carolyn,
Here is a link to an article with more information: Are Affordable Ground-Source Heat Pumps On the Horizon?
Ground source heat pumps just have more parts, require more trades (excavators, electricians, plumbers, maybe soils engineers, etc.) For a new house, 35K is a lot of money for a heating system. For a new, tight and well insulated house, most people are looking at mini-splits. They are much simpler to install and don't need to be individually designed. GSHP also take up considerable space. That might not matter if you have a big cellar.
My house is a little smaller than yours and two mini-splits installed cost about $6500 in total. So far this winter, we're warm and comfortable.
Here in Maine, people are still installing ground source heat pumps, but I don't know why. For less money, you can install mini-splits and enough PV to run your whole house and spend a lot less than $900 per year for heat, A/C, hot water, cooking, lights, etc.
How did you decide on geothermal? They promise more efficiency than mini-splits, especially in really cold weather, but the additional cost doesn't seem to justify the extra cost.
I do like the mini split option for energy efficiency, but, to be honest, hate the look of them in rooms. That may seem shallow, but I just think they look like an eye sore. Are there any more attractive options?
If we did go with a forced air system, what would be the most energy efficient option? We definitely need AC.
If your 99% outside design temp is -5F or higher (or even if it's a bit lower, if your inspectors will allow it), you can get there with Fujitsu's mini-ducted mini-splits. Pretty much all of MI (except parts of the U.P.) has 99% outside design temps in positive single digits, and almost no locations are in negative double-digits:
https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf
https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf
What is your 99% outside design temp, and what is your heat load at that temp? (And, how was that load number derived?)
Is this new construction, or retrofit?
In new construction, breaking down that $35K quote for geothermal and redirecting it, judiciously spending $10K on better than code minimums on the building envelope to reduce the load and spending $10K on rooftop PV to offset power use, and $15K on a mini-ducted mini-split solution would be money better spent.
Per your original question, some additional data might be useful.
For instance, how deep is your water well? Are you pulling water from a few hundred feet down, or fifty? Does your water well have a casing for a good distance? Was that water well casing grouted when it was installed? Do you have any insight into the stone formations in your area? Very porous or multiple layers of somewhat horizontal rock?
Do you know if any “fusion” splices will be done in your horizontal geothermal system? How far away will they be? Is there any chance of future digging near the geothermal field? Do you have any idea what the backfill will be on top of the geothermal lines? Sand, or native material with potentially sharp stones?
Finally, if you do go geothermal, is your heart set on a horizontal system? I am led to believe that they sometimes under-perform, particularly as the ground around the lines gets colder as the winter goes on. Were you given a quote that contained an auxiliary heat system?
Anyhow, just some thoughts from a geothermal and water well owner. (And one with a wife that doesn't want to see any vestige of mechanical systems.)
Carolyn,
Since this thread seems to be morphing into an exploration of other options, you might be interested in the responses to a question I posted a couple months ago at https://www.greenbuildingadvisor.com/community/forum/mechanicals/45996/hvac-concept-selection
I am debating HVAC options for a new house of similar size being built in Linden, MI (near Flint but not on the Flint water system). Where in Michigan are you building?
Reid,
Thank you so much for your response! We are building in Milford and I know right where Linden is. I am very glad to hear that you are not on the Flint water system - what an absolute tragedy that is. I am really interested to hear what you are leaning towards. My husband is not quite so into the "energy efficient, healthy indoor air quality" building that I am. I am pretty overwhelmed with learning everything I can and am definitely no where near as knowledgable as you are about this issue. I am really having difficulty getting my husband on board with the mini splits (he does not like them aesthetically and thinks they will be a bad option in the winter and for resale). We are putting in laminate (green, no voc, etc.) flooring throughout, so I am concerned about radiant floors with that. We are all framed up and the roof is about to go on, so we really need to make a decision quickly. Why didn't you go with geothermal? Do you have any local contractor recommendations that are more knowledgeable about indoor air quality and energy efficiency? I am having a heck of a time finding some. Thank you!!!! Crazy small world we live in...
To answer Dana and Andrew's questions (to the best of my ability at least - sorry for my lack of knowledge about this area - I am really having difficulty learning so much information so quickly - the learning curve is very steep):
- It is new construction
- I am not sure of my heat load - our home is similar to Reid's home in terms of climate and square footage. It is a 2200 square foot single story with a walkout basement. We are planning to finish the basement immediately with two bedrooms and a bathroom (we need the space)
- The well is not in yet, so we don't know the depth. We just know the location. Not sure about the casing length, but it will be grouted. Not very rocky soil. We actually built the grade up with a lot of fill dirt (clean)
- I don't know about any fusion splices.
- No future digging is planned.
- Back fill will probably be clean fill dirt (sand is probably too expensive) - we can minimize the rocks in it the best we can.
We are not set on a horizontal system. We would consider a vertical as well. The quote we got included all of the outside and inside HVAC work. We will have natural gas and it will kick on when it gets too cold. Otherwise it will be all electric.
I urge you to reconsider laminate flooring. Most of the stuff is really lousy and has very little scratch and water resistance. If you pay more to get better laminate, you're in the territory where engineered hardwood or pre-finished real hardwoods are cost-competitive. If you have a wooden subfloor you can put fasteners into, it's hard to beat solid hardwood. There are a wide variety of discount firms that sell the stuff, and for something like solid hardwood I have no reservation buying from them because for the most part, what you see is what you get. Solid bamboo is a good option too.
We have had about 30 samples of laminate, engineered hardwood, bamboo, and pre-finished hardwoods. We have pretty much subjected them to everything. It is not a decision we take lightly since it will be our entire house. The engineered hardwood, bamboo, and pre-finshined hardwoods were much less durable than the laminate. They dented, scratched, warped with water, etc. We have two young kids, 3 big dogs, etc. Do you have suggestions of more durable hardwoods? I would love to use something real, but don't want the hassle of refinishing them and having worn/scratched floors (we are doing a dark color).
I largely faced the same conundrum (2 small kids, one dog) when I decided to put new wood floors in my house. I settled on an engineered wirebrushed wood and haven't regretted it for a second. The beauty of a wirebrushed wood is that if it gets scratched (and it will; they all will), the scratches just become character marks indistinguishable from the existing texture. If you get one that's plywood-backed, it should have very high moisture resistance and extreme dimensional stability.
Check out the samples you can get from some of these guys:
https://www.builddirect.com/Wire-Brushed-Engineered-Hardwood-Floors/Result_N_4294967288+4294966291+4294959172.aspx
http://www.weshipfloors.com/flooring-type/wirebrushed-engineered-hardwood-flooring
I also wound up with a box of like 30 samples before I made a decision and ended up going with something from the weshipfloors folks. No affiliation, just had a pleasant transaction and am very pleased with the result.
Is the 2200' the first floor, with 2200' of walk out basement (4400' of total conditioned space), or is it 1100' up/ 1100' down?
If you're building a 2200' walk-out to merely code-min and dropping $35,000 on an HVAC system to support the heating & cooling loads it's usually a mistake. It's usually better overall to build a more efficient house, and use cheaper mechanical systems.
In Milford the 99th percentile temperature bin is about +3F. A code-min 2200' house with a reasonably efficient shape and code-max air tightness should come in at a heat load of 23-26,000 BTU/hr @ +3F, even without the benefits of being a walk-out basement. If it's 1100' up/1100' down, it's even lower- the lower heat load of the below grade aspects means it's probably on the order of 18-22,000 BTU/hr at code-min. If you go a bit better than code min everywhere you could bring even the 2200' up/2200' down scenario well under 20K. Making the house less lossy buys more comfort than making the mechanical systems more efficient, or just throwing more BTUs at it.
The heat loss characteristics of the fully-above grade portion that also has heat loss out the attic are different from the lower walk-out level, so it's probably best to zone them separately.
A single mini-ducted 1.5 ton Fujitsu -18RLFCD is good for about 20,000 BTU/hr @ +17F, and should be more than sufficient for covering your upper floor zone even at code-min if it's designed & built carefully, with some limitations on total window area. (You'd have to consult the extended temperature tables to figure out what it's capacity is at +3, but it's over 15,000 BTU/hr. They have fully specified capacities down to -5F.) It's also likely that a 3/4 ton or 1 ton mini-duct cassette system could manage the lower level, if you can't stand the look of ceiling or wall units. If it's a fairly open floor plan you can often get away with a single ductless wall or ceiling cassette. Planning ahead with the HVAC contractor and house builder to figure out how to accommodate the mini-duct air handler and duct system(s) fully inside conditioned space, and NOT up in the attic. The mini-duct cassettes need ~10-12" of vertical space if mounted horizontally in a ceiling or floor joisted system,which may affect the framing, but the ducts can fit between joists. Unlike most competitors, the Fujitsu units can also be mounted vertically.
If recent history in my area (Massachussetts) is any guide, a pair of appropriately sized mini-ducted systems should run less than $15K, installed, ducts & all. A single mini-duct + one ductless would be under $12K, probably under $10K. A pair of ductless, under $10, probably ~$8K. Mini-splits are not as efficient as a best-in-class ground source heat pump (GSHP), but the difference in installed cost buys a LOT in thermal upgrades on the house (or even rooftop solar) so that the power bills can be the same or lower. And being a pre-engineered "system in a can", there is far less design risk than GSHP, where every system is a custom design. The number of local contractors that can service & support mini-splits are also usually more than with a GSHP.
Carolyn: This statement of yours has me confused:
"We will have natural gas and it will kick on when it gets too cold. Otherwise it will be all electric."
Are you planning both an electric geothermal system and a separate natural gas fired furnace or boiler? A benefit to geothermal, as opposed to a mini-split, is that the temperature in the ground doesn't fluctuate much, if at all, with the weather, so you don't take a big efficiency hit in extreme cold, like you with a mini-split when the temp goes way below zero F. Thus, you shouldn't need a separate system for when it gets too cold.
I wonder if the backup gas system is actually a CYA move on the part of the GSHP contractor, implicitly acknowledging the possibility that the system they install will be defective or exhibit unsatisfactory performance due to poor engineering.
If you don't want the wall cassettes (and they are, indeed, ugly), you can duct the units instead. There is something of a hit to efficiency, but I don't know how bad it is. I agree with everyone else that geo is crazy. I have always refused to be involved with projects using them.
Do you have a designer involved? If so does s/he have any experience with energy efficiency? If not, find someone, quick like a bunny. You're about to spend a boatload of money and may waste much of it if you don't get someone on board with experience.
Carolyn,
I have not reached a conclusion about which system to go with. I got one round of price quotes which proved that my intuition about what should be more expensive was way off. The contractor was not able to explain their quotes to my satisfaction, so I am in the process of getting quotes from someone else. If you would like me to name names, please send an email to [email protected]. I don't want to do that on a public forum.
At one point in time, I was excited about ground source heat pumps (GSHPs). As I learned more, I concluded that the extra cost of installation would never be recouped relative to either an air source heat pump (ASHP) or a natural gas furnace. The efficiency of a heat pump is determined by the temperature delta that must be generated in the refrigerant. That temperature delta has two parts: i) the temperature difference between the house and the source, and ii) the temperature difference across any required heat exchangers. A forced air GSHP has three heat exchangers: soil-glycol, glycol-refrigerant, and refrigerant-air. A forced air ASHP has only two: air-refrigerant and refrigerant-air. In the coldest part of winter, the GSHP is more efficient due to the higher source temperature, although not by as much as you might expect because the ground cools down. In middle seasons, the ASHP is more efficient because there are fewer heat exchanges. Even if the GSHP is a little more efficient on average, it is not enough more efficient to make up for the extra cost. (This explanation is simplified, but hopefully not over-simplified in this context.)
We would not have a separate furnace or boiler, but was told that if we already have natural gas, they would hook that up as a back up heat source when it gets super cold here. The system is a Hydron HYT036. The quote was "on the coldest days, it uses internal auxiliary heat."
I'm still confused. Natural gas has to be burned in something to make heat. The Hydron system is electric, I assume. Is the contractor talking about a NG fired water heater that could supplement the hot water produced by the heat pump? Sorry if I'm being dense. maybe an HVAC pro can weigh in.
Just a FYI, methyl alcohol supposedly has a half-life of 1 to 7 days in soil. Of course the hydrology and porosity of the soil in your area (sand/rock vs clay) will determine whether the half-life is on the 7 to 1 day scale. At 20 percent solution I doubt you'd have a problem with anything but a catastrophic leak.
How deep is the well and water table?
Stephen - you are probably asking the wrong person. I am actually daily embarrassed by how little I knew about a system I was going to pay $35k for. You all put me to shame on the energy efficiency knowledge front.
Carolyn-we all have lots to learn, so don't be too hard on yourself.
Dan Kolbert gave good advice. Find a designer or architect ASAP to look over the project and advise you on energy issues generally, not just whether your plan for heat is a good one. There are lots of things to do to reduce the amount of heat you'll need from whatever system you install. Air sealing and good insulation make a tremendous difference in comfort and cost. The best heating system in the world, in a leaky, poorly insulted house, will leave you uncomfortable or broke or both.
GBA is a great resource to help you understand the issues and ask the right questions.
Is the 2200' the first floor, with 2200' of walk out basement (4400' of total conditioned space), or is it 1100' up/ 1100' down?
If you're building a 2200' walk-out to merely code-min and dropping $35,000 on an HVAC system to support the heating & cooling loads it's usually a mistake. It's usually better overall to build a more efficient house, and use cheaper mechanical systems.
In Milford the 99th percentile temperature bin is about +3F. A code-min 2200' house with a reasonably efficient shape and code-max air tightness should come in at a heat load of 23-26,000 BTU/hr @ +3F, even without the benefits of being a walk-out basement. If it's 1100' up/1100' down, it's even lower- the lower heat load of the below grade aspects means it's probably on the order of 18-22,000 BTU/hr at code-min. If you go a bit better than code min everywhere you could bring even the 2200' up/2200' down scenario well under 20K. Making the house less lossy buys more comfort than making the mechanical systems more efficient, or just throwing more BTUs at it.
The heat loss characteristics of the fully-above grade portion that also has heat loss out the attic are different from the lower walk-out level, so it's probably best to zone them separately.
A single mini-ducted 1.5 ton Fujitsu -18RLFCD is good for about 20,000 BTU/hr @ +17F, and should be more than sufficient for covering your upper floor zone even at code-min if it's designed & built carefully, with some limitations on total window area. (You'd have to consult the extended temperature tables to figure out what it's capacity is at +3, but it's over 15,000 BTU/hr. They have fully specified capacities down to -5F.) It's also likely that a 3/4 ton or 1 ton mini-duct cassette system could manage the lower level, if you can't stand the look of ceiling or wall units. If it's a fairly open floor plan you can often get away with a single ductless wall or ceiling cassette. Planning ahead with the HVAC contractor and house builder to figure out how to accommodate the mini-duct air handler and duct system(s) fully inside conditioned space, and NOT up in the attic. The mini-duct cassettes need ~10-12" of vertical space if mounted horizontally in a ceiling or floor joisted system,which may affect the framing, but the ducts can fit between joists. Unlike most competitors, the Fujitsu units can also be mounted vertically.
If recent history in my area (Massachussetts) is any guide, a pair of appropriately sized mini-ducted systems should run less than $15K, installed, ducts & all. A single mini-duct + one ductless would be under $12K, probably under $10K. A pair of ductless, under $10, probably ~$8K. Mini-splits are not as efficient as a best-in-class ground source heat pump (GSHP), but the difference in installed cost buys a LOT in thermal upgrades on the house (or even rooftop solar) so that the power bills can be the same or lower. And being a pre-engineered "system in a can", there is far less design risk than GSHP, where every system is a custom design. The number of local contractors that can service & support mini-splits are also usually more than with a GSHP.
Sorry I didn't respond to your comment Dana! The 2200 is on the main level. The basement will have about 1200 square feet of finished space. Thank you so much for all of the information you have provided. I want to focus on sealing the house and making it the most energy efficient that we can. We would love to go ductless (especially for allergy and asthma reasons). We are thinking about radiant heat flooring, as I just talked to the floor manufacturer and it is fine. That leaves us with air conditioning and, from the sounds of it, mini splits would be the only option? Not sure what to do.
Hi Carolyn
Over several decades, I've installed a variety of heating systems - hot air, hot water, radiant, and lately, mini splits. After installing them in several homes I removed my fossil fuel systems and installed mini splits in my own, older home. Your dislike seems to be based on appearance - and they are different, but less obtrusive (imo) than baseboards or hot air system grilles & grates. The upsides: the least expensive heating and cooling system I've used, the quietest system I've used and the most comfortable summer and winter. Everywhere I've installed them, including a few homes where the initial response was the same as yours, they have been praised by the homeowners. And while I cannot say there will never be issues, in five years there have been no complaints or problems.
The ranges vary but are important - mine shut off at -20F, so if your temps go below that you'll need supplemental heating. If your temperatures stay higher, they should be fine. And by the way - make sure your house is well air sealed.
Whether it's finished and actively heated or not, the whole basement is still inside of conditioned space, and contributes to the heat load numbers. An IRC 2012 and later code-minimum basement wall still has to be insulated to the equivalent of R15 continuous coverage, above grade and below, even if it's not a finished basement or whether unfinished part of the basement isn't actively heated & cooled. So is the basement also 2200'?
Whether ducted or unducted, mini-splits have about the same amount of dust issues. Both have fairly low air velocity, most of the time, but ramp up as it gets colder outside. The air being moved is dramatically lower than most on/off gas-fired hot air heating systems that you may be familiar with- they run continuously at or near it's lowest speed. From an asthma point of view it's generally better than most other hot air delivery, but not as good as hydronic heating. Radiant floors are a VERY expensive route (with the exception of radiant slabs), and it might be worth considering low temp panel radiators as a less costly means of getting the operating temperatures low enough to work efficiently with GSHP (or other.)
A 2-ton Chilltrix air source chiller may be enough to run the place with radiant if you have low enough water temp requirements, but there's a bit more design work to be done to get the most out of it. With mini-split type wall coils it could also be used for cooling:
http://www.chiltrix.com/
http://www.chiltrix.com/chiller-technology.html
If your radiant floors &/or panel radiators only needed 95-100F water when it's +3F outside it would be able to deliver about 15,000 BTU/hr, but not much more. Something like this would have to be designed, which unlike specifying a mini-split takes some system design engineering time, which adds cost.
It's silly to attempt to specify the mechanicals before settling in on what the real load numbers are, since everything else derives from those numbers. Until you decide how far you're going on upgrading the building envelope, you won't have those numbers to work from. A radiant floor that needs to supply 5 BTU/hr per square foot to meet the 99% load has much much lower water temperature requirements than a radiant floor that needs to deliver 25 BTU/hr per square foot. That affects both the size and efficiency of any hydronic heat pump system, whether GSHP or air-source. It's not clear how one can estimate that the GSHP system necessary to support the unspecified load is going to cost around $35,000 USD. A 4 ton system is going to be more expensive than a 2 ton system, and the size of the ground heat exchanger loops are going to be dramatically different too.
Is the cost of the radiant floors included in that $35K number, or is the floor radiation in addition to the $35K ?
If you hate the in-your face high mounted wall-blob look of ductless systems, most vendors also have floor units that work as efficiently as the wall units. They tend to be thinner and taller than the air-conditioning type wall units:
http://www.fujitsugeneral.com/floor_mount_RLFF.htm
https://www.greenbuildingadvisor.com/sites/default/files/Floor-mounted%20indoor%20unit.jpg
Being closer to the floor, there is an efficiency advantage in heating mode too, since it's taking in the cooler stratified air near the floor, not the warmer layer near the ceiling, and it's easier to service them (clean the air filters, etc.)
You had me at natural gas... In our northern heating dominated climate it's hard to beat the economies of a "plain vanilla" natural gas furnace.
Reading your comments and desires, I wonder if a “Munchkin” style wall mount boiler might be your best bet. This would allow you to use radiant heat in your ground floor slab where I think you said you planned a few bedrooms. That would make those rooms very toasty.
Another advantage of gas fired radiant, you can make water hot enough to use almost any style of flooring on your first floor, that is something that a geothermal system just can't do. We jumped through a lot of hoops in our geo heated house because of that problem.
So maybe some radiant heat coupled with a few of the discussed mini-splits for cooling (and backup heat).
Oh, and I certainly agree with others, look for a builder or HVAC person that can explain what a Manual J (HVAC) calculation is and how they will use that data (or that from corresponding programs) to match your home's construction with the equipment selected. If they start out by asking “how many square feet”, run the other way.
Carolyn ,
You have gotten some very good advice so far , with lots of options . I'll give a real world example that is up and running with no complaints in your area .
Spend the money to construct a good building . This home is 100% above ground and is ICF construction , larger than your planned home . Cooling is not quite as necessary in your area as this home has 206 cooling degree days and well over 7000 Heating degree days .
The source for heating in this home is a water heater with a space heating heat exchanger , it does heat and domestic hot water and utilizes natural gas . Estimated ng usage is 705.00 per year for all gas usage , so far we are right on target to hit or even surpass (lower) that number . It is a radiant slab .
If you really need to have a renewable technology for whatever reason I would forego the GSHP and look into solar thermal , designed right , not like the failed systems built in the past by geniuses whose biggest concern was first cost . Those couple thousand they may have saved doomed those systems . You can read about them on this very site . You'll notice that the sunroom with the greatest exposure has the greatest heat loss and requires the highest temps , even when the Sun is out
I have names and contact information for folks in your area that can help you build it right .
Please take a look at the reports attached and ask whatever questions you may have as well as others who have commented . I'll gladly answer them as I check back from time to time .
Richard's example of a house with 35,400 BTU/hr @ +7F for a bit over 3800 square feet of fully above grade conditioned space is an average of about 9 BTU/hr per square foot, which is about 25% less than typical code-min, but still quite a bit more more than the "Pretty Good House" standard.
For house half of which is a walk out basement you'd probably be looking at 10-11 BTU/hr per foot^2 if code-min, but 6-7 BTU/hr per ft^2 if you spent another $10-15K carefully on thermal upgrades to the house instead of the mechanical systems.