Mini-Split Choice?
Last Post 25 Oct 2014 06:53 AM by jdebree. 8 Replies.
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guruunoUser is Offline
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22 Oct 2014 09:19 PM
After ditching the radiant floor (circulating water) idea (real long story, everyone looking to do home run + other matters), we are now faced with making a decision on which mini split system to choose, and the primary concern is warmth/heat. Fujitsu or Mitibushi? I spent 3 hours watching YouTube videos, reading in various forums, and once again, I have to say, the overwhelming amount of personal opinion and not professional advice is bewildering. What I am saying is that for 25 years I swung a hammer and know contracting. Now that I have hung up my hammer and moved on to other things, getting REPUTABLE estimates, in-range pricing, KNOWLEDGABLE contractors, VALID REFERENCES, REAL LIFE CUSTOMER EXAMPLES OF HISTORY USAGE, etc., seems next to impossible, and without creating a massive back and forth war of words between contributors here, it seems like lots of contractors are looking to make HOME RUNS (charging double and triple pricing) from what should be the norm. That aside, a few questions and I'd really appreciate some serious professional replies. So with a 14' x 18' room with a sloped ceiling that goes from 12' to 8', 3 exterior walls with windows and doors and the 1 remaining wall attached to an unheated garage (diagrams attached), a floor that is a concrete slab with a 2x10 floor joist constructed on joist hangers with 1" of dead air space below the joists and 6 mil poly on the slab with 2" XPS foam boards (R-10) on the poly/slab (leaving 1" dead air space to the bottom of the floor joist), R-30 Roxul insulation between floor joists (giving me an R-40 on the floor), R-15 Roxul in the walls and ceiling, what model mini-split should I use for the primary A/C~heat unit? (and how many BTU's). Also, considering an electric floor grid, undecided between 'WarmFloor' and a 'normal' electric grid system. WarmFloor for 250 Sq. Ft. is $3200 for materials (!!!!!!!), the mat/grid system is $850 materials. Step WarmFloor is a 24 volt system with PTC Polymer Heating Panel Sets. Nailing or stapling of PTC polymer heating panel sets shall be done through the polymer material but at least 6mm (1/4 Inch) from the bus conductors. Nails, staples or other fasteners shall not penetrate the current-carrying bus conductors. Whereas the normal electric grid system is just 230V running through wires in mats and a floating wood floor has to be used. Decisions, choices, confusion.
guruunoUser is Offline
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22 Oct 2014 09:21 PM
Attachments not showing, uploading, all under 100k, ??
jdebreeUser is Offline
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23 Oct 2014 06:41 AM
Why so much floor insulation, and so little in the walls and ceiling? You really need to do a Manual J to calculate the heat loss and gain for any kind of useful answer. I used a $50 program to design the system for our house. What is your climate? If in the far north, a mini might not handle the heating, although they now go below 0 F.
guruunoUser is Offline
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23 Oct 2014 09:11 AM
Floor is on slab, (a floor that is a concrete slab with a 2x10 floor joist constructed on joist hangers) was always ice cold, want to super insulate it, think of it as a garage. Walls are 2x4 and ceilings 2x6, so Roxul with R-15 is highest R value available without using Foam (wife a tree hugger and no chemicals allowed, etc., etc.).' Central New Jersey is the locatation
jdebreeUser is Offline
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24 Oct 2014 06:19 AM
As built, you won't net R-15 because of heat transfer through the studs. It can amount to a 25% loss. At least go to 2X6 walls. Ideally, you would want external insulation over the sheathing to stop thermal transfer. You'll want to pay attention to air sealing, too. R-15 in a ceiling is really skimpy; nowhere near code anywhere. Here in mild SC, it has to be R-38.

As for the minis, we are running Mitsubishi HyperHeat units. We have found one 12K unit does a good job of cooling our 1300 sq ft, but this is an ICF home with R-24 walls, R-49 ceiling, good windows, and very tight construction. We have a second 9K unit in the master suite, but haven't really needed it yet. We haven't been through a winter yet, but the Manual J calcs show we have more than enough capacity even at 0 F. The units are incredibly quiet, both inside and out. Most people can't hear the inside unit even when you point it out.
guruunoUser is Offline
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24 Oct 2014 10:44 AM
The existing room is gutted (50+ year old addition), no consideration for "expanding" framing members over existing 2x4's to achieve 2x6 as suggested, no siding being installed over existing wood shakes (in very good to excellent condition, well maintained, no need to incur residing to achieve a Polyisocyanate or Foam Board R-Value yet.....possibly in the future if we stay here or die first [as in ..read NJ Highest Taxes in US]....+ we are in our 60's), so existing 2x4 construction is all we have and desire and get. Cathedral/sloped ceiling is 8'0 to 12'0 the length of the room (18'6"), and the roof rafters are 6". Roxul insulation is R-15 for 3-1/2", R-24 for 7-1/2" framing members. Given the ceiling is as stated, what do people do to achieve an R-38 as you propose in a cavity that is only 5-1/2"??? I called Fujitsu, they were very helpful, I also called Mitsubishi, they have no "pre-sales" person to ask questions. However, I did find this: Laboratory Test Report for Fujitsu 12RLS and Mitsubishi FE12NA Mini-Split Heat Pumps, at: http://www.nrel.gov/docs/fy11osti/52175.pdf

Bottom line is looking to keep the floor warm, create a tighter, more enjoyable "envelope" for a 250 sq. ft. office/tv room year round and do not want to undersize or oversize the mini-split, so, 9,000 of 12,000 unit (BTU), worst case/best case if under or oversized?

Also, this floor heating is nuts, so many choices, so many opinions, and quite frankly, in NJ, next to nobody does it, most just buy a rug and throw it on the floor and wear warm socks. This is 2014, is it not? We are not adverse to investing in the proper technology and would love to enjoy the benefits of doing things correctly, however, as initially stated, too many 'contractors' are cutting their teeth, looking to make home run's or just plain do not know. And the ones who do know are so far and few in between when you do find one, if you are lucky, they are swamped and not really interested in such a small (250 sq. ft.) project, so they bid high that in the event they get the job, it's a home run.

Not that I ran my business that way, but generally saw it with tons of "snakes" ot there that I sub-contracted from in the early years, and you see things, you hear stories, you learn from them, you benefit you lose, but that's life, it's an ongoing learning experience and we are all guinea pigs, right?
mtrentwUser is Offline
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24 Oct 2014 11:26 AM
Don't rule out Daikin LV series mini-splits. Only had mine this year, but ratings and reviews were good.
Dana1User is Offline
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24 Oct 2014 01:53 PM
At at 25% framing fraction a wood-sheathed 2x4 wall with R15 Roxul comes in at "whole-wall R" of about R10, with a U-factor of about 0.10 BTU per square foot per degree F.

The 99% outside design temps for central NJ are about +15F, so assuming an interior design temp of +70F that's a delta-T of 55F.

So the wall losses for the wall area only are about 5.5 BTU per square foot. Measure it all up and do the multiplication arithmetic yourself.

The U-factors of the windows are published by the manufacturer. If you don't have the necessary information, assume clear-glass double panes to be about 0.5 BTU/degree-ft^2 , if they are low-E assume 0.34 BTU/degree-ft^2. Measure 'em all up, do the math: 55F x U0.xx x area= head loss.

The ceiling has a lower framing fraction, so you're probably running a U-factor of about 0.08 BTU/degree-ft^2 there.

Ignore the floor losses, ignore the losses to the unheated garage- they're " in the noise", of all the other error in the calculation, since we're ignoring solar gain, interior heat sources etc.

If you are going to add 1.5" thickness to the walls instead of scabbing on some 2x2s to the existing foam, cover it with foil-faced polyisocynaurate (seams taped with FSK tape, and edges & electrical boxes sealed with can-foam) and long-screw the wallboard to the studs. Doing that would cut the wall losses literally in half.

Add it all up, what's the number?  Bump that by 25% to cover any infiltration loss, losses to the garage, etc, now what's the number? I'll bet it's less than 7000BTU/hr, might only be half that, depending on how much window glass you have.

The new -FHxxNA Mitsubishi units are ~20% more efficient than the -FE12NAtested in that bench test bit Ecotope did for the NEEA, and even noses out the -xxRLS2 Fujitsu units a bit. http://www.mitsubishipro.com/media/946493/fh_product_guide.pdf

The MSZ-FE09NA has an output in excess of 10,000 BTU/hr @ +5F, and even if you have quite a bit of window area it probably covers your load. The AOU-9RLS2 would probably do it too.

If you have a lot of west facing glass and you intend to air-condition the place down to 75F you may need a bigger unit than a 3/4 tonner. But that would have to be a LOT of west facing glass! A 14 x 18 room is only 250 square feet- typical cooling loads run about a ton per 1000', and even at the old-school lousy rule of thumb of 2- tons per 1000' (that reliably oversizes most rooms/houses) would have you well within the cooling capacity of a 3/4 ton mini-split.

Which one to buy comes down to price and how well supported they are in your neighborhood. (Mitsubishi has the lion's share of the market in my neighborhood, with a training certification & design center and dozens of contractors installing them. YMMV.)

The minimum operating temperature for the -xxRLS2s is -4F, the Mitsubishi -FHxxNA still have a rated output at -13F. The Daikin LV series min-temp is +5F, and though it'll keep putting out some unspecified amount of heat during the polar vortex events, it's probably not the optimal choice in central NJ. Even though the 99% outside temps are in the teens, 0F isn't exactly rare. It's hard to go wrong with the RLS2 or FH series minisplits. Even the older design FE Mitsubishis are pretty good, delivering an average COP of about 3.0 in locations like Idaho Falls ID, where the binned hourly average temp in January is +21F (measured in-situ in one of the NEEA studies.)

FWIW: I have a relative in the pacific northwest in a location where the 99% outside design temp is +21F who is heating about 1000' of sub-code-R cottage with an FE18 (about 2x the output of the FH09), and is completely satisfied with that choice.  I have another relative near her in a location with a modestly warmer design temp and a much better insulated house heating more than 2x that space with an FE18, also very satisfied with the performance.

So, make a little spreadsheet calculation based on the U-factors above, see what you come up with- it'll be within the output of almost any 3/4 ton. If Mitsubishi, the FH09 is a better bet than the FE09, if Fujitsu the -9RLS2 is a better choice in your location than the -9RLS2-H. 

With either of those you would only use about only 1/3 the amount of electricity for heating than you would with electric radiant floors or any other resistance heating method.
jdebreeUser is Offline
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25 Oct 2014 06:53 AM
I misunderstood; i didn't realize it was existing construction. Dana did a great job of putting some real-world numbers to it.
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