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  1. #11
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    Default Re: Add a Cold Air Return?

    Nuff said on this post

  2. #12
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by rdesigns View Post
    To fix this problem, it's important to understand some basics of how a forced-air system is supposed to work.
    Yep ------ as I draw juice up a straw from my tetra pac. ---- I think I have a pretty good understanding how forced air systems work.


    Having both the supplies and the return(s) in the ceiling is not necessarily a problem if the supplies have adequate throw and velocity. If the supplies are lacking these things, the re-location of returns will not fix the problem, but the size of the return could.

    If you doubt this, look up at the duct system of any Wal-mart or other big-box store: you will see supply ducts and registers branching out all across the ceiling, but you will see only one return, and it will be located in the ceiling right under the rooftop unit.
    Interesting --- as Sten mentioned comparing apples and oranges.

    The many commercial offices I do work in pretty much have the supplies and returns in the ceiling. This setup results in poor performance and less than desirable results.The complaints from the folks working in these offices are the same ---- in one area people are freeziing while people in another area are too warm.
    Considering in many cases you will find returns 4 feet away from supplies --- some times closer. There's absolutely no way you can convince me this type of setup doesn't negatively impact the performance and without short cicuits in air flow.

    I can tell you this ------- I've taken readings with an infrared thermometer and find huge stratification issues with those types of setups. The lower level ( the human level ) is far cooler with warmer layers upward toward the ceiling and beyond .
    When I open a ceiling tile the temperature level is even warmer above the drop ceiling.

    gulp ---- another sip from the juice pac.



    Why does the air not simply get sucked from the ceiling into the return, or, in other words, simply short-circuit without actually heating or cooling the store? Because returns do not suck air; they are no exception to the law of physics which states that air, water and other fluids always flow from an area of greater pressure to an area of lower pressure. The supplies drive the performance of any forced-air system, not the returns. Returns are simply a path for pressure relief.
    There are 3 states ---- negative ---- equallibrium ---- positive.
    Differentials exist until they reach equallibrium.
    We have mechanisims that affect the different states ---- natural and mechanical. Of course we have displacement in which this is also one mechanism being dealt with here.

    Introduce the mechanical blower --- air is drawn to the inlet ( you could say being sucked ) at one side --- with the design of the vanes ---- pushes air through the outlet side. If this was in sealed container the net would be zero air flow because there would neither be a negative or a positive pressure differential --- they would be at equilibrium.

    Now cut an opening in the box only for the outlet --- you would end up with a negative pressure inside the box because the blower would remove the air inside and without anything to displace this would create a vacuum and the box would collapse.

    .... he says while the juice in the the tera pac is emptied and drawing on the straw collapses the empty tetra pac ............

    As for the ceiling supply / return scenerio ------- if the return was drawing more volume of air than being supplied then the airstream could be strong enough to draw the heat being introduced away before having a chance to benifit ---- this is more of the short circuit.

    Hence a balanced system will provide optimum supply and return volumes maintaining proper air flow.



    If your system had been designed and installed properly, the supplies at the ceiling of the lower floor would easily heat and cool that area even with the one central return on the upper level.
    Personally I don't believe that's a good design.





    What to do now? Increasing the size of the return air path will help, because an undersized return increases the resistance that the furnace blower must overcome to move the air. If you can reduce that resistance on the return side, the supply side airflow (both velocity and volume) will increase, and you will notice improved performance in terms of better throw and mixing from the supply registers.

    Running the blower on low speed constantly will also help mix the air better, thereby averaging out the temperatures of upper and lower floors.
    Perhaps running the blower may help. The expeience with upper and lower levels is cooler air wants to settle on the lower level and running the blower creates more of an uncomfortable draft in those situations.

    The OP's setup is really not ideal and understandably has issues. This really should be evaluated properly by a HVAC professional.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #13
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by Sten View Post
    but you say it's gravity bringing back the return air. *** thanks for the schooling.

    I did not intend to convey that gravity brings back the return air, I only referred to the fact that gravity is what is responsible for the stratification of air. This, as you undoubtedly already know, is why it can help an under-performing system to add returns where the air is stratifying--high for heating puposes and low for A/C.

    My comments are intended mainly for helping the original poster to understand what is happening in his system, and why. I regret that you may have been offended by feeling that what I said is an attempt to instruct you.

  4. #14
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by canuk View Post
    Yep ------ as I draw juice up a straw from my tetra pac. ---- I think I have a pretty good understanding how forced air systems work.


    Interesting --- as Sten mentioned comparing apples and oranges.

    The many commercial offices I do work in pretty much have the supplies and returns in the ceiling. This setup results in poor performance and less than desirable results.The complaints from the folks working in these offices are the same ---- in one area people are freeziing while people in another area are too warm.
    Considering in many cases you will find returns 4 feet away from supplies --- some times closer. There's absolutely no way you can convince me this type of setup doesn't negatively impact the performance and without short cicuits in air flow.

    I can tell you this ------- I've taken readings with an infrared thermometer and find huge stratification issues with those types of setups. The lower level ( the human level ) is far cooler with warmer layers upward toward the ceiling and beyond .
    When I open a ceiling tile the temperature level is even warmer above the drop ceiling.

    gulp ---- another sip from the juice pac.



    There are 3 states ---- negative ---- equallibrium ---- positive.
    Differentials exist until they reach equallibrium.
    We have mechanisims that affect the different states ---- natural and mechanical. Of course we have displacement in which this is also one mechanism being dealt with here.

    Introduce the mechanical blower --- air is drawn to the inlet ( you could say being sucked ) at one side --- with the design of the vanes ---- pushes air through the outlet side. If this was in sealed container the net would be zero air flow because there would neither be a negative or a positive pressure differential --- they would be at equilibrium.

    Now cut an opening in the box only for the outlet --- you would end up with a negative pressure inside the box because the blower would remove the air inside and without anything to displace this would create a vacuum and the box would collapse.

    .... he says while the juice in the the tera pac is emptied and drawing on the straw collapses the empty tetra pac ............

    As for the ceiling supply / return scenerio ------- if the return was drawing more volume of air than being supplied then the airstream could be strong enough to draw the heat being introduced away before having a chance to benifit ---- this is more of the short circuit.

    Hence a balanced system will provide optimum supply and return volumes maintaining proper air flow.



    Personally I don't believe that's a good design.





    Perhaps running the blower may help. The expeience with upper and lower levels is cooler air wants to settle on the lower level and running the blower creates more of an uncomfortable draft in those situations.

    The OP's setup is really not ideal and understandably has issues. This really should be evaluated properly by a HVAC professional.
    I thought we were professionals?

  5. #15
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by rdesigns View Post
    I did not intend to convey that gravity brings back the return air, I only referred to the fact that gravity is what is responsible for the stratification of air. This, as you undoubtedly already know, is why it can help an under-performing system to add returns where the air is stratifying--high for heating puposes and low for A/C.

    My comments are intended mainly for helping the original poster to understand what is happening in his system, and why. I regret that you may have been offended by feeling that what I said is an attempt to instruct you.

    Don't worry, while you sound intelligent your not instructing me

  6. #16
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by Sten View Post
    I thought we were professionals?
    Was it the juice thing ?
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #17
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by canuk View Post
    Was it the juice thing ?
    LOL absolutely LOL

  8. #18
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    Default Re: Add a Cold Air Return?

    I needs my juice
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #19
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    Aug 2007
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    612

    Default Re: Add a Cold Air Return?

    Some things my in-laws did in a similar situation which improved things dramatically (an 8 or 9 degree delta was reduced to a 1 or 2 degree delta between upstairs and down....

    Added a return in the colder space where there was none (floor level location to catch the cooler air),

    throttled back the supply lines in the warmer space which increased the air flow in the supply vents in the cooler space,

    hung a blanket in the opening at the top of the steps to minimize the warm airflow up the steps. It would have probably been more effective if they put it at the bottom of the steps, but the decorating committee wouldn't approve it.

    by the way....whattsa tetra pac?
    Last edited by bp21901; 02-03-2010 at 09:48 PM.

  10. #20
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    Feb 2010
    Location
    Iowa, Quad-Cities area
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    129

    Default Re: Add a Cold Air Return?

    I'm from the midwest where we (normally) have basements.
    To put a furnace on the second floor and try to heat a first floor seems like a dumb idea to me since heat rises.
    Where is the thermostat located? I would recommend zoning the system. Obviously, the ductwork needs to be right first.
    Unfortunately, most new homes today (midwest or not) have poorly designed duct systems.

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