A/C Sizing Chart

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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Re: A/C Sizing Chart

Postby claynlr » Thu Oct 30, 2014 7:52 pm

Pip-

Ran that formula and came up with 54,852 which is about 3 times what all the other calculators say. Am I doing something wrong?
64 m2 divided by 14=4.571
4.571 x 12,000=54,852BTU
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Re: A/C Sizing Chart

Postby pipoz » Thu Oct 30, 2014 9:29 pm

claynlr wrote:Pip-

Ran that formula and came up with 54,852 which is about 3 times what all the other calculators say. Am I doing something wrong?
64 m2 divided by 14=4.571
4.571 x 12,000=54,852BTU


No your calculation is correct.

This is just a rule of thumb formula that my old MEP Engineer gave me, but then we are in the Middle East, not in Thailand and our outside air temperature is some 15-20 higher in mid summer. The lounge in this Villa is 54 m2 (with 3 m high ceilings) hand we run 2 x 24,000 BTU Westinghouse AC Splits, that 48,000 BTUs for 54m2.

There are portably other formulas on the web, that apply more to tropical areas, which I suspect may suggest less BTU's per m2. I found one that suggested 24,000 would do 55m2, which tends to indicates you would only need around 28,000 BTU for your 64 m2 in a tropical area?

Yes my run of thumb formula is conservative, but as I said, I like to cool the room down quickly and my ceilings are high

I will check the formula again with him, as maybe I stuffed it the formula.

Ian's will probably know

The key when you install the splits, is to make sure outdoor compressor/condenser unit, has good air flow around/through it. Don't hide it in a dead corner and regularly clean out the outdoor unit condenser fin part


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Re: A/C Sizing Chart

Postby Klondyke » Thu Oct 30, 2014 11:16 pm

I have 50m2 with 3 sliding windows 110/140cm (not very tight) and glass outside door, inside door opening without door to another room, the ceiling to the flat roof not overly insulated, 2 ouside walls are by double block. It is serviced by 24,000 BTU.

(in fact, the cooling capacity is not given much by the room area (m2) but more by the surface area connected to the heat source (outside walls, ceiling).

Have to admit that we do not cool too much down to zero Celsius. And in case it is not enough the fireplace will help a lot :D

Image


Image
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Re: A/C Sizing Chart

Postby Sometimewoodworker » Fri Oct 31, 2014 5:11 pm

claynlr wrote:Pip-

Ran that formula and came up with 54,852 which is about 3 times what all the other calculators say. Am I doing something wrong?
64 m2 divided by 14=4.571
4.571 x 12,000=54,852BTU

No accordion to pipoz it is about right. But his calculations more than double what most people would use. If you go up to Jazman's post it works out to about 2/5 of pipoz.

Don't forget that over sizing aircon is a bad idea as it can't dry out the air if it cools too fast. And you need a lower air temperature to feel comfortable if the humidity is high.
image.jpg

image.jpg


As everyone has their own idea of what is good then that is an even bigger reason to go for 2 (or more) smaller units.
You can always fit a second unit if the first is undersized.


Just for interest we have just got a 9,000BTU Mr Slim including fitting from a shop in Udon 60km away for 16,400 Bhat (500 Bhat discount for installation on a day of their choice)
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Re: A/C Sizing Chart

Postby Klondyke » Sat Nov 01, 2014 11:32 am

I too have been buying for most of my rooms 9000 (9,600?) BTU and it has been always enough even for rooms of different areas. Then the start of the compressor does not disturb the other electrical distribution, it is only some 800 W motor.

Of course we never run under 25 C. Only Thai people mostly do not regard the temperature adjusting, they just turn the controller down to minimum (18C) for the whole year. I always say that the a/c (and the stereo speakers as well) are sold in Thailand without such nonsense as temperature and volume controller, nobody needs it.

For sleeping - when with a/c (in the North not necessarilly needed for every night) - is good to leave a small gap at the window for oxygen exchange and so the air does not get too dry.
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Re: A/C Sizing Chart

Postby pipoz » Sat Nov 01, 2014 2:41 pm

I might have to rethink my numbers and lower my BTUs per room down

Over here where I am, and this is for a hotter climate although the humidity is much less. Its much more dry and the temperature is constantly above 30 and 40C, during the day

Room 1: I am in a room 6.2 x 4.3 m = 26.2 m2 and it is services by a AC Split of 2.0 Ton or 24,000 BTU and it fine, in fact often a little too cold. Ceiling height is 2.6 meters, hence the Room Volume is 68 m3. So as far as averages go, that’s BTU 353 per cubic meter or BTU 916 per square meter of floor area, and room is often a little to cold.

Room 2 : The adjacent room is larger at 8.25 x 7.2 = 59.4 m2 and has two AC Splits of 2.0 Ton or total 48,000. Ceiling height is 2.6 meters, hence the Room Volume is 154 m3. So as far as averages go, that’s BTU 311 per cubic meter or BTU 808 per square meter of floor area.

So I will use the less of the two figures BTU 311 per cubic meter or BTU 808 per square meter of floor area. Rooms 1 and 2 both have
About 1.8 m2 of glass window facing exposed to the sun, with no external shade cover, only internal blinds
Both rooms have good insulation over the ceiling area, namely a concrete slab above, so the only direct heat is via the glass area of the window.
Both have a single door entry

Persons: Room 1 generally has one-two persons and Room 2 can have up to 10.


So for my Building in Udon Thani, if I was to adopt the same (lowest) average rates/ principal (and I think these averages are a little high for the Udon climate), as a maximum I would need,

UT Main Bedroom - 2 person, 3 if she is open minded?: 9.0 x 4.0 x 3.15m = 113.40 m3 x 311 BTU = Total 35,267
UT Living Area - 4 person, 2 sets of large open doors 6.5 x 6.0 x 3.15m = 122.85 m3 x 311 BTU = Total 38,206
UT Bedroom No 2 - 2 persons: 5.0 x 4.0 x 3.15m = 63.00 m3 x 311 BTU = Total 19,593
UT Bedroom No 3 - 2 persons: 4.0 x 4.0 x 3.15m = 50.40 m3 x 311 BTU = Total 15,674

I guess, given the difference in climate between where I am (much hotter)and Udon Thani, and also keeping in mind that AC's are mostly used mostly at night in Udon Thani when the outside temperature is heading towards its lowest, and not all Thais like AC, then I could probably drop my BTU numbers by another 15%, and target an average BTU number of 265 BTU's per cubic meter of room volume .

How does this measure with others up around Udon Thani, with sizing their ACs

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Re: A/C Sizing Chart

Postby Sometimewoodworker » Sun Nov 02, 2014 5:33 am

pipoz wrote:
UT Main Bedroom - 2 person, 3 if she is open minded?: 9.0 x 4.0 x 3.15m = 113.40 m3 x 311 BTU = Total 35,267
UT Living Area - 4 person, 2 sets of large open doors 6.5 x 6.0 x 3.15m = 122.85 m3 x 311 BTU = Total 38,206
UT Bedroom No 2 - 2 persons: 5.0 x 4.0 x 3.15m = 63.00 m3 x 311 BTU = Total 19,593
UT Bedroom No 3 - 2 persons: 4.0 x 4.0 x 3.15m = 50.40 m3 x 311 BTU = Total 15,674

I guess, given the difference in climate between where I am (much hotter)and Udon Thani, and also keeping in mind that AC's are mostly used mostly at night in Udon Thani when the outside temperature is heading towards its lowest, and not all Thais like AC, then I could probably drop my BTU numbers by another 15%, and target an average BTU number of 265 BTU's per cubic meter of room volume .

How does this measure with others up around Udon Thani, with sizing their ACs

pipoz


It still looks to be twice as much as I would put in. We have a 4.0 x 4.0 room and I think that the smallest I can get is still oversized, probably by 40%, and that's without planning on fan use.


I will be able to let you know in a few days time as SWBMO's getting a 9,000 unit installed today, we hope, but there's no glass in the windows until later in the week.

http://www.calculator.net/btu-calculator.html?roomwidth=4&roomwidthunit=meters&roomlength=4&roomlengthunit=meters&ceilingheight=3.15&ceilingheightunit=meters&insulation=poor&temperature=10&temperatureunit=c&calctype=heat&x=79&y=11

image.jpg


The other point is that you can, and probably should, still use fans. We are going to plan on fan + AC and this will drop the sizes needed even further.
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Re: A/C Sizing Chart

Postby pipoz » Sun Nov 02, 2014 10:48 am

Sometimewoodworker wrote:
pipoz wrote:
UT Main Bedroom - 2 person, 3 if she is open minded?: 9.0 x 4.0 x 3.15m = 113.40 m3 x 311 BTU = Total 35,267
UT Living Area - 4 person, 2 sets of large open doors 6.5 x 6.0 x 3.15m = 122.85 m3 x 311 BTU = Total 38,206
UT Bedroom No 2 - 2 persons: 5.0 x 4.0 x 3.15m = 63.00 m3 x 311 BTU = Total 19,593
UT Bedroom No 3 - 2 persons: 4.0 x 4.0 x 3.15m = 50.40 m3 x 311 BTU = Total 15,674

I guess, given the difference in climate between where I am (much hotter)and Udon Thani, and also keeping in mind that AC's are mostly used mostly at night in Udon Thani when the outside temperature is heading towards its lowest, and not all Thais like AC, then I could probably drop my BTU numbers by another 15%, and target an average BTU number of 265 BTU's per cubic meter of room volume .

How does this measure with others up around Udon Thani, with sizing their ACs

pipoz


It still looks to be twice as much as I would put in. We have a 4.0 x 4.0 room and I think that the smallest I can get is still oversized, probably by 40%, and that's without planning on fan use.


I will be able to let you know in a few days time as SWBMO's getting a 9,000 unit installed today, we hope, but there's no glass in the windows until later in the week.

http://www.calculator.net/btu-calculator.html?roomwidth=4&roomwidthunit=meters&roomlength=4&roomlengthunit=meters&ceilingheight=3.15&ceilingheightunit=meters&insulation=poor&temperature=10&temperatureunit=c&calctype=heat&x=79&y=11

image.jpg


The other point is that you can, and probably should, still use fans. We are going to plan on fan + AC and this will drop the sizes needed even further.


Agree, its still looks heavy compared to what the on line calculators and others say, and as I said I would probably trim 15% maybe more off, because this is the ME and not Thailand. Nevertheless, these are the AC sizes where I am sitting in over here.

So far I have only put one AC in a house in Thailand and it was a Samsung BTU 18,000 in a bedroom of some 15 m2 and it has worked great for 3 years, but according to the calculators it should only be around 9,000
,
Guess I will have to check out a real live home down in Thailand. If your 9000 works, in your 16m2 please let me know

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Re: A/C Sizing Chart

Postby Sometimewoodworker » Sun Nov 02, 2014 5:41 pm

pipoz wrote:
So far I have only put one AC in a house in Thailand and it was a Samsung BTU 18,000 in a bedroom of some 15 m2 and it has worked great for 3 years, but according to the calculators it should only be around 9,000

What do you mean by that has worked great? Do you mean it gets cold quickly and then turns off? Do you mean that when it comes on it gets down to temperature quickly and turns off?

If that's what you mean then I wouldn't say that it works very well. It will certainly get the room cool. But that doesn't mean to say that it's working very well. It really needs to work for quite a time to drop the humidity.

As to the units you've currently got where you are. Do you know how old they are? Do you know how often they've been cleaned? If they're older and aren't cleaned often and then they're probably not working as well as they can.

Cycling 3 to 4 times an hour in warm weather and virtually non stop when it's really hot and your aircon is correctly sized.

If you have really hot weather and the AC is still cycling you are oversized. If your AC never runs non stop you are oversized.
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Re: A/C Sizing Chart

Postby Roger Ramjet » Sun Nov 02, 2014 9:21 pm

Sometimewoodworker wrote:If you have really hot weather and the AC is still cycling you are oversized. If your AC never runs non stop you are oversized.

None of my air conditioners run non-stop in the hot weather. They were not designed to do that, perhaps because they are inverter air conditioning units?
My three units have been serviced every six months and are less than two - three years old. I put a dehumidifier unit in the main bedroom to see how effective they really were and it took zip out of the air in a four hour run. Air conditioning units are not designed to run the whole time.
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Re: A/C Sizing Chart

Postby pipoz » Sun Nov 02, 2014 9:38 pm

Sometimewoodworker wrote:
pipoz wrote:
So far I have only put one AC in a house in Thailand and it was a Samsung BTU 18,000 in a bedroom of some 15 m2 and it has worked great for 3 years, but according to the calculators it should only be around 9,000

What do you mean by that has worked great? Do you mean it gets cold quickly and then turns off? Do you mean that when it comes on it gets down to temperature quickly and turns off?

If that's what you mean then I wouldn't say that it works very well. It will certainly get the room cool. But that doesn't mean to say that it's working very well. It really needs to work for quite a time to drop the humidity.

As to the units you've currently got where you are. Do you know how old they are? Do you know how often they've been cleaned? If they're older and aren't cleaned often and then they're probably not working as well as they can.

Cycling 3 to 4 times an hour in warm weather and virtually non stop when it's really hot and your aircon is correctly sized.

If you have really hot weather and the AC is still cycling you are oversized. If your AC never runs non stop you are oversized.


I meant it (the Samsung in Thailand) cools the room quickly like in 10 minutes and keeps it at a steady 19C which I like all night. Not sure whether it turns itself on or off, never noticed. Haven't had to re-gas or do anything to it, other than wash out the filter, in three years. So I don't really know if it working well or at it optimum. Just know that it is comfortable for me when sleeping.

The 0ffice ones here (as per my post on 01 Nov) are only 12 months old, so will need to wait and see how they last or perform long term. They are "General Brand".

The Villa ones (that I mentioned in my post on 30 Oct) are 3 years old Westinghouse AC Splits. Good cooling units, but at the two year mark we had to replace all the Capacitors at US 70 each per unit. Plus they are near impossible to clean the drain lines if the clog up. You near need to strip the Evaporator apart to clean that drain line, so for this reason I would recommend buying a Westinghouse AC Split.

I will try and check the cycle times per hour, thanks

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Re: A/C Sizing Chart

Postby Sometimewoodworker » Sun Nov 02, 2014 9:38 pm

Roger Ramjet wrote:
Sometimewoodworker wrote:If you have really hot weather and the AC is still cycling you are oversized. If your AC never runs non stop you are oversized.

None of my air conditioners run non-stop in the hot weather. They were not designed to do that, perhaps because they are inverter air conditioning units?
My three units have been serviced every six months and are less than two - three years old. I put a dehumidifier unit in the main bedroom to see how effective they really were and it took zip out of the air in a four hour run. Air conditioning units are not designed to run the whole time.

Sorry that is not correct.

When the airconditioner is correctly sized then at the hottest time of day at the hottest time of year you should get run times of several hours.

If they are still cycling during the hottest time of day at the hottest time of year they are oversized, and being inverters makes no difference.

The best way to check humidity is with a meter.

http://www.ccacac.com/23/how-long-should-my-ac-run/
http://www.ccacac.com/maintenance-tips/tips/bigger-is-not-better/
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Re: A/C Sizing Chart

Postby Roger Ramjet » Sun Nov 02, 2014 10:27 pm

Sometimewoodworker wrote:When the airconditioner is correctly sized then at the hottest time of day at the hottest time of year you should get run times of several hours.

Not true at all, it is the speed of the fan/compressor and amount of refrigerant coolant that goes through the system.
http://www.airconditioner.me.uk/Benefit ... oning.html
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Re: A/C Sizing Chart

Postby Sometimewoodworker » Sun Nov 02, 2014 10:38 pm

Roger Ramjet wrote:
Sometimewoodworker wrote:When the airconditioner is correctly sized then at the hottest time of day at the hottest time of year you should get run times of several hours.

Not true at all, it is the speed of the fan/compressor and amount of refrigerant coolant that goes through the system.
http://www.airconditioner.me.uk/Benefit ... oning.html


No. I'm not wrong. You are talking about times when the unit is not working at its maximum.

If air conditioner units never operate at maximum they are oversized.
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Re: A/C Sizing Chart

Postby Roger Ramjet » Mon Nov 03, 2014 12:00 am

Sometimewoodworker wrote:If air conditioner units never operate at maximum they are oversized.

Could you please show me one professional website that says that?
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