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  1. #1

    Supply ventilation assistance

    I want to install a supply ventilation system in my home. As it isn't exceptionally tight, the positive pressure would do me good in terms of minimizing untreated air infiltration.

    My problem is I need any incoming air to be filtered, and, for half the year, dehumidified. The current simplest method appears to be throwing an aircycler on and connecting to furnace. I have a good filter on my air handler (an entirely different discussion.) I still would likely need to dehumidify the air as it comes in. That's scenario 1.

    What I would prefer is a simple dedicated system. I'd like a central fan, small ducts, and an outside supply that runs through a good filter and gets dehumidified. In that case, I'd just bring in 100cfm continuously. Scenario 2.

    I'm aiming for efficiency if possible, but really am going for air quality above and beyond everything else. I have treatment resistant asthma with sensitivities to things in my crawl and things outside in Spring. If I could get constant ventilation of fresh air, and get a little positive pressure going, it should help a lot.

    Can anyone recommend a simple system for this?
    Can anyone recommend one that works separately from my furnace fan?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,533
    What kind of a climate are you in? Considering the limitations of operating a furnace/ac blower to provide enough fresh air, a small ventilating dehumidifier like the Ultra-Aire 90H 0r 65H would be the most practical device to provide 60-100 cfm of fresh air, blending the fresh air with house air, filtering to the desire level, circulating, and dehumidifying when needed. The standard filter is MERV 11 or higher is available. The desired amount of fresh air and maintaining <50%RH throughout your home with UA and using your heating/cooling ducts for distribution along with minimal operating cost is hard to beat. We have been refining the system for 15 years.
    http://www.ultra-aire.com/images/pdfs/UA-65_sheet.pdf
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    Quote Originally Posted by teddy bear View Post
    What kind of a climate are you in? Considering the limitations of operating a furnace/ac blower to provide enough fresh air, a small ventilating dehumidifier like the Ultra-Aire 90H 0r 65H would be the most practical device to provide 60-100 cfm of fresh air, blending the fresh air with house air, filtering to the desire level, circulating, and dehumidifying when needed. The standard filter is MERV 11 or higher is available. The desired amount of fresh air and maintaining <50%RH throughout your home with UA and using your heating/cooling ducts for distribution along with minimal operating cost is hard to beat. We have been refining the system for 15 years.
    http://www.ultra-aire.com/images/pdfs/UA-65_sheet.pdf
    Regards TB
    I'm in the Southeast, so it is a very humid climate. My concern with the ventilating dehumidifier is twofold. One, I need Merv16 (I need HEPA, but don't think I can get the air movement) filtration, and Two, I don't want the dehumidifier constantly running.

    So, if the humidity is 45% inside, will the dehumidifier just stop pulling air, or will it pull it through, and simply not dehumidify it, or will it constantly try to dehumidify all air, costing me a lot in energy?

    If it would only dehumidify when the humidity is either high inside or very high outside (so I'm not dumping wet air in), but would pull in fresh air the entire time, that would get me closer to using one. Any thoughts?

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,533
    Quote Originally Posted by takeitdown View Post
    I'm in the Southeast, so it is a very humid climate. My concern with the ventilating dehumidifier is twofold. One, I need Merv16 (I need HEPA, but don't think I can get the air movement) filtration, and Two, I don't want the dehumidifier constantly running.

    So, if the humidity is 45% inside, will the dehumidifier just stop pulling air, or will it pull it through, and simply not dehumidify it, or will it constantly try to dehumidify all air, costing me a lot in energy?

    If it would only dehumidify when the humidity is either high inside or very high outside (so I'm not dumping wet air in), but would pull in fresh air the entire time, that would get me closer to using one. Any thoughts?
    The fresh air operates independently of the dehumidifier. The dehu operates on a dehustat located in the home responding to the settings inside the home. During high cooling loads, the a/c may be able to maintain <50%RH. The dehu only operates when the interior humidity is above the setting. There is an optional filter available with a near hepa filter.
    We have been refining the design for +15 years. Check out the Ultra-Aire. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Quote Originally Posted by teddy bear View Post
    The fresh air operates independently of the dehumidifier. The dehu operates on a dehustat located in the home responding to the settings inside the home. During high cooling loads, the a/c may be able to maintain <50%RH. The dehu only operates when the interior humidity is above the setting. There is an optional filter available with a near hepa filter.
    We have been refining the design for +15 years. Check out the Ultra-Aire. Regards TB
    Ok. So, it doesn't rely on the furnace fan, and sends a continual amount of fresh air? How much (cfm)? And is there a difference between Honeywell DH90 and Ultra-Aire 90?

    I thought the dehus only brought in 40 cfm or so, but if they'll bring in 100, that might be a good option for me.

  6. #6
    Join Date
    Nov 2009
    Location
    Saskatchewan
    Posts
    492
    An air cylinder? What am I missing here. Positive pressure goes against my training also.
    Positive pressure also causes door locks to fill with ice in cold weather, plus busts windows.

    Go back to the drawing board and rethink that a bit.

  7. #7
    Join Date
    Nov 2009
    Location
    Saskatchewan
    Posts
    492
    Asthma causing things like dust mites do die below 50% rh. I can see the dehum thing.

  8. #8
    Deux,

    I am highly allergic to certain things outside the household. If there is negative pressure (which there generally is in a house), these things get sucked into the living space. So, the air changes occur with very high pollen outside air, and very high mold crawl space air.

    I want a dedicated supply of fresh air coming indoors, so it's not coming in through the gaps around vents, switches, windows, etc.

    So, I'm not trying to create a large amount of positive pressure. I'm trying to create a mild amount of positive pressure, or at least minimize negative pressure. Plus, in a warm, humid climate, I think mild positive pressure is fine, as it "pushes" drier out toward the outside, instead of "pulling" wetter air into the house.

    I'm comfortable with the concept of mild positive pressure, I'm just trying to figure out how to get it.

    I just want to bring a constant supply of fresh air into the house, with it being filtered and not too humid. That last sentence is really the size of it.

    I appreciate all of the advice thus far.

  9. #9
    TB, since it seems you know a lot about the UA, can you tell me how many cfm of fresh air it brings in? I know the fan is 220, but I assume it isn't pulling 220 of fresh air in all the time.

    Please let me know if you know. Thanks.

    Any other opinions on other ways to do this (An uneven ERV for instance) would be greatly appreciated.

  10. #10
    Join Date
    Oct 2009
    Location
    Murfreesboro, TN
    Posts
    108
    The VisionPro IAQ thermostat now allows the fresh air control to be part of the set up during only certain block times during the day. That way you can have the fresh air open a certain percentage of the time when you are home and not while your are away or during the night if you want. By a certain percentage I mean that the motorized damper will only be open enough to meet your hourly fresh air requirements. If you have everyone over for Thanksgiving and want more fresh air you can change the fresh air damper setting to 100% open while the house is full of people. That will work if dinner gets burned and you want to air things out too.

    You will need to be flexible with the dehumidifier's performance during certain times of the summer. This summer had many more unseasonally warm days with it raining at the same time throughout the southeast. Those are times when the ventilating dehumidifier may not keep up. The design capacity is based on 80 dgrs at 60% rh, not 80 degrs when it is raining. Should you buy the bigger, 150H model just for those times? The real debate is to have the smaller 65H run longer or get the bigger one and run less, but be there for whatever comes your way.

    ThemaStor makes dehumidifiers for Honeywell.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,533
    Quote Originally Posted by takeitdown View Post
    Ok. So, it doesn't rely on the furnace fan, and sends a continual amount of fresh air? How much (cfm)? And is there a difference between Honeywell DH90 and Ultra-Aire 90?

    I thought the dehus only brought in 40 cfm or so, but if they'll bring in 100, that might be a good option for me.
    The amount of fresh air is adjustable from 0 cfm to 220 cfm. Usually, less than 50% of the total air flow is outside air. There is schedule for fresh air and ratio of on/off minutes. The 90 pint unit is made for several other brands. This a very durable and efficient unit.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    aERV would work for you as well, I would suggest a dedicated install instead of just hooking into the existing furnace/air handler and have a dehumistat or a percentage run timer wired in to control your usage. I recently installed a Renewaire ERV, requires no drain lines and I have it running on a percentage run timer e.g. 10%, 20%, 30% up to a 100% run time per hour and can also have push button timers for ares such as bathroom with or without showers/tubs.

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