Question About Air Conditioner Power Consumption

[Naam]

If you are going to spend a lot of time home in the day then the design criteria have to shift in that direction. But a well-designed house inThailand should still be liveable most of the time, and especially most mornings, without aircon. I agree that on especially hot times of day or when you might want a daytime snooze aircon is ok, but only ok because aircon in Thailand either cycles on and off which is uncomfortable or if it is kept running produces cold clammy air. Aircon is in general not really good at dealing with humidity and humidity is the big problem in Thailand. Ron

you, Honourable Sir, seem to possess a wealth of "no idea" about airconditioning and dehumidification. where do you think the liquid which drips out of the aircon drains comes from? perhaps from people climbing on a ladder and peeing into their inside units? however, you are right that an overdimensioned unit cycles on and off and therefore lacks proper dehumidification. but the case you experienced does not warrant the generalising comment "aircons in Thailand...".

[elkangorito]

^Good one doc

[PattayaParent]

I used to work with a HVAC engineer that could tell you the approximate BTU to be used if you told him the volume of the room.

He multiplied the volume by a factor to get the BTU. Does anyone know what that factor is?

Edit: Obvioulsy for a confirmation of sizing other factors have to be considered but for estimating purposes the factor is close enough.

that would be the equivalent of estimating the boob size of your girlfriend if you tell him which day and month she celebrates her birthday.

I understand where you're coming from Naam but nevertheless HVAC people use volume as a rough estimate of sizing assuming 'standard' construction when estimating.

Of course if your house is entirely glass walled or cavity wall with foam insulation and no windows, or an igloo, the rule of thumb would not apply.

Even the per m2 table given above has to assume a 'standard' height of ceiling.

[rgs2001uk]

I used to work with a HVAC engineer that could tell you the approximate BTU to be used if you told him the volume of the room.

He multiplied the volume by a factor to get the BTU. Does anyone know what that factor is?

Edit: Obvioulsy for a confirmation of sizing other factors have to be considered but for estimating purposes the factor is close enough.

that would be the equivalent of estimating the boob size of your girlfriend if you tell him which day and month she celebrates her birthday.

I understand where you're coming from Naam but nevertheless HVAC people use volume as a rough estimate of sizing assuming 'standard' construction when estimating.

Of course if your house is entirely glass walled or cavity wall with foam insulation and no windows, or an igloo, the rule of thumb would not apply.

Even the per m2 table given above has to assume a 'standard' height of ceiling.

There was a guy on another thread saying he has an eight metre high ceiling, think he was living in a barn.

Whats the average ceiling height, somewhere between 3 an 4 metres?

As PP mentions above a normal per m2 table isnt going to be much use if your ceiling is double the average height.

[PattayaParent]

^typical soffit heights are 2.8~3m in a condo, and with a suspended ceiling the height could be anywhere between 2.4m and 2.8m.

I'm assuming Naam's philosphy is based on hot air rising and cool air falling so an equilibrium is reached at 2.4m and it doesn't matter that your ceiling is 8m high, your thermostat measuring the ambient temperature is going to be in the AC and it won't work to cool the air above it whatever the temperature.

[PattayaParent]

OK I'll ask my question this way.

I have a room 13.640m long by 3.900m wide with a ceiling height of 2.800m.

It has a window at one end of 3.9m X 2.8m. It will get the morning sun and be shaded in the hottest part of the day and the afternoon (by the condo next door)

The AC will not be used continually.

What size and how many AC do I need? Would inverters be any benefit if the AC is not used continuously?

[Crossy]

What size and how many AC do I need? Would inverters be any benefit if the AC is not used continuously?

I am not an expert so others may have other ideas. You may wish to consult your local aircon shop

With a long narrow room using two units would improve the air circulation, and you could run one unit when it's not too hot.

Finger in the air says 2 x 18,000 BTU units.

Inverters will save on energy when they're not being run flat-out.

YMMV

[PattayaParent]

I always assume my local aircon shop is interested in selling me the largest units possible rather than what I actually need but your answer is just what I'd calculated myself Crossy.

I wouldn't actually be planning on running them both at the same time as one half of the room would be living and the other half dining and entrance and I don't like it too cold so can survive in 25C temperatures (with a sweater).

[rexnong]

Can anyone help , i have a Hitachi 9000btu which worked great for about 18 months in our bedroom but for the last 6 months it dosent seem to get the room cool like before

It was last cleaned 2 weeks ago and all topped up by the local air con company

The stores dont /wont listen and say ah yes you need a new air con unit as your room needs a bigger unit although it worked great before and we never set it lower than 25 on automatic when it would switch on and off

Now we leave it on 16 fan 3 flat out and it dosent do much at all

If you put your hand near the fan area it feels o.k but not like before

The unit has always been serviced and topped up full every 3-4 months but talking to the stores they just want to sell a new inverter air conditioner and dont listen to one word about the problem ?

Anyone can help would be great

[stgrhe]

If you need to pop up the freon every three to four months you must have a leakage somewhere in the system. It is not difficult to find the leakage for a professional serviceman.

What about the condensor at the back of the outdoor unit, have you cleaned it so the heat exchange can take place? If it is dirty the system will be working poorly but this lack of heat exchange can easily be detected on the meters by the serviceman as the pressure on the pressure side of the compressor will be high.

Too much freon is also not good as this will reduce the efficiency of the system, but if the compressor is working ok, your freon level is balanced and the filter is cleaned and if it still doesn't work properly the fault is probably due to a faulty expansion valve.

[rexnong]

If you need to pop up the freon every three to four months you must have a leakage somewhere in the system. It is not difficult to find the leakage for a professional serviceman.

What about the condensor at the back of the outdoor unit, have you cleaned it so the heat exchange can take place? If it is dirty the system will be working poorly but this lack of heat exchange can easily be detected on the meters by the serviceman as the pressure on the pressure side of the compressor will be high.

Too much freon is also not good as this will reduce the efficiency of the system, but if the compressor is working ok, your freon level is balanced and the filter is cleaned and if it still doesn't work properly the fault is probably due to a faulty expansion valve.

Thanks for your reply i might be getting somewhere

Never cleaned anything let alone locate a condensor or even know how to?

I will get it looked at but my guess is the guy that comes will say no problem good good with a smile

Thanks i will have a look if its easy to do

[Macmundi]

What has room height got to do with BTU? I thought BTU is the cold air circulating at a height of no more than 2 meters. Regardless of height, that much square meters can be cooled to the tune of 18 cel. I normally multiply the square meters by 800 to determine the BTU for home use, but for offices or more populated spaces, multiply by 1200.

[Naam]

What has room height got to do with BTU? I thought BTU is the cold air circulating at a height of no more than 2 meters. Regardless of height, that much square meters can be cooled to the tune of 18 cel. I normally multiply the square meters by 800 to determine the BTU for home use, but for offices or more populated spaces, multiply by 1200.

if your room height is 3.5m and the aircons are mounted at 3.0m you recirculate 50% more air to be cooled (not cold air).

by the way, cooling a room down to 18ºC in a tropical country with ambient temperatures of 32-35ºC requires much more than 800btu/m².

[jfchandler]

Can someone clarify on this...

Our main bedroom has a wall mounted Fujitsu 9000 BTU air con unit...

It has several operating mode settings, including:

--Cool

--Quiet

--Dehumidify

As best as I can tell, the Quiet setting seems to use less power than the regular Cool setting.

But what about the Dehumidify setting by comparison?

If I set the thermostat at 25C, how's the power usage going to be running the Cool or Quiet setting vs. the Dehumidify setting?

[wpcoe]

My experience with a couple air cons with a "dry" setting (which I assume would correspond to your "dehumidify") is that you cannot specify a target temp.

I read someplace that the dry/dehumidify setting measures the ambient temp when it starts at that setting and will cool to no more than 2 degrees (not sure if F or C) below that initial temp. The air con unit only operates at the slowest fan setting(s) to maximize the air contact with the cold coils to remove maximum humidity.

Edited June 14, 2011 by wpcoe

[Pacificperson]

I don't understand the need or desire for 18 or 20ºC air conditioner settings. I thought that one moved to the tropics to be warm and not to sit indoors shivering.

[seriouseats]

Gonna sound stupid but i just read everything i dont get the difference between inverted units and regular ones? I will be furnishing my house with 5 ACs next month and i have no idea what to buy. Only one room will be large but that room won't need to be freezing cold.

[jfchandler]

My experience with a couple air cons with a "dry" setting (which I assume would correspond to your "dehumidify") is that you cannot specify a target temp.

I read someplace that the dry/dehumidify setting measures the ambient temp when it starts at that setting and will cool to no more than 2 degrees (not sure if F or C) below that initial temp. The air con unit only operates at the slowest fan setting(s) to maximize the air contact with the cold coils to remove maximum humidity.

My unit has an "auto" setting (as opposed to cool or dry or quiet) that allows a 2 degree C adjustment up or down...

But for my "dry" setting, it seems to allow the thermostat control to be set at any temperature in the unit's range, same as the "cool" setting.

I've been trying the "dry" setting the past few nights set to 26 C, and it's been fine and comfortable. Though it's not been particularly warm outside of late.

However, still no idea whether the "dry" setting is a power saver vs. the "quiet" setting, assuming both are run at the same thermostat setting.

I've got an older style floor unit in the living room that gulps AC, so it's hard to get any clear picture of how much power the wall-mounted Fujitsu bedroom unit itself is using.

[wpcoe]

Interesting. Seems like the Dry/Dehumidify setting is as understandable and consistent between models as the Sleep setting.

[rijb]

Gonna sound stupid but i just read everything i dont get the difference between inverted units and regular ones? I will be furnishing my house with 5 ACs next month and i have no idea what to buy. Only one room will be large but that room won't need to be freezing cold.

We just put 4 ACs (Hitachi) in our second house. We had 3 ACs (Hitachi) in our first house. The installer told us we were smart to stay away from inverters. He said inverters don't do well in Thailand. He's making a lot of money on inverter service calls.

[transam]

Gonna sound stupid but i just read everything i dont get the difference between inverted units and regular ones? I will be furnishing my house with 5 ACs next month and i have no idea what to buy. Only one room will be large but that room won't need to be freezing cold.

We just put 4 ACs (Hitachi) in our second house. We had 3 ACs (Hitachi) in our first house. The installer told us we were smart to stay away from inverters. He said inverters don't do well in Thailand. He's making a lot of money on inverter service calls.

Inverter will save you running costs. Five years now with Daikin and nooooooooooooo probs.

Daikin do not make hi-fi's, wash machines or TV's only aircon.

[electau]

The inverter airconditoners are the norm now, they are more energy efficient and for every 1kW input electrical you will obtain about 3kW cooling.

I kW = 3410 BTUs.

Cooling temperatures 27C enconomy, 25C normal conditions, 22C minimum.

Fujitsu-General are a good product.

[kokesaat]

I apologize if this has been covered already in this thread......I didn't see anything related:

We have two Daikin 18,000btu inverters......very good performance in cooling, quiet, and both suck out lots of water from the air. As we're now in rainy season and cooler temps, I'm curious about power consumption differences between running the inverter in cooling mode, versus drying mode.

Other than my power concerns, are there any other issues I should be aware of in choosing drying mode over cooling?

[Naam]

The inverter airconditoners are the norm now, they are more energy efficient and for every 1kW input electrical you will obtain about 3kW cooling.

I kW = 3410 BTUs.

Cooling temperatures 27C enconomy, 25C normal conditions, 22C minimum.

Fujitsu-General are a good product.

input/output of modern 'conventional' units having fixed speed compressors is exactly the same. the claim 'more energy' efficient referring to the afore-said is therefore not justified but plain wrong.

howver, inverter units can be more efficient than conventional ones under certain circumstances respectively usage/demand. the latter was explained ad nauseam in at least dozen different threads here in Thaivisa.

[Naam]

I apologize if this has been covered already in this thread......I didn't see anything related:

We have two Daikin 18,000btu inverters......very good performance in cooling, quiet, and both suck out lots of water from the air. As we're now in rainy season and cooler temps, I'm curious about power consumption differences between running the inverter in cooling mode, versus drying mode.

Other than my power concerns, are there any other issues I should be aware of in choosing drying mode over cooling?

there is indeed another issue which is negligible as long as there is no malfunction. "drying mode" is achieved by reducing fan speed of the inside unit to an absolute minimum (some brands even stop the inside fan temporarily) but keeping the compressor speed constant. during this cycle the surface temperature of the evaporator fins drops considerably which in turn enhances dehumidification. fan speed is regulated by a sensor which measures the afore-said fin temperature and starts fan or increases fan speed if that temperature drops below a certain preset minimum.

if this is not the case the liquid refrigerant might not be converted completely into a gaseous medium and reach the compressor partly in liquid form. we all (or most of us know) know that liquids cannot be compressed and therefore the compressor might be either damaged or suffer extremely wear and tear when trying to compress liquid.

summary:

-to be on the safe side "drying mode" should not be used continously.

-difference in power consumtion is negligible.

-converter units are not the norm nowadays because their advantages depend on specific demands.

Edited July 1, 2011 by Naam

[kokesaat]

Thanks, Naam, for the informative post on my question about dehumidification versus cooling.

[mortenaa]

We just put 4 ACs (Hitachi) in our second house. We had 3 ACs (Hitachi) in our first house. The installer told us we were smart to stay away from inverters. He said inverters don't do well in Thailand. He's making a lot of money on inverter service calls.

I think you should do better research. They are famous for the need of less maintenance, because of the compressor runs constantly on much less power. And don't have to suffer from hard stops and starts, as a conventional air conditioners. They are not popular in Thailand because of higher purchase price.

So far my inverters have not just run constantly (24/7) for years without problems. They also improved my quality of life

- Constant temperatures (not fluctuating like normal air conditions)

- About 35% drop in the electricity bill

- Less humidity

- No compressor noise

- Better sleep

So I wouldn't even consider buying anything else than an Inverter

[kokesaat]

I second everything mortenaa said about inverters: We installed two 18k btu daiken inverters in March 2011. Electricity bills are about 30+% less than 10 years previous using non inverters, house is much much drier as the daikens suck out lots more water, the compressors are extremely quiet, and there's not a smidgen of power drop when the compressors kick in. More expensive, yes, but easily worth the extra money!

[stgrhe]

I second everything mortenaa said about inverters: We installed two 18k btu daiken inverters in March 2011. Electricity bills are about 30+% less than 10 years previous using non inverters, house is much much drier as the daikens suck out lots more water, the compressors are extremely quiet, and there's not a smidgen of power drop when the compressors kick in. More expensive, yes, but easily worth the extra money!

Amen

[Damrongsak]

On 7/27/2009 at 9:05 PM, johnnyk said:

I don't understand what m2 has to do with it.

If two rooms are 10X20 but one has an 8-foot ceiling and the other has a 12-foot ceiling isn't it obvious that one has a lot more air to push around?

The a/c isn[t cooling the floor!

Calculate the volume then it can be discussed sensibly.

It's more a matter of the surface area that allows heat transfer between inside and outside.  A long, narrow room will have more surface area than a perfect cube for a given volume.  Yes, a high room may have a greater temperature gradient between floor and ceiling unless you stir the air.  But with aircon, the heat goes up and the cool stays down, to a degree. Actually heat is the same.  (I have a 2 story house - 2nd floor is always hotter.)

Edited August 28, 2022 by Damrongsak