Payback period for inverter aircon

[Oxx]

Anyone know how long the payback period is for an inverter aircon unit (a type which allegedly costs a lot less to run) versus a conventional unit?

 

I'm thinking of replacing the 8 year old unit in my sitting room which is 37 m² with the aircon running perhaps 8 hours/day.

[Pib]

All depends on how long you run it....if you run it 24/7 then payback will probably be in around 15 months.  Of course other factors can apply like ensuring you get a properly sized inverter A/C....if it undersized it will simply run full bore all the time like a standard A/C....you will not save anything.  

 

The 15 months perioid was the pay back period for the 23K BTU Mitsubitshi inverter A/C I bought to replace a standard 18K BTU A/C which ran 24/7.

 

[scorecard]

And before you buy check if you need to press a button on the remote to get the electricity savings.

 

The LG remote has a button right side, 3 buttons up from the bottom, it's marked 'SAVING'.

 

After switch on if you press the SAVING button it cuts electricity usage quite a lot. Have to do this every time you start the A/C, not difficult.

 

How this works on other brands I don't know.

 

[Delight]

 Just to explain.

With a conventional AC unit the compressor is either ON or OFF

When the compressor starts the start up current is twice the running current. Lots of starts means lots of wasted energy

An inverter system never stops-unless the whole unit is switched off.

What happens is that the compressor alters it speed to suit demand -but never switches off and thus never starts during its total opertating cycle-except at the beginning.

[KittenKong]

6 hours ago, Delight said:

What happens is that the compressor alters it speed to suit demand -but never switches off and thus never starts during its total opertating cycle-except at the beginning.

Mine does, or at least the fan stops going round and it makes no noise which I suppose means that it's off.

 

As for the pay-back period, mine paid for itself in just over a year but I'm not sure how much of the saving was down to the new one being an inverter or just being new. Certainly the old one was very old and didnt work very well, so the saving could have been greater for that reason.

[Delight]

3 hours ago, KittenKong said:

Mine does, or at least the fan stops going round and it makes no noise which I suppose means that it's off.

 

 

 The invertor process refers to the compressor not the fan on the air blast heat exchanger

[KittenKong]

9 minutes ago, Delight said:

 The invertor process refers to the compressor not the fan on the air blast heat exchanger

I know. But a compressor that is working at all would be likely to make some sort of noise I think.

[Delight]

1 hour ago, KittenKong said:

I know. But a compressor that is working at all would be likely to make some sort of noise I think.

 Fans make noise due to the movement of the air.

The compressor on a  system is located outside -so not heard inside.

Outside is the 2nd air blast system -that you will hear.

[tlandtday]

I run one invertor and one non invertor in two rooms almost identical size and for an identical time and the savings if any are minimal...

[Pib]

On my Mitsubishi inverter A/C the outdoor unit is very quiet.  During cooler parts of the year when I'm still using the A/C for some cooling the outside unit will often be totally silent and the fan is not running.  Other times you can see the outside fan turning slowly (even the fan is variable speed) but you can still not hear any compressor running when standing directly under it....it's about 3 meters up on the house outside wall.  

 

Now, when it's hot you can hear the compressor run and the fan will be running faster.  

 

While I know the basic technology behind an inverter A/C is that the compressor acts a variable speed compressor based on my googling I think the compressor will actually cut off "when the cooling requirement drops below its minimum cooling capacity."  Similar to an inverter water pump that is only running at a variable speed when water is being drawn....when no water is being drawn the pump will completely turn off.

 

The particular inverter A/C I'm talking about is a Mitsubitshi inverter model number MSY-GN24VF with a "nominal" cooling capacity of 22,519 BTU but since it's an inverter A/C it's cooling capacity actually ranges from 5,118 BTU to 24,566 BTU.   When the cooling requirement drops below 5,118 BTU that is when I think the compressor cuts off completely.

 

 

 

[Pib]

18 minutes ago, tlandtday said:

I run one invertor and one non invertor in two rooms almost identical size and for an identical time and the savings if any are minimal...

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.

[CGW]

On 4/19/2019 at 9:25 PM, scorecard said:

After switch on if you press the SAVING button it cuts electricity usage quite a lot. Have to do this every time you start the A/C, not difficult.

Every "saving" control I have had changes the temperature settings, meaning it increases the temp you have previously set, I can't consider this as a genuine "saving"

Maybe LG is different - but I doubt it?

[watboy]

I like my condo to be suitable for polar bears and had an electric bill to match (~6,000/month). Changed compressor to an inverter and my electric bill dropped to 3500. Paid for itself in about 16 months.

[KittenKong]

48 minutes ago, Delight said:

Fans make noise due to the movement of the air.

The compressor on a  system is located outside -so not heard inside.

Outside is the 2nd air blast system -that you will hear.

I am talking about outside.

[KittenKong]

34 minutes ago, Pib said:

On my Mitsubishi inverter A/C the outdoor unit is very quiet.  During cooler parts of the year when I'm still using the A/C for some cooling the outside unit will often be totally silent and the fan is not running.  Other times you can see the outside fan turning slowly (even the fan is variable speed) but you can still not hear any compressor running when standing directly under it....it's about 3 meters up on the house outside wall.  

 

Now, when it's hot you can hear the compressor run and the fan will be running faster.  

 

While I know the basic technology behind an inverter A/C is that the compressor acts a variable speed compressor based on my googling I think the compressor will actually cut off "when the cooling requirement drops below its minimum cooling capacity."

That is exactly my experience of my air-con. If the outside is running all the time, then at the lowest speed it is 100% silent and causes no vibration at all. That seems unlikely to me. I can certainly tell when it is running full speed and also when it is running at reduced speed as both are very audible to me. When it appears to be off it is completely silent though.

So it still seems to me that my outdoor unit turns itself off completely from time to time when demand is minimal. This mostly seems to be in what passes for winter here.

[The Fat Controller]

My Daikin outside unit also stops completely in the cool season with the indoor unit still running.

[johng]

1 minute ago, The Fat Controller said:

My Daikin outside unit also stops completely in the cool season with the indoor unit still running.

Then it will be just running the fan of the indoor (evaporator) unit..might as well just turn it off completely and use a conventional pedestal fan,  if the compressor (outdoor unit) is not running then there will be no cooling action.

[The Fat Controller]

20 minutes ago, johng said:

Then it will be just running the fan of the indoor (evaporator) unit..might as well just turn it off completely and use a conventional pedestal fan,  if the compressor (outdoor unit) is not running then there will be no cooling action.

 

Yes, I realise that's the case, but as the unit controls the temperature so accurately, I just leave it to come back on as necessary when the temperature rises.

 

I also find I sleep better with the noise of the fan and prefer the air distribution of the A/C unit than a pedestal fan.

[scorecard]

2 hours ago, CGW said:

Every "saving" control I have had changes the temperature settings, meaning it increases the temp you have previously set, I can't consider this as a genuine "saving"

Maybe LG is different - but I doubt it?

Point taken however we've been using the 'SAVINGS' button in three bedrooms every night for quite a few months, nobody has mentioned the temp going up and I haven't noticed it in my bedroom but our bill has come down a lot. 

[CGW]

16 minutes ago, scorecard said:

Point taken however we've been using the 'SAVINGS' button in three bedrooms every night for quite a few months, nobody has mentioned the temp going up and I haven't noticed it in my bedroom but our bill has come down a lot. 

We use AC a lot, have eight units around the house, electric bill is not astronomical as we run units on higher settings than most do, you don't need the AC on low to get the benefits, as an example the past week has been over 40c everyday, we have had AC on 30c, makes the house comfortable and the heat bearable, takes a lot of the moisture out of the air which is one of the reasons it gets so uncomfortable. Bedroom is on 24c night-time only.

[Delight]

As we are on the topic of aircons. I have written this piece

How an aircon system works.

 

Consider a pan of water sat on a electric heater.

The temperature will rise until boiling point is achieved –at normal pressure this is 100C

Then consider putting the arrangement into a sealed

Box.

 If the air in this box is pressurized  the water will still boil –but at a higher temperature. (conversely if the pressure is reduced to below atmospheric –then the water will boil –but at a lower temperature)

 The boiling point  of fluids at a higher temperatures is important for air con systems.

Also if a fluid changes from liquid to vapour- then the boiling process must occur-important.

Consider a horizontal pipe and in this pipe is an orifice plate i.e a plate with a orifice (hole) of precise dimensions. Further imagine that this orifice can be opened and closed externally.

The left hand side of the pipe is filled with a pressurized refrigerant fluid .  The temperature of this fluid will also be high, The orifice is closed

Typical refrigerant fluid is R134 . It has a normal boiling point of about minus 48C

When the orifice is opened the right hand side of the orifice will now be vapour. As I said for that to happen a boiling process must occur.

Prior to opening the orifice the R134 will now be at a much higher than normal pressure and temperature –therefore the boiling point will increase. The system is designed such that the boiling point  changes from minus 48C of R34  to plus 10C(my arbitrary figure)when the orifice is opened

Therefore the vapour ,on the right hand side of the orifice will now be at 10C. The science to explain this change is complex.Too complex for me.

This vapour(at 10C) is now pushed to the  heat exchanger bedroom –collects heat. This causes bedroom temperature to drop

The vapour  is further pushed to the inlet side of the compressor. The now high pressure/temperature vapour(output from compressor) is pushed to heat exchanger sited in fresh air.

Providing that the temperature of the vapour is higher than the fresh air temperature then the vapour will cool such that the fluid leaving the  heat exchange sited in fresh air will be liquid .

This liquid then meet the orifice and the process continues.

All the pushing is carried out by the compressor.

In practice a fixed orifice is never used.

A device called an expansion valve. In effect it is a variable orifice system. It takes information from parts of the system total and varies the orifice. It is sometimes called metering valve. Changing the orifice size meters/controls the thruput.

 Changing the speed of the compressor will also serve to improve energy efficiency.

Where are the components sited? The expansion vave is in the bedroom 'box on the wall'.

The compressor is sited with the heat exchanger in fresh air

With reference to the OP’s Q i.e how much time to recover the cost of an inverter system. The regular time quoted is 2 years. This value relates to the relative cost of a new(lower cost)  conventional unit versus  a new (higher cost) inverter system.

After this 2 year period has passed –then it must be a simple case of money in the bank

More than 2 years is required if you are replacing a conventional system in good order.

A lot more time I think! May take many years.

Edited April 23, 2019 by Delight

[alacrity]

On 4/22/2019 at 12:01 PM, KittenKong said:

I know. But a compressor that is working at all would be likely to make some sort of noise I think.

Correct. The outside fan would also run as heat would need to be extracted from the heat exchanger. Overall the noise generated in extended use would be lower than a conventional system but will continue for much longer periods. Not really a problem as that part of the system is usually located away from the cooled area.

Slower running motors and fans generate lower noise frequencies which are more audible than higher frequencies at the same noise level though.

 

I currently project that it will take 7-8 years just to recoup the 30% extra I paid for my 2 inverter systems. If over time the efficiencies degrade to a level where that effectively becomes lifetime of the system. I would have wasted my money.

[apknug]

As mentioned above, difficult to "count it home" om energy savings alone of you are throughing out a fine working unit.

But One should consider the increased Comfort level achivded as well. Lower noice and a stable temprature. I cant wait to have My old on off unite replaced.

Skickat från min Lenovo TB-X704F via Tapatalk

[alacrity]

On 4/26/2019 at 9:15 PM, apknug said:

As mentioned above, difficult to "count it home" om energy savings alone of you are throughing out a fine working unit.

But One should consider the increased Comfort level achivded as well. Lower noice and a stable temprature. I cant wait to have My old on off unite replaced.

Skickat från min Lenovo TB-X704F via Tapatalk
 

Yes, for sure there's fewer periods of icy blasts needed to maintain a comfortable temperature and the fan is marginally quieter compared to slow speed on my standard units. Conventional units don't have the 400Hz whine from the power supply though.

 

Uncertain if not being noisy will be a strong selling point in Thailand and I'm sure efficiency figures were calculated out by Volkswagen.

[Beggar]

What is your experience with moisture removal when using an inverter aircon? Same as conventional aircon or less? 

[Pib]

24 minutes ago, Beggar said:

What is your experience with moisture removal when using an inverter aircon? Same as conventional aircon or less? 

same-same

[VocalNeal]

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.  Of course other factors can apply like ensuring you get a properly sized inverter A/C....if it undersized it will simply run full bore all the time like a standard A/C....you will not save anything. 

I'm having a hard time with this. The heat load required to cool a room is the same no matter the size of the AC. If a small one running constantly can't cool the room but the larger one still needs to remove the same amount of heat. Unless larger units are more efficient the energy input should be no different. 

 

The above sounds like the logic of someone who turns a car AC to minimum temperature when starting up because they think on minimum it gets colder quicker.

Edited April 28, 2019 by VocalNeal

[Beggar]

2 minutes ago, VocalNeal said:

I'm having a hard time with this. The heat load required to cool a room is the same no matter the size of the AC. If a small one running constantly can't cool the room but the larger one still needs to remove the same amount of heat. Unless larger units are more efficient the energy input should be no different. 

 

The above sounds like the logic of someone who turns a car AC to minimum temperature when starting up because they think on minimum it gets colder quicker.

What I have learned is that that if an inverter runs at 100 % it will need more power than a conventional aircon because the power needs to get transformed and this increases the power consumption. 

[Fruit Trader]

1 hour ago, VocalNeal said:

I'm having a hard time with this. The heat load required to cool a room is the same no matter the size of the AC. If a small one running constantly can't cool the room but the larger one still needs to remove the same amount of heat. Unless larger units are more efficient the energy input should be no different. 

 

The above sounds like the logic of someone who turns a car AC to minimum temperature when starting up because they think on minimum it gets colder quicker.

You are having a hard time with the explanation because it failed to include any values. Load is indeed the same for conventional and inverter AC's if the conditions are identical.

 

There is no mysterious magic inside inverter AC's. Its simple proportional control against on/off control plus some conversion loss.
 

[alacrity]

1 hour ago, VocalNeal said:

I'm having a hard time with this. The heat load required to cool a room is the same no matter the size of the AC. If a small one running constantly can't cool the room but the larger one still needs to remove the same amount of heat. Unless larger units are more efficient the energy input should be no different. 

 

The above sounds like the logic of someone who turns a car AC to minimum temperature when starting up because they think on minimum it gets colder quicker.

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.