Temperature difference

[jtjgvle]

I know, there are variables, but approximately what should be the difference in temperature between return air and register air? I have a brand new system and it is running almost constantly on hot days. The installer came back and checked the charge but that was in late January at it was barely 70 degrees outside. Should I insist they come back again? My difference in temp from return to register is 15 degrees. I measured the register air at a register halfway down the trunk line in order to get the average when taking heat gain from the attic into account. Thanks in advance.

[coolcray3]

the temp diff sounds right it is usally about 10 to 15 degrees difference.it sounds to me like you have a problem with your insulation or something letting your air escape or allowing the heat get in and also where is your thermostat located. it should be in a central spot or close to the return air to get atrue reading and make sure its not in a spot where the sun is on it.also do you have a return at the highest point in the house that would make a difference.

[jtjgvle]

Thanks for the reply coolcray, I actually have two ceiling returns, one is directly above the thermostat. My house very old and I'm in the process of restoring it. Currently the only insulation is in the attic. I know more insulation will help, but the heat worked very well. If the problem is purely the lack of insulation I'll just have to grin and bear the utility bill unitl I get around to adding more. I have added an attic fan to help reduce heat transfer to the ductwork. Someone in another forum suggested addin additional insulation to the ducts. My main concern is that if something is wrong with the unit I want to get it right before too much time passes. I'm just about to the point of hanging blankets over the windows when I think of the electric meter spinning away!

[coolcray3]

if all the ducts are insulated with duct wrap and the house is old thats all you can do the heat from out side is radiating right through the walls and any air gaps it can get through. the unit is right on with the temp of the air. sometimes the attic fan will cause a air pull through the house and pull the heat in as well as venting the attic space. you want to make sure your attic is sealed from the house and not pulling out the ac and pulling in the heat at the same time

[cem-bsee]

white blinds, reflective film &solar screening will prevent considerable heat gain -- awnings will even more.

insulation in attic will decrease energy needs both for cooling & heating.

[jtjgvle]

Thanks again coolcray. I guess I'll get some cans of spray foam and go to work plugging any gaps in the attic. I have two windows up there open, but I guess there could still be some air pulling through around ceiling fixtures and stuff.

[jtjgvle]

Cem, I have white plantation blinds on most of the windows, but there is one room with BIG windows that don't have blinds yet. I might have to improvise something to cover those windows with for the time being. Thanks for the input.

[coolcray3]

if you have open windows up there that should be plenty of intake air for the fan to pull from. i think i would consentrate on making sure that your attic opening to the house is sealed and try some window coverings that will deflect the sun and heat

[jtjgvle]

Thanks to both of you for being so helpful with my first participation in this forum!

[Freezeking2000]

A properly sized cooling system will run 100% of the time at design temperature. Has it been hot?

[berad]

look at the hole in the wall where the thermostat wires come out behind the stat. Is the hole sealed, filled with caulk or something? If not it should be, hot air can be cruising through your wall like an chimney and right into your thermostat.

[jtjgvle]

The high temperature has approached 95 for the last week, unusually hot for the area. I plugged up th ehole behind the thermostat when I changed it to a programable one (which cut the natural gas bill in half)

[dan sw fl]

Originally posted by coolcray3
the temp diff sounds right it is usally about 10 to 15 degrees difference.

TEMPERATURE DIFFERENCE as stated SHOULD BE > 17'F.
For Example,
77'F Room Temperature
60'F Diffuser

That should provide R.H. of << 58%.

AND that's just for an average system without Variable Speed air handler.

Did you try Medium air flow setting on air handler instead of High?

[dan sw fl]

Originally posted by Freezeking2000
A properly sized cooling system will run 100% of the time at design temperature. Has it been hot?

AND maintain the residence at ~20'F less than the Outside Temperature.

(i.e. East Coast, NOT AZ or similar where Delta T >> 30'F)

Thanks, King!

[jtjgvle]

To my knowledge I don't have a variable speed air handler. I have adjusted the thermostat enough so that the AC will at least cycle some (although it doesn't stay off for very long) rather than running constantly (77-78) I'll just have to get used to it I guess. Unfortunately my work building is always about 71 so I get used to it being really cool! I'm going to pursue some more window coverings and see what happens. Thanks to everyone for your continued suggestions.

[Panama]

The temperature drop should be measured just before and just after the evaporator coil. You'd be surprised how much the air can warm up in both the return ducts and the supply ducts. If you have a 15 °F difference between a supply grille and a return grille, you just may have a 17°F or more difference at the coil itself.

The best way to find out where your cool is going is to hire an expert to test for leaks in the house with a blower door and for leaks in the ducts with a Minneapolis Duct Blaster. The right expert can also suggest insulation improvements.

One place to look for an expert is at http://www.energyconservatory.com.

[zzyzzx]

Originally posted by Freezeking2000
A properly sized cooling system will run 100% of the time at design temperature. Has it been hot?

I was going to say this too! I moved into a townhouse about 1.5 years ago after living in basement apartments for more than 10 years. The amount of time I have to keep the A/C on is way more!

[jtjgvle]

ZZYZZX, I guess alot of th eproblem is getting used to a new type of home. This is my 2nd summer in a 4000 sq ft historic home, previously I lived in various small apartments, last summer I used 2 window units to cool the most frequently used rooms in my house and this is my first summer with the new HVAC installed.

[coco]

delta should be 15-20 degrees not 10-15

[bornriding]

With relative humidity between 40 & 60 % - The delta 't' I look for is 20 degrees 'f' between return & supply.
And yes, with a 15 I would be calling the installer

I am in Alabama, so I know what conditions you have in Atlanta. But if you have a hgh eff. system, with a variabl speed blower, you may not get the delta 't'.