[kirbinster]

Wow a lot to digest here, hope I don't miss any points. The system was sized using some sort of computer program. They measured the size of all the rooms and the number of existing ducts and returns. They also measured the windows. The house is a contemporary A-Frame with lots of glass. It is all double pane. The roof is pitched north and south. The south side is covered with 9.99kw of solar electric panels, which actually reduce the heat load on the house as there is an air gap of about 6" between the panels and the roof. There are big windows facing both east and west on that top level, they cover perhaps half of each wall - so yes there is solar heat gain.

The 0.38 static is on the low stage, I think about 875 CFM. When I have the fan running full which is 1475 CFM is shows 0.51 as the static pressure and that is with three of the ducts closed off on level one.

I think maybe the word "stratification" that I used is not the correct word. I think the problem is just one that it is very hard for the system to push cold air up from level one to level three. I am guessing that there is just too much flow to level one and not enough to level three because of the air density. The system is A/C and forced air heat, so I guess it is a compromise for each. Unfortunately it is not possible to change any of the trunk lines or duct runs without major wall and ceiling tear-out which are not an option.

My gut tells me with it being so cold on level one and so warm on level three that there has to be some methodolog whereby we can either dump that hot air downstairs or dump the cold air upstairs and balance things out. That is why I was suggesting a separate blower off of the system to cirulate air form level one and three to acheive what the blower on the HVAC system does not seem to be able to do. Has anyone here ever done anything like that, and can it work. How much air flow could I expect to move through that 8" return duct if I disconnected it from the system and used a separate blower on it. My guess is that maybe as a return it is moving 200 CFM. I am guessing this as there are two smaller returns on level three, one small one on level one and two one the mid-level that are each the size of the space between floor joists (14" by 10"). I am guessing that we should be able to move over 800 CFM through that pipe - is that a good guess?

The owner of the HVAC company wants to work with me on this, within reason. I have an air mover that is typically used when you have a flood in a basement that is three speed and can go as high as 2500 CFM. As a trial he said he could get me an 8" flex duct that we could run down the open stair area from level three to level one and use this blower as a test with to see if we could circulate the air. The staircase itself should work as the return for that. Should we try to blow hot air downstairs or cold air upstairs for the test?

 

[Chuck]

Its almost impossible to make a multi story house comfy without zoning, either adding zones or multiple systems help a lot.

I'm with the guys that talked about building performance, reduce the heat gain in the upper levels, and then see where your at. More return up there would probably help, but if everything is covered with sheetrock sounds nearly impossible.

 

[kirbinster]

Is it worse then with the old system?

You can "latch" the system to run in high,above a selected outdoor temperature.

Sounds like the original duct system was not designed correctly. Time for a Manual J,and D,to size the system and designe the ducts.

Yes it is actually slightly worse, I believe due to the lower CFM. The HVAC company actually called me yesterday and had me do just that. We set it to run on HIGH when the outside temperature is above 80 degrees. Don't know how that will work as it is 72 and raining today.

I turned the A/C off a couple of hours ago, and just have the fan running on high. As I said it is 72 degrees outside with rain and no sun - so very little heat coming from outside. The temperatures have not equalized yet, downstairs is now 69 mid-level is 75 and upstairs is 77. When system was on it had been 64/75/79 by level, so the circulation from the system over the last couple of hours is slowly warming level one and cooling level three.

 

[genduct]

Get a good commercial exhaust/ supply fan that can be adapted to that 8" return hit on the upper level. When the upstairs temp gets above set point (new stat) turn it and your main airhandler on to circulate the air through the entire home.
It would have been better to have 100%ducted return from the upper level, or have the AH on the highest level would have been even better.The 100% high return will also help your winter conditions as well.
Let us know how it works, regards, Mike

 

[kirbinster]

Get a good commercial exhaust/ supply fan that can be adapted to that 8" return hit on the upper level. When the upstairs temp gets above set point (new stat) turn it and your main airhandler on to circulate the air through the entire home.
It would have been better to have 100%ducted return from the upper level, or have the AH on the highest level would have been even better.The 100% high return will also help your winter conditions as well.
Let us know how it works, regards, Mike

Mike, are you saying I should run another fan to blow this 8" line through the airhandler as well? Won't that over load the entire system with too much air flow? Are you suggesting blocking off the returns (at least partially) on the first and second level?

 

[genduct]

Don't know if your "new *" hit is a home run, sounded like it is, therefore the object of the exercise is to get and continue to remove the warm air the is collecting high because of the stack effect, to circulate through the entire home.
No, shoving more air back through that return will not unbalance the air system. The other returns will not be called upon as much, so you won't need to block anything off

Again< it is a home run or it may just squirt out some place else and not get the full home effect we are looking for

 

[genduct]

PS if you get real tricky, maybe low speed when your upstars stat calls for circulation of that warm air

 

[kirbinster]

As a test I just blocked off the two large returns on the middle level, it only increased the static pressure by .04" and seems to have already dropped the temperature upstairs by 1 degree.

 

[tedkidd]

Too MUCH return! Light bulbs are flashing!!

Some nicer houses have high and low returns in bedrooms. In summer you cover the low return, this allows the cold air to "fill" the room, pushing the hot air at the ceiling back to the furnace.

In winter you cover the high return. The heated air fills downwards, pushing the cold air out the low return. Your HOUSE is like some bedrooms.

Sounds like you'll need to do some experimentation for both heating and cooling seasons, but given you don't seem to have undersized duct work, choking different areas may not be a problem. May want to take some thorough notes so next spring you don't have to experiment all over again.

 

[genduct]

Ted, can we have a different opinion and still be friends?
I understand that many people believe they can "suck" air into a room to make it comfortable. I don't think you believe that but I go as far as recognizing that if the air can't get out of a room because the door is closed for instance then air can't get in. we deliver comfort when we provide the design temp and quanity of air we need.
All I know is that those extensive returns don't work because they use up our available external static pressure that it cost fan HP to produce and you can't blow out a match by inhale ling ( sorry Bill Clinton ) and finally warm air rises in the summer and winter, therefore I believe a single, ducted, high return with separate, short transfer ducts ( or undercut doors is the answer to a good duct system.

 

[Brian GC]

Too MUCH return! Light bulbs are flashing!!

Some nicer houses have high and low returns in bedrooms. In summer you cover the low return, this allows the cold air to "fill" the room, pushing the hot air at the ceiling back to the furnace.

In winter you cover the high return. The heated air fills downwards, pushing the cold air out the low return. Your HOUSE is like some bedrooms.

Sounds like you'll need to do some experimentation for both heating and cooling seasons, but given you don't seem to have undersized duct work, choking different areas may not be a problem. May want to take some thorough notes so next spring you don't have to experiment all over again.

A very good idea!

Wow, you, me and three other posters have recommended adjusting the airflow at the returns. Whenever I said it before Beenthere would go into attack mode. Why isn’t he jumping all over you guys like he has me?

The best idea is a combination of blocking the low returns and supplies in the summer (and high returns and supplies in the winter) along with genduct’s idea of “Get a good commercial exhaust/ supply fan that can be adapted to that 8" return hit on the upper level.” The net effect would be the hot upstairs will disappear and the house will be completely cooled with a lot less energy.

Brian

 

[Chuck]

A very good idea!

Wow, you and two other posters [aside from me] have recommended adjusting the airflow at the returns. Whenever I said it before Beenthere would go into attack mode. Why isn’t he jumping all over you guys like he has me?

Brian

I don't think BT or anyone else said return placement was never an issue. It won't help every air "management" problem in every house like you give the impression it will. Every house has different problems and different fixes for those problems.

 

[Brian GC]

I don't think BT or anyone else said return placement was never an issue. It won't help every air "management" problem in every house like you give the impression it will. Every house has different problems and different fixes for those problems.

I know all too well what BT professes because I have been going round and round with him for years over this. Have you gone back to read the old threads I referenced?

I recognize that return placement is not always a solution and is nearly ineffective with good air mixing. But a situation like this has return problems written all over it. If I was the only one pushing return air changes on this thread then he would push H&C supply grills. But since I am one of four, his colors will likely change.

Brian

 

[lynn comstock]

If It were my problem I would continue experimenting. Clearly zoning could solve the problem if the ductwork were properly sized for zoning. I would close off all of the first floor supply vents and observe the results. If the top floor still did not get adequate air, I would close off half of the 2nd floor supply vents. If the problem persisted, I would close off all of the supply vents on the first and 2nd floor (knowing that they would be leaking 10 to 20% in spite of being closed. If the problem still persists, the ductwork to the top floor is hopelessly undersized for the actural heat load. An IR camera or even IR thermometer might reveal insulation problems that contribute to the problem.

If the top floor can be successfully cooled during any of these tests, zoning would work. Even though you cannot get to the ducts, grille zoning dampers exist and would work making no more noise than you saw during the testing.

Test away. Post 29 is my kind of thinking. Testing is cheap and you can learn a lot. AND leave all inside doors open for the testing.

 

[kirbinster]

I've got a Fluke IR thermometer, what would you suggest I measure? I can tell you now that the air coming out of the vents on the third floor is only about 60-63 degrees while it is about 50 on the first floor and 50-55 on the middle level.

 

[lynn comstock]

I've got a Fluke IR thermometer, what would you suggest I measure? I can tell you now that the air coming out of the vents on the third floor is only about 60-63 degrees while it is about 50 on the first floor and 50-55 on the middle level.

You should have told us this at the beginning. What about the middle floor? The ducts apparently are in the combination roof and ceiling and losing at least 1/3 of the cooling capacity through heat gain. Still test the duct capacity for air delivery as I suggested.

The IR thermometer can be used to scan the walls and ceilings for hot spots. Insulation voids can really warp the cooling load.

 

[Brian GC]

You should have told us this at the beginning. What about the middle floor? The ducts apparently are in the combination roof and ceiling and losing at least 1/3 of the cooling capacity through heat gain.

This does bring new information and reveals an apparent problem. But if fixed it might not totally resolve the stratification problem. The delta T between the upstairs and downstairs is 25deg while the supply delta is only 13deg. But these might not have been measured under the came conditions.

Kirbinster,
Have the downstairs returns and supplies ever been closed?

Has the flow rate of the upstairs 8" return ever been checked... and is it positioned so it draws the hottest of the upstairs air?

Brian

 

[kirbinster]

This does bring new information and reveals an apparent problem. But if fixed it might not totally resolve the stratification problem. The delta T between the upstairs and downstairs is 25deg while the supply delta is only 13deg. But these might not have been measured under the came conditions.

Have the downstairs returns and supplies ever been closed?

Has the flow rate of the upstairs 8" return ever been checked... and is it positioned so it draws the hottest of the upstairs air?

Brian

No flow rates have ever been checked. The first floor has half the ducts low and half high, with one small return that is connected about five feet from the HVAC unit. I have closed off four of the seven supply ducts on that level. The mid level has all of the supply ducts either low on the wall or on the floor, and two very large returns. I am running right now with both of those returns mostly blocked off. The third level has six supplies, four at the top of the knee walls and two at the bottom of the knee walls. The two old returns are high up on the back wall about three feet away from the windows, the new larger return is almost at the apex by the big front windows (on the left when viewed from the outside) - as high as you can get.

These windows are about 10' by 14' at apex.

There are three large casements in this 8'x6' opening

The additition in the front left of the contractor is handled by a separate system.

 

[beenthere]

Zone it.

Doesn't matter what you do to that return system. The top level will always be warmer.

You can have all of your return on the top level. The bottom level will still be the coolest level. The middle level with the stat will be where the stat is set for, and the top level will be warmer then the lower or middle level.

3 floors on an open plan. Zoned or independent units.

 

[beshvac]

How big are the 3 attic fans? Are there air baffles behind the insulation (against the roof deck) in the sloped part of the ceilings. Are there soffit vents?