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  1. #1

    HRV with Dehumidifier and radiant floor heating

    Need some clarification on HRV and dehumidification on an atypical new residential construction.

    The new house is 3600 sqft split evenly between basement, first, and second floors. The house will be extremely tight and well insulated with SIP panels (e.g. R42 walls/roof, ICF basement walls, 6" rigid foam in the basement floor), so it doesn't require a lot of energy to heat or cool (25% of a standard sized home). The heat will be provided by radiant heating, and there are no plans for air conditioning. Therefore, there is no central air handler.

    However, since the house is so tight, an HRV with ductwork is mandatory.

    Even though the house is tight, there is nothing to prevent humidity from coming into the house; so it was assumed that a dehumidifier would be needed to take out some of the moisture in the humid summers. A portable unit is not going to cut it, so is there some way to hook up the dehumidifier directly to the HRV, so that they share the same ductwork or should it just remain two distinct systems due to different air flow requirements and usage patterns?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,260
    Knowing the climate would help. Number of occupants and better description of the basement use. Is there a clothes drier, bath fans, and kitchen exhaust?
    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"

  3. #3
    Join Date
    Jul 2004
    Location
    Massachusetts
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    A very tight home has a number of issues with which to deal. First up is, as you've stated, humidity control. Absent any AC cooling, then you'd be well advised to have a whole house dehumidifier installed. The exact location of the humidifier ducts isn't as important as being sure the interior doors are not moisture tight. An HRV or ERV (depends on what weather you're designing) should be sized as appropriate to the blower door results achieved when your new home is tested for tightness. The third item is make-up air or air that's needed to account for air being exfiltrated from the home by clothes dryers, stove hood, bathroom exhaust fan or any other device that might be used to extract air. In a home as tight as you've described, I'll assume any fossil fuel combustion products are sealed combustion and bringing in their combustion directly from outdoors and not using house air. If you've got a fireplace, that to needs copious amounts of air when in use and until the damper is closed after use.
    If YOU want change, YOU have to first change.

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  4. #4

    Additional Info

    More info ... although the first occupants will only be two, we should probably assume this house could have 4 and possibly 6 occupants in its life on a regular basis.

    No clothes dryer currently planned, but, again, it is a standard feature and there is space for it, so the design should account for it.

    Climate is central Indiana, so cold winters (average 0-40 temps), hot/humid summers (a few weeks at 90+), wet Fall and Springs.

    Basement will initially be unfinished, but there is an egress window, and rough-in for plumbing, so eventually it'll be an extra bedroom, I'm sure.

    There are three bathroom exhaust fans planned, as well as a kitchen exhaust fan - however, the kitchen fan is just run through the charcoal filter and not truly exhausted.

    No plans for a fireplace, but I suspect if one were added later, they would need to bring make up air directly from the outside.

    No plans for internal combustible fuels either - the hot water will come from an electric boiler, natural gas is not even being run to the house - so cooktop and oven would be electric as well.

    Definitely agree with the 60-100 cfm and <50% RH - just figuring the best way to make that work.

    Hope that helps and thanks in advance

  5. #5
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Sounds like an open windows spring/summer/fall.
    I suggest a small HRV exhausting the main bath and kitchen space away from the hood. Bring the fresh air into the master bedroom and open part of the home. Get a good dehumidifier like a the Santa Fe Advance with a duct kit to draw air from the mainfloor and supply to the basement. This will keep the basement dry with the windows open or dry the whole house with the windows closed. Also suggest a minimum of through the walll a/c in the master bedroom or a mini split a/c for the main floor.
    I seldom suggest an HRV but with the electric heat and extremely air tight, a HRV may be warranted. It is important to have a quality dehumidifier with capacity to keep the home dry <50% RH when the windows are closed.
    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. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    I would vent the kitchen exhaust outside. I'd look at central ventilation as I mentioned tied to the HRV.

    No AC in central IN? OK. MAybe in a berm home which has natural earth cooling. But you talked about ICF's so that's eliminated. You're still looking at a good number of warm nights at or near 80F. With the HRV transferring 150CFM or so and the dehumidifer adding heat. That's going to be at least 3000BTU's. I think you'll be looking at 85F indoors temps without AC on warmer days. The average daily temp in summer I think is around 80F.

    R40 is still only R40. You'll have a heat gain of ar least 5000BTU's plus occupants and appliances. If you have a dozen guests over, you'll be amazed at how warm it will get.

    You're going to want at least 6-9k BTU of cooling I think. It's not a lot, but it will be well appreciated.


    I'm just curious why you think you won't need AC unless you've been in the same type of home with no AC on a 95F humid day around 5-6PM and were comfortable.

  7. #7

    Agreed the lack of air conditioning is a bit whack

    The lack of air conditioning is a bit whack, I know - but it's a personal preference more than anything and the way the house evolved.

    The house has been designed to make the house as comfortable as possible during summer (overhangs to limit solar gain, cross ventilating windows, whole house fan, reflecting metal roof, etc) - we even made the screen porch big enough for sleeping outside, but we know that we'll still have uncomfortable days in summer when day time temps reach 95 and the humidity is high. And all those tricks won't prevent the internal heat sources from warming up the house.

    For us the key is less about the daily high, but the nightly low ... if it cools off enough at night, it can cool the house before closing it up during the day - counterintuitive, I know, but those crazy Europeans having been using that trick for centuries.

    But even then, I'm not deluding myself into thinking a bit of cooling would be welcomed, but putting in a wall unit or mini-split is a whole lot different than going with the central air conditioner.

    Stay tuned, once the house is built and we've lived through an Indiana summer, I'll post the findings.

  8. #8
    As promised (20 months later), here is the update on our HVAC experiment

    It worked. You can comfortably live in a climate with 100+ degree summers and 80% humidity without an air conditioner. It just takes some thought and a little effort.

    The specifics of the final house that all made that possible
    PRODUCTS
    SIP R42 walls (from Thermocore)
    ICF Basement
    Whole House Dehumidifer
    Heat Recovery Ventilator (Venmar)
    Fiberglass double and triple pane windows (Fibertech)
    Silver metal roof (to reflect heat)
    Automatic skylights (Velux)
    BUILDING TECHNIQUES
    Rainscreen for the siding and roof (furring strips create a 1 gap from the house and siding to minimize radiant heat coming into the house.
    Windows tuned to let in heat during the winter, but not during the summer they were also strategically placed and their swings specified to catch prevailing winds.
    Blower door and infrared camera inspection test pre-drywall best $100 bucks I ever spent, since it showed us invisible air leakages. final test came back at .80.
    2500 gallon tank of water in the basement that acts as a thermal battery to minimize temperature swings
    Concrete floor it also acts like a thermal battery in winter and summer, and it always feels cooler to the feet.

    We did have a relatively mild summer for Indiana (only a few nights in the mid 80's and rarely over 95 during the day). But there were a few nights where we had to slow down and sit on the porch.

    But those days were fundamentally preferable to high air conditioning bills (both on install and monthly power). And that's just not the hippie talking ... if a 95 month is going to melt you, it is cheaper to just go on vacation up north (our electricity is really high)

    But basically the way the summer worked was if it was going to be below 75 at night, then we opened up some windows and closed them in the morning. We set up some wiring to automate this, but thats a future project. We then basically closed up the house during the day I know its not something were used to in the US, but this is basically how Europe gets through their summers without air conditioning.

    We also have a backup plan for cooling the house in summer we installed a radiant heating system, and we could easily enhance it to do radiant cooling. Of course, we still have to watch the dew point, but its an option. We were also holding off on the whole house fan (bigassfans.com) due to evaporation it makes you feel a bit cooler, but I dont know if a $2000 fan is worth it.

    As you can see there really wasnt one decision that made a no air-conditioned house in Indiana possible all kind of made their own contribution. and the little things (eg concrete floors, good windows to Catch a breeze) really add up

    I dont think were a bunch of hippies, were just cheap twits who dont care too much for air conditioning. Dont get me wrong, when its really hot and humid, its a godsend but having to take a sweater into a restaurant during the summer because the air conditioner is so low is just nuts.

  9. #9
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    6,260
    What kind of %RH you getting? Brand of whole house dehumidifier? Radient cooling sounds like an option. The dehu will keep the dew point below the radient cooling surface. A bed in the basement also sounds like a option. My basement is <70^F, <50%Rh with a whole house dehu and fresh air ventilation.
    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"

  10. #10
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    1,649
    I also wonder, if the house is just barely a little hot on the worst days, if using a dehumid that had a heat rejection option might be enough. Temp high and the dehumid turns into a small a/c, rejecting it's heat outside, instead of back into the air stream.

  11. #11
    Quote Originally Posted by teddy bear View Post
    What kind of %RH you getting? Brand of whole house dehumidifier? Radient cooling sounds like an option. The dehu will keep the dew point below the radient cooling surface. A bed in the basement also sounds like a option. My basement is <70^F, <50%Rh with a whole house dehu and fresh air ventilation.
    Regards TB
    %RH was <50% ... Santa Fe whole house dehumidifier (let me know if you're curious to model number, since I can't seem to find an old email or pic of it)... just set the bad boy to 50% and let her rip. Honestly, she wasn't on the much due to the mild summer. But I did what you said by pulling from the first floor and dumping it in the basement. Even with quite a few fish tanks and a 2500 gallon tank (albeit with a loose lid), the basement is as dry as a bone.

    All in all, we seldom used the dehumidifier due to the fact you really needed to plan on it being unbearably hot and humid for several days to really make it worthwhile and feel its effects - and we just didn't have that kind of summer. Even if the summer of 2012 returns (weeks easily over 100 during the day), I think we have enough tricks up our sleeve to make it bearable (in order of implementation ... fans, sleeping on the porch or basement, dehumidifier, radiant cooling, trip to Alaska).

    Heat from the dehumidifier probably won't be an issue ... we put it in a far corner in the basement, and it has to radiate through 3" of concrete to affect us on the first floor. Yes, it's extra BTU's in an enclosed space, but I don't see it being any worse than a stove or (worse) oven. Which reminds me of cooling strategy #423 ... we seldom used the oven in summer (preferring the grill and foods that don't require baking), but that was more because we just eat differently in summer anyway. It's always counterproductive, but the effects are more easily noticeable when the house is basically a coleman cooler.

    As an aside, it's really a shame that radiant heating hasn't taken off in the US and still remains relatively expensive (our first estimate was over $45K) ... I'll never go back to forced air after one winter alone with radiant floor heating. So I see us trying out the cooling just for curiosity (the additional cost is minor now). I wouldn't have made it my only solution though, since I'm not sure how effective radiant cooling would be since my water is stored in the basement already at 70 - I suppose it would be a way of getting the relatively cool environment in basement up to the first floor.

  12. #12
    Join Date
    Aug 2009
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    Quote Originally Posted by dwsmith1000 View Post
    Heat from the dehumidifier probably won't be an issue ... we put it in a far corner in the basement, and it has to radiate through 3" of concrete to affect us on the first floor. Yes, it's extra BTU's in an enclosed space, but I don't see it being any worse than a stove or (worse) oven. Which reminds me of cooling strategy #423 ... we seldom used the oven in summer (preferring the grill and foods that don't require baking), but that was more because we just eat differently in summer anyway. It's always counterproductive, but the effects are more easily noticeable when the house is basically a coleman cooler.
    I was not trying to imply the heat added by the dehumidifier was significant, but it is removing likely 4 times more heat from the evaporator than it is net generating in the space. If it did have the capability of switching to an external condenser, you could actually remove all those BTUs from the space - turning it into a conventional air conditioner (albeit, very small). The only downside, is that since it is currently discharging into the basement, that is where the cooling will go first.

    comparison:
    Dehumidification: 4 units of heat removed by evaporator - 5 units of heat produced at the condenser = 1 unit of heat added to the space
    Cooling: 4 units of heat removed by the evaporator - 5 units of heat discharged outdoors = 4 units of heat removed from the space

    both with the same electrical demand, and could be selected based on the needs of the current time (high humidity, low temperature - run in dehumid. high/low humidity, high temperature - run in cooling).

    Perhaps more of a discussion for the Building Science forum than AOP Residential - but I thought I might bring it up, as this is the key difference that needs to be considered when choosing between an air conditioned, and a dehumidifier (and personally, I feel the ideal would be a single piece of equipment that could correctly fulfil both roles).

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by CraziFuzzy View Post
    I was not trying to imply the heat added by the dehumidifier was significant, but it is removing likely 4 times more heat from the evaporator than it is net generating in the space. If it did have the capability of switching to an external condenser, you could actually remove all those BTUs from the space - turning it into a conventional air conditioner (albeit, very small). The only downside, is that since it is currently discharging into the basement, that is where the cooling will go first.

    comparison:
    Dehumidification: 4 units of heat removed by evaporator - 5 units of heat produced at the condenser = 1 unit of heat added to the space
    Cooling: 4 units of heat removed by the evaporator - 5 units of heat discharged outdoors = 4 units of heat removed from the space

    both with the same electrical demand, and could be selected based on the needs of the current time (high humidity, low temperature - run in dehumid. high/low humidity, high temperature - run in cooling).

    Perhaps more of a discussion for the Building Science forum than AOP Residential - but I thought I might bring it up, as this is the key difference that needs to be considered when choosing between an air conditioned, and a dehumidifier (and personally, I feel the ideal would be a single piece of equipment that could correctly fulfil both roles).
    I love it. Unfortunatly, unaffordable. Most of the time retaining the heat helps like in the case of the basement. We do make to dehu with a remote condensor, Ultra-Aire SD. To pricey for residiental application. A home like we are talking about may be better served by a small mini-split and a small dehumidifier?
    High efficiency dehumidifiers add less heat back to the home by a high %. The heat added back (Btus)is the( kwh used X 3414btus/kwh) plus (1055 btus X lbs. of moisture removed). Premium dehus add back +50% less btus.
    The battle of ideas goes on.
    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"

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