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Thread: Hrv Erv ?

  1. #14
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    Quote Originally Posted by teddy bear View Post
    You have many exhaust devices in your home that need make-up air to function. The bathfans, clothes drier, kitchen hood, and water heater need make-up air. ERV is a balance flow device that does not supply make-up air. During wet outside conditions, an ERV brings in moisture. About half of the outside moisture makes it through the ERV along as dry air is exhausted. If you plan on a air change every 4 hours, you are still introducing 2 lbs. of moisture an hour. Plan on some supplemental dehumidification even with an ERV. Plus the make-up air that your exhaust devices need adds up to many lbs. of moisture that must be removed everyday during damp days in green grass climates. ERVs are expensive but do save energy, about $150/year. For about the same investment, a whole house ventilating will provide fresh year around make-up air ventilation for your exhaust devices, for your family IAQ, and maintain <50&#37;RH during wet cool weather. Very comfortable and healthy. If you can afford both, great. With an ERV you should have a 90 pint per day dehumdifier. I consider the whole house dehu primary. Now is the time to investigate both. If you go with the ERV, monitor your indoor %RH, particularly in the lower levels of the home. Check my other post for more discussion if interested. Regards TB

    You should be pushing dehumidifiers where they are really needed like damp musty crawlspaces or houses with poor HVAC systems where it is more economical to add a dehu than to rip open walls and ceilings to replace the duct work.

    If someone truly wants that steady non stop fresh air the erv is the way to go, and with a tight home a small inexpensive 40 pint dehumidifers are going to remove all the moisture in 'shoulder seasons'

    Intermittent exhausts are not problematic until you get into the magnitude of Jenn Air grilles, stainless steel hoods. In that case the 50 CFM brought in by an over priced thermastor dehumidifer is going to be very insignificant.

    With a tight home the original poster should be looking at the combustion appliances to be all sealed combustion and directly vented and it is wrong to even suggest a little bit of ventialtion air is even sufficient for combustion purposes.

  2. #15
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    carnak

    Thanks for adding your info here as well. The more the better usually

    Just a quick update for you and maybe you can add some info

    New Construction home 2500 sq ft, 2 story. Spray foam insulation Low E-4 anderson windows Home should be very tight

    They had the home sized for 2.5 ton upstairs and 2 ton downstairs Lennox XP16 heat pumps. (found out they don't make 1/2 ton sizes addressing this with a new manual J)

    G61V furnaces backup natural gas (how are these vented are they sealed?

    The only other gas appliance is a water heater and Im sure its a spec water heater and is naturally vented.

    Kitchen as a microwave oven that vents outside all 3 baths have vents that vent outside as well and a electric dryer.

    So my questions are that all my estimates and encluding contacting the reps about the foam they all said I need some type of way to introduce fresh air into the house such as an ERV.

    They guys over at energywise structures said even the tighest homes have enough leaks that supplemental air infiltration is not neaded? any info would help

    Here were my questions. Spray foam guy said you need some type of ERV for your home

  3. #16
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    Quote Originally Posted by acnoob1 View Post

    New Construction home 2500 sq ft, 2 story. Spray foam insulation Low E-4 anderson windows Home should be very tight

    They had the home sized for 2.5 ton upstairs and 2 ton downstairs Lennox XP16 heat pumps. (found out they don't make 1/2 ton sizes addressing this with a new manual J)
    Not 100% sure how running another Manual J addresses the no 2.5 ton 2 stage Lennox.
    Unless they fudged the loads to begin with.

    For as tight, and well constructed as your house is suppose to be. 4.5 tons sounds like a lot of cooling.

    Have you seen the actual numbers, or just told what it came out to.

    The GV61 is a sealed combustion furnace.
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  4. #17
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    I think they fudged the numbers quite a bit and that was part of the deal I could have a manual J done by a 3rd party to see what they came out with. I have a fealing that I could get by with 2 2ton units. Actually I probably could get by with smaller but they don't make anything smaller, Then again I will wait and see what the manual J comes up with.

  5. #18
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    Your house may only need 1.5 tons on the first floor and 2 tons on the second.
    They make single staged 1.5 ton units.

    If your floor plan is open to the second floor, even a 2 stage 2 ton, may not be able to remove enough moisture.
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  6. #19
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    The first to second is not really open just the stair case that goes from 1st to second

  7. #20
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    OK.

    Is this new Manual J coming from a third party.
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  8. #21
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    yes a 3rd party uninvolved with this.

  9. #22
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    Quote Originally Posted by acnoob1 View Post
    They guys over at energywise structures said even the tighest homes have enough leaks that supplemental air infiltration is not neaded? any info would help
    House do leak, and the use of small intermitent fans is not a problem with respect to the house sturcture and moisture moving through the building envelope.

    Drying a couple loads of laundry is not problematic with respect to how mositure moves through the wall.

    Something that constantly exhausts air without any make up air can be very problematic in the cooling season, especially in a humid climate.

    The ERV is its own exhaust and make up air system. So if you want a steady supply of fresh air with the lowest energy bills, this is the way to go.

    Where intermittent exhaust can be a problem is with respect to combustion appliances, and the best way of taking this out of the equation is to use sealed combustion appliances that have combustion air directly connected to the outside as well as their own vents directly to the outside.The exhausts can make air flow down the chimney in some cases.

    When you start taking about large exhaust appliances like Jenn Air down draft grilles and eleborate kitchen hoods with commercial grade cooking appliances under them, then you will start running into a lot of problems, and something of this scale will need an interlocked make up air system that runs whenever the exhaust runs.

  10. #23
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    Quote Originally Posted by teddy bear View Post
    Thanks for allowing me to explain the concept. Most a/c contractors have not attempted to use this new concept yet. They are attempting to avoid fresh air and using full featured a/c systems to provide comfort.
    UA has the option of being your make-up ventilating device. The fresh air is duct to the UA. The UA mixes the desire amount of fresh with the air in your home. The UA filters and supplies air to supply side of your a/c for distribution throughout the home. The UA has an occupancy timer that provides make-up air when you are routinely in your home. The amount of fresh air is adjustable. So make-up air when and as much as you want. When the indoor %RH rises above the desired level (<50%RH), the dehu is activated. All of this without any a/c/furnace operation. As your typical exhaust appliances are operated when you are in your home, make-up air available to aid their operation. Hot water tanks should be power exhaust to avoid any possibility of back-drafting. The cost of UA is a little more than a ERV. You will have fresh make-up air, humidity control, and a simple system without interaction of the other systems in your home. I will attach my daily data graph showing 14 hours of fresh air during occupancy and the a/c cycle later. You will notice the humidity levels throughout the home. I just started up the ventilation system and am fine tuning it. I do not any graphs will rainy cool weather like you have today. Fresh make-up weather during cool weather is the greatest challange. I use 7kw/day on the dehu and 15-18 kw/day on the a/c. you should do better with your new home. Regards TB
    Here is the attachment on my 2,300 sqft home. We were dry yesterday, 83^F with a 60^F outdoor dew point. Today we get your weather. The make up fresh air yesterday would have made my basement 70%RH without a dehumdifier. My dehu removed 30 lbs. of moisture. An ERV would have started out removing half of moistue in the make-up air. That only slows the wetting of your home. After an air change of fresh, the air exiting through the ERV has more moisture. The more moist air removes less moisture from the incoming damp air. After several air changes, the air exiting your home is as wet as the being bought in. Once your home is wet, the ERV exhaust wet air which will wet incoming dry air. Thus slowing the drying of your home with dry outside air. They only work if you can keep your home dry. During wet cool weather, a good dehumidifier works well.

    The other issue is the size of the a/c. With supplemental dehumidification, you are not dependent on the a/c to keep your home dry during wet cool weather. My graph shows the point. I have a 50%RH home with less than 2 hours of cooling. My 2 ton a/c is grossly oversized for a 2 hour cooling, but I have 50%RH with 58 cfm of fresh make-up air.

    Check out the dew points in MO today. They are as high Miami.
    http://www.weather.com/maps/maptype/...nts_large.html
    We are getting your weather today. Hoping for wet weather to collect more data. Are you having fun yet? Regards TB
    Attached Images Attached Images  
    Attached Images Attached Images
    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"

  11. #24
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    You run your air handler fan steady, a known way of elevating your Rh but still the main floor hovers around 50&#37; RH, and the cooler basement was 55%

    then you start pumping in outside air, the mainfloor rises a little and the basement starts rising up towards 60%.

    The AC cycles on RH drops right down below 45% and as soon as it cycles off the main floor RH the constant fan re-evaporates 0.25 pounds off of that 2 ton coil and gives a slight increase in RH.

    All in all it looks like everything is good even with the constant fan until you deliberately pump in the outside air.

    The RH from that fresh air goes into the solid portions of the home, perhaps try and see how many air changes it will take to get the outdoor dewpoint down in your basement. I think that you will find it quickly rises up to half the initial difference between inside and outside, then it slowly climbs up. Moisture is being driven into your dry wall, furniture

    An ERV would need maybe 3.5 pounds of water removed
    Last edited by Carnak; 07-25-2008 at 03:48 PM.

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