Sizing an A/C unit

[Swimman]

How does one determine the size of unit required for a room 10 X 5 metres which has a ceiling height of approx 4 metres?  

 

Any advice will be welcomed. 

Edited April 16, 2018 by Swimman

[BEVUP]

There are a few threads on here (but make your own mind up )

There are also aids on google

As far as I'm concerned the advice from the shops here concerning BTU ratings is rubbish ( those ratings are for the perfectly built house )

[Crossy]

The standard Thai guesstimate is 600-700 BTU per m². This does tend to over-size somewhat.

 

10x5 = 50m² => 30,000 - 35,000 BTU.

 

That's a pretty big aircon. I would suggest going for two smaller units (say 2 x 15,000 BTU) which would give you the option of running one only during the cool season.

 

Are there any significant heat sources, people, computers, huge windows, un-insulated roof space etc.?

 

[tropo]

1 hour ago, BEVUP said:

There are a few threads on here (but make your own mind up )

There are also aids on google

As far as I'm concerned the advice from the shops here concerning BTU ratings is rubbish ( those ratings are for the perfectly built house )

Google aids may not apply to these tropical climates. I'm sure most of us living here are happy with 26 - 27C temperature settings, which doesn't require nearly as much compressor power. Also, if the unit doesn't stay on for long to bring the room down to temperature the humidity will not be reduced as much compared to a compressor staying on for longer... meaning smaller could be better. Humidity is a big factor in room comfort. 

 

In other words, a smaller unit that is only required to drop the room temperature down to 26C (for example) will stay on long enough to keep the humidity lower.

 

Of course, if you need arctic room temperatures you're going to need a much bigger unit.

 

Edited April 16, 2018 by tropo

[bankruatsteve]

I suggest two "12K BTU" "inverter' type.  Unless you need 18-21C you don't need anything bigger.  Uh huh.

[BEVUP]

1 hour ago, tropo said:

In other words, a smaller unit that is only required to drop the room temperature down to 26C (for example) will stay on long enough to keep the humidity lower.

 

Alot to take into consideration

I put one in my bedroom 5 x 5 x 3 , upstairs 12 btu (I think recommended by Do Home ) Usless

So i put that in my sons smaller room & got a 18 btu ok set at 25 

I have a 32 btu down stairs for a 8 x 3.5 x 3 & also a small kitchen 2.5 x 3.5 x 3 set at 26 

 

This is a Thai Moo Baan house not sure what some of these other people have

[tropo]

1 hour ago, bankruatsteve said:

I suggest two "12K BTU" "inverter' type.  Unless you need 18-21C you don't need anything bigger.  Uh huh.

You have to consider the volume of the room, which in the OP's case is very big when you also take into consideration the ceiling height of 4m. That's 200 cubic meters - huge!

 

I use 18 BTU units in rooms of about 50 - 60 cubic meters. The ceiling height is about 2.4m, about average for a condo. The rooms are well insulated. These units are just big enough to do the job of getting the rooms down to 25C and would work hard to get them down lower, although I rarely set them lower than 26C.

 

I would suggest the OP needs units bigger than 30 BTU, or 2 smaller ones.

[BEVUP]

3 minutes ago, tropo said:

You have to consider the volume of the room, which in the OP's case is very big when you also take into consideration the ceiling height of 4m. That's 200 cubic meters - huge!

 

I use 18 BTU units in rooms of about 50 - 60 cubic meters. The ceiling height is about 2.4m, about average for a condo. The rooms are well insulated. These units are just big enough to do the job of getting the rooms down to 25C and would work hard to get them down lower, although I rarely set them lower than 26C.

 

I would suggest the OP needs units bigger than 30 BTU, or 2 smaller ones.

I would go for the 2 units as this may push the air flow around a lot better 

[tropo]

1 hour ago, BEVUP said:

I would go for the 2 units as this may push the air flow around a lot better 

You have to consider other factors if you want to go for two such as room aesthetics and double the ducting and 2 outdoor units to position somewhere. It's not always easy to find a good place to put them. One unit may be much more practical... having said that, I have 2x 25,000 BTU units in my living room, but the evaporators are hidden inside a ceiling space behind the wall, so they're out of sight.

[VocalNeal]

We have a 12 x 4 workshop on the ground floor and a 10 x 4 office on the second floor they both have 2.5m ceilings and 24,000 BTU units at one end. Temp is OK but the "breeze" doesn't quite travel all the way. So I would say 2 x 12000-ish units one at each end. If you generally tend to sit at one end then one 24 will do the job. 

 

If aesthetically pleasing mount the inside units say 2.25 - 2.5 m from the floor. You don't occupy the 4m ceiling space so it doesn't really matter what happens up there. Unless you have a mezzanine floor.? Then put one of the units up there. 

Edited April 17, 2018 by VocalNeal

[Dazinoz]

There are many things to consider. Volume of room, number, size and orientation of windows, insulated or not, shading, adjacent rooms cooled or not.

 

I did a post on here sometime back with a calculator written by and HVAC engineer but can't find link.

[Swimman]

21 hours ago, Crossy said:

The standard Thai guesstimate is 600-700 BTU per m². This does tend to over-size somewhat.

 

10x5 = 50m² => 30,000 - 35,000 BTU.

 

That's a pretty big aircon. I would suggest going for two smaller units (say 2 x 15,000 BTU) which would give you the option of running one only during the cool season.

 

Are there any significant heat sources, people, computers, huge windows, un-insulated roof space etc.?

 

Thank you. No significant heat sources or uninsulated roof space.  All windows are externally shaded so no excessive solar gain.  I like the idea of two units which could be installed at either end of the room. 

[Swimman]

Thanks to all contributors - 

[Crossy]

If the budget runs to it and you have reasonably stable power (important) I would be looking at inverter units. If not sure about power quality go for non-inverter types.

 

[Lacessit]

If it's any help, an 18,000 BTU unit was entirely adequate for a 36 sqm unit. 6 inches of insulation in the roof space.

A Thai sales person at Global house tried to bullshit me into buying a 40,000 BTU unit. I was too polite to point out he didn't know his arse from his elbow.

[KKr]

 

5 hours ago, Dazinoz said:

There are many things to consider. Volume of room, number, size and orientation of windows, insulated or not, shading, adjacent rooms cooled or not.

 

I did a post on here sometime back with a calculator written by and HVAC engineer but can't find link.

https://asm-air.com/airconditioning/what-size-central-air-conditioner-for-my-house/
looks like giving the information OP is after in a detailed calculation 

[Aforek]

Last year , before buying my ( small ) air condition unit, I calculated it from one site  on the Internet; very satisfied of it, calculator was good

buy an inverter unit, very good to save money !

[dddave]

I have a 60 sq.m studio room, 9th floor, older bldg. One long, south facing wall that gets warm to the touch midday with a 3mx1m window, sheltered rear balcony, 4m ceiling.  I use a single 18,000 btu Samsung inverter ac unit and it cools quickly and holds temp consistently. (25-26 degrees) I use a pedestal fan to move air around.  Average power bill at direct rate during moderate months is around B2500-B3000..  This includes running a medium sized fridge and lights.

My ac unit is 4 years old and I have had yearly repairs amounting to around B3-4000.  Overuse could possibly be a factor in my higher than normal repairs but my experience with Samsung Service has been abysmal.  Always 5 or more days to get a tech and nothing wrong is ever covered by the supposed 5 year warranty.  I would not recommend a Samsung ac unit.

If I were buying now, I would opt for a 24,000btu inverter unit rather than a 18,000btu.  I would also consider two 12,000btu units, closing off my sleeping area.

Edited April 17, 2018 by dddave

[mserror]

In January I installed 2 split systems.

 

Here is an Australian app, I suggest using Alice Springs to approximate Thailand:

http://www.fairair.com.au/Calculator.Size.aspx

 

I suggest getting an inverter, they control temperature much better (control output, not on/off), you can set the temp higher and save. Even inverters have a minimum power, and will revert to on/off below this, so if your demand is low consider this - one reason I made the choice below.

 

Also there is a big difference in efficiency, the best units were around 5, the worst around 3. This is output cooling power / input elec. power.

 

Also Panasonic rated best for reliability: 

https://www.canstarblue.com.au/appliances/cooling-heating/air-conditioners/

 

Also I installed roof insulation, this premium product was cheap and so was installation:

https://www.homepro.co.th/product/213896?lang=en

It has an R value of 3.6 (from the specs, I could not make sense of the number on the packet).

 

I bought Panasonic CS-U9TKT, very happy with them. But I turn off the nanoe-G, I think it creates ozone.

 

[sandyf]

On 4/17/2018 at 2:41 PM, Swimman said:

Thank you. No significant heat sources or uninsulated roof space.  All windows are externally shaded so no excessive solar gain.  I like the idea of two units which could be installed at either end of the room. 

My lounge is 8 x 5 with a 3 metre ceiling and the 18K unit is quite adequate. The room is fairly well insulated with cavity wall construction and small windows. The patio end wall never gets the sun. 

You are right to consider 2 units, although mine is adequate it is towards one end and there is a temperature differential. I regret now not putting in 2 x 12K as there is times when I am sure one would be sufficient.

[Crossy]

20 hours ago, mserror said:

ere is an Australian app, I suggest using Alice Springs to approximate Thailand:

http://www.fairair.com.au/Calculator.Size.aspx

 

Handy, and agrees pretty well with the Thai 600 BTU/m² guesstimate. For our room the Aussie calculator comes out about 10% lower than the guesstimate.

[bandito]

On ‎4‎/‎16‎/‎2018 at 4:28 PM, Swimman said:

Any advice will be welcomed.

 For split-air take 10x5=50x650=BTU 12500.

Ceiling height included, same height in all Thai houses.

Piece of advise: Do not buy an inverter,are worthless pieces of junk.

Inverters will cost you a fortune on repairs.

[Crossy]

15 minutes ago, bandito said:

For split-air take 10x5=50x650=BTU 12500.

Ceiling height included, same height in all Thai houses.

Piece of advise: Do not buy an inverter,are worthless pieces of junk.

Inverters will cost you a fortune on repairs.

50*650 = 32,500 BTU which would be better as 2 off 12-15k BTU units to spread air movement and allow the use of one only in the cool(er) season.

 

Inverters can and do save on running costs but can also be susceptible to power surges (and be expensive to repair), if you have poor power get conventional units if available.

 

 

[bandito]

1 minute ago, Crossy said:

50*650 = 32,500 BTU which would be better as 2 off 12-15k BTU units to spread air movement and allow the use of one only in the cool(er) season.

 

Inverters can and do save on running costs but can also be susceptible to power surges (and be expensive to repair), if you have poor power get conventional units if available.

 

 

 

Aah, Crossy my bad, you're right about all.

32500 is the right BTU.

Used a calculator under low lamplight and saw the 3 for a 1.

Old eyes you know.

[Dazinoz]

1 hour ago, Crossy said:

Inverters can and do save on running costs but can also be susceptible to power surges (and be expensive to repair), if you have poor power get conventional units if available.

 When I did my split AC installation course in Australia the lecturer was a dual refrigeration/electrical engineer and he had more negatives than positives for inverter type ACs. This was about 7 years ago so things have probably changed.

 

They were very susceptible to vermin, mice, geckos, etc crawling on the electronic boards and shorting them out. I think they now coat them in an epoxy or the like for protection. As Crossy mentioned they don't like power surges. They have a lot of electronics which has been mentioned they are very expensive to repair. It is usually cheaper to install new unit. Another thing the lecturer mentioned was that because of the electronics they produce more heat and, again, more susceptible to heat on very hot days  so if they get too hot they will actually downrate themselves until they cool down.

 

The guy behind me where I lived in Australia came and saw me and told me that his AC was not working could I have a look. He told me he had got a mob out and said would be too expensive to repair as it was an inverter type. I had a look and the fan in the outdoor unit did not start. A quick flick of the fan and it ran. So I replaced the starting capacitor and ran beautifully. I was back for a visit in March an I visited him and it was still running.

 

Having said all that I have had an inverter and it was great and was just hoping for no failures.

[lwn320]

 
Handy, and agrees pretty well with the Thai 600 BTU/m² guesstimate. For our room the Aussie calculator comes out about 10% lower than the guesstimate.

Thanks mate. Information and app a great help. About to put AC in my house in Korat, understand the size now but still undecided about using inverters ????

Any advice about brands in Thailand. I know everybody has favourites but thinking of using Daikin, would only run AC a few hours a day. Is added expense warranted, probably 18000 BTU and above.

Any advice appreciated.


Sent from my iPhone using Tapatalk Pro

[bankruatsteve]

Last night the power dropped to 60v in my area.  I have an AVS but not much it can do at that voltage (I thought it would shut down - but it didn't).  Anyway... my "inverter" AC had shut down except for a blinking light (a Daikin).  My "inverter" refrigerator had also shut down (Samsung).  After I got my genset running, everything back to normal.

[bankruatsteve]

4 minutes ago, lwn320 said:

 

Thanks mate. Information and app a great help. About to put AC in my house in Korat, understand the size now but still undecided about using inverters ????

Any advice about brands in Thailand. I know everybody has favourites but thinking of using Daikin, would only run AC a few hours a day. Is added expense warranted, probably 18000 BTU and above.

Any advice appreciated.


Sent from my iPhone using Tapatalk Pro

 

The nice thing about "inverter" AC is that it will use 30-50% of conventional.  I have a "1200 BTU" Daikin that pulls just under 5 amps when first started, 3 amps when coasting, and only 1 amp when just maintaining like at night.  It gets where it doesn't use much more energy than a fan.  My AC and fridge have handled voltage variations for over 2 years without issue where my conventional fridge units did not.  There you go.

[Fruit Trader]

The AC in our yard office is on from 7:30am to 6pm and cleaned regularly. The conventional Daikin was replaced with equivalent inverter type early last year because a truck hit the outdoor unit. Electricity to the office is metered separately and the inverter AC has on the very best month maybe saved 15% which is nothing like the 40% claimed during a sales brainwashing session. On very hot days the AC will run flat out so to make a fair comparison test we would need temperature outside our office for the past few years along with daily power usage. 

Our doom and gloom AC guy says its a lotto game because there is a good chance our unreliable power will eventually wipe out the inverter taking with it our power savings and some on top. But he is happy to take nice profit from replacement part and promises to fix with a big smile.

 

If anyone asks me how well the inverter AC is doing I keep Thai face and tell them the huge savings have changed our life for the best. 

[sandyf]

6 hours ago, Dazinoz said:

 When I did my split AC installation course in Australia the lecturer was a dual refrigeration/electrical engineer and he had more negatives than positives for inverter type ACs. This was about 7 years ago so things have probably changed.

 

They were very susceptible to vermin, mice, geckos, etc crawling on the electronic boards and shorting them out. I think they now coat them in an epoxy or the like for protection. As Crossy mentioned they don't like power surges. They have a lot of electronics which has been mentioned they are very expensive to repair. It is usually cheaper to install new unit. Another thing the lecturer mentioned was that because of the electronics they produce more heat and, again, more susceptible to heat on very hot days  so if they get too hot they will actually downrate themselves until they cool down.

 

The guy behind me where I lived in Australia came and saw me and told me that his AC was not working could I have a look. He told me he had got a mob out and said would be too expensive to repair as it was an inverter type. I had a look and the fan in the outdoor unit did not start. A quick flick of the fan and it ran. So I replaced the starting capacitor and ran beautifully. I was back for a visit in March an I visited him and it was still running.

 

Having said all that I have had an inverter and it was great and was just hoping for no failures.

Modern technology is all well and good but not without risk in this climate. I have had several appliance die on me where I am fairly sure the ambient was a contributing factor. I have a fairly large combi microwave that I brought over from the UK which during the warmer weather is prone to starting up on its own. When I got married someone gave us a floor standing fan with digital switching, that lasted about 6 years. I managed to source a new board and replaced it but for a few more baht I could have got a new unit with a mechanical switch, my sister in law has had hers best part of 30 years.

My aircons are fairly basic LG units and have been running ok for about 9 years now so do not owe me a great deal.

 

Some early computers I worked on were full of IVGs (infinitely variable gearboxes), I wouldn't go that far, just use a cooling pad.