Air Conditioner

[aletta]

Just about to put in an air conditioner and wondered what the standard number of BTUs is per square foot.

[jayenram]

Just about to put in an air conditioner and wondered what the standard number of BTUs is per square foot.

<{POST_SNAPBACK}>

There may be someone who can provide the accurate calculations, but I had one installed a couple of years ago, 18,000 Btu for a room of 58 m3 (4.50 x 4.00 x 3.20 high). It's more than adequate.

[Gary A]

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

[Jai Dee]

Here is an air conditioning calculator... may be of use.

[Lancelot]

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

<{POST_SNAPBACK}>

Gary is 100% correct. Better to slightly undersize than to oversize. Oversize A/C=cold, clammy atmosphere. My 2 satang

Lance

[Ajarn]

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

<{POST_SNAPBACK}>

Gary is 100% correct. Better to slightly undersize than to oversize. Oversize A/C=cold, clammy atmosphere. My 2 satang

Lance

<{POST_SNAPBACK}>

I'm no expert, but doesn't A/C, by it's very design, dehumidify any room it's in? I mean, that's what all that water coming off of them is, right? It can come from nowhere else but the air, it seems... When traveling, I've found clothing dries much faster in an air con room than a room without... At home, I keep my window open a bit, otherwise I awaken with a very dry mouth and throat from the dryness of just the A/C...

I have an office and bedroom, both about 18 square meters. The office has 9,500 BTU's, which simply isn't good enough on some days, like today...

The bedroom has 18,500 BTU, which is perfect for me.

[chownah]

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

<{POST_SNAPBACK}>

I don't understand. Doesn't an oversized aircon cycle alot.....meaning that it goes on and off many times? An undersized aircon would just stay on and would not cycle at all....I think....but I don't have aircon myself so I'm relying mostly on engineering theory.

[Gary A]

The only time the air con removes moisture is when the compressor is running so the longer the air con cycles the more moisture is removed. If the room is cooled too quickly and the compressor turns off, it feels cold and clammy because too much moisture remains in the air.

I used the calculator with the ceiling and floor in meters. It came up with 774 watts. To come up with the BTU number you need the EER rating. Mine is 11.5 thus 11.5 times 774 equals 8,901 BTUs. According to that my unit is sized properly. Here in Loei it gets pretty cool during the night so the unit quits cycling once the setting is reached. (27 C). Tonight I'm going to try the timer and have the unit shut down maybe about midnight.

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

<{POST_SNAPBACK}>

Gary is 100% correct. Better to slightly undersize than to oversize. Oversize A/C=cold, clammy atmosphere. My 2 satang

Lance

<{POST_SNAPBACK}>

I'm no expert, but doesn't A/C, by it's very design, dehumidify any room it's in? I mean, that's what all that water coming off of them is, right? It can come from nowhere else but the air, it seems... When traveling, I've found clothing dries much faster in an air con room than a room without... At home, I keep my window open a bit, otherwise I awaken with a very dry mouth and throat from the dryness of just the A/C...

I have an office and bedroom, both about 18 square meters. The office has 9,500 BTU's, which simply isn't good enough on some days, like today...

The bedroom has 18,500 BTU, which is perfect for me.

<{POST_SNAPBACK}>

[Ajarn]

The only time the air con removes moisture is when the compressor is running so the longer the air con cycles the more moisture is removed. If the room is cooled too quickly and the compressor turns off, it feels cold and clammy because too much moisture remains in the air.

That makes some sense, and it would seem the dehumidifing action will continue for at least a few moments,- and there's the question of the next cycle... I don't know about you guys, but it sure isn't long, like maybe a minute or two, before it starts up again at my place... (even with window closed) Hence, seeming to negate any concerns about there ever being enough moisture in the air here to creat a clammy feeling...

Maybe other forces at work here for this feeling? Sometimes in the middle of the night, my body will sweat a bit, when that 'temperature balance' I think a lot of us look for is likely to change, either from our own body cooling in reaction to the sleep cycle, or from getting colder as the cold building up in reaction to outsides temps cooling... Of course, with my window open, sometimes my aircon might have more of a heating effect, especially in the cooler season..

Maybe simply the moisture being 'forced' out by the lowering temps (higher temps support more moisture, right?) and sticking on you or your walls? But then that would ne long-gone by morn, I would think, from the on-going dehumidifying effect from the aircon...(I still remember about my wet clothes in the hotel being always bone-dry in the morning when in an air room, otherwise, still wet, even when under a fan...)

Oi! too much to space on... Off for a dip

Edited May 17, 2005 by Ajarn

[Gary A]

On and off, that's the exact problem. When the compressor comes on it is quite inefficient for a little while. (Waste of electricity). It then compresses the gas and changes it to a liquid. It then pumps liquid refrigerant to the evaporator, that's the part in the house. The refrigerant then boils at a VERY low temperature and the evaporator gets cold. Moisture condenses on the evaporator coil and drains to a pipe that takes it outside. The coil is by design able to conduct heat and cold very quickly so when the compressor shuts off the coil warms up quickly and no more moisture condenses. By the unit being smaller the compressor will run more efficiently and the evaporator coil will stay cold longer thus condensing more moisture.

One problem here in Thailand is that many times the technician over charges the unit which results in too much pressure in the system. This causes the evaporator to get too cold. The moisture then freezes and the unit basically is running full speed and doing very little cooling because air can no longer circulate around the coil. Your unit should NEVER have ice in it.

I just went through that same thing. One answer I got was 400 BTU per square meter for a typical Thai house. Typical being no insulation and poorly sealed doors and windows. Sometimes they refer to how many tons are needed. I have found out that a one ton unit is 12,000 BTUs. That said I put a 9000 BTU unit in my 18 square meter bedroom and it may be too big. Too large of a unit will not do a good job of removing humidity besides costing more to start with. Also watch the EER rating. That number is how many BTUs is produced per watt of power. My Sansung is rated at 11.5. All the units I looked at here had the ratings on a sticker. I don't understand Thai but just ask which number is BTU per watt.

I do think my unit is too big for the room. It feels fine shortly after it is turned on but by morning the air feels a little clammy because the unit cycles very little. I'll buy a humidistat the next time I see one.

<{POST_SNAPBACK}>

I don't understand. Doesn't an oversized aircon cycle alot.....meaning that it goes on and off many times? An undersized aircon would just stay on and would not cycle at all....I think....but I don't have aircon myself so I'm relying mostly on engineering theory.

<{POST_SNAPBACK}>

[lopburi3]

The normal guide here is about:

9000 BTU for 9-14 sq. meters

12/13000 BTU for 14-22 sq. meters

18000 BTU for 24-32 sq. meters

22/24000 BTU for 29-40 sq. meters

Believe these are probably large for ground floor shaded rooms but may be needed under hot attic of most home bedrooms.

[Ajarn]

On and off, that's the exact problem. When the compressor comes on it is quite inefficient for a little while. (Waste of electricity). It then compresses the gas and changes it to a liquid. It then pumps liquid refrigerant to the evaporator, that's the part in the house. The refrigerant then boils at a VERY low temperature and the evaporator gets cold. Moisture condenses on the evaporator coil and drains to a pipe that takes it outside. The coil is by design able to conduct heat and cold very quickly so when the compressor shuts off the coil warms up quickly and no more moisture condenses. By the unit being smaller the compressor will run more efficiently and the evaporator coil will stay cold longer thus condensing more moisture.

I still don't quite get it, it seems...

The compressor goes off when the temperature reaches the set temp, right? And small and large units operate the same way, right? So, it seems to me both units would be going off at the same point (though a larger unit would maybe go off sooner) and on again at the same exact point/time for both, since that's on ambient room temperature... For example, the 18000 unit takes 3 minutes to get to temp, while the smaller unit takes 6 minutes. But both are relying on the change in ambient temp to trigger the compressor back on again, and that'll take the exact same time for the same room, right? So, the smaller unit runs more. But is that really more efficient?

The larger unit pushes more air volumme (and more radiator surface?), too, right? So it would seem that it would be dehumidifying at a considerably faster rate, which would seem to at least cancel out any advantage the smaller compressor might be percieved as having in terms of dehumidifying...

The only advantage I can see with a smaller compressor is purchase price and possibly the electricity costs to run. As I said, I've never have had this described clamminess from an A/C, so I prefer the superior cooling power of a larger unit, over a smaller one that's working constantly to maintain it's set temp, though, with saying that, I must admit that my larger compressor rarely goes off because my bedroom temp is set for 21c

[autonomous_unit]

I don't have the physics chops to explain it, but I've definitely seen it with a/c for computer equipment rooms. The cooling capacity is in energy/time and should be balanced against the heat introduced to the room through leakage and internal sources like people and equipment. We had a room that didn't have enough gear in it yet for its designed load and the result was a horrible humidity and odor problem from the a/c not running frequently enough. The proposed solutions from the building engineers were to replace the a/c unit with a smaller one or put more heat-generating equipment in the room so that the a/c could operate properly to cool it!

Perhaps there is a difference between slowly cooling (and drying) all the air versus super cooling (and super-drying) a small amount and tossing it back into the room to mix with the humid air? Maybe you can remove the heat energy from the air in a way that is not proportional to how much water you remove...

I wonder if these "inverter" units avoid this problem? If I understand the graphs in the marketing material, they seem to be able to adjust their compressor speed rather than having to turn full on or off based on the thermostat.

[autonomous_unit]

I meant to add that if your compressor is switching on after only a minute, it must not be too large for your leaky room.

At night in BKK, I have to leave ours w/ a manual fan speed setting or it turns off for a long time and then wakes me when it starts going again on fully automatic mode. I don't notice the temp swing too much when this happens but am bothered by the sudden change in the sound...

[buadhai]

We just put an air con in a 9 square meter room. The ceiling is insulated and it has only one, short outside wall. 5000 BTU would have been plenty, but we could find no such beast in Korat. The smallest is a 9000 BTU. I suspect that the compressor will cycle only rarely and the room will feel damp as a result.

We have a 12000 BTU in our 16 sq. m. insulated bedroom. It's a Mitsubishi with the fuzzy logic they call "I Feel". When you use that setting it also becomes so compressor-efficient that the room actually feels too damp. Setting a specific temperature causes the compressor to cycle often enough to keep the dampness down.

[aletta]

Thanks for all the replies.

Got a 18 square metre room so depending on the EER rating going to stick in a 10/12000 BTU unit.

Is all this silver nano treatment a load of old &lt;deleted&gt;?Wife's seen adverts saying the coating kills bacteria and stops allergens.

I'm inclined to suspect it's a marketing ploy by the Korean firms to move up market from the cut-throat competition in standard air conditioners.

Edited May 18, 2005 by aletta

[lopburi3]

Thanks for all the replies.

Got a 18 square metre room so depending on the EER rating going to stick in a 10/12000 BTU unit.

Is all this silver nano treatment a load of old &lt;deleted&gt;?Wife's seen adverts saying the coating kills bacteria and stops allergens.

I'm inclined to suspect it's a marketing ploy by the Korean firms to move up market from the cut-throat competition in standard air conditioners.

<{POST_SNAPBACK}>

Silver has been used for years in water filters so suspect that there is some truth to it. At first it seemed a very high ticket item but seems to have become mainstream now with a number of models using it.

[chownah]

........ and there's the question of the next cycle... I don't know about you guys, but it sure isn't long, like maybe a minute or two, before it starts up again at my place... (even with window closed) Hence, seeming to negate any concerns about there ever being enough moisture in the air here to creat a clammy feeling...

<{POST_SNAPBACK}>

One thing that can cause aircon to shut off and then on again after only a short off period is when the cold air from the aircon unit blows onto the thermostat controlling it. What happens is that the thermostat quickly cools enough to turn the unit off because the cold air is blowing right on it....but the room hasn't cooled down yet. Since the room hasn't cooled down yet the thermostat warms up very quickly when the cold air stops blowing on it and it turns the unit on again.

As to the clammy feeling....my limited experience with aircon is that when they are first turned on in a warm humid room you get a really strong dose of that clammy feeling. It may take awhile for the unit to 'capture' all the humidity and eject it as water....but....if the room is more or less air tight so no new humid air enters then the clammy feeling goes away because all the air in the room has been dehumidified and even the porous surfaces in the room have given up their excess moisture. If there is a source of entry for humid air then it will tend to create that clammy feeling to varying degrees depending on how much air and how humid it is and....very important....where does it enter relative to the people in the room. If you like to keep a room vented a bit to keep the air fresher it is probably better to have the vent away from the occupied space so that it has time to mix with the dry air and loose its ability to create the clammy feeling.

[jayenram]

We have a 12000 BTU in our 16 sq. m. insulated bedroom.

<{POST_SNAPBACK}>

I am no expert in the matter of aircons (as I've realised reading the replies herein), but shouldn't we be talking cubic metres here and not square metres?

[buadhai]

We have a 12000 BTU in our 16 sq. m. insulated bedroom.

<{POST_SNAPBACK}>

I am no expert in the matter of aircons (as I've realised reading the replies herein), but shouldn't we be talking cubic metres here and not square metres?

<{POST_SNAPBACK}>

Technically, you are correct. However, most of these calculations assume a normal ceiling height and use square meters to simplify things. If you have a cathedral ceiling or some other unusual architectural feature (dungeon?) then you'd have to take that into account.

[jayenram]

We have a 12000 BTU in our 16 sq. m. insulated bedroom.

<{POST_SNAPBACK}>

I am no expert in the matter of aircons (as I've realised reading the replies herein), but shouldn't we be talking cubic metres here and not square metres?

<{POST_SNAPBACK}>

Technically, you are correct. However, most of these calculations assume a normal ceiling height and use square meters to simplify things. If you have a cathedral ceiling or some other unusual architectural feature (dungeon?) then you'd have to take that into account.

<{POST_SNAPBACK}>

My ceiling height is 3.20 metres. Would that be considered normal? I've never really noticed the height of other people's ceilings.

[buadhai]

My ceiling height is 3.20 metres. Would that be considered normal? I've never really noticed the height of other people's ceilings.

<{POST_SNAPBACK}>

That seems very high. In this house they are 2.8 meters. In the US, I think the standard height for residential structures is 8.5 feet.

[jayenram]

My ceiling height is 3.20 metres. Would that be considered normal? I've never really noticed the height of other people's ceilings.

<{POST_SNAPBACK}>

That seems very high. In this house they are 2.8 meters. In the US, I think the standard height for residential structures is 8.5 feet.

<{POST_SNAPBACK}>

I'm 1.92 meters tall. Given my arm length of about 0.80 meters I could reach the ceiling fans if the ceiling were any lower. Then I wouldn't be able to order the beer.

[PeaceBlondie]

I lived in the USA for almost 60 years and the standard ceiling height is 8 feet (thus, wall panels were 4x8).

I shopped for an air/con unit in my rental condo. The main room is 55 sq. meters, standard ceilings, but there's an incredible amount of exterior permiter walls with huge windows and glass doors to the east, north and west. The guy at the store suggested I get 33,000 BTU, but I'm afraid those windows add at least 15%. Plus, the area includes two bathrooms. Do you think 36,000 BTU is enough? I couldn't get the calculator to run. I tried various online BTU calculators and they were designed for wintry areas more than 40 degrees above the equator.

I noticed that the brand "Mitsubishi Electric" is priced higher than the simple brand name "Mitsubishi." Did I understand correctly from the previous thread that Mitsubishi Electric is much better?

Also, those rainbow stickers on the electric appliances don't tell much by the single-digit rating. Everything is now rated 5 on a scale of 1 to 5. If you can't find the EER rating, there's another one that states how many BTU's or baht the unit costs per year.

Edited May 21, 2005 by PeaceBlondie

[Gary A]

I lived in the USA for almost 60 years and the standard ceiling height is 8 feet

(thus, wall panels were 4x8). 

I shopped for an air/con unit in my rental condo.  The main room is 55 sq. meters, standard ceilings, but there's an incredible amount of exterior permiter walls with huge windows and glass doors to the east, north and west.  The guy at the store suggested I get 33,000 BTU, but I'm afraid those windows add at least 15%.  Plus, the area includes two bathrooms.  Do you think 36,000 BTU is enough?  I couldn't get the calculator to run.  I tried various online BTU calculators and they were designed for wintry areas more than 40 degrees above the equator. 

I noticed that the brand "Mitsubishi Electric" is priced higher than the simple brand name "Mitsubishi."  Did I understand correctly from the previous thread that Mitsubishi Electric is much better?

Also, those rainbow stickers on the electric appliances don't tell much by the single-digit rating.  Everything is now rated 5 on a scale of 1 to 5.  If you can't find the EER rating, there's another one that states how many BTU's or baht the unit costs per year.

<{POST_SNAPBACK}>

On that sticker that has the big "5" there should be a series of numbers below that. On my new unit the very first number is the EER rating. Mine is 11.45. Anything over 10.5 should be acceptable.

I also have a condo in Jomtien. Mine is 60 square meters with a separate bedroom. The unit in my bedroom is only a 12,000 btu. The main unit is 24,000 btu. On a VERY hot day I will run the old less efficient main unit for a while to cool things down then I open the bedroom door and run the much more efficient smaller unit. It keeps thing at least comfortable by itself. The 33,000 btu unit is probably much more than you need. It takes no more than 15 minutes to cool off my entire condo using both units combined at 36,000.

I have no idea what brand is the best. Mitsubishi uses a rotary compressor on at least some of their units. That may be the difference in price with the rotary compressor being better.

[Gary A]

All these posts about air conditioners got me to thinking about the numbers. I just went outside and looked at me Samsung compressor. It is rated at 9,200 btu and It says 2,700 watts. Obviously I got bad information from the salesman. He told me the EER was 11.45. If you divide 9,200 by 2,700 it comes up to about 3.4 not 11.45. I guess the best way to figure efficiency is to do the math yourself.

[SpaceKadet]

Slightly off-topic, but aircon related.

What's the maximum distance for the piping between the compressor (the outdoor unit) and evaporator (indoor unit)? If I put the evaporator in the 2nd story bedroom, can I keep the compressor on the ground level?

[aletta]

I would think that the piping can be any length but will make the system less efficient the longer it is as the coolness will be lost to the atmosphere.i.e you might need more BTUs to do the same amount of cooling.

[thymode91]

Slightly off-topic, but aircon related.

What's the maximum distance for the piping between the compressor (the outdoor unit) and evaporator (indoor unit)? If I put the evaporator in the 2nd story bedroom, can I keep the compressor on the ground level?

<{POST_SNAPBACK}>

I am not quite professional with this field but your case can be done. the first things you should consider is the capacity of Aircon unit you wanted to install. because different capacity got different range of distance between indoor and outdoor unit. you better consult the manufacturer or the dealer about this case, sometimes it varies in accordance with the brand of the airconditioners but generally the difference is not quite big. I hope this may help you

[SpaceKadet]

Thanks for info. I think that added insulation on the pipes would allow me to go 6 meters between the units. I thought that somebody might have done it, and could share their experiences. I'll will check with an A/C professional thou...