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  1. #1
    Join Date
    Nov 2012
    Location
    NE Ohio
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    7

    ERV vs Floor Model Dehum for Winter Humidity Control

    Long-time lurker, new poster...hello, all!

    First full winter (moved in 3/2012) in our new home....

    NE Ohio, 1500 sq.ft (each of 2 levels), super tight ICF construction, R60/foam ceilings, Carrier Infinity system air to air heat pump/ERV, EnergyStar rated, blah, blah, blah

    ...and our problem is not keeping it warm (we actually heated it to mid-60's inside temps last Feb. with a 1500w milk house heater prior to heat pump install), but de-humidifying it in cooler (30's to high 20's so far) weather.

    I'm treating this as a separate issue from fresh air control, which I think we have handled OK, including slight positive pressure in the house (.12/83 cfm in... .08/70 cfm out per labeling on the ERV). We have just been leaving the ERV set on LOW during our waking hours till this point, but the humidity is climbing into the 50% range.

    The Infinity controller has an AUTO setting for the ERV which according to the manual should run the system to achieve a pre-selected humidity level. I played with that some over the weekend, and for most of the time, the ERV was on HIGH and the furnace fan was on at least medium.

    Now to the specific question.. Is it more efficient energy-wise to use the ERV for humidity control in this manner (and suffer the hit of heating all that incoming air), or should I revert to ERV for replacement air control only and use a 50 pt dehumidifier I already have to control the moisture content in the house?

    An associated thought.....although the dehum uses 500 watts when on (thanks Killawatt!), some of the energy actually heats the house (warm air coming off the unit when running), and there's no indoor/outdoor air exhange.

    Thanks to anyone who takes the time to comment on this very specific question, or any other comments.

    Jim
    Last edited by PilotsKnob; 11-26-2012 at 08:18 AM. Reason: my spelling sux

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,537
    How many occupants are in the home and hours of occupancy? This tells us the amount of moisture we are dealing with.
    You should have an air change of the space in 4-5 hours when occupied regardless of the %RH. Air flow sounds ok and you are getting the natural infiltration, together should be enough to maintain control the %RH. How do you know the amount of air flow through the ERV? You need the air flow number you have when the home is occupied.
    Dehumidifiers are not efficient at the 35-45%RH range that you need for winter moisture control. Great in the summer? You are not getting enough fresh at the low setting if the high setting is the 80 cfm during calm weather. Once you establish adequate fresh air, maintain that air flow all year when the home is occpied.
    The heat content of 80 cfm of fresh air that has come through the ERV is minimal and cost should not be the concern.
    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"

  3. #3
    Join Date
    Nov 2012
    Location
    NE Ohio
    Posts
    7
    Quote Originally Posted by teddy bear View Post
    How many occupants are in the home and hours of occupancy? This tells us the amount of moisture we are dealing with.

    How do you know the amount of air flow through the ERV? You need the air flow number you have when the home is occupied.

    Dehumidifiers are not efficient at the 35-45%RH range that you need for winter moisture control. Great in the summer? You are not getting enough fresh at the low setting if the high setting is the 80 cfm during calm weather. Once you establish adequate fresh air, maintain that air flow all year when the home is occpied.
    The heat content of 80 cfm of fresh air that has come through the ERV is minimal and cost should not be the concern.
    Keep us posted.
    Regards TB

    Hi, TB....Thanks for the response!

    Two occupants...one almost 24/7, the other probably averages 16/7 (gone on business trips, then back 24/7 for a few days). We are moisture-conscious (separate exhaust fans in each bathroom..with spring-loaded closers disallowing infilatration when the wind blows).

    Hopefully, we're not get much air un-intended infiltration...I dug the EnergyStar stuff out. The blower door test was "Htg:203CFMM50" (which you probably know more about than I do). Duct Leakage to outside "0.00 CFM". The HERS index for the house is 50, if that's helpful, and the rater listed the ventilation system as "Balanced:ERV, 80 cfm, 84.0 watts"

    The air flow figures I quoted above (.12/83 cfm in... .08/70 cfm out) were permanent-markered onto the ERV case by the installer. No idea if those are the high or low settings. Is there a methodology for me to determine the airflow thru the ERV, or is that what the EStar guy did?

    Thanks!
    Jim

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by PilotsKnob View Post
    Hi, TB....Thanks for the response!

    Two occupants...one almost 24/7, the other probably averages 16/7 (gone on business trips, then back 24/7 for a few days). We are moisture-conscious (separate exhaust fans in each bathroom..with spring-loaded closers disallowing infilatration when the wind blows).

    Hopefully, we're not get much air un-intended infiltration...I dug the EnergyStar stuff out. The blower door test was "Htg:203CFMM50" (which you probably know more about than I do). Duct Leakage to outside "0.00 CFM". The HERS index for the house is 50, if that's helpful, and the rater listed the ventilation system as "Balanced:ERV, 80 cfm, 84.0 watts"

    The air flow figures I quoted above (.12/83 cfm in... .08/70 cfm out) were permanent-markered onto the ERV case by the installer. No idea if those are the high or low settings. Is there a methodology for me to determine the airflow thru the ERV, or is that what the EStar guy did?

    Thanks!
    Jim
    The figures quoted are probabaly on high and optimistic. Operate the ERV on high 24/7 until the indoor dew point is +10^F outside. NE Ohio has a 25^F dewpoint. With two occupants, expect a 35^F dew point indoor dew point. At 68^F, 30%RH is a 35^F indoor dew point. During extreme cold, expect an increase in natural infiltration, reducing the mechanical ventilation may be necessary. Otherwise high when occupied whenever the windows are closed and winds are <7mph. should be the rule. None of these ERVs hit there specs after all the ducts are connected. I assume the ERV exhaust from a distance from the exhaust and that your fan is on low mixing the fresh air into the home. Operate dehumidifier is +50%rh when the grass is green. When your residential dehu quits, consider an Ultra-Aire whole dehu as an efficient method of controlling summer %rH.
    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"

  5. #5
    Join Date
    Nov 2012
    Location
    NE Ohio
    Posts
    7
    All your assumptions regarding the exhaust and fan are correct.

    "until the indoor dew point is +10^F outside"....confirm you referring to the outside dewpoint? I know...newbie questions...thanks for you patience.

    I'll give it a shot and post back.

    Jim

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by PilotsKnob View Post
    All your assumptions regarding the exhaust and fan are correct.

    "until the indoor dew point is +10^F outside"....confirm you referring to the outside dewpoint? I know...newbie questions...thanks for you patience.

    I'll give it a shot and post back.

    Jim
    Dry air entering your and exiting at a higher dew point removes moisture. Moisture from the occupants is about 1 lb. per hour when occupied. The more air passing through the home, the drier the home will be. Usually moisture on windows is the limiting factor. Dripping windows should be avoided.
    Keep up posted on the %Rh in the home along with outdoor dew point.
    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"

  7. #7
    Join Date
    Nov 2012
    Location
    NE Ohio
    Posts
    7
    Current outside is 37^F, DP 28^F, RH 70%, no wind (the airport reporting this is virtually in my back yard :-)

    FYI...The ERV has been on high since 9AM, and the RH has decreased from 48% to 44%.

    For an inside temp of 73^F, and assuming a preferred DP of 38^F (outside +10), I'm trying to get to a RH of 28% and change, according to the calculator I found. Sound right?

    Again...thanks for helping!

    Jim

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by PilotsKnob View Post
    Current outside is 37^F, DP 28^F, RH 70%, no wind (the airport reporting this is virtually in my back yard :-)

    FYI...The ERV has been on high since 9AM, and the RH has decreased from 48% to 44%.

    For an inside temp of 73^F, and assuming a preferred DP of 38^F (outside +10), I'm trying to get to a RH of 28% and change, according to the calculator I found. Sound right?

    Again...thanks for helping!

    Jim
    You are on the right track. The house and materials takes a couple days to adjust. If you getting 70 cfm of fresh air in/out when occupied, let things settle down. As long as the windows do not sweat and the home is not sparky dry, let the ERV run 24/7. Any preception on the freshness of the home with 24/7 ventilation? You are now assured of pruging indoor pollutants and maintain high oxygen levels. This is costing you pennies per day for little heat and electricity for the best indoor air quality. During extended windy cold weather, you may see the indoor/outdoor dew narrow, switch to med/low speed ventilation.
    Keep us posted. I wish more the a/c trade was into this like you are.
    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
    Nov 2012
    Location
    NE Ohio
    Posts
    7
    Quote Originally Posted by teddy bear View Post
    You are on the right track. The house and materials takes a couple days to adjust. If you getting 70 cfm of fresh air in/out when occupied, let things settle down. As long as the windows do not sweat and the home is not sparky dry, let the ERV run 24/7. Any preception on the freshness of the home with 24/7 ventilation? You are now assured of pruging indoor pollutants and maintain high oxygen levels."

    I can notice a difference in my perceived 'stuffiness' of the house...a definite improvement!! A very slight down-side is I noticed a very slight cool breeze last night in the bedroom, which I'm sure is a result of the fan accomodating the ERV's wishes...no biggee there. We dropped 2% more RH overnight.

    This is costing you pennies per day for little heat and electricity for the best indoor air quality. During extended windy cold weather, you may see the indoor/outdoor dew narrow, switch to med/low speed ventilation.

    Not sure what your background is, other than it must be extensive based on your systems knowledge. I would like to be able to monitor the 'pennies' it's costing as part of my over-all energy reduction plan, and I vaguely perceive reading somewhere that the Infinity controller has the capability to output that. Do you know about those specifics?

    Keep us posted. I wish more the a/c trade was into this like you are.
    Regards TB
    Thanks for the nice compliment! I've recently retired from a computer geek background, and the house/energy-reduction 'thing' is my geekness taking over. Once we're to a minimum on overall energy consumption, I'll be ready to size solar/wind as back-up. Anybody with thoughts on that as relates to HVAC is more than welcome to chime in, or (he asks, being a newbie) is that better in a separate thread?)

    Mr. Bear...you, sir, ROCK!

    Jim

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