NEW CONSTRUCTION: Acceptable cooling temps in Texas

[motoguy128]

Merely a comment, but can someone in the architectural world, design world, or builder world please tell me why a single story house in far south Texas really needs ceilings that peak at 26 feet??

The scant info I found online about Contec wall systems show a minimum thickness of 4".

Because it makes a home appear very impressive wthout dramatically increasing construction costs. Taller walls, but the same roof area. The roof and roof joists drive construciotn costs. that's why you don;t see deep overhangs anymore on home, since we all have AC. Who needs natural shading when you have AC?


With high ceilings, sometiems it's best to take advantage of it and let hte how air stratify up there and locate supply registers near the ground level. Then use ceiling fans in winter ot push that warm air down.

Older homes frequently had high ceilings SPECIFICALLY to address comfort in the summer by allowing hot air to hang at hte ceiling. You then had very tall double hung windows where you vented how air out hte top sash, and allowed convection to drive cool air in the lower sash. Rooms were divided and not open concept, walls and floors ahd a lot of mass and that all inhibits convection between floors. When open cencept was popularized by Frank Lloyd Wright, you'll notice that ALL of his homes are single story, but use naturla stone or brick facades, and very, very, very deep overhangs for natural shading and usually had plenty of trees and shade. His homes cooled very well and gave an open connected sense to the outdoors while still allowing privacy with a shaded facade. Middle class Foursquare craftsman homes usually had dormers to vent how ait out of the upper floor.


I'm wondering if the solar heat gain was not correctly calculated on this home. Either that, or the air leaksage and insulation value was overestimated. I'm not sure how well manual J factors in the sun baking a composite low mass wall assembly and heat soaking it. Those tall walls means that shading is minimal at all times of the day on those walls.

[motoguy128]

That Contec is some sort of prefab tongue and groove hallow steel wall panel. Depending on the cladding, it could end up having pretty highly conductive thermal properties. It looks liek it's intended for commerical and industrial use. I think we're used a version of these with foam core insulation for building siding/cladding/wall assemblies on industrial buildings. I'd guess that the 3" thick panels we have are about R4 at best. You normally fasten these to structural steel. They are not structural assemblies.

[motoguy128]

I just reread the first post. A home this sizewith stucco and open cell foam, should have pretty ow heat gain. The roof and windows must be dirivng the heat gain. It's a low mass structure and thsoe tall ceilings are makign hte home act more similarly to a nearly 8-10,000 sqft structure. However, with the R value that you should have, 11 tosn of cooling should be plenty. It does sound like the large area (which tends to have the highest internal heat loads ofrm cooking, appliances, occupancy, lights, is causign the issue.

Where is the equipment and ductwork located? Attic space?

[BAVE]

I just reread the first post. A home this sizewith stucco and open cell foam, should have pretty ow heat gain. The roof and windows must be dirivng the heat gain. It's a low mass structure and thsoe tall ceilings are makign hte home act more similarly to a nearly 8-10,000 sqft structure. However, with the R value that you should have, 11 tosn of cooling should be plenty. It does sound like the large area (which tends to have the highest internal heat loads ofrm cooking, appliances, occupancy, lights, is causign the issue.

Where is the equipment and ductwork located? Attic space?

When the house was designed we specified the equipment to be housed inside the home (not attic space). Each unit has a closet. The doors were fitted with 25x30 wood louvered grilles that were built with more spacing than traditional metal grilles. However, the large room does not have a return in it (as mentioned previously it is around the corner in the hallway).

[BAVE]

The block is basically a cement panel that is attached over the framing, foam sheets (not sure what they are called) and barrier. This is instead of the typical design of framing and mesh used here. The block isn't for structural stability.

[motoguy128]

Too bad tha block isn't inside the insulated space of the home so you gain that thermal mass. I personally would have put insulation on the exterior of the block, then the stucco. But getting wire mesh attached to the block kthrough foam board to hold the stucco is tricky. Then just leave an air gap and then drywall. But this isn't a common construction method.

Honestly, given the wall construction, I'm a little confused as to why your having issues. On paper, I would think that would be plenty of cooling if not oversized.

You might want to look at a getting someone in with a IR camera to verify the wall insulation and compare different parts of the home. Basically an energy audit.

Another question... do you have one of thsoe GIANT vent hoods in the kitchen that are popular now? When running, those can add over 2 tons of cooling capacity on a 90F humid day. However, your system should have caught up overnight.

[BAVE]

Too bad tha block isn't inside the insulated space of the home so you gain that thermal mass. I personally would have put insulation on the exterior of the block, then the stucco. But getting wire mesh attached to the block kthrough foam board to hold the stucco is tricky. Then just leave an air gap and then drywall. But this isn't a common construction method.

Honestly, given the wall construction, I'm a little confused as to why your having issues. On paper, I would think that would be plenty of cooling if not oversized.

You might want to look at a getting someone in with a IR camera to verify the wall insulation and compare different parts of the home. Basically an energy audit.

Another question... do you have one of thsoe GIANT vent hoods in the kitchen that are popular now? When running, those can add over 2 tons of cooling capacity on a 90F humid day. However, your system should have caught up overnight.

I've been looking for someone local to do an energy audit since I was advised to do so a couple of weeks back. Unfortunately I've had no luck. We do have a very large vent system over the range but it has not been in use during the past week when temperature issues became more apparent.

Today we had the system running at a lower setting (75) since the early morning. The inside temperature dropped to the 75-76 range while outside temps remained at 98-99. My wife cooked a bit, TV on, doors open with kids coming in and out and the temp remained in the same range. Can the difference be the system was removing more humidity yesterday because the overnight setting was higher?

[t527ed]

When the house was designed we specified the equipment to be housed inside the home (not attic space). Each unit has a closet. The doors were fitted with 25x30 wood louvered grilles that were built with more spacing than traditional metal grilles. However, the large room does not have a return in it (as mentioned previously it is around the corner in the hallway).

post a picture of the return grill and the unit sitting in the closet.

[dan sw fl]

Remember,high ceiling do not require more AC. It is the sq. ft. of the walls and roof, not the volume.

THAAT'S DOUBLE-SPEAK, if I've ever heard it!!

x
c
v
b
MORE VOLUME = MORE AREA
or
is
it
MORE AREA = MORE VOLUME
Q
W
E
R
T
Y

[BAVE]

post a picture of the return grill and the unit sitting in the closet.

unit & zone equip

[BAVE]

BTW, I have no idea what the additional ductwork on the side is but Im assuming it is related to the zoning of the theater room as it was added at that time and not present with other units.

[Shophound]

THAAT'S DOUBLE-SPEAK, if I've ever heard it!!

x
c
v
b
MORE VOLUME = MORE AREA
or
is
it
MORE AREA = MORE VOLUME
Q
W
E
R
T
Y

Yep. Let's take a square slab of concrete on the ground, say 50 x 50, which makes for 2,500 square feet, not an uncommon size for RNC today. Run up the walls evenly to nine feet, and slap a roof on. Now we have 25,000 cubic feet.

But now let's run up the walls to the OP's height of 26 feet. That's now 65,000 cubic feet.

Let's take one wall of the lower height building and find its surface area: 450 square feet. Let's expose it to a temperature difference of 25 degrees between interior and exterior. 100 degrees outside, 75 degrees inside. No windows or doors. No sun beating on this wall...just a simple air temperature difference. Let's also give it a consistent R value of 19 (no thermal bridging or framing factor to worry about here). Total heat gain for this wall: 592 BTU.

Now run it on up to 26 feet, other parameters unchanged: 1,250 square feet at 1,645 BTU. Yikes.

But...but...we don't have to cool all that air...just the air in the occupied zone...right? So...you want to purposely trap a lot of air that you can't adequately condition for moisture, dust control, etc.?

[energy_rater_La]

and what type of insulation did you say you have in the
attic?

what types of windows? solar heat gain & ufactor numbers?
low e...argon? what types of frames?

for an energy rater visit www.resnet.org
quite a few in texas.

best of luck.