Buying An Energy-Efficient Air Conditioner

[Mekong Bob]

I am shopping for a wall-mounted split-type air conditioner, and found a Mitsubishi 9000 BTU (inverter-type) at Siam TV. A Thai government sticker (see attached photo) indicates that this model will use an estimated 1,667.03 "units" (kWh, or kilowatt-hours) per year of energy at a cost of 5,467.85 baht per year.

Can anyone tell me: Based on how many hours of use per day? Days per month? Per year?

Also, at what temperature setting was this determination made?

The friendly Thai salesman, wearing a Mitsubishi shirt, did not know these details.

energy sticker.pdf

[mamborobert]

You might be flat out of luck getting details on this.

Mitsubishi establish what "stars" should go on their systems and it varies country to country (as models vary slightly).

The EER rating ( Energy Efficiency Ratio) has been surpassed by the SEER (Seasonal EER) as measures a "season". There are different SEER's for Europe, Nth America etc. EER measures how efficient the system will go against a standard outside temperature of 95 degrees F. That's a pretty much universal measure and all in all not much good in Thailand (for humidity etc) where the "real feel" is higher than 95 degrees F.

This is probably be the number that the determination was made at (the 15.1). Also when they do these tests they make sure that all pipes are insulated (as well as walls/ceilings), that there is a programmable thermostat that ups and lowers the temperature at certain times of the day, and that the room is EXACTLY the optimum size that the unit was designed for.

In the end beyond the EER it is largely subjective (what is cold to you may not be cold to me)....Now you would not use the aircon at all but this cool season seems to have started later than usual by my experience. All I mean by that is that in a particularly longer season you may use it more therefore the expected electricity costs would be more (equally could be less if cold and some tolerance to heat, good crossflow ventilation, good insulation etc). We all know people that spend a lot more and a lot less that have aircon units, tolerance, unit and insulation will have an make massive swings.

Having said that the EER of this product (15.1) is pretty good and better than all the other larger Mitsubishi split system units I have seen about. If it is right for that room size would be fine. Personally I would go for a bigger BTU for the same size room (with probably a lower EER) but would be a bit more assured that unit would cope in longer hotter spells than rely on a unit that is at its design limit if pushed over 95 degrees F (when poor insulation, not airtight, humidity etc). Its horrible having an undersized unit (aircon I mean) when you really need it on the hotter days.

Also if the electrical unit price changes so would your costs...so again the sticker is rather hindsight orientated in some ways.

Important is the BTU, room size and EER. It ain't no good paying for a unit and the electricity if it does not function well when you really need it.

And without teaching granny to suck eggs...make sure your circuit can handle the drain if in an older place or you have lots of electrical items on at once.

Realising that my post has been of very limited use...you could try ringing up Mitsubishi Thailand but would not be that confident that you could get someone that could actually tell you how they arrived at these numbers for use/costs...or send them an email? (beyond the factory settings for BTU/EER etc)

Edited December 17, 2012 by mamborobert

[hellodolly]

You might be flat out of luck getting details on this.

Mitsubishi establish what "stars" should go on their systems and it varies country to country (as models vary slightly).

The EER rating ( Energy Efficiency Ratio) has been surpassed by the SEER (Seasonal EER) as measures a "season". There are different SEER's for Europe, Nth America etc. EER measures how efficient the system will go against a standard outside temperature of 95 degrees F. That's a pretty much universal measure and all in all not much good in Thailand (for humidity etc) where the "real feel" is higher than 95 degrees F.

This is probably be the number that the determination was made at (the 15.1). Also when they do these tests they make sure that all pipes are insulated (as well as walls/ceilings), that there is a programmable thermostat that ups and lowers the temperature at certain times of the day, and that the room is EXACTLY the optimum size that the unit was designed for.

In the end beyond the EER it is largely subjective (what is cold to you may not be cold to me)....Now you would not use the aircon at all but this cool season seems to have started later than usual by my experience. All I mean by that is that in a particularly longer season you may use it more therefore the expected electricity costs would be more (equally could be less if cold and some tolerance to heat, good crossflow ventilation, good insulation etc). We all know people that spend a lot more and a lot less that have aircon units, tolerance, unit and insulation will have an make massive swings.

Having said that the EER of this product (15.1) is pretty good and better than all the other larger Mitsubishi split system units I have seen about. If it is right for that room size would be fine. Personally I would go for a bigger BTU for the same size room (with probably a lower EER) but would be a bit more assured that unit would cope in longer hotter spells than rely on a unit that is at its design limit if pushed over 95 degrees F (when poor insulation, not airtight, humidity etc). Its horrible having an undersized unit (aircon I mean) when you really need it on the hotter days.

Also if the electrical unit price changes so would your costs...so again the sticker is rather hindsight orientated in some ways.

Important is the BTU, room size and EER. It ain't no good paying for a unit and the electricity if it does not function well when you really need it.

And without teaching granny to suck eggs...make sure your circuit can handle the drain if in an older place or you have lots of electrical items on at once.

Realising that my post has been of very limited use...you could try ringing up Mitsubishi Thailand but would not be that confident that you could get someone that could actually tell you how they arrived at these numbers for use/costs...or send them an email? (beyond the factory settings for BTU/EER etc)

I personally found your post very informative. I am was wondering how much the humidity would effect the temperature.

As you said there is a lot of unknowns here for the poster. How big a room do they have and what temperature do they want. If it is year round there will be no way to tell.

Mine is an old one but I notice there is a big difference in the time it is running when I set it at 26 as compared to 27.

[mamborobert]

Humidity has a significant impact as it makes the unit work much harder.

An aircon unit reduces the temperature and relative humidity in a room (to the air outside). Often you will see droplets of water from aircon units (even on split systems) which is why they have to be placed carefully like not over a tv etc). Its also why you see the "drain" or copper pipe from the back of the external unit.

Air in your room tries to absorb moisture wherever it finds it (ie everything is dry after a while).

As hotter air is blown over the coils condensation occurs as the room gets to the "dew point". Higher (or in our case probably constant) humidity outside means more (or initially constant) condensation inside and (constant) in the external unit. Higher levels of condensation generates more heat in the unit and for the unit to remove from the air...(outside ) until the air inside becomes "dry" . The unit works more...it uses more electricity. The dry effect really only happens in more temperate climates (as again you possibly do not get a fully sealed/insulated room here).

Upping the settings by a degree or two really does make a big difference to costs, wear on the unit, and how much you need it on. Also there is less shock to the your body when you venture out (so your first reaction when entering your home again is not to reduce temperature). I know some people here that have aircon set at 21c all the time...costs a heap and they actually venture out less as it always seems "hot" which it will of course by contrast with 21.

Side track but eons ago I worked in trucks in very hot temperatures, we had aircon but there was an issue with drivers passing out as they stepped out from 20 degrees to often 40 plus. In the end they modified the aircons to high 20's and put in small fridges in truck cabins so that you had cold water (only) always available...was actually much healthier and the guys lost a heap of weight as they drank water through the day.

Edited December 17, 2012 by mamborobert

[Mekong Bob]

In order to establish a frame of reference, I must assume that my room is exactly the same size as recommended by this Thai Ministry of Energy for a 9000 BTU system, and also that the outdoor temperature and humidity match the conditions set for these Thai government tests. Additionally, I must accept the desired room temperature of the room as determined by the Thai agency's tests.

If we keep all these variables constant, the key item remaining is the number of hours in operation for these tests. Without this number, the estimated annual energy consumption is meaningless, agreed?

I am e-mailing the Ministry of Energy.

[kaptainrob]

I believe the US DOE standard test for airconditioners is based on an average of 750 hours p/a. You may find more detail here http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/41

As recommended by others, buy a unit suitable for the room size. Carrier, Daikin and Mitsubishi are all top quality. Cheaper units tend to be noisy as well as less efficient.

[NeverSure]

There are some things you can do to help some here. If the house is well sealed, once the aircon removes the excess humidity, it won't work as hard. In other words, it only has to dehumidify once, assuming constant running of the aircon.

You can make sure you have and use vent fans in the kitchen and bathrooms. You can avoid drying hanging clothes inside the house. You can even put the cover on pots and pans when boiling things.

[Mekong Bob]

According to EGAT officials, air conditioners are tested at the Thailand Industrial Standards Institute (TISI) under these conditions:

"8 hours per day, 30 days per month, 12 months per year. " Wow! That's 2,880 hours a year.

"indoor conditions: 27 +/- 1° C and 19+/- 0.5 %RH" and "outdoor conditions: 35 +/- 1° C and 24+/- 0.5 %RH"

The EGAT sticker on this 9000 BTU unit indicates 1,667.03 kWh units per year consumed. That's 0.579 kWh per hour, or 4.631 kWh per 8-hour day of operation. About 15-16 baht per 8-hour day. Fantastic!

I just purchased two of these inverter-type energy-saving air conditioners.

[kaptainrob]

According to EGAT officials, air conditioners are tested at the Thailand Industrial Standards Institute (TISI) under these conditions:

"8 hours per day, 30 days per month, 12 months per year. " Wow! That's 2,880 hours a year.

"indoor conditions: 27 +/- 1° C and 19+/- 0.5 %RH" and "outdoor conditions: 35 +/- 1° C and 24+/- 0.5 %RH"

The EGAT sticker on this 9000 BTU unit indicates 1,667.03 kWh units per year consumed. That's 0.579 kWh per hour, or 4.631 kWh per 8-hour day of operation. About 15-16 baht per 8-hour day. Fantastic!

I just purchased two of these inverter-type energy-saving air conditioners.

Good info MB... I'm sure many ppl think those stickers are just BS, or based on a World-wide standard.

[bitewhentested]

my 18.000 btu samsung aircon if used for 8 hours a night at around 25 dont like it to cold costs me about a 1000 bhat a month bargin

[kaptainrob]

my 18.000 btu samsung aircon if used for 8 hours a night at around 25 dont like it to cold costs me about a 1000 bhat a month bargin

Holy crap, that's near double our total power bill!

[Jobo]

Does somebody have the formula for calculating the size of AC needed (BTU) based on room size?

I seem to recall you need the L * W of the room in metres but how does that translate to BTU?

And why wouldn't the ceiling height be important - in other words the room size in cubic metres?

[bitewhentested]

a 1000 a month for a good night sleep is nothing when you think about what people pay out every day on food beer little trips to the massage shops lol

i could not live here without it i stayed in a hotel for a few days coz my aircon broke down needed to wait for parts

[jombom]

A 9000 btu unit is 2.64 kw or 2.64 units of elec per hour.

In my experience the dealers use conversion sizing charts which are completely over-rated, sometimes by 300%.

They don't want the compressors running at a high duty cycle, as they are afraid of motor burn-out and system failure.

[jingjoke]

#8 Hey Mekong Bob, What brand of inverter-aircons did you decide on? Thnx

[Mekong Bob]

#8 Hey Mekong Bob, What brand of inverter-aircons did you decide on? Thnx

Mitsubishi's "Mister Slim" line.

[Rancid]

my 18.000 btu samsung aircon if used for 8 hours a night at around 25 dont like it to cold costs me about a 1000 bhat a month bargin

Holy crap, that's near double our total power bill!

Yes but not everybody uses kerosine lamps, cold showers and and a hand fan.

[Naam]

Humidity has a significant impact as it makes the unit work much harder.

sorry Sir Robert, but it's the other way round based on the logical assumption that if inside humidity is high, so is outside humidity.

high outside humidity helps with evaporation cooling on the condenser fins to increase the cooling capacity of the unit. people who don't know what evaporation cooling is should wet a finger and blow against it, et voilà.

As hotter air is blown over the coils condensation occurs as the room gets to the "dew point". Higher (or in our case probably constant) humidity outside means more (or initially constant) condensation inside and (constant) in the external unit. Higher levels of condensation generates more heat in the unit and for the unit to remove from the air...(outside ) until the air inside becomes "dry" . The unit works more...it uses more electricity.

i rfrain frm cmmenting on tht becase laughng ut ludly i splled a drink ovr my kybord nd spold it

[Naam]

A 9000 btu unit is 2.64 kw or 2.64 units of elec per hour.

In my experience the dealers use conversion sizing charts which are completely over-rated, sometimes by 300%.

They don't want the compressors running at a high duty cycle, as they are afraid of motor burn-out and system failure.

objection Your Honour! a 9k btu/h unit uses less than 0.9kW (units) per hour. conventional compressors (not inverters) run at a constant speed. there's no such thing like a high or low duty cycle.

[Naam]

I personally found your post very informative. I am was wondering how much the humidity would effect the temperature.

As you said there is a lot of unknowns here for the poster. How big a room do they have and what temperature do they want. If it is year round there will be no way to tell.

Mine is an old one but I notice there is a big difference in the time it is running when I set it at 26 as compared to 27.

humidity does not affect the temperature but it affects how you feel. a room with an air temperature of 27ºC and 55% relative humidity feels for the average human being much more comfortable than a room with an air temperature of 25ºC and 85% relative humidity.

that's why the capacity of an aircon can be divided in "direct" and "latent" cooling. in olden times (i refer to the 70s) aircon manufacturers took into consideration for which climatical area their units were meant and designed the evaporators (emphasis on dehumidification/latent cooling or not) accordingly.

[cloudhopper]

high outside humidity helps with evaporation cooling on the condenser fins to increase the cooling capacity of the unit. people who don't know what evaporation cooling is should wet a finger and blow against it, et voilà.

I'm drinking heavily tonight doc but don't the hot condenser fins outside cool by radiation, conduction and convection? There is no liquid water evaporating on the surface of the outside fins regardless of the humidity, is there?

Edited December 26, 2012 by cloudhopper

[Pond Life]

Unless the condensate from your bedroom wall unit is fed to the outdoor unit perhaps.

I don't know, anyone else ?

[jbrain]

A 9000 btu unit is 2.64 kw or 2.64 units of elec per hour.

In my experience the dealers use conversion sizing charts which are completely over-rated, sometimes by 300%.

They don't want the compressors running at a high duty cycle, as they are afraid of motor burn-out and system failure.

objection Your Honour! a 9k btu/h unit uses less than 0.9kW (units) per hour. conventional compressors (not inverters) run at a constant speed. there's no such thing like a high or low duty cycle.

I thought the power usage of an aircon unit was related to the SEER rating of the unit, so saying how much power a 9000 Btu aircon use without knowing the seer rating is just making a shot in the dark.

[Naam]

A 9000 btu unit is 2.64 kw or 2.64 units of elec per hour.

In my experience the dealers use conversion sizing charts which are completely over-rated, sometimes by 300%.

They don't want the compressors running at a high duty cycle, as they are afraid of motor burn-out and system failure.

objection Your Honour! a 9k btu/h unit uses less than 0.9kW (units) per hour. conventional compressors (not inverters) run at a constant speed. there's no such thing like a high or low duty cycle.

I thought the power usage of an aircon unit was related to the SEER rating of the unit, so saying how much power a 9000 Btu aircon use without knowing the seer rating is just making a shot in the dark.

SEER denotes the efficiency of a unit's cooling capacity. the actual power usage in kWh is determined by the energy drawn by the compressor, the condenser fan and the evaporator fan irrespective of the SEER rating... and irrespective of "brain" people who think they can shoot like a sniper.

[Naam]

high outside humidity helps with evaporation cooling on the condenser fins to increase the cooling capacity of the unit. people who don't know what evaporation cooling is should wet a finger and blow against it, et voilà.

I'm drinking heavily tonight doc but don't the hot condenser fins outside cool by radiation, conduction and convection? There is no liquid water evaporating on the surface of the outside fins regardless of the humidity, is there?

no need for liquid water CH. high relative humidity in the ambient air is doing a good job raising cooling capacity by evaporation even though not visible. that's why the manufacturers also mention relative humidity in/outside when quoting rated cooling capacity.

[cloudhopper]

high outside humidity helps with evaporation cooling on the condenser fins to increase the cooling capacity of the unit. people who don't know what evaporation cooling is should wet a finger and blow against it, et voilà.

I'm drinking heavily tonight doc but don't the hot condenser fins outside cool by radiation, conduction and convection? There is no liquid water evaporating on the surface of the outside fins regardless of the humidity, is there?

no need for liquid water CH. high relative humidity in the ambient air is doing a good job raising cooling capacity by evaporation even though not visible. that's why the manufacturers also mention relative humidity in/outside when quoting rated cooling capacity.

I'm sober now but I'm still calling BS doc. High humidity might increase the ability of the outside air to conduct heat away from the condenser fins but evaporative cooling requires a phase change from liquid water to vapor leaving cooler liquid behind on the surface. Swamp coolers work by evaporative cooling but only when the outside air has low humidity not high.

[Naam]

I'm sober now but I'm still calling BS doc. High humidity might increase the ability of the outside air to conduct heat away from the condenser fins but evaporative cooling requires a phase change from liquid water to vapor leaving cooler liquid behind on the surface. Swamp coolers work by evaporative cooling but only when the outside air has low humidity not high.

i yield to your technical supreme knowledge CH. how could i forget that you spend quite some months working in Matsushita's Research & Development 'Airconditioning' in Osaka and Kyoto, Japan.

[Diablo Bob]

I'm sober now but I'm still calling BS doc. High humidity might increase the ability of the outside air to conduct heat away from the condenser fins but evaporative cooling requires a phase change from liquid water to vapor leaving cooler liquid behind on the surface. Swamp coolers work by evaporative cooling but only when the outside air has low humidity not high.

i yield to your technical supreme knowledge CH. how could i forget that you spend quite some months working in Matsushita's Research & Development 'Airconditioning' in Osaka and Kyoto, Japan.

I think that Cloudhopper has you on this one Nam

[Naam]

I'm sober now but I'm still calling BS doc. High humidity might increase the ability of the outside air to conduct heat away from the condenser fins but evaporative cooling requires a phase change from liquid water to vapor leaving cooler liquid behind on the surface. Swamp coolers work by evaporative cooling but only when the outside air has low humidity not high.

i yield to your technical supreme knowledge CH. how could i forget that you spend quite some months working in Matsushita's Research & Development 'Airconditioning' in Osaka and Kyoto, Japan.

I think that Cloudhopper has you on this one Nam

because i mixed up who was working in aircon R&D?

[jbrain]

A 9000 btu unit is 2.64 kw or 2.64 units of elec per hour.

In my experience the dealers use conversion sizing charts which are completely over-rated, sometimes by 300%.

They don't want the compressors running at a high duty cycle, as they are afraid of motor burn-out and system failure.

objection Your Honour! a 9k btu/h unit uses less than 0.9kW (units) per hour. conventional compressors (not inverters) run at a constant speed. there's no such thing like a high or low duty cycle.

I thought the power usage of an aircon unit was related to the SEER rating of the unit, so saying how much power a 9000 Btu aircon use without knowing the seer rating is just making a shot in the dark.

SEER denotes the efficiency of a unit's cooling capacity. the actual power usage in kWh is determined by the energy drawn by the compressor, the condenser fan and the evaporator fan irrespective of the SEER rating... and irrespective of "brain" people who think they can shoot like a sniper.

Well the sniper shoots again Seems that Jombom was quite right