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  1. #1
    Join Date
    Mar 2003
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    46
    . . . in letting the fan on the handler on 24/7? Also any fire hazard in a booster fan in the duct running 24/7 in a hot Florida attic?

    I'm such a worry wart of late

    Chipper

  2. #2
    Join Date
    Mar 2004
    Location
    SE Michigan
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    17,898
    No, if installed properly. Motors like not being turned off and on.
    " Kill a Commie for Mommy! "

    - Colonel David Hackworth (1930-2005), Korean War Vet

  3. #3
    Join Date
    Feb 2005
    Location
    Alabama
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    534
    I would double check humidity level first though. Have seen mold problems as a result of running AH fans all the time. Recirculates moisture back through the duct work.
    "If you can't fix it, don't break it."

  4. #4
    Join Date
    Jun 2004
    Location
    Florida
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    556
    Make sure you don't have any leaks in the system. I would normally advise you not to since there is a possibility that more outside air would be brought into the building without being conditioned. If you do decide to do this hake sure you check the humidity often or install controls that will enhance the dehumidification of the unit.

    As far as the booster fan it is less of a concern since it is smaller. However if it is left on it might defeat it's purpose. Perhaps the booster fan is improving the air flow to a hot room. If the unit isn't cooling the fan would be bringing warmer air into that room and the room would warm up quicker. The room might get uncomfortable before the unit calls for cooling again.

  5. #5
    Originally posted by duct dr
    I would double check humidity level first though. Have seen mold problems as a result of running AH fans all the time. Recirculates moisture back through the duct work.
    What? Not so sure I understand what you mean Duct Dr., as the moisture would NOT collect in the ductwork if the fans are run 24/7. Instead the moisture would collect elsewhere, even if running at night with OA ~ TDB=60, RH=90%. Those fans would drag in that moist outside air and dump it in the space, not collect it in the duct. If there isn't any outside air being pulled in and it is still being exhausted, then infiltration is being forced through walls, floors, roof, etc. And that's where the moisture is going to start collecting, at the dew point in the walls where it sneaks around the vapor barrier. Have you seen the mold problems inside the duct or outside?

    Running the fans 24/7 would bring in the outside moisture if the cooling isn't kept on 24/7 too. Running the fans at night to take advantage of the cooler air also drags in a higher moisture content, something that the cooling has to wring out of the air during the day to make up for all of the moisture collected in the place at night. And during the night, you collected all that moisture... And when you have moisture...

  6. #6
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Humidity from fan running

    Here is what I have been told: There have been case studies of high humidity (and resulting mold problems in the house) where the problem was aggravated by running the fan all the time. I live in a hot-humid climate too and have been very clearly told it is a bad thing to run the fan all the time.

    When the AC runs, the coil is cold and water drips off it, removed from the air and running down a drain tube in liquid form. In the couple minutes after the AC cycle ends, there is a still-cold coil which gradually warms up to ambient temperature. With the fan off, that condensate mainly drips off the coil and does not re-enter the house air. With the fan on during these couple minutes, there is substantial re-evaporation into the house air, adding to humidity.

    Does the original poster want to cycle air through the house more? Another way to achieve *that* goal would be to add a gadget called AirCycler. This has been designed with the approval of Lstiburek and runs the fan a chosen percentage of the time. The great thing about this is, the Aircycler knows enough to have the off-time in the minutes following the end of an A/C cycle. A couple of high end thermostats can also do this (at higher cost) but the Honeywell corporation is clueless about the humidity problem. Dang Yankee Minnesotans <g>.

    Hope this helps -- P.Student

  7. #7
    Join Date
    Jun 2004
    Location
    Florida
    Posts
    556

    Re: Humidity from fan running

    Originally posted by perpetual_student


    When the AC runs, the coil is cold and water drips off it, removed from the air and running down a drain tube in liquid form. In the couple minutes after the AC cycle ends, there is a still-cold coil which gradually warms up to ambient temperature. With the fan off, that condensate mainly drips off the coil and does not re-enter the house air. With the fan on during these couple minutes, there is substantial re-evaporation into the house air, adding to humidity.

    Hope this helps -- P.Student
    It's true that the evaporation that occurs while the fan continues to run after the compressor stops adds humidity to the building. However, disabling the time delay function of the indoor fan reduces the efficiency of the system. IMO trying to stop that little bit of humidity is not worth the reduction of efficiency.

  8. #8
    Join Date
    Mar 2003
    Posts
    46
    Well since we have a booster fan in the duct now, I don't really see why we were told to run the handler fan continuously, except to possibly cool the house better by constant air flow??? Too, supposedly keeping the air quality better with continuous filtration?

    Thanks,
    Chipper

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,317
    A couple of high end thermostats can also do this (at higher cost) but the Honeywell corporation is clueless about the humidity problem. Dang Yankee Minnesotans <g>.
    I wouldn't lean so hard on Honeywell, P. After all, me mother be from Minnysoda, along with a good chunk o' me family.



    Seriously, the issue you have with the VisionPro stat's "Circ" feature certainly isn't a deal killer for me to use and recommend the stat, even in humid climes like ours. Honeywell got a lot of stuff right with this stat, not to mention it's one of the coolest looking digital programmables out there.

    Service techs love them because they can stock, with a few exceptions, one stat for many applications. An 8100 covers all the single stage equipment and the 8320 and 8321 cover the multiple stage stuff handily. One stat for heat pumps, gas or electric heat, and comfort cooling. Same subbase for all of them (except "Vision", but a pro won't have that on his truck. He'll want the VisionPRO ). You gotta like that.

    As for the humidity issue, I guess I'll have to play with my 8100 at home this summer when the weather turns sticky and see just how this "Circ" feature affects humidity levels. As it is I made substantial tweaks to my home system last year (return air leaks, critical refrigerant charge, etc.) and this year plan to add a TXV to the indoor coil and run the blower at medium high vs. blast-you-out-of-the-house high, all along monitoring the system's performance along with temperature and humidity levels in the house.

    I personally think the sum of these tweaks will give me good temperature and humidity control without the need for the "Circ" feature of the stat, or swapping the 8100 out for an 8321 with humidistat. Though the latter might remain a consideration since we substantially upgraded our attic insulation last year and may not find enough heat load to keep the humidity levels down on cool but sticky days.

    Suffice it to say I am pleased with the VisionPro series for several reasons and would not hesistate to recommend it to anyone.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #10
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Please explain

    Dhanna wrote:

    >>It's true that the evaporation that occurs while the fan continues to run after the compressor stops adds humidity to the building.
    >>However, disabling the time delay function of the indoor fan reduces the efficiency of the system.
    >>IMO trying to stop that little bit of humidity is not worth the reduction of efficiency.

    Dhanna I assume you really know what you are talking about, it sure sounds like it. However I do not even know what a "time delay function of the indoor fan" is, and would have no intention of disabling anything designed into the system.

    All I would do is to refrain from extra fan time, selected by the user one way or another, in the minutes just after the normal AC cycle ends. If it helps, let me tell you one of my two systems is already set up with Trane's "Comfort-R" and I understand they do a controlled amount of fan flow along with the cycle end. The other system will be similarly upgraded before too long. But that was designed by good engineers who know what it is like to live in Texas (something Honeywell refuses to look at).

    In my climate I would never advocate running the fan in "Continuous" mode, I would always leave it in "Auto". If I had the right model of White-Rogers they have a 3rd choice and I would use theirs. But the 3rd choice that Honeywell offers, is only random fan runtime and I would not want that. Not in a humid climate, thank you.

    But I respect the air conditioning system engineers in general and would not yield to any tinkering in an attempt to prove myself smarter than them. Sorry if I gave that impression.

    To Shophound -- Maybe you could get one of your family to talk some sense into Honeywell? All they gotta do is to rewrite their software so that its off-time counter resets upon the end of a cooling call. Sofware is trivially cheap, what the hey?

    And Shophound, when you finally get some results from trying the "circ" on vs. off, please do post and help us figure out how much it matters. Honeyewll made a step in the wrong direction, but I admit it may be a small step. When they patch their software, I'm ready to buy!

    Best wishes -- P.Student

    P.S. DHanna, after this message was originally posted, I came across this from FSEC:
    http://www.fsec.ucf.edu/bldg/science/mold/index.htm
    Notice what they say under " Practices That Will Minimize Mold Growth". Now that I understand what you are saying, I will have to side with FSEC until I learn otherwise. How much efficiency is at stake? How much in remediation, remodeling, or even hospital bills?

    [Edited by perpetual_student on 03-23-2005 at 01:10 PM]

  11. #11
    Join Date
    Mar 2003
    Posts
    46

    Mold

    How much mold can get in the ducts, or does it grow in the attic? Also what type of health hazard is this. Does it affects all people or just some?

    Chip

  12. #12
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304

    Not in ducts, not in attic, in the house

    >>How much mold can get in the ducts, or does it grow in the attic?

    What I am referring to, is mold in the interior of the house. As far as I know it is a lot less likely in the ducts, or in the attic. This is a scary thing but only likely to occur if the humidity makes the dewpoint higher than the temperature of some object in your house. When that happens you will have condensation, a slow but long term source of water. If you keep your house relative humidity below 70% this is not likely to occur. Instead you will just feel muggy and may feel the need to overcool the house to feel comfortable.

    Try this link:
    http://www.energystar.gov/index.cfm?...ent_moldmildew

    I would recommend to anyone that they spend $15 and buy a humidity meter from the local Wal-Mart. Buy several. You will now have more instruments than some service techs, and can know objectively whether you have a problem.

    >>Also what type of health hazard is this. Does it affects all people or just some?

    People seem to have highly varying sensitivity. Mold is a natural thing and many people seem unaffected. Yet others seem to be dangerously allergic. One former teacher had a water leak around a window, feeding a mold colony which evidently made his family sick. When I first emailed him, he was in the hospital for sinus surgery and afraid he would die on the operating table. Later on the mold was discovered, when it was fixed the problems went away.

    This link tells more, from a good source:
    http://www.epa.gov/iaq/molds/moldbasics.html

    Best of luck -- P.Student

    P.S. READ THIS IF NOTHING ELSE -- from FSEC, it tells us explicitly:
    ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++
    http://www.fsec.ucf.edu/pubs/consumer/2002-sept22.htm

    "Don’t move the fan setting on your air conditioner to the “on” position. Leave it set to “auto.” Setting it to “on” keeps the blower fan running continuously, resulting in the moisture that has condensed on the air conditioner’s evaporator coil during cooling being re-evaporated and blown back into the home. As a result, the indoor relative humidity will be a lot greater than if the fan switch had been set to “auto.”

    [Edited by perpetual_student on 03-23-2005 at 12:41 PM]

  13. #13
    Join Date
    Jun 2004
    Location
    Florida
    Posts
    556
    I read the link you provided p student and the fan delay I was talking about 1-3 minute delay they say should be disabled. This delay improves efficiency by ringing out what cooling is left in the coil. Disabling this feature is a common practice to maximize dehumidification here in Florida. I think it is misapplied to often. The thinking is that the blowing the air across a wet coil for three minutes will add moisture to the air through evaporation of what water is left on the coil. How much water can there be. I don't know, but I can't imagine it's very much.

    Now disabling the fan delay will help dehumidification a lot more if there is fresh air connected to the system because the fresh air will not be introduced into the building during those 3 minutes. I assumed the posted didn't have fresh air on his system since were in the residential section.

    Anyway there is no need to disable the time delay as a policy. The only time I would advise it is when there is a humidity problem. But the chances are there is something else the is causing the high humidity levels.

    Just my .02

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