This passive solar stuff with ICF is amazing.  My new ICF build is holding 68F against overnight lows of 48F-51F with NO energy input other than the sun.  What's more is that the cold-designed areas, like the wine cellar, are holding 58F and they don't even have doors on, yet.

During the day, the place stays cool because of the sun/angle engineering and the mass.  Other places locally are running heat every night and morning and cooling during the latter part of the afternoon and evening.  Evven though temperatures have been cool with a marine layer persisting in the morning, the July sun comes out in force in the afternoon, smoking things up quickly.

Modest insulation, done right and attention to air sealing appears to be helping here.  I could even tell a difference, room by room, with the additional air sealing I did, once the insulators simply couldn't do any more.

You can imagine that I'm not overwhelmed at maintaining 68F overnight in JULY, eh? ;-)

What is your mean outdoor temp running? (The overnight lows are somewhat meaningless without the highs.)

The decent-R mass wall helps, but the air-sealing is still the best thing you've done to be able to take advantage of the available performance. Sounds like you've done a pretty good job on that front. Is there a blower-door test in your future to quantify it in cfm/50 or ACH/50 terms?

You can imagine that I'm not overwhelmed at maintaining 68F overnight in JULY, eh? ;-)

Worst "Summer" weather EVER this year. :-)

Daytime temps are getting to 72F but only after morning overcast burns off. I have a 10' X 12' hole covered with plastic for the front door and two other doors with about 3 square feet of hole between them. This is really pretty impressive. Everyone else is still in heating mode. I have a couple other places that are burning oil and running the geo every morning to come up to temp, then they have to run air in the afternoon to keep cool. This one takes no input.

A few weeks back we had overnights of 38F-40F, so we ran a single 9K mini-split head to hold overnight temp, but come morning, it didn't run anymore.

Is there a blower-door test in your future to quantify it in cfm/50 or ACH/50 terms?

I may have to buy one. Still haven't uncovered someone with enough capacity.

Posted By ICFHybrid on 12 Jul 2012 01:15 PM
This passive solar stuff with ICF is amazing. 

It does make a difference.

It areas of rapid temperature swings, the concrete moderates these swings a lot better than non-mass structures. It's less noticeable in areas that stay cold and remain cold. Hence areas like Alaska and Minnesota would probably be better off with 2x6 double insulated walls. Not that ICF wouldn't work out there but the thermal mass has less of an effect in areas like that.

Let us know how things turn out with the blower door test and once completed, and how things go during winter.

You can invite us for the house warming party!

ICFHybrid-

I am not sure what the ICF is doing for you, but good air sealing and insulation should allow good performance at the conditions that you mentioned.

No ICF here, but today's outdoor low and high were 50 F and 88 F, respecitively, and indoor low and high were 68 F and 72 F with no heat or A/C. A couple of windows were opened last night to cool the house down to 68 F, then closed this morning to limit the heatup.

Hopefully overhangs were designed to limit passive solar this time of year. The better test of passive solar will be the performance in the winter. And a good measure of "effective thermal inertia" that combines air tightness, insulation, and thermal mass is the cool-down rate with the heat off at say 11 PM until morning with outdoor tempeeratures below freezing.

I am not sure what the ICF is doing for you

I'm not either, yet. But, like Lbear says, my sense is that it is helping buffer these temperature swings. It really feels like that when you walk in during the hot of the day and find it cool without any air conditioning or in the early morning and find it warm when you just left a building where the furnace is running. It's still not completely sealed as I have two temporary "doors" made out of shoddy plywood sheathing that have about 3 square feet missing and my front door is 120 square feet of plastic sheeting with lots of staple holes in it.

BIG overhangs. Bigger than anyone had seen and even bigger than the architect thought. They are darn near perfect. The sun barely gets in right now but for the bottoms of some french doors. I'm also pretty pleased with some big windows that will get marble sills. I was concerned that the sills would get hit by the sun and contribute too much warmth during the Summer, but they have been shaded and cool, too. They work well in the Winter, too. The place was flooded with sun (on the few days we had it).

the cool-down rate with the heat off at say 11 PM until morning with outdoor tempeeratures below freezing

We didn't put as much insulation on the house as we might have because we wanted the radiant floors to be working by morning for the COZY feeling. There's a nod to comfort over efficiency.

Posted By ICFHybrid on 12 Jul 2012 05:29 PM

You can imagine that I'm not overwhelmed at maintaining 68F overnight in JULY, eh? ;-)

Worst "Summer" weather EVER this year. :-)

Daytime temps are getting to 72F but only after morning overcast burns off. I have a 10' X 12' hole covered with plastic for the front door and two other doors with about 3 square feet of hole between them. This is really pretty impressive. Everyone else is still in heating mode. I have a couple other places that are burning oil and running the geo every morning to come up to temp, then they have to run air in the afternoon to keep cool. This one takes no input.

A few weeks back we had overnights of 38F-40F, so we ran a single 9K mini-split head to hold overnight temp, but come morning, it didn't run anymore.

Is there a blower-door test in your future to quantify it in cfm/50 or ACH/50 terms?

I may have to buy one. Still haven't uncovered someone with enough capacity.

My mother in Port Orchard flipped her mini-split into cooling mode for the first time this season just last week, in her low-R low-mass place.  While the rest of the country has been roasting the PNW has been pretty temperate so far this summer.

the PNW has been pretty temperate

Ha ha. Temperate, you say. Ridiculously cold is what it has been. Fuel and energy use has been way above normal and it is directly related to the marginal insulating characteristics of classic construction here. A difference of only a few degrees over time can cause the heating or cooling units to run quite a bit more when the home construction can't bridge the gap.

what you do have as your heat storage mass?

6" ICF Walls, with a combination of 7+3 Insul-Deck and 4" concrete slab on main floor. And a masonry chimney chase.

Not yet installed:

Double 5/8" sheetrock in the solar atrium
Ledgestone wall and 6" radiant slab in the full sunroom.

so your 4" slab is your collector. what are you using for windows? glass, window size vs floor area sqft, etc

Windows are Pella Architects series with u-values around 0.27-0.30. It's a bit dicey to attempt to calculate what the window size vs floor area is, as the system is necessarily complex. For example, right now, there is very little insolation coming through the windows due to overhangs and other obstructions. In the winter, the windows are fully utilized in collecting the solar radiation. What I will say is that it is substantially larger than any home in the area, yet no one recognizes it because the windows were made as large as possible.

The window schedule shows 1100 sf of glazing and a heated floor area of 6000 sf. In addition, there is at least another 400 sf of glazing in french door assemblies.