Minimising sizing of aircon

[cheeryble]

 

 

In the sizing charts for aircons, I believe it errs very much on oversizing.

I think it allows for the air to go to the lowest temp on the remote (18degrees C?) on the hottest day of the year.

I personally never would need less than 25C, and for extra hot weather would be happy to run a fan too.

Therefore can't the AC size be reduced a LOT? (very little sun through windows)

We replaced a pair of aircons with 12kBTU less than half the recommended....fine so far but they haven't been right through a hot season yet to feel the real life efficacy.

As for smaller machines staying on more of the time an engineer friend of mine says they are designed to run and more breakdowns are caused by on off switching (they are not inverters)

Anyone care to comment, and also if they have experience with Midea. They look good, are quiet and blow well. They are way way cheaper than the Daikins we bought in the past with no 5 yr guarantee.

i see they're a huge company which reinvests x% in research, Toshiba bought 20% of the stock, and they were the only brand offering a 5 yr guarantee on both outer and inner units.

[brufi]

Hi,

I undersized our units both in the house and offices by about 50%. We are in Amantcharoen which has very hot summers. Built quality is typical thai which equals double carboard with some holes in it. We never had an issue with lack of cooling capacity while running target temperatures of 25°C.

[KittenKong]

On 17/10/2017 at 1:43 PM, cheeryble said:

they were the only brand offering a 5 yr guarantee on both outer and inner units.

 

I would not hold my breath waiting for that.

 

I use a ceiling fan on the slowest setting and I like my room temperature to be around 27-28 degrees. My inverter aircon is about half the recommended size for my condo. It works fine and does not run constantly.

[Pilotman]

Depends I would say.  In our bedroom, the air-con is under sized for the room, but because of its location, directly behind the bed, it does the job.  The open plan areas have two air-cons that are also  undersized and they can't cope on the hottest days, but a couple of fans helps.  My issue is my study, a large open plan and the undersized air-con doesn't do well at all. As I spend a good deal of time in that room, I should have upgraded to a larger model.  The sizing charts are not at all good at predicting how they will work for any particular individual and their tastes and you can find yourself with huge machines, costing lots of electricity when you dont need them. 

[Formaleins]

If you undersize or oversize you will risk the aircon not doing what it is supposed to do. It will not remove humidity correctly, it could be running inefficiently wasting electric, best to try and get it as close to specification as possible.

[waza46]

Better to be a bit under than a lot over. If you are a lot over the unit does not run long enough to reduce the humidity.

[DiDiChok]

I found the comment by "Brufi" most amusing when he said the Thai build quality was 'double cardboard with some holes'.  It sums up what happened to me in a house Lamphun last year all too well.  I only wanted to cool the bedroom in the bungalow and thought along the 'over specified' lines "Cheeryble" is thinking about.  The sun doesn't shine in the windows so I thought I'd be all right.

 

The bedroom is only 3 metres by 3.5 Metres by 3 metres high. The air con is a new Samsung 13,000 BThU and cost ฿19,000 fitted.  I thought that was huge for the room and would be much better than the cheap 9,000 BThU air conditioners which would be bound to be too small.  Well, while it's a lot better than nothing, 13,000 BThU just simply isn't big enough to hold 29C when the outside temperature goes over 40C.  Worse still, it means that you can't get the temperature down very quickly if you return home to a roasting bedroom.  Now, if you leave it on so that everything inside the room is cooled during the day, then it will hold 29C at 4 pm but only just.  Before anyone suggests that it's not working properly, it's been checked and I can confirm that the air coming out of the heat exchanger could cook an egg.  So very soon, I shall fit a 19 or 20,000 BThU one and move the existing one to another room.

 

The amount of cooling required is all about overcoming the latent heat in the room being cooled and then continually overcoming the incoming heat.  That's why you need an expert to do the calculations.  I hadn't accounted for the oven like space in the loft beneath the roof and above the bedroom.  Insulation in the loft in Thailand?  "Do for what?" as the locals say but now I understand only too well.

 

If you 'only' want 25C, get more than one company to recommend units and helpful changes to your room to suit your circumstances or like me, you'll buy cheap and buy twice.

[shaurene]

You will find these 5 yr guarantees are for ONLY the motor NOT anything else. And that would be IFFY here. The dealer will come up with some sort of an excuse not to cover it, like proof you had it serviced every 3-6 months.

[tryasimight]

15 hours ago, Pilotman said:

Depends I would say.  In our bedroom, the air-con is under sized for the room, but because of its location, directly behind the bed, it does the job.  The open plan areas have two air-cons that are also  undersized and they can't cope on the hottest days, but a couple of fans helps.  My issue is my study, a large open plan and the undersized air-con doesn't do well at all. As I spend a good deal of time in that room, I should have upgraded to a larger model.  The sizing charts are not at all good at predicting how they will work for any particular individual and their tastes and you can find yourself with huge machines, costing lots of electricity when you dont need them. 

What is a study?.. A place you go and hide in? Get away from the thai family........?

[tryasimight]

3 hours ago, waza46 said:

Better to be a bit under than a lot over. If you are a lot over the unit does not run long enough to reduce the humidity.

The first thing an air conditioner does is to reduce the temperatures of the air. This then drops the dew point of the air. This then removes water from the air.  That is how they work.  Look outside...they have a drain with water coming out.

 

[Crossy]

4 hours ago, tryasimight said:

The first thing an air conditioner does is to reduce the temperatures of the air. This then drops the dew point of the air. This then removes water from the air.  That is how they work.  Look outside...they have a drain with water coming out.

Indeed.

 

But the theory is that a small unit running longer exposes more of the room air to the chiller vanes where the water can condense out into the drip tray. A big unit running for a short time won't be moving so much air in the time it's operating.

 

Personal experience (rented condo) shows that a significantly oversized unit cools the room very quickly, but leaves the air feeling clammy and damp.

 

[jacko45k]

4 hours ago, tryasimight said:

The first thing an air conditioner does is to reduce the temperatures of the air. This then drops the dew point of the air. This then removes water from the air.  That is how they work.  Look outside...they have a drain with water coming out.

 

Yes, but cooling 99%  humidity at 32 DegC to 99% humidity at 25 DegC will still leave the room pretty humid, despite removing some water.

[newnative]

   The first condo we bought in Pattaya was a View Talay studio shell, 48sqm, interior space of around 35sqm.  We were told we should buy, I think, an 18,000 btu a/c unit.  Instead, we went with a 10,000 btu unit and had no problems at all.  If you want to make it snow in your room, then maybe go bigger.  If you are comfortable with a setting of around 22c or higher then smaller should be fine.  We prefer a setting of around 25 or 26c.

      Our current condo has a huge York a/c in the not huge living room. There does not seem to be a way to regulate the fan and we are practically blown out of the room when we turn it on.  We have to keep the temp. at 27 or 28 or it feels way too cold.  The bedrooms have smaller units that work much better and the same size should have been used in the living room as well.  I would check the energy usage ratings when shopping for an air con.

[Jonnapat]

Interesting conversations, I've learned lots of things about aircon of which I was unaware. Thanks to all.

[sometimewoodworker]

13 hours ago, jacko45k said:

Yes, but cooling 99%  humidity at 32 DegC to 99% humidity at 25 DegC will still leave the room pretty humid, despite removing some water.

apart from never seeing 99% humidity indoors as the AC continues to run it also drops the humidity down to a much more comfortable 60% ~50%. Lucky they don't get as low as I get here in winter when 10% to 20% is not unusual and a humidifier running 24/7 is needed.

[waza46]

13 hours ago, jacko45k said:

Yes, but cooling 99%  humidity at 32 DegC to 99% humidity at 25 DegC will still leave the room pretty humid, despite removing some water.

Humidity is water in the air, so removing water is lowering humidity.

[jacko45k]

9 hours ago, waza46 said:

Humidity is water in the air, so removing water is lowering humidity.

Not necessarily if the temperature also changes.

Removing water is incidental. If that was the aim one would need to overcool and reheat.

Relative humidity depends on temperature and the pressure of the system

[Naam]

On 10/17/2017 at 1:43 PM, cheeryble said:

As for smaller machines staying on more of the time an engineer friend of mine says they are designed to run and more breakdowns are caused by on off switching (they are not inverters)

Anyone care to comment,

your friend's claim is correct. on/off causes more wear and tear than continous running. that applies to most gadgets with moving parts and thermal load.

[Naam]

5 hours ago, jacko45k said:

Not necessarily if the temperature also changes.

Removing water is incidental. If that was the aim one would need to overcool and reheat.

Relative humidity depends on temperature and the pressure of the system

causing a latent cooling effect by dehumidification is a desired feature of aircons. manufacturers are even producing slightly different units with emphasis on high dehumidification in humid tropical areas and low dehumidification for arid areas.

[Naam]

On 11/10/2017 at 5:15 AM, jacko45k said:

Yes, but cooling 99%  humidity at 32 DegC to 99% humidity at 25 DegC will still leave the room pretty humid, despite removing some water.

you scenario is not possible (laws of physics).

[mikiea]

On 11/9/2017 at 8:15 PM, Formaleins said:

If you undersize or oversize you will risk the aircon not doing what it is supposed to do. It will not remove humidity correctly, it could be running inefficiently wasting electric, best to try and get it as close to specification as possible.

true words ...undersize allows for constant running to maintain during hot times of day or season . slightly oversize prevents constant compression of coolant , both  motors run less (fan & compressor). under sized units will run constantly to keep up . oversize use a little more elect , but do not run as much .....close to a toss up on the elect bill if your dwelling is tight  and sunlight shining in your home is  at a min.  

[Laza 45]

3 hours ago, mikiea said:

true words ...undersize allows for constant running to maintain during hot times of day or season . slightly oversize prevents constant compression of coolant , both  motors run less (fan & compressor). under sized units will run constantly to keep up . oversize use a little more elect , but do not run as much .....close to a toss up on the elect bill if your dwelling is tight  and sunlight shining in your home is  at a min.  

I'm getting confused now..  I have a room (daughter's bedroom).. (4m X 5m ..3 high)..(downstairs...concrete floor above so no radiated heat from above).. it is a bit unusual for here... cavity walls .. with insulating block.. verandas ...so no sun on external walls.. the temp stays fairly constant.. doesn't ever go above 31 C .. but... can be a bit to warm for sleeping comfortably.. the main problem is that it gets stuffy and humid.. the daughter keeps the curtains closed  so even with windows open it gets minimal air circulation..   from what I've been reading here.. 10,000 BTU should be adequate for cooling  and perhaps keep the humidity down.. now not so sure... ?? 

[Crossy]

30 minutes ago, Laza 45 said:

from what I've been reading here.. 10,000 BTU should be adequate for cooling  and perhaps keep the humidity down.. now not so sure... ?? 

Classic Thai guesstimate gives 12k BTU, from what you describe 9-10k should be just the ticket.

 

Most, if not all, have a "dry" mode too, intended to dehumidify.

 

[Pilotman]

29 minutes ago, Laza 45 said:

I'm getting confused now..  I have a room (daughter's bedroom).. (4m X 5m ..3 high)..(downstairs...concrete floor above so no radiated heat from above).. it is a bit unusual for here... cavity walls .. with insulating block.. verandas ...so no sun on external walls.. the temp stays fairly constant.. doesn't ever go above 31 C .. but... can be a bit to warm for sleeping comfortably.. the main problem is that it gets stuffy and humid.. the daughter keeps the curtains closed  so even with windows open it gets minimal air circulation..   from what I've been reading here.. 10,000 BTU should be adequate for cooling  and perhaps keep the humidity down.. now not so sure... ?? 

There are a lot of very knowlegable people on this forum, about almost every subject. I find their discussions and input very interesting, but confusing sometimes, as they get quite techinical quite quickly.  My advice would be to check the charts on ewhat is optimul for the square meterage you have and then reduce the BTU by a third, as a starting point.  I did that, and it seems to work.

[Laza 45]

1 hour ago, Pilotman said:

There are a lot of very knowlegable people on this forum, about almost every subject. I find their discussions and input very interesting, but confusing sometimes, as they get quite techinical quite quickly.  My advice would be to check the charts on ewhat is optimul for the square meterage you have and then reduce the BTU by a third, as a starting point.  I did that, and it seems to work.

Thank you..

[Laza 45]

1 hour ago, Crossy said:

Classic Thai guesstimate gives 12k BTU, from what you describe 9-10k should be just the ticket.

 

Most, if not all, have a "dry" mode too, intended to dehumidify.

 

Much appreciated.. thank you..

 

[claynlr]

From all the info I have received on an AC sizing question for a room in my house, from other Thai building sites, online BTU calculators, and esteemed members of the board... it seems the correct size is a crap shoot at best. For a 48 sq. meter room I have an advice range of 9,000-24,000 BTU's. And it seems you won't get a good answer from the "professionals" at the AC store because they will upsize you for a Thai style house or to make more money on a more expensive unit.

 

Guess I' ll guess and go with 15,000.......

 

 

[Naam]

7 minutes ago, claynlr said:

From all the info I have received on an AC sizing question for a room in my house, from other Thai building sites, online BTU calculators, and esteemed members of the board... it seems the correct size is a crap shoot at best. For a 48 sq. meter room I have an advice range of 9,000-24,000 BTU's. And it seems you won't get a good answer from the "professionals" at the AC store because they will upsize you for a Thai style house or to make more money on a more expensive unit.

 

Guess I' ll guess and go with 15,000.......

 

 

it all depends what average temperature you desire when ambient temp is 32ºC and of course what the heat load of this room is. only one thing is clear... the suggestion 9k btu/h is a joke and it could be that 24k btu/h is too small.

[claynlr]

And 24K might be too large and won't bring the humidity down! My point is there does not seem to be anywhere (Thailand or on-line) to get a valid answer by inputting room size, level of insulation, shading of walls, etc. My original post had these inputs and I received the wide range of size choices.

[Naam]

8 minutes ago, claynlr said:

And 24K might be too large and won't bring the humidity down!

what is the desired temperature? how many persons? any 70" plasma TV belching out 2,000 btu/h heat, open kitchen, sun on walls, window sizes, how many outside walls, thermal resistance of outside walls, condo or house, ceiling to another floor or to attic????