Payback period for inverter aircon

[Delight]

21 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.

 

How do you measure this? How do you control this? . The humidity at 27 is higher than that at 25.

Dehumidifiers extract water from air that passes through the unit.

A Humidifier adds water into the air

 

 

As I said in my answer I am no expert on these devices.

The problems with air cons is that they remove water and the now dry air can be uncomfortable .

If I had this problem I would seek advice from an expert.

 

[KittenKong]

8 hours ago, Delight said:

How do you measure this? How do you control this? . The humidity at 27 is higher than that at 25.

Dehumidifiers extract water from air that passes through the unit.

A Humidifier adds water into the air

As I mentioned, my desktop digital thermometer shows the ambient humidity. That's how I measure it. I dont need to control it because with my air-con running normally in my room I get the humidity level of around 50% that I like. If your air-con is running too much the humidity may be too low and if the air-con isnt running enough it may be too high, but I dont have those problems.

[sometimewoodworker]

19 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. 

The advice for non inverter AC units was (as you have found out) do not oversize them. However with inverter AC units that is less clear as slight to moderate oversizing will just mean that the fan, cooling and dehumidifier is running at a lower level, but still running. 

 

Only you can tell from your current experience which size inverter to replace your current ones with. 

 

1) do the current AC units cool the room enough (if not get a bigger inverter)

2) does the compressor run all the time (get a bigger inverter)

3) does the compressor run more than 75% of the time after an hour or so of use time (get a bigger inverter)

 

If the answers are Yes, No, No then an inverter of about the same rating should be about right.

 

However since you have 4 then start with replacing 1.

 

[Beggar]

19 minutes ago, sometimewoodworker said:

The advice for non inverter AC units was (as you have found out) do not oversize them. However with inverter AC units that is less clear as slight to moderate oversizing will just mean that the fan, cooling and dehumidifier is running at a lower level, but still running. 

 

Only you can tell from your current experience which size inverter to replace your current ones with. 

 

1) do the current AC units cool the room enough (if not get a bigger inverter)

2) does the compressor run all the time (get a bigger inverter)

3) does the compressor run more than 75% of the time after an hour or so of use time (get a bigger inverter)

 

If the answers are Yes, No, No then an inverter of about the same rating should be about right.

 

However since you have 4 then start with replacing 1.

 

This is for sure the best idea to replace 1 first and check the result. My biggest worry is that when the desired room temperature is reached the compressor will reduce the speed and so the cooling - what it should do if it is an inverter. But is it still cold enough at the evaporator unit to reduce enough moisture?

[sometimewoodworker]

23 minutes ago, Beggar said:

This is for sure the best idea to replace 1 first and check the result. My biggest worry is that when the desired room temperature is reached the compressor will reduce the speed and so the cooling - what it should do if it is an inverter. But is it still cold enough at the evaporator unit to reduce enough moisture?

My practical experience is that even when our inverters do run the fans slower the humidity is kept in the comfortable range which is between 40% & 70%.

 

As long as the cooling fins are below the dew point they will dehumidify the air

 

to give some examples

29C humidity 90% dew point = 27.2C

25C humidity 80% dew point = 21.3C

25C humidity 40% dew point = 10.4C

 

Daikin do advertise that you can set the humidity so they could be the ideal for you.

[Delight]

Humidity is the percentage value of the amount of water that exists in air.

When the air is the bedroom makes contact with the heat exchanger in the same bedroom then the water will precipitate out i.e. liquid water will appear on the heat exchanger.

The lower the bedroom temperature  –the more water.

This has the potential to make the air too dry.

Solution-theoretical.

1)Increase the pressure of the refrigerant liquid . This can only be done by reducing the orifice  size.

2)Compressors (and pumps ) do not create pressure. They simply create a  flow of fluid in a system. The resistance in that system creates the pressure. The compressor or pump simply has to cope with that increased pressure. An in crease  in pressure will always produce a loss of output from the compressor/pump .Internal slip will occur.

3)By reducing the orifice size –the system pressure will increase. That increase of pressure acting on the refrigerant fluid will increase the boiling point of that fluid. In my piece explaining how an air system works I chose an arbitrary value of +10c. With the reduced orifice size -let’s raise that to +15C

This will result in less precipitation –more water remains in the bedroom air.

Of course by increasing the temperature in the bedroom heat exchanger- more time will be required to cool the bedroom.

Answer -a larger heat exchanger in the bedroom. This in practice will mean a system with a higher BTU rating plus a system where the orifice size can be externally adjusted.

Inverter style systems are more suited to this approach.

[Delight]

 The term Humidity has been used on the blog.

So I thought that I would have ago at explaining it.

Feel free to correct my offering if appropriate.

Understanding Humidity

 

Air comprises Nitrogen molecules-N2- (78%) and Oxygen molecules-O2 -(21%). That is 99% . The other1% is not relevant to this piece.

However the other component which is highly relevant is Space.

Space is not air –it is just Space.

The molecules present do rapidly move about in the Space.

 

If air comprises N2 + O2 + Space and no water vapour is present then it has relative humidity of zero%.

Relative humidity is the space occupied by water vapour molecules relative to the Space available to accept water vapour molecules.

0% Humidity in every day experience never occurs.

When water vapour molecules enter the air the relative humidity increases i.e now the air  has water vapour molecules  –they have displaced the  Space.

When the water vapor molecules occupy the same volume of space as the Space. We have 50% humidity.

When the air temperature drops the Space contracts. The other molecules do not contract.

When the Space cannot contract any further  then saturation has occurred . 100% humidity

When the temperature drops even further then some of the water vapour molecules are in effect expelled from the air.

(100% humidity can stay in that state if there is no further drop in temperature .It is not pleasant to humans)

-Expelled is probably not the correct scientific term –however I think that it makes it easier to understand-.

The temperature at which this occurs is called the Dew point.

When trying to imagine humidity think firstly about the Space -then add water vapour molecules to the Space.

 

So where do they-the water vapour molecules- go. They will go to a cold surface.

The heat exchanger in the A.C circumstance. In nature they will go ,typically .to cold leaves.

The next stage is the same –A.C or leaf.

Condensation will occur.

Liquid water will appear.

The falling of this water is called precipitation.

If the cold surface is below zero  C  then frost will occur . In nature and potentially in a badly adjusted AC system.

 With an A.C -because water  is being removed from the system total –the air must be dryer.

A symptom of this is waking up in the morning with a dry mouth.

[alacrity]

On 5/6/2019 at 10:24 PM, Delight said:

 The term Humidity has been used on the blog.

So I thought that I would have ago at explaining it.

Feel free to correct my offering if appropriate.

Understanding Humidity

 

Air comprises Nitrogen molecules-N2- (78%) and Oxygen molecules-O2 -(21%). That is 99% . The other1% is not relevant to this piece.

However the other component which is highly relevant is Space.

Space is not air –it is just Space.

The molecules present do rapidly move about in the Space.

 

If air comprises N2 + O2 + Space and no water vapour is present then it has relative humidity of zero%.

Relative humidity is the space occupied by water vapour molecules relative to the Space available to accept water vapour molecules.

0% Humidity in every day experience never occurs.

When water vapour molecules enter the air the relative humidity increases i.e now the air  has water vapour molecules  –they have displaced the  Space.

When the water vapor molecules occupy the same volume of space as the Space. We have 50% humidity.

When the air temperature drops the Space contracts. The other molecules do not contract.

When the Space cannot contract any further  then saturation has occurred . 100% humidity

When the temperature drops even further then some of the water vapour molecules are in effect expelled from the air.

(100% humidity can stay in that state if there is no further drop in temperature .It is not pleasant to humans) to

-Expelled is probably not the correct scientific term –however I think that it makes it easier to understand-.

The temperature at which this occurs is called the Dew point.

When trying to imagine humidity think firstly about the Space -then add water vapour molecules to the Space.

 

So where do they-the water vapour molecules- go. They will go to a cold surface.

The heat exchanger in the A.C circumstance. In nature they will go ,typically .to cold leaves.

The next stage is the same –A.C or leaf.

Condensation will occur.

Liquid water will appear.

The falling of this water is called precipitation.

If the cold surface is below zero  C  then frost will occur . In nature and potentially in a badly adjusted AC system.

 With an A.C -because water  is being removed from the system total –the air must be dryer.

A symptom of this is waking up in the morning with a dry mouth.

Precipitation is not the correct term unless it rains. Condensation is correct and the condensate should be carried away via the drain.

There is a relationship between air temperature and relative humidity. Relative humidity decreases with decrementing temperatures. But the level of humidity is relative not fixed. Dew point is a true measure of humidity. You can also have a hot gas with a low dewpoint.

Icing of the heat exchanger is due to contamination of the filament. Seldom have I seen an a.c that will cool to zero degrees or less. Environmental chambers and freezers/ice-boxes will.

Simple humidity values are given as a resultant algorithmic value extrapolated from a temperature measurement. Dew point is determined differently and can be used as a metric of air/gas contamination.

You can also get a dry mouth from your body's dehydrated state. Don't blame the a.c. for your hangover every time.

 

Basically cooling air with an a.c. unit will reduce the dew point/relative humidity of the air in the cooled area.

Reduced humidity in the area will also help your body to cool by evaporation of sweat because there's less water vapour in the air enabling a higher rate of moisture absorption within that area.

 

Maintaining a reasonably consistent temperature and thus level of humidity in a building will also prolong the life of electronics and materials in that area. We keep 3 units (not inverter)running 24/7 all year and the additional running cost isn't that high. Less than 8% by my reckoning.