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  1. #1
    Join Date
    May 2011
    Posts
    7

    New Retrofit IAQ Build Sanity Check / Ultra-Aire XT150H efficiency with constant fan

    Hi,

    My house had been sprayfoamed last year, and the soffit vents have been sealed which made the home much tighter, and the amount of fresh air in the house has been reduced considerably, requiring mechanical ventilation.

    I'm in south florida, so humidity is a major concern. My plan has been to install as follows:
    Ultra-Aire XT150H with filter removed, input side connected to Lennox Pure-Air. Lennox Pure-Air with ducts connected to both inside return, as well as a fresh-air vent from outside connected to a Honeywell EARD6 damper. I was planning on putting MERV8 filters at both the input from outside air as well as the source return to catch the large particulate matter and spare the HEPA filter in the Pure-Air.

    The output side of the Ultra-Aire XT150H will be connected to dedicated ductwork to all bedrooms, living room, family room, dining room (no kitchen, bathrooms -- don't want positive pressure in areas with potentially low air quality).

    This plan seems to make a lot of sense to me as it will have positive pressure in all living spaces with HEPA filtered outside air.

    The system will not be connected to the existing HVAC system at all, and will be ducted into both zones of the house. The two zones are the main living space (with 3 bedrooms), and the master bedroom as a separate zone. The house is all one level.

    The two questions are:
    1) Sanity check on this build, does it make sense?
    2) I will have a VisionPro IAQ controlling the system, as well as the main living space zone. I'd like to wire it up to have the fan in the XT150H constantly running, and have the DHUM leads hooked up to turn the XT150H compressor on and off, and the VENT leads hooked up to open or close the EARD6 damper. The idea behind this is to always have air circulating around the house to minimize hotspots, always have filters running, and always maintain positive pressure in the bedrooms. My concern is that having the fan constantly running will cause signifigant amounts of condensation on the coils to re-humidify.

    Thanks in advance!

  2. #2
    Join Date
    Aug 2003
    Posts
    907
    I can guarantee that you'll hate getting the hot air from the dehu delivered directly to the living space. If you don't have a basement to deliver it into, the next best bet is to deliver it either to the return of an HVAC system so it gets cooled, or the supply side so the ducts won't "sweat" (condense water).

    Positive pressure will be present throughout the house, no need to deliver it room by room. Whenever the damper will close you'll lose positive pressure. No point in running the fan then.

    Having an extra filter on the fresh air entrance is mandatory. Fresh air is surprisingly dirty, and you'll also foil insects wanting entry that way. Oversize it so you don't have to change it often, and if you buy the 1" kind they are all the same price regardless of size so you might as well get the largest one. You can then also put in a MERV 11 without having a significant pressure drop.
    -If you won't turn it on then nothing else matters.

  3. #3
    Join Date
    Aug 2003
    Posts
    907
    Other suggestions: get rid of the damper if you want constant positive pressure. Use the dehu's fan, an independent fan, or a small ducted HEPA fan to bring in fresh air. Leave the HVAC fans off (on "auto") -- the amount of humidity caused by having the fans running constantly is amazing.

    (BTW I meant having a MERV 11 prefilter for outside air *instead* of the MERV 8, not in addition).
    -If you won't turn it on then nothing else matters.

  4. #4
    Join Date
    May 2011
    Posts
    7
    Quote Originally Posted by pmeunier View Post
    I can guarantee that you'll hate getting the hot air from the dehu delivered directly to the living space. If you don't have a basement to deliver it into, the next best bet is to deliver it either to the return of an HVAC system so it gets cooled, or the supply side so the ducts won't "sweat" (condense water).
    There is no basement. I don't want to have it go into the HVAC ducts because I want it into both zones of the house.

    I thought about this, but decided the "hot air" probably isn't an issue -- the amount of CFM will be very low -- 400 for an entire house, of which only 100 CFM will be from the outside, so while it will be warmer, it won't be significantly so. Also, I will be putting the vents specifically in places that will not be aimed at humans. In corners that are inaccessible, etc. Also, the house has 11 foot high ceilings, and with only 400 CFM distirbuted through the whole house, it's very unlikely you will be able to notice the air from that high at all.

    I've been in similar houses in my area that have constant outside ventilation distributed in a similar way (pos pressure to every room), and unless you have your hands right by the vents, you don't notice it.


    Quote Originally Posted by pmeunier View Post

    Positive pressure will be present throughout the house, no need to deliver it room by room. Whenever the damper will close you'll lose positive pressure. No point in running the fan then.
    a) the fan running will still pull air through the Pureair filter, so there is still a point, as well as constant mixing of the house air -- but perhaps limited benefit.
    b) True, if the damper closes, there is a loss of positive pressure.

    Quote Originally Posted by pmeunier View Post
    Having an extra filter on the fresh air entrance is mandatory. Fresh air is surprisingly dirty, and you'll also foil insects wanting entry that way. Oversize it so you don't have to change it often, and if you buy the 1" kind they are all the same price regardless of size so you might as well get the largest one. You can then also put in a MERV 11 without having a significant pressure drop.
    I absolutely agree on the prefilter -- I was thinking of putting a huge 6" filter in to minimize the pressure drop, but was unsure of the best way of building this in -- any advice on how to do this?


    Quote Originally Posted by pmeunier View Post
    Other suggestions: get rid of the damper if you want constant positive pressure. Use the dehu's fan, an independent fan, or a small ducted HEPA fan to bring in fresh air. Leave the HVAC fans off (on "auto") -- the amount of humidity caused by having the fans running constantly is amazing.

    (BTW I meant having a MERV 11 prefilter for outside air *instead* of the MERV 8, not in addition).
    a) I want to have the damper there so there is at least the option of closing it off easily if there is some reason to (eg: known pollution release in the area)
    b) I was already planning on using the dehu fan to bring the air in, the HVAC fan will be in auto -- the question I was asking before though is, if the dehu fan stays constant on, will it cause the same problem of re-atomizing the condensation on the dehu's coils?

    Being in south florida, I'm pretty sure that if I wanted to just have the damper constantly open, I'd probably have to run the dehu constantly as well, the humidity levels here are well known to be very, very high in the summer, and high the rest of the year.

  5. #5
    Join Date
    Aug 2003
    Posts
    907
    What you say makes sense, but it's different when the compressor runs. The heat output is significant -- I didn't like it. If you don't mind it then that's fine.

    Quote Originally Posted by somedude View Post

    I absolutely agree on the prefilter -- I was thinking of putting a huge 6" filter in to minimize the pressure drop, but was unsure of the best way of building this in -- any advice on how to do this?
    I've seen it done with a piece of sheet metal on both sides of a full size furnace filter holder (4", 6", whatever thickness you want), with a duct from the fresh air intake on one side and a duct to the Pure-Air on the other. The air flow is slow enough that transitions are not really needed. The contractor may have better ideas.

    Quote Originally Posted by somedude View Post

    a) I want to have the damper there so there is at least the option of closing it off easily if there is some reason to (eg: known pollution release in the area)
    I worry that an electric one that may wear out if it's on almost all the time? But it should take many years.

    Quote Originally Posted by somedude View Post

    b) I was already planning on using the dehu fan to bring the air in, the HVAC fan will be in auto -- the question I was asking before though is, if the dehu fan stays constant on, will it cause the same problem of re-atomizing the condensation on the dehu's coils?
    Yes, you want the smallest dehu you need for the job to minimize this.

    Quote Originally Posted by somedude View Post
    Being in south florida, I'm pretty sure that if I wanted to just have the damper constantly open, I'd probably have to run the dehu constantly as well, the humidity levels here are well known to be very, very high in the summer, and high the rest of the year.
    It depends on how much air actually comes in. If you install a manual damper instead of the full-on full-closed one, then you can meter and control how much air you get. CO2 meters and particle counters are wonderful things.

    If Carnak was still with us he'd argue that it's much, much more efficient to have the fresh air ducted to the return of the HVAC systems instead of to a dehu, and to ventilate only when cooling but ventilate more to make up for the no-ventilation periods. Then Teddy Bear would point out that you'd get no ventilation when there's no need to cool...

    If you wanted the best of all worlds you'd need 3 fresh air intakes: one for each HVAC system, with a damper that opens when they cool, with an electric system (a few simple relays) that close the damper to the dehumidifier and turn it off while the A/C is running.
    -If you won't turn it on then nothing else matters.

  6. #6
    I am searching for the same info on how to connect the fresh air supply so it is filtered and conditioned. My challenge is doing it to a mobile home. They come connected to the supply, no damper, unfiltered, and unconditioned.

    In a home why not connect the fresh air supply (with manual vent closure) to the return, prior to filter and use a multi speed fan to distribute. Overall lower maintenance using existing system.

    I am a telephone man and not claiming to know anything about hvac.

  7. #7
    Join Date
    Mar 2011
    Location
    Edna Bay, Alaska Highest concentration of black bears in the US
    Posts
    623
    Mobile home fresh air usually is a drop straight from the roof jack to the top of the furnace/airhandler. I've not seen one in the supply, as that would blow air out of the house.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,642
    Quote Originally Posted by somedude View Post
    Hi,

    My house had been sprayfoamed last year, and the soffit vents have been sealed which made the home much tighter, and the amount of fresh air in the house has been reduced considerably, requiring mechanical ventilation.

    I'm in south florida, so humidity is a major concern. My plan has been to install as follows:
    Ultra-Aire XT150H with filter removed, input side connected to Lennox Pure-Air. Lennox Pure-Air with ducts connected to both inside return, as well as a fresh-air vent from outside connected to a Honeywell EARD6 damper. I was planning on putting MERV8 filters at both the input from outside air as well as the source return to catch the large particulate matter and spare the HEPA filter in the Pure-Air.

    The output side of the Ultra-Aire XT150H will be connected to dedicated ductwork to all bedrooms, living room, family room, dining room (no kitchen, bathrooms -- don't want positive pressure in areas with potentially low air quality).

    This plan seems to make a lot of sense to me as it will have positive pressure in all living spaces with HEPA filtered outside air.

    The system will not be connected to the existing HVAC system at all, and will be ducted into both zones of the house. The two zones are the main living space (with 3 bedrooms), and the master bedroom as a separate zone. The house is all one level.

    The two questions are:
    1) Sanity check on this build, does it make sense?
    2) I will have a VisionPro IAQ controlling the system, as well as the main living space zone. I'd like to wire it up to have the fan in the XT150H constantly running, and have the DHUM leads hooked up to turn the XT150H compressor on and off, and the VENT leads hooked up to open or close the EARD6 damper. The idea behind this is to always have air circulating around the house to minimize hotspots, always have filters running, and always maintain positive pressure in the bedrooms. My concern is that having the fan constantly running will cause signifigant amounts of condensation on the coils to re-humidify.

    Thanks in advance!
    It is important to have a minimum of a merv 11 air filter on the return to the dehumidifier. If all of the air flowing to the Ultra-Aire passes through the Pure Aire Merv 16 filter, ok. Operating the fan on the UA constant is ok but does a increase the re-evaporation rate. This may be unavoidable and is minimized by a wide band on the dehumidistat. Suggest 8%RH dead band. Remember during high cooling loads, the a/c should be able to maintain <50%RH even with fresh air and the occupants in the home. As the a/c cycle declines during low/no cooling loads, the UA will dehumidify as needed to maintain <50%RH. Thus the heat from the dehumidifier should not be noticeable when distributed throughout the home. I suggest best connect the fresh air to the dehumidifier as the many hours of fresh air ventilation and dehumidification are need throughout the year. Dehumidifying the fresh air as before it enters the home is a benefit. There are more hours of dehumidification than cooling in a foam insulated home in FL. There is a Merv 14 filter option available for the Ultra-Aire that filters fresh and house air before the mixed air enters the Ultra-Aire.
    It is not clear how you are going to operate your air handler with the UA. If the home is not occupied 24/7, why ventilate 24/7? The UA DEH 3000 controller has an adjustable ventilation schedule and and an adjustable dead band dehumidistat.
    Sorry about missing your post. Thank you for choosing the UA product. It is the best dehu.
    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"

  9. #9
    Join Date
    May 2011
    Posts
    7
    Teddy Bear,

    Thanks! The house is occupied most of the day -- I work from home. Also, the sprayfoam is still offgassing somewhat, and I'd like to accelerate the curing process as much as possible, and increasing ventilation while keeping humidity low seems like the best way.

    Install will begin on Friday.

    Final design looks like:


    Outside -> Damper -> 4" 20x24 MERV11 filter -> Box
    Inside -> 1" Merv11 12x12 filter -> Box

    Box -> Pure-air Merv16 + PCO -> XT150H -> Supply to all bedrooms / living room / family room


    VisionPro IAQ will control both the main HVAC and the XT150H, configured:

    0300 - 1 Auto changeover
    0379 - 3 Whole House Dehumidifier
    0384 - 1 Dehumidifier Operates independent of fan
    0405 - 2 Ventilation does not force fan on
    0400 - 1 Ventilation always allowed
    0401 - 4 Bedrooms
    0402 - 4000 Sqft (house is actually 3200 sqft, but ceilings are
    10 ft vs avg of 8 ft, compensating for extra air volume by adding extra space
    0403 - Ventilation Level (set to measured CFM from fresh air supply)
    0390 - 1 Dehumidification Away Mode - Yes
    0391 - 2 Dhum away mode - Circulate
    0404 - Max Ventilation Limit - Adjust to minimum amount with "P" (Pass), measure CO2 concentrations, adjust if necessary.

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,642
    Most impressive! Keep us posted on the install and preformance.
    Thank you for the support.
    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"

  11. #11
    Join Date
    May 2011
    Posts
    7
    System is now 90% installed, just a bunch of little things to fine-tune at this point. System was first powered on about 4 hours ago. I have it configured to try and maintain 40% RH and run the vent 100% of the time.

    Just 4 hours later, the air quality is already very noticeably better. RH hasn't yet reached 40%. With all the work being done, the doors were open for much of the day, and the air conditioner was also off for much of the time, temps got up to about 80F and 55% RH. HVAC was able to get temps back down to 76 very quickly (a couple of hours), but RH is taking more time, only at about 48%.

    We didn't yet measure the amount of airflow, but I'd guess it's 200CFM from the fresh air intake -- it's been upgraded to an EARD8 instead of EARD6.

    I'm going to fine-tune it a bit as time goes on -- If it can maintain 40% without running the dehumidifier excessively, and have constant ventilation, I think that's probably an ideal setup -- constant positive pressure. If it can't maintain 40%, or has to excessively run the dehu, then I'll start stepping the ventilation back, and then maybe get more aggressive on the RH% (35%? 30% -- I know I prefer it very dry indoors, but I have never had the ability to regulate it directly before)

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,642
    Quote Originally Posted by somedude View Post
    System is now 90% installed, just a bunch of little things to fine-tune at this point. System was first powered on about 4 hours ago. I have it configured to try and maintain 40% RH and run the vent 100% of the time.

    Just 4 hours later, the air quality is already very noticeably better. RH hasn't yet reached 40%. With all the work being done, the doors were open for much of the day, and the air conditioner was also off for much of the time, temps got up to about 80F and 55% RH. HVAC was able to get temps back down to 76 very quickly (a couple of hours), but RH is taking more time, only at about 48%.

    We didn't yet measure the amount of airflow, but I'd guess it's 200CFM from the fresh air intake -- it's been upgraded to an EARD8 instead of EARD6.

    I'm going to fine-tune it a bit as time goes on -- If it can maintain 40% without running the dehumidifier excessively, and have constant ventilation, I think that's probably an ideal setup -- constant positive pressure. If it can't maintain 40%, or has to excessively run the dehu, then I'll start stepping the ventilation back, and then maybe get more aggressive on the RH% (35%? 30% -- I know I prefer it very dry indoors, but I have never had the ability to regulate it directly before)
    Anything less than 45%RH will make the dehu operate extensively. 200 cfm of fresh air would be a 8 lbs. of dehumidification per hour plus the moisture from the occupants at .5 lb. moisture per occupant is significant. Dehus operating at 45%RH have reduced capacity. Operating at warmer temperature reduces the amount of moisture that needs to be removed. In other words 78^F, 45%RH is more easily obtained than 72^F, 50%RH.
    Very interesting strategy, continue to post.
    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"

  13. #13
    Join Date
    May 2011
    Posts
    7
    So, I found that achieving 40% may be possible after letting it run constant for a few days (retained moisture in building contents takes a while to dry out??), but it is probably not desirable. At 40% RH, my eyes/throat started to dry out, so I think 45% may just be the better target.

    As far as amount of ventilation, 100% of the time is perhaps desirable, but not strictly necessary -- I found 60% ventilation eliminates all household odors, but at 40% you can still smell the sprayfoam insulation in the area where the smell was strongest. One of the "fine tuning" aspects that hasn't yet been complete (work being done today) is a fantech exhaust fan in the attic to try and create a slight negative pressure in the attic. I bought a unit capable of 300CFM, but plan on using a fan speed controller to have it set to 50CFM the majority of the time, and configured to run from a relay only when the fresh air ventilation fan is running. The higher levels may be nice when having future home improvements done -- eg if more foam needs to be sprayed, it will reduce the impact of the offgassing, or if contractors will be spending a long amount of time running wires, it will increase their comfort and therefore probably increase their work quality.

    Using a CO2 Meter, it seems that no matter the amount of ventilation, CO2 levels never fall below 500 ppm, even when the house is unoccupied for most of the day, but it seems easy to stabilize below 600PPM even when sleeping overnight with a door closed. I'm trying to figure out what the source of the CO2 is -- The house has all electric appliances, with the only combustion being the propane range, which is obviously not constantly in use (and never when unoccupied!), the only pet is a spider, and there are plants in the house which should generally reduce the amount of CO2 further (during the day anyway, but might elevate it slightly during the night). I think the ultimate answer may just be that with occupant CO2 gets diluted, and is therefore going to follow a logarithmic curve for elimination.

    At this point, the main complaints about the system is actually the Honeywell VisionPro IAQ controller -- I'm not sure if there's anything better, but this leaves a lot to be desired in many ways. Eg: It only displays "Heat On" or "Cool On", but not "Vent On" or "Dehumidifier On" -- it would be nice to know when it wants to run those. Also, it seems that when you configure the Ventilation Limit (setting 404), it really only sets the limit, not the actual runtime -- so if it calculates that you only need 40% venting and you set the limit to 100%, it won't make any difference, though there does seem to be some logic there I can't figure out, as it will run the vent continuously during some hours, and rarely during others, but I can't find any documentation for it.

    Another big question I have is -- does the dew point of the discharge air from the XT150H vary depending on the input? Specifically -- if the return air is mostly outside air at 85F / 70% RH or inside air at 78F / 46%RH, does the discharge air dewpoint change considerably, and just the temperature changes (IE: it's more efficient the more humid the air is?) or is there an ultimate limit on how much humidity it can remove at a certain time, and the dewpoint will gradually fall as the return air becomes drier?

    Thanks!

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