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  1. #1
    Join Date
    Jan 2005
    Posts
    21

    Question

    I am getting conflicting scenarios from HVAC vendors at the Home Shows. Before hiring an HVAC contractor, I would like to be able to talk intelligently, so any thoughts or suggestions would be greatly appreciated.

    I am currently designing a new ranch (cathedral ceiling front to back and I-joist floors making duct work difficult) with radiant in floor heating. Possibly using Icynene for an airtight home. Possibly going mini-split for zoning and no duct work. However, I am concerned with ventilation. With all of the exhaust fans (2 bathroom, kitchen, dryer, central vac, fireplace and hot water heater) it seems I will end up with negative air pressure.

    Can an EVR balance air flow with this much exhaust?
    Is there a way to provide just a fresh air intake (w/ energy recovery) and use programmable exhaust ventilation (Airetrak)?
    Should I go with a traditional ducted ac and connect the EVR to it?

    Thanks in advance.





  2. #2
    Join Date
    Sep 2002
    Posts
    3,708
    Erv or hrv comes in all different sizes.If you design for all bath fan,ranges and fireplace then yes you will and can
    find a system that can meet your needs,along with fresh air
    requirement as well.

    Erv or not recommended where temperture falls below 25 degree for more then five days.If this is you,then you will
    need a hrv.

    As with any duct system it need to be design properly in order for system to operate at it maximum efficiency.

    And yes you could pipe the fresh air into your system but,I
    would drop some fresh air vents into the living space and keep it seperate from the ac system all together.

    Check this site if you have any more question.

    http://www.lifebreath.com


  3. #3
    Join Date
    Jan 2005
    Posts
    21
    Thanks simple

    We don't usually have a week straight of below 25 degrees here in CT. Of course, it was about 5 degrees this morning.

    Is it true that an HRV can contribute to an overly dry house in the winter, where as an ERV will help level humidity year round?

    Do ERV/HRV have an equal intake and exhaust flow rate? If so, then I would think the house would continually have a negative pressure.

    How do you achieve a positively pressurized house?

    Sorry for all the questions. I just feel the need to be informed and somewhat intelligent when talking to contractors.

  4. #4
    Join Date
    Sep 2002
    Posts
    3,708
    Good morning Fins.

    Hrv,not sure how to anwser that question because i have no experience with them.
    But what I read about them is the hrv is a machine that only recover sensible heat.So yes I would have to say if its bring cold outside air in and only recovering the sensible then it has to make the home dryer.

    Erv,because of its enthalpic core is able to recover both,
    sensible heat and latent heat.

    The fan can only put out what it takes in,so yes would be
    the anwser to your second question,I think,but then again no
    experience with an hrv.

    By bringing in outside air,all tho I'm lost here at times
    because one would assume if there no where for the air to leave then the pressure would have to equalize inside the
    envelope.

    May get lucky and get one of our envelope expert to chime in
    on that issue.

    Being inform is a good thing! Thanks for asking.




  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,449
    Originally posted by finhead

    I am currently designing a new ranch (cathedral ceiling front to back and I-joist floors making duct work difficult) with radiant in floor heating. Possibly using Icynene for an airtight home. Possibly going mini-split for zoning and no duct work. However, I am concerned with ventilation. With all of the exhaust fans (2 bathroom, kitchen, dryer, central vac, fireplace and hot water heater) it seems I will end up with negative air pressure.

    Can an EVR balance air flow with this much exhaust?
    Is there a way to provide just a fresh air intake (w/ energy recovery) and use programmable exhaust ventilation (Airetrak)?
    Should I go with a traditional ducted ac and connect the EVR to it?
    Suggest you chechout the ventilating dehumidifier for make-up air ventilation and summer humidity control. With all the exhaust devices you mention, providing 50 cfm of make-up air when your home is occupied purges indoor pollutants, replaces oxygen, and helps exhaust devices to function. In addition, the ventilating dehumidifier is capable of keeping your below 50% RH regardless of the style or load on the a/c. Humidity control is important with high humidity summer ventilation and low cooling load. Keeping the indoor %RH below 50% eliminates mold potiential in the basement and dust mites in the home. When no exhaust devices are operating, the 50 cfm will leak out through exhaust devices. Several makes of ventilating dehumidifiers are available. I peddle Ultra-Aire made by Therma-Stor which is available from most major brand contractors.

  6. #6
    Join Date
    Apr 2002
    Posts
    11,808
    In a northern climate and with a tight home I would suspect that humidity will be primarily a winter problem for you.

    The HRVs and ERVs are designed to give you adequate fresh air and they will keep humidity levels down in the winter to avoid window condensation.

    You could duct them to give you some fresh supply air in each bedroom and perhaps in the common living area.

    It is hard to make a recommendation without actually seeing the plans, however an HRV would be most suited to your climate.

    I would duct fresh air from an HRV to each bedroom as well as one up high in the main living area if possible.

    I would not have the supply air blow at the beds.

    You can get an inline electric heater with an SCR control that you can set to temper the fresh air from the 45 to 50 degree supply temp in the dead of winter up to room temperature. If you had baseboard radiators you could probably eliminate the electric heaters, but you are going radiant floor.

    The HRV will have nothing to do with the intermittent bathroom exhaust fans, do not worry about this. The house is going to be naturally negative in the winter.

    You seem to think you need a large make-up air system to counter all the exhaust in your home, this is not the case.

    IMHO, woodburning fireplaces do not belong in a modern home, but if you use one there must be some direct vent type out there, and you could probably find out in the fireplace forum. Gas fireplaces are available as direct vent. Direct vent means they have there own sealed combustion air intake/exhaust system.

    As I think we discussed before Jenn Aires may need a dedicated make up air system.

    Dryer and Central vac, unless there is a radon problem I would not be too worried about them either, however you could possibly tie this in to the make up system for the Jenn Aire.

    The water heater will need a combustion air syatem.

    I don't think in your climate that you will need a dehumidifier with the small ductless splits.

    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/

  7. #7
    Join Date
    Jan 2005
    Posts
    21
    Thanks guys for the input. I do appreciate you can't make specific recommendations based on the limited knowledge of plans. Did not mean to imply I was asking for one. This has been one hell of an education for me.

    It appears I have been over thinking the exhaust spot ventilation. I can appreciate how a wood burning fire place is not appropriate in a highly efficient house, however, I really like them, and more importantly so does the wifey.

    I do plan on ducting fresh air to all rooms. Open floor plan. The ERV is being considered as it will help with humidity in both summer and winter. When I contact local contractors, I will be getting recommendations from them.

    Bottom line is, as long as I ventilate and provide fresh air, my spot ventialtion should not be an issue. Now to figure out the best way to do this.

    Thanks, Fin

    Life is a lesson, you learn it when you're through.

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