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Chris Hobson
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I cannot give you exact numbers, but I seem to recall that a 9000BTU is only good for the smallest of rooms (around 16m^2). A 12000 BTU is good up to around 25. Obviously, the higher you go, the better the duty cycle, it cools better, etc. So you're likely looking at the next size up from 12000BTU, whatever that is.

 

Largest I have in my home is a 12000 BTU.

 

What type? Inverter if you can. They don't have the large spike when they start up. It's easier on your inverter. Even the small 9000BTU compressors (non-inverter) have a 5kw startup spike.

 

That's as far as my knowledge goes on that.

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Hi Guys,

Hope all well. In our Server room we installed a Daikin Inverter Unit. Here is a fair BTU requirement calculator based on room volume: http://www.daikinairconditioninglondon.com/calculator.php

Sure you guys aware that the inverter units are able to slow and speed up the compressor apposed to the conventional off and on one speed compressors. This saving power and surge power.

One does get direct DC aircons- more used for Telecom shelters. Such as : https://www.dantherm.com/(They LOUD! ) :>

 

This is all to the best of my knowlege. Offsetting Aircon with Solar has always been a great interest to me.

I have had good results with a Grid Tie Solar in the Day- (Thus offsetting the 800W or so that the Daikin uses from 10am till 3pm)

 

And then shutting off the aircon at night and making use of a roof chimney to get the natural convention. I was shocked how well that works. 

Computer water cooling and so forth has always been a great interest to me, So excited to read what your guys expirences are with aircons on solar and cooling.

Sincerely

Jason

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  • 4 weeks later...

Where to start...

 

There is a lot of things to keep in mind before you decide to have an aircon installed. I'll share some tips and personal experiences.

 

I'm only going to refer to when the aircon is going to be used for cooling, but the opposite applies for heating. You'll have to look at room size, sources of heat, e.g. stove or built-in fireplace or computers etc., number of occupants, does the room have large windows, does the room get direct sun, in the morning, midday and/or afternoon, does the room have proper insulation on the ceiling, can the area be closed off pretty well, e.g. is it an open-area living room/kitchen or perhaps a bedroom with walk-in closet or bedroom with on-suite bathroom or perhaps just a small bedroom? 

 

Then you have to take the outdoor temperature into account - it is usually cooler closer to the sea compared to inland areas and you are most probably going to use the aircon when it is hotter outside rather than when it is cooler. Look at the aircon specs before you make your decision - I have not had an aircon installed recently, but 5 -7 years ago, when I did, the Samsung units were rated for an outdoor temperature of 43

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I recently learned something else about the inverter units. Another contact of mine (on facebook) explained that there is a point in the cooling process where things get very inefficient. I have not been able to find stuff on the science behind this, just marketing material mostly, but I suspect it is similar to the kind of thing you get with a centrifugal water pump: There is a flow/pressure combination where the pump works optimally, at all other points it is less efficient. Now with that principle in the back of your mind: Apparently inverter AC units have a sensor where they detect that point in the air, and then they back off just a little to avoid it. A non-AC unit just powers right through that point until it reaches the desired temperature...

 

Maybe someone else here knows more about the science?

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  • 5 months later...
I have a 17000btu Daiken inverter aircon in my bedroom. 300 to 400w draw max and as low as 50 once at temp. Amazing. Run it all night in summer with out seeing a increase in my power consumption.

Sent from my SM-G920F using Tapatalk

Does realy draw that low power? Where can we buy the Daiken aircons?

Sent from my SM-G920F using Tapatalk

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On 6/26/2016 at 6:45 AM, Manie said:

Does realy draw that low power? Where can we buy the Daiken aircons?

The compressor motor of an inverter aircon runs on DC and the speed it runs at is adjusted according to the difference in temperature between what it is set at and what it currently is at.  I'll try and explain it by means of an example.  If the aircon is running in cooling mode and the temperature is set to 22°C and currently the room temperature is at 24°C the compressor motor will not run at full speed but say at 25% because the delta T is not much and if the aircon was specced correctly and no other unforeseen external factors are present (e.g. a fireplace heating up the room at that moment) the aircon should be able to reach the set temperature quite soon. If however the aircon is set to 22°C, but currently the room temperature is at 30°C, the compressor motor will probably run at full speed or close to that since the delta T is quite big. Obviously the faster the compressor motor runs, the more power is used. Therefor the aircon might use as little as 300 to 400W if the room has almost reached temperature and just have to maintain that temperature, but on the other hand it will use a lot of power (run at max) if you've set the temperature to 16°C and it is 40°C outside and all the doors and windows are open. :D

Conventional aircons work like typical refrigerators where the compressor always runs at maximum speed until the set temperature is reached and then it switches off completely until the temperature has changed by a degree or two and then the compressor is turned on fully again until the set temperature is reached again - this is called cycling. Obviously if you've set the temperature to 16°C and it is 40°C outside and all the doors and windows are open the compressor will also run continuously and theoretically draw the same amount of power as an inverter aircon under the same circumstances.

Where an inverter aircon also use less power is where an aircon is specced incorrectly or used incorrectly. Unfortunately aircons are frequently underspecced, because things like insulation on the ceiling, sun shining directly onto a window, large windows, a room on the second story / highest part of the house to name a few all influences the size of the aircon required and in most instances only room size is used to determine the size of the required aircon. The the biggest problem is user training - a comfortable temperature to set the aircon at is between 22 and 26°C for cooling and around 18 - 20°C for heating and most people does not know that and often sets aircons at 16 or 18°C (lowest possible setting) for cooling and 30°C for heating and most of the time the aircon will never be able to reach those extreme temperatures unless they were initially overspecced for the specific room / area. In such an instance a non-inverter aircon's compressor will constantly run and never reach the set temperature and obviously constantly use maximum power, but under the same circumstances an inverter aircon's compressor motor might initially run at full power but will gradually start to run slower and use less power as the delta T becomes smaller and therefor an inverter aircon might use less power than a non-inverter aircon.

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The compressor motor of an inverter aircon runs on DC and the speed it runs at is adjusted according to the difference in temperature between what it is set at and what it currently is at.  I'll try and explain it by means of an example.  If the aircon is running in cooling mode and the temperature is set to 22°C and currently the room temperature is at 24°C the compressor motor will not run at full speed but say at 25% because the delta T is not much and if the aircon was specced correctly and no other unforeseen external factors are present (e.g. a fireplace heating up the room at that moment) the aircon should be able to reach the set temperature quite soon. If however the aircon is set to 22°C, but currently the room temperature is at 30°C, the compressor motor will probably run at full speed or close to that since the delta T is quite big. Obviously the faster the compressor motor runs, the more power is used. Therefor the aircon might use as little as 300 to 400W if the room has almost reached temperature and just have to maintain that temperature, but on the other hand it will use a lot of power (run at max) if you've set the temperature to 16°C and it is 40°C outside and all the doors and windows are open. default_biggrin.png

Conventional aircons work like typical refrigerators where the compressor always runs at maximum speed until the set temperature is reached and then it switches off completely until the temperature has changed by a degree or two and then the compressor is turned on fully again until the set temperature is reached again - this is called cycling. Obviously if you've set the temperature to 16°C and it is 40°C outside and all the doors and windows are open the compressor will also run continuously and theoretically draw the same amount of power as an inverter aircon under the same circumstances.

Where an inverter aircon also use less power is where an aircon is specced incorrectly or used incorrectly. Unfortunately aircons are frequently underspecced, because things like insulation on the ceiling, sun shining directly onto a window, large windows, a room on the second story / highest part of the house to name a few all influences the size of the aircon required and in most instances only room size is used to determine the size of the required aircon. The the biggest problem is user training - a comfortable temperature to set the aircon at is between 22 and 26°C for cooling and around 18 - 20°C for heating and most people does not know that and often sets aircons at 16 or 18°C (lowest possible setting) for cooling and 30°C for heating and most of the time the aircon will never be able to reach those extreme temperatures unless they were initially overspecced for the specific room / area. In such an instance a non-inverter aircon's compressor will constantly run and never reach the set temperature and obviously constantly use maximum power, but under the same circumstances an inverter aircon's compressor motor might initially run at full power but will gradually start to run slower and use less power as the delta T becomes smaller and therefor an inverter aircon might use less power than a non-inverter aircon.

Thanks for the explanation. Makes total sense. Do you know were i can buy one of these inverters at a good price

Sent from my SM-G920F using Tapatalk

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1 hour ago, superdiy said:

speed it runs at is adjusted according to the difference in temperature between what it is set at and what it currently is at

Good inverter ACs have a humidity sensor as well, and they can avoid wasting power at the dew point. At least, this is what I have been led to understand. If my physics don't forsake me, when you hit the dew point (temperature) water starts to condense out of the air, and this state change robs some of the energy that would normally go into making the air cold. So an inverter-AC can back off the power just a bit. A conventional AC cannot do that, and will just repeatedly power right through the dew point, especially if you set it too low.

It also has to be said, and @superdiy touched on this already, that if your room isn't properly insulated, then the AC consumption will equal the leakage from the room. If it runs at 50W or less, that's an indication that the leakage on the room is really low.

On my conventional 12000btu unit at home, I was lying awake one night (shortly after my daughter was born) listening to the AC switch on and off (because newborns need to be kept quite warm, and it was the middle of July), worried about how much this was blowing the budget (I was pushing 4.5k in electricity that winter)... so I started watching the alarm clock, and pretty soon realised the AC was spending more time "on" than "off", that is to say, it was working at a duty cycle above 50%. I knew it wasn't undersized, 12000btu is enough for a small to medium bedroom... so I installed ceiling insulation within two days. It made a massive difference to my power consumption and the duty cycle on the AC.

My advice: If you want to save power, install the ceiling insulation first.

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14 minutes ago, plonkster said:

My advice: If you want to save power, install the ceiling insulation first.

Very good advice indeed. I've experienced a similar situation, but with cooling.  On the hot summer days you could feel the heat radiating through the ceiling if you held your hand about 30cm away and the ceiling was warm when touched. Then I decided to install isotherm and did a test in one of the rooms by covering only a section of the ceiling with some isotherm and you could clearly feel the difference below - no more heat radiating from the ceiling where the isotherm was installed and the ceiling was not warm if touched although the section not covered with isotherm still radiated heat and was warm when touched.

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Just now, superdiy said:

did a test in one of the rooms by covering only a section of the ceiling

My house has a party trick: I could not insulate the living room area, because I have an open beam roof construction and the blow-in insulation we used everywhere else could not be used there. So that part of the house literally has 32mm of rafter between the roof tiles and a knotty-pine ceiling, no insulation. Walk through the arch into either the kitchen or bedroom area and you literally feel the floor getting cold beneath your feet. I've had family visiting remarking how nice it is that we have air conditioning in that part of the house... :-)

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  • 2 weeks later...

@Chris Hobson Have a home office - approx 20 sqm (High Ceilings) and we installed a Samsung AR7000 12000BTU about a year ago - very happy. 

 

Another requirement for me personally is how quiet both the outside unit and the internal fans are - and I have never experienced an aircon in "quite" mode that is actually this quite -you cannot hear a thing. When "idling" around 22 deg in quite mode during summer it was under kw - probably around 500w as well.

Daikins are great - just be prepared to pay more... as long as you stay away from the cheapies  - the "buy one get two free" types - installers will tell you its all "made in the same place" - ignore that. 

Last thing to help decide - go with a good installer, and use what they install most so that parts and service afterwards is up to scratch..

 

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14 hours ago, Igubu said:

Have a home office - approx 20 sqm (High Ceilings) and we installed a Samsung AR7000 12000BTU about a year ago - very happy. 

When "idling" around 22 deg in quite mode during summer it was under kw - probably around 500w as well.

12000BTU for 20m2 and high ceilings - that is quite remarkable or rather say a bit under-specced. I guess it is as I've described in a post above - the aircon will not really manage to get to 22°C in cooling mode, but since it is an inverter aircon and it might get close to 22°C, the compressor is not running at full power because it thinks the set temperature is almost in reach. Well thinking of it again, my Samsung non-inverter 12000BTU aircons run at 1KW, so if yours is running at "under kw - probably around 500w" that confirms what I've said above and this is a perfect example where the inverter aircon will save you money compared to a non-inverter aircon, which will run at full power without cycling because it can also not reach 22°C as in this case.

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1 hour ago, plonkster said:

Dude... I know it is uncool to nitpick spelling... but quiet vs quite... my knee is jerking something terribly :-)

I am fortunate in that English is my mother tongue and since for many on this forum English is the second and maybe even third language I think we can let it slide. I wonder whether I would manage if this was in Afrikaans. Plonky you are particularly bilingual but English is like no other language closest to Scandinavian languages and Frisian a language spoken by about ½ million people in the province of Friesland and small part of Germany. When I was in the Netherlands on more than one occasion I was mistaken for a Frieslander on the mainland. English is however has elements of German,Dutch, French, Latin, Celt and Greek (via Latin), hence the plethora of synonyms.

Anyway I have managed to sidetracked myself. I think as more people join the forum from the sub-continent and elsewhere we need to be tolerant.Quiet and quite is a pet peeve of  mine too :D

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Just now, Chris Hobson said:

I think we can let it slide

Oh absolutely, do not get me wrong... it's just the pet peeve thing you mentioned. Absolutely no malice intended. The worst one for me: When people write "could of" instead of "could have". Man... that sends me running for the hills.

You're right as well about English being like none of the others. Rain reign rein. Read and Lead (as in leadership), but also Read (past tense) and Lead (the metal). Break and Steak, but Bleak and Streak...

Of course not limited to English either. Die, die die, die die anzeigen, die die Äpfel klauen, werden belohnt.

And I did mention it was knee-jerk :-)

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@plonkster :) Thanks for pointing it out!  The reason for my very poor spelling : the Microsoft Phone I'm using! (640) Must be the worst auto correct ever designed, to make it worse, the phone auto switches between English US, English UK and Afrikaans between words!  It's quite something to experience! Hope your knee is ok... ;)

Wir können auch Deutsch verwenden!

..but on topic.. yes very happy with the Samsung..

Bütha

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  • 4 weeks later...

Blow me down.

Company that services my aircons, asked them why not sell 2nd hand aircons, the ones they are servicing, on to the next customer so that one can upgrade to the newer better inverter models?

He says: I will not install a inverter unit for myself at home.
"What!", says I, "Why not?" I ask.

The comebacks are escalating to a point where they do not want to sell them anymore. Apparently the PC board attracts a lot of goggas with inevitable problems. Plus the savings you make on electricity is not as attractive as claimed, so the more expensive inverter models takes years to recoup the savings, IF you have no failures in the interim, and what they are seeing, you are going to have to spend on repairs in a few years.

So that sorts my problem quite neatly. I am not changing what I have if the guys who supply, install and maintain aircons, advise me that they do not want to sell me one.

 

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6 minutes ago, The Terrible Triplett said:

Blow me down.

Company that services my aircons, asked them why not sell 2nd hand aircons, the ones they are servicing, on to the next customer so that one can upgrade to the newer better inverter models?

He says: I will not install a inverter unit for myself at home.
"What!", says I, "Why not?" I ask.

The comebacks are escalating to a point where they do not want to sell them anymore. Apparently the PC board attracts a lot of goggas with inevitable problems. Plus the savings you make on electricity is not as attractive as claimed, so the more expensive inverter models takes years to recoup the savings, IF you have no failures in the interim, and what they are seeing, you are going to have to spend on repairs in a few years.

So that sorts my problem quite neatly. I am not changing what I have if the guys who supply, install and maintain aircons, advise me that they do not want to sell me one.

My next door neighbour from a few years ago was an aircon installer and he told me that the power supplies of the inverter aircons fail a lot because of loadshedding and the unstable grid. I have only one inverter aircon, a 30000 BTU jobbie, which I keep switched off at the DB and only switch on when we want to make use of it for the reason mentioned above.

The main reason why I went for the inverter type instead of the non-inverter type when I had it installed was for the fact that the startup current on the 30000 BTU non-inverter aircon of the same brand was almost 80 amps and that meant that I had to have my main breaker upgraded to at least a 100A and that would have had an enormous effect on my monthly connection fee. So I went for the inverter type, with a startup current of less than 20A and I could keep my 40A main breaker and much lower monthly connection fee as is. The other advantage is the lower claimed running current. According to the product information stickers on the aircons, the 30000 BTU inverter aircon's maximum consumption / running current is less than the maximum consumption / running current of each of the 18000 BTU non-inverter aircons I have.

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