Houston: 3.5 tons for 5,200 sq ft house?

[Freezeking2000]

A big problem i see is the fact that the air aroung a condenser gets about 10 degrees hotter than the ambient. So look at the numbers with 120 to 130 degree condensing temps for the outdoor unit and your 3 ton is not 2.5 tons.

[slice]

House built in Spring tx ( slighlty outside and north of houston) 3200 sq ft, single story insulated it with Icynene, (expanding foam insulation) Sealed the attic NO OUTSIDE AIR IN THERE, 3.5 tons maintains temp and 50% humidity, THis stuff is the up and coming thing,

[Panama]

Originally posted by tuccillo

Originally posted by Panama

Originally posted by uktra
The other big question on the theoretical home is : are the ducts and air handler inside conditioned space? If they are, then a 3 ton will work fine. ....

It was figured with attic ducts for the 2nd floor - R6.

Be aware that 3 tons nominal is probably really 2.5 tons at high outside temperatures ( when you need capacity the most ).

The engineering data shows about a 5% drop in total capacity when the outdoor DB rises from 95 °F to 105°F. Most of the drop is in latent capacity, and so the sensible capacity drops only about 3%. The increase in cooling load is far more pronounced -- about 25%.

[Mr Bill]

Slice:
House built in Spring tx ( slighlty outside and north of houston) 3200 sq ft, single story insulated it with Icynene, (expanding foam insulation) Sealed the attic NO OUTSIDE AIR IN THERE, 3.5 tons maintains temp and 50% humidity, THis stuff is the up and coming thing,


He is talking about 2000 sq. ft more than that with a 3.5 ton lots of difference there, as I said I will be here waiting let me know when you get that 3.5 ton on that 5200 sq.ft. home and I want to hear the customers feedback after a hot June like we have had were it's 100 and the humidity is 100% and he gets a couple high light bills because the unit will have to run 24/7.

[Panama]

[QUOTE]Originally posted by dash
[B]

Originally posted by Panama

Originally posted by dash
Dash,

The "Lennox Engineering Data" I have has indoor DBs of 75 °F 80 °F, and 85 °F. Thus, no adjustments are needed.

Lennox should get a Gold Star, if the commonly provide the data needed that way,I wish they all did. Hoping ARI will start doing it.

I think they all provide such data. I have some from Trane, and I think Goodman/Amana has it on their internet site.

I suspect Lennox provides it only to their dealers.

[Panama]

Originally posted by Freezeking2000
A big problem i see is the fact that the air aroung a condenser gets about 10 degrees hotter than the ambient. So look at the numbers with 120 to 130 degree condensing temps for the outdoor unit and your 3 ton is not 2.5 tons.

Those wonderful Texas alleys!

[uktra]

The reason I brought up the duct issue is that manual j7 has minimum 25% over capacity built in for the problems of duct leakage and extra infiltration caused by duct leakage.

[classical]

For all you guys prognosticating in regards to what will and won't work in Houston remember this. There is a new law in Texas that requires that you warranty the system for two years and it must maintain a maximum of 78* in the center of the room.
I don't doubt that there are some homes that can be built that 3.5-tons can and will cool 5200 Sq. Ft. but not the one described by Panama. The house described by Slice is an example of such a house; it however is exactly what Bill described a cave.

Uktra you have post your assertion about homes and HVAC systems here for the past year or so and do not provide any clue as to your background. I suspect that you work for a builder and have a background in Architecture or an ME. That is all well and good but I go to houses every day that have nice quality load calcs by builders and systems are inadequate. As Dash states many don't work because they are inadequately installed and poorly charged and or maintained. However many even after addressing ductwork and return issues adjusting charge to spec they still end up being undersized by as much as 2-tons granted most are more like 1-ton undersized.

Theory is great but I deal in comfort and satisfying my customers.

[Special Ed]

There's doing things all on computer & then there's the real world. Mrbillpro & I live in the real world so we've both come to the conclusion that there is no way in a million years that 3 1/2 tons will cool a 5200sq.ft. home. Then, of course, you would have to zone it....

[slice]

mrbillpro: MY post was stating as well as that house is insulated, at 3200 sq ft that it required 3.5 tons So I agree that a 5000 sq ft dream home 3.5 tons will never have a chance.......

[Panama]

By the way, do you guys all belong to the Flat Earth Society?

[Mr Bill]

No, but I do belong to the "Realistic Society"

[classical]

No we exist in the REAL WORLD!!

[Mr Bill]

Originally posted by Panama
By the way, do you guys all belong to the Flat Earth Society?

He lives in Colorado and is trying to convince us were out of touch,boy they must grow some good erb up in them there mountains.

[uktra]

Classical--You and I have had this go around before. Yes I am an ME that has also studied building science. I am also a licensed contractor. I do not work for a builder, I work for people who want a better built home than most of what is being built today. I help design both the thermal envelope as well as the HVAC system. I have been in hot attics and dirty crawl spaces, so I live in the real world. In the real world (even in Houston) homes exsist that work at manual j numbers and work better than 95% of all other homes. The homes also guarrantee comfort and heating and cooling costs. I also live in a climate very much like Houston and have designed and help build homes that work in that type of climate without the 2-3 ton oversizing that I normally run into. To say a normal, run of the mill code home of 5200 sq. ft. can be cooled properly in your climate by 3.5 tons is not a reality. But for someone to say Panamas 5200 sq. ft home cannot be cooled by 3.5 tons is also not a reality.

[Edited by uktra on 06-29-2005 at 09:37 PM]

[Mr Bill]

Originally posted by uktra
I also live in a climate very much like Houston and have designed and help build homes that work in that type of climate without the 2-3 ton oversizing that I normally run into.

If the homes you run into you say are oversized are we comparing apples to apples? in good old Texan that would mean that they would have to be close to the same home type your designing or it would not be a fair statement to say there oversized, that would be just an opinion.

[uktra]

well you can call it opinion if you want, but I run into a lot of folks that have short cycle times and high humidity.

[Carnak]

The latent load seems too low for Houston.

I don't use manual j but when they say 47 grains for 50% does that mean that the ambient air holds 47 grains more than the room air?

If so that would imply that Houston has a design ambient of 112 grains, I would guess it would be more like 130 or higher.

All I have is worst case humidity data for Houston and it ranges from 137 to 147 grains.

I would guess the latent load would be more than double what was calculated considering 0.3 air changes, plus six occupants and mama simmering some chili.

[jared]

3.5 tons on 5200 square feet. I'd say run the Manual J one more time. Might be a good idea to take into consideration internal load...lights...computers, TV sets, people, pets, refrigerators and the like. Going to be interesting on a 4th of July party with 25 people over too.

Double check your stuff. I'd want at least 2 systems with that square footage if it were MY home. I'm just a homeowner and not an HVAC pro, but I would consider slightly oversizing 2 stage cooling.

[Mr Bill]

He is talking about only one occupant a cave man no chili there, only buffalo meat.