Hi all,
My first post so be kind ;-)

I'll be building a 20x28 2 storey ICF in the Maritimes [Canada] on an R20 slab with R60 in the attic and have a question re anyone's experience with the air being *too dry* in the winter...my HVAC guy is suggesting I go with an ERV rather than an HRV because he's finding passive solar ICF homes in our area are too dry in the winter.

This is the opposite of what I was expecting so I'm hoping to learn from others' experiences ;-)  I have extreme sensitivities so IAQ is critical for me.

I've been looking at the Venmar EKO 1.5; he's suggesting the Duo 1.2 instead. I'd appreciate comments on people's experiences with either of those as well?

Help?!

And thanks in advance.
AR

Posted By aggirose on 15 Feb 2012 03:48 PM
Hi all,
My first post so be kind ;-)

I'll be building a 20x28 2 storey ICF in the Maritimes [Canada] on an R20 slab with R60 in the attic and have a question re anyone's experience with the air being *too dry* in the winter...my HVAC guy is suggesting I go with an ERV rather than an HRV because he's finding passive solar ICF homes in our area are too dry in the winter.

This is the opposite of what I was expecting so I'm hoping to learn from others' experiences ;-)  I have extreme sensitivities so IAQ is critical for me.

I've been looking at the Venmar EKO 1.5; he's suggesting the Duo 1.2 instead. I'd appreciate comments on people's experiences with either of those as well?

Help?!

And thanks in advance.
AR

Interior winter air that is "too dry" is a symptom of a number of factors, the primary being too high a ventilation rate. In houses that have not been detailed for air tightness the minimum ventilation rate is outside of your control- it's whatever infiltration rates happen from wind and stack effect forces. ICF homes are comparatively easy to air-seal compared to timber-frames, but it doesn't happen all by itself.  It's easiest and best when a continuous 360 degree primary air barrier is defined in the construction drawings, and are followed meticulously during construction.  With ICF the walls are inherently air-tight, but the windows/doors/ceilings are not, and will need detailing to become part of the continuous air barrier that would also include those tight concrete walls.

The definition of "how tight is tight enough" varies, but the Canadian R-2000 spec calls out 1.5 air exchanges per hour max at 50 pascals pressure (ACH/50), as measured with a calibrated blower door.  PassiveHouse calls out 0.6 ACH/50.  In practice it's tough to retrofit to that level, but meeting R-2000 tightness levels aren't too difficult to meet if you're planning for it during design and construction.

If you can make it R-2000 tight you can control the wintertime interior humidity by raising and lowering the ventilation rates.  An ERV would allow you higher ventilation rates than you could go with HRV without drying it out too much, but it's not a huge distinction.  In non-smoking families either would provide enough ventilation for healthy air, but with multiple smokers indoors you'd probably need to run higher ventilation rates and add humidity with a humidifier (not ideal.)

If the occupancy rate of the house is low (say a 2 person family both of whom work outside the home and are gone 12 out of every 24 hours) not much moisture is being emitted into the house, and the ventilation rates would have to be quite low to not dry out the house.

In a tight house the ERV/HRV question is more relevant in the summer, in climates where the outdoor dew points are higher than would be most-comfortable or healthy as indoor air.   In massive well insulated homes the sensible cooling loads are practically non-existent in the maritimes, and air conditioning for sensible cooling may not be needed at all.  Outdoor dew points of over 15C are pretty common in NB  & NS in July/August, sometimes exceeding 20C.  While this isn't a HUGE latent load to be handled by a dehumidifier,  it does mean that there will be days/weeks where you can't dry out the interior by increasing the ventilation rate.  But the average dew points are low enough that there's no "payback" on installing ERV to cut that latent load down- simply lowering the ventilation rate and running a dehumidifier during the few sticky days would be enough.  )Most of the time a night-time ventilation strategy such as opening the windows for sensible-cooling would work without introducing more moisture into the house.)

Since the cores of ERVs are more readily damaged by frost  it's probably better to just build tight and not overventilate in winter and instead go with HRV in your location.  Most of the year your ventilation rates can be VERY high without overdrying, but December-March you might have to back it off a bit, particularly during cold-snaps.

Thx Dana.

I'm trying to make this an as close-to-Passiv-house as I can, given the constraints of being in an area where unfortunately there are few people who understand what that's about and even fewer options re who you work with! Having said that my ICF guy does understand - better than most at least, although we've already had a disagreement over my wish/efforts to not have electric outlets on the outside walls; he figures it's not enough of a break to matter but I figure the little bits add up. Raceway or floor boxes are an easy fix for the few outlets which couldn't be located on interior walls; needed only to meet code requirements not because they will actually ever be used! We still have to discuss the window bucks - I'm hoping he's used to Nudura's newer proprietary bucks and won't dig in his heels about using 2xs as is the norm here. I'll have a blower door test done as soon as it makes sense, just to be sure any additional sealing can be done before we get too far along ;-) The upper ceiling joists will sit inside the ICF so that will help re sealing at the ceiling/roof intersection, plus I'm being adamant about no penetrations through the upper ceiling other than the requisite stack vent. [It helps that I'm actually designing the house - my third one - so I at least don't have an uninformed architect to fight with ;-) ]

Anywaaay, from my conversation with the ventilation guy, it seems it's a too dry in winter issue [I concur re the best way to deal with our summers here is to open the windows at night! It's a 2 storey house - technically a gambrel with southfacing shed over 1 storey - so the upper windows and cross-ventilation will help. ]

The ventilation guy seemed to be blaming it on too much sun drying the air but I assured him my window/floor area ratio is within recommended levels at just a smidge over 9%. And the way our climate is changing we actually get less sun in the winter than even a few years ago. I could reduce the windows a tad but I have a strong need for light and I think it strikes a good balance as is.

I'm a bit concerned he may be inclined to over-ventilate. Might that be a problem because of the building code requirements, which I've read are based on a worst case scenario re occupant behaviour, VOC levels etc? My intention is that the house will have as close to nil levels of VOCs as I can make it [easier for me because I can't be anywhere near products or materials that off-gas, including the often overlooked fragranced personal care & cleaning products]. No smokers allowed and shoes off in the vestibule makes it easier too!

If he is over-ventilating it would make sense the indoor air would be too dry as our outdoor air certainly is dry in the winter.

Venmar seems to be saying their ERVs are fine in cold climates but I *really* would be happier with an HRV re energy use, efficiency & life expectancy so I'm glad to know you're thinking that's the better way to go.

Are you familiar with the EKO1.5 and if so, does it allow the homeowner to adjust the rates fairly easily? It seemed to me that it is more user friendly than some other ones I was looking at and I have a feeling I may need to be able to fine-tune the system for my own needs, rather than rely on the standard code rates.

Thx again for your assistance - much appreciated!
AR

oops - that should read "upper floor/ceiling joists will sit inside the ICF"...

You say you are in the Maritimes, I've just built an ICF passive solar with an HRV dual core Lifebreath.

I have built in southern NB if you're nearby could dicuss some of the issues I went through.

That would be great! I'll send a pm so we can connect.
AR

If you're really taking it to PassiveHouse levels of air-tightness, wintertime air dryness is NOT going a problem unless you OVER ventilate, which is completely within your control.

There is no such thing as "...sun drying the air...". You can have as much or as little passive solar as you like, it doesn't change a thing, since heating or cooling air does not change it's moisture content. The dew point (=absolute humidity) will remain constant, even though the RELATIVE humidity changes. Unless you're replacing the volume of air with drier outdoor air, moisture will build up inside the house from all of that bathing /cooking/breathing behaviours of the occupants. Putting the HRV under dehumidistat control you can pretty much "set and forget", the interior RH will never drop below the dehumidistat setting in a 0.6ACH/50 PassiveHouse, and in a low/no VOC house with no smokers etc that is a perfectly safe thing to do from an indoor air quality point of view. This is quite different from a house that tests at 7ACH/50, (the maximum leakage spec under IRC2009, and tighter than most homes in North America), which probably WILL leak enough air for the interior just from stack effect driven infiltration to drop below 30%RH @ 20C during the coldest periods.

The initial humidity in an ICF house will be a bit on the high side due to the (necessary for proper curing) excess water in the concrete, but that falls to background in under a year.

Yeah, I suspect it's a combination of he's over-ventilating and the houses he's talking about are not as tight as they could/should be. May also be a case of 2 people in a McMansion - as most of the ICFs here are - will have less of an impact on the humidity levels than 2 people in a sensible 1000 sq ft house ;-)

Anyway, I've asked him to quote me for a EKO 1.5 ERV just to keep him happy at this point but I'm quite sure I'll end up going with the EKO 1.5 HRV. Apparently it's an easy switch out if I later find I do need to have an ERV instead of HRV - can't see that happening though. I expect I'll be having the blower door test done before he installs the ventilation equipment so that may tell the story.

I also spoke to one of my sisters who lives in an ICF house [not passivhouse] and she says if/when they turn off their ventilation system the humidity does go up too high [as I'd expect] so there definitely is no issue of dryness for her. [Apparently they turn it off sometimes because of the draft from it so I suspect it's over-ventilating. I'm younger than she is though so I'm biting my tongue on that one;-)]

Thanks again. I'm learning a *lot* from this forum - it's a wonderful resource!
AR

I installed an UltimateAir 200DX ERV in a 2000 sq ft ICF house in SW Idaho. The winter RH outdoors is on the order of 20%. Indoor RH stays around 35 to 40%. The ERV runs on a timer at slow speed for 20 minutes every 2 hours. That's the lowest cycle setting on the controller and the speed is near the bottom. Air stays comfortable all the time, winter and summer. I chose the 200DX as it was the only one I could find that had a provision to turn off the exchange wheel and allow straight air exchange. I have it connected to a thermostat to bring in cold night air to help in cooling the house during the summer. My ERV serves as a year round whole house ventilator, bathroom, utility room, and kitchen (not hood) exhaust fan, and summer cool night air supply fan.

Posted By dmaceld on 17 Feb 2012 05:22 PM
I installed an UltimateAir 200DX ERV in a 2000 sq ft ICF house in SW Idaho. The winter RH outdoors is on the order of 20%. Indoor RH stays around 35 to 40%. The ERV runs on a timer at slow speed for 20 minutes every 2 hours. That's the lowest cycle setting on the controller and the speed is near the bottom. Air stays comfortable all the time, winter and summer. I chose the 200DX as it was the only one I could find that had a provision to turn off the exchange wheel and allow straight air exchange. I have it connected to a thermostat to bring in cold night air to help in cooling the house during the summer. My ERV serves as a year round whole house ventilator, bathroom, utility room, and kitchen (not hood) exhaust fan, and summer cool night air supply fan.

So do you NOT have a kitchen hood exhaust fan? How about bathroom vents?

When you turn off the exchange wheel and allow straight air exchange, is that air filtered?

Posted By Lbear on 18 Feb 2012 12:01 AM

So do you NOT have a kitchen hood exhaust fan? How about bathroom vents?

When you turn off the exchange wheel and allow straight air exchange, is that air filtered?

Yes, I do have a hood over the cooktop. Code requires a lot more for exhaust there than what a ventilator would do, plus you don't want cooking air going through the ventilator. There is a duct from the kitchen ceiling to the ventilator to pull out kitchen odors and aromas as part of the normal ventilator operation. I don't have a switch for the ventilator in the kitchen. Same thing for the utility room. The ventilator serves as the bathroom exhaust. I have two switches in each bathroom, a timer and a humidistat. The humidistat in the master bath does turn on the ventilator for a few minutes after a shower. The timer switch is used when it's prudent to exhaust the bathroom air.

I suppose other brands of ventilators allow for multiple switches, but the 200DX makes it easy. The switches above all tie into the "boost" mode of the ventilator, which means it gets turned on at full speed. There are two controllers in the hallway. One is the cycle controller. The other is an on/off switch with speed control. The cycle controller runs the ventilator at the speed that the speed control is set at.

I made a minor custom modification in that I installed a mechanical thermostat in the inlet side of the ventilator that is connected in series with the hall cooling thermostat. What this does is it prevents the ventilator from going into its "Economy" mode if the incoming air is warmer than the house air.  The Economy mode is the one where the wheel stops and the fresh air in does not exchange heat with the exhaust air.

The heat exchange wheel is the filter, so yes, the air is filtered even when the wheel is off. Plus there is a flat mesh filter in each air streams.

The ventilator pulls exhaust air from five points, the two bathrooms, the utility room, the kitchen, and the attic. The attic is the return air duct for my heating/cooling system. A duct then goes down from the attic to the air handler which is in the crawl space. The fresh air that comes in through the ventilator is dumped into the return air duct that goes to the air handler. The air handler fan runs constantly at low speed.

In case you've not seen my descriptions in other posts, I have an air to air Daikin heat pump with the indoor unit in the crawl space. I use the crawl space as my supply duct and air is circulating all the time through the house. Heat registers are all around the perimeter and just open into the crawl space. Return grills are scattered all around in the ceiling around the perimeter of the house and open up into the attic.