Simple effective addition of AC to dome home?
I’m looking to add a touch of AC to my Colorado dome home, and I’d like to hide the unit and ducting inside my loft bedroom closet, pictured below. Hoping for some ideas on equipment selection and ducting design.
Some specs:
House is in climate zone 5. House is a 2400 square foot (above ground) concrete dome with R21 continuous spray foam and 1.5ACH. No existing ducting, no attic, no crawl space, finished basement. I am adding an ERV system for ventilation. I had a manual J done for heating but don’t think we did it for cooling. Calculated 40k BTU heating needed above ground.
Max indoor temp last summer was 74.5 degrees in the loft and 72.5 degrees on the main floor without AC, with one person living there. Large stairwell to the 64 degree basement was open last year, will be closed in this year, not sure if that will have an impact.
I’d like the option to drop the indoor temp ~6 degrees to handle the highest temps of the year, but also keep a simple system.
Hoping to add a heat pump in the loft closet to pull return air from the top of the dome and push cool air back out into the open space to circulate. I’d also like to push some cool air into the loft bedroom.
This does ignore the two main floor bedrooms but I don’t know if it’s necessary to address those or not.
Looking for suggestions and ideas I’d this seems like a good idea and how you’d go about pulling it off.
video walkthrough:
Comments
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Illustration of what I’d like to do.
Closet is currently 23” deep stud to stud. It could be increased to 24” or possible more if needed.
I’d like to keep the closet as functional as possible.Supply could run under the floor but not sure where to place the vent then.
If this idea could work, should I be looking at concealed low static ducted units or a smaller standard ducted unit? Any idea on size?
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ducted mini split
Low mid static.
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I'd put a ducted minisplit in the ceiling of the closet with ducts going both ways. Run the refrigerant lines through the 2x4 walls into the floor. They have to somehow get outside. Same with condensate drains.
Are there any interior walls below or is it all open plan? Is the ceiling below boxed in or are the joists visible?
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Thank you, the basement ceiling is open currently, but not the first floor or loft. I’ll open what is needed though.
Are you suggesting to fit the mini split above the header of the closet door? Not a ton of space there, could you show me what mini split you’re picturing?
My understanding is that the shape of a concealed low static pressure ducted mini split might not fit within the 23” available but a normal ducted mini split would in the space to the left of the closet door.
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One of the multiposition air handlers would be a better options. Something like this (there is a hyper heat version for cold climate as well if you want to use it for heat):
These can be configured for downflow so it makes the ducting much simpler. They are also narrower than the slim units so it is an easier fit in the closet. The form factor is also closer to what HVAC techs are used to.
All major manufacturers have similar units out there, just make sure they can be installed in downflow orientation. ie. Carrier/Midea:
https://ashp.neep.org/#!/product/164035/7/25000/95/7500/0///0
With short duct runs like that use duct board or install duct liner inside the ducting to reduce noise. The nice part about all these units is they are modulating so most of the time when running at low speed, they are pretty much silent.
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If you're at the framing stage I would pick the air handler and then frame the closet to fit it.
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And Please read the instructions for clerance / service!
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Thanks guys, appreciate your comments!
Do you think this simple setup pushing cool air from the open loft to the open main floor below will be effective in bringing temps down ~5 degrees on the main floor and loft?
There are also two main floor bedrooms below where this mini split would be placed which are not currently included in this cooling plan. They are north facing and don’t get any sun. Any suggestions on if I should worry about these? I could drop a duct to one through the floor but the other is a few joist bays over so I’m not sure how to duct to that one.
Does the short ducting seem ok for both the main trunk like as well as a small short takeoff to the loft bedroom? Hoping to not be noisy (noted comments above about duct board).
Framing is done, it would be a lot of work to redo at this point so hoping to find an effective solution for the space that I have.Any idea on mini split sizing or duct sizing? Is there a recommended online Manual J for cooling I can work through?
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"Framing is done, it would be a lot of work to redo at this point so hoping to find an effective solution for the space that I have."
Disabuse yourself of that notion. Framing is the quickest, easiest part of the job. Rework is done all the time. It's just nuts to try to work your mechanical system around how a closet has already been framed.
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I totally understand why you’re saying this as a general statement, but the curved concrete walls make framing very difficult and slow (2-3 days for 2 guys to redo just the closet), and the small space for a bedroom/closet/office limits what changes I can make.
If there is a great reason to rework this space I am open to it, but what specifically needs to be changed?
I’m not saying it’s a hard no, but there has to be a strong reason for it.
I’m asking the questions above to establish the best cooling and ducting solution first and foremost, but one there are also some challenges and constraints.
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A minisplit AC cooler/ heater will require you to drill a hole through your concrete dome? I have an alternative. Consider installing a Heat Pump Electric hot water tank instead. ( disable the resistive heating element) Use the cold coils and a fan to cool and dehumidify your indoor air. Use the hot water however you want to. If you want more cold just dump the hot water outside of the house ( into an outdoor hottup or pool perhaps. Dehumidifying your indoor air by itself might solve your indoor comfort problem. Most people like 70s F temperature? Have you measured the humidity?
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Re: "Use the hot water however you want to": You can't use a HPWH for space heating, it's taking heat from inside the space, it would be like a perpetual motion machine.
It does provide some free cooling and dehumidification.
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The idea is don't shop for equipment that fits in the closet, select the equipment that best fits your needs and then if necessary adjust the size of the closet to fit it. Adding a couple of inches to one side of that closet is not going to be a big job.
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I agree with you — this is why I asked for help identifying the equipment first that solved my problem, considering all factors.
Do you have a suggestion on equipment I should be looking at?
My understanding is that the size of most multi position air handler heat pumps wouldn’t require a modification to the width of the closet so it feels a bit out of order to be focusing on that right now if there hasn’t been any progress toward ideal equipment choices and what space they require.
I’m asking about heat pump selection and how to determine ducting size — if anyone can help point me in the right direction it would be a HUGE help in getting the ball rolling again on a difficult rehab that has stalled out.Thanks again to all who are taking the time to provide input.
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I work on very old houses, so I understand the time and cost to make even what seem like simple changes.
Still, let this be a learning experience about how not to design a house. You are far from alone in designing your spaces before designing your mechanicals.
You now have to “reverse engineer” in order to fit an HVAC system into your house. Something almost always has to give.
For the house you have built, minus any interior partitions, a ducted mini is a fine choice for year-round comfort at low operating costs.
The air handler that Kaos recommends is a very good choice. As pecmsg mentions, make sure you read up on clearances and available space for servicing the equipment.
Now may be the time to bring in a HVAC contractor who works with Mitsubishi ducted minis, and ask if they’ll do the duct design for a fee (if you agree to give them the install job). Tell them right off the bat that you want to work within the existing layout as much as possible, and then go from there.
Wishing you the best in your very unique project.
Swinging hammers and fitting pipe…bringing the dream to life
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Run your place through one of the online calculators like coolcalc. Not sure how to exactly deal with the lack of roof and walls, maybe treat all as roof and set up each rooms with a ceiling only.
In a area that doesn't need much cooling and in a tight structure with not much windows, the cooling load will be very small, I would guess in the range of 1500 to 2000 sqft/ton.
I would definitely duct to each bedroom, nobody will ever complain about bedrooms having extra cooling. Try to put the supply so they are not directly blowing at people or spec register to deflect the flow away.
With a downflow configuration you'll have a plenum under the air handler. From there you can run a straight duct run to the wall to the living room and take offs off the bottom of the plenum through the subfloor and through the floor joists to the bedrooms. Once you have a rough load for each room you can size the ducting from there. As a rough rule of thumb it will about a 5" hard pipe supply to a small bed, 6" to a larger bed.
With a high mounted return/supply and an open living space bellow you'll get good cooling there without any extra ducting.
I would install the largest filter box you can fit on top of the air handler. With that SVZ air handler a 16x20x4 filter (if in some area go for 16x20x5 so you can fit a carbon one ontop a 4" filter when needed). Make sure the filter opening is the right direction so you can easily pull and replace it. A door right by the air handler will make your life significantly easier. Since it is not a fuel burner, the door doesn't need any louvers, it can be a solid door. Air handlers are quiet but I would still insulate the partition wall there.
Try to get the condensate to gravity drain to a tub over flow/washer riser/sink tailstock bellow. Condensate pumps are quiet but not silent and you'll notice it running.
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Wide open floor plans do not need much duct work. One issue is heat rising in the winter and cool air falling in the summer. Those ceiling fans WILL help but there will be a few degrees difference between floors.
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I also think that the unit that @Kaos linked to is a good choice.
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Thank you for the additional feedback and ideas — I am going to pursue this further and try to move it forward with your suggestions.
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Could I ask for input on the efficacy of placing a single ductless mini split in the open area of the home in order to manage temps in the open area of the loft as well as the open area of the main floor? This would skip the main floor bedrooms but hopefully they will stay reasonable as well.
(I would place a small wall unit inside the loft bedroom for cooling as well.)I also have a ceiling fan at top right of image that should help mix the air temps.
From an aesthetics standpoint, a floor unit represented by the blue square in the image would be acceptable and possibly the best mix of function and form. Do we think this would effectively cool the loft and main floor (with the help of the ceiling fan)?
From a function standpoint a wall unit represented by the purple square would likely be the most functional option, but is the worst for aesthetics which is why I am trying to find an alternative.
The yellow rectangle would represent a ceiling cassette in the main floor but I fear this wouldn’t compromise cooling the open loft area. This would be the best option aesthetically if it could work (again with the ceiling fan). I’d love to do this, if it would work with the ceiling fan.
I’m just questioning if the ducted idea I proposed above had more difficulty than benefit overall (and cost, and issue with contractors knowing what they’re doing). I’ve been getting quotes on it and it just feels a bit messy and most installers caution about noise as well as imbalanced flow between open space and bedrooms below if I have a bunch of short takeoffs.
If you all still prefer this though please let me know.
If those with a good feel for airflow and results for cooling from a single point ductless mini split could share their input I’d really appreciate it!0 -
a wall unit is the simplest and easiest to service. Just make sure there’s drainage available.
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Understood that those are factors as well, but I’m really asking about efficacy of cooling of the three locations I discussed and are pictured above. Balancing function and form is my primary goal, knowing if the ceiling unit or the wall unit would perform well enough while looking more subtle than a high mounted wall unit front and center in an otherwise very clean simple space.
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your over thinking it!
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Ah yes, another reply that doesn’t contribute anything or answer my question at all. Thank you so much.
If anyone else has any thoughts about the question I posted, they’d be appreciated :).0 -
you asked!
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I have a rental unit with similar configuration (1 bed in a loft, living +2nd bed on open concept main floor). The place is cooled by a single wallmount in your red location. It works reasonably well, loft bed is fine with doors open. The main floor bed is a bit too hot as it is more isolated plus has west facing window. Living space is comfortable.
I think either red or purple would work equally well for cooling, red is slightly better as you can angle the discharge to blow towards the upstairs bed if needed at night. The other two spots would put the intake too low so it won't cool well even with mixing from a ceiling fan.
As with anything wallmount, they are fine as a retrofit but if you have the place open like that, I would just go for ducts. This way you can have cooling in all the rooms even with the doors closed.
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Is this the same home?
52473_1714930093_BRYAN_TROLL_EVERGREEN_MAY_SET-copy-edited.pdfUploaded Oct 25, 20241.15 MBEdward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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One other data point: it has been a high of 88 degrees the last two days which is pretty much record hot in my town — inside temp was a high of 70.3 F on the main floor and 74.5 F in the loft.
Variables when the home is lived in will likely raise the indoor temps slightly, but just important to consider that the home doesn’t need much cooling.
Kaos - thank you, your input is always helpful and appreciated. I worked through an air handler with short ducting that leads to three bedrooms plus the loft open area and the main floor open area but just haven’t found a contractor who I feel confident can pull it off effectively. It takes up half the closet and I’m concerned that it would lead to an imbalance in temp in different rooms. I’d love to do it if it could be done well, but just having doubts (and frustrations).
This has me circling back to wonder if a simple 2 head ductless setup can effectively take the edge off on those hottest days in a simpler, cheaper way — a 6k wall unit in the loft bedroom and an 18k unit in the open common area.
Ed — yes this is the same house.
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