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  1. #1
    Join Date
    Mar 2013
    Posts
    112

    HRV tied into HVAC or not

    Hi

    I am thinking of adding an HRV when I get my heat pump system installed. From what I have read it seems that when it it tied into the HRV ducting the AH has to run continuously to move he fresh air throughout the house. The climate here is fairly humid and the HRV should do most of the dehumidifing.

    Is this the best way to hook theses up or should I run seperate ducting for the HRV. Also is it necessary to have the HRV as it may increase needed BTU's by bringing in cold outside air in the winter.

    Thanks

    Jimmy

  2. #2
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,198
    what is your location?
    how is the hrv dehumidifying? by ducting it to return air plenum??

    here in the hot humid south erv is sometimes used..when
    house is tested & verified that it is tight enough to require fresh air intake.
    have you blower door tested the house?
    tested ducts for duct leakage?
    how do you know you need fresh air?

    have you thought about a simple filtered fresh air with
    a barometric damper to return for fresh air source...IF
    needed?

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  3. #3
    Join Date
    Mar 2013
    Posts
    112

    Location Eastern Canada

    Hi
    Thanks for the questions.

    It is a fairly new place ~3 years. in the countryside, a vacation place that is used 80% of the time and will be 100% on retirement. No ducting in place. Here in canada mechanical ventilation is code if in the city for new builds. No blower door test and don't know if there is even a company that does it here in this neck of the woods. The HRV's, from what I gather exhaust the moisture to the outside. They recommend the exhaust returns come from the bathrooms and kitchen taking the moisture . They also bring in humid air so I dont know how that would work. They have humidiastats that adjust the cfms based on humidity, I think to remove more if required.

    Jimmy

  4. #4
    Join Date
    Mar 2013
    Location
    nh seacoast
    Posts
    150
    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

    You can find the rules for posting and qualifications here.

    Additional infractions may result in loss of posting privileges.
    Last edited by jpsmith1cm; 04-22-2013 at 05:23 AM. Reason: non AOP Pro Member

  5. #5
    Join Date
    Mar 2013
    Posts
    112
    Quote Originally Posted by combustioneer View Post
    need mechanical cooling to reduce humidity. hrv or erv recovers heat or cooling from exhausted air via core that separates airstreams and exchanges heat. get a good contractor to set up the proper control scenario with a variable speed air handler.
    Ok thanks for the reply, so the HVAC takes out the moisture that the HRV brings in, could you not use the HRV in the summer or use it less so as to not bring in too much humid air? I am thinking of a carrier infinity system and they have a HRV that goes with thier HP AH. Would that be controled with the infinity stat? Would the AH have to run continuous?

    Jimmy

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,198
    running the fan in the air handlercontinously, re-evaporates the humidity that the a/c has
    removed back into the house.
    here in my humid climate, running fan continously isn't recommended.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,714
    combustioneer

    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

    You can find the rules for posting and qualifications here.

    Additional infractions may result in loss of posting privileges.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,467
    Quote Originally Posted by JimmyP View Post
    Ok thanks for the reply, so the HVAC takes out the moisture that the HRV brings in, could you not use the HRV in the summer or use it less so as to not bring in too much humid air? I am thinking of a carrier infinity system and they have a HRV that goes with thier HP AH. Would that be controled with the infinity stat? Would the AH have to run continuous?

    Jimmy
    HOmes naturally ventilate max during cold, windy weather. During calm, moderate weather, little or no fresh air passes through the home. Mechanical ventilation is need during calm warmer weather. The moisture removal or addition to the home depends on the outdoor dew point. The ideal indoor dew point of a home is 30-45^F during winter conditions. During mild weather, the max indoor dew point is 55-60^F to avoid mold and dust mites. Occupants add 1-2 lbs. of moisture per hour. Homes need a fresh air change in 4-5 hours when they are occupied. The fresh air change purges indoor pollutants and renew oxygen.
    HRVs dry or wet the home depending on the dew point of the outdoor air. During moderate weather, 1-4 lbs./hr. of dehumidification is needed. During high cooling loads the a/c will keep the home dry. During low/no cooling loads, supplemental dehumidification is needed.
    In most homes, fresh air is not needed during weather. This reduces the benefit of an HRV to the point where there is no payback. Add the fact that many of the kitchen fan and clothes drier need make-up air to function, basic make-up fresh air a better choice is green grass climates.
    Consider all of this, consider a small whole house ventilating dehumidifier a better choice for fresh filtered air and ideal %RH throughout the year. The trick is to operate the fresh air ventilation system when the home is occupied during calm moderate weather. Check out one of the sponsors of this site, Ultra-Aire whole house dehumidifier with fresh air option.
    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
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I think hte best HRV set-up is independant ductwork where you continously exhaust form high humidity and location with poor IAQ. Bathrooms and kitchen space. They can almost replace exhaust fans in soem cases in those locations. You an also use timers in those room to increase the HRV ot high speed on demand. Then duct the fresh air to the most commonly occupied spaces like bedrooms, living room or a central hallway. Then you don't have to run the fan on your furnace all the time saving energy. You will bring in some humidity in mid summer,but your not in a very humid climate so it shouldn't be a major issue. Most home allow in the same amount of humid air jsut through leaks anyway.... that's why you need a HRV. You could always go with an ERV for a little more money, but it won't dehumidify the space as well in winter if that's an issue.

    However, Teddy is right. You might be better off with a venting dehumidifer. When you factor in the purchase price, energy consumption and energy recovered, HRV's don't save all that much energy. They aren't high volume economizers like on commercial HVAC systems.

  10. #10
    Join Date
    Mar 2013
    Posts
    112
    Thanks for the information.
    I don't see any condensation buildup on windows during the cold months. I have a range hood and 2 bathroom fans that exahust directly to the outside. I have a wooden pine interior on all walls and ceiling. so I don't want things too dry. It there some way to tell if I am getting enough fresh air without adding ventilation without a blower door test?

  11. #11
    Join Date
    Mar 2013
    Posts
    112
    I think the RH here for may is between 63 and 96 so it can be very humid. We are on an Island. i am looking for the yearly averages. One site says it ranges from 86% in the morning to 75% in the afternoon.

    I don't like the idea of running the fan continuous if it isnt needed. I like the independant setup.

    Thanks

  12. #12
    Join Date
    Mar 2013
    Posts
    112
    Name:  humidity levels.jpg
Views: 206
Size:  50.7 KBhere is a table of average RH for the year

  13. #13
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by JimmyP View Post
    I think the RH here for may is between 63 and 96 so it can be very humid. We are on an Island. i am looking for the yearly averages. One site says it ranges from 86% in the morning to 75% in the afternoon.

    I don't like the idea of running the fan continuous if it isnt needed. I like the independant setup.

    Thanks
    You're also on a cooler ocean. Outdoor RH isn't important, it's the dewpoint that matters. That's the actual amount of moisture in the aire. 100% RH at 32F is called frost, but a dewpoint of 32F when it's 70F indoors is pretty dry, just 25%RH. Dewpoints of about 50-58F are ideal for 75F indoor temperature. That' and RH of 45-55%.

    Ducting the air to the furnace and runing it's blower won't improve the situation. And ERV will help in summer, but then you can't ventilate effectively to dehumidify in winter.

    I'd probably lean towards a ERV, then a whole house dehumidifier on a properly sized AC system.

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