ReplyWhat indoor temperature do you run your system at to achieve ~52% RH?
Regular Guest
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!!!
Professional Member*
What indoor temperature do you run your system at to achieve ~52% RH?
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Professional Member*
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?
Regular Guest
AC is set at 76 or 77 degrees when we're home. Wife likes it at 78.Originally Posted by Shophound
Regular Guest
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.
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Last edited by jpsmith1cm; 05-01-2013 at 08:22 PM. Reason: non AOP Pro Member
Regular Guest
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%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.
Professional Member
helpmehvac
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Sponsor & Professional Member*
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"
God Speed, Jim. We'll miss you - 2-26-23
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.
Regular Guest
Teddy Bear - Glad you arrived.
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?
Regular Guest
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.
Sponsor & Professional Member*
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.Teddy Bear - Glad you arrived.
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?
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"
Professional Member*
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.
Regular Guest
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.
Regular Guest
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.
Sponsor & Professional Member*
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"
Regular Guest
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.
Sponsor & Professional Member*
VS AC RH Control .pdf
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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