Mini-split zone and placement recommendations
brandons
| Posted in Mechanicals on
Floor plans attached with heat loads and windows called out. What would you recommend for zones and placement?
Thank you
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Here are the attachements.
Thank you,
Good morning. Are there any opinions on this? I'm hoping to get a better understanding of the head/ducted head placement and if that necessitates adjusting the construction details.
Thank you,
Brandon
Brandon,
I'm just guessing, but it's possible that people who provide advice on GBA are getting donor fatigue when it comes to providing free heating system design.
Most people pay for heating system design. Those who don't often live to regret it. While the free design services that can sometimes be offered on GBA are often better than what is provided by your local HVAC contractor, I don't think that GBA can continue to offer free design services without burning out the advice-providers.
For information on who you should contact for heating system design, see this article: Who Can Perform My Load Calculations?
Good luck with your project.
Hi Martin,
I actually did hire (and paid) an engineer to run the calcs and design the system...Per your and Dana's recommendation on my first post here at GBA. The report I attached is his with the firm information removed, but I labeled the rooms in MS paint in lieu of attaching the 18 page report. Unfortunately, where I am located I'm largely on my own making decisions on these "green" details. The engineer I hired is out of state and roughly an hour away. He has experience with mini-split systems but I don't think my proposal of mini-split as the primary source is common. To give you an example, despite my insulation details the first engineer I consulted suggested a top of the line mitubishi MSZ system with Four 6K heads on the upper level alone. I perform as much due diligence as I can and try to hire the right folks but I would trust GBA's opinion overall just because of the experience.
I understand your explanantion, but I don't want readers and contributors to think I'm trying to take advantage of folks.
Thanks,
Brandon,
Thanks for the further explanation. That's a big house, and a tough layout for ductless minisplits. I would advise either a conventional forced-air system or ducted minisplits -- but I know you want more detailed advice.
The trouble with designing the heating system after the house design is complete is that a good HVAC design often needs a centrally located mechanical room, and duct layouts need to be finalized early in the design process. Are any of these spaces available for mechanical equipment?
Brandon, in general terms, if you have a super-insulated building envelope, a relatively open floor plan and well-designed glazing (some solar gain but not too much, nor too much loss), you can get away with centrally located heads, and either wire for or install some electric resistance heat in bedrooms.
I'm not an HVAC expert but based on your heat load it looks like your shell is probably slightly better than code, but not greatly so, which means individual rooms will have a harder time staying at room temperature. Without knowing more about your situation, I would agree with Martin, that a ducted system is worth considering.
Minor point, I don't think that the 2.4 tons of AC accounted for the Manual S "one-half of the unused latent capacity as additional sensible capacity". Which gives me 2 tons, not 2.4.
I'd also consider a Chiltrix hydronic heat pump with fan coils, especially if time of electricity use may be important.
Thank you for your responses. The home is 2850sq/ft... 850sq/ft per main and basement level, 1150sq/ft on the upper level. The home will be well insulated R20 slab R30 below grade walls R40 above grade walls and R70ish roof. I know without a doubt the upstairs unit will need to be ducted. I hoped the main and basement level could use a single head per level. The mechanical room is in the bottom right corner of the basement.
Do you think a single head per the main and basement levels would work? I could use a slim ducted cassette to serve the upper level, concealed in a soffit above the kitchen or main level bath. We will also have an HRV recirculating the air. This doesn't substitute ducting the heat but it may help enough to keep the main/basement levels to a central head?
I appreciate your help!
Brandon,
It looks like every level has at least one bedroom. Whether or not you can heat the basement or the first floor with a single ductless minisplit depends in part on the comfort expectations (and the privacy expectations) of the people who will be using those bedrooms.
Keep in mind I do not have experience...My first thoughts were placing the head on the bedroom/great room common wall facing towards the great room. I could duplicate that for the basement also. The bedroom on the main will be my office and the basement bedroom is for guests...I would opt for the single mini split per the main and basement. I appreciate that you mentioned the comfort though, had it been the master suite I would have reconsidered!
Thank you,
Brandon, those are very good envelope numbers. Do you have good windows as well? Is the great room open or are those separate spaces? A project I designed was recently completed with fairly similar details, and they have just one wall-mounted mini-split on each of the three levels with living space, electric baseboards in the bathrooms and the bedrooms are wired for electric baseboards if the owners find they need them. There is also an HRV system providing supply air to all bedrooms. They understand that any rooms with doors closed at night will be cool. If you need very consistent heat in every room, you want a ducted system. HVAC engineers are used to making every room the same temperature, and code essentially requires it, but you can work around that requirement if you want.
It matters a little which way the indoor units face, but the air will circulate around eventually so you shouldn't have cold spots. This is different from a conventional house, where you want to throw heat into the corners.
Michael,
The windows are OK. Andersen 100 series. I believe .29 U factor. We have a lot of glass it and found it isn't cost effective to upgrade. However, we used minimal operating windows and those that do are casement or awning. Both the great room and family room are open. The main-upper stairs are open along with the upper level hallway. All upstairs bedrooms are essentially ensuites with the closets permanently open to the corresponding bathroom. Practically speaking each occupant can leave their upstairs bathroom door open unless in use.
We will be using the HRV similarly. I like the simplicity of 1 wall mounted mini-split per level. That'd be great if it worked on my house!
Brandon, it's too bad you couldn't use better windows, as the rest of your envelope is 50% to 100% better than code, but your windows are only 10% better. But I understand when budgets rule. Big, so-so windows will skew performance a lot, so your best bet is to find a local engineer and/or contractor you trust. If you don't trust the engineer you worked with, you might need to find somebody else, more familiar with high performance construction.
Thank you Michael. I have faith in my engineer and he is familiar with green building. However with the direction from GBA I can influence the design. My biggest concern is moving forward with a concept that ultimately doesn't work in the field or practically. I'm also concerned with "over engineering" just with past experience.
I appreciate your help!