A/C Sizing Chart

Air conditioning, fans, and anything related to keeping it cool, such as insulation. This would include any posts generally discussing how to keep it cool, such as which types of blocks are better insulators.... ideal wall thickness for keeping an A/C house cool, etc.

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Re: A/C Sizing Chart

Postby Roger Ramjet » Mon Nov 03, 2014 1:31 am

Now I've looked at a few dozen websites, both before I bought my inverter air conditioners and also in the last few days. There is continuos argument about size and over-size, but few have dealt with inverter technology and what it does. Here's one that does: https://www.bijlibachao.com/air-conditi ... india.html which includes a graph showing exactly how it works.
Even on other sites that claim normal air conditioners should not be over-sized they talk about the compressor running for just 2 to 4 hours, not at maximum the whole time and they also contradict themselves in other areas, especially about how to calculate areas or tonnage to get the BTU you require. If these "professional" websites are all in conflict how can we rely on them to find out the correct British Thermal Unit sized air conditioner we require to cool a room here in Thailand.
I would be asking what sort of building material was used in the walls, whether the correct insulation both in the walls and above the ceiling was also used as well, the type of windows, what size they are, how many people lived in the room and what the tonnage for the room worked out at. I'd also be asking what sort of wiring was used and was it the recommended type and thickness for the appliance.
I used two of the calculators and both gave me a different answer. As well, different air conditioning makers said that their different models performed differently in different circumstances and in some cases they would recommend a 1 1/2 ton unit but for a different model a 1 ton unit was sufficient.
If the companies that make the air conditioners are in conflict, and they do all the R and D, how can websites use a calculator that is just a general guide that has little bearing on the eventual outcome?
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Re: A/C Sizing Chart

Postby Sometimewoodworker » Mon Nov 03, 2014 6:13 am

Roger Ramjet wrote:
Sometimewoodworker wrote:If air conditioner units never operate at maximum they are oversized.

Could you please show me one professional website that says that?


If your air conditioner is cycling even at four in the afternoon on the hottest days, it is a sure sign it is oversized

http://www.homeenergy.org/show/article/year/1995/magazine/91/id/1128

“A bigger air conditioner will make me more comfortable.” Unfortunately, the intuitive way to achieve comfort—put in a bigger air conditioner—is incorrect.

http://www.bestofbuildingscience.com/pdf/Smart%20and%20cool%20the%20art%20of%20air%20conditioning%20HEM_SP05_p46-52.pdf

Q. How long should my air conditioning system run in a cycle?
There is no exact answer for how long your system should run during each cycle. The average air conditioner is sized to remove the heat from your home as fast as it comes in. Therefore, ideally, on a 100° day the system should be able to keep up with the incoming heat, but not gain on it and not be able to turn off. The cooler it is below 100°, the more the system will cycle on and off. So it depends on the environment of each individual home and the condition of the equipment.



http://www.horizonservicesinc.com/reference/faqs/faq-heating



When outdoor conditions are at the design temperature, an air conditioner should run pretty much continuously and be able to keep the house at the ACCA recommended indoor design temperature of 75 degrees Fahrenheit. When outdoor conditions go above the design temperature, the AC should run continuously and not quite keep the house at 75 degrees.


http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/24645/How-to-Tell-If-You-Have-an-Oversized-Air-Conditioner

Enough?
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Re: A/C Sizing Chart

Postby Roger Ramjet » Mon Nov 03, 2014 7:42 am

Sometimewoodworker wrote:Enough?

Have you read the sites you posted?
I read most of them in the last week and not one mentions anything about the insulation in a house, the wiring, the actual house design (what it's built out of) and the use of inverter air conditioners. In fact some are old web sites, some as old as 10 years ago before inverters were designed.
I have two clocks with digital read-outs for humidity, my dehumidifier also has a digital read-out (which you claimed was the only way to test the humidity), so are you claiming, well just what are you claiming?
If you read the web sites you posted they contradict each other because they never give the calculations you should use for any of the above. Who can say from one day to the next how hot the outside temperature will be compared to the inside temperature. Even I can't do that with my "locked" house and all the "green" things I have like sunshades over windows, Colorbond roofing with insulation, Superblock, reflective blinds indoors, blinds on all the windows and that's without even thinking about the wet season, dry season and the other seasons inbetween.
If your air conditioner is running flatout the whole time and not keeping the inside temperature to the degree you like it, then it is burning energy, wasted energy. If it is doing the job of cycling on and off in two to four hour runs and removing the humidity, then, according to what you said it is oversized and should be running the whole time.
Not one of those websites talk about what different models, let alone brands were designed to do and what is the benefit or not of having inverter air conditioners. They also don't mention house design, insulation or much else related to building in Thailand.
All you're doing is quoting what "they" say, which, in most cases relates to countries other than Thailand.
And then you posted this;
Sometimewoodworker wrote:Q. How long should my air conditioning system run in a cycle?
There is no exact answer for how long your system should run during each cycle. The average air conditioner is sized to remove the heat from your home as fast as it comes in. Therefore, ideally, on a 100° day the system should be able to keep up with the incoming heat, but not gain on it and not be able to turn off. The cooler it is below 100°, the more the system will cycle on and off. So it depends on the environment of each individual home and the condition of the equipment.

Which is exactly what I have been saying, but you insist it should be running flatout the whole time to be the "right" size.
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Re: A/C Sizing Chart

Postby Sometimewoodworker » Mon Nov 03, 2014 8:46 am

Roger Ramjet wrote:Which is exactly what I have been saying, but you insist it should be running flatout the whole time to be the "right" size.

I have never said that. I said
me wrote:If air conditioner units never operate at maximum they are oversized.


It would be stupid to suggest that an AC could be correctly sized if it ran at maximum all the time, if it did that it would be drastically undersized.

Just because the sites don't directly address Thailand and inverters doesn't make the information less relevant.

Inverters save energy at times when the full cooling isn't needed, and that is for most of the cooling season but not all.

Over sizing is over sizing what ever the AC type and is a waste of money and energy.
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Re: A/C Sizing Chart

Postby Roger Ramjet » Mon Nov 03, 2014 1:03 pm

Sometimewoodworker wrote:Just because the sites don't directly address Thailand and inverters doesn't make the information less relevant.

Firstly the information contradicts itself from one website to another. Secondly, inverters do make a difference on both the run time and the inside/outside temperature as they control the compressor speed and amount of refrigerant being released through the system (see the graph on the website I posted). And finally if you read most peoples' complaints about their air conditioners (ten years ago) it was the fact they ran constantly from 2 in the afternoon through to 8 at night and their electricity bills were huge and not one air condition mechanic could agree with another on the reason why. HVAC suppliers have a five page checklist for the house/building construction before they even look at making a caculation about the size (BTUs) of the air conditioner needed and that varies from brand to brand and inverter to non-inverter type.
If my air conditioners (3) ran continuously during the hottest part of the day without cycling on and off I would be calling Mitsubishi Thailand to find out why!
People can post all the charts they like, but without taking into account all the other features of a house in Thailand they are wasting their time and guestimating.
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Re: A/C Sizing Chart

Postby Sometimewoodworker » Mon Nov 03, 2014 9:32 pm

Roger Ramjet wrote:If my air conditioners (3) ran continuously during the hottest part of the day without cycling on and off I would be calling Mitsubishi Thailand to find out why!

If that were on the hottest days in the year, the answer would be that they had been optimally sized.

You like to over size, no problem, your choice, your house, your money.
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Re: A/C Sizing Chart

Postby juehoe » Sun Jan 11, 2015 9:32 am

The recommended sizes you find in HomePro etc. are too big. The Thai like this high power rates, because they want to cool down their non-insulated over-heated rooms as fast as possible.

I uses the rule of thumb of 100 W per square meter and my works fine in my standard Thai house (with ceiling insulation of course). I can cool my office (4x12 m, 3.5 m high) with a 18,000 BTU/h unit (Samsung Smart Inverter), in combination with ceiling fans.
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Re: A/C Sizing Chart

Postby Andyfteeze » Thu Jan 15, 2015 9:41 am

Of coarse i have an opinion too, Chl :D
I would err on the side of more than less.
With modern inverter systems that cycle when required, a larger unit will stay on, ie use power, less than one which is blazing away contiuously. The trade off is that below a certain size they are very very efficient . But as they get bigger the efficiency drops off a few percent. I cant quite remember the figures as i looked at this quite a while ago.
Obviously house efficiency is also very important. Standard thai brick means the aircon runs a hell of alot longer irrespective of size. But the principle remains, smaller runs longer, bigger runs less.
The thorny question is what size do you need. I have always gone by the manufactures suggestions ( not home pro , please) As they do all the research, i would suggest maybe, just maybe they are right.
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Re: A/C Sizing Chart

Postby Andyfteeze » Thu Jan 15, 2015 10:25 am

I have just gone through my papers and looked at what i had previously found.
Just to clarify what i found about efficiency and aircon units. 3-4kw units was the efficiency turning point. Larger units started to increase by a few percent.
For an 8x5m room i used a 5kw split system. Setting the temperature at 22-25c meant minimal usage, 10-20% on time.
This was for a well insulated apartment in melbourne. For the uninitiated, its four season in one day. 40c one day, 12c and wet the next. So location isnt a real variable but insulation is.

Trying to cool a whole house with one unit is asking a lot. Unless you have very efficient airflow throughout the house, you will get hotspots and cold spots. The unit will run a lot longer or irrationally. Maybe more efficient to have a few smaller localised units cycling. ie bedrooms, living rooms. ( hey, isnt that what the manufacturers say?)
Ok, so maybe i should rephrase the statement in the last post.
Larger units work less time than smaller units in a unified area. When walls and extra rooms are added to the desired cooling area, this rule of thumb breaks down due to insufficient airflow and irregular air/heat distribution.

My experience with thais and aircon is that they think its normal for the temp to be 18c and the aircon on all night. Thats why homepro recommend large units. Something to do with red bricks acting like radiators? :lol:
Another issue is noise. Do you really want that thing making noise all night?
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Re: A/C Sizing Chart

Postby Cheeryble » Sun Jun 28, 2015 12:49 am

Andyfteeze wrote: I have always gone by the manufactures suggestions ( not home pro , please) As they do all the research, i would suggest maybe, just maybe they are right.



they may be right for the extreme parameters they set themselves.

This would presumably be to size the unit so that on the hottest possible day the unit will cool the air to the lowest temperature on the remote.
I was in a place today where the lowest was 16 degrees C.
This may have only been a setting for the remote which was bought as a later add on apparently, but I'm sure the lowest is 20 deg C or under.
I personally would never dream of going under 25.

So the question is does one need to allow for this great temperature drop and my guess is in the vast majority of situations......no.

Seems to me what is needed is a "normal person's guide to aircon sizing".
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Re: A/C Sizing Chart

Postby BKKBILL » Sun Jun 28, 2015 10:44 am

Cheeryble wrote:

So the question is does one need to allow for this great temperature drop and my guess is in the vast majority of situations......no.

Seems to me what is needed is a "normal person's guide to aircon sizing".


Makes sense, we hear over and over if the unit is oversized humidity will not be reduced making a room feel warmer. I’m sure there are other good points to be made.
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Re: A/C Sizing Chart

Postby Roger Ramjet » Sun Jun 28, 2015 11:31 am

Cheeryble wrote:This may have only been a setting for the remote which was bought as a later add on apparently, but I'm sure the lowest is 20 deg C or under.

The normal lowest setting is 18 degrees.
BKKBILL wrote:Makes sense, we hear over and over if the unit is oversized humidity will not be reduced making a room feel warmer. I’m sure there are other good points to be made.

I doubt that's true Bill. The new inverter air conditioners have a setting for humidity, as do the older models. What you'll find is the person doesn't have it set properly. You need to be a brain surgeon to work out all the settings, my remotes all have a pull down slide that gives you another 12 settings on top of the normal ones. You can control the humidity in the air, as many people with asthma need to have some humidity in the air. The older ones used to have a Dry setting and I forget what the other option was called.
The real reason Thais install larger than necessary air conditioners is because they have red brick walls and no insulation in their roof. When I had my three new ones put in the shop had also done the wallpapering and the blinds, so they knew the walls were insulated and the windows had blinds over them, both inside and outside. The humidity is caused by both the red bricks and the windows. http://inspectapedia.com/Energy/Moisture_Problems.php http://www.thermalwindows.com/condensation.php http://www.doityourself.com/stry/preventmoisture#b
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