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  1. #1
    Join Date
    Jun 2009
    Location
    Boston, MA
    Posts
    3

    Temperature control through air circulation

    Hi all,

    My house is three stories plus a basement, and, not surprisingly, there's often quite a range of temperatures across levels. My current central forced air system has a single thermostat on the second floor, and often kicks into cooling or heating mode, when I feel like some clever air circulation (i.e. just the fan running, with the right intake ducts open) would do the trick.

    For instance, it's often hot on the second or third floors while the first floor is cool, and just circulating the air should drop the upstairs temperature without having to run the power-hungry AC condenser. Alternatively, the whole house might be hot, but the basement is cool (even in the summer), or the outside air is cooler than inside (e.g. in the evening after a hot day). It seems like having a basement or external intake for this purpose would be a more efficient source of cool air.

    My questions, then, are roughly as follows:

    1. Is it plausible that some plan along these lines would actually save power, or is this unlikely to be significant in practice?

    2. Are there thermostats that have temperature-controlled fan operation, as opposed to temperature-controlled heater/AC operation? Or maybe fan operation triggered by the temperature difference between multiple sensors (one on each floor)?

    3. Assuming the answers to the above are yes, would it make sense to install basement or external intakes, along with automatic opening/closing of the intake vent and a basement/external temperature sensor?

    My limited searching at local home improvement stores and online hasn't turned up any sufficiently advanced thermostats that would be able to handle this..

    Thanks in advance for any thoughts or suggestions.

  2. #2
    Join Date
    Nov 2004
    Location
    Skokie , IL near chicago
    Posts
    1,134

    Confused basement intakes

    Quote Originally Posted by chukcha View Post
    Hi all,

    My house is three stories plus a basement, and, not surprisingly, there's often quite a range of temperatures across levels. My current central forced air system has a single thermostat on the second floor, and often kicks into cooling or heating mode, when I feel like some clever air circulation (i.e. just the fan running, with the right intake ducts open) would do the trick.

    For instance, it's often hot on the second or third floors while the first floor is cool, and just circulating the air should drop the upstairs temperature without having to run the power-hungry AC condenser. Alternatively, the whole house might be hot, but the basement is cool (even in the summer), or the outside air is cooler than inside (e.g. in the evening after a hot day). It seems like having a basement or external intake for this purpose would be a more efficient source of cool air.

    My questions, then, are roughly as follows:

    1. Is it plausible that some plan along these lines would actually save power, or is this unlikely to be significant in practice?

    2. Are there thermostats that have temperature-controlled fan operation, as opposed to temperature-controlled heater/AC operation? Or maybe fan operation triggered by the temperature difference between multiple sensors (one on each floor)?

    3. Assuming the answers to the above are yes, would it make sense to install basement or external intakes, along with automatic opening/closing of the intake vent and a basement/external temperature sensor?

    My limited searching at local home improvement stores and online hasn't turned up any sufficiently advanced thermostats that would be able to handle this..

    Thanks in advance for any thoughts or suggestions.
    i would not install any air intakes in the basement to cause a serious negative in the area of your hw heater , dryer , or any other gas burning appliances. please rethink a location for your air recirc idea............Jack

  3. #3
    Join Date
    Jun 2009
    Location
    Fridley, Mn
    Posts
    45
    basically...

    to automatically control the fan on a thermostat basis has to do with somewhat complex commercial controls, and wouldn't be cost efficient, and it would control how much airflow went into each room or zone.

    I think your best bet is to cycle the blower fan on (thermostat to "on") when the house is in use, maybe a local hvac company can design a system if you're encouraged to go with the commercial control route

  4. #4
    Join Date
    Jan 2009
    Location
    Sterling Heights, MI
    Posts
    60
    Why not have a few returns in the basement if you also install the same amount of supply vents too in order to balance the pressure out?

  5. #5
    Join Date
    Jun 2009
    Location
    Fridley, Mn
    Posts
    45
    if there's atleast 1 correctly sized return and 1 correctly sized supply in each room of the house that wouldn't do anything

    again, a local hvac design/install company could help better

  6. #6
    Quote Originally Posted by chukcha View Post

    Alternatively, the whole house might be hot, but the basement is cool (even in the summer), or the outside air is cooler than inside (e.g. in the evening after a hot day). It seems like having a basement or external intake for this purpose would be a more efficient source of cool air.
    Thanks for bringing this subject because I was tormented by the very same questions for a LONG LONG time. First of all, I was also considering reverse cycle during heating season, especially during bright sunny days when attic air will be relatively warm from direct sun light beating your roof. Secondly your handle “chukcha”, isn’t it defines nationality in deep central Siberia? Just curious

    Quote Originally Posted by chukcha View Post
    1. Is it plausible that some plan along these lines would actually save power, or is this unlikely to be significant in practice?
    It is possible but volume of cool / warm air inside those areas would be very limited to achieve any significant savings.

    Quote Originally Posted by chukcha View Post
    2. Are there thermostats that have temperature-controlled fan operation, as opposed to temperature-controlled heater/AC operation? Or maybe fan operation triggered by the temperature difference between multiple sensors (one on each floor)?
    As far as I know there are plenty of various sensors currently available, the question is who will integrate them with the smart ventilation system we are both thinking about.

    Quote Originally Posted by chukcha View Post
    3. Assuming the answers to the above are yes, would it make sense to install basement or external intakes, along with automatic opening/closing of the intake vent and a basement/external temperature sensor?

    Thanks in advance for any thoughts or suggestions.
    Absolutely!! Smart, power sensible ventilation / energy recovery (exchange) system should precede any power hungry cooling and heating equipment. I have no clue why HVAC industry is only trying to push "NEW" and "IMPROVED" heating and A/C systems instead of bringing proper attention to the subject of "Smart Ventilation".

    Let me guess. Substantially lower profit margins? Less revenue from selling overpriced high efficiency equipment? Decreasing profits for Wall Street? Anything else I forgot not mention?

  7. #7
    Join Date
    Jun 2009
    Location
    Boston, MA
    Posts
    3
    Thanks for the feedback, rojacman and Denny; I hadn't considered the basement's negative pressure back-drafting air through the exhaust of the gas appliances in the basement.

    I'm already switching the thermostat's fan control to "always on" when I'm at home and need to equalize the temperature, but this doesn't help me with getting external air into the house, if that happens to be colder. (The solution to that is a box fan and an open window.)

    It sounds like having these features integrated into the central air system would be expensive and probably not worth the energy savings, though I'm not quite sure why (surely the commercial controller that Danny refers to can't be that expensive?).

    Does anyone know if there are highly-programmable thermostats I can use to play around with these ideas? An ideal solution would really be just a computer interface to the HVAC sensors and controls, so I can write my own control logic.

    energy_freak: I could imagine plenty of reasons why HVAC professionals don't try to sell air circulation systems -- it doesn't seem to be for every house, and depends strongly on the specifics of an individual house and its use patterns, as opposed to the usual cooling and heating units, that will work in any situation. And I am from Siberia originally.
    Last edited by chukcha; 06-28-2009 at 09:23 PM. Reason: typo

  8. #8
    Join Date
    Dec 2003
    Posts
    709
    To use outside air for cooling this is called an economizer and is used commonly in commercial hvac, you can look into that, maybe worth the investment if its a big house and you are going to live there for a long time.

    To move the air amongst the 3 levels would probably require some extra ductwork but it could be done, you will need a good hvac design build guy to design it for you

  9. #9

  10. #10

  11. #11
    Join Date
    Jun 2009
    Location
    Boston, MA
    Posts
    3
    Thanks, energy_freak! That's very useful information for what I was thinking about (apparently called an air-side economizer). In my case, the result seems to be that installing such a system won't be worth the energy savings, based on my house/system size and climate, but it's interesting nonetheless.

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