Posted By arkie6 on 27 Sep 2014 10:40 AM

But it really does factor in.

Correct. The interior 2.5" of insulation doesn't make the concrete thermal mass effect go to zero. There is a very viable thermal mass benefit to the ICF wall. Is may not be as high as some claim but it's also not as low as some detractors claim. It falls somewhere in the middle. Climate and diurnal swings make a huge factor in determining on how the thermal mass of ICF walls will play out in your home.

The studies done show areas that experience vast diurnal swings see the greatest benefit. Dry/desert climates or those in high elevations see the biggest gains with ICF walls.

My solution to the problem noted in this thread is to LEAVE THE WINDOWS OPEN all night until sunrise. This will cool the home and the thermal mass will get a chance to drop down in temp by morning. Closing the windows at night is limiting the stack effect and how it interacts with the thermal mass. The interior air temp will initially drop by bedtime but the ICF wall is still putting out heat all night until morning sunrise. Closing the windows at nighttime will make the interior temp heat up once again by morning.

I understand that leaving windows open at night while you sleep in a single story ranch is not always feasible due to an intruder. Ideally, this is where 2-story homes, homes in rural areas, and tilt & turn windows have an advantage. One can leave the 2nd floor windows open without fear of someone crawling through the window. One can leave the T&T window in the "tilt" position and let fresh air/stack effect take place all night without fear of someone coming in. In the morning one could close up the windows and the thermal mass will prevent the home from overheating during the day. This is repeated daily and requires the homeowner to be "active" and of course is not meant for humid climates that have high dew points since the stack effect wouldn't help if the humidity is high all day and night. That requires an A/C that removes interior moisture.

The interior 2.5" of insulation doesn't make the concrete thermal mass effect go to zero.

Correct, just very close to zero for the small temperature deltas involved in the "open windows, how long to cool down" situation. On the other hand, drywall (and everything else in the room) makes a big difference when you are trying to heat/cool a room with modest amounts of low delta-T airflow. Not to mention the radiant effects on comfort (MRT). When I come back from vacation, it takes about 12 hours before my house is fully comfortable, even though the furnace can achieve the right air temperature in minutes.

If you use the calculator, you will find that opening more windows typically has greater flow than preserving the stack effect by only opening low and high ones. Even more so if there is any wind. So open all the windows if you want a rapid effect.

I'd be fine leaving the windows open all night, but at 54 degrees outside, 'management' said it was too cold to leave them open. I say, that's what blankets are for. We're out in the country, and most of our windows aren't accessible from the ground due to the sloping topography. This is my first house with casement windows, and you can really catch the wind if you open the right ones.

Right, stack effect and opening/closing windows will get the job done, but as we previously recommended:

“We prefer and we always recommend active ventilation cooling accomplished by using an ERV/HRV system even when we can take full advantage of passive solar cooling stack effect. While we have successfully designed automated window opening/closing systems and automated drape opening/closing systems at the specific request of clients, it is really hard to beat the operational simplicity of an autonomous ERV/HRV system and a properly designed passive solar roof overhang. The energy usage and associated cost of operating an ERV/HRV system the small amount of time that is necessary to actually cool a building in a diurnal temperature, low humidity climate is negligible. Furthermore, high performance buildings will require active ventilation anyhow and these buildings will preferably use an energy efficient ERV/HRV system to accomplish this.”

This autonomous active ventilation cooling strategy avoids any security issue, ensures that the house will not get colder during night time than is desired, and ensures lowering the interior thermal mass temp the required amount to ensure it will provide the required daytime cooling effect when the sun and higher outdoor temps return. Again, this cooling strategy only works very well for cooling high performance homes in low humidity climates that have a significant diurnal temperature variation. If you do not have a high performance house or you are located where you don’t have this climate situation, you will need a different cooling strategy as previously recommended.

I use it to flush the home of heat during the inevitable overheating you can get with passive solar. But, I'm sure every home has this condition at times. Because we are talking about a volume far larger than a ventilation system can move and because there is no energy cost to it, it seems like a good strategy to use in the shoulder season before you need to go to A/C. Doesn't this have widespread usage potential?

I am not sure I am following your train of thought ICF? This discussion was about avoiding the need for any AC during the hot summer time months. Are you saying the CFM of your ventilation system can’t keep up with your passive solar heat gain at times and you are opening windows to take advantage of a stronger CFM stack effect to deal with this? It is always preferable to not allow the passive solar heat gain to exceed the heat loss of the building. Presumably you would use you passive solar roof overhang (and perhaps additional moveable solar shading devices if necessary) and your thermal mass system (either passive thermal mass or preferably active hydronic thermal mass) to address this before using any significant ventilation or AC.

This discussion was about avoiding the need for any AC during the hot summer time months.

I'm sure there is always a time some places when A/C is needed during the middle of the cooling season. But, even in those places, there must a be a shoulder season where it may or may not be needed. That is the time for alternative cooling methods, particularly when there is no energy cost.

It is always preferable to not allow the passive solar heat gain to exceed the heat loss of the building

We allowed a larger amount of solar gain in order to extend the number of days in the heating season that solar can cover the heating needs. That means we needed to have a ventilation system that could handle the inevitable overheats towards the end of summer.

Presumably you would use you passive solar roof overhang (and perhaps additional moveable solar shading devices if necessary

That is correct, but, nevertheless, there are peak days. We had more days over 80F this year than in the last four years combined. I did plan for shades on the West, but the company who took the deposit went out of business without delivering product and I've been too busy to get another source. So far, the low westerly sun hasn't really been the primary source of the overheating.

Yes, this has been one of the most glorious NW summers that I can recall. We have had many days over 100F in Rogue River, OR and we have done fine without AC by taking full advantage of our dry diurnal climate.  As I know you already know ICF, there are three strategies that often get invoked when designing passive solar buildings. Just so anyone who happens to read this better understands, I pasted an excerpt from our passive solar altitude angle software instructions below:

"If you will be using standard height passive solar fenestration (e.g., passive solar fenestration that is between 4 to 6 feet in height) and locating passive solar fenestration in the wall as is typically done (e.g., having the bottom of the passive solar fenestration 2 feet above the floor), there are three options to address this issue. First, in climates that require very little winter heating, the best solution is to design the passive roof overhang to provide mostly full shade to the passive solar fenestration during the Spring Equinox and Fall Equinox dates and restrict significant solar heat gain to only occur during the two months centered on the Winter Solstice (December 21st). Second, in climates that require considerable winter heating, the best solution is to design the passive solar roof overhang to provide mostly full sun to the passive solar fenestration during the Spring Equinox and Fall Equinox dates and plan to use moveable shades during late Summer and early Fall to prevent overheating. Third, in climates that are between the first and second condition, the best solution is to design the passive solar roof overhang to provide about 50% solar exposure to the passive solar fenestration during the Spring Equinox and Fall Equinox dates. This third compromise solution may sacrifice some solar heat in March when it may be desired and may also require the use of moveable shades during September to prevent overheating.

If you are willing deviate from only using standard height passive solar fenestration (e.g., passive solar fenestration that is between 4 to 6 feet in height) and only locating passive solar fenestration in the wall as is typically done (e.g., having the bottom of the passive solar fenestration 2 feet above the floor), there is another option called Winter Passive Solar Fenestration that will only provide the required heat gain during the desired winter months. Winter Passive Solar Fenestration is accomplished by using reduced height fenestration (e.g., perhaps 2 feet in height) and locating this fenestration in the wall up near the ceiling. While Winter Passive Solar Fenestration does not allow direct line of sight for building occupants, Winter Passive Solar Fenestration does still provide valuable daylighting. More importantly, Winter Passive Solar Fenestration can be designed so as to only provide the required heat gain during the desired winter months without providing any heat gain during the spring, summer, and fall months."

ICF, it sounds like you went with either the second or the third aforementioned passive solar design strategy. As such, you should certainly pursue moveable shades. Please also keep in mind that moveable shades can be vegetation that grows leaves and loses leaves at the right time. You will suffer a slight performance loss when using vegetation as your moveable shade approach because even without leaves, the vegetation branches will cause you to lose some irradiance when all of it is desired. However, this may be a worthwhile tradeoff in some circumstances to avoid the additional time, effort, and expense associated with using manual moveable shades.

Our 1900 SF, single-story ICF, single-bedroom, ranch style home in Rogue River, OR doesn’t have any windows on the west side (which is a master bedroom/bathroom wall).  The east side (which is a screened porch and utility/dining room wall) only has the east side of a corner dining room window (because of our mountain and stream/waterfall view). There are very few windows on the north side. Nearly all the windows are on the south side where there is a hydronic floor zone dedicated to keeping this solar exposed thermal mass temp where it needs to be by moving or rejecting any excess captured solar heat as required.  Our passive solar roof overhang is nearly 4.5'.  During the Spring Equinox and Fall Equinox, our passive solar fenestration receives 55% solar exposure.  So our home is of the third passive solar design strategy.  I should also mention that we have detached guest quarters in our garage/shop building which is only heated when we actually have guests, which is typically only in the Spring, Summer and Fall months.  And as my husband says, the garage/shop is significantly larger than the house which is as it must be...

There is no question that if you go with either the second or the third aforementioned passive solar design strategy, that you will eventually encounter a situation that will require dealing with more solar heat gain than the normal building heat loss will handle. In fact, even the first passive solar design strategy isn’t 100% risk free…it seems like we often get a couple days of +70F in February! So your only options for dealing with this are to provide moveable shades, increased ventilation, active hydronic thermal mass capability, or some combination of all of these mitigation strategies.

Random Q, say you have a high performance house, with animal dander in the air (due to pets), would an ERV/HRV's likely recycle the air and make it healthy? Opinion?

Posted By James02 on 02 Oct 2014 01:10 PM
Random Q, say you have a high performance house, with animal dander in the air (due to pets), would an ERV/HRV's likely recycle the air and make it healthy? Opinion?

That's what the air cleaner is for, but they have a tendency to make the blower motor work harder.

While increased ventilation may help, you will likely need to do more… A central vacuum system that exhausts everything outside would be one example of doing more. You will find some good recommendations here:

Asthma & Allergy Foundation of America Recommendations

Thanks sailaway and Jelly!!

Posted By patonbike on 21 Sep 2014 07:09 PM
Do people use whole house fans (like Tamtech HV1600) in high performance homes?  We live by ours in the summer here in central VT where it seems to dip into the 60s most summer nights.   I love a cold bedroom and lots of fresh Vermont air.   What I've found is that if I leave the downstairs windows and doors closed, and open windows/door upstairs, I can get the upstairs cold for sleeping while keeping the downstairs relatively warm which is comfortable when you wake up. 

But I don't know if it's needed in  a high performance home (R43 walls, R80 roof, etc.) with mini split.  I suppose you could turn on the A/C for a few minutes ?

The Tamtech  whole house fans best automatic doors are "only" R50. 

Alternatively could we possibly just run higher power Panasonic bathroom fans?  Those go up to 130CFM. Three of those would be 390CFM.  Two of them would be upstairs on a ~900 sq ft. level.

Have you looked at the Panasonic FV-40NLF1 in-line exhaust fan?  440 CFM.  8" duct. Quiet @ 2.1 sones.  130 Watts or 1.1 Amps @ 120 VAC.  Cost <$200 online.  Will also need a ceiling air grille approximately 14" x 14" plus an 8" backdraft damper.  This is what I'm planning on installing in my new ICF home. 

You can run it for 1 hour in the evening when the temperatures are cooler and do a complete air exchange in a 3000 sq ft home with 9' ceilings for less than a nickle (<$0.05) cost in electricity.

http://www.amazon.com/gp/product/B001BM1NUC/ref=ox_sc_act_title_5?ie=UTF8&psc=1&smid=A33PLCZAV8KG8V

Arkie, why have you decided to use exhaust ventilation in lieu of ERV/HRV, or will this be in addition to ERV/HRV?

The exhaust fan is in addition to an ERV, albeit a small one connected to HVAC supply and return ducts. I'm not sure how much the exhaust fan will be used, but it relatively easy and inexpensive to install it now (all DIY) while the house is under construction.

I also have fresh air intake pipes (2 x 4" dia.) routed around my basement backfill that will supply my mechanical room (average depth ~6', ~80' long, >1/4"/ft slope to intake). These are intended to supply make-up air for when the bathroom exhaust fans are run.