Help me plan minisplits for my new construction house?
Last Post 26 Mar 2018 08:44 PM by Dana1. 2 Replies.
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ahrenoUser is Offline
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25 Mar 2018 05:40 PM
I'm in the middle of building a house... framing almost done. I'm in northern california and would like to use mini splits for air conditioning. I have in floor radiant heat and also a wood fire place for heat so i have no need for heat. Was told mini splits are a good energy efficient way to add air conditioning as a big central air system is not in the plans/budget.

Heres the floor plan:




My thinking was one three zone on the right side (three bedrooms, each approx ± 14'x12')

Then maybe a dual zone for the great room and master? or a separate one for each?

Going with mini splits allows me to do it in stages (budget) but i need to run power now. I've been told its efficient for cooling but not the best for heating.

I just looked into some 3 zone ones and they seem to only come with 16' of hose. am i able to do longer runs?

where is a good supplier to look at units?

any recommendations as to go with ceiling vents (look better but another hole in the envelope) the big ass wall blowers, or something else?

here's a simplified version of my floor plan too:

no idea why the formating is all jacked up and i cant get images to display. heres an imgur link: https://imgur.com/a/5LXBE

Attachment: FLOOR-PLAN.jpg
Attachment: FLOOR-PLAN-simple.jpg

ahrenoUser is Offline
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25 Mar 2018 05:44 PM
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Dana1User is Offline
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26 Mar 2018 08:44 PM
The attachment with the dimensions is too low-res to read.

Longer refrigerant lines are allowed, but beyond some limit it decreases the total capacity of that head while taking a toll on efficiency. It varies (a lot) from model to model, manufacturer to manufacturer.

To get this right requires a careful room by room Manual-J load calculation (which is also a requirement under California Title 24, but when performed by HVAC contractors they're often not worth the paper they're printed on.)

If going by a "rule of thumb" approach (NOT recommended), most current code-min house come out to about a ton of cooling per 1500' of conditioned space (give or take 800'- like I said, not really recommended).

Ceiling cassettes tend to have a commercial-office HVAC ceiling diffuser type of look, which can be a bit much, but works in big rooms with big ceilings. There are also floor level wall coils that don't stick out quite as much as the more typical high-wall wall coils that everybody seems to hate.

Mini-duct cassettes work best when designed with short hard-piped runs and tapered register boots with small register grilles designed for maximum "throw", mounted on an interior side wall or ceiling, not the traditional duct over/under a window on the exterior wall. See John Semmelhack's pictures in response #14 in this thread:

http://www.greenbuildingadvisor.com/community/forum/mechanicals/93846/mitsubishi-minisplits-horizontally-ducted

Fujitsu's mini-duct cassettes have better specs than the competition's, and the single-zone mini-duct units also have a very favorable turn-down ratio, so they'll modulate at low speed very quietly & efficiently most of the time, only ramping up when it's really torrid outside. Fujitsu units can also be installed vertically (as in Semmelhack's mini-utility closet), others need to be be horizontal for the condensate drains to work. With full basements or crawlspace foundations it's usually possible to mount mini-ducts under the floor joists and use floor registers, but for slab-on grade a utility closet or mounting in the top of a closet and running ducts in soffits under the ceiling to multiple rooms (no ceiling penetrations necessary in many installations) can work. This can't be just handed over to contractors accustomed to whole-house split-systems with a Medusa of oversized flex in the attic. Hard piped ducts and a true Manual-D duct design is called for. It's not rocket science, but it's not 5th grade arithmetic either.

Mini-splits sized correctly can be cost-competitive on an operating cost, close to that of natural gas boilers in most markets. Cold climate mini-splits can also work well down to -15F or colder too- temperatures not often seen below 7000' of altitude in N-CA. A mini-split solution is often cheaper up-front than condensing gas boilers and radiant floors. A project I was involved with on a code-min house in coastal MA a few years ago on a ~3000' house, half of which was built in the 1970s, and nowhere near code minimum came in at about $15K, all-in, which was ten grand cheaper than a condensing propane gas-burner + 3 ton split cooling proposal on the same house, at HALF the heating cost of condensing propane, despite 22-25 cents/kwh electricity, nearly twice the national average, in part due to high local propane pricing. The 99% outside design temperature there was +13F, pretty temperate for MA, but due to being downwind of ocean water no matter what direction the wind blows.

What are your 99% and 1% outside design temperatures? (Find your city in this list- all CA municipalities are in there: https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf )

All multi-zone mini-splits are heat pumps, but not all are capable of delivering much heat at sub-zero temperatures.



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