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

[donphillipe]

In Dallas, my 2 story 3200 sq ft has 8 tons that I would call "adequate". We entertain upstairs frequently (25-30 people). We have to start around noon and crank both 4 ton units down to 70 and stablize at that temp, then guests arrive by 8PM and then by midnight, we are lucky if we have kept it down to 78. So I guess it depends on the load.

Also I had rather have an inefficient overcapacity unit than a flashing wife :-)

[dan sw fl]

Originally posted by mrbillpro

Originally posted by uktra
Do we have the correct imput on our calcs and do we design the house for the few days of abnormal conditions?

... 5200 sq. ft. home
... a lot of occupants or a lot of parties call it abnormal conditions may be perfectly normal to some and you brought up a good point as to why you can't totally rely on old J & D. ...
[Edited by mrbillpro on 06-29-2005 at 10:37 PM]

Simplifying___
Windows ......11,000 BTUh ( 600 S.F. + )
Ceiling....... 6,000
Walls......... 5,000
Floor......... _____
Duct ......... 4,000
Infiltration . 4,000
Internal Gain. 4,500
People ....... 3,500
TOTAL ........38,000 BTUh +++
_______ THAT'S in a PERFECT (VIRTUAL) WORLD.

35' x 70' = 2,450 x 2 = 4,900 S.F.

How does one get < 4-ton to maintain
77'F at 92'F outside temperature?
I suspect that a _4-ton may cool home
to _14'F less than the Outside Temperature.

& __5-ton _17'F

Window area as stated
( Glass to Floor area ratio = 11% )
DOES lean towards a
"Cave Like" Environment.

NOTE that this VIRTUAL house has ONLY 75 S.F.
of glass on the EAST and WEST Sides.
.. Just Ain't GOING TO HAPPEN IN REALITY
... perhaps, a 1 in 280,000 real world chance.

This is a GREAT THREAD
which ENABLES people to _STRETCH Their VIRTUAL Minds.

However, most people visiting HVAC-TALK forum
will need to STAY IN REALITY.

[uktra]

Panama--I can't believe mrbillpro called you a "know it all". That must have hurt your feelings! But since we are having fun and also mentioning litigation, we to have fun with the other side of the coin. New IRC code on new construction requires a manual J. Now we all know that oversizing can lead to lack of humidity control. We also know that lack of humidity control can lead to MOLD. You fellas in Texas heard of mold? Guess what is going to happen when Joe Don Looney, the lawyer, finds out a manual J has not been done? Ah, more fun.

Dan sw fl--While I agree that panamas house does not have the normal amount of window sq. area, one cannot design for what is normal. One must design to what is built. If Panamas house had more windows, manual j would show more load.

This "many parties" b. s. is a pitiful argument to oversize. I never said don't take into account life style, heat generating equipment or any other imput to a load calc. A designer gives the best solution to the problem. Explain to the customer that 2 stage is the better way to go if he has large parties. If he doesn't want to do that, let him sign a disclaimer that you are not responsible for humidity control.

[Edited by uktra on 06-30-2005 at 08:12 AM]

[dash]

Originally posted by uktra
Panama--I can't believe mrbillpro called you a "know it all". That must have hurt your feelings! But since we are having fun and also mentioning litigation, we to have fun with the other side of the coin. New IRC code on new construction requires a manual J. Now we all know that oversizing can lead to lack of humidity control. We also know that lack of humidity control can lead to MOLD. You fellas in Texas heard of mold? Guess what is going to happen when Joe Don Looney, the lawyer, finds out a manual J has not been done? Ah, more fun.

Dan sw fl--While I agree that panamas house does not have the normal amount of window sq. area, one cannot design for what is normal. One must design to what is built. If Panamas house had more windows, manual j would show more load.

This "many parties" b. s. is a pitiful argument to oversize. I never said don't take into account life style, heat generating equipment or any other imput to a load calc. A designer gives the best solution to the problem. Explain to the customer that 2 stage is the better way to go if he has large parties. If he doesn't want to do that, let him sign a disclaimer that you are not responsible for humidity control.

[Edited by uktra on 06-30-2005 at 08:12 AM]

That's the way to handle it.

[Mr Bill]

Originally posted by dash

Originally posted by uktra
Panama--I can't believe mrbillpro called you a "know it all". That must have hurt your feelings! But since we are having fun and also mentioning litigation, we to have fun with the other side of the coin. New IRC code on new construction requires a manual J. Now we all know that oversizing can lead to lack of humidity control. We also know that lack of humidity control can lead to MOLD. You fellas in Texas heard of mold? Guess what is going to happen when Joe Don Looney, the lawyer, finds out a manual J has not been done? Ah, more fun.

Dan sw fl--While I agree that panamas house does not have the normal amount of window sq. area, one cannot design for what is normal. One must design to what is built. If Panamas house had more windows, manual j would show more load.

This "many parties" b. s. is a pitiful argument to oversize. I never said don't take into account life style, heat generating equipment or any other imput to a load calc. A designer gives the best solution to the problem. Explain to the customer that 2 stage is the better way to go if he has large parties. If he doesn't want to do that, let him sign a disclaimer that you are not responsible for humidity control.

[Edited by uktra on 06-30-2005 at 08:12 AM]

That's the way to handle it.

Thats the way to handle what be in agree with the master dash! an airflow legend in his own mind.

I still want those addresses in Houston so I can go by and see how happy the homeowners are when you provide that then we will see if the proof is in the pudding.

[Panama]

Originally posted by donphillipe
In Dallas, my 2 story 3200 sq ft has 8 tons that I would call "adequate". We entertain upstairs frequently (25-30 people). We have to start around noon and crank both 4 ton units down to 70 and stablize at that temp, then guests arrive by 8PM and then by midnight, we are lucky if we have kept it down to 78. So I guess it depends on the load.

Also I had rather have an inefficient overcapacity unit than a flashing wife :-)

Hmmmmm. Bordello?

[dash]

Originally posted by mrbillpro

Originally posted by dash

Originally posted by uktra
Panama--I can't believe mrbillpro called you a "know it all". That must have hurt your feelings! But since we are having fun and also mentioning litigation, we to have fun with the other side of the coin. New IRC code on new construction requires a manual J. Now we all know that oversizing can lead to lack of humidity control. We also know that lack of humidity control can lead to MOLD. You fellas in Texas heard of mold? Guess what is going to happen when Joe Don Looney, the lawyer, finds out a manual J has not been done? Ah, more fun.

Dan sw fl--While I agree that panamas house does not have the normal amount of window sq. area, one cannot design for what is normal. One must design to what is built. If Panamas house had more windows, manual j would show more load.

This "many parties" b. s. is a pitiful argument to oversize. I never said don't take into account life style, heat generating equipment or any other imput to a load calc. A designer gives the best solution to the problem. Explain to the customer that 2 stage is the better way to go if he has large parties. If he doesn't want to do that, let him sign a disclaimer that you are not responsible for humidity control.

[Edited by uktra on 06-30-2005 at 08:12 AM]

That's the way to handle it.

Thats the way to handle what be in agree with the master dash! an airflow legend in his own mind.

I still want those addresses in Houston so I can go by and see how happy the homeowners are when you provide that then we will see if the proof is in the pudding.

You know the problem,Mr Bill?

Like Yogi said,"YOU don't know ,what you don't know."

[Mr Bill]

Yes I do, As Yogi Bear says, "You need to be smarter than the average bear" in order to complete your task on the bear hunt. Happy bear hunting!

[uktra]

Guys--I am finding "educating mrbillpro" a lot of fun! Mrbillpro--do a google search on Building America--click research projects on left. Click picture of Texas (thats the big state on the bottom thats large, like their a/c units). Click on Houston (thats a large city in large Texas that has large a/c's--You guys love large don't ya!)
You will find 14 subdivisions (that's large!) from 3 builders in this program. Find out the HVAC contractors and talk to them. Talk to the customers. I know this is a large task, but I know you are up to it.

[Panama]

Originally posted by dan sw fl

Originally posted by mrbillpro

Originally posted by uktra
Do we have the correct imput on our calcs and do we design the house for the few days of abnormal conditions?

... 5200 sq. ft. home
... a lot of occupants or a lot of parties call it abnormal conditions may be perfectly normal to some and you brought up a good point as to why you can't totally rely on old J & D. ...
[Edited by mrbillpro on 06-29-2005 at 10:37 PM]

Simplifying___
Windows ......11,000 BTUh ( 600 S.F. + )
Ceiling....... 6,000
Walls......... 5,000
Floor......... _____
Duct ......... 4,000
Infiltration . 4,000
Internal Gain. 4,500
People ....... 3,500
TOTAL ........38,000 BTUh +++
_______ THAT'S in a PERFECT (VIRTUAL) WORLD.

35' x 70' = 2,450 x 2 = 4,900 S.F.

How does one get < 4-ton to maintain
77'F at 92'F outside temperature?
I suspect that a _4-ton may cool home
to _14'F less than the Outside Temperature.

& __5-ton _17'F

Window area as stated
( Glass to Floor area ratio = 11% )
DOES lean towards a
"Cave Like" Environment.

NOTE that this VIRTUAL house has ONLY 75 S.F.
of glass on the EAST and WEST Sides.
.. Just Ain't GOING TO HAPPEN IN REALITY
... perhaps, a 1 in 280,000 real world chance.

This is a GREAT THREAD
which ENABLES people to _STRETCH Their VIRTUAL Minds.

However, most people visiting HVAC-TALK forum
will need to STAY IN REALITY.

Very good, Dan.

I used a 15% glazing ratio on the first floor and 10% (code minimum) on the second floor. This should be quite satisfactory for those interested in lowering their utility bills. Putting most of the glazing on the north and south just makes good sense if the orientation and interior layout of the house permits.

But you don't say whether your figures are sensible or total. You seem very high on the ceiling, duct losses, and internal gains that you don't explain. I used R-38 for the attic and J7 duct losses only for the 2nd floor.

I suspect you never use manufacturers' engineering data to select equipment. This is a major mistake by most people in the HVAC industry. I suggest you take a look at some, as it can be very enlightening. You also might get a copy of ACCA Manual S; it's an outstanding booklet that explains all sorts of things that are usually ignored.

[Mr Bill]

Originally posted by trane
Yes but then again there is no perfect size for any house due to changing outside conditions.

uktra, I do sincerely appreciate your thoughtfulness "and I really mean that" but I got to get right now to many calls, but I will check that out when I get some time but I think what trane above said pretty much says it all. Happy A/Cing and have a safe 4th.

[bluetooth751]

I assume the home must have 2x6 exterior walls.

Don't try to cool the 2-story home with one system.

I would talk with the homeowner and learn some of their habbits before I size the equipment.

Manual J does work it was made by a group of people who probably are alot more intelligent than us.

You can't size an air conditioner because the homeowner has two parties in the home every year. Oversized 363 days sized right 2.

[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. For all those like mrbillpro that don't think it will work, I suggest they visit some Building America homes in his area and talk to the customers that bought them. He also might want to read Home Energy magazine (july/August 05) just out, about a customer in West Columbia, Texas. People are becoming more educated through the internet and demand it be done right. The old "insufficient air movement" b.s. and "I have been doing it this way for 25 years" won't cut it anymore.

Uktra,

I read the Home Energy article this morning. Thanks for directing me to it.

Paul Blaha probably made more money by listening to his customer than Mr. Bill would have by hooking up a couple of Goodmans to some flex duct. Those 2-stage Lennox systems ain't cheap.

Thanks for all your support. Have a great Independence Day.

PNM