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Thread: HRV or ERV?

  1. #1
    Join Date
    May 2004
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    58
    Building a Foam insulated house (very tight), so indoor air quality is a concern. The Foam insulator insist on a ventilator (HRV, ERV)

    The concern is a build up of humidity in the winter when the house is closed up tight for 5 months.
    (Maryland)

    Currently an Aprilair ERV is being installed, but reading about them (aprilair ERV), They transfer the heat AND humidity to the incoming air in the winter time, thus retaining indoor humidity.

    The Carrier ERV lit. states that it's core will, remove indoor humidity in the winter AND remove humidity from the fresh incoming air in the summer.

    Is this possible ? I though an ERV transfered the humidity from the high to the low, no matter what.

    But it sounds like the carrier acts as an HRV in the summer, and an ERV in the winter.

    Any thoughts ?

    Nick

  2. #2
    Join Date
    Apr 2002
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    11,808
    Originally posted by nicholasa
    Building a Foam insulated house (very tight), so indoor air quality is a concern. The Foam insulator insist on a ventilator (HRV, ERV)

    The concern is a build up of humidity in the winter when the house is closed up tight for 5 months.
    (Maryland)

    Currently an Aprilair ERV is being installed, but reading about them (aprilair ERV), They transfer the heat AND humidity to the incoming air in the winter time, thus retaining indoor humidity.

    The Carrier ERV lit. states that it's core will, remove indoor humidity in the winter AND remove humidity from the fresh incoming air in the summer.

    Is this possible ? I though an ERV transfered the humidity from the high to the low, no matter what.

    But it sounds like the carrier acts as an HRV in the summer, and an ERV in the winter.

    Any thoughts ?

    Nick
    In the winter, the dry air stream is the fresh air being brought in. The ERV will remove humidity from the indoor air being exhausted and tranfer some of it to the fresh air coming in so as not to over dry the home. I am only familiar with the venmar residential ERVs. On a rise in indoor humidity, a bypass port opens to allow indoor air being exhausted to bypass the energy exchange wheel until the indoor RH level drops. An HRV can overdry homes in more northern locartions than yours.

    In the summer, a significant portion of the humidity of the fresh air is transfered to the dry air being exhausted. The HRV again does not transfer this humidity.

    In your location I would recommend the ERV, however no comments on the carrier model. Companies like venmar and renewaire are way ahead on the technology, maybe carrier is relabelling someone elses machine.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  3. #3
    Join Date
    Dec 2000
    Location
    Michigan
    Posts
    724

    Hmm Data!

    Read the literature very carefully, as I have in the past 15 years of watching the development of ERV and HRV they some times adjust the exchange of air from 1 to 1 to more out then in to accomplish some advertising gimmick! Then the home most have outside air enter “uncontrolled!”

    Furthermore no ERV or HRV is designed to ADD air to a home!!
    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

  4. #4
    Join Date
    Apr 2002
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    11,808

    Re: Data!

    Originally posted by Xavier
    Read the literature very carefully, as I have in the past 15 years of watching the development of ERV and HRV they some times adjust the exchange of air from 1 to 1 to more out then in to accomplish some advertising gimmick! Then the home most have outside air enter “uncontrolled!”

    Furthermore no ERV or HRV is designed to ADD air to a home!!
    I know reading comprehension is difficult for you, but read the original post very carefully X. This will be a well insulated and tightly constructed home, something which you have only read about but have never experienced.

    There will be minimal infiltration in this type of home, so controlled mechanical ventialtion is required.

    You never seem to grasp this concept.

    This is not a drafty home where the positive pressure gimmick you sell, would be of any use except as an aesthetically pleasing combustion air intake. In fact of all the partial quotes listed on your site, the only good thing it says about your product is that it makes a good combustion air intake.

    You also have only read about HRVs and ERVs and yet because they are competition for the POS positive pressure ventilation device that you sell, you always criticize them even though you do not totally understand them.

    How are the old ROI's coming along with the price of energy these days?





    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,545
    The new super tight and insulated homes has series of needs that current HVAC systems may not deal with. We use cloths drier, bath fans, kitchen hood, water heater, fireplaces, and central vac that need make-up air. The sensible cooling load is much less than normal which leaves a high latent cooling ratio,(moisture). Make-up air ventilation with dehumidification is the best system for green grass/humid climates. You provide the filtered make-up air required for the various mechanical appliances and purging indoor pollutants. These systems also filtering and controlling the humidity of the entire home winter and summer. In NE U.S. during winter, there a $50 increase in heating compared to HRV/ERV. During summer, you break even because of higher thermastat set points. Controlling humidity makes entire home vary comfortable including the basement.

  6. #6
    Join Date
    May 2004
    Posts
    58
    Thanks TB,

    Still trying to finish off this house.
    (2 Bryant infinnity systems, and 1 april air ERV up stairs)

    I am adding an Ultra-Aire Dehumid to the basement/1st floor system. can't find ANY local Ultra-aires, only April-aire units, guess I'll have to have 1 shipped.

    My problem with the ERV's in general is that they "recover" indoor humidity in the winter, Not what I need in this tight house. BUT carriers ERV claims to remove humidity from the indoors in the winter too ???

    http://www.xpedio.carrier.com/idc/gr...v00-042104.pdf

    As far as controlling make-up air, does any one make a controller with inddor and outdoor pressure sensors ?
    So the fresh air damper would open only as needed ?

    This being a tight house with UNVENTED cathedral ceilings, I donot want to over pressurize in the winter, thus forcing warm/moist interior air in contact with cool exterior surfaces, My aim is nuetral pressure.

    Thanks,
    Nick


  7. #7
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    Apr 2002
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    11,808


    [Edited by Carnak on 09-06-2004 at 08:18 AM]
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,545
    Originally posted by nicholasa
    Thanks TB,

    Still trying to finish off this house.
    (2 Bryant infinnity systems, and 1 april air ERV up stairs)

    I am adding an Ultra-Aire Dehumid to the basement/1st floor system. can't find ANY local Ultra-aires, only April-aire units, guess I'll have to have 1 shipped.

    My problem with the ERV's in general is that they "recover" indoor humidity in the winter, Not what I need in this tight house. BUT carriers ERV claims to remove humidity from the indoors in the winter too ???

    As far as controlling make-up air, does any one make a controller with inddor and outdoor pressure sensors ?
    So the fresh air damper would open only as needed ?

    This being a tight house with UNVENTED cathedral ceilings, I donot want to over pressurize in the winter, thus forcing warm/moist interior air in contact with cool exterior surfaces, My aim is nuetral pressure.
    Your current local a/c company can get you a Ultra-Aire system. Regarding winter humidity, ERVs recover a portion of moisture from the outgoing exhaust air, roughly 50%. They will dryout the home but require more operation than HRV, makeup air, or exhaust air.

    Regarding neutral pressure, with no ventilation the neutral pressure is midway between the top and bottom of the home. The top of the home is positive pressure and the bottom is negative. The colder the outside temperature, the greater the positive and negative pressures. At +15^F, a very tight 3,000 sq.ft. home leaks 50 cfm of inside air out through the high part of the home including the catherdral ceiling. An equal amount of fresh air infiltrates low in the home like around the rim joist. An HRV/ERV does not change the neutral point but adds to the air change rate. Exhaust ventilation like bath fans, clothes drier, and kitchen fans raises the neutral point and decreases the exfiltration. Make-up air ventilation like Ultra-Aire increases the exfiltration through the ceiling. Ideally, use make-up ventilation during the spring/summer/fall and exhaust ventilation during cold weather. The most critical issue is keeping the home dry enough to avoid condensation of exfiltrating air in the catherdral ceiling. The rest is your choice.

  9. #9
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    Apr 2002
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    Yes some positive pressure with air brought in through the dehumidifier would be good in the summer. Dehumidifier is not really designed to control humidity in winter application, temperatures and RH levels too low.

    A switch to exhaust ventialtion, even wired in to a dehumidistat creating a slight negative in winter would not be a bad thing especially if the heating appliances were direct vent, and there was no problem with radon.

    Slight positive in summer and slight negative in winter keep humid air out of wall cavities.

    System would work great as long as there is no big exhaust appliances like a Jenn Air, its just that it is expensive operate.

    X will be foaming at the mouth about now.

    Commercially, ERVs and HRVs are run out of balance to maintain the desired positive/negative pressures.

    The residential ERVs that I have installed in Canada, use a bypass port. On a rise in indoor RH above the setpoint, the port opens and air is exhausted temporarily without the heat/moisture transfer to the fresh air. It allows constant fresh air with as much humidity as the windows can take.

    HRVs when run steady will over dry a home, where as the ERV will not.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  10. #10
    Join Date
    May 2004
    Posts
    58
    And You just know a JennAir is going in this house

    The AprilAire ERV is a continous run type unit, with dampers to adjust for neutral pressure.

    Could I adjust the dampers to run out of balance in the winter, creating a neg pressure during the heating season ?

    Then the Ultra-Aire Dehumid w/fresh air intake would run in the summer creating a pos pressure ?

    The kitchen and laudry are back to back, I am thinking about a dampered 6" fresh air make up for this area, Wired into the JennAir and dryer.

    Wood stove/ pellet stove will have its own combust air intake., Water htr, HVAC, etc all electric, so no back drafting problems in the winter ?

    Also What is the ideal indoor RH while the outside temps are in the 20's, so that condensation will not be a problem ?

    Carnak,
    Will the Ultra Air not help with winter time indoor RH ?

    Thanks,
    Nick






  11. #11
    Join Date
    Dec 2000
    Location
    Michigan
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    724

    Hmm Data

    As far as controlling make-up air, does any one make a controller with inddor and outdoor pressure sensors ?
    So the fresh air damper would open only as needed ?



    Yes there is!


    "It is easy to be humble, when you are perfect!"


    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

  12. #12
    Join Date
    Apr 2002
    Posts
    11,808
    All electric HVAC, electric water heater, DIRECT VENT wood stove where combustion air is directly ducted to the stove, no problems with downdrafting. I would not recommend a pellet stove that drew air from the house and an indirect combustion air intake that allowed cold air into the house.

    Jenn Air in a tight house needs a make up air damper interlocked with the Jenn Air fan. Recommend dumping the air into an area of basement where there are no water pipes in the vicinity. I have never had problems with an intermittent dryer exhaust, but you could also interlock with the damper. Try not to cook and dry laundry in the winter at the same time in the winter or X will break a window on your house.

    Make sure there is no Radon problem where you are.

    Your ideal RH will be determined by your windows. The better the window, the warmer the inside surface temperature, the more humidity you can have.

    I would avoid windows with metal frames or metal spacers between the panes as these short circuit heat out of your house and will be very prone to U shaped condensate patterns around the bottom of the window.

    Glass with an R-value of 2 or better would allow you 40% RH (actually higher) in your winter climate. I would not recommend anything higher than 40%.

    TB's system with the dehumidifier with fresh air intake in summer, and negative point exhaust in the winter is an alternative to using an ERV. The dehumidifier is designed for warmer more humid air in the summer time, especially with the fresh air intake. Using it in the winter time, the air is cooler inside the house. You would have to damper off the fresh air intake as well. The dehumidifier could frost up in the winter, at least it would in a colder climate like Canada. Therefore the dehumidifier would control summer time humidity and the exhaust fan would control winter time humidity.

    You could be prone to prolonged periods of mild temps and high humidity and you may want a humidifier.

    How about a link to your april air ERV before I comment further?

    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  13. #13
    Join Date
    May 2004
    Posts
    58
    Carnak,

    http://www.aprilair.com/product.asp?...D14F348EB3FF1e

    I am thinking of going with a HRV instead, for winter time use only. It will keep the winter time indoor RH lower than an ERV will ? I am told that You can rot a super tight house out in the winter (from the inside out), if You do not ventalate and keep the RH down.

    Xavier,
    Do You have a link to the damper control with differental pressure sensors ?

    Thanks,
    Nick

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