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Formula To Calculate Btu For Aircon?


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#1 tartempion

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Posted 2006-12-01 18:15:04

What is the formula to calculate required BTU for airconditioning?

I have a 4*5*2.8m bedroom, approx 60m3
I did build a double westwall and will insulate the ceiling with fiberglass, that should reduce electricity bill.

Thanks.

Edited by tartempion, 2006-12-01 18:17:07.


#2 Nawtilus

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Posted 2006-12-01 19:06:18

I have been told a couple of times now by seperate aircon guys, multiply the area by 700.....so 60sqm x 700 = 42,000

Thats a big sucker ?? I just saw you said 60 cubic meters, so if the bedroom is 4m x 5m = 20sqm x 700 = 14000btu, thats more like it.

#3 worzel

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Posted 2006-12-01 19:08:58

hi ya i was a plumber in the uk i now its differant but sure same applies . when working out radiator btu requirements we used a thing called a meires calculator (like a little disc) which takes into accont room size structure of walls floors ect iam sure air con engineers use similar diffice as formula is very complex beat of luck

#4 PeaceBlondie

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Posted 2006-12-01 19:38:45

Some of the variables include glass windows (and whether the glass is insulated), curtains, exposure to the south or west, whether areas outside the area to be cooled are also cooled, thickness of insulation, humidity conditions, etc.

I had a huge room with roughly 10 square meters of thin glass facing west, another 15 sq. mt. of glass facing north and east, two showers, etc. I decided not to buy 59,000 BTU of air con.

#5 think_too_mut

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Posted 2006-12-01 19:45:11

That's the beauty of Japan.

Each house/apartment has floor plans and how many tatamis each room covers. In print and schemes.

Aircons have the stickers on them what they are capable to heat/cool.

Just faxed to the shop what I have and adequate hardware came in, their staff mounted it and all perfect. No tips, just their job.

#6 tutsiwarrior

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Posted 2006-12-02 12:25:39

A/C load calculations are straightforward...do a google on ASHRAE or Carrier. However, thermal conductivities related to building materials, insulation are important. To illustrate, I installed a 2 ton split unit in my bedroom without ceiling insulation. During the hot months you could only feel it if you were standing directly in front. I wised up and installed 6" fiberglass blankets in the roof space with a hugely significant inside temperature difference due to the 'R' value of the insulation. Now I just use the A/C to sleep and can make do with just a fan during the day. Before I had to spend all day downstairs as the bedroom was a hotbox, even with the A/C.

Take the time to consider these little things and you will be amazed about the money you will save on A/C power costs...

#7 China Lady

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Posted 2006-12-02 12:27:28

That's the beauty of Japan.

Each house/apartment has floor plans and how many tatamis each room covers. In print and schemes.

Aircons have the stickers on them what they are capable to heat/cool.

Just faxed to the shop what I have and adequate hardware came in, their staff mounted it and all perfect. No tips, just their job.



Do any of you know a comprehensive means to calculate requirements here in Thailand - based on the above it is difficult to calculate requirements.

Surely there is a ball park means to finding the requirements

BKC

#8 think_too_mut

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Posted 2006-12-02 18:22:14


That's the beauty of Japan.

Each house/apartment has floor plans and how many tatamis each room covers. In print and schemes.

Aircons have the stickers on them what they are capable to heat/cool.

Just faxed to the shop what I have and adequate hardware came in, their staff mounted it and all perfect. No tips, just their job.



Do any of you know a comprehensive means to calculate requirements here in Thailand - based on the above it is difficult to calculate requirements.

Surely there is a ball park means to finding the requirements

BKC


The staff manning the aircon department in the stores should be able to tell you on the spot what you need.

Then, anyone can google it and find something like this:

As a guide to the cooling capacity required in British Thermal Units (BTU's), calculate the volume of your room ie length x width x height (in feet). As a general rule of thumb, each cubic foot of space requires 5 BTU's of cooling capacity, so you need to multiply the volume by 5.


In addition, you need to add in the heat gain from other sources. These include people (400 BTU's each if there are more than two in the room) as well as computers and photocopiers (400 BTU's each).


For example, a room 10ft x 20ft x 8ft = 1600 x 5 = 8000 BTU's. With three people in the room, add 1 x 400 = 8400 BTU's. Add three PC's, 3 x 400 = 9600 BTU's total.

#9 ezzra

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Posted 2006-12-03 12:46:46

The staff manning the air-con department in the stores should be able to tell you on the spot what you need.
:o :D :D

you should consider the position of the room and the room widows as to the directions,
i.e. facing the heat from the sun, that make a lot of different to the a/c cooling capacity,

















That's the beauty of Japan.

Each house/apartment has floor plans and how many tatamis each room covers. In print and schemes.

Aircons have the stickers on them what they are capable to heat/cool.

Just faxed to the shop what I have and adequate hardware came in, their staff mounted it and all perfect. No tips, just their job.



Do any of you know a comprehensive means to calculate requirements here in Thailand - based on the above it is difficult to calculate requirements.

Surely there is a ball park means to finding the requirements

BKC


The staff manning the aircon department in the stores should be able to tell you on the spot what you need.

Then, anyone can google it and find something like this:

As a guide to the cooling capacity required in British Thermal Units (BTU's), calculate the volume of your room ie length x width x height (in feet). As a general rule of thumb, each cubic foot of space requires 5 BTU's of cooling capacity, so you need to multiply the volume by 5.


In addition, you need to add in the heat gain from other sources. These include people (400 BTU's each if there are more than two in the room) as well as computers and photocopiers (400 BTU's each).


For example, a room 10ft x 20ft x 8ft = 1600 x 5 = 8000 BTU's. With three people in the room, add 1 x 400 = 8400 BTU's. Add three PC's, 3 x 400 = 9600 BTU's total.



#10 PeaceBlondie

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Posted 2006-12-03 13:05:29

That general rule of thumb, 5 BTU per cubic foot: is that for Calgary, or Phuket?

#11 think_too_mut

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Posted 2006-12-03 16:06:55

That general rule of thumb, 5 BTU per cubic foot: is that for Calgary, or Phuket?


I googled it, did not even read carefully what it says. It was an example out of thousand serch results.

The remote control for the aircon in here in the room has almost as many buttons as a TV remote.

Now, 2 are important: heating or cooling.

25C in the winter is heating. In the summer when it is 45C outside it's good cooling. A switch on the remote tells the unit whether maintain the temp by heating or by cooling.

The BTU sticker on the aircons did not say what they are worth in winter and what in summer. So I guess, they should be as good in Calgary as in Phuket.
Winter here can bring some snow or you can have 5-8C for months. Insummer it can stretch into 2-3 months of over 40C.

Edited by think_too_mut, 2006-12-03 16:11:36.


#12 Nawtilus

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Posted 2006-12-03 19:17:46

Anyone know what the electric cost is for these units per hour, however it is calculated for the various sized untis etc.

#13 think_too_mut

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Posted 2006-12-03 19:38:28

Anyone know what the electric cost is for these units per hour, however it is calculated for the various sized untis etc.


I just looked at the sticker on the bigger aircon that I have here. There are figures in kW, it's kanji what they are for, sorry, can't read it.
There are 8 of them, ranging from 0.62kW ph to 5.2kW per hour.

I guess, depends what you want them to do. The lowest one could be, the aircon is serving as a plain fan, just shuffling the air. The highest one (5.2kW) could be to maintain 15C or whatever while it is 45C outside.

Edit: there were more figures, the highest one is not 3.8, it is 5.2kW per hour.

So, the worst case scenario with this model of aircon would be (if you pay electricity directly, at 2.2B per unit) = 11.44 Baht per hour. More likely, half or near half that.

Then, if you use it under the haviest possible load, 10 hours per day, you get the picture: 3300B per month or so.

Edited by think_too_mut, 2006-12-03 19:51:02.


#14 Naam

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Posted 2006-12-03 20:35:51

"I guess, depends what you want them to do"

******

stop guessing, try to write more science fiction (as in your posting) and make some money with it.

:o

#15 think_too_mut

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Posted 2006-12-03 20:41:59

"I guess, depends what you want them to do"

******

stop guessing, try to write more science fiction (as in your posting) and make some money with it.

:o


It's a science fiction for you? Appliances ?

Start with a toaster, look at it for a day, try to understand it.

If it is too complicated, go with a laddle.

Edited by think_too_mut, 2006-12-03 21:00:43.


#16 astral

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Posted 2006-12-06 10:59:00

The staff manning the air-con department in the stores should be able to tell you on the spot what you need.
:o :D :D

Do not buy in a department store.
Check with a local shop that specialises in AC units and take his advice.
He will also be able to install and later maintain the unit.

#17 Nawtilus

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Posted 2006-12-06 18:07:59

Thats right, but also check sevral of these small stores, prices vary a lot.

I had house plans with me some time ago when i was in HonePro looking at kitchens, out of interest while I was there, I gave them to the aircon dept, asked them to calculate how many units needed, they told me 15.....I could not help myself but giggle just a little bit.

#18 wpcoe

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Posted 2006-12-06 21:44:51

I had house plans with me some time ago when i was in HonePro looking at kitchens, out of interest while I was there, I gave them to the aircon dept, asked them to calculate how many units needed, they told me 15.....I could not help myself but giggle just a little bit.

Welcome to Home Pro/KanYong/HomeWorks. The folks working the sales floor are mostly useless. I guess the stores think they can make up in quantity (# of people staring at you) what they fail to provide in quality (very few of them have credible product knowledge).

Example: I went to the tile section of Home Pro looking for grout. After pantomiming (anybody know the Thai word for "grout"? <g>) and pointing to the floor tiles under our very feet, they called in the store "Interpreter". They said they "no have" grout. I later found a huge display rack of grouts less than ten feet from where were standing. Then, I wanted the tool to spread it. They pointed to metal putty knives insisting that's what I needed.

I once wanted just a plain white paint for the doors in my condo. The paint pro, wearing a paint company-sponsored shirt, insisted that a gallon of paint base (the base they use to make custom colors) would work. I stupidly believed him until I had to scrape off the paint to be able to apply a proper paint and still be able to close the door.

I've had the same type of experiences at HomeWorks and KanYong. I could go on, but I won't...

#19 mtcone

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Posted 2008-05-20 23:39:12

I think all you need to do is use a Heat Load Calculator. That should tell you how many BTUs are required.

#20 elkangorito

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Posted 2008-05-21 00:58:20

My comments in blue.


That's the beauty of Japan.

Each house/apartment has floor plans and how many tatamis each room covers. In print and schemes.

Aircons have the stickers on them what they are capable to heat/cool.

Just faxed to the shop what I have and adequate hardware came in, their staff mounted it and all perfect. No tips, just their job.



Do any of you know a comprehensive means to calculate requirements here in Thailand - based on the above it is difficult to calculate requirements.

Surely there is a ball park means to finding the requirements

BKC


The staff manning the aircon department in the stores should be able to tell you on the spot what you need.
What a joke.

Then, anyone can google it and find something like this:

As a guide to the cooling capacity required in British Thermal Units (BTU's), calculate the volume of your room ie length x width x height (in feet). As a general rule of thumb, each cubic foot of space requires 5 BTU's of cooling capacity, so you need to multiply the volume by 5.
I suppose you could "google" electrical requirements too.......NOT!!!!


In addition, you need to add in the heat gain from other sources. These include people (400 BTU's each if there are more than two in the room) as well as computers and photocopiers (400 BTU's each).
Is this why each country has its' own "regional" method for calculating heat gain? BTW, Australia (Northern States & Territories) have weather conditions very similar or the same (if in far North Queensland or Northern Territory) to Thailand.


For example, a room 10ft x 20ft x 8ft = 1600 x 5 = 8000 BTU's. With three people in the room, add 1 x 400 = 8400 BTU's. Add three PC's, 3 x 400 = 9600 BTU's total.


Geez, one Australian contractor I have used in the past, spent over $1000.00 for some software to do his calculations for him. I asked him why did he did such a thing, if he could calculate things himself. He told me that he would spend more than quadruple the time on calculations if he had to do them "by hand", for the same result. He also told me that his money was well spent.
I guess this means that "google" is really accurate. :o

This whole thread is not only hilarious, it's nonsensical. Too much guessing....not enough engineering "fact". BTW, you have to PAY for engineering fact, less stick with the "guesswork".


#21 Crossy

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Posted 2008-05-21 07:50:09

OK, let's try and bring a tad of common sense into this thread. I would agree with Elkangorito IF we were talking about an industrial/office environment where the calculations are very complex and getting it wrong could cost huge amounts of cash.

BUT

We're talking about a domestic enviroment where the calculations ought to be a lot simpler. This thread http://www.thaivisa....howtopic=185082 shows a simple table as apparently used by Homepro.

Obviously such a simple 'calculator' has to make a lot of assumptions. Since it was obtained in Thailand I think we can safely assume that values for things like:-
  • Temperature differential
  • Wall insulation
  • Roof insulation
  • Window ratio and (lack of) insulation (not double glazed)
  • Insolation (yes that is the correct word)
  • etc etc etc
have sensible values for 'normal' usage (whatever that is) and local construction methods.

Obviously if we have unusual conditions such as lots of people, lots of computers, a kitchen or other heat generators then all bets are off and you (or the professionals you've called in) have to get out the expensive software.

Using the table, our OP's bedroom at 20m2 comes out at the top end of the 12,000 BTU range. I would suggest that since this is a bedroom then a 12k unit would do the job fine. A 9k may also be ok since the room will be occupied at night (when it's cooler) and people don't tend to generate much heat when in bed (at least when they're sleeping :D ), supported by the fact that our bedroom is slightly bigger (25m2) and the 12k unit we have makes it positively freezing if left to its own devices, that said, neither my wife or myself like it particularly cool at night anyway.

A couple of points:-
If you're one of those (Naam) who likes arctic aircon then you're obviously going to need a bigger unit.
If you have huge south facing windows with no shading you'll need a bigger unit.
Use several small units rather than a single large one if you have a big room. It makes for more even cooling and if you don't need all the capacity you can run just one unit, this is more efficient than running a big cooler at tick-over and you'll get a better de-humidifying effect meaning you feel comfortable at higher temperatures and thus saves even more money :o

Install ceiling fans, they make a massive difference even when turning slowly, we rarely use the aircon in the lounge, just have the windows open and the fans on speed 1 (anything higher is like being near a Chinook on takeoff).

Finally, if you have a 'special' situation (such as big windows etc) and do call someone in to do the sums then please get your local aircon specialist rather than the goons at Homepro etc.

Edited by Crossy, 2008-05-21 08:13:39.


#22 Rimmer

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Posted 2008-05-21 09:52:13

As a rough guide.
Floor area X by 600 gives you the size of the aircon.

#23 Crossy

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Posted 2008-05-21 09:59:22

As a rough guide.
Floor area (in square metres) X by 600 gives you the size of the aircon (in BTUs).

Yup, with the modifications in red this ties up with the Homepro table :o

#24 Rimmer

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Posted 2008-05-21 11:07:17

As a rough guide.
Floor area (in square metres) X by 600 gives you the size of the aircon (in BTUs).

Yup, with the modifications in red this ties up with the Homepro table :o


Thanks for that Mr. C
When I tried to edit my post IP Stop and Start just gave me a blank page so I gave up and made a coffee instead. :D





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