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  1. #27
    beenthere - unfortunately, their promotional brochures indicate that they will; have since found out they don't. Would an HRV do any better at lowering indoor humidy?

  2. #28
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    In the winter time yes it will. In the summer time, it won't. Some brands can have either core put in it.

    Atleast 1 member of this board has both cores. And changes tot eh one he needs for each season. You may wish to find out if your brand and model can use either core.
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  3. #29

    ERV/HRV ?

    Well I'm still puzzled. An HRV will remove excess humidity in the winter but not the summer - is that simply because of the usually lower outside RH in the winter? I have a Carrier/Bryant ERV unit that I believe acutally could swap cores with some HRV models. But am I to understand that the ERV core prevents outside humidity from coming in during the summer, while somehow the HRV core allows inside humidity to pass to to the outside only because of the humidity differential? The bottom line is how do I get inside humidity to go outside. One other quick issue I can't seem to get an answer for: let's say my ERV is not running, just setting there, but interconnected to my HVAC ductwork. Now I run the clothes dryer or bathroom exhaust fan, or whatever. Will the ERV/HRV allow passive pass-through air flow to compensate for the air I am exhausting from the house? Thank you so much!

  4. #30
    Join Date
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    An HRV doesn't do anything to the moisture in the air it is moving.
    So the moisture in stale air from the house is exhausted to the outside. And the moisture in the outside air is brought into the house.

    So in winter, it exhaust your higher humidity air. And brings in the lower humidity outside air. Thats how it reduces the inside humidity.

    An ERV exchanges not only the heat like an HRV, but also the moisture of the stale inside air is transferred to the fresh incoming air.

    The ERV core, transfers the moisture from the higher containing air, to the air that contains the lower moisture content.

    So your ERV is transferring the moisture in the stale air, to the fresh air as you bring it in. And that is why your humidity is not dropping.

    Some air will come in passively. How much? Can't say.
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  5. #31
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by weathermanks View Post
    Well I'm still puzzled. A But am I to understand that the ERV core prevents outside humidity from coming in during the summer, while somehow the HRV core allows inside humidity to pass to to the outside only because of the humidity differential?

    The bottom line is how do I get inside humidity to go outside. One other quick issue I can't seem to get an answer for: let's say my ERV is not running, just setting there, but interconnected to my HVAC ductwork. Now I run the clothes dryer or bathroom exhaust fan, or whatever. Will the ERV/HRV allow passive pass-through air flow to compensate for the air I am exhausting from the house? Thank you so much!
    ERVs moderately reduce the amount of moisture entering your home if you exhaust dry air to the outside while introducing moist air, 40%RH reduction.
    When exhausting moist air, like from a bath, moisture transfers to the incoming fresh air. So a reduction in moisture at best. A good whole house ventilating dehumidifier is better for most homes in green grass climates. I have been designing ventilation for homes for 20 plus years. If you want a dry home with adequate fresh air ventilation, a good dehumidifier is the key component during times when the outdoor dew point is +60^F with low/no cooling loads.
    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"

  6. #32
    Join Date
    Apr 2002
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    11,808
    The ERVs with the wheels can reduce about 75% of the heat content in the outside air, I usually consider they cut the moisture load in half here but I have no shortage of ambient humidity.

    The ones with a 'paper like' HRV core may transfer 30 to 40% of the total heat.

    I installed a venmar ERV in a hypochondriacs home back in the mid 90s. I liked it because it would not over dry the home so you were not ventilating the hell out of the place and then having to humidify the place to get the RH up high enough not to get nose bleeds.

    The same venmar model then had a small bypass port that would pop open on a rise in RH. If the house would get too humid, the port opened and it reduce the moisture transfer until RH dropped down low enough to keep the windows clear of condensation.

    If you ventilate continuously to code levels in a cold climate you will need to humidify the air. You can also ventilate intermittently at rates 2 to 3 times higher than code required rates, get the same IAQ and not have the problem of being too dry.

    In a cold climate your windows tell you when you have enough fresh air or not. If they are sweating you need more air.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

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  7. #33
    Join Date
    Jul 2008
    Location
    Rochester NY
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    Each situation is different and basing design decisions solely on rules of thumb often get clumsy results, as the decision to get an hrv instead of erv may have done in this situation.

    WEATHERMANKS, where is the moisture coming from? From the ground, occupants, something else? That's where you need to start.

    AUDITOR, sounds like you might want to swap cores with WEATHERMANKS as It sounds like your HRV and his erv assumptions were wrong. As BEENTHERE implied your house is not as tight as super efficient houses that require DEHUMIDIFICATION in winter. Sounds like you need to recover latent rather than expelling it.

    Furthermore, have you tested your IAQ or are you basing your fresh air requirements on rules of thumb as well? Ive been in leaky houses with crap iaq and tight houses that were fine. Standards are just starting points, not guarantees.

    You may also want to check your Evo settings. Set only to humidify when heating? You may never get enough humidification with that setting particularly if the furnace is oversized. Ditto if you have a flow through humidifier running cold water. Did you get a water saver or one of those water wasters?

    Finally, depending on your hrv integration you may not need to run it at all. Is it piped to your furnace return? Running the furnace fan will run air in and out due to the pressure imbalance. Do you run the evo fan full time?

    Cycling equipment will shorten it's life. I run my erv on constant.
    Last edited by tedkidd; 03-13-2010 at 04:45 PM.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #34
    Join Date
    Apr 2002
    Posts
    11,808
    i can see cycling equipment, like an over sized furnace shortening the life of a heat exchanger, but in the hundreds of HRVs I have done, I can't say I prematurely burned out a fan motor from cycling. The 3 amp inrush starting those little fans is not a killer
    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/

  9. #35
    Join Date
    Apr 2002
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    11,808
    Quote Originally Posted by teddy bear View Post
    ERVs moderately reduce the amount of moisture entering your home if you exhaust dry air to the outside while introducing moist air, 40%RH reduction.
    When exhausting moist air, like from a bath, moisture transfers to the incoming fresh air. So a reduction in moisture at best. A good whole house ventilating dehumidifier is better for most homes in green grass climates. I have been designing ventilation for homes for 20 plus years. If you want a dry home with adequate fresh air ventilation, a good dehumidifier is the key component during times when the outdoor dew point is +60^F with low/no cooling loads.
    Regards TB
    it's not like you are taking a two hour shower.

    I always am amazed that somehow, a product that makes you use extra power in the summer and wastes energy in the winter is better than something that saves energy all year round.
    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. #36
    First, I want to thank you all for the input!! Now, a few details for anyone joining late: my house is 31 years old, on a slab, two adult occupants. 6 year old high end Bryant air source heat pump, air handler, Infinity computer controls, etc. All the good stuff. House has spray foam insulation in walls and a seal coat of spray foam in attic. Really good new doors and windows. Ridge roof venting, full eves venting. Haven't done blower door testing yet, but intend to. All exhaust fans vented outside. ERV added less than two years ago. Limited space to work with but did a good job; plumed into return air duct. All ducting run in attic. Well insulated.

    For some reason, the conventional wisdom calls for an ERV in my climate instead of an HRV, even though we have 6X heating degree days over cooling DD. Right now outside temp is 49F, RH is 80%, indoor temp 72F, and indoor RH is 55%, determined by my own sling psychrometer.

    Indoor RH is okay during the dead of winter, but that's only about two months. The rest of the time, like now when we're still heating, and in the summer, indoor RH is higher than I'd like. Isn't 50% kind of the area where you start to have problems?

    I obviously can't change to a ventilating dehumidifier at this point. What's my best course of action?

    One statement from somebody that has me puzzled: "I always am amazed that somehow, a product that makes you use extra power in the summer and wastes energy in the winter is better than something that saves energy all year round." What is that referring to?

    I appreciate your continued advice.

  11. #37
    Join Date
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    Location
    Rochester NY
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    I think he was taking a shot at ventilating dehumidifiers. In the food chain I think he's saying they are erv/hrv's illiterate cousin. (I think everything has it's best application and ventilating dehumidifiers are probably best in mild climates with high humidity. You need a fair temperature delta to justify recovery. That's why saying "it depends" is a good habit to get into.)

    What you may want to consider is a regular dehumidifier for periods you will not be using your air conditioner for moisture removal. ERV core might be best for this time to keep moisture out if possible. Lot of dependencies in assessing that.

    Moisture is neither created nor destroyed, it's moved. It goes from high concentrations to low. Typically inside has more moisture than outside without dehumidification because of loading from ADL. Venting moisture and pulling in dry mixes down. Sounds like you do not have more moisture indoors than outdoors (based upon those numbers the grains are about the same).

    If outdoors has higher concentrations of moisture than you want indoors, you will have to remove the moisture because mixing "down" when there is no down accomplishes nothing. The moisture inside and outside are the same. And yes, try to stay below 50%.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #38
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,341
    Quote Originally Posted by weathermanks View Post
    First, I want to thank you all for the input!! Now, a few details for anyone joining late: my house is 31 years old, on a slab, two adult occupants. 6 year old high end Bryant air source heat pump, air handler, Infinity computer controls, etc. All the good stuff. House has spray foam insulation in walls and a seal coat of spray foam in attic. Really good new doors and windows. Ridge roof venting, full eves venting. Haven't done blower door testing yet, but intend to. All exhaust fans vented outside. ERV added less than two years ago. Limited space to work with but did a good job; plumed into return air duct. All ducting run in attic. Well insulated.

    For some reason, the conventional wisdom calls for an ERV in my climate instead of an HRV, even though we have 6X heating degree days over cooling DD. Right now outside temp is 49F, RH is 80%, indoor temp 72F, and indoor RH is 55%, determined by my own sling psychrometer.

    Indoor RH is okay during the dead of winter, but that's only about two months. The rest of the time, like now when we're still heating, and in the summer, indoor RH is higher than I'd like. Isn't 50% kind of the area where you start to have problems?

    I obviously can't change to a ventilating dehumidifier at this point. What's my best course of action?

    One statement from somebody that has me puzzled: "I always am amazed that somehow, a product that makes you use extra power in the summer and wastes energy in the winter is better than something that saves energy all year round." What is that referring to?

    I appreciate your continued advice.
    The issue is to have an air change every 4-5 hours when the home is occupied. When the outdoor dew point is +60^F, adequate ventilation contributes moisture to the home. If your home is above 55%RH, operate a good dehumidifier to remove the excess moisture. The distributor that sold your contractor the venmar ERV sells a good dehumidifier to use during the humid times of the year. The Santa Fe compact is a high effieciency dehu that can be connected to the heating ducts. For homes that do not have HRV/ERVs and leak enough fresh air during cold weather, the whole house ventilating dehumidifier is a good option. Basement/crawlspace homes in green grass climates also need supplemental dehumidification during the +60^F dew point times of the year. If you have a regular household dehu, operate it until is fails, you get tired of the noise, or high operating cost. 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. #39
    Join Date
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    Location
    Rochester NY
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    Quote Originally Posted by teddy bear View Post
    When the outdoor dew point is +60^F, adequate ventilation contributes moisture to the home. If your home is above 55%RH, operate a good dehumidifier to remove the excess moisture.

    Basement/crawlspace homes in green grass climates also MAY need supplemental dehumidification during the +60^F dew point times of the year.

    If you have a regular household dehu, operate it until is fails, you get tired of the noise, or high operating cost. Regards TB
    Of course! Take indoor temp target 50% rh and you have the outdoor dew point to keep track of!!! IE: 75f 50% = 57f dewpoint above which you'll need a/c or dehumid. Thanks!!!!!

    SOMETIMES should be here. (cold basement, moisture/air leakage to outside, to inside... House's dehumidification may be sufficient.)

    FUNNY, and true.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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