Is there any harm . . . - Page 2
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  1. #14
    Join Date
    Mar 2003
    Posts
    46
    Basically, the engineer just wanted us to run the fan continuously to get better flow throughout the house, since we were having trouble with our two rooms in the front of house (sun baked), and the booster fan was to help get more air movement in that area too.

    I just don't like to have something running in my attic 24/7, but they said it would be fine. I just worry about heat, electric and fires.

    I leave my computer on 24/7

    Thanks,
    Chip

  2. #15
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Look at this paragraph...

    I would like to invite both Chipper and Dhanna to peruse this report which I posted earlier:
    http://www.fsec.ucf.edu/bldg/science/mold/index.htm

    Look on page 3 or thereabouts for the table titled:
    "Impact of Indoor Set Temperature and Fan Operation Mode
    on Interior Relative Humidity"

    FSEC is in Florida so their experiment should be more valid for Chipper than any of us. They attribute sometimes a 10% increase in relative humidity when continuously running the eentral fan. What Dhanna says about a fresh air intake, is a very important point -- one could more easily over-ventilate if you have one. A tight house will require some kind of fresh air ventilation, it just has to be fully taken into account.

    I am listening to Dhanna's concern about energy use. The question I would like to ask someone who knows is... how big is this factor? Are we talking about possibly $10/month in a typical summer? More? Less? Only with that number, could we judge whether it is worth it. Perhaps someone from FSEC itself could give an honest estimate, hopefully based on measurement.

    From Chipper's last post, it really does appear that this is an application the AirCycler was designed for. You can get air mixing within the house without 100% runtime (however a week of continuous fan to test out the idea is in order). A ventilating dehumidifier or ERV would probably not accomplish this goal, unless you did something really clever with ductwork. Is there any chance that someone like Dash could give you consulting on this matter? Or somebody he knows and would recommend?

    One last thought. The central fan is rated for continuous use. It should be no more likely to cause a fire than your refrigerator, your computer, etc. IMO the things to concern yourself with are more importantly humidity and energy.

    Hope this helps -- P.Student

    [Edited by perpetual_student on 03-23-2005 at 04:35 PM]

  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,694
    P student.

    The question is, did they do that test with a VS blower with humidity control, or a standart blower, and was the unit over sized?


    We have a customer that runs his fan 24/7/365, and in the summer his rh is doesn't rise above 50, and usually is 42 to 46.
    Its a 2 stage stealth. heat pump, 15 seer.

    I think the auto, or on question is best answered by the type of system you have.

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  4. #17
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Easy questions, harder answers

    Beenthere, you asked some detail questions about the FSEC experiment. In the footnotes there are referenced two papers which probably document the answers you seek. I have not yet studied the papers. Might be necessary to access them through ASHRAE or to phone the authors to know details like this.

    Since the papers are dated 1987 and 2001, and the mandate of FSEC is to help the majority of people (vs. the top-end buyers), I would be very surprised if their experiment didn't reflect simple and cheap equipment. No VS blowers, no humidistats, typical system sizing in other words. For the 71-degree part of the test the equipment ran 80% of the time. Does that answer your question about appropriate sizing?

    Are you in Pennsylvania as your profile says? Is your customer? Are PA summers comparable to Florida summers? Both Chipper and FSEC are located in FL (I am in S.Texas which has many similarities). My thinking is that humidity fighting is a regional thing and I would not expect a PA customer to be proving what could be done in a FL environment. Either you (or I) gain experience with comparable climates, or we master the laws of physics like Lstiburek and gain experience everywhere.

    I would be the first to admit that *adding* humidity is highly important in most of the country, and that is something we never have to do in the hot-humid South and practically never think about. Possibly our climate offers corresponding challenges to you regarding keeping humidity down?

    Hope this helps -- P.Student

  5. #18
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,694
    While neither our temp or humidity is as high as florida, around here peolpe keep their stats set to 74 and lower.

    The fan running 24/7 should have the same effect of raising humidity.

    Duct leakage, will increase the effect, and should be taken into account also

    As far as having run 80% of the time at 71, since it doesn't mention od temp, it could have been 98 degrees out, or 88.

    The main point is with the VS blower, 2 stage condenser, sealed duct work and humidistat, you can run the fan 24/7 for filtration, and keep the humidity reasonable.

    Ps: of course in PA.
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  6. #19
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Pennsylvania a hot-humid climate?

    Let me try to use terms that others will recognize, so we can compare apples and apples. My book "Builder's Guide for Hot-Humid Climates" describes the more important points this way:

    Tallahassee, Florida
    Average annual precipitation -- 66 inches
    2518 cooling degree days
    Summer design temperature 92F dry bulb, 76F wet bulb

    Fort Myers, Florida
    Average annual precipitation -- 53 inches
    3702 cooling degree days
    Summer design temperature 93F dry bulb, 80F wet bulb

    Houston, Texas
    Average annual precipitation -- 46 inches
    2700 cooling degree days
    Summer design temperature 94F dry bulb, 77F wet bulb

    If you could quote similar numbers for your chosen site in Pennsylvania, it would help me feel more comfortable that we are talking about similar climate challenges. People in Texas and Florida often like to set their thermostats at 74 degrees also, actually I thought that was pretty normal behavior.

    Anecdotally some more info: I was volunteering at the elementary school library and the librarian was having her mother visit from Pennsylvania just now. I asked her what the summers were like there. What she told me makes me think you have lesser challenges in terms of temperature and humidity. One of the less great things about the Houston area is, in the summer it really doesn't cool down below mid or high 70's at night. It seems to me the humidity is near 100% most nights, then the warming air has close to the same number of grains moisture, with a lower number for relative humidity than you might expect -- but still a lot of water to be wrung out of the air by the A/C every day.

    Hope this helps -- P.Student

  7. #20
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,279
    P. Student, I've been to both Pennsylvania and Houston during the peak of summer. I'm here to tell you Penn can get miserably muggy in the summer, but Houston's nights take the cake for remaining very warm and humid all night long.

    I have family in Deer Park near Houston (the former Minnesotans, mind you! ). When I visit them and ride around town, I notice that most of the composition roofs have mildew streaks on them. I've been in Deer Park winter and summer and regardless of season, unless a strong norther has blown through (bringing the stink of the refineries on the north side of 225 into Deer Park), the nights are humid year round. My cousins in Deer Park will run their a/c in their large tract home in the winter to keep the humidity down.

    What I'm distilling from this discussion is that if one's system in a humid climate has tight ducts (especially return), running the indoor blower 24/7 is likely to have little effect on relative humidity, other than the shot one may get off the evap once the compressor stops. A variable speed blower appears to mitigate this effect due to reduced blower speeds and evaporation rate of water off the coil into the airstream before the next call for cooling.

    I've been poring over a psychometric chart and walking around with my digital sling psychrometer since this discussion over humidity control has started. I'm learning a lot (still trying to piece all the aspects together, however!) and I know it will be useful for me in the field when it comes to performance checks on systems and the like.

    And as for the VisionPro thermostat, one thing worth mentioning is that the "Circ" feature times are programmable in that if you wish for that feature to be active during, say, a setback period when nobody is home and inactive during occupied hours, that can be done. This way one can accomplish increased air filtration with higher end filtration systems, and with the higher temps maintained during a setback period, less dehumidification will occur due to a higher setpoint (unless a humidistat model is used) which translates to less time the coil is getting wet and then being dried again during the "circ" cycles with compressor off.
    With the adaptive intelligent recovery, the stat will lower temps and humidity to setpoint prior to your arrival and then disable the "circ" feature for the occupied times, if so programmed.

    At least that seems how it should work....
    • 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.

  8. #21
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,694
    Our 95db, and 72wb is not as much as florida as I said.

    The apple to apple comparison is the system size, design, and install, thats what will make the difference.

    didn't you buy a higher end trane, with VS.

    Why spend all that money, if it doesn't do much for keeping you comfortable in cooling.

    With 2 stage, VS, and humidistat, you can keep the fan 24/7, and the rh down, if the contractor did his job right. If he didn't, your screwed. Thats the bottom line.
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