Interesting Dehumidifier Question for Whole House
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  1. #1

    Interesting Dehumidifier Question for Whole House

    I have a properly installed GREENSPEED system which is able to pull down the humidity in the house to ~ 52% in Summer. Not bad, but I'd like to get it 10 points less - to ~ 42%-45% max (or whatever you experts believe is optimum for Summer conditions). I have been eyeing the Ultra-Aire XT105H or the equivalent Santa Fe Impact XT due to its efficiencies. My house is a Rancher, ~ 2200 sq' upstairs and ~ 2000sq' in finished, cemented basement. These 2 similar units can handle the basement square footage easily. Benefit would be that I can raise my AC temp a degree or two and be more comfortable at same time.

    I called 2 installers. One believes in venting (and wiring) the dehumidifier into the Greenspeed system, and the other suggests strongly to leave it "stand-alone" in basement. First installer believes in the "whole house" theory of lowering humidity, and the 2nd installer believes that most of my humidity is derived or settles in basement (because its cooler) so if I can bring basement humidity down to, say, 40%, he believes that the AC function will naturally circulate and distribute air all throughout the house (GREENSPEED practically operates all the time due to its perfect sizing for my home so air is constantly being distributed thru ductwork), bringing the whole house's humidity down below 50% easily and therefore to my setpoint of <45% humidity. It is also an easier and less complicated install. Lastly, it wouldn't interfere with the GREENSPEED's daily ductwork test which can be thrown off if this system is plumbed into the current system.

    What are your thoughts to this matter? I'm open to all suggestions - just trying to further lower humidity another 10%. House already has R70 in attic, new windows, and a blower door test lower than 3200 - I went thru all that work about 2 years ago so its not a matter about making my house any tighter or bringing in fresh air.

    Thanks in advance!!!

  2. #2
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    What indoor temperature do you run your system at to achieve ~52% RH?
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  3. #3
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    Where are you getting these recomendations? 45-50%RH @ 72-75F is considered ideal for summer for most people. Since you hoem is so tight, 48-50% might be challenging to accomplish since you have so much insulation. You need more sensible load ot increase latent removal. So a whole house dehumidifer might not be a bad idea. It would allow you to keep it just a little warmer.

    Have you tried setting the Infinity Control to 48 or 50%? What were the results? IS it at minimum airflow already? What are you normal indoor temperature setpoints?

  4. #4
    Quote Originally Posted by Shophound View Post
    What indoor temperature do you run your system at to achieve ~52% RH?
    AC is set at 76 or 77 degrees when we're home. Wife likes it at 78.

  5. #5
    Quote Originally Posted by motoguy128 View Post
    Where are you getting these recomendations? 45-50%RH @ 72-75F is considered ideal for summer for most people. Since you hoem is so tight, 48-50% might be challenging to accomplish since you have so much insulation. You need more sensible load ot increase latent removal. So a whole house dehumidifer might not be a bad idea. It would allow you to keep it just a little warmer.

    Have you tried setting the Infinity Control to 48 or 50%? What were the results? IS it at minimum airflow already? What are you normal indoor temperature setpoints?
    With GREENSPEED set at 72-75 degrees, this house would be FREEZING because of the low relative humidity. What I want is 78 degrees w/45% humidity at most. This GREENSPEED can't do it because its undersized, unfortunately, and I need to set the air at fastest in order to get the proper volume into a sunroom to keep it cool @ setpoint. I KNOW that if I lowered the speed of air, I'd achieve lower humidity in house, but this is not an option.

    So the question is, do I get a supplemental dehumidifier? AND, if so, should I keep it stand-alone or tie it into the system? There seems to be 2 schools of thought here.

    Keep the questions coming, because maybe there is something I don't know about the GREENSPEED settings. I also have, FWIW, the WIFI version of the (new) thermostat.

  6. #6
    Join Date
    Apr 2013
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    Indiana
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    3

    greenspeed humidity set to 40%

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    Last edited by jpsmith1cm; 05-01-2013 at 08:22 PM. Reason: non AOP Pro Member

  7. #7
    Quote Originally Posted by helpmehvac View Post
    Greenspeed Infinity 20 should reach 40% humidity during the summer and if you were thinking humidifier i would install it into the system to cover the whole home. Do you have zone dampers installed, that may help also? just some ideas anyway.
    HELPMEHVAC: Your answer is a bit confusing to me. Do you mean DEhumidifier or humidifier like you said? I already have a humidifier tied into system (whole house). For the DEHUMIDIFIER on GREENSPEED, because I only have a 2T system and not a 3T, I need it to operate at fastest airspeed setting, only allowing for, at best, low 50's % RH. I want to get it to low 40%'s RH. If I had purchased a 3T, I'm sure this issue wouldn't exist. So are you a proponent of tying the Dehumidifier into the system? Yes, this s 2-zone system where both zones are roughly the same exact sq' but one zone contains a sunroom generating a lot of heat gain. If I set GREENSPEEED to "comfort" speed, the sunroom never hits setpoint - that's why I need to set speed of air at fastest output. Result is both zones hit set point temps but at the detriment of RH never achieving <52%

  8. #8
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    helpmehvac

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  9. #9
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    Quote Originally Posted by Short Circuit View Post
    I have a properly installed GREENSPEED system which is able to pull down the humidity in the house to ~ 52% in Summer. Not bad, but I'd like to get it 10 points less - to ~ 42%-45% max (or whatever you experts believe is optimum for Summer conditions). I have been eyeing the Ultra-Aire XT105H or the equivalent Santa Fe Impact XT due to its efficiencies. My house is a Rancher, ~ 2200 sq' upstairs and ~ 2000sq' in finished, cemented basement. These 2 similar units can handle the basement square footage easily. Benefit would be that I can raise my AC temp a degree or two and be more comfortable at same time.

    I called 2 installers. One believes in venting (and wiring) the dehumidifier into the Greenspeed system, and the other suggests strongly to leave it "stand-alone" in basement. First installer believes in the "whole house" theory of lowering humidity, and the 2nd installer believes that most of my humidity is derived or settles in basement (because its cooler) so if I can bring basement humidity down to, say, 40%, he believes that the AC function will naturally circulate and distribute air all throughout the house (GREENSPEED practically operates all the time due to its perfect sizing for my home so air is constantly being distributed thru ductwork), bringing the whole house's humidity down below 50% easily and therefore to my setpoint of <45% humidity. It is also an easier and less complicated install. Lastly, it wouldn't interfere with the GREENSPEED's daily ductwork test which can be thrown off if this system is plumbed into the current system.

    What are your thoughts to this matter? I'm open to all suggestions - just trying to further lower humidity another 10%. House already has R70 in attic, new windows, and a blower door test lower than 3200 - I went thru all that work about 2 years ago so its not a matter about making my house any tighter or bringing in fresh air.

    Thanks in advance!!!
    If you want to lower the %RH throughout the home, connect the Ultra-Aire supply to the a/c supply ahead of the zone dampers. I would also have a dehumidifier supply with an adjustable damper to the basement zone make the basement space drier. As you lower the dew point of the air in the home, expect your a/c to remove less moisture and the dehumidifier to remove more.
    During cool outdoor temps and high dew points, the a/c is unable to provide indoor humidity control. The dehumidifier does all of the moisture removal. The soft spot with all vs a/cs is reduced air flow and over cooling during light cooling loads. The homes are cooler than desired and the circulation of conditioned air is not adequate to the far corners of the home.
    Keep us posted on the addition of the Ultra-Aire and the comfort of the home. The vs a/cs are better than single speeds but unable to maintain <50%RH during low/no cooling loads. The whole house dehumidifier will keep the home <50%RH without any cooling.
    Any fresh air ventilation involved here?
    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"

  10. #10
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    Whole house tied into the A/C.

    Sounds like the zone with the sunroom isn't balanced out. And that is why you have to run the blower at a higher speed.
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  11. #11
    Quote Originally Posted by teddy bear View Post
    If you want to lower the %RH throughout the home, connect the Ultra-Aire supply to the a/c supply ahead of the zone dampers. I would also have a dehumidifier supply with an adjustable damper to the basement zone make the basement space drier. As you lower the dew point of the air in the home, expect your a/c to remove less moisture and the dehumidifier to remove more.
    During cool outdoor temps and high dew points, the a/c is unable to provide indoor humidity control. The dehumidifier does all of the moisture removal. The soft spot with all vs a/cs is reduced air flow and over cooling during light cooling loads. The homes are cooler than desired and the circulation of conditioned air is not adequate to the far corners of the home.
    Keep us posted on the addition of the Ultra-Aire and the comfort of the home. The vs a/cs are better than single speeds but unable to maintain <50%RH during low/no cooling loads. The whole house dehumidifier will keep the home <50%RH without any cooling.
    Any fresh air ventilation involved here?
    Regards TB
    Teddy Bear - Glad you arrived. Understand the statement to tie it in to supply before zone dampers. However, why have adjustable (supply) damper to the basement at all? Why not have it pull 100% from basement? Wouldn't that make more sense? I could, in theory, pull from return duct but my basement - I suspect - is the source of the house moisture among all other things, so why not pull 100% from basement and distribute dryer air via supply ducts throughout home? No fresh air needs or ventilation involved...

    Regarding sizing, if I want to pull an extra 10 points of RH from this home, what size unit should I get from HVAC company? I'm immediately drawn to the Ultra-Aire XT105H because of its efficiency, but is that overkill? Basement is 2000 sq', upstairs (its a rancher) is 2200 sq'. GREENSPEED brings things down to ~ 52%. So you're right - I don't want the GREENSPEED to enter an overcool phase yet I want the dehumidifier to "assist" my AC unit to achieve ~ 42-45% RH. Will the Ultra-Aire XT105H be overkill to bring house down 10 points of RH? I would not be relying on this unit singularly in Summer as AC would be on too... Thoughts?

  12. #12
    Quote Originally Posted by beenthere View Post
    Whole house tied into the A/C.

    Sounds like the zone with the sunroom isn't balanced out. And that is why you have to run the blower at a higher speed.
    BEENTHERE - Excellent observation from a distance. The Sunroom was an add-on about 10 years ago, and the previous owner had construction crew pull from existing ductwork to cool & heat that extra area of about 400sq'. Ductwork being pulled from is living/dining room areas. So when house was original, ductwork was balanced. Now, its not because not only was ductwork not enlarged to handle the sunroom, but the Sunroom itself generates a heat gain on top of stealing from existing ductwork. So that side of house (zoned) is opened probably 2/3 to 3/4 of time, while other side of house (zoned) is the remainder and/or closed a lot of the time when setpoint temps are reached.

    This is why I need to override standard Carrier thermostat speeds and over-speed the air of the system (to max) to compensate for this added room + heat gain. Setting air speed to max moves air too fast over the coil, and that is why I can't achieve <50% RH in this house.

  13. #13
    Join Date
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    Quote Originally Posted by Short Circuit View Post
    Teddy Bear - Glad you arrived. Understand the statement to tie it in to supply before zone dampers. However, why have adjustable (supply) damper to the basement at all? Why not have it pull 100% from basement? Wouldn't that make more sense? I could, in theory, pull from return duct but my basement - I suspect - is the source of the house moisture among all other things, so why not pull 100% from basement and distribute dryer air via supply ducts throughout home? No fresh air needs or ventilation involved...

    Regarding sizing, if I want to pull an extra 10 points of RH from this home, what size unit should I get from HVAC company? I'm immediately drawn to the Ultra-Aire XT105H because of its efficiency, but is that overkill? Basement is 2000 sq', upstairs (its a rancher) is 2200 sq'. GREENSPEED brings things down to ~ 52%. So you're right - I don't want the GREENSPEED to enter an overcool phase yet I want the dehumidifier to "assist" my AC unit to achieve ~ 42-45% RH. Will the Ultra-Aire XT105H be overkill to bring house down 10 points of RH? I would not be relying on this unit singularly in Summer as AC would be on too... Thoughts?
    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
    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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