Air -cons: Do Two 9000 Btu Use More Than 1 18,000 Btu?

[gdhm]

I don't know if this is a daft question or not.

Facts

NON inverter type

18000 BTU to run flat out cooling most time in use.

My questions

1): would two 9000 btu units use more, less or approximately he same amount of electricity when running flat out.

I am not knowledgeable on Air con logic. Is there a rough guide how much Kilowatts are used (when cooling flat out per hour) with the different btu ratings of Air-cons.

2) Assuming a Maker's efficiency is similar between units does electrical usage rise proportionately to btu rating

3) What would be the normally expected Kilowatts used in one hours flat out cooling mode.

4) I expect to be buying 12,000 btu or 18,000 but units mainly.

a) Are there considered to be preferable manufacturers at present bearing in mind cost, electricity usage and reliability (NON inverter types).

Are there thought to be famous manufacturers LESS desirable at present.

Thanks

Dave

Edited July 8, 2008 by gdhm

[Naam]

Facts

NON inverter type

18000 BTU to run flat out cooling most time in use.

My questions

1): would two 9000 btu units use more, less or approximately he same amount of electricity when running flat out.

slightly more but you gain more flexibility with two units (especially when demand is low), have increased dehumidification and a better air distribution. if the higher purchase price is no concern then go for two units.

[Crossy]

I tend to agree with Naam and would go with the added flexibility of two smaller units, in a bigger room this also gives better distribution of cooling avoiding the arctic and tropical corners

What is your application and what makes you say your 18k unit will be running flat out all the time? (suggests that it's marginal size wise)

If it's essential cooling (servers maybe) then two units is definately the way to go and maybe two 12k units, then when one fails you don't lose all your cooling. Just a thought.

Edited July 8, 2008 by Crossy

[gdhm]

I tend to agree with Naam and would go with the added flexibility of two smaller units, in a bigger room this also gives better distribution of cooling avoiding the arctic and tropical corners

What is your application and what makes you say your 18k unit will be running flat out all the time? (suggests that it's marginal size wise)

If it's essential cooling (servers maybe) then two units is definately the way to go and maybe two 12k units, then when one fails you don't lose all your cooling. Just a thought.

Thank you Naam and Crossy.

My large lounge is an easy decision, namely 2 air con of 18000 Btu each. BUT the main bedroom I am unsure about.

Its size will be 10 x 5 metres about 2.8 metres high, 10cm thick QCON Blocks on all walls (interior and exterior) with 6 inch foil and fibre glass roll insulation across the attic floor and insulation foil under the tiles.

I have read the extensive recommendations for Btu for room sizes but have no idea how well the Qcon and insulation will impact on keeping rooms cool and thus allow lower (maybe much lower btu ratings for the air-cons Certainly I like my room down to 22 to 23C approx.

The problem as money IS limited now is IF I get one air con at first for the bed end of the bedroom would that possibly cope without the need for another to cool the rest of the room. Obviously I would up the btu rating for that air-con but not double .

If so, I have to make a choice. A sizable single one but maybe not as much as twice 2 air-cons. or 2 lower rated air cons which may be excessive if it is only one part of the room that really needs cooling directed at the bed.

It is useful to know 2 air- cons adding up to the same btu as one will use slightly more electricity than 1. Of course 2 will cost much more than 1 larger one to buy.

Not sure in all honesty which way to go or what btu would do the job.

I am mindful of much previous advice about pushing lower rating to near limit than having over capacity and it keeps tripping and cycling. Problem is, I do not want a situation I have in my current rental where the 9000btu Panasonic is struggling with a 3.2 x 3.2 x 2.5 high bedroom where there is no roof insulation and hot Thai bricks on all walls (including the interior ones as the Landing area is very hot at present)

Interestingly a Mitsubishi Air con (same btu rating) is doing a better job in my stepson's bedroom in the next bedroom which is identical size and has a much larger window area.

Not sure if that suggests the Mitsubishi is better, or has been gassed and set up better or the Panasonic is not performing as well as it should. Both bought by the owner at the same time a year ago (no idea why two different makes - maybe shop did not have 2 of each make in stock)

Called a technician out and was told gas was OK and it is working OK. Personally I think it was capable of cooler temperatures and faster cooling of the room up until 3 months ago (so it HAS operated during the hot season). Still as we are to move out hopefully before mid September to our new home I will not now worry too much about that.

Regards

Dave

[Naam]

BUT the main bedroom I am unsure about.

Its size will be 10 x 5 metres about 2.8 metres high, 10cm thick QCON Blocks on all walls (interior and exterior) with 6 inch foil and fibre glass roll insulation across the attic floor and insulation foil under the tiles.

I have read the extensive recommendations for Btu for room sizes but have no idea how well the Qcon and insulation will impact on keeping rooms cool and thus allow lower (maybe much lower btu ratings for the air-cons Certainly I like my room down to 22 to 23C approx.

our master bedroom is much smaller (8.00 x 4.50m) but 3.60 high. walls are superblock 20cm, good ceiling insulation BUT three outside walls. even though we have no problems to cool it down to 18ºC with two units each 13,000 btu. ACs are switched on around 21.00 hours, 18º are reached (depending on outside temperature) after 2-3 hours. when we (actually it's only me) go to bed i switch off one unit and set the other one on 26º which renders at bed level a comfortable 25º. as Mrs Naam goes to bed when i get up (around 04.00 hrs) she sets the temperature as she pleases (most of the time freezing cold).

[gdhm]

BUT the main bedroom I am unsure about.

Its size will be 10 x 5 metres about 2.8 metres high, 10cm thick QCON Blocks on all walls (interior and exterior) with 6 inch foil and fibre glass roll insulation across the attic floor and insulation foil under the tiles.

I have read the extensive recommendations for Btu for room sizes but have no idea how well the Qcon and insulation will impact on keeping rooms cool and thus allow lower (maybe much lower btu ratings for the air-cons Certainly I like my room down to 22 to 23C approx.

our master bedroom is much smaller (8.00 x 4.50m) but 3.60 high. walls are superblock 20cm, good ceiling insulation BUT three outside walls. even though we have no problems to cool it down to 18ºC with two units each 13,000 btu. ACs are switched on around 21.00 hours, 18º are reached (depending on outside temperature) after 2-3 hours. when we (actually it's only me) go to bed i switch off one unit and set the other one on 26º which renders at bed level a comfortable 25º. as Mrs Naam goes to bed when I get up (around 04.00 hrs) she sets the temperature as she pleases (most of the time freezing cold).

Thanks very much for you input Naam it is really helping me build up a picture and game plan.

By my calcs you have around 130 sq mtrs compared to my 140 sq mtrs. From what you have and your experience if I get about the same I will probably be OK or get an 18,000 and a 12,000. Your insulation seems very close to mine by comparison.

It is interesting as I tried to allow for the insulation factor and as a guesstimate had come up with 2 x 13btu (your scenario but my room is a little bigger. I was thinking IF 2 13,000 but were a little under-powered that if I had ONLY 1 in the bed area at 26000 Btu or a little lower it would probably easily keep that part of the room down to the temperature desired 22C approx.

May I ask how far do you have your air-con from the floor. I seem to recall in another thread you once said yours are not too close to the ceiling as you feel that is preferable. May I also ask whether your air-cons are over a window. (I am assuming air-cons directly over a bed or too close are not good idea due to lack of humidity reasons).

Mrs Naam sounds closer to my likes than your 25C but I am a very overweight man at 146 kilos so I need it to be cool or I get too hot in bed. ( good excuse to encourage the missus to cuddle up close to me, as she feels the cold at only 42 kilos) I don't' need it to be 18C though.

May I also ask please:

When Mrs Naam sets the the temperature much lower than you does she set Both Air cons or does one deal with lowering the temperature from 25C to much lower.

I would be very interested to know what in your opinion the one nearest your bed would achieve by itself around the bed area of the room. (maybe you have experimented in the past).

Kind regards

Dave

[technocracy]

I am staggered at some of the temperatures people are mentioning here!

The rooms must be absolutely freezing! Surely you've climatised enough not need that level of cooling? I use fans all day (which often I switch off) and at night our air con is at 27C anything less and I wake up cold (even 26!).

Our bedroom is an L shaped 8m x 5m (the L bit is 2.5m x 2.5m) and 3m high - we have a single 22000btu which is highly efficient at cooling this space. The walls are 20cm thick being double skinned brick (not blocks) the roof has the CPAC heat shielding, glass fibre insulation and for good measure a whirly. Also the house is north facing and gets minimal sun to the room having 2 outside wall.

Although we don't go for 22C or the like I have previously tested the aircon by cooling the room down 20C which it did with relative ease - not exactly sure on the time it took.

[Naam]

Thanks very much for you input Naam it is really helping me build up a picture and game plan.

By my calcs you have around 130 sq mtrs compared to my 140 sq mtrs. From what you have and your experience if I get about the same I will probably be OK or get an 18,000 and a 12,000. Your insulation seems very close to mine by comparison.

i think there is some misunderstanding. we were talking about bedrooms only. in your case 50m², in my case 36m².

It is interesting as I tried to allow for the insulation factor and as a guesstimate had come up with 2 x 13btu (your scenario but my room is a little bigger. I was thinking IF 2 13,000 but were a little under-powered that if I had ONLY 1 in the bed area at 26000 Btu or a little lower it would probably easily keep that part of the room down to the temperature desired 22C approx.

assuming that the heat load on your bedroom is similar to mine 26k btu should do the trick.

May I ask how far do you have your air-con from the floor. I seem to recall in another thread you once said yours are not too close to the ceiling as you feel that is preferable. May I also ask whether your air-cons are over a window. (I am assuming air-cons directly over a bed or too close are not good idea due to lack of humidity reasons).

all my aircons are mounted at heights of 2.20-2.60m (depending on different room heights) in order to leave the upper layer of air undisturbed as much as possible. in the master bedroom one unit is mounted above a window, the other one above the bed. there is no recognizable difference in humidity in an individual airconditioned room. i like it comfortable but i hate draft, that's why the unit that runs during the night is mounted above the bed.

Mrs Naam sounds closer to my likes than your 25C but I am a very overweight man at 146 kilos so I need it to be cool or I get too hot in bed. ( good excuse to encourage the missus to cuddle up close to me, as she feels the cold at only 42 kilos) I don't' need it to be 18C though.

i too realized that increased body weight demands lower temperatures. when i was about half your weight i wore a tie in ambient temperatures of 45ºC without sweating being 30 years older now and having gained ample pounds i start sweating at 28ºC

May I also ask please:

When Mrs Naam sets the the temperature much lower than you does she set Both Air cons or does one deal with lowering the temperature from 25C to much lower.

she uses just one but changes the airflow and air direction. i think she sets the thermostat to 22º which the unit can achieve due to less heat load in the night and mornings.

I would be very interested to know what in your opinion the one nearest your bed would achieve by itself around the bed area of the room. (maybe you have experimented in the past).

that all depends on the outside temperature. in the "cool" season one unit will definitely cool the room down to 18º. anything lower is not possible because the minimum setting is 18. nowadays with night temperatures of 26-27º one unit can only manage 22º.

[Naam]

I am staggered at some of the temperatures people are mentioning here!

The rooms must be absolutely freezing! Surely you've climatised enough not need that level of cooling? I use fans all day (which often I switch off) and at night our air con is at 27C anything less and I wake up cold (even 26!).

in many cases the opposite applies T-cracy! being used to aircondition for 35 years i became dependable on relative constant temperatures to the extent that i feel uncomfortably warm at 27º and cold at 26º (the latter does not apply when i sleep covered by a thin sheet). that's the reason why i maintain an average temperature in most areas of my home at ~26.5º. to achieve that result it was necessary to arrange all units accordingly which was not an easy task.

anyway, hot, warm, cold and comfortable is based on the individual perception and liking. no rule applies! fans? i hate them but my wife loves them

[jaideeguy]

So Naam, with all your aircon usage and your pool...how much is your average monthly electric bill?? [if I'm not being too personal]

[Naam]

So Naam, with all your aircon usage and your pool...how much is your average monthly electric bill?? [if I'm not being too personal]

last month ~10,500, next bill i estimate ~11,500 out of which less than 50% is aircondition use.

[gdhm]

Naam,

Thanks for your informative and extensive and detailed reply to all my questions. I am extremely grateful and I now I think I have all the answers I need for my purchasing and fitting decisions.

Your comments about the air-con over the bed are VERY interesting.

If I put my air-cons over my "favoured" bed positions (although marginally noisier) that solution would be wonderful as I was going to have to put them over windows in order to be on an outside wall (bed backing on to the only other outside (non windowed) back wall of house.

Had they been over a window they would of course be higher than the height you recommend and I agree seems a good idea).

Additionally, all 4 upper bedroom windows are on the more attractive side walls of the house.

I have eliminated all windows on the back wall of the house (except a small extra one in kitchen next to door, and a lounge one).

If I follow your idea of "over the beds" I get no drafts on the bed (something I know my wife will be happy with) AND I can place the air con lower and place 2 bedroom's air-cons on the unimportant, out of main views, windowless back walls.

Seems to me all gains (unless condensation drips from the air-con (which has only ever happened to me with one air-con)

I do not know why but I was under the mistaken impression air-cons above beds were not considered healthy or desirable (less humidity than in the room overall - but I was unable to find any source confirming that view on the Internet).

Certainly with an air con above the bed it would keep the immediate bed area cool (if by any chance slightly underpowered or only one switched on).

Comfortable Temperatures

I agree with you Naam. Fans just move hot air around -be there draft, better than nothing but poor cooling. In truth it astonishes me when people talk about 25C or 26C in their bedrooms.

Firstly, one does get used to being cooler,

Secondly in the UK the recommended healthy temperatures for living rooms is 21°C, 18°C for bedrooms and 16°C in halls. Even allowing for reduction in humidity I fail to understand why those temperatures are not still valid in Thailand.

To be honest I set my air-con to 21C and it runs all night so I think it gets to 22C which with the reduced humidity does seem OK for me here in Thailand even a little cold after a while if outside the light duvet too long - cannot sleep as well without something over me (purely psychological I know). BUT 25C upwards would NEVER be OK for me as I'd overheat and sweat all night, as I do in that type of heat outside the house (even in lower humidities).

Finally of course you are oh so correct, that each has his/her own comfort levels.

Once again thank you so much Naam

Kindest regards

Dave