[kirbinster]

I have an "A" Frame house with three levels. The main part of the house (on this new system) has a downstairs with a large open room, a small bedroom and an HVAC closet. The mid level has Dining room, living room, kitchen, and the top level of the "A" is a very large open room. This is all on this new 4 ton system. Additionally, there is another section of the house on a different system that has a bedroom and bath on level one, and three bedrooms and two baths on level two. The problem is the new system.

We always had problems that it was too cold downstairs, and too hot upstairs - the thermostat is on the middle level. To try to solve this the contractor raised four of the six supply ducts that were at the bottom of kneewalls all the way upstairs to the top of the knee walls. There are two returns up there and they added a third with 8" piping. The problem is that the system runs on low fan almost all the time. These past two days it has been over 100 degrees outside and we have had the system set at 75 degrees. It has maintained 75 on the middle level while the lower level is 65 or lower and the upper level approaches 90 degrees.

The infinity thermostat does not let me force the fan onto high all the time without going into the advanced programming and changing comfort to maximum flow - but I'm sure that is screwing the efficiency. When we do that we get a little better performance - but still not great.

I would love to hear some suggestions on what if anything can be done.

I have one idea and would like comments on that as well. My thought is maybe we should disconnect the new return at the furnace/AC and install a separate blower/fan to it that would let us either circulate cold air from level one directly up to level three or pull hot air from level three and dump it into level one. Do you think this would help, and which airflow direction would have a greater impact ?

Thanks

 

[Shophound]

Low tech solution...put a ceiling fan at the peak of the A frame, turn it on high speed, and set it to blow air straight down. It will at first push hot air toward the lowest level, but as it continues running, the air temperature differences between the floors may become less over time.

 

[kirbinster]

Low tech solution...put a ceiling fan at the peak of the A frame, turn it on high speed, and set it to blow air straight down. It will at first push hot air toward the lowest level, but as it continues running, the air temperature differences between the floors may become less over time.

You are right it is a good low tech solution, only problem is that I already have one there doing exactly that

 

[btuhack]

What is the roof/attic insulation situation.

Any guess what % of return air is collected from "high" returns? Sounds like 100% should be the number. There is a lively thread here/recent that might be of interest to you about return placement. Your symptoms are supporting one of two contentious opinions.

Changing the circulated volume will increase your op costs some but why settle for being efficiently miserable? The speed/volume change would have the lowest upfront cost.

 

[kirbinster]

Its an "A" frame design so the top level only has whatever insulation originally fit between the sheetrock and the roof joists - in a word not that much. I do have thee power exhaust fans in the roof that take out any of the superheat up there.

As for how much of the air is taken from the high returns I really have no way of knowing. There is one small one on level one, two good size returns on level two and two mid-size on level three plus the new 8" return line on that level that was just added. We need all of them as the situation is reversed for heat in the winter - not enought downstairs.

I have the system off of automatic fan control now and it is running all the time. That improves the balance a little, but I don't think the system removes as much humidity that way.

Do you have the link to the thread you were talking about - I would like to check it out.

 

[dash]

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.

 

[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.

How do you do that with the Infinity control - my HVAC guy does not seem to know how to do that. I believed they used "Manual J" (or something that sounded like that) to spec everything. It was required by the state to get various rebates. The duct system cannot be redone without major expense as everything is buried behind walls and ceilings.

I would say it is actually worse than the old system because it is more efficient and does not circulate as much air.

 

[tedkidd]

What is the static pressure at each stage?

How big is the house?

Where are you?

Which 4 ton outdoor unit do you have?

Can you shut the downstairs supplies? (Do static check)

Love to understand what moving supplies up on walls accomplished. Was that poke n hope? If the ductwork was extended you likely REDUCED flow to those rooms. Flex duct used?

 

[kirbinster]

The house is about 3,500 sqft, but about 1,400 sqft is on a different HVAC system. I am in Northern NJ. Not sure exactly what you are asking about the outdoor unit, its a Carrier Infinity series high eff unit. Stands about 4 foot high. The static pressure on the system is about .28" according to the thermostat. I did shut two of the vents downstairs already.

I agree with you on the upstairs vents. Their concept was that by moving them up on the wall and directing them towards the ceiling would provide more air ciculation than dumping the cold air on the floor. I don't think there is much loss as they went from the 5" lines to 6" lines for the roughly 5' they ran and actually replaced uninsulated pipe with insulated.

Do you think my idea of disconnecting the new 8" return that was run to the top level and connecting a second blower to it to just pull hot air down from level three and dumping it on level one might help. The big open staircase should let cooler air get pulled up from this circulation.

What is the static pressure at each stage?

How big is the house?

Where are you?

Which 4 ton outdoor unit do you have?

Can you shut the downstairs supplies? (Do static check)

Love to understand what moving supplies up on walls accomplished. Was that poke n hope? If the ductwork was extended you likely REDUCED flow to those rooms. Flex duct used?

 

[Sleuth]

Yep ... Stratification

That 8" return that was added was way short of what you need.

Refer to post #4 about 100% return ... and high.

Fan "on continuous" will probably help.


...

 

[kirbinster]

That 8" return that was added was way short of what you need.

Refer to post #4 about 100% return ... and high.

Fan "on continuous" will probably help.

...

I agree, but that was all that was possible to run without MAJOR construction. Fan on continuous helped when it was 102 degrees, but when the temperature is more normal it makes it worse as the unit does not dehumidify as well at high fan.

Do you think my idea of taking that return off the system and running it with just a blower to circulate air from level three and dumping it to level one might help the situation. There is a big open staircase that should let cooler air get pulled back up if we do this. Thanks.

 

[energy star]

How many recessed lights you have in the top floor ceiling? (The A)
Is the back side of the knee wall insulated or the underside of the roof? Or both?
How many feet is it from the top of the A to the floor?
What pitch is the roof?

 

[kirbinster]

How many recessed lights you have in the top floor ceiling? (The A)
Is the back side of the knee wall insulated or the underside of the roof? Or both?
How many feet is it from the top of the A to the floor?
What pitch is the roof?

There are no recessed lights. The back of the knee wall is insulated, as is the area between the sheetrock and the roof over the finished portion. I the unfinished portion the roof is not insulated but there is insulation on the floor between the joists. There are three atic vent fans to suck out the superheat. The knee walls are five feet high then the ceiling curves up from there to the apex where it is about 7.5 feet from the floor. The front by the staircase has three double pane windows facing east that are about 10' by 11' total. The back (due west) has three windows that are double pane casements that total 6' by 8'. The roof pitch is 22 degrees. The southside of the roof is 85% covered with 9.99kw of photovoltaic panels. I believe these actually help eliminate heatload as there is about a 4" to 6" air gap between the roof an the panels.

 

[udarrell]

The house is about 3,500 sqft, but about 1,400 sqft is on a different HVAC system. I am in Northern NJ. Not sure exactly what you are asking about the outdoor unit, its a Carrier Infinity series high eff unit. Stands about 4 foot high. The static pressure on the system is about .28" according to the thermostat. I did shut two of the vents downstairs already.

I don't see how the static could be as low as 0.28 of an inch.
Actual airflow needs checking along with the duct system.

 

[kirbinster]

I don't see how the static could be as low as 0.28 of an inch.
Actual airflow needs checking along with the duct system.

My bad, typo The static pressure is 0.38 not 0.28. I am not sure how the system does this, but I assume there is some sort of pressure transducer and when you run the setup it calculates this. Perhaps it is off of motor amps when it runs low enough to have no actual airflow - don't really know, but the computer in the system does this.

 

[DavidNJ]

Zoning? The ICS supports it and I'm guessing the house is full of windows. Do the windows point east and west?

Has a thermal imaging test been done? Do you have the pictures? It would put some detail behind the insulation question.

In another thread on ducting two themes seem to be widely agreed to: air mixing and the amount and location of thermal gain/loss affect the room.

Air mixing depends on how stratified the temps get. Air does not stratify by temperature, it actually moves to a uniform temperature. If hot or cold air is introduced and not mixed, it stratifies because of the different air densities. The fan suggestion was to deal with this. In the other there beenthere makes quite a few examples of using the right registers to achieve that. Net, if your supply registers are not blocked by furniture, they need to have the right registers and have the registers configured to do the necessary mixing. If you don't, your first problem is fighting an air stratification problem during heating and cooling cycles.

The second problem, which btuhack here zoomed in on, is where is the heat or cooling going? It sounds like you may have some huge thermal holes. We have a contemporary house with lots of windows; I would imagine an "A" frame is also. If so, they are probably a source of both heat loss and radiant heat gain. Preliminary sizing on my house has the windows contributing over a quarter of the heat gain from radiant heat gain. Since you are posting in July during a major heat wave, my guess is your problem is heat gain and cooling. I have a hypothesis that the modeling techniques used underestimate the radiant heat gain from east/west ceiling/roofs, especially uninsulated ones. From your insulation comment that may also be a problem.

The ICS three stage furnace will provide more even and constant heat that will lead to more even temperatures. The AC is a two stage with minimal differences between the stages, the low stage being 70% of the high stage. Net...it isn't modulating much on cooling to even the temps.

How you deal with the insulation could be a big issue in getting it right. Maybe beenthere could chime in on how he might use the registers for air mixing.

 

[Brian GC]

Do you have the link to the thread you were talking about - I would like to check it out.

There have been many hotly contested threads about air stratification. As you read the posts try to determine which are based on opinions, biases, experience, or common sense.

http://hvac-talk.com/vbb/showthread.php?t=584222&page=15

http://hvac-talk.com/vbb/showthread.php?t=561322&page=6

http://hvac-talk.com/vbb/showthread.php?t=553742&page=6

http://hvac-talk.com/vbb/showthread.php?t=448852&page=21

http://hvac-talk.com/vbb/showthread.php?t=438722&page=2

http://hvac-talk.com/vbb/showthread.php?t=116659&page=35

Any guess what % of return air is collected from "high" returns? Sounds like 100% should be the number. There is a lively thread here/recent that might be of interest to you about return placement. Your symptoms are supporting one of two contentious opinions.

That 8" return that was added was way short of what you need.

Refer to post #4 about 100% return ... and high.

As you will gather from my posts from the above threads my solution is with the two above quotes.

You seem to be very attuned to your situation and determined to resolve it and the pros here seem to be out of suggestions. After reading the threads you will be up on the two camps. Please let us know how you end up minimizing stratification.

Brian

 

[tedkidd]

Yep, zoning might be next step, although with an oversized system, even on low he may have too much air to dump to gain enough redirect. Sounds like oversized - even low stage is too big to run continuous when there is fair load. Too bad, 3 ton might have been more comfortable.

.38 on what stage? You have to stand there through the test and take notes for each stage.

Experimentation with different fan settings might help. Take notes on observations as these notes can uncover clues to problems.

Next step is get the house tested. Since you are in NJ did they perform an audit? Was your contractor BPI certified? For how long?

 

[DavidNJ]

Yep, zoning might be next step, although with an oversized system, even on low he may have too much air to dump to gain enough redirect. Sounds like oversized - even low stage is too big to run continuous when there is fair load. Too bad, 3 ton might have been more comfortable.

.38 on what stage? You have to stand there through the test and take notes for each stage.

Experimentation with different fan settings might help. Take notes on observations as these notes can uncover clues to problems.

Next step is get the house tested. Since you are in NJ did they perform an audit?

If it is just dehumidification, a dehumdifier could be added to the system. I thought the ICS would manage is cycles intelligently. With 2100 sq ft of high volume (20,000cuft? more?) in a weakly insulated environment with probably lots of windows, based on sizing sensitivities I've seen in HVAC-Calc it is unlikely the 4-ton is way oversized. Why do you think it is oversized?

 

[tedkidd]

If it is just dehumidification, a dehumdifier could be added to the system. I thought the ICS would manage is cycles intelligently. With 2100 sq ft of high volume (20,000cuft? more?) in a weakly insulated environment with probably lots of windows, based on sizing sensitivities I've seen in HVAC-Calc it is unlikely the 4-ton is way oversized. Why do you think it is oversized?

Because he has problems with comfort and humidity, and they're worse when it's mild. Don't overestimate load of a little extra volume, that 3500 sf house I regularly refer too has some 2+ story cathedral areas and high ceilings in general, it's very happy with a 60mbtu/3 ton infinity hybrid.

This house could simply be a corn crib, and reverse stack effect means infiltration high causes variation, but seems he has fair comfort close to design temps so that's not the only issue.