Air Consitioner Size Chart

[lopburi3]

BTU - - - - - - - Sq Meters

9,000 - - - - - - 9-15

12,000 - - - - - 16-20

18,000 - - - - - 21-30

24,000 - - - - - 31-35

30,000 - - - - - 40-50

36,000 - - - - - 50-55

[phutoie2]

BTU - - - - - - - Sq Meters

9,000 - - - - - - 9-15

12,000 - - - - - 16-20

18,000 - - - - - 21-30

24,000 - - - - - 31-35

30,000 - - - - - 40-50

36,000 - - - - - 50-55

Thanks for that Lop3, I am just about to purchase a Mitsubishi Slim Econ air -MS-SGD13VC. According to the spec sheet its 12,488 BTU.

Its for our main bedroom which is 20 sqm.

[Tywais]

Thanks for that Lop3, I am just about to purchase a Mitsubishi Slim Econ air -MS-SGD13VC. According to the spec sheet its 12,488 BTU.

Its for our main bedroom which is 20 sqm.

Coincidently I'm having that same model installed tomorrow in the master bedroom to replace a 9000 BTU unit that just can't keep up. Room size a hair over 20 sqm.

[ClaudeFeller]

The given figures are OK. But must consider the sun exposed windows and the kind of glass (tinted or clear).

[longball53098]

It would be interesting to know if this size chart from Home Pro was put together by Home Pro or an air conditioner company?

Did they make some calculations to allow for volume of the room? Say an average height for the ceiling? And for any windows/doors?

Just curious how accurate this type of chart can be. Probably close.

[Tywais]

Just curious how accurate this type of chart can be. Probably close.

Looking around the net I've seen these charts vary dramatically from site to site. For example, two sites indicate 20 sqm 7000 BTU is enough! A fixed chart is a very rough guide and several other variables need taken into account. The reason I am switching from 9000 BTU to 12000 BTU is due to the fact my bedroom is on the 2nd floor below an uninsulated attic and that the windows are facing east/west and always in the sun.

Some info based on US DOE article.

This one seems a bit better allowing one to take in the different variables in calculating sizing > Air Conditioning Chart

[lopburi3]

Believe you will find the US calculations very much off the mark (low) for the weather in Thailand (hot/humid) and the normal construction (uninsulated brick/cement). At least when I tried to plug numbers into them years ago they came up with results I know from experience here were not even close.

But as said there can be a huge variance with shade/insulation/ventilation.

Perhaps this is another reason to consider the more expensive inverter units - which operate efficiently at the required BTU.

[wpcoe]

Since lopburi3 introduced the term, this is as good a place as any to ask: what exactly is an "inverter"?

When I lived in Japan, I thought the term applied to "heat pump" type of units that cooled in the summer and heated in the winter.

I understand the basics (the function of the compressor, condenser and evaporator) of an a "standard" air con system. What does an inverter do differently?

[lopburi3]

Inverter (air conditioning)

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The inverter tag found on some air conditioners signifies the ability of the unit to continuously regulate its thermal power flow.

Traditional reverse-cycle air-conditioners use a heat pump that is either working at maximum capability or switched off, as the compressor's speed cannot be varied. In order to regulate temperature a thermistor is used to measure the ambient air temperature and switch the compressor on when the ambient air temperature is too far from the desired temperature

Air-conditioners bearing the inverter tag use a variable-frequency drive to control the speed of the motor and thus the compressor. The variable-frequency drive uses a rectifier to convert the incoming AC current to DC and then uses pulse-width modulation of the DC current within an inverter (electrical) to produce AC current of a desired frequency. The AC current is used to drive a brushless motor or an induction motor. As the speed of a brushless motor is synchronised to the frequency of the AC current, it is thus possible to build a compressor that can be run at different speeds. Similarly, the voltage and frequency can be varied as needed to efficiently run an induction motor at different speeds. A microcontroller can then sample the current ambient air temperature and adjust the speed of the compressor appropriately.

The effect of eliminating stop-start cycles is to increase efficiency, extend the life of components and eliminate sharp fluctuations in the load the air-conditioner places on the power supply.

Instead of start/stop compressor to maintain cooling (always at full power) it adjusts the compressor motor to vary speed and stay on but at less than full capacity and the efficiency becomes much higher. As long as the unit is not too much undersized it can save a good deal of money (30% or so). You also have a spot on temperature control and less start/stop noise from compressor. They do cost a lot more so if seldom used would not be cost effective.

[Naam]

Inverter (air conditioning)

From Wikipedia, the free encyclopedia

Jump to: navigation, search

The inverter tag found on some air conditioners signifies the ability of the unit to continuously regulate its thermal power flow.

Traditional reverse-cycle air-conditioners use a heat pump that is either working at maximum capability or switched off, as the compressor's speed cannot be varied. In order to regulate temperature a thermistor is used to measure the ambient air temperature and switch the compressor on when the ambient air temperature is too far from the desired temperature

Air-conditioners bearing the inverter tag use a variable-frequency drive to control the speed of the motor and thus the compressor. The variable-frequency drive uses a rectifier to convert the incoming AC current to DC and then uses pulse-width modulation of the DC current within an inverter (electrical) to produce AC current of a desired frequency. The AC current is used to drive a brushless motor or an induction motor. As the speed of a brushless motor is synchronised to the frequency of the AC current, it is thus possible to build a compressor that can be run at different speeds. Similarly, the voltage and frequency can be varied as needed to efficiently run an induction motor at different speeds. A microcontroller can then sample the current ambient air temperature and adjust the speed of the compressor appropriately.

The effect of eliminating stop-start cycles is to increase efficiency, extend the life of components and eliminate sharp fluctuations in the load the air-conditioner places on the power supply.

Instead of start/stop compressor to maintain cooling (always at full power) it adjusts the compressor motor to vary speed and stay on but at less than full capacity and the efficiency becomes much higher. As long as the unit is not too much undersized it can save a good deal of money (30% or so). You also have a spot on temperature control and less start/stop noise from compressor. They do cost a lot more so if seldom used would not be cost effective.

there is one word missing and that could be misleading. variable speed commpressors do not increase the cooling efficiency but the energy efficiency.

[lopburi3]

I was speaking of the EER but was trying to avoid going into discussion of that - believe the Panasonic is rated up to about 19 in current advertising when running at lower range.

[Pushit]

Since lopburi3 introduced the term, this is as good a place as any to ask: what exactly is an "inverter"?

When I lived in Japan, I thought the term applied to "heat pump" type of units that cooled in the summer and heated in the winter.

I understand the basics (the function of the compressor, condenser and evaporator) of an a "standard" air con system. What does an inverter do differently?

An Inverter changes Alternating Elecrical Curent to Direct Current ie AC to DC.

Areas for aircn calcs should be in cubic metres not square metres, however whatever.

Cheers

[Tywais]

An Inverter changes Alternating Elecrical Curent to Direct Current ie AC to DC.

Not in the use of the term for air conditioners though, which has been described above.

Plus your electronics definition of an inverter is wrong and it converts DC to AC. The other way is a rectifier.

[Naam]

Since lopburi3 introduced the term, this is as good a place as any to ask: what exactly is an "inverter"?

When I lived in Japan, I thought the term applied to "heat pump" type of units that cooled in the summer and heated in the winter.

I understand the basics (the function of the compressor, condenser and evaporator) of an a "standard" air con system. What does an inverter do differently?

An Inverter changes Alternating Elecrical Curent to Direct Current ie AC to DC.

Areas for aircn calcs should be in cubic metres not square metres, however whatever.

Cheers

you are wrong my friend

[Naam]

I was speaking of the EER but was trying to avoid going into discussion of that - believe the Panasonic is rated up to about 19 in current advertising when running at lower range.

i am trying hard not to let anybody know my opion concerning EER... which is

[Naam]

I was speaking of the EER but was trying to avoid going into discussion of that - believe the Panasonic is rated up to about 19 in current advertising when running at lower range.

i am trying hard not to let anybody know my opion concerning EER... which is

just a short explanation. it's not that i think SEER or EER = what i am trying to say is that companies cheat by bending, twisting, abusing and misinterpreting these standards in their favour since many years.

[Gary A]

Unfortunately I think it is common practice to overstate BTU capacity to improve the EER rating.

[Lazy Sod]

BTU - - - - - - - Sq Meters

9,000 - - - - - - 9-15

12,000 - - - - - 16-20

18,000 - - - - - 21-30

24,000 - - - - - 31-35

30,000 - - - - - 40-50

36,000 - - - - - 50-55

Downstairs at our house is 50m2 and it has open staircase. Based upon a similar chart to the above we purchased a 36,000BTU unit but it is far too powerful. It quickly cools down the area, but then cycles on/off every 3 minutes with a loud starting noise, it's driving me nuts.

[lopburi3]

Why would it be starting every 3 minutes if already down to temperature? It should not start again until there is a change and that should take longer than 3 minutes if sensor is properly located. I had a wall unit do that when the sensor was making direct contact with a cooling coil but that never allowed the unit to cool enough.

[Lazy Sod]

Why would it be starting every 3 minutes if already down to temperature? It should not start again until there is a change and that should take longer than 3 minutes if sensor is properly located. I had a wall unit do that when the sensor was making direct contact with a cooling coil but that never allowed the unit to cool enough.

I think the room warms up by 1 degree in 3-5 minutes, it feels like that. Noticed that after running the unit for an hour the cycles reduce to say 5-6 minutes off and 3 minutes on, probably due to the walls/floor being cooler then. I tried moving the sensor and also covering it with insulation tape but it didn't make much difference. I think the chart from HomePro is generally ok, I'm just pointing out that there are variables to consider especially for larger areas.

Edited April 29, 2008 by Lazy Sod

[Naam]

I think the room warms up by 1 degree in 3-5 minutes, it feels like that. Noticed that after running the unit for an hour the cycles reduce to say 5-6 minutes off and 3 minutes on, probably due to the walls/floor being cooler then. I tried moving the sensor and also covering it with insulation tape but it didn't make much difference. I think the chart from HomePro is generally ok, I'm just pointing out that there are variables to consider especially for larger areas.

a basic rule is "always use several smaller units instead of one big unit". although this is more expensive, it not only pays in the long run but it also adds to comfort. a big unit cycling on/off will never dehumidy any area properly. dehumidification (latent cooling) is for personal comfort as important as temperature cooling AND it saves energy.

[lopburi3]

Agree with above and that there are a number of variables (first floor usually much easier to cool for one).

Do you have a setting to allow a two degree change before restart (sleep/econ or something). Can you use low fan speed? Can you perhaps make a trade with someone to get a smaller unit? Installation by itself is really not that expensive.

[tjo o tjim]

Unfortunately I think it is common practice to overstate BTU capacity to improve the EER rating.

Usually it is actually the reverse; they de-rate a unit to get a higher EER/SEER. While Nominal and Actual cooling capacity often vary widely, both are usually readily available.

[dotcom]

I have always used 1000 BTU per 1 sq M floor space.

To my experience you shold go a little higher if you room falls in between.

So in the above 20 sq M bedroom I would use 24,000 BTU. 18,000 will be running locked up most of the time.

I have a 24 in my bedroom & it will bring it down from 32 to 26 in about 10 minutes. No problem whatsoever to dehumidify.

btw I always use 52 inch celing fans in addition to stir the air from ceiling to floor. Makes a huge difference. Use a table fan if in rented premises.

btw. Any wall mounted unit like Mister Slim is a lot less effecient than traditional. That's because they are designed to be very quiet but the air flow is not as good as a traditional unit.

I just use one wall mount 9k BTU & I am forever having to get the condenser cleaned. It plugs up with gunk which resembles algae.

[lopburi3]

I don't know how you can require 1k btu per square meter. I just installed a reserve 9k Panasonic in my 27 square meter ground floor bedroom last week (intending it to be for emergency use when 18k main unit failed) and it has been all I have used since. It fully cools room. Another bedroom of the same size has used a 12k unit for many years and is fully cooled.

[dotcom]

I have another bedroom thats about 5 x 5 meter. Has an 18k BTU ceiling mounted unit. Room faces North. Poorly insulated. This aircon will take about 3 hours to bring the temp down from 32~33 to 26~27. Emperical evidence. I use lots of thermometers.

[RouxTheDay]

It's interesting to me that there is apparently no central air conditioning in LOS... anybody know why?

[lopburi3]

There is a lot of central air conditioning but it is used in commercial establishments rather than homes where only one room normally needs to be cooled. To keep a normal cement house cooled here (little insulation used) would be extremely costly and wasteful. I am sure that are also other reasons but this is what jumps out at me.