Pricing a Ground source system
Hi,
I am researching mechanicals for my new house build near Brunswick, ME and was just quoted what I feel are astronomical numbers for a ground source heat pump system. What I would love to do is a radiant floor/wall heating/cooling system with an additional ERV + dehumidifier system with some brand of smart controller to regulate all of that together to prevent condensation from cooling (Messana possibly? not sure on availability) Other option is GSHP to ducted air system which would cover all 4 issues. Last option is just to go ASHP/mini splits like a lot are doing up here but I worry about their efficiency in cold winters. I don’t like the look of the heads so I’d go ducted, but I want all the bedrooms heated so it would be costly as well. We’ll have a good wood burning fireplace insert as backup in any case. I’m not a huge fan of hot air heating so I was hoping the radiant would be feasible, and I want to be fossil free. House will be 4 br around 3200 sf, on a tidal cove, 1 1/2 story, 10′ ceilings + lot of cathedral areas, lot of windows but I’ll be going triple pane high efficiency. Solar with battery backup going for net zero. Some solar gain but most South facing windows will be under a covered deck. Should be super air tight SIP or metal ISP panel construction with R somewhere between 28-36. Super insulated slab from GO Logic (passive building co). Not sure on roof yet but will do the best I can with all cathedral ceilings.
I was just told a ballpark estimate that I’d probably need a 6 ton (!) system, and she said just the radiant would be $80k. I said what about 4 ton, that was $60k. She later said that didn’t include the heat pump or wells. GS to air heat pump ducted option was $12k a ton everything included – $66k for 2 zones. (I already got quoted $20k for a closed loop 2 well drill.)
This can’t be right can it?? There is no way it costs $60k to lay pex tubing in a floor. I will be doing it myself for that kind of money. I’m a fisherman not a rich vacationer. This is my dream house – I’ve always wanted to build an energy efficient house and I found an underpriced piece of land and am trying to get it done but these numbers are crazy!
Anyone have any input?? Thanks!!
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Replies
Minisplits.
Martin,
What's your 2nd choice of heating system? One thing I hate about minisplits is you have to clean the filter every month. Knowing myself, that ain't ever gonna happen lol. Especially if there are more than 1 of them. Yes I am lazy haha. It's driving a lot of my decisions on this house (like siding I won't ever have to paint!) to be as low maintenance and cheap to heat and run as possible. More likely months will go by and I won't realize how long it's been since I cleaned it. Especially if I have to go through the added hassle of getting a stepstool to reach it! haha.
The chiltrix air to water hp looks nice but it only works down to -4F and that just makes me nervous. When you need it the most it doesn't work?? That's why i was looking into geo in the first place.
You can have a buffer tank with backup heat for when its too cold and the heat pump is not able to do its job anymore (eco ultra for instance).
Go ducted ASHP, spend some of your savings on improving your envelope insulation and air sealing (underslab, and perimeter insulation for example), and you'll spend less upfront, and operating and have better comfort. If you really want cozy floors splurge and put some electric in floor heat in your bathrooms that have showers.
IMHO, having some well designed ductwork is key for comfort in a truly cold climate with any sort of air based heat. Point source heating can get the job done but at a lower comfort level.
Really even though they aren’t as efficient as gshp’s? It gets very cold up here in the winter sometimes. I’m looking forward to hopefully being a little warmer on the coast than inland Maine is though. How noisy are the ducted systems? I grew up with forced hot air and never liked it, was cold anywhere besides on top of the register blowing on you and the furnace and blower was very noisy, and dusty. I understand things have come a long way since then but ugh. Tall ceilings I worry all the hot air will go up there. I read the ducted minisplits have very small ducting and it might not work for a large area. And How do you integrate erv into that? Thanks
I live in Whitefield ME, about 20 miles from you and our house stays warm and comfortable with two ductless minisplits. Open plan, 13' ceilings, 1650 square feet of conditioned space.
Key to comfort is a good building envelope.
Most folks around here don't recommend heat in the floor, because with a really good envelope, your floor doesn't need to get warm enough to give you the warm toes you think you'll get.
In my area (central MA, design temps in low single digits) GSHP using ducted air (not radiant) runs about $9-12K/ton. A project I'm advising on in SE MA has gone ahead with a 4 ton GSHP solution to be retrofitted onto existing ducts. The homeowner told me it was "...only $5K more than the mini-split proposals, with a seemingly more competent contractor..." . If you like I'll ask them, not that it's particularly relevant given that it's air output, not hydronic, and there isn't going to be a new radiant floor installed there, which is a fairly significant upcharge.
Almost no "normal" sized house would need 6 tons of GSHP, and most new houses won't even need 4 unless it's fairly large with lots of windows. The 4 ton system on that house I'm advising on was specified to avoid all use of auxiliary strip heat, and that a 3 tonner would have been more appropriate. The power fails in that area regularly, and a 3 tonner + strip heat pushed the total power budget for the house beyond what the existing propane fired backup generator could handle (?). I wasn't directly involved in that decision. This is a circa 1960 2x4 framed 2200' Cape type house with a drive-under garage and lots of foundation exposure on one end, in a location with a design temp of +6F, only 4F warmer than Brunswick's +2F design temp:
https://farm-energy.extension.org/wp-content/uploads/2019/04/7.-Outdoor_Design_Conditions_508.pdf
I would expect that exact house built as a 2x4/R13 + R10 c.i. type of performance house (current IRC code min for zone 6, which is your climate zone) with R15 c.i. foundation insulation (also code-min) could do it with 2 tons of GSHP with a bit of strip heat to cover the shortfall during Polar Vortex disturbance cold snaps.
A higher performance 3200' house (50% bigger than that retrofit) with triple glazed windows and higher than code-min R is more likely to call for a 2-3 tons (+ strip heat) not more.
>"How noisy are the ducted systems? I grew up with forced hot air and never liked it, was cold anywhere besides on top of the register blowing on you and the furnace and blower was very noisy, and dusty."
Modulating "right sized" ASHP or GSHP systems do not resemble that description. Most fossil fired hot air furnaces installed out there are single speed and 3x oversized for the design heat load, delivering a noisy hot-flash followed by an extended chill. A modulating right sized system will run at nearly a 100% duty cycle whenever it's actually cold out, but at a much more modest cfm with almost no noise. Even a 2-stage right-sized gas furnace is pretty quiet & comfortable. The BIG problem is the residential HVAC industry's habit of GROSS OVERSIZING!
It's worth spending some money to have a certified professional engineer or a competent architect run an aggressive (per the manual's instructions) Manual-J heat load analysis on this. Do NOT leave it up to the HVAC contractor. Almost all contractors will err to the high side out of fear of getting that 5AM call on the coldest night of the year from an irate shivering customer, but that fear is unfounded. Even when using Manual-J calculation tools the contractors as a rule put a heavy thumb on the scale, and that is NOT going to optimize comfort (or cost).
ASHRAE recommends no more than 1.4x oversizing for the load at the 99% outside design temp. For a single stage system that means when it's +2F out (Brunswicks 99% design temp) the system would be running a 1/1.4= 71% duty cycle. That's delivering the "warm slow summer breeze" effect more than 2/3 of the time, with off cycles less than half as long as the on cycles. With modulating equipment it will run nearly 100% duty cycles starting at temps much higher than +2F (assuming it's right sized).
A house I consulted on a few years ago was a~4000' early 1960s mid-century modern previously heated with a ~200,000 BTU/hr output boiler using radiant ceilings (all original equipment.) After replacing the massive expanse of single-pane windows with U0.30-ish glass and building a very low R36 continuous insulation gable over the bare insulated flat roof it was fitted with a 2-stage ~60KBTU-in (less than 5 tons of output) condensing gas furnace, and a 3 or 4 ton AC coil housed in the micro-height attic. (I couldn't even sit up fully in that attic anywhere but directly under the ridge). This house was in a location with a +5F outside design temp. More than a year after the HVAC installation I had dinner with that family over the winter holidays when it was in the low teens outdoors. It was AMAZINGLY comfortable, and it was only possible to hear the furnace running when no one was talking. It was comparable to the sound levels the refrigerator in the kitchen heard through the open door to the dining area.
I doubt your house needs 4 tons, and a modulating forced air system properly sized with proper duct design (and vibe-isolation with sections of flex duct, as needed) would be plenty comfortable, though not as cushy in bare feet as radiant floor.
Thank you for your thorough reply. I thought 6 tons sounded absurd. 2 tons at $12k a ton sounds much more reasonable although this discussion makes me think I may not want to use this company for my system design! Are there any recommended honest smart companies that do the design for you, and you can just give it to the installers you hire? I want to get real cost estimates on air vs ground source heat pump system and ducted vs radiant system, plus what the electric cost would be for each since I will need to offset that with PV. I do plan on buying a higher end fireplace insert which can vent into heating ducts apparently, which can be my backup source on very cold nights. My reasoning there is it is renewable, independent of electricity, and i want a fireplace anyway for ambiance. I like the idea of the hydronic heating/cooling but I would also need some ducting for the ERV/dehumidifier so it may be too pricey all together. If I lay the tubing myself though I don't see how it would be much more than a full ductwork system throughout the house. I feel like there is less room for error/leakage & less dust with hydronics than ducts. But then i will lose some efficiency by using hardwood flooring.
The way I see it when the contractors see radiant floor heat in the plans it is clear this is money is no object project lets double up the profit on this bid but wait it gets worse when they see geothermal it becomes a gold plated project lets bump up the prices again. Also saying the word passive does not help.
I hate rules of thumb but yours at sqf/ ton =533 that number is about right for an uninsulated garage with the cheapest window imaginable.
Since this project is still just a plan reconsider your goals. Passive house does have a nice sound to it but at it hart is a math formula that fails to include a dollar sign. The money spent on insulation will never save enough energy to pay for its cost. The way I see that is not green at all.
Have a look at the PGH pretty good house standard.
Model your house with BEopt it will help you understand what investments have the best return given your local weather, interest rate and local costs per square foot.
I have yet to see a BEopt model where geothermal was the winner.
https://beopt.nrel.gov/home
Walta
Thanks, from what you all are saying it does sound like she was seeing dollar signs. There are a lot of rich out of staters buying up waterfront land all down the coast right now and putting up multi million dollar mansions to get away from covid. Sounds like I'm getting lumped into that group haha. I'm not going for passive house though, I was actually aiming for the Pretty Good House standard. I was aiming for R-30 or a little less but one of the panel co's I am considering makes their panels at R-36 so it would be easy to go higher. The FPSF insulated slab we are still looking into but GO Logic makes a nice product so I was considering using it. I was told by a PGH architect to go for high insulation on the roof and slab as that is more important than the walls for heat loss. I will check out the BEopt model. Thanks!
Be sure to find and watch the BEopt training videos. My guess is you will have over 20 hours invested in training and a good model. I think it was well worth the effort for my house.
Walta
"What I would love to do is a radiant floor/wall heating/cooling system with an additional ERV + dehumidifier system with some brand of smart controller to regulate all of that together to prevent condensation from cooling (Messana possibly? not sure on availability)."
Comment on this, because I've been going through a similar thought process.
The only time you ever want to be running a dehumidifier is when you're not cooling. A dehumidifier does exactly the same thing as an air conditioner -- cool the air to the point of condensation -- but when it's done, instead of dumping the heat outside like a good air conditioner, it dumps it back into the house. All that heat you just paid to have removed from the air? It's back.
In commercial buildings hydronic cooling is common, the cooled water is run through an air fan unit that has a condensation drip tray. They are similar in size and appearance to mini-split heads. Those units have a lower sensible heat ratio (SHR) than conventional AC's -- they're good at removing humidity. A few of those placed strategically will do all of your dehumidification. If you need more sensible cooling -- like when the sun is baking down -- then you can talk about running cool water through your radiant tubing.
My experience is that guys who do residential HVAC are very reluctant to get outside of their comfort zone. I bet if you were to probe them you'd hear some horror stories.
"The only time you ever want to be running a dehumidifier is when you're not cooling."
This is climate dependent. My experience is almost the exact opposite. The dehumidifier only runs when the AC is on. For months on end in the summer, the minisplits running on dry mode can't come close to removing enough moisture to even maintain the relative humidity, let alone reduce it. Yes, it's removing moisture, but the temperature is being reduced more so the relative humidity can actually go up.
I guess I should have qualified my statement to say that a system shouldn't be designed to run a dehumidifier.
The SHR of your system is too high, it's not up to the demands of your climate. That's poor system design. It may be that the way to deal with that is by running a dehumidifier but that's less efficient than having a proper design.
One of the nice things about hydronic fan units is that the SHR can be set just by adjusting the water temperature, which you set at the chiller. With conventional HVAC you can try to fiddle with the airflow but your range of adjustment is limited.
Everything I've read about hydronic cooling is that condensation will form on your floors/walls if you cool below the dew point, so you have to remove moisture from the air in order to get the set point temp you want. It is humid in summer here and very dry in winter (at least inland, I'm also looking forward to not having cracked dry skin in winter being on the coast, fingers crossed!) which is why I want the ERV, to hold onto my humidity levels inside in winter, and to not bring in more humidity in summer since I would have to remove it again. Messana makes an HRV or ERV + dehumidifier system to go with their radiant heating+cooling panels, plus a control system which senses temp and humidity and tells the equipment what to do to keep it cool without going below the dew point. Not sure how megabucks that system is though. I read older threads of people saying they couldn't wait for such a system to be invented and it seems it has been. That is interesting about the hydronic fan units. **I just got off the phone with Messana and they recommend an air to water HP plus their controls and then will work with hydronic fan coil or radiant or both together and controls will regulate climate between all systems. Sounds pretty good.
Tekmar 406 controller might be a cheaper option than Messana panels (they were quite expensive last time I checked).
Yes, you have to have latent cooling -- humidity removal -- in addition to sensible cooling -- reducing the temperature of air. My point is that that a dehumidifier is a really inefficient way of doing latent cooling if you're also doing sensible cooling, because you're adding the latent heat that you removed from the air to the sensible cooling load, plus the heat produced by the electricity needed to run the dehumidifier.
Radiant tubing can do sensible cooling, but in order to do latent cooling you need a device that collects and removes the condensation. So you can use the radiant tubing for some of your cooling, but you will also need a device that blows air over a surface that is cold enough that water condenses out. That device can be a minisplit, a conventional AC, or a hydronic fan unit.
When you have a Manual J done it will include latent heat load and sensible heat load. The latent load comes from the occupants -- their breathing as well as activities like bathing and cooking -- and also from humid air infiltration. The occupant load is relatively constant, but the air infiltration load depends upon the house construction and the local climate. With those numbers you can calculate the system SHR -- sensible heat ratio -- which is the percentage of the total cooling that is sensible (as opposed to latent). In the specs for your equipment it will specify the SHR, and what you need to do is match the combined SHR of your equipment to the SHR of your house. Minisplits vary a lot but 0.80 seems typical. A hydronic fan unit with 45F water might do 0.60. Radiant tubing is 1.00 (no latent cooling).
I just went through this with a house I'm building. the SHR for the house was 0.90. Total heating load was 24,000 BTU so that's 2400 BTU of latent and 21,600 of sensible. The hydronic fan units I'm using are 0.60 SHR, so to get 2400 BTU of latent I need 6,000 BTU of total capacity. That should provide enough dehumidification that I could get the remaining 18,000 BTU out of the radiant loops.
For practical reasons I ended up putting a fan unit on each floor so they ended up producing 50% of the capacity and the radiant loops the remaining 50%.
I think you're overlooking a few factors when you say you can simply design the system such that no dehumidifier is required. Firstly it presumes that such equipment exists that has the required SHR, while meeting other design criteria and while staying within a budget. It sounds like something like a Chiltrix system is better at humidity control. However, if that is the only option other than minisplit and dehumidifier, I think most people would choose to save the $20,000 or so premium that comes with the Chiltrix and pay maybe a a dollar a day for a couple of months to run a dehumidifier. As for selecting a minisplit, most of them don't even report SHR. I am skeptical that there's a heck of a lot of difference between most of them. In a heating dominated climate, the primary design consideration has to be cold temperature performance. Once you get that squared away, the options you have left to try to meet the SHR requirements are quite limited.
Secondly, if you're going by manual J to make this determination, you have to keep in mind that those values are extremes. Let's say your manual J says 10kbtu sensible, 2kbtu latent. That sensible load is actually going to be much, much lower most of the time. The latent load probably isn't going to change as much, and it's not necessarily going to be in sync with the changes in sensible load. So you could easily be facing conditions where you have a sensible load of 4kBTU and latent load of 2kBTU, meaning a SHR of 0.67. Meanwhile if you "designed it properly" based on manual J, your system has an SHR of 0.83.
In my case, the heat/loss gain report said 10kBTU sensible, 3.5kBTU latent so SHR of 0.74. However, practice is much different than theory. Based on my energy monitoring, a more typical SHR for the summer here is closer to 0.5. There are times when it's actually zero; no sensible cooling required, but the humidity is >70%. I don't care what cooling system you have, it's not going to handle that scenario without either excess house cooling or supplemental dehumidification.
The forum software limits the number of levels of nesting but I'm replying to Trevor's comment. With a system as I have described, you also need a control mechanism that measures the humidity and determines what kind of cooling is needed, and then activates the appropriate system. So if humidity is high, the low-SHR fan unit is activated. If humidity is low, the 1.00 SHR radiant coils are activated.
I understand that. What happens when the latent load is too high for even the low SHR unit? I think in your example system you said the low SHR fan unit was something like 0.6. How does it work when the load SHR is 0.4?
Other than the heat pump itself, what system parameter will affect the SHR?
The general rule is that the cooler the output air the lower the SHR. For a given flow of refrigerant, the less air flowing over the coil the colder it will exit. So slowing the fan down is the usual method of improving dehumidification.
Usually the problem is the opposite, if you slow the air down too much the coil gets too cold and ice forms, blocking the airflow. If you can't get the coil good and cold I'd check the refrigerant level.
The penalty is not as big as you make it. Converting latent heat to sensible heat always take the same amount of energy. It's a constant value. It doesn't matter if the conversion is done by the AC or the dehumifier unless there is a big efficiency difference between the two.
Most of the time the heat dumped by your dehumidifier is a good thing because the dehumidifier in general is running during shoulder seasons when some heating is needed in a cold climate. If it dumps too much heat in the room, than you just let your AC handles it. There is a small penalty from having two devices instead of one dealing with the humidity (two compressors running instead of one) but it's not huge.
To the author, the best way to have an hydronic system that doesn't cost huge amout of money and that is responsive is an air to water heat pump and radiant ceilings but you'll have to do it yourself as almost no residential HVAC contractors have experience with these kinds of systems. They are very common in Europe and Asia though.
>The penalty is not as big as you make it. Converting latent heat to sensible heat always take the same amount of energy. It's a constant value. It doesn't matter if the conversion is done by the AC or the dehumifier unless there is a big efficiency difference between the two.
This is just not true. The latent heat removed by an air conditioner gets dumped outside. The latent heat removed by a dehumidifier gets dumped back into the building. Yes, it's the same amount of heat both ways, but with the dehumidifier you're adding it to the sensible load of the building. You're also adding the heat from whatever electricity was used to run the dehumidifier.
For a tight building the SHR might be 0.90, for a looser building it might be 0.80. So relying on a dehumidifier for latent heat removing increases your cooling cost by 10 to 20%. If you look at the lengths people go to on this site for efficiency I'd say most people would consider that significant.
To the comment about the heat being beneficial during shoulder seasons, right in the beginning of my comment I said, "The only time you ever want to be running a dehumidifier is when you're not cooling."
With a dehumidifier, you're basically just trading latent and sensible heat. Once it's converted to sensible heat, the minisplit (or whatever your A/C is) removes that heat. The electrical energy that the dehumidifier used is the only excess energy added to the system. Let's not forget that when you run a minisplit in dry mode, effectively reducing the SHR, it's inherently less efficient. So having a unit with lower SHR isn't necessarily a free lunch. It may just mean you have a lower efficiency to begin with. You'd have to compare the total energy used by each system to determine how much more one costs than the other.
"The only time you ever want to be running a dehumidifier is when you're not cooling."
I'm not sure what value there is in this distinction. There's a continuum of sensible heating ratio from 0-1. So at 0 SHR, dehumidifier is ok but at 0.1 SHR then dehumidifer is bad? I don't agree. Unless you've got a cooling system with a variable SHR that can go down to 0.01.
With regard to geothermal, this is what the Chiltrix air-to-water heat pump says on their website (https://www.chiltrix.com/documents/CX34-spec-sheet.pdf):
Geothermal Performance
There is no Energy Star program for air to water heat pumps.
However, the Chiltrix air-cooled chiller exceeds the Energy
Star EER requirements for geothermal water-to-water
systems.
Make of that what you will, I have no firsthand experience to relay. But the general consensus here seems to be that while ground-source heat pumps have the theoretical advantage, in the real world air-source heat pumps meet or beat that performance due to greater refinement.
That is interesting. Thanks!
To confirm what Dana said about tonnage required, my own house is around 4,000 sq.ft. of conditioned space on two levels, in central NH (CZ 6), heated quite nicely by a two-ton GSHP system. The house is in the PGH category, with double-frame exterior insulated to R40, R60 attic, insulated slab and foundation walls to R20, triple pane windows, and very tight. The area distributor and two of their installers all wanted to put in a five-ton system, when my own spreadsheet heat loss calculation showed that a two-ton unit would be more than adequate. I ordered the two-ton unit, and it has done the job well, keeping the house at 70 in just first stage down to our design minimum -3 F outside temperature.
I think part of the problem is that HVAC contractors just don't know how to do a really detailed heat loss calculation for a superinsulated house, or they won't take the time it takes to do it in great detail, even when they are given all the details to use. They take shortcuts, using rules of thumb, and make unwarranted assumptions. In my case, one load calculation had nearly a ton of load in there for "fireplace," when there is none. I do have a small wood stove on the lower level, but it has its own outside air duct connected directly.
So my advice would be to put your first money into the exterior shell (PGH level of efficiency). The heating system, whatever you choose, will be far smaller and thus less costly. The house will be far more comfortable to live in, year round. I wouldn't shy from a ducted air delivery system, based on prior experience. In our case, the air velocities are so low that we can't hear it. The ducts were sized for a three-ton unit, since at the time the first blower door test had not been done. Also, think carefully about window area, and avoid overdoing it. Even a good triple pane window with fixed glass is an R6 "hole" in an otherwise highly insulated wall area.