Preview: A/C Sizing help needed.... Dazed and confused

Air conditioning, fans, and anything related to keeping it cool, such as insulation. This would include any posts generally discussing how to keep it cool, such as which types of blocks are better insulators.... ideal wall thickness for keeping an A/C house cool, etc.

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Preview: A/C Sizing help needed.... Dazed and confused

Postby Baht Man » Mon Apr 21, 2014 8:15 am

Can someone please help me out here in Udon.

I'm currently building and called 2 local a/c folks out here.

Nimitz Air quoted a 36,000 btu cheap China model for about 50,000 Baht.
Standard Air quoted 2, 44,700 Mitubishi Mr. Slim units at about 176,000 Baht, more than double to capacity of Nimitz.

I quized both of them and Nimitz said due to ceiling height and insulated walls and ceiling, a single unit was enough.
They then requoted using Carrier, Mit etc.

Standard said maybe I could use one large unit at about 42,000 and a smaller one at 35,000.

These are cassette, ceiling mounted units.

Why such a differece ????

The room is 75 sq.m (810 sf.) and most walls are double block walls with insulation between.I will insulate the ceiling as well.

A lot of the ceiling height is at 5.5m and I calculated total room cu.ft. at 19,400 and cu.meter at 550.

Any help would be appreciated.
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby Sometimewoodworker » Mon Apr 21, 2014 10:12 am

Baht Man wrote:.


Any help would be appreciated.


A mistake often made, and encouraged by the seller is to get a unit that is too big. This will then have short run times so not take out as much water as a smaller unit that is running longer. Also insulateing the ceiling is more important than the walls, and even more important is to reduce or eliminate drafts. Down-lights look nice but are seldom sealed so you loose conditioned air.
Another point is that loose fill insulation like fibreglass is less good than solid, and it seems that spray PU is even better as it will seal leaks.

Personally I will be using room fans as well as AC to raise the temp the AC is set at for a comfortable room.
I'm not a fan of 17 deg AC. 25 ish and fan will do me
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby thailazer » Mon Apr 21, 2014 10:48 am

Baht man... I agree with woodworker; Don't get too big of a unit. I used a few of the online calculators for your specs, and unless your room has a lot of windows, an AC unit of around 32,000 BTU ought to work. The two unit estimate sounds like overkill to me, but would be appropriate for a place of business where the doors open a lot and there might be equipment running and heating the place up. To be on the safe size, get a unit around 40,000 BTU and you should be fine.
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby Baht Man » Mon Apr 21, 2014 10:56 am

I understand about oversized units with short run times not eliminating the humidity.
I also understand about their desire to "oversell".

There are a number of houses built in a area near me that have 2 units in large rooms, and most owners tell me that they use both to cool it down and then revert to using only one to maintain temps.

Ceiling insulation will be double faced R something and although the room I'm talking about is an interior room, the double block walls were stuffed to eliminate low frequency "rumble" from the quasi home theater subs.

Most downlights will be built into a soffit around the rooms perimeter although some will be placed in the ceiling at about 4 meters, and I'll be on hand to assure proper sealing. That's not an issue here.

Just trying to get a handle on sizing for the room.
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby schuimpge » Mon Apr 21, 2014 11:24 am

From 1 website I got this:
For a room between 700 and 1000 square foot, recommended sizing is 18,000 BTU/hr.
However, your ceiling is almost double that of a typical room, so double that amount to 36,000 BTU/hr.
Because your room is heavily insulated ('shaded'), you can deduct 10% of that amount needed.
So your verdict would be anywhere between 30k and 35k BTU

But the next one:
New Well Insulated Villa: 7x8m Room 2.4m Ceiling = 134.4m³ x 55watts per m³ = 7.4 Kw 25256 24000BTU

So I can imagine there's some different quotations possible.
Where will the zircon units be installed? At the top? Or will you have them floor standing?
Leaving them lower than your ceiling height will save a ton and could bring down required BTU's.
Floor-standing units would be ideal.
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby Baht Man » Mon Apr 21, 2014 7:04 pm

schuimpge wrote:Where will the zircon units be installed? At the top? Or will you have them floor standing?
Leaving them lower than your ceiling height will save a ton and could bring down required BTU's.
Floor-standing units would be ideal.


Units would be cassette type, ceiling mounted, but I'll look into floor type.Never thought about that.
Thanks a lot.
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Re: Preview: A/C Sizing help needed.... Dazed and confused

Postby schuimpge » Mon Apr 21, 2014 8:42 pm

Baht Man wrote:
schuimpge wrote:Where will the zircon units be installed? At the top? Or will you have them floor standing?
Leaving them lower than your ceiling height will save a ton and could bring down required BTU's.
Floor-standing units would be ideal.


Units would be cassette type, ceiling mounted, but I'll look into floor type.Never thought about that.
Thanks a lot.


It's one of the things they tout in swampy as being so env. friendly...
Cheers,
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