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Discussion Forum

Solving the make-up air problem

Damien Stokholm | Posted in General Discussion on September 17, 2007 05:09am

I currently have an HRV and hate it. I mean, I like that we get fresh air circulating, but it doesn’t keep up with the humidity, and it doesn’t get rid of the SMELL in bathrooms!

I’m designing a new house for my family, and I am re-thinking the whole topic of ventilation. I live in northern Ontario Canada (cold in winter), and tight houses need thoughtfull ventilation. I’m planning to have radiant floor heat, so no ductwork.

My latest theory is to go back to high quality exhasut fans in baths and kitchen, but provide for make-up air. I am thinking of putting a duct into my mechanical room with a warming coil to temper the cold air. I also want to put a fan on this to draw air in. This is my dilemma: How do I make this fan come on whenever any exhaust fan is on?

Could I put all the fans on one circuit, with the neutral feeding the Make-up air fan – would this work? Or maybe the neutral could power a relay that in turn would power the make-up fan. I’m assuming the neutral has some power whenever the curcuit is complete (fan running).

Any sparkys listening?

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  1. User avater
    McDesign | Sep 17, 2007 05:15pm | #1

    Just went to a building seminar.  Their HVAC recommendation was to have a small spring-loaded damper connecting the intake side of the air handler to the outside.  House (tight one) will pressurize slightly; normal leakage will take care of exhausting the air.

    The problem with an HRV in a humid or mixed-humid climate seems to be that the energy needed to de-humidify (too much) incoming air is greater than the energy needed to cool it.

    Adjust your intake damper spring to get the desired outside air intake.

    Forrest - repeating what I learned

    1. homedesign | Sep 18, 2007 12:25am | #4

      Forrest,

      nice tip ...that sounds very interesting

      what kind of building seminar was it? do they have a website with any links?

      I'm glad people are talkin about this ventilation thing and humidity

      when an exhaust fan comes on that air has to come from somewhere... and we need to figure out where somewhere is.

      John B

      1. User avater
        McDesign | Sep 18, 2007 02:23am | #5

        It was actually an ICF seminar, but they had a short module on HVAC for the resulting "really tight" houses.

        PolySteel is the company.  Don't know that their site specifically addresses HVAC.

        Forrest

        1. User avater
          shelternerd | Sep 18, 2007 03:59am | #6

          We've been planning to use poly steel as an insulated slab edge for two radiant slab jobs we have coming up this year. Great local sales guy. I'll need to get in on that seminar next time it's offered. Thanks for spreading the word. They sure seem to be the most termite resistant ICF on the market. m------------------

          "You cannot work hard enough to make up for a sloppy estimate."

    2. Damien Stokholm | Sep 18, 2007 04:40am | #9

      I don't understand how the house pressurizes with a passive damper like you mentioned. Is this somehow because a furnace draws more than it pushes? At anyrate, I won't have an airhandler with the radiant floor heat, so it's kind of moot. I need to come-up with a low-tech/high-tech solution... I think a powered intake is the ticket.

  2. formula1 | Sep 17, 2007 05:47pm | #2

    Yes, the neutral carries current when the circuits are operating, but its best (required) to wire controls on the black side and let the neutral be the neutral.

    If you wire all the bath fans on one circuit, you could place an Aprilaire 50 current sense relay on the black wire feeding them to actuate the coil on a 24V relay/contactor giving you a set of contacts that close when any bath fan is on. This contact could then turn your ventilation system on.

    Current sense relays are neat little devices that can tell when power is flowing (without contacting the actual electrical circuit) by the magnetic field around the wire. They're nice to use when you've got low voltage controls, like in HVAC applications, and for safety's sake you don't want to mix the voltages. But, there's no reason you can't be creative and apply them elsewhere.

    Your existing furnace transformer may have enough extra capacity to run the combination of the above sense relay and extra contactor. Otherwise, wire a separate 24V transformer to power it, or they make an Aprilaire 51 current sense relay which is a 120V version. Other copycat brands are also available. I've bought them on eBay for as little as $10 or so.

    The specs. are listed as 4 amps minimum current to actuate the sense relay. Your fans may well be below this. Just wind extra loops of the black supply wire through the current sense loop to gain sensitivity and drop this requirement - 2 loops drops it to 2 Amps, 3 loops 1 1/3 Amps, 4 loops, 1 Amp, etc. (My relay actuates on two 150 watt flood lamps - equaling 2.5 Amps, so there is some leeway in the specs.)

    http://www.amazon.com/Aprilaire-24V-Sensing-Relay-50/dp/B000K1BDIC/ref=pd_bxgy_k_img_b/002-6423815-4176067

     



    Edited 9/17/2007 10:56 am ET by formula1

    1. Damien Stokholm | Sep 18, 2007 04:35am | #8

      Thanks for your thorough knowledge - as I mentioned, I wondered if a relay would help, but I didn't understand them well enough to tell if multiple switches would work. I will definitely look into those models.

      Edited 9/17/2007 9:41 pm ET by Damien Stokholm

  3. frenchy | Sep 17, 2007 07:08pm | #3

    Damien Stokholm,

      You make an extremely interesting point..  MY issue is that HRV can't provide enough humidity.  I need to supliment it with a humidifier and that seems to cause issues with the HRV..

     Can you give me details about your issue?  Do you have a humidifier?, a lot of plants?  Take a lot of showers?  I assume that you have a tight home?  How did you achieve that tightness?   

     I'm wondering if mine is oversized, undersized for my application..  

    1. Damien Stokholm | Sep 18, 2007 04:32am | #7

      Frenchy, my problem seems to be that the house is so tight, that the humidity has nowhere to go. I asked my hvac guy to upstep the size of the hrv, I assume he did, but it didn't work. When it is really cold (-25 - -30c) the weak spots in the envelope are tell tale. Sometimes my insulated metal front door gets so much frost at the edge that it freezes shut! My door latch assembly also condensates to the point of freezing. I have three layers (two I installed) of weatherstriping on this door!But to be honest, humidity is only one issue - I also want to address the issue of kitchen exhaust and bathroom odours, while making-up the air.

      1. rich1 | Sep 18, 2007 05:32am | #10

        You need someone to look at your system.  If you are getting frost it's either a design or installation issue.  Was it ever balanced with a magnehelic?

      2. homedesign | Sep 18, 2007 01:24pm | #11

        Sometimes my insulated metal front door gets so much frost at the edge that it freezes shut! My door latch assembly also condensates to the point of freezing.

        Damien, I am not from  a cold climate...so beware

        How do you know you have a humdity problem? Do you measure it?

        It sounds like you have an indoor air quality problem in your bathrooms.

        Why don't you get a wood door or thermally broken door.

        If you have condensation ..you must have a cool surface.

        There must be ways to keep the toublesome surfaces warmer.

        What other areas of your house show signs of trouble?

        Edited 9/18/2007 9:19 am by homedesign

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