New Trane XR14 AC Not Cooling Properly

[adrianf]

do a search at the FSEC on radient barrier and read tell you're drunk with knowledge.

Oh yeah if your psuedonym was Rocky2000 we would have alot of jokes at our disposal.

in most all cases the PAV does way more harm than good on multiple fronts.

[pstu]

Measuring attic temps is not as straightforward as I thought. For years I had a temperature probe stuck up through the attic floor, about 12 inches above the insulation and I thought I was "measuring the attic temperature". Well that point is very different from other places to measure. In addition to that I have a remote temperature sensor hanging in the air just below the radiant barrier, and another placed above the RB.

As I write this at 10am in July, the measurement is 88F below the RB and 93F above it. The point above the attic floor is 84F. I did a study on typical temperatures in Sep-Oct 2007, when the reported peak was still low-mid 90's. Generally saw 125F commonly above the RB in late afternoon, with about 110F below the RB and 95F at the attic floor. On such day (10/4/2007 I think) the official high was reported at 92F but my back porch saw only 86F. All that looks pretty nice plotted on a graph but it's hard to figure out what it all means. Whenever someone say "attic with RB should be within 10 degrees of outside temperature" I listen to them but don't know whether I need to do something else to live up to that claim. IMO there is no one number which clearly describes attic temperature.

This is as good a time as any to say I REALLY admire the toughness of those Texas AC guys who have to go up into these attics on summer days!

Hope this helps -- Pstu

[adrianf]

Adrian F....one of your links strongly suggested that in addition to disabling PAV's that a homeowner should close foundation vents which it said causes mold and mildew when open by bringing in hot, humid air ....is that also your recommendation? All the houses in my (Richmond, VA) neighborhood open foundation vents in the spring, summer and fall....sounds like we may not be doing the right thing ....?????

I don't have any experience with crawl spaces but what the building sceince folks are saying is you can't reduce the humidity using hot humid air to ventilate.

[Rambo2000]

Well, more fun. The contractor now believes there is probably a problem with the coil. They measured different temps from the top to the bottom of the coil, so they moved the TXV valve to see if there would be any effect, and they are going to have the local Trane rep come out and check out the system. They think there is an issue with the coil but they indicated that the Trane rep will probably want them to replace the TXV first.

They also aren't 100% sure that my old furnace is moving enough air across the coils. However I told then that since they rebuilt the ducts and plenum, I have better air flow than I've ever had (of course, the old system never worked right either). But, first things first. They want to get the coil operating properly.

Thanks again to all for the informaton and insights. When I'm done with the process I'll know more about residential HVAC than I ever imagined I would!

PSTU,

I actually measured different temps (by 15 degrees) between my East and West facing actic walls this morning. So, I can believe that it's not a straight forward process.

Thanks,

[amigadude]

I'm just another novice, but somehow your problem does not sound like the system to me. You are in Hotlanta area (same here), and in the evening have:

(input air temp) 76 --> Furnace --> 61 (supply vent temp)

I seem to remember that 15-20 degree drop was all that you should expect, which by itself should cool the house down. Anyway, my experience in this area has been to reduce the load on the house and duct work, by any means possible. I replaced turbines with continous ridge vents, sealed the ducts in the attic, AND installed 2 Power Vents. The power vents are THE main reason I can keep my systems in the 75-76 range. Recently one died, and the upstairs went to 78, you can believe I replaced that motor quickly!

Two conclusions that I've come to:

1) Attic temps bake the ducts unmercifully, even if they are insulated.
2) South / West facing brick walls store massive amounts of heat from the sun, and keep pumping it into the house till late in the night.

I'll be anxious to see what you come up with, since I can only dream of waking up to 72.