Payback period for inverter aircon

[Pib]

For those of you who want details/values/info on the inverter A/C I bought in Jan 18 to replace a fixed speed/stand A/C, please go to below topic I started in Jan 18.    I provided frequent updates as to the savings from installing the inverter.   And keep in mind every person's experience/savings will be different as we all live in different residences, use A/C differently, etc.  

 

 

[Beggar]

On 4/19/2019 at 9:01 PM, Pib said:

All depends on how long you run it....if you run it 24/7 then payback will probably be in around 15 months. 

 

A friend of mine with inverter aircons needed a repair - the board needed to be replaced. It was expensive. So perhaps in case of payback it can go the other direction. 

[VocalNeal]

1 hour ago, alacrity said:

If the smaller unit can't cool the room to the desired temperature (because it doesn't have the capacity to do so) it will run at full load forever. The larger unit can cool the room to the desired temperature (because it has the capacity to do so) so has no need to continuously run at full load. Once the desired temperature is achieved the unit will cycle (standard unit) or modify the motor speed (inverter) to maintain the set temperature.

 

The repeated inrush current to start the motor when a standard unit is cycling is lessened by modifying the motor speed of an inverter unit. Reducing the overall current drawn over a prolonged period of time.

 

On initial start-up an inverter unit can draw more current than a standard unit (of the same capacity) until the desired temperature is achieved.

Yes but will the larger unit use less energy to remove the same amount of heat?

[Fruit Trader]

15 minutes ago, VocalNeal said:

Yes but will the larger unit use less energy to remove the same amount of heat?

The answer to that is likely to be no if the smaller unit is running constantly at peak efficiency. 

[Pib]

In the thread I posted/linked to a little earlier titled, "Your Opinion of Mitsubishi Inverter A/Cs", I gave cost savings over a 12 month period after installing the A/C.   I now have 15 months of cost sayings. 

 

I have a spreadsheet of my monthly electricity KWH usage going back to Jan 2009 and for those of you have lived here for years with your electricity account "in your name" versus a landlord enhanced bill you know the total cost per kilowatt hour including basic cost/tax/meter fee has been pretty stable averaging around Bt4.41 per KWH...or at least for me with MEA which is electric company for the Bangkok.  I also have almost all my actual paper bills going back to Jan 2009....just a particular monthly bill I've monitored very closely over the years.   Like for my latest bill of 13 Apr 2019 the total cost per KWH was Bt4.476 and in Apr 2009 it was Bt4.089.    

 

Anyway, last night I played with my spreadsheet some more to see what my monthly KWH usage average per month based on 9 (nine) years of data "before" installing the inverter A/C....using that as a baseline.  In that other thread I used a 3 year period for my baseline.   For me, I was using an average of 1,884KWH per month over those 9 years....the pre-inverter A/C years.  1,884 times Bt4.41 gives me an average monthly bill of Bt8,308.  Keep in mind this is a monthly bill for my two story house I have lived in since late 2008 which runs one large A/C 24/7 and another large A/C for approx 12 hours every night along with all the other electrical equipment in my house like 3 frigs, big screen TVs, fans, clothes dryer and washer, TV/internet settop boxes, water heaters, lights.....etc....etc...etc.  But these two A/C eat the majority of my monthly household electricity usage.

 

Ok, I replaced the standard 18K BTU A/C in Jan 18 with a 23K BTU inverter A/C.  This is the A/C that runs 24/7.  I disregard the Jan 18 bill since it represented part of the month with the old and new A/Cs.  For the 15 ensuring months from Jan 18 consisting of 15 monthly bills I was now using an average of 1,250 KWH/month with my average bill now being Bt5,512.   

 

Average bill before inverter Bt8,308 minus average bill after inverter of Bt5,512 equals an average monthly savings of Bt2,796 savings per month.    For the inverter A/C I paid a total of Bt38,800 which included installation.   Bt38,800 divided by the Bt2,736 monthly electric bill savings equates to a 14.2 month payback period. 

 

Once again, that is savings I have received based on my electricity usage....my home....your results will vary.   For someone living in a small residence and say only running an A/C in the bedroom at night then your electric bill and payback period for an inverter A/C is going to be much longer.

 

Now I'm also seriously considering replacing that A/C (a 20K BTU standard A/C) that runs approx 12 hours each and every night.    Since it only runs 12 hours and only during the night I guesstimating that if I replace it with another 23K BTU Mitsubishi inverter A/C just like the other one I bought that the payback period will probably be 36 to 40 months...probably only save around Bt1,000 per month in my electric bill since it will be used half as much and only at night when the cooling load is easier than during the day.   

 

 

[Beggar]

47 minutes ago, Pib said:

 

Average bill before inverter Bt8,308 minus average bill after inverter of Bt5,512 equals an average monthly savings of Bt2,796 savings per month.    For the inverter A/C I paid a total of Bt38,800 which included installation.   Bt38,800 divided by the Bt2,736 monthly electric bill savings equates to a 14.2 month payback period. 

 

Is it correct to see it like this? You compare an old aircon with a new (expensive) inverter. You might have a lot of savings with a new conventional aircon too. This was my experience when I replaced my old aircon. So do you save so much because of the inverter or just because it is new.

[Fruit Trader]

17 minutes ago, Beggar said:

Is it correct to see it like this? You compare an old aircon with a new (expensive) inverter. You might have a lot of savings with a new conventional aircon too. This was my experience when I replaced my old aircon. So do you save so much because of the inverter or just because it is new.

Food for thought.

 

Bob and Bill live in identical rooms with conventional AC units operating 24/7 at 26 deg. Both recently replaced their AC units with identical inverter types but Bob has only experienced a 15% energy saving compared to Bills 25%. Further investigation found Bills old conventional AC to be a lot less efficient than Bobs.

[moontang]

If you are still having doubts about the inverter, consider yourself a failure at both science and economics.  

[Fruit Trader]

9 minutes ago, moontang said:

If you are still having doubts about the inverter, consider yourself a failure at both science and economics.  

I don't think anyone is doubting the science but the economics might be another story for some.

[Pib]

51 minutes ago, Beggar said:

Is it correct to see it like this? You compare an old aircon with a new (expensive) inverter. You might have a lot of savings with a new conventional aircon too. This was my experience when I replaced my old aircon. So do you save so much because of the inverter or just because it is new.

A lot of savings with a "new" conventional A/C?  Highly doubtful if both old and new were properly sized/same size/old one kept clean as it still boils down to the "compressor" that eats the 90% of the energy being consumed by an A/C.  Conventional A/C compressor technology of today is basically the same from 20 years ago.  Yes, today's conventional compressors are probably more reliable, but their operating principle/technology is still the same. 

 

Sorry, an inverter A/C is going to save you significant money each month assuming it's properly sized and how it's used.  How long the payback period will be will depend on numerous factors such as BTU size, size of area being cooled, length of time used day and night, desired temperate setting, etc...etc. 

 

For a proven fact, the inverter saved me very significant baht each month in my electric bill and it's purchase/installation price was fully recouped in 14.2 months in my case.  

 

And if today I went out and bought a new conventional 23K BTU Mitsubishi (a quality A/C) it would cost me approx Bt34.3K plus Bt3K to install for a total of Bt37.3K.   But go buy an inverter 23K BTU Mitsubishi (a quality A/C) it would cost Bt41.5K plus Bt3K to install for a total of Bt44.5K.   You only pay Bt7.2K more for an inverter A/C which is going to reduce your electric bill....but the new conventional A/C is probably not to reduce your bill at all/very little.

 

Conventional A/C Pricing

 

Inverter A/C Pricing

 

[moontang]

The energy stickers consistently show the inverters using about a third less.  My 17000 BTU inverter sticker says 11,169 per year to operate or 2820 units.  

[Pib]

29 minutes ago, moontang said:

The energy stickers consistently show the inverters using about a third less.  My 17000 BTU inverter sticker says 11,169 per year to operate or 2820 units.  

Yea....for as long as I can remember the advertising associated with inverter A/Cs is they use approx 30% less power than a conventional A/C.    I was always skeptical of this advertising...figured in the real world it would fall far short of that....probably get around 15%. 

 

But what I do know once I replaced my conventional 18K BTU A/C that run 24/7 with a 23K BTU inverter A/C my whole house electric usage dropped by an average of  32.76% per month over a 12 month period.  Some months was a little below 30%.....some months far above....all depended on how hot/humid it was during any particular month....but when averaging 12 months it worked out to 32.76%. 

 

Since that was my whole household electric decrease I expect if I could have broken out only that one A/C's reduced electricity usage it would be significantly above 30%.

 

[Beggar]

2 hours ago, Pib said:

A lot of savings with a "new" conventional A/C?  Highly doubtful if both old and new were properly sized/same size/old one kept clean as it still boils down to the "compressor" that eats the 90% of the energy being consumed by an A/C.  Conventional A/C compressor technology of today is basically the same from 20 years ago.  Yes, today's conventional compressors are probably more reliable, but their operating principle/technology is still the same. 

 

 

I saved a lot with the new aircon. I am not kidding now but it was for sure 30 percent or more. I have to look if still have the electricity bills from this time. But I didn't think much about the savings because at the old aircon the compressor was broken and so I needed a replacement. 

 

But anyhow - you only can compare a new conventional aircon with a new inverter aircon and this under the same conditions. Everything else are just baseless assumptions. 

[alacrity]

15 minutes ago, Beggar said:

I saved a lot with the new aircon. I am not kidding now but it was for sure 30 percent or more. I have to look if still have the electricity bills from this time. But I didn't think much about the savings because at the old aircon the compressor was broken and so I needed a replacement. 

 

But anyhow - you only can compare a new conventional aircon with a new inverter aircon and this under the same conditions. Everything else are just baseless assumptions. 

Done that already. Have 5 standard units and 2 inverter units. Compared a new inverter unit to a 6 year old standard unit of comparable capacity and in a similar sized and located room over a period of time. The energy saving was 3%. Even a 500% error in measurement and method would only equate to a 15% saving. Far short of the manufacturers claims and you pay 30% more than a standard unit. That nulls any potential saving in the short to medium term of the units lifespan.

 

If you could reproduce the manufacturers test conditions it is highly likely you could reproduce their empirical data. Given the complexity of variables in real life conditions it would be extremely unlikely for anyone to achieve that.

 

Would I purchase an inverter based on potential savings again? Answer: No. Because it doesn't do what it says on the label.

[moontang]

My March bill was 23% less than February.. And March was three days longer... and way hotter.. I replaced on the fourth day of the March bill. 

[Pib]

21 minutes ago, alacrity said:

Done that already. Have 5 standard units and 2 inverter units. Compared a new inverter unit to a 6 year old standard unit of comparable capacity and in a similar sized and located room over a period of time. The energy saving was 3%. Even a 500% error in measurement and method would only equate to a 15% saving. Far short of the manufacturers claims and you pay 30% more than a standard unit. That nulls any potential saving in the short to medium term of the units lifespan.

 

Sounds like a classic example of an undersized inverter A/C which causes it to work pretty much at full capacity all the time....just like a conventional A/C.

[Beggar]

8 minutes ago, moontang said:

My March bill was 23% less than February.. And March was three days longer... and way hotter.. I replaced on the fourth day of the March bill. 

Can be. But you are still comparing your old aircon with a new one. And the 23 % might be correct for you and your aircon that you replaced. But not everyone has your old aircon and your usage pattern and your condo insulation and... It is a number that fits for your specific situation - nothing else. 

[Fruit Trader]

If someone asks me what I think about the inverter AC cooling our office I simply say its very quiet with adequate features and there appears to be some reduction in energy consumption because the office has its own meter. The unit replaced a very new conventional AC and runs all day every day. Some ask how much energy it has saved and I just say its nothing to get excited about.

 

Our office is well insulated with the inverter receiving requests to reduce output quite quickly after startup.

Later this year I will be moving the unit and replacing it with a nearly new LG conventional AC of smaller output. A good opportunity to see how much more energy we consume.

[tlandtday]

On 4/22/2019 at 2:07 PM, Pib said:

I expect the inverter is undersized for the room which causes it to run at upper capacity most/all of the time resulting in no electricity savings over a standard A/C of same size.   When that occurs your inverter A/C is nothing more than a standard fixed speed A/C.

Actually quite the opposite. The unit is larger than the non inverter.  And the non inverter is in a bigger room to boot.

[Oxx]

13 hours ago, Pib said:

for as long as I can remember the advertising associated with inverter A/Cs is they use approx 30% less power than a conventional A/C.

 

LG is now advertising a 70% energy saving for its inverters.  See, for example, https://www.lg.com/my/inverter-air-conditioners

 

Whilst apparently supported by independent testing, I'm not sure how believable this is in the real world.

[Beggar]

2 hours ago, Oxx said:

 

LG is now advertising a 70% energy saving for its inverters.  See, for example, https://www.lg.com/my/inverter-air-conditioners

 

Whilst apparently supported by independent testing, I'm not sure how believable this is in the real world.

That sounds great but they write "up to". I don't like this "up to"... My aircon saves up to 100% *) 

 

*) when switched off

[Delight]

3 hours ago, Beggar said:

That sounds great but they write "up to". I don't like this "up to"... My aircon saves up to 100% *) 

 

*) when switched off

 Consider 2 phases of the typical system.

Phase 1 -Full blast i.e cooling down a hot room. There will be very little saving in this phase between either technology. Later systems tend to have lighter less energy consuming fans

Phase 2 -Tickover. When the room is at it's desired temperature then heat removal from the room  matches the heat that has leaked into the room.

 During a 8 hour period the sytem will be in phase 2 most of the time.

Old technology can only off on. The room may become uncomfotable before heat ejection  resumes with old technology. Also it is relatively expensive,

This is where inverter wins. Precise control of room temperature at lowest possible cost.

So the savings may refer to the comparison between both systems on 'tickover'

A conventional system only really has 2 phases -Full blast or off

 

 

[Beggar]

1 hour ago, Delight said:

 Consider 2 phases of the typical system.

Phase 1 -Full blast i.e cooling down a hot room. There will be very little saving in this phase between either technology. Later systems tend to have lighter less energy consuming fans

Phase 2 -Tickover. When the room is at it's desired temperature then heat removal from the room  matches the heat that has leaked into the room.

 During a 8 hour period the sytem will be in phase 2 most of the time.

Old technology can only off on. The room may become uncomfotable before heat ejection  resumes with old technology. Also it is relatively expensive,

This is where inverter wins. Precise control of room temperature at lowest possible cost.

So the savings may refer to the comparison between both systems on 'tickover'

A conventional system only really has 2 phases -Full blast or off

 

 

This sounds great but I have a conventional aircon with 12000 BTU now - to be more precise 4 of them.  What inverter do I need to replace them? Very important to me is that the aircon reduces the humidity. I suffer more because of this than because of the heat. I had an oversized aircon and because the compressor wasn't running long enough it didn't reduce the humidity a lot. I also had an undersized aircon that didn't cool very much but the humidity was around 30% because the compressor was running all the time. It was a problem for the eyes. Since an inverter changes the compressor speed I don't know how many BTU I need. 

[Delight]

7 hours ago, Beggar said:

This sounds great but I have a conventional aircon with 12000 BTU now - to be more precise 4 of them.  What inverter do I need to replace them? Very important to me is that the aircon reduces the humidity. I suffer more because of this than because of the heat. I had an oversized aircon and because the compressor wasn't running long enough it didn't reduce the humidity a lot. I also had an undersized aircon that didn't cool very much but the humidity was around 30% because the compressor was running all the time. It was a problem for the eyes. Since an inverter changes the compressor speed I don't know how many BTU I need. 

In general terms hot air is wet air. Cold air is dry air. A modern  airconditioning system should be more accurately described as an air chilling system. Not true air conditioning.

Air cons give cold dry air. The water that was in the original hot air  now precipitates out and ends up in the drain. There is a water drain pipe from every Heat Exchanger on the wall.

What you need is a humidifier. I have no experience of such devices. Maybe other subscribers have and can help.

As far as heat ejectiion capability of systems. The quicker that the heat is ejected in the Full blast mode -the quicker the room will cool and the quicker the system gets to tickover. Take guidance from suppliers.The calculation is complex.

 

[Beggar]

1 hour ago, Delight said:

 

What you need is a humidifier. I have no experience of such devices. 

 

I have aircons and need in addition humidifiers? 

 

I would say - without wanting to insult you - that you have no idea what you are talking about. You just say inverters are great. But you just copy the advertisement. It is not that easy. Inverters have their place especially if they run all the time. But not everyone has this usage pattern. And then the answer what is better is not so easy anymore. You also didn't give me the answer how many BTU I need to replace my existing conventional aircons. I don't blame you because it is very difficult to find this out. 

[KittenKong]

19 minutes ago, Beggar said:

I have aircons and need in addition humidifiers? Humidifiers are nothing else than small aircons. They have a compressor and you always have to be careful that the water they remove doesn't fill their container. 

No, that's a de-humidifier. A humidifier adds moisture to the air in the room, like a boiling kettle does.

 

Though it seems to me that anyone who is using both an air-con and a de-humidifier probably has an air-con that is too powerful for his room. My air-con puts the ambient humidity at around 40-50% which I find comfortable when combined with an ambient temperature of around 26-27 degrees. I take this to mean that my air-con is the right size for my room.

 

[Beggar]

2 minutes ago, KittenKong said:

No, that's a de-humidifier. A humidifier adds moisture to the air in the room, like a boiling kettle does.

 

Though it seems to me that anyone who is using both an air-con and a de-humidifier probably has an air-con that is too powerful for his room. My air-con puts the ambient humidity at around 40-50% which I find comfortable when combined with an ambient temperature of around 26-27 degrees. I take this to mean that my air-con is the right size for my room.

 

I understood that he was talking about a humidifier and not about a de-humitifier and corrected my posting. But anyhow - do I need such an additional device if I have aircons?

 

So how many BTU do I need to replace a conventional correct sized aircon with 12000 BTU with an inverter so that I have the same moisture removal and the same cooling? 

[Delight]

43 minutes ago, Beggar said:

I have aircons and need in addition humidifiers? 

 

I would say - without wanting to insult you - that you have no idea what you are talking about. You just say inverters are great. But you just copy the advertisement. It is not that easy. Inverters have their place especially if they run all the time. But not everyone has this usage pattern. And then the answer what is better is not so easy anymore. You also didn't give me the answer how many BTU I need to replace my existing conventional aircons. I don't blame you because it is very difficult to find this out. 

 I attempted tp assist

Now you insult me.

I will never communicate with you again

[KittenKong]

11 minutes ago, Beggar said:

I understood that he was talking about a humidifier and not about a de-humitifier and corrected my posting. But anyhow - do I need such an additional device if I have aircons?

I dont need anything more than my air-con. For a couple of hundred Baht on Lazada you can buy a combined digital desk thermometer and hygrometer which might help you see if your air-con is correctly sized for your room.

 

Actual air-con size seems to depend a lot on the type of room and the exposure it has to the sun. I leave my air-con on 24/7 even when I'm out for a few hours as I find this is the most economical and comfortable way of doing it.

[Beggar]

2 minutes ago, Delight said:

 I attempted tp assist

Now you insult me.

I will never communicate with you again

Please forgive me. I really didn't want to insult you and I thank you for your response. I am really very sorry that I made you unhappy. I just have enough of the idea that inverters are always better. I really want to apologize. Sorry again.