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Thread: AC Sizing

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    AC Sizing

    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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    12,000 BTU Inverter would suffice?

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    9,000 BTU enough, unless you are Thai who likes always 18 deg only... (but do not ask for advice in the shop)

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    Quote Originally Posted by jabir View Post
    Very good tool!

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    The international value is 100 Wh per sqm (about 340 BTU). HomePro etc. recommend much higher values. The reason is that Thai people want to cool down their hot condos (because of bd design and build quality without insulation) within some minutes.

    I use a 19,000 BTU (Samsung inverter) unit for my 64 sqm big office in a conventional townhouse since 3 years and it works great. I use it together with ceiling fans. Perhaps I would change it to 2 smaller units for better distribution.

    As others, I highly recommend a inverter unit. These are a little bit more expensive, but save a lot of energy and are also quieter than standard units. The inverter AC adjust the power consumption ans so the AC seldom runs on full power. My 19,000 BTU units runs about on 40% according to the electric bill.

    Modern inverter AC also have an intelligent cooling principle. They cool fast, first and then reduce the power and dry the air. So you don't have to adjust the AC. Some brands offer to control the AC by your phone. So you cam start the AC about 30 minutes before entering you house/condo.

    A good insulation of the house (ceiling, walls, windows, shading) not also reduces the electric bill. The room is also more comfortable.

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    Quote Originally Posted by Airportwo View Post
    12,000 BTU Inverter would suffice?
    Should.

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    Quote Originally Posted by Luigi View Post
    Should.
    Should - maybe? there are so many variables, how cool does the OP want the room to be 28c or 18c, windows, a lot or a few, are they south facing, is the room South facing? I would rather oversize than go too small, so 12k BTU 'should' be ample, though if the room is a dark North facing room with no windows, well insulated and the OP is content with 28c 9k BTU would be ample? The difference in price and running costs between 9k or 12k is also minimal which is another reason I would go for the larger sized unit, I would also buy a Daikin AC from Lazada and get fitted as far cheaper than going to a 'shop"

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    Quote Originally Posted by juehoe View Post
    The international value is 100 Wh per sqm (about 340 BTU). HomePro etc. recommend much higher values.
    There are so many other deciding factors - as correctly pointed out above - than BTU/sqm...

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    Quote Originally Posted by claynlr View Post
    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.

    I would say 160 watts per square metre for rooms with north or south facing walls. with standard windows. Rooms with east and west facing walls with larger windows use 180 - 200 watts per square metre. L shaped rooms tend to have dead air spaces in the part where the cooling unit is not blowing directly. I would suggest 2 separate units as you may be only sitting in one section and the other section of the L shape will be cooled for nothing. The initial purchase cost will be higher but running costs will be lower than a multi head unit if you are only running one of the 2 systems. Failing that a multi head unit with 2 indoor coils and 1 outdoor unit controlling both.
    When weighing up the merits of an inverter weight up how many hours per day the unit will be used as opposed to the difference in cost between an inverter and a standard unit. Sometimes the cost difference is not justified on a unit that is used sparingly. Also an inverter is more sensitive to breakdown from power surges/fluctuations. Check the quality of your local power supply as failures due to power supply faults are not covered under warranty and an inverter replacement can be very expensive. Some compressors have the inverter "built on" which means they are both replaced if either fails, again a very expensive repair. Be careful of the brand many are poor quality and hard to get warranty with poor parts availability. I have known of people waiting on parts for 8 to 12 weeks. I would suggest Panasonic or Mitsubishi electric. Use an authorised service agent if possible as you have more accountability from these companies, unless you know of a good local installer.

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