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  1. #14
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    If the basement is unfinished, it also usually lacks a vapor barrier between the ground and concrete. Concrete will slowly wick some moisture into the space. But otherwise, that is correct, the dewpoints are pretty similar to the rest of the house, just cooler so the RH is higher. It is a common misconception that basement are particularly damp. I think that perception comes from how common foundation leaks are, poor humidity control in homes, lack of basement ventilation and leaks sill plates allowing outside humidity into a basement, and finally older homes often had stone foundations which actually allow some moisture to continously leech through the mortar. IT was just how they were and you kept the basement ventilated, only stored things in the middle and in winter it helped humidify the home and in summer it provided some evaporative cooling.

  2. #15
    Quote Originally Posted by teddy bear View Post
    Most basements have high humidity because the temps are cooler than the rest of the home. The dew point of air in the basement is very similar to the rest of the home. Every ^F cooler basement is, cooler lowers the %RH 2.5%. A separate dehu supply to the basement allows adjusting the amount of dry air the basement receives. If your basement has a water leakage problem, then there idea of circulation could be ok.
    A 105 pint per day dehu is not overkill if you want <45%RH. This low %RH will reduce the amount of moisture the a/c can remove. The Ultra-Aire 105H is the most efficient dehu made in the world. It removes+8 pints per KW. Your a/c removes 1-2 pints per KWH plus over cooling making the home uncomfortable on occasion of forced dehumidification.
    Still curious about the fresh air ventilation part of your system. All homes should have fresh air change in 4-5 hours to renew oxygen and purge indoor pollutants. This is a minor conditioning load. Most home get the needed fresh air when the wind blows. Mechanical is suggested during periods of calm weather and the home is occupied.
    Keep us posted.
    Regards TB
    Last Spring, I spent a considerable sum of $$ to insulate attic to R70, apply 1/4" foam board around whole house under new Hardy Board exterior, New Roof, and also sealed attic professionally underneath the R70. That got the CFM50 tests leakage of house to around 3200 from a practically unreadable blower door test north of 7500. That's the best I could get given its a 1972 house. With this work, plus the new Greenspeed install (2T) replacing a 22 year old Carrier system (4T), previous owners bills to mine are 1/3 of what he was paying - very significant. So with CFM50 @ 3200, my thoughts are I don't need fresh air intake as I still have leakage.

    Nevertheless, should I take 100% air input from Basement into the Ultra-Aire 105H input and pipe the dehumidified air into the supply before the zone dampers? There is a 3'x3' transition box perfect for this connection. So all the installer would have to do is pipe it in and somehow hang the Ultra-Aire from rafters or sit it on an "L" pedestal drilled into my cinder block wall, if Ultra-Aire makes such an optional accessory.

  3. #16
    Quote Originally Posted by motoguy128 View Post
    If the basement is unfinished, it also usually lacks a vapor barrier between the ground and concrete. Concrete will slowly wick some moisture into the space. But otherwise, that is correct, the dewpoints are pretty similar to the rest of the house, just cooler so the RH is higher. It is a common misconception that basement are particularly damp. I think that perception comes from how common foundation leaks are, poor humidity control in homes, lack of basement ventilation and leaks sill plates allowing outside humidity into a basement, and finally older homes often had stone foundations which actually allow some moisture to continously leech through the mortar. IT was just how they were and you kept the basement ventilated, only stored things in the middle and in winter it helped humidify the home and in summer it provided some evaporative cooling.
    Basement is 100% finished. Have no idea if there is a vapor barrier between the ground and concrete, but I would suspect NOT since that was probably not code back in 1972 when the house was built. So the GREENSPEED AC needs to overcome all these things and, again, it *does* bring it down to 52% at best.

  4. #17
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,260
    Quote Originally Posted by Short Circuit View Post
    Last Spring, I spent a considerable sum of $$ to insulate attic to R70, apply 1/4" foam board around whole house under new Hardy Board exterior, New Roof, and also sealed attic professionally underneath the R70. That got the CFM50 tests leakage of house to around 3200 from a practically unreadable blower door test north of 7500. That's the best I could get given its a 1972 house. With this work, plus the new Greenspeed install (2T) replacing a 22 year old Carrier system (4T), previous owners bills to mine are 1/3 of what he was paying - very significant. So with CFM50 @ 3200, my thoughts are I don't need fresh air intake as I still have leakage.

    Nevertheless, should I take 100% air input from Basement into the Ultra-Aire 105H input and pipe the dehumidified air into the supply before the zone dampers? There is a 3'x3' transition box perfect for this connection. So all the installer would have to do is pipe it in and somehow hang the Ultra-Aire from rafters or sit it on an "L" pedestal drilled into my cinder block wall, if Ultra-Aire makes such an optional accessory.
    Blower door test are an estimate of the natural air infiltration at your average winter temperature and wind. Wind is usually 7 mph. I also agree that you do not need mechanical ventilation with +7 mph winds. During calm, moderate temp weather, the natural infiltration will decline to near zero. Most homes will not have adequater air change during the calm conditions. Monitor CO2 levels for conformation of air change rates during all of the typical conditions your home is exposed while being occupied.
    Back to the pressing issues, If you have access to the down stream zone dampers to each area, ducting the dry air into the after zone valve ducts would allow adjusting the amount of dry to the basement verses the mainfloor. This could be a little better than before the zone dampers. Also eliminates a seperate supply to the basement. What is the separation from the basement to the mainfloor, open stairwell or closed door? Open between between spaces makes return from the basement an easy decision.
    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. #18
    Quote Originally Posted by teddy bear View Post
    Blower door test are an estimate of the natural air infiltration at your average winter temperature and wind. Wind is usually 7 mph. I also agree that you do not need mechanical ventilation with +7 mph winds. During calm, moderate temp weather, the natural infiltration will decline to near zero. Most homes will not have adequater air change during the calm conditions. Monitor CO2 levels for conformation of air change rates during all of the typical conditions your home is exposed while being occupied.
    Back to the pressing issues, If you have access to the down stream zone dampers to each area, ducting the dry air into the after zone valve ducts would allow adjusting the amount of dry to the basement verses the mainfloor. This could be a little better than before the zone dampers. Also eliminates a seperate supply to the basement. What is the separation from the basement to the mainfloor, open stairwell or closed door? Open between between spaces makes return from the basement an easy decision.
    Regards TB
    From my GREENSPEED furnace blower, the supply goes into that transition box I described, and then hits a "T" whereby it takes a 90 degree turn each way - left and right. Installing HVAC contractor placed a v-shaped vane inside this dead-end so that air turbulence was minimized. About 3' from each 90 degree turn sits zone controllers. So I have 2 zones; zone #1 serves 3 bedrooms and hallway & 2 bathrooms, and zone #2 serves kitchen, living, dining & sunroom. From basement to upstairs is completely open - no doors. There are steps leading up to main floor. From where the HVAC equipment sits, I can see the back of one of the staircases and can easily have the installer tap into that staircase wall to create a "return" which can be the input into the dehumidifier if that was advantageous. Otherwise, the dehumidifier will be pulling 100% from the basement. Regarding the output of the dehumidifier, if I didn't have the installer vent its output into the transition BEFORE the "T", then what you're suggesting would be a bit more difficult because the installation spot I envisioned would have to be moved to make the output of the dehumidifier after the zone controllers shorter, but it would then make the input (if a return from the staircase area was a good thing) much longer.

    I still have in my mind what one of the installers I called said, where he stated that it is better (in his opinion) to keep it stand-alone, and have it drain into the work-sink in basement. Have input and output of dehumidifier totally from and into basement, since HVAC cooling is practically on all the time in Summer with GREENSPEED and I have a supply and return in that general area where the dehumidifier would be placed. Dryer air would be disbursed throughout home eventually over time and eventually hit my dehumidifier setpoint (say 42%). I know that makes his job immensely easier, but is he correct in his thoughts or is it way better to tie output into the HVAC supply without question? TIA.

  6. #19
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,260
    VS AC RH Control .pdf
    Quote Originally Posted by Short Circuit View Post
    From my GREENSPEED furnace blower, the supply goes into that transition box I described, and then hits a "T" whereby it takes a 90 degree turn each way - left and right. Installing HVAC contractor placed a v-shaped vane inside this dead-end so that air turbulence was minimized. About 3' from each 90 degree turn sits zone controllers. So I have 2 zones; zone #1 serves 3 bedrooms and hallway & 2 bathrooms, and zone #2 serves kitchen, living, dining & sunroom. From basement to upstairs is completely open - no doors. There are steps leading up to main floor. From where the HVAC equipment sits, I can see the back of one of the staircases and can easily have the installer tap into that staircase wall to create a "return" which can be the input into the dehumidifier if that was advantageous. Otherwise, the dehumidifier will be pulling 100% from the basement. Regarding the output of the dehumidifier, if I didn't have the installer vent its output into the transition BEFORE the "T", then what you're suggesting would be a bit more difficult because the installation spot I envisioned would have to be moved to make the output of the dehumidifier after the zone controllers shorter, but it would then make the input (if a return from the staircase area was a good thing) much longer.

    I still have in my mind what one of the installers I called said, where he stated that it is better (in his opinion) to keep it stand-alone, and have it drain into the work-sink in basement. Have input and output of dehumidifier totally from and into basement, since HVAC cooling is practically on all the time in Summer with GREENSPEED and I have a supply and return in that general area where the dehumidifier would be placed. Dryer air would be disbursed throughout home eventually over time and eventually hit my dehumidifier setpoint (say 42%). I know that makes his job immensely easier, but is he correct in his thoughts or is it way better to tie output into the HVAC supply without question? TIA.
    The idea is cause circulation of the dry air throghout the home. All the dry air into the basement ok but makes circulation slower but basement drier. Your choice. Greenspeed has a recirculation mode that may force recirculation on a time cycle. I am attaching logger data the shows the fan cycling periodically. This could work for mixing air in the home.
    Sucking on the open space and blowing the tee before the dampers would work also. Usually you can set the dampers to open during the off cycle. This would allow dry to both zones.
    If the dampers are closed but have some bypass, ok.
    Keep us posted. Moisture readily mixes with the air in the home with open stairwell.
    Regards TB

    VS AC RH Control .pdf
    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"

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