Air con efficiency

[Kenny202]

Just wondering is an air con more or less efficient / effective with fan speed higher or lower? I would have thought a lower fan speed would give the air passing the condensor more time to cool.

 

Our bedroom aircon struggles when temps up around 40 plus. I noticed today I turned the fan speed up and it did seem to pull the room temp down more. Is there any science to this?

 

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[NightSky]

I don't know about fan speed and im not an aircon engineer but from my own experience, when the aircon isn't working first job is to get it cleaned properly (usually once every 4 to 6 months).

 

If its a very old unit it needs replacing (this might also reflect in the electricity bill and performance and noise of the unit), dont put up with over inflated electricity bill because running a good aircon shouldn't cost a fortune.

 

Also the unit needs to be the right size for the room area (BTU/square meter)

 

[ianezy0]

A fan at low speed gives the compressor and coil time to dehumidify the air. If the fan is at high speed it will cool the air faster but reduce the ability to dehumidify.

[Snow Leopard]

Insulation helps and decent double glazing. 

[Thainesss]

23 minutes ago, Kenny202 said:

Just wondering is an air con more or less efficient / effective with fan speed higher or lower? I would have thought a lower fan speed would give the air passing the condensor more time to cool.

 

Our bedroom aircon struggles when temps up around 40 plus. I noticed today I turned the fan speed up and it did seem to pull the room temp down more. Is there any science to this?

 

If everything is functioning properly then of course if you use the higher fan speed settings its going to cool the room faster. Just like when you get in a hot car, you crank it up on high until you get comfortable then dial the fan speed and temp back. Still blows cold air on high or low settings. Part of the way the aircon works is by circulating the air in the room and pulling the warmer air from up high and blowing cold air down - over and over again. 

 

I had the same issue in my living room when it gets up around 40 outside (high fan speed), so I broke down and bought a bigger aircon (27k BTU Super Inverter) just for those really HOT days. I could never get the room below 28 or 29 on the really scorching days. Now its a cool 24 (or 22) no matter how hot it is outside. 

 

Step one would be to get the aircon professionally serviced (about 500 baht) and you could also try out your 'auto' fan setting on the unit. 

[Kenny202]

1 hour ago, NightSky said:

I don't know about fan speed and im not an aircon engineer but from my own experience, when the aircon isn't working first job is to get it cleaned properly (usually once every 4 to 6 months).

 

If its a very old unit it needs replacing (this might also reflect in the electricity bill and performance and noise of the unit), dont put up with over inflated electricity bill because running a good aircon shouldn't cost a fortune.

 

Also the unit needs to be the right size for the room area (BTU/square meter)

 

It is an older unit but it should be big enough for the bedroom. It has been cleaned recently and is cleaned every 3 or 4 months. If it was my place (we're renting) I'd put an inverter in. The air coming out of the unit always feels chilly. Buggered if I know. One of the problems I see is the external unit is in a corner under the covered area outside which is always hot when the air con is on, obviously hard for the warm air to get away from the fan unit, probably recycling hot air

[Kenny202]

45 minutes ago, Thainesss said:

 

If everything is functioning properly then of course if you use the higher fan speed settings its going to cool the room faster. Just like when you get in a hot car, you crank it up on high until you get comfortable then dial the fan speed and temp back. Still blows cold air on high or low settings. Part of the way the aircon works is by circulating the air in the room and pulling the warmer air from up high and blowing cold air down - over and over again. 

 

I had the same issue in my living room when it gets up around 40 outside (high fan speed), so I broke down and bought a bigger aircon (27k BTU Super Inverter) just for those really HOT days. I could never get the room below 28 or 29 on the really scorching days. Now its a cool 24 (or 22) no matter how hot it is outside. 

 

Step one would be to get the aircon professionally serviced (about 500 baht) and you could also try out your 'auto' fan setting on the unit. 

I believe most air cons wont pull down more than 10-12 degrees or so below the outside ambient. Sounds like the one you have is a cracker. Like I said in a previous post not my house so stuck with it. Always better to buy a good brand and plenty of capacity what with the cost of electricity being expensive here now. I'd be putting an inverter in for sure

Not sure you can compare a car air con either. Having the fan higher appears to be cooler because it os blowing straight on you. 

[Thainesss]

1 minute ago, Kenny202 said:

It is an older unit but it should be big enough for the bedroom. It has been cleaned recently and is cleaned every 3 or 4 months. If it was my place (we're renting) I'd put an inverter in. The air coming out of the unit always feels chilly. Buggered if I know. One of the problems I see is the external unit is in a corner under the covered area outside which is always hot when the air con is on, obviously hard for the warm air to get away from the fan unit, probably recycling hot air

 

If the air is cool, and everything is functioning properly, and its been serviced recently (pressure washed inside and out) then its just too small of a unit. 

 

You can give us the room size, and the BTU of the unit now, and what kind of windows & everything for a calculation, but at the end of the day if everything is clean and working properly, then its just too small.

[Thainesss]

2 minutes ago, Kenny202 said:

I believe most air cons wont pull down more than 10-12 degrees or so below the outside ambient. 

 

Thats just plain false and its weird because ive seen that same logic posted before and could never figure out why anyone would say that, or where that idea comes from. I used to live in Saudi where it gets over 50C outside and my home was still 22-24C inside using split units. Its all about how many BTU's (or whatever cooling capacity metric) times the room size. 

 

8 minutes ago, Kenny202 said:

Not sure you can compare a car air con either. Having the fan higher appears to be cooler because it os blowing straight on you. 

 

Most car air conditioning systems function exactly like a non-inverter split unit air-conditioner in your home. You have fan speed settings and a 'temp' setting and the compressor cycles on and off as needed vs your desired temp. it may be blowing straight on you, but its still cooling the air in your car until your desired temp setting then cutting out the compressor until it warms up again. 

 

The logic is exactly the same. If you put a thermometer in the aircon vents in your home or your car and measure the temp coming out on high and low settings they should be almost the same. 

[tjo o tjim]

46 minutes ago, Thainesss said:

 

Thats just plain false and its weird because ive seen that same logic posted before and could never figure out why anyone would say that, or where that idea comes from. I used to live in Saudi where it gets over 50C outside and my home was still 22-24C inside using split units. Its all about how many BTU's (or whatever cooling capacity metric) times the room size. 

Refrigerant type can play a role, but it really depends on the pressure differential of liquid and gas lines rather than the mass flow rate of refrigerant, which is BTU/hr. Most will continue to operate at higher temperatures, but at reduced capacities. 

[Thainesss]

2 minutes ago, tjo o tjim said:

Most will continue to operate at higher temperatures, but at reduced capacities. 

 

True, but thats why more BTU's (or tons or horsepower) is required to do the job. The logic that an air-conditioning system will not bring the temp down more than 10-12 degrees is demonstrably false and I don't know where that idea comes from. 

 

Most air conditioners that ive tested blow air at about 16 degrees measured with a thermometer at the air handler. It'll do that regardless of wether its 30 degrees outside or 50 degrees outside if the unit is sized properly. 

[BritManToo]

2 hours ago, Thainesss said:

I had the same issue in my living room when it gets up around 40 outside (high fan speed), so I broke down and bought a bigger aircon (27k BTU Super Inverter) just for those really HOT days. I could never get the room below 28 or 29 on the really scorching days. Now its a cool 24 (or 22) no matter how hot it is outside. 

I'm happy with 28c.

[bankruatsteve]

Use fan speed "Auto". 

[tjo o tjim]

Did a quick lookup, standard condensing units are rated at 35C DB and 25C WB.  So, at 40C, you are likely limited to about 70% capacity, and 45C less than 50%. If the unit is in the sun that will increase its operating temperature of course.