Inverter or regular A/C? Any advice please

[thedemon]

I know there have been several threads on this subject already and I have read through some of those but I still can’t make a decision about this so hoping for some advice.

The room concerned is approx. 40 M3. It is a corner room with all glass facing south and west and a vaulted ceiling so little insulation. Apart from the glass being mildly green tinted the room is about as inefficiently designed for cooling as you could get. I’m half expecting this room to get so hot during the afternoons that trying to cool it adequately might be hopeless. So it could be that this room will only be used mornings and evenings.

My questions are;

It seems that 24k BTU is the largest sized inverter type on sale in Thailand. Is this correct?

Would a 24k BTU be sufficiently powerful for this room?

Would an inverter be more efficient in this scenario and therefore worth the extra cost or would I be better off with a large sized standard A/C?

Any advice welcome. Cheers

[lopburi3]

Are you really talking about a large room of 40 square meters (40 cubic meters in vaulted ceiling would be a small room - maybe 15 square meters?)?

[thedemon]

Are you really talking about a large room of 40 square meters (40 cubic meters in vaulted ceiling would be a small room - maybe 15 square meters?)?

The room is roughly square - 6.5M x 6.5M.

Haven't tried to calculate the volume. I thought that the vaulted ceiling wouldn't make a very big difference apart from meaning not much insulation. Maybe wrong?

[KittenKong]

The living area (excluding the bathroom and balcony) of my square open-plan condo is somewhat larger than that with one entire wall in glass, though not exposed to direct sunlight except for an hour or so very early and very late in the day. The glass is single-glazed and the units are not airtight by any stretch of the imagination. My ceiling is not vaulted but there is no insulation apart from the plasterboard. I recently installed a new 24kBTU Hitachi inverter aircon that cools the whole room perfectly well and my total electricity consumption is only about 35% of what is used to be with the old 24kBTU (non-inverter) unit it replaced.

I have the aircon fan on minimum and also use two ceiling fans at the lowest speed. I set the thermostat to 27/28 degrees as what I'm really after is to reduce humidity (which I dont like) without freezing myself to death. The aircon runs more or less all the time, unless I'm away or the temperature is extremely low outside, but the outdoor unit rarely runs fast.

[thedemon]

The living area (excluding the bathroom and balcony) of my square open-plan condo is somewhat larger than that with one entire wall in glass, though not exposed to direct sunlight except for an hour or so very early and very late in the day. The glass is single-glazed and the units are not airtight by any stretch of the imagination. My ceiling is not vaulted but there is no insulation apart from the plasterboard. I recently installed a new 24kBTU Hitachi inverter aircon that cools the whole room perfectly well and my total electricity consumption is only about 35% of what is used to be with the old 24kBTU (non-inverter) unit it replaced.

I have the aircon fan on minimum and also use two ceiling fans at the lowest speed. I set the thermostat to 27/28 degrees as what I'm really after is to reduce humidity (which I dont like) without freezing myself to death. The aircon runs more or less all the time, unless I'm away or the temperature is extremely low outside, but the outdoor unit rarely runs fast.

Thanks, that's good to know that 24k can cope with the area and still run efficiently.

From reading some of the other threads on this subject I have gathered that inverter A/C's are most efficient when they are somewhat over capacity for the room size. So my concern is that if 24k BTU (apparently the largest available) won't have any excess capacity then there will be no energy saving benefit to outweigh the extra cost and other cons of an inverter vs standard A/C.

It will be used a 2nd living room, not for sleeping, so doesn't need to be kept particularly cool though 27/28C is too warm for me. 23-24C would suit me better.

[thedemon]

An update that maybe answers my question about 24k being the largest available. I asked one of my office staff do some checking and this is what she came up with.

Update for 30,000 BTU, today we found more information ka.

Daikin – FTKS33JV2S : 27,300 BTU (Full load – 30,000 BTU)

1. 50,000 THB - Air Best Buy (http://www.airbestbuy.com/contactus.php ) (price include Standard-Installation and bracket) + 1 time service in one year

**Yesterday he not offer this model because it is old model

2. 51,900 THB – Itzanan Ltd.,Part (price include Standard-Installation but bracket not include ka) + 1 time service in one year

*Payment – Credit card no surcharge / Cash

3. 52,000 THB – Union Air (www.union.co.th) (price include Standard-Installation and bracket) service not include

Saijo Denki – Grand Hybrid : 30,000 BTU

1. 52,000 THB – Itzanan Ltd.,Part (price include Standard-Installation but bracket not include ka)

2. 54,000 THB - Air Best Buy (http://www.airbestbuy.com/contactus.php ) (price include Standard-Installation and bracket) + 1 time service in one year

Fujitsu – I Power II : 27,300 BTU (Full load – 30,000 BTU)

1. 50,000 THB – Itzanan Ltd.,Part (price include Standard-Installation but bracket not include ka)

*Good Brand and good quality, but it may be hard to find spare parts

Where they say "Full load - 30,000 BTU", is that something meaningful or just technical mumbo jumbo?

Regarding the prices. The quotes I have for 26k, either Daikin or Mitsubishi are in the THB40k-42k range. So if these really are 30k BTU then at THB50-54k, the price is OK? Does anyone have recent experience on prices?

Daikin_FTKS_J_Series.pdf

Fujitsu Inverter wall.pdf

saijo_catalogue1.pdf

[AsiaCheese]

The living area (excluding the bathroom and balcony) of my square open-plan condo is somewhat larger than that with one entire wall in glass, though not exposed to direct sunlight except for an hour or so very early and very late in the day. The glass is single-glazed and the units are not airtight by any stretch of the imagination. My ceiling is not vaulted but there is no insulation apart from the plasterboard. I recently installed a new 24kBTU Hitachi inverter aircon that cools the whole room perfectly well and my total electricity consumption is only about 35% of what is used to be with the old 24kBTU (non-inverter) unit it replaced.

I have the aircon fan on minimum and also use two ceiling fans at the lowest speed. I set the thermostat to 27/28 degrees as what I'm really after is to reduce humidity (which I dont like) without freezing myself to death. The aircon runs more or less all the time, unless I'm away or the temperature is extremely low outside, but the outdoor unit rarely runs fast.

Thanks, that's good to know that 24k can cope with the area and still run efficiently.

From reading some of the other threads on this subject I have gathered that inverter A/C's are most efficient when they are somewhat over capacity for the room size. So my concern is that if 24k BTU (apparently the largest available) won't have any excess capacity then there will be no energy saving benefit to outweigh the extra cost and other cons of an inverter vs standard A/C.

It will be used a 2nd living room, not for sleeping, so doesn't need to be kept particularly cool though 27/28C is too warm for me. 23-24C would suit me better.

I read somewhere in an Australian aircon seller's website that you should not overshoot with BTUs, because when the A/C is too quick/efficient with bringing down the temperature, there won't be enough time to take care of humidity, leaving you in a cold but clammy room. With your m2, I would shoot for an 18kBTU unit (saving you money in the deal).

The bit with temperatures is deceptive: you may well set it to 27-28° (on the remote) and find that at bed level, the actual (measured there) temperature will be something in the vicinity of 24-25°. Physics at work...

@KittenKong: are you serious with only 35% power consumption vs. your old A/C? Was the old A/C working "properly"? I heard about power savings of 20-30% for inverter units, but I'd certainly welcome any additional % ;-)

[IMHO]

Saijo make a 36K BTU hybrid inverter (single phase 220v) - if you want something that will really cool the room down, no matter how hot it gets.

50K sounds about right for a top model 30K BTU inverter.

Inverters by nature vary their cooling power - generally in a range of 50% to 100% (some Daikins go down to 25%) -so full power would be referencing the upper end of the cooling range.

[aliep]

Inverter A/C's are less efficient if running continuously (you're converting AC to DC to run a motor with losses in the conversion process). Inverter A/C's are more efficient if they are oversized or set to run so that the compressor is running on half or a third speed speed in the outside unit.

The inefficiency is in stopping & starting, for several reasons. A correctly sized inverter will run on full speed for a shortwhile and then the compressor will slow down (but not stop).

By far the best solution is to fit 2 A/C units. A conventional unit that you set at 1 or 2 degrees lower than your inverter unit (so it runs continuously) and an inverter unit set slightly higher that actually decides the temperature in the room.

Personally, I would go for 2 of 18,000 BTU units, one conventional and one inverter. The conventional unit will provide 0 or 18,000 BTU of cooling, the inverter unit will provide 0, or 6,000-18,000 variable BTU of cooling.

For efficiency, keep refrigerant pipe runs as short as possible and don't put the outside engine in the sun.

[IMHO]

@KittenKong: are you serious with only 35% power consumption vs. your old A/C? Was the old A/C working "properly"? I heard about power savings of 20-30% for inverter units, but I'd certainly welcome any additional % ;-)

I can't answer for KittenKong, but a typical 10 year old 3 star unit manages only about EER=5 - the best units today are in the EER=19 range, so savings of > 70% could be possible if upgrading an old system.

[connda]

We have inverters for our house. Quieter, more stable temperature range, less electricity. I've had regular A/Cs before. I'd never go back. Sure, more expensive, but over time they'll pay for themselves in electricity savings. We're very happy with them.

[brimacthai]

Yes with standard units over-sizing will lead to higher humidity in the area cooled.

With inverters they are most energy efficient at around 50 to 60% part load. Not sure about buying one over-sized though... what happens is once the area reaches temperature the compressor starts to slow down. Doing maintenance cooling is always cheaper on power than to let a space get hot then turn on the air conditioner to cool it down.

My office at home I set at 26 when I'm working, humidity seems to stay around 45%. And when I'm not working I leave the air set at 28. The humidity rises to around 60%.

This helps keep my office reasonably dry for the printer papers and books. I have a lot of different paper for my printers for brochures and immages etc and keeping them dry is a must.

[mortenaa]

Inverter Inverter Inverter. Since its running constantly, it helps to keep the air dry and nice. Actually, I think 24 feels a bit too cool in a living-room when the air is dry. 25 is usually sufficient. My advice is not to buy an over-sized one. If the compressor stops, the air becomes humid. I've always been recommended larger Inverter than I need. My bedroom for instance. The experienced owner of an aircon sales/service shop said that 12,000 BTU just wasn't enough for my ~16sqm bedroom. But I really wanted that Daikin model, as its small, very quiet. But absolutely no problem. It cools the room easy to 21c all year around. I have single pane glass sliding doors, not very well insulated. The compressor runs quiet once the room is cooled down.

Edited October 30, 2014 by mortenaa

[mortenaa]

Inverter A/C's are less efficient if running continuously (you're converting AC to DC to run a motor with losses in the conversion process). Inverter A/C's are more efficient if they are oversized or set to run so that the compressor is running on half or a third speed speed in the outside unit.

The inefficiency is in stopping & starting, for several reasons. A correctly sized inverter will run on full speed for a shortwhile and then the compressor will slow down (but not stop).

By far the best solution is to fit 2 A/C units. A conventional unit that you set at 1 or 2 degrees lower than your inverter unit (so it runs continuously) and an inverter unit set slightly higher that actually decides the temperature in the room.

Personally, I would go for 2 of 18,000 BTU units, one conventional and one inverter. The conventional unit will provide 0 or 18,000 BTU of cooling, the inverter unit will provide 0, or 6,000-18,000 variable BTU of cooling.

For efficiency, keep refrigerant pipe runs as short as possible and don't put the outside engine in the sun.

If the inverter is oversized, it stops. I have a 35,000 BTU unit (Daikin sealing mount cassette) in my livingroom. About 60sqm. This is already too big, and the compressor stops quite often. In this season, I just run it for half and hour to cool the room, then i leave my 9000 BTU one in a connecting room on, just to keep the air dry.

Buying a conventional unit today sounds totally pointless. Unless you're looking to save a few pennies on the purchase.

[KittenKong]

@KittenKong: are you serious with only 35% power consumption vs. your old A/C? Was the old A/C working "properly"? I heard about power savings of 20-30% for inverter units, but I'd certainly welcome any additional %

Absolutely serious, and these are total figures including fridge, water heating, PC, big TV etc. So it is possible that the aircon unit only uses perhaps 25% of the electricity that the old one used.

The old one was a cheap model and about 12 years old. It did produce cool air and was cleaned every year, but it was noisy and the compressor was often running.

With the new one the compressor is off or running very slow much of the time, there is no "thump" when it turns on, and it all generally seems much quieter and less active and stressed. I estimate that the replacement will pay for itself in reduced electric bills in little more than a year.

I got a 24kBTU model because that was the rating of the old one, and that was cold enough. Shop calculations suggested 30kBTU or more would be needed, but I suspect that shops calculate for a much larger cooling capacity than I need. As I mentioned, what I'm really after is dryness with a bit of coolness and the new inverter unit seems to do this fine. When first turned on after being off for a while it does produce plenty of very cold air very fast, and so I suppose that it would also be suitable for permanently cooling down to low temperatures like 23 or so, but that's not what I want and I wont be doing that.

[KittenKong]

The bit with temperatures is deceptive: you may well set it to 27-28° (on the remote) and find that at bed level, the actual (measured there) temperature will be something in the vicinity of 24-25°. Physics at work...

This is why I also run two ceiling fans on the slowest speed 24/7. They keep the air at more of an even temperature throughout the whole area, and the moving air increases the sensation of coolness/dryness. I dont like high-speed fans though, just a gentle movement.

[shaurene]

You have approx 46sqr mt not cubic. With a vaulted ceiling the heat will rise to the top, with an air conditioner the cooling will sink to the floor and it takes a long time to cool a room like this if you turn it on at say 11am you will not feel much difference at say 1pm, get a normal a/c at least 28,000btu or 2 x 18,000btu the inverter will not cool it down faster than the normal one it will just save you a little power but I believe no benefit. Work out 5-6 cubic mt to each kw of cooling power in this country. 12,000btu is around 3 kW. So measure the width x depth x hight to get your cubic mt.

I would go for the 2 x 18,000 btu that would work out to 9 kW of power, should do the trick and get your windows tinted correctly and a couple ceiling fans to move the heat around from the top.

Best of luck.

[shaurene]

@KittenKong: are you serious with only 35% power consumption vs. your old A/C? Was the old A/C working "properly"? I heard about power savings of 20-30% for inverter units, but I'd certainly welcome any additional %

Absolutely serious, and these are total figures including fridge, water heating, PC, big TV etc. So it is possible that the aircon unit only uses perhaps 25% of the electricity that the old one used.

The old one was a cheap model and about 12 years old. It did produce cool air and was cleaned every year, but it was noisy and the compressor was often running.

With the new one the compressor is off or running very slow much of the time, there is no "thump" when it turns on, and it all generally seems much quieter and less active and stressed. I estimate that the replacement will pay for itself in reduced electric bills in little more than a year.

I got a 24kBTU model because that was the rating of the old one, and that was cold enough. Shop calculations suggested 30kBTU or more would be needed, but I suspect that shops calculate for a much larger cooling capacity than I need. As I mentioned, what I'm really after is dryness with a bit of coolness and the new inverter unit seems to do this fine. When first turned on after being off for a while it does produce plenty of very cold air very fast, and so I suppose that it would also be suitable for permanently cooling down to low temperatures like 23 or so, but that's not what I want and I wont be doing that.

To help your dryness get a dehumidifier, we send Dehumidifiers from our warehouse in New Zealand to a Thai company that supply's to hospitals, takes out 50lts of water in 24hrs.

[weedywhaoo]

When I worked in a condominium, we used the formula area×800 to get the BTU needed. In your case it would suggest 36800 or larger.

Conventional AC is cheaper to refill gas, about 500 baht. Inverter cost 1500 baht.

[armadillo215]

I have been in the trade 40 years. An inverter unit is for capacity control so say for instance you have a 24,000BTU unit that will unload or slow to 6000BTU that is your capacity range. It is basically a dimmer switch. You want your unit to run until the space is at the temp. you want but you don't want the unit to satisfy before it removes the moisture from the air. So as the temp approaches the set point the compressor slows down to keep the suction pressure/capacity at the most efficient point. You see along with the capacity control making the unit more efficient it keeps the unit running longer. The starting of a fan motor or the motor in the compressor is ware and tare on that motor shortening the life. That starting surge of electricity expands the winding or motor coil dramatically every time it starts and that leads to basically, metal fatigue and failure. Have someone do the math and size the unit correctly

[KittenKong]

To help your dryness get a dehumidifier, we send Dehumidifiers from our warehouse in New Zealand to a Thai company that supply's to hospitals, takes out 50lts of water in 24hrs.

I'd rather not install and run two different machines. The inverter aircon seems to give me reasonable dryness (I'm not an Egyptian mummy) and reasonable coolness for relatively low purchase and running costs, whilst running at low speeds and without any surges in temperature humidity or noise, which is exactly what I want.

[Mudcrab]

Never have so few, dribbled so much garbage, in such a short time...My apologies to Winston Churchill.

"Conventional AC is cheaper to refill gas, about 500 baht. Inverter cost 1500 baht." Dear God spare me.

[malt25]

OMG... I was contemplating getting "AIR" in our small house, bungalow, next year.... Mainly the bedroom, but maybe the whole house. After reading all the "expert advice" above, I'm more confused than ever.

Maybe send the house dimensions to a reputable dealer back home & ask their advice ??

What to do ??????

[ThaiSmarterThanYou]

What is the real difference with an inverter ? The compressor of an inverter can "work" slower, right ?

[misterphil]

I see you've had a lot of confusing replies to your questions. Let me give you the answers in layman's terms.

It seems that 24k BTU is the largest sized inverter type on sale in Thailand. Is this correct? No

Would a 24k BTU be sufficiently powerful for this room? Yes

Would an inverter be more efficient in this scenario and therefore worth the extra cost Inverters are cheaper to run, Yes more expensive to buy, but cheaper to run in the long run.

or would I be better off with a large sized standard A/C? It doesn't work like that. You have to get the right size AC to suit the size of your room. If you get a too small AC it will work constantly and wear out, freeze up and all sorts of problems. If you get a too big AC it will not work efficiently. It has to cycle start, stop, start, stop for it to perform to its best ability. Plus if your windows are facing South they will get a lot of sun through them most of the day, and this will add to the amount of BTU you require.

Your room is 42.5sqm so 24K BTU will be ok, I would think about using a window film, and maybe some blackout curtains from Homepro for those very hot afternoons.

I have Daikin inverters AC's in my house. I cant fault them, they're as quiet as a mouse. Had 1 problem in 3 years, where the remote sensor failed and got that replaced for 1,000 baht.

http://www.northernac.com/newcalc.htm

[KittenKong]

What is the real difference with an inverter ? The compressor of an inverter can "work" slower, right ?

Regular compressors are either on or off. Inverters can vary anywhere from zero to full, and they do so smoothly as needed.

So with an inverter you get a more steady air temperature and no sudden on/off noises etc. As a result of this they are more efficient and cost less to run.

[IMHO]

What is the real difference with an inverter ? The compressor of an inverter can "work" slower, right ?

Regular compressors are either on or off. Inverters can vary anywhere from zero to full, and they do so smoothly as needed.

So with an inverter you get a more steady air temperature and no sudden on/off noises etc. As a result of this they are more efficient and cost less to run.

All correct, they can go down to zero (i.e. off), but while they're actually running, the speed/cooling capacity actually only varies within a range - for most inverter units the range is between 50% to 100% of rated cooling capacity, but some newer models can go down to around 25%, before they start cycling on/off like a regular AC.

For example, a typical 18,000 BTU inverter AC can vary it's power between 9,000 and 18,000 BTU. If less than 9,000 BTU is needed, it will cycle off/on like the old machines used to do.

[IMHO]

I read somewhere in an Australian aircon seller's website that you should not overshoot with BTUs, because when the A/C is too quick/efficient with bringing down the temperature, there won't be enough time to take care of humidity, leaving you in a cold but clammy room. With your m2, I would shoot for an 18kBTU unit (saving you money in the deal).

The standard Thai rule of thumb of 600-800 BTU per square meter isn't universally recommended without reason

The point of this range is, that even on the hottest Thai day the AC will be able to bring the temperature down. Undersize it, and it might be just fine for 40 weeks of the year, but it might let you down when you need it the most.

Use 600 BTU/sqm if the room doesn't get direct sunlight and it's well insulated. Otherwise, use 800 BTU/sqm.

This is not a challenging time of year for an AC.. so what works now might not necessarily work so well when the real heat comes..

[HerbalEd]

OMG... I was contemplating getting "AIR" in our small house, bungalow, next year.... Mainly the bedroom, but maybe the whole house. After reading all the "expert advice" above, I'm more confused than ever.

Maybe send the house dimensions to a reputable dealer back home & ask their advice ??

What to do ??????

What to do????? It's called Google.

[kennw]

You seem to have received much good practical advice but little about the basics. Room air conditioner are temperature control units. The air passing thru the fan-coil unit is cooled and in the process some moisture is condensed, the amount depends on the dewpoint. The higher you set air temperature the higher the humidity will be assuming the air was above the dewpoint to start with. If you want to condition air based on a desired humidity level you have to cool the air way down so that the amount of moisture left in the air is small and then reheat the air to the temperature you want. In other words you are drying the air by cooling it sufficiently to condense the moisture out to a level such that when it is reheated to the temperature you want the lbs of moisture per lbs of dry are at the humidity level (or below) the level you want. Normal room air conditioners are a compromise. You can set them to a temperature but not humidity level, the latter depends on what humidity level you start with, how much air is recirculated thru the fan-coil unit, what the level of air ingress is (outside air leaking in), and thermal gain (heat coming in thru windows and walls). Suggestion, get someone to do the calculations to determine what size unit you need based on the specific parameters for your room. ie. window size orientation, air ingress, etc etc.