Two Story - Cool Up/Hot Down...

[mr big]

You need to get a competent Hvac contractor to do a capacity check on the system, including measuring the airflow with a flow hood. From the capacity & airflow checks, perhaps they can find where hot air is infiltrating the duct system, or where it is blocked. A zoned system cannot overcome an inadequate duct system, if that be the case. Capacity check involves measuring wet bulb temperatures & using enthalpy figures; unfortunately, many contractors do not know how. Many contractors just like to say it is doing fine , or it feels fine. The only true way to address the problem is to take the measurements & go from there.

[dan sw fl]

Originally posted by mr big
You need to get a competent Hvac contractor to do a capacity check on the system, including measuring the airflow with a flow hood. From the capacity & airflow checks, perhaps they can find where hot air is infiltrating the duct system, or where it is blocked.

Based on my thorough Manual J load analysis on Berkshire 1,192 as noted in "Meeting Street Homes" link, a 2.5 ton would be needed if your windows are indeed Clear (i.e. S.H.G.C = 0.75 and U-value 1.1) and residence faces East or West.

520 CFM is needed upstairs
and _______ 480 CFM Down.
Living Room 216 CFM.
Dining Room_ 49 CFM
Closet _____ 70 CFM
Kitchen ___ 145 CFM

Previous post by Mr Big has well stated the TESTING and steps required.





[Edited by dan sw fl on 08-19-2005 at 04:06 PM]

[rohalon]

With only 2 returns, one at the top of the stairs and the other on a landing most of the way down the stairs, any cold air trying to fall down the stairs is just getting sucked back into the system and redistributed to the bedrooms.

[Panama]

The home of an aquaintance of mine has an attic system with a single return at the top of the staircase. There are no supply ducts to the first floor, yet it stays nice and cool. You can feel the colder air falling down the stairs. The humidty stays a little higher downstairs, but never gets too high.

This house and its duct system are very tight.

[Panama]

Originally posted by dan sw fl
Based on my thorough Manual J load analysis on Berkshire 1,192 as noted in "Meeting Street Homes" link, a 2.5 ton would be needed if your windows are indeed Clear (i.e. S.H.G.C = 0.75 and U-value 1.1) and residence faces East or West.

520 CFM is needed upstairs
and _______ 480 CFM Down.
Living Room 216 CFM.
Dining Room_ 49 CFM
Closet _____ 70 CFM
Kitchen ___ 145 CFM

Previous post by Mr Big has well stated the TESTING and steps required.

I guess not all Manual Js are the same!

My Manual J calculation comes up with a sensible load of 11,000 Btuh and a latent load of 1,600 Btuh. If this is correct, this townhouse needs only a 1.5-ton system running 600 CFM. Engineering data for one suitable system shows it provides 25% excess sensible capacity at 75 °F inside and 95 °F outside, and almost twice the design latent capacity.

I assumed clear dual pane glass rather than clear single pane glass. Do they still use single pane glass in North Carolina? 96 square feet of window area for Manual J purposes.

I also assumed the owner would close the blinds on a hot sunny day. R-30 in the attic, R-11 in the walls. Urethane foam steel doors. Tight construction (it's new). Four persons. Faces west. Internal unit; add 1,000 Btuh for an end unit. R-6 duct insulation.

What have I done wrong, Dan?




[Edited by Panama on 08-19-2005 at 10:21 PM]

[dan sw fl]

[QUOTE]Originally posted by Panama
[B][QUOTE]Originally posted by dan sw fl
[B] I guess not all Manual Js are the same!

My Manual J calculation comes up with a sensible load of 11,000 Btuh and a latent load of 1,600 Btuh. If this is correct, this townhouse needs only a 1.5-ton system running 600 CFM.

Do they still use single pane glass in North Carolina? 96 square feet of window area for Manual J purposes.

[Edited by dan sw fl on 08-20-2005 at 05:20 AM]

[dan sw fl]

[QUOTE]Originally posted by Panama
[B]

Originally posted by dan sw fl
I guess not all Manual Js are the same!

My Manual J calculation comes up with a sensible load of 11,000 Btuh and a latent load of 1,600 Btuh. If this is correct, this townhouse needs only a 1.5-ton system running 600 CFM.

I assumed clear dual pane glass rather than clear single pane glass. Do they still use single pane glass in North Carolina? 96 square feet of window area for Manual J purposes.

[Edited by Panama on 08-19-2005 at 10:21 PM]

IT'S ALL ABOUT WINDOWS

Based on my careful Manual J 8th edition load analysis on Berkshire 1,192 as noted in "Meeting Street Homes" link a 2.0 ton would be needed if the 9 windows totalling 129 Sq. Ft. are indeed Double Pane

500 CFM is needed upstairs
and _______ 345 CFM Down.

Living Room 162 CFM
Dining Room_ 40 CFM
Closet _____ 34 CFM
Kitchen ____ 99 CFM
Stairs _____ 10 CFM

Differences:
Glass area ( 129 S.F. vs 96)
Internal gains (8 people and 1 200 BTUh kitchen)
Ducts
A.H.U. location
Manual J 8th edition

Master Bedroom: 2 people
Bedroom 2: 1
Dining: 3 or 4
Living: 2

Walls Doors and Ceiling loads are rather small.

Wall ______ 1,050 BTUh
Windows __ 10,107
Doors ________ 603
Ceiling ______ 681
Infiltration__ 238
Ducts _____ 1,373
Ventilation_ 1,313
Internal_____ 3,630 << depends on one performing calc
Gains
___________ 18,993 BTUh Sensible
___________ 18,253 BTUh with 0.96 Rate/Swing Multiplier

With the AHU in the attic
and the associated "Extra" losses TRANE model 4TWR2024/ 4TEE3F031 or equal is recommended with Sensible Capacity of 18,542 BTUh.

Latent Load_ 4,212
Capacity ___ 6,858 BTUh

The key to cooling Downstairs is to provide
__160 CFM MINIMUM in the Living Room
___50 CFM in the Dining area
& 100 CFM in the Kitchen.

FOCUS on the Air Flow Measurement.

[bornriding]

63* supply air from registers and very little airflow compared to upstairs

I am leaning toward too large a duct to downstairs registers, or too long of run causing lack of velocity to downstairs registers. ( maybe too many bends ). Or they
might have come off of end of trunk line supplying one register, which would reduce duct pressure.

Air should be around 55* from all registers and the veocity
of the airflow should feel pretty much the same from all
registers.

If duct is too big, then even dampes would not help. Is there any way to replace main duct to downstairs??

Richard

[Edited by bornriding on 08-20-2005 at 11:41 AM]

[t527ed]

i have never seen tract housing with any duct that were to big. my vote remains blockage or something came apart or.....................

[dan sw fl]

Originally posted by bornriding
Is there any way to replace main duct to downstairs??
[Edited by bornriding on 08-20-2005 at 11:41 AM]

Remove drywall in order to access the chase.

[jramunni]

Originally posted by vwmann


The temperature from the vents downstairs is about 63 degrees, which appears to be pretty good, however the airflow is barely noticeable. While the airflow upstairs is extremely noticeable.

Many Thanks!
-Greg

Why all the talk about duct size, duct restriction, capacity...but yet no one thinks that 63 deg air is an issue.

Has any one checked the refrigeration side of this system?

I would expect to see supply air temperature of no highr than 57 deg.

jr

[CB24]

I would retro fit a zoning system into your house. That will fix the temp diffrence
between the 2 floors and save you money.