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  1. #1
    Join Date
    Sep 2011
    Location
    New Jersey
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    5

    Venting Dehumidfier Through an ERV/HRV?

    Hello,

    I have been trolling here for awhile and finally have a question I haven't found already answered. For background: I have a fully closed cell spray foam encapsulated new home, so rafters to slab all sealed. Because the build started to get to a breaking point with cost and we were way behind I opted to leave out the V in the HVAC system and use strategicly opened windows to get my ventilation for the time being, so I am retrofitting now. I am in central New Jersey, house is 4000 sqft spread fairly evenly across finished basement, first and second floors. I have two Lennox XC21 2ton ACs and two G61V 45MBTU 94% AFUE furnaces one in the "attic" and one in the basement.

    I have concluded that I want a venting dehumidifier to pressurize the house, but I think I may need to add an ERV/HRV, maybe two, to get sufficient efficient ventilation. The first question I have is: Can I connect the fresh air intake of a UA 90H dehumidifier directly to the fresh air supply of an ERV/HRV and still balance the ERV/HRV and improve on the energy efficiency of just installing them separately?

    My thinking was that I could then keep the number of 6" holes in the house down to two and maybe improve on the efficiency of the venting dehumidifier. Venting dehumidifier and ERV/HRV would be in the conditioned "attic". I would remove two bathroom fans on the second level and connect them to the exhaust on the ERV/HRV. I would duct the dehumidifier return down to the basement and the supply into the second level furnace supply trunk. All bedrooms are on the second floor.

    I have been investigating the Venmar AVS EKO 1.5 ERV or HRV, but I have not determined if I would really benefit considerably from the ERV over the HRV. That is as far as I have gotten.

    Thanks in advance for any guidance.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,339
    Quote Originally Posted by catawampus View Post
    Hello,
    I am in central New Jersey, house is 4000 sqft spread fairly evenly across finished basement, first and second floors. I have two Lennox XC21 2ton ACs and two G61V 45MBTU 94% AFUE furnaces one in the "attic" and one in the basement.

    I have concluded that I want a venting dehumidifier to pressurize the house, but I think I may need to add an ERV/HRV, maybe two, to get sufficient efficient ventilation. The first question I have is: Can I connect the fresh air intake of a UA 90H dehumidifier directly to the fresh air supply of an ERV/HRV and still balance the ERV/HRV and improve on the energy efficiency of just installing them separately?

    My thinking was that I could then keep the number of 6" holes in the house down to two and maybe improve on the efficiency of the venting dehumidifier. Venting dehumidifier and ERV/HRV would be in the conditioned "attic". I would remove two bathroom fans on the second level and connect them to the exhaust on the ERV/HRV. I would duct the dehumidifier return down to the basement and the supply into the second level furnace supply trunk. All bedrooms are on the second floor.

    I have been investigating the Venmar AVS EKO 1.5 ERV or HRV, but I have not determined if I would really benefit considerably from the ERV over the HRV. That is as far as I have gotten.

    Thanks in advance for any guidance.
    Considering that you need make-up air to operate your clothes drier, kitchen exhaust, bath exhaust, central vac, and etc, make-up fresh air ventilation has advantage year around.
    You need about 100 cfm of fresh air when the home is occupied of the NJ air that must be cooled, dried, and humidified/dehumidified.

    Using weather underground for the winter summer temps, I estimate the heat for 12 hours/day of 100 cfm of additional fresh make-up air for 120 days of your average winter temp (34^F) at 58 therms of natural gas. If you have 3-4 occupants, no humidification is required. NG cost ?? in NJ determines the cost of winter fresh air.
    The ERV reduces the cost by 50-60%.
    The average outdoor conditions for Newark from Wunderground weather for summer load for 90 cooling days from 6-1----9-1 for the 100 cfm for 12 hours from average outside of 80^F to 75^F is 539 btus per hour of sensible cooling per hour and 1,671 btus per hour of latent per hour.
    A 3 ton a/c will operate 15 min per day to remove the sensible heat from the 12 hours of 100 cfm of warm fresh air.
    The total ventilation latent load for the 12 hours is 1,671 btus per hour X 12 hour= 20,052 btus of latent cooling per day. The latent cooling load from the occpants are 500 btus per hour per occupant. Four occupants for 12 hours would add an additional 24,000 btus of latent load. This is a total latent load of 44,000 btus of latent load. A 3 ton ac removes 9,000 btus of latent load per hour. When the a/c operates for 5 hours per day cooling the home, the indoor %RH will be <50%RH while the a/c is operating.
    During the days the a/c does not operate enough to remove the 44,000 btus a dehumidifier is needed. Using an Ultra-Aire on a non-cooling day avearge energy would be 8 Kwh. An ERV would reduce dehumidification load on the ventilation part of the latent load by 2 Kwh on a non a/c day and 3 kwh on an average summer a/c day. The ERV saves 3 Kwh X 120 days X $.?? per kwh = Savings for the summer.
    Yes, you can connect the ERV fresh air supply to the Ultra-Aire ventilating dehumidifier fresh air inlet. Inadditon connect a 8" return from the open part of the home to the dehu inlet. Connect the supply of the dehu to the supply of the a/c. Keep in mind that the ERV stops the dehu from supply fresh air for the appliances and stop positive pressure throughout the home. Positive pressure slow infiltration of fresh air in through the air leaks in the structure.
    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
    Sep 2011
    Location
    New Jersey
    Posts
    5
    So if I apply actual cost to these number I get:
    Heating season savings: 58 therms x $1.13 x 60% = $39.24
    Cooling season savings: 3kWh x 120 days x $0.16 = $57.60
    Yearly Savings = @ $100
    ROI Breakeven: $1500 approx/$100 = 15 years!

    Well that makes me think that there really isn't a significant argument for installing the ERV.

    So onto a couple follow up questions that your post got me thinking about.

    Would it really make sense to run the fan in the dehumidifier constantly to provide the positive pressure or is there a better way? I really need the positive pressure as it is also being used to help a sub-slab radon remediation system maintain a below 4 pCi/l level.

    I had not thought about the need for humidification since the house has so low infiltration as to never really dry out in the winter. My lowest RH last winter was about 38% at 68 degrees and that was after running the wood stove for something like three weeks straight. I guess with proper ventilation now I may actually need to think about that. Could I get away with only putting humidification on the basement system as there is no water supply in the "attic"?

    Thank you very much Teddy Bear for your thorough answer.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,339
    Quote Originally Posted by catawampus View Post
    So if
    So onto a couple follow up questions that your post got me thinking about.

    Would it really make sense to run the fan in the dehumidifier constantly to provide the positive pressure or is there a better way? I really need the positive pressure as it is also being used to help a sub-slab radon remediation system maintain a below 4 pCi/l level.

    I had not thought about the need for humidification since the house has so low infiltration as to never really dry out in the winter. My lowest RH last winter was about 38% at 68 degrees and that was after running the wood stove for something like three weeks straight. I guess with proper ventilation now I may actually need to think about that. Could I get away with only putting humidification on the basement system as there is no water supply in the "attic"?

    Thank you very much Teddy Bear for your thorough answer.
    Wood burner and radon mitigation are two more real good reasons to consider the merits of positive pressure ventilation as you state. I would operate the fresh air only when the home is occupied unless the radon levels built up or the wood burner smoked into the home.
    Humidification depends on the your desires but should be limited to avoid moisture on the windows and other cool surfaces. Water on the stove may be a choice. Moisture in the basement will work its way throughout the home. The home has infiltration low and exfiltration high which carries the moisture throughout.
    Try the whole house ventilating dehumidifier without ERV or humidifier. You can always add more equipment if needed. Keep us posted. How many occupants in the home?
    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
    Sep 2011
    Location
    New Jersey
    Posts
    5

    Smile

    There are 2 adults and 2 young children. The wood burner is a high efficiency built-in stove with its own fresh air intake, so there is little smoke introduced into the house, unless I happen to try to light it with one of the bathroom fans on and no windows open. Of course that also eliminates the option of keeping a pot of water on it to provide humidity.

    My short term radon test revealed a radon level of 30 pCi/l in the basement with a passive vent and I have not retested yet after adding a fan to the vent. I have read that modest positive pressure can all but stop radon infiltration, hopefully that holds true.

    Would you recommend something fancy like a CO2 based switch to control ventilation. There are relatively short periods of time when the house is actually empty, so I was leaning toward always having it on since I have also have the radon problem to contend with.

    Should I maybe consider some kind of modulating damper for the fresh air intake to adjust the amount of air brought in to the conditions. I was intending to just use an EARD from Honeywell, but that may end up being a waste.

    Thanks again Teddy Bear. I feel like I should being paying you!

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,339
    Quote Originally Posted by catawampus View Post
    There are 2 adults and 2 young children. The wood burner is a high efficiency
    My short term radon test revealed a radon level of 30 pCi/l in the basement with a passive vent and I have not retested yet after adding a fan to the vent. I have read that modest positive pressure can all but stop radon infiltration, hopefully that holds true.

    Would you recommend something fancy like a CO2 based switch to control ventilation. There are relatively short periods of time when the house is actually empty, so I was leaning toward always having it on since I have also have the radon problem to contend with.

    Should I maybe consider some kind of modulating damper for the fresh air intake to adjust the amount of air brought in to the conditions. I was intending to just use an EARD from Honeywell, but that may end up being a waste.

    Thanks again Teddy Bear. I feel like I should being paying you!
    Your radon levels are high. That is nothing to mess with. I assume you are going to suck on the passive radon vent. Use a fan capable of 1" of negative pressure. Than pressurize the home with 100 cfm of fresh make up air 24/7with focus on the basement space. Return air from the main floor to the dehumidifier and fresh air from outside. The supply from the dehumidifier should be discharge into the basement space to cause a positive pressure in the basement space. the Ultra-aire 90H would be a good unit for this application. That will be pay enough.

    With high radon levels, no need to on/off control for the ventilation until you prove you have eliminated the radon problem. You do need a dehumidistat for the 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"

  7. #7
    Join Date
    Sep 2011
    Location
    New Jersey
    Posts
    5
    Teddy Bear do you have any opinion on the Ultimate Air RecoupAerator ERV http://www.ultimateair.com/ . It seems like a really interesting concept that it can actually monitor and attempt to maintain a given pressure differential. It also appears to be the only ERV that is designed to be intentionally unbalanced. I would still get the ventilating dehumidifier but I wonder if I could then duct the dehu through the RecoupAerator and let it manage positive pressure function.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,339
    Quote Originally Posted by catawampus View Post
    Teddy Bear do you have any opinion on the Ultimate Air RecoupAerator ERV http://www.ultimateair.com/ . It seems like a really interesting concept that it can actually monitor and attempt to maintain a given pressure differential. It also appears to be the only ERV that is designed to be intentionally unbalanced. I would still get the ventilating dehumidifier but I wonder if I could then duct the dehu through the RecoupAerator and let it manage positive pressure function.
    With your wood burner and radon mitigation (negative pressure on the basement slab), you need some make-up air which will be all of the fresh air ventilation that you need.
    The small amount of potiential energy savings will be pennies at best.
    More make-up cold air and less warm exhaust will freeze-up the heat exchanger.
    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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