Temperature Differential

[bamamule]

I have been reading on here that the normal temperature differential between the supply and discharge air on an a/c is 18-20 degrees. Is this measured in the hot part of the day or at night? On my new Lennox system the difference is 13 degrees in hot part of day and 18 degrees after sunset. It maintains temperature setpoint well (76) except when it gets 98-100 outside then it drifts up about 1 degree inside the house. Is this acceptable performance? Unit cycles on and off except for about 3-4 hours in afternoon then it runs continuosly. I live in Alabama where humidity and high temperatures are extreme. Ductwork is in the attic.

[Edited by bamamule on 07-12-2006 at 05:22 AM]

[danglerb]

On the hot part of the day, turn off the AC and run just the fan and see what return grill vs outlets temps are. Just my no nothing guess, but could be you need a dose more insulation on the ductwork.

[beenthere]

If its maintaining a 23° difference from the outside temp when its 98 plus, its doing great.

[bornriding]

Since I am also in Bama, I will respond.
The 13 'f' delta 't' ( difference in return - supply ) during the day indicates that yur ductwork may be absorbing heat from the attic space. Especially since yu say it goes up to 18 'f' during the night.
Sounds like you either need more insulation on yur ducts or yu need more attic exhaust to get out the hot air.
A good tech should be able to determine this.

Richard

[mjk_na]

How was the AC sized?

Did you consider extreme temperatures within your area? How long do you experience that extreme temperature? What is your design indoor temperature? How is your house designed to reduce heat gain and loss?

All of these will effect the sizing of your AC

I can maintain my AC at 68 F, when outside temperature is 95 F.

[dash]

Originally posted by bornriding
Since I am also in Bama, I will respond.
The 13 'f' delta 't' ( difference in return - supply ) during the day indicates that yur ductwork may be absorbing heat from the attic space. Especially since yu say it goes up to 18 'f' during the night.
Sounds like you either need more insulation on yur ducts or yu need more attic exhaust to get out the hot air.
A good tech should be able to determine this.

Richard

I agee,you should have the ducts checked.