AC Sizing

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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AC Sizing

Postby claynlr » Tue Oct 03, 2017 2:29 pm

Hello Building Board-

Building a small 1 bedroom bungalow consisting of 15 cm q-con walls, gypsum ceiling with R-37, 6" staycool above, colorbond roof sprayed with 1" foam to the underside, soffit vents for attic intake and whirlybirds for exhaust. As far as AC sizing, The 4m x 4m x 3m (ceiling ht.) bedroom I know will be the minimum 9000btu. The kitchen/dining/ living room is an L-shaped ( consisting of 3- 4m x 4m , also 3m high ). I want to use 1 AC for this area. BTU recommendations?

Yes, I know there are sizing charts online....wondering on real life what worked.
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Re: AC Sizing

Postby Klondyke » Tue Oct 03, 2017 6:48 pm

It surely will be enough if you do not want freeze with 18 deg.C. However, in the shops they will advise you for a bigger type...
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Re: AC Sizing

Postby Sometimewoodworker » Wed Oct 04, 2017 5:10 pm

claynlr wrote:Hello Building Board-

Building a small 1 bedroom bungalow consisting of 15 cm q-con walls, gypsum ceiling with R-37, 6" staycool above, colorbond roof sprayed with 1" foam to the underside, soffit vents for attic intake and whirlybirds for exhaust. As far as AC sizing, The 4m x 4m x 3m (ceiling ht.) bedroom I know will be the minimum 9000btu. The kitchen/dining/ living room is an L-shaped ( consisting of 3- 4m x 4m , also 3m high ). I want to use 1 AC for this area. BTU recommendations?

Yes, I know there are sizing charts online....wondering on real life what worked.

If you could get a smaller than 9000btu unit, assuming you don't want to drop more than 10 to 15 degrees, I would do it. Our non insulated cinder block wall bedroom has a 9000btu unit and it's almost overkill, we should have got an inverter but as we may well leave it behind I wasn't sure of the ROI.

As to the other area it's difficult to say the thing you want to be careful of is oversizing even with an inverter. I would be inclined to go for a maximum of an 18,000 BTU inverter unit.

A typical inverter should be sized so that it seldom reaches either extreme of its operating range.

A regular AC should be sized so that it usually runs for at least 30 minutes, preferably longer, before getting down to the set temperature. This is because, for the first 15 minutes of run time it isn't dehumidifying, so if it cools the space fast then switches off you will probably have dust mites, mildew, mould, and humidity problems. Not to mention higher power consumption and faster wear.

Of course if you like temperatures 20 or more degrees colder than ambient, advice would change


FWIW
http://www.orionair.co.uk/Inverter_aircon_sizing.htm wrote:Typical Inverter Air Conditioning Operating Ranges:

2.5kW / 9000Btu Inverter air Conditioning units (0.9kW to 2.5kW)

3.5kW / 12000Btu Inverter air Conditioning units (0.9kW to 3.7kW)

5.0kW / 17000Btu Inverter air Conditioning units (1.3kW to 5.4kW)

7.0kW / 24000Btu Inverter air Conditioning units (1.9kW to
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Re: AC Sizing

Postby Roger Ramjet » Thu Oct 05, 2017 12:11 am

claynlr wrote:Yes, I know there are sizing charts online....wondering on real life what worked.

If you find a good A/C shop and they come out and measure, they should also recommend the correct size.
Make sure you point out that the walls and ceiling are insulated, which is the normal reason why they go for overkill as Thai houses rarely are. I have three inverter A/C units and all are now 4 years old (Mitsubishi) and are serviced every 6 months. We have had absolutely no problems with any of them except a burnt out thermostat on the 9,000 BTU one that was replaced from their truck. If the A/C appears not to be functioning properly it's a simple matter of opening the front panel and checking the filter isn't clogged and if it is, a hit with the pressure cleaner will fix that quickly.
Inverters are the way to go, they are quick, silent and if you set them to dehumidify that's just what they do. They do it quickly and then settle down to just the fan running. Our electricity bill is less that our townhouse which has only two A/Cs and this house is three times the size.
Just make sure the A/C people understand that everything is insulated and you should get a reasonable quote without them adding in the "Thai factor". All decent A/Cs have a filter that is EPA recognised so if you have bed bugs etc, it didn't come from the A/C.
We use satin/cotton sheets so we don't have that problem anyway.
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Re: AC Sizing

Postby claynlr » Fri Oct 06, 2017 12:48 pm

Thanks guys. From reading other posts, it sounds like Mitsubishi and Daiken inverters are top rated by most posters. Will check those out. Getting the spray foam done today.
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Re: AC Sizing

Postby Andyfteeze » Sat Oct 07, 2017 6:12 pm

I second what roger said. We have a 9000btu daikin for bed room and even thats too much. (30m2) We have a daikin 18,000btu for the living area (60m2) and it works well. This part of the house has no insulation. In my music room, 40m2, i have put a 9000btu unit. I was threatened with all sorts of s**t like no warranty, unit is too small. But this room has like a refrigerator standard insulation make up. Cant test it yet till we get power this week.
If your walls are going to radiate, you will need to go thai style. But any reasonablly insulated area will not need a massive system.
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Re: AC Sizing

Postby Ians » Sun Oct 08, 2017 3:33 pm

It seems that most suppliers go for over-kill, when it comes to AC units - "bigger is not better", especially in your case when you have as well insulated home.
Plenty calculation data about, and if the calculation indicates you are on the upper limit, I wouldn't just jump to the next size without due consideration. In our main bedroom we were a bit above the max. volume and went against the supplier who was insisting on the next size unit - our choice was the correct one, the room is very comfortable even the hottest nights (mainly only evening use) and is sufficient during the odd times it is used during the daytime.
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Re: AC Sizing

Postby Cheeryble » Fri Oct 20, 2017 2:21 pm

Sure standard sizing must cater for the worst case scenario, i.e. bottom temp (18deg?) on the hottest part of the year.

As Ive lived almost without aircon for 15 years here I will be more than happy to get 25deg and will always undersize a lot, knowing a fan can be used to supplement.
I was in a supplier yesterday and asked about the BTU for 80sqm, not great insulation, but with very little direct sun in the roof windows and walls. (They had a deal buy an 18, get a 12 free.)
He made no adjustment for no window sun and told me 55kBTU.
I'm thinking the 18 and a 12 will do fine.
Agreed?
(LG, have to install myself, 28900bt the pair........can I do better?)
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