Looking into AC (any engineer's out there?)

[Dakoda]

Maybe a google search is needed for this, but just wondering if there is a formula to figure out # of BTU's needed for room sizes Also does this number change if you have insulated walls and ceilings

eg: 21 sq meter room (length 5.1 x width 4.1) will need how btu's and does this number go down if you have insulated walls & ceilings?

In my rented place had 16 sq meter room with 9 BTU's, un-insulated, fact is it had brick walls, which released the heat at night, and the ceiling forget it. But the room was fine with the AC on, and it didn't need to run all the time.


help

[mackayae]

Btu/hr = room area (sq. m.) x 400
This is a ballpark figure.
There are many other variables, such as : number of windows, doors, occupants; electrical load in the room; south facing/north facing, etc.

[jetdoc]

Dakoda, I'm not an engineer but had a small company in Hawaii and did some ac/refrigeration work, mostly on boats. I had a really good manual, that had charts for calculating air-conditioner sizes and so forth. I didn't want to bring the weight and gave it away. I would think you can find info on the internet that would help. I did bring a inferred thermometer with me which makes temp. readings quick and easy. If you are dealing with ambient temps. only calculations are much simpler but, if you also have radiated heat from the walls (as I do--gets like a pizza oven in the afternoon) they become a little more complex. Feel free to pm me if you have specific questions.

[Dakoda]

but, if you also have radiated heat from the walls (as I do--gets like a pizza oven in the afternoon) they become a little more complex. Feel free to pm me if you have specific questions.

Thats like the house I rented. So come home 5 or 6, its like a pizza oven, but as the night gets later and cooler outside, the inside temp would rise.

This house has superblock walls and 3" ceiling insulation. So, I am looking to get the smallest unit for the areas, that will not be overworked. The numbers the dealer gave me, would mean I would need to get two 18k btu's. But thats a lot of money if you don't need a unit that big. Rooms are 21 and 25 sq M.

So that would be 21 * 400 = 8,400 btu/hr and 25 * 400 = 10,000 btu/hr.

So, what I am looking at is two Daikin's rated at 12,300 btu/h

Numbers they gave me (think they make more on larger units) 9k for 12 sq M , 12k for 16 sq M, 18k for 24 sq M

But by the formula Btu/hr = room area (sq. m.) x 400

looks like I could put a 9k unit in the 21 sq M bedroom and a 12k unit in the kitchen

Thanks both jetdoc and mackayae

Oh, I should also say that the house stays 6 degree's (C) cool than outside during the daytime. But when it 41 outside and inside is 36, its too dam hot

[papaguido]

I found these sites a while back. Good luck...

http://www.consumerreports.org/cro/appl ... /index.htm

http://mj-services.com/aircon/aircon-calc.php

[Dakoda]

I found these sites a while back. Good luck...

http://www.consumerreports.org/cro/appl ... /index.htm

http://mj-services.com/aircon/aircon-calc.php

Need more than luck

[jetdoc]

The good news is --- if you use the current temps. to make your calculations you will more than likely choose adequate systems. In addition to the aforementioned, consider your personal habits, for instance if you frequently entertain, you would want to consider each human emits heat equal to a 40 watt light bulb.

[TJ]

The good news is --- if you use the current temps. to make your calculations you will more than likely choose adequate systems. In addition to the aforementioned, consider your personal habits, for instance if you frequently entertain, you would want to consider each human emits heat equal to a 40 watt light bulb.

My experience is that Thai ladies are likely to be rated at higher wattage than myself. Maybe they can be blamed for global warming?

[jetdoc]

Good one TJ;o)

[jetdoc]

A easy to use calculator.

http://www.csgnetwork.com/acroomsizecalc.html



Or if a purist

Sensible Heat
The sensible heat in a heating or cooling process of air can be expressed as
hs = 1.08 q dt (1)
where
hs = sensible heat (btu/hr)
q = air volume flow (cfm, cubic feet per minute)
dt = temperature difference (oF)
Latent Heat
The latent heat due to moisture in the air can be expressed as:
hl = 0.68 q dwgr (2)
or
hl = 4,840 q dwlb (3)
where
hl= latent heat (btu/hr)
q = air volume flow (cfm, cubic feet per minute)
dwgr = humidity ratio difference (gram water/lb dry air)
dwlb = humidity ratio difference (lb water/lb dry air)
Total Heat - Latent and Sensible Heat
Total heat due to both temperature and moisture can be expressed as:
ht = 4.5 q dh (4)
where
ht= total heat (btu/hr)
q = air volume flow (cfm, cubic feet per minute)
dh = enthalpy difference (btu/lb dry air)
Total heat can also be expressed as:
ht = hs + hl

[Dakoda]

Thanks for the link. Simple to use, even I managed. First need to convert meters to feet. Everything is pointing to what I thought would be ok. As far as the bedroom, don't plan on too many people, well unless I get real lucky.

[jetdoc]

If it were me I would bump it up 10% because we are in the tropics.

[Dakoda]

I have been thinking along the lines of 2 units rated at 12,300 btu/hr. Just the numbers given by a shop wanting me to get 17,750 units. Now, thinking the bedroom will be fine with 8,900 btu/hr which is about 10% higher. Had a 9,000 unit in a 19 sq M room with brick walls and thin tiles for a ceiling and nothing else, and it was fine. Ran it for sleeping and during the day for computer @ around 28.

This place should be cheap to run the air

thanks everybody.