Posted By ICFHybrid on 28 Dec 2011 10:20 PM

attached to the house with a common ICF wall, and has ICF on the other three sides.

Okay, that's four sides. Is there a side of the garage that has big doors on it, like the ones you would drive a vehicle through?

Welllllllllllllll, yeah, there are! Two of them in fact, 8' high x 10' wide, Amaar Olympus brand, something on the order of R value 15. There's 4' of ICF wall between them and on each side, and over 2' above them. So there is a fair amount of ICF in that wall, so my bad is only 1/2 bad, right?

Posted By Ray Gladstone on 28 Dec 2011 10:26 PM
One other thing. If an R24 double framed sprayed foam 2x6 wall saves me 10 bucks a month in HVAC costs over a 6" ICF wall, I'm going for the ICF. You are arguing over pennies in HVAC costs and that's meaningless in the grand scheme of things. You should get a little perspective.

Energy efficiency is only one small part of the ICF choice.

As would I- any R24 (whole-wall R, not TexasICF's straw man wall) wall using exclusively cc spray foam is a brain-dead way to spend the money. 

Getting to R24 in 2x6 frame using cellulose cavity fill and R10 exterior rigid iso or EPS is half the cost of any all-cc foam solution, and cheaper than ICF, but there's still an argument for ICF on structural grounds, more important in some regions than others. (It may not read like it when I criticize some of the postings here, but I'm very much in favor of concrete construction for homes, particularly in hurricane zones.)
 
I wouldn't recommend building schools using timber-frame on a number of grounds, but there's often an economic argument for structural steel rather than concrete.

When building a school with concrete, ICF will often incur an energy use penalty over a standard concrete walls insulated with exterior cladding of EPS at a more climate & building-use appropriate R value.  (CMU cavity walls can also be built to meet the minimum mass for a mass-wall, and are more flexible in R value at the low end too.)  The whole ASHRAE 50% document is about cutting energy use in school buildings by half, and the topic of this thread is that the document is making "....- a strong case in favor of ICF". But that case isn't made at all- quite the contrary.  The fact that even a minimal ICF is un-optimally high in R value for  that type of building in most of the US seems to argue against ICF, not for it.

When focusing on single family residential construction it's easy to miss the fact that the R values of walls on other type of buildings & uses reach a point where energy starts to go up with increasing R value on walls, and where that knee in the R value occurs isn't very high for school buildings.

Posted By dmaceld on 28 Dec 2011 08:39 PM
I downloaded the report and took a quick review of it, but not thoroughly. Does it discuss the impact of temperature set backs? I'm thinking specifically about schools in the Northern part of the country.

I'm wondering about this because of my experience with my garage, which is attached to the house with a common ICF wall, and has ICF on the other three sides. I use a pellet stove to heat it. What I'm seeing is that once the heat is turned off the garage drops temperature fairly quickly. It'll go from 70F to 50F in about 3 or 4 hours when it's 32F or colder outside. It stays in the 50 to 55F temp range though pretty much all the time, unless it's only about 0F or so for days on end. I put a thermometer through the foam and up against the concrete. It showed a temp around 45F to 50F. The wall surface temp is about the same as the room temp so there definitely is no "cold" wall feeling.

I'm beginning to wonder, for a garage that is heated only part time, if ICF really has a lot of advantage over a well insulated and sealed frame wall. By extension I wonder how well it will work for a building like a school. I'm sure most every school is going to set the temp back overnight and on weekends when the building is not used. Will the mass effect of the concrete, typically behind about 2.5" of foam, make Monday morning heating sluggish? Would the school be looking at having to have excess heating capacity to overcome this sluggishness?

I have a 3 ton Daikin heat pump for my house. It works great, but it is has little excess capacity, especially when the outdoor temp drops to 10F and colder. At 0F the performance chart lists its output at about 30,000 Btuh. When we first moved in I tried nighttime temp setback but gave up on it after about 3 days! Morning temp recovery was so slow. I think a school would have to contend with the same situation.

dmaceld,  I have basically the same ICF garage design.   I wouldn't expect the garage to hold the heat unless you heated it for a number of days.  When you go out there and work in your garage are you heating it for more than a few hours?   If you're out there for a few hours, I'd say about all your heating is the air -- particulary with the mass being insulated on the inside.  Nor would you necessarily want to use the energy to heat these walls in the garage-.  In a cold climate, I would think it would take much longer to "achieve" the target (temporarily or otherwise) if the mass was exposed but thats another discussion entirely.

A Texas energy expert (Richard Rue) tells his clients not to even bother with the setback.  That it really doesn't make much difference.  I've experimented with it over the past five years and found that its more or less a wash because you are comparing running only in stage one to perhaps kicking off a second stage to get to set point.   Obviously, it is more effecient to stay in stage one unless the systems running a great deal.

I too have done a bit of temperature prob stuff in the walls and found that the wall (concrete) is usually within about 5-8 degrees of the set point and within a degree or two during seasonal changes hot to cold, cold to hot etc.   If I turn my heat off at night I only loose a couple of degrees.  I can turn my AC off when it's over 100 (as it was for 30 consecutive days this year) and it takes about 24 hours before you really notice.

I'll do some checking on the set back for schools and get back to you.   It can't be too big a problem though because the best performing schools in the US (by a somewhat significant margin) are mass wall systems (most including the top performer but not all are ICF).   Regards.

The penalty for going 100% above the optimal R value on walls isn't huge (wall gains & losses are very small piece of the pie in a school building) and not nearly as big as going 50% too low. Excessive R alone wouldn't be a strong reason NOT to go with ICF, even if it's not always a plus.

Of the 7 case study examples given in that document only one of them was ICF and at most 3 were mass-wall designs:

1 Gloria Marshall (TX) metal stud, R13 whole-wall

2 Marin County (CA) metal framed, wood clad, U/R value of walls not specified (but they made LEED platinum)

3 Manassas Park (VA) metal stud, R20.8 whole-wall

> 4 Richardsville Elementary (KY) ICF, R28.6 <<< ICF, inherently massive

5 Greenburg K12 (KS) SIP, R30 some walls, R40 others

> 6 Kinard Jr High (CO)- CMU cavity wall w/ brick veneer, R20 <<<< mass wall by design

7 Two Harbors (MN)- hybrid with CMU cavity wall/brick on south side (R25), precast insulated panels (R21) on north side. < Mass not specified, but maybe, at least on some walls...

Mass walls, schmasch walls, meeting the design goals is about the WHOLE design, silly. :-) (The walls are the least of it in a school building.)

In any particular design for lowering energy use, all factors are on the table, and optimizing one will affect another, eg: higher efficiency lighting==lower air conditioning loads, but higher heating loads, shifting the optimal points for U values of the walls. The shape, orientation to the sun etc also affect the optimal wall designs- most of the examples opted for multi-story buildings in order to reduce the heat gains though roofs and reduce the ratio of exterior surface area to usable square feet. I'm a bit surprised they went so high in wall R on the SIP building in Greenburg KS, but going that thick may have been necessary for structural reasons.

ICF became something of a paradigm for school buildings in KY (on a different project, unrelated to 50% energy reduction targets) after it was demonstrated the the speed of installation & simplification of construction schedules can make it competitive with the CMU & brick school construction common in that state, quite independently of energy use factors (a good selling point of ICF.) This is the closest thing to a "strong case in favor of ICF" I could find in the document. See page 98.

Richard Rue is right- with multi-stage or modulating HVAC systems setbacks tend to use as-much (or sometimes more) energy by having to run at a lower-efficiency operating point during the recovery ramp than was saved via setback. This is true whether it's a massive building or a lightweight, but with bang-bang one-speed mechanicals the savings of setbacks greater with low-mass buildings. (The rate of heat loss/gain only changes with a bigger temperature change, and the mass moderates the temperature.) The COP of a continuously variable mini-split can be more than 2x higher at the minimum compressor speed than at max, and setbacks could actually harm efficiency. There are similar issues with modulating condensing boilers, but not quite to the same degree.

Dana1, Please explain your complex discussion of setback in the context of this quote from the Clearview architect for we mere mortals:

"As a test, the school heating system was shut down at 1 p.m. in mid-February when the high temperature outside reached only 40°F. Nighttime temperatures fell to 22°F., but the classrooms cooled by only 4 ½°F. When the furnace was restarted at 5:30 a.m. the next morning, the desired room temperature was regained in less than an hour. Architect John Boecker, says, “The insulating concrete form wall provided us with a high-performance thermal envelope that contributed significantly to downsizing our HVAC system and reducing energy consumption.”

Posted By Ray Gladstone on 29 Dec 2011 03:35 PM
Dana1, Please explain your complex discussion of setback in the context of this quote from the Clearview architect for we mere mortals:

"As a test, the school heating system was shut down at 1 p.m. in mid-February when the high temperature outside reached only 40°F. Nighttime temperatures fell to 22°F., but the classrooms cooled by only 4 ½°F. When the furnace was restarted at 5:30 a.m. the next morning, the desired room temperature was regained in less than an hour. Architect John Boecker, says, “The insulating concrete form wall provided us with a high-performance thermal envelope that contributed significantly to downsizing our HVAC system and reducing energy consumption.”

The setback test on the building in question didn't come with an identical low-mass control subject building to compare it to, did it?  Nor is the thermal mass of the rest of the building defined, nor was the solar gain and heat gains from from 1pm on measured.   All we have is the architect's one line report. 

Right sizing the HVAC to the peak load has benefits, and by reducing the peak heating load a high R building can use smaller systems.  In most school buildings the heat loss out the windows would dominate the nighttime heat loss picture- the wall-R is still the smallest part.  Wall surface area is also typically less area than the roofs. So how does the a WALL system become the magical critical contributor to performance? (It doesn't model or measure that way.) Significant? Maybe- show me the building design, run a DOE-2 on it, fiddle with the various parameters. Every design has many factors that affect performance, and it's easy to over-attribute performance to single factors.  Designing a high performance building is an iterative process, modeling all of the interactive parameters.

Most school buildings will have a cooling load at outdoor temps above 50-55F from internal heat sources, independent of solar gains. A tighter/better/high-R school building can easily still have a cooling load at 40F (the stated high in the example), particularly on a sunny day with solar gains through glazing. (Most homes wouldn't have a cooling load at +40F,  but a tight house with decent windows and R20 whole walls can easily have zero heating load at 40F on a sunny day, and if there's enough mass on the interior it could  also lose less than 5 degrees as temps drop to 22F.) A plot of the temperature with time, along with a description of use on that day would be more interesting. If school didn't let out until 2:45 and the sun was hitting the south and west windows the classrooms could well have been picking up temperature during the 1-2:45 period, but we don't really know if it was heating, cooling or steady-state.

Having substantial thermal mass in a building does reduce peak loads, but there's no great energy-use benefit to having that mass in the exterior walls compared to elsewhere (even though there's sometimes a comfort aspect to having it in the exterior wall.)  In an ICF wall that mass is isolated from the interior by the interior EPS layer, making that mass somewhat less useful.  A mass wall of equivalent R with all the mass on the interior side and all the insulation on the exterior will outperform ICF.  Taking the mass out of the wall and incorporating the same amount of thermal mass into the floors, partition walls etc would also exceed the performance of an ICF from an energy use point of view, but wouldn't be as comfortable standing next to the exterior wall during the temperature extremes, but that's a very subtle aspect once you are at R20 whole-wall or higher (if obvious at R5).

From the HVAC systems' perspective, a high mass building is a thermal storage buffer, so even when the equipment is somewhat oversized for the immediate load, the on-cycles are long enough to always hit near its steady-state efficiency.  The drawback of ICF compared to other mass wall systems at equivalent U-value is that the buffering mass isn't fully accessible to the interior.  That's not to say that it's completely isolated though- quite the contrary.  2-D energy use models  can still model the heat transfer of ICF designs pretty well- there's definitely a peak-shaving on heating & AC loads due to the mass, but not nearly the amount you get with all the mass inside the thermal envelope.

In a setback situation  a low mass building of identical U-values as the massive building will drop in temperature faster & deeper, reducing the delta-T between exterior & interior that a massive building would, losing less heat.  It would also heat up more quickly on the recovery ramp, and would be more prone to short-cycling at part load. HVAC systems always do better with a buffering mass, and the increase in system efficiency due to the mass of the building is one aspect of getting the best efficiency out of it.  In a school building the unoccupied 5AM heating load can easily be 25-50x the 1pm fully-occupied heating load on an average day, and right-sizing the systems (and system control) is not nearly as simple as in residential situations.

The issues with night-time setback of a thermostat are straightforward, even if the answers are not. The goal of night-time setback is to reduce the heat losses by reducing the differential temperature across the building envelope. In the example by RayGladstone, let us assume an average night-time temperature of 25 F. If the thermostat was set to 72 F during the day, and it dropped by 4.5 F over the afternoon and night, then let us assume that the average temperature during that time was 69 F. So the heat loss, being proportional to the temperature difference, is reduced by (1 - (69-25)/(72-25))*100% or 6.4%. If the furnace efficiency is independent of heating output (Dana's single-firing-rate furnace or "bang-bang"), then the fuel consumption is reduced by 6.4%.

However, for modulating furnaces, which many new homes and commercial buildings have (mine included), the efficiency is better at lower heating outputs since the exhaust gas temperatures are lower and exhaust heat represents a loss thermodynamically, and there are lower pumping losses (pressure losses) in the duct when operating the fan at lower speed. So in the case of using a setback, the control system sees that the "error" between the desired and actual temperature is high, and turns the furnace on to a high heating rate and a high fan speed, increasing pumping losses and increasing combustion rates, increasing exhaust gas temperatures. Let's say the efficiency of the furnace drops by 10% compared to operating at a low heating output which could be used if the building were not allowed to cool down. Then instead of saving 6.4% in fuel use using the setback, the actual fuel use would be increased by 10% - 6.4% = 3.6%. Now the 10% value is not based on fact, but just for illustration. I don't know how my furnace efficiency changes with power output, or what is typical.

The question is not completely academic to me. I use setback with a modulating furnace. The daytime set-point is 67 F, and from 10:30 PM to 6:15 AM the setpoint changes to 60 F. Even on recent nights that reached -13 F and - 10 F, I think the house temperature only dropped to 62 F before the furnace kicked on in the morning (and there is no ICF in this house). I don't know if I am saving money or losing money using the setback, but I know that I like it cooler at night for sleeping, and the cooler air allows for slightly higher relative humidity.

Good thing this forum doesn't charge Lee and Dana1 by the word like the newspaper does for an obituary.

So guys, since you've both proved that you can either dazzle us with brilliance or baffle us with bullsh*t (we really can't tell the difference at this point). Is a 4.5 degree heat loss under those circumstances good performance or not good performance?

Better yet, what we simpletons do know about is money. I think we're still talking about pennies in monthly heating and cooling costs between the high mass ICF building and the double studded R24 wood wall, and no one has given us any reason to think otherwise.

as an arch that actually designs schools, ICF would be the last of the options (cmu and metal framed) types we would select. People are too focused on the thermal performance of the ICF wall. I personally do not buy into ICF thermal mass gains due to the insulated mass. (get to why in a sec). Also from a school durability side of things, most schools do not want gyp on their walls and perfer cmu or precast. We do use some gyp typicaly as a cost savings in areas that will see less abuse. Obviously with the use of ICF they would need gyp on the exterior walls. Our typical go to system for schools is 8" cmu, 2.5-3" of exterior closed cell foam, air space, veneer of brick/block/metal panels, etc. I did a community center that had a FEMA saferoom as part of it. THe walls were 12" CORE logix blocks. If any building would prove any mass effect, this certainly would. The rest of the building (2/3rd of it) is 2x6 framed walls, blown fiberglass insulation, 1.5" exterior XPS, tyvek and 5/8" sheathing. Combination of cement board siding and brick is on all parts. By using super unscientific testing (simply putting thermometers in various areas) we are noticing the temp drops in the ICF part of the building is higher and faster then in the other wood insulated areas. Heat sources are shut off at the same time and left over night. Night time temps are around 10, day time around 30. Before anyone starts blaming the "screen door" roof, I would argue the ICF part is much tighter. It has a 6" site cast concrete cap that is poured into the tops of the ICF walls. Then there is a typical wood truss roof and blown fiberglass over the entire roof. The building has not had a blower door test done yet. As I still try to pin down the wall construction of my own personal home (between ICF walls vs double stud 10"), I have convinced myself if I select ICF, it will have to be for the other pros and not due to thermal performance. (ICF costs roughly $8k more for the shell) However after reading that report, it still fails to sway my choice to continue to use the systems I currently do. ICF for a school is a very costly system. Talking it over with some of our mechanical engineers, they claimed they would have to actually INCREASE the size of the cooling units for the building.

Ray-
make sure your "pennies" includes the high upfront cost of ICF vs higher r wood framing methods. Those pennies change to many dollars very quickly. Again...from purely a thermal performance standpoint only....

Izzie - Two things:
1) Higher up front cost of has actually been overcome due to speed of construction and associated reductions in costs of other trades, like electricians (they don't need to be on site all the time like with CMU. Want to talk about reduction in construction interest costs? ICF is costing $12 - $14 per sqft of wall and goes up in 25% of the time as CMU. How much the wood frame costing you (including insulation)?

2) No need to use gyp board as interior wall finish, PermaCrete and PlasterMax are terrific high-abuse finishes and have proven successes in the field. I hear they use PlasterMax in Kentucky -- How cool that Kentucky leads the nation in high performance schools! (Take that CA and NY!)

"Talking it over with some of our mechanical engineers, they claimed they would have to actually INCREASE the size of the cooling units for the building."

You need to tell those guys to quit smoking crack, it'll damage their ability to reason effectively, cause their wives to leave them and annoy their mothers.

Posted By Dana1 on 29 Dec 2011 03:25 PM
The penalty for going 100% above the optimal R value on walls isn't huge (wall gains & losses are very small piece of the pie in a school building) and not nearly as big as going 50% too low. Excessive R alone wouldn't be a strong reason NOT to go with ICF, even if it's not always a plus.

Of the 7 case study examples given in that document only one of them was ICF and at most 3 were mass-wall designs:

1 Gloria Marshall (TX) metal stud, R13 whole-wall

2 Marin County (CA) metal framed, wood clad, U/R value of walls not specified (but they made LEED platinum)

3 Manassas Park (VA) metal stud, R20.8 whole-wall

> 4 Richardsville Elementary (KY) ICF, R28.6 <<< ICF, inherently massive

5 Greenburg K12 (KS) SIP, R30 some walls, R40 others

> 6 Kinard Jr High (CO)- CMU cavity wall w/ brick veneer, R20 <<<< mass wall by design

7 Two Harbors (MN)- hybrid with CMU cavity wall/brick on south side (R25), precast insulated panels (R21) on north side. < Mass not specified, but maybe, at least on some walls...

Mass walls, schmasch walls, meeting the design goals is about the WHOLE design, silly. :-) (The walls are the least of it in a school building.)

Your not really going there are you?  After dozens of posts about how it's easy to exceed the thermal performance of ICF with wood construction your going to say that ICF has too much R-value?    

Regarding the schools let me point something out that you may have missed.   I am going to re-order your list by energy consumption:

MASS  (ICF)          Richardsville Elementary (KY)    17kBTU/sqft/yr  (now has 1 year of data)
MASS  (CMU)        Kinard Jr. High (CO)                   25 kBTU/sqft/yr (now has more than 1 year data)
**Metal Stud        Gloria Marshall (TX)                    33.4 kBTU/sqft/yr (based on their simulation)
*SIPS                   Greenburg K12 (KS)                  36  kBTU/sqft/yr (Not stated - estimated based on 50% target in modeling).
Metal Stud            Manassas Park (VA)                   37.5 kBTU/sqft/yr
*Metal Framed      Marin County (CA)                     Not stated - but perhaps hight 30s based on beating target 24 by 40%).
-------                    Energy Star Target                    50 kBTU/sqft/yr
MASS  (Precast)    Two Harbors (MN)                      56 kBTU/sqft/yr  Built in 2005
-------                    National Average                       73 kBTU/sqft/yr

If you choose to delete the schools that didn't report results* or simulated results** (likely they did not yet have a year of data) you would be eliminating virtually all of the low mass schools (e.g. SIPS school, Metal Framed, and Metal Stud) so I chose to leave them in. 

If we add some of the Warren County Kentucky Schools to this list (see page 55 for these figures) then we have:

MASS (ICF)           Richardsville Elementary (KY)        17 kBTU/sqft/yr
MASS (CMU)         Kinard Jr. High (CO)                       25 kBTU/sqft/yr
MASS (CMU)         Plano Elementary (KY)                   26 kBTU/sqft/yr
**Metal Stud        Gloria Marshall (TX)                       33.4 kBTU/sqft/yr
MASS (ICF)           Alvaton Elementary (KY)               35 kBTU/sqft/yr  Built in 2005
*SIPS                   Greenburg K12 (KS)                      36 kBTU/sqft/yr (not stated - estimated based 50% target in modeling).
Metal Stud           Manassas Park (VA)                      37.5 kBTU/sqft/yr
*Metal Framed     Marin County (CA)                         Not stated - but perhaps high 30s based beating target 24 by 40%).
MASS (CMU)         Henry Moss Middle School (KY)     42 kBTU/sqft/yr Built in 2002
MASS (CMU)         Drakes Creek Middle School (KY)  43 kBTU/sqft/yr Built in 2002
MASS (CMU)         Warren East Middle School (KY)    43 kBTU/sqft/yr Built in 2002
------                     Energy Star Target                       50 kBTU/sqft/yr 
MASS (Precast)     Two Harbors (MN)                        56 kBTU/sqft/yr  Built in 2005
------                     National Average                          73 kBTU/sqft/yr

In addition, we now have more than 20 additional energy star ICF schools in the US.

I'm beginning to wonder, for a garage that is heated only part time, if ICF really has a lot of advantage over a well insulated and sealed frame wall.

I just talked with a small contractor yesterday who has found a niche replacing the foundations of vacation homes with ICF. Many of the "cabins" were built with minimal underpinning in the first place and he can jack them up and replace the foundation relatively cheaply. What the owners have found is that they don't have to worry about the yearly ritual of freeze-proofing their places with the new ICF foundations.

dmaceld - is it possible that the rapid decline in ambient temperature in your garage is due to normal air infiltration once heat input ceases?

Ray I think I will trust their calculations.... Also I ran your recommendations by a couple masonry/concrete contractors (who have done ICF so there is no learning curve tax) as well as some gyp/plastering contractors yesterday. Using ICF plus the couple finish types you suggested, you have successfully added 10%+ to my project! I guess all contractors around here smoke crack. I wish you could come build the schools for us...we could save millions. I am not knocking ICF as I have used it on projects in the past. I am just saying it is not the answer to everything.

The presumption that the CMU-built Warren County schools in KY all meet the ASHRAE definition of a mass wall (or even that the schools listed are CMU) is to assume facts not in evidence.

The stellar performance of Richardsville was due to the fact that it was designed as a Net Zero building (with a large grant not typical for most school construction budgets) and apparently modeled extensively for daylighting & passive solar heating as part of the design process. The stated reasons for using ICF was thermal performance, enhanced air tightness, and construction speed- all good reasons for supporting use of ICF, but neither prescriptive nor necessary. To ascribe the energy performance of this building to wall construction type would be over-reaching beyond merely ridiculous. (But clearly use of ICF didn't get in the way of the performance goals.)

The Alvaton school was also ICF, but uses more than 2x the energy pf the Richardsville school, and more than the Plano school, the wall construction of which is not described. Nor is the construction of the Henry Moss Middle School, Drakes Creek Middle School, or the Warren East Middle School described in the ASHRAE document. From website of the engineers & architects who built them it's clear that they have brick cladding, but the mass and structure behind it is not at all clear: http://www.cmtaegrs.com/?page_id=87

And yes, DOE2 models will show increasing energy use on buildings of this type with increasing wall-R beyond some optimum value (yup, I'm reluctantly going there, but only because the facts lead me there), but that penalty is small, and not a reason to rule out ICF, given how small a role wall-R plays in the bigger picture. In residential applications there is no such thing as too much R- despite diminishing returns it never reaches the point of negative returns. But that point exists with schools & commercial buildings. (Some have erroneously used the commercial building case to argue against going high R on single family homes in cooling dominated climates.

BTW: Where is the target BTU/ft listed for the Marin County CA? The target mentioned in the ASHRAE document was 40% below California Title 24 standards, but it would take some digging to find out what that is for the California state specified climate zone for Marin County. Speculating "...high 30s..." is devoid of actual data to support that. The ASHRAE specified target for US climate zone 3C (which includes Marin county) is 27KBTU/ft for primary schools, 28K for secondary schools. Title 24 compliant buildings are already well below the national averages, so 40% below Title 24 that could easily (or even likely) meet or beat the ASHRAE target. (Searching the http://www.energy.ca.gov website does not quickly come up with simple numbers for comparison.) Given the very temperate climate (including very low latent AC loads) I'd be very surprised if any LEEDs platinum school hit the"high-30s"- a number that could probably be met at Title 24 code min with a bit of care with site design & building shape. (Corte Madera CA design temps are 35F heating, 88F cooling- nothing too tough.)

I agree with Lee that the effectiveness of setback where there is a variable efficiency heat source is a good question. But note that the morning warm up time is short (relative to the entire night), so setback is much more favorable than the numbers used (the 10% loss is only for a short period, the 6% gain is for the entire night).

Active thermal mass (eg, water tank) is one solution (the heater works slowly all night to store up heat and then the storage has a large excess capacity to heat up quickly in the morning). Such a system would still be less expensive than ICFs, require no oversizing, maintain efficient operation and warm up the house quickly. Might even get lower (nighttime) rates on electricity (say in the case of a ground source heat pump).

Masonry/foam/mansonry makes more sense to me than foam/masonry/foam (ie, ICF) from a cost and durability standpoint.

Posted By jonr on 03 Jan 2012 12:22 PM
I agree with Lee that the effectiveness of setback where there is a variable efficiency heat source is a good question.

Active thermal mass (eg, water tank) is one solution (the heater works slowly all night to store up heat and then the storage has a large excess capacity to heat up quickly in the morning). Such a system would still be less expensive than ICFs, require no oversizing, maintain efficient operation and warm up the house quickly. Might even get lower (nighttime) rates on electricity (say in the case of a ground source heat pump).

Masonry/foam/mansonry makes more sense to me than foam/masonry/foam (ie, ICF) from a cost and durability standpoint.

The costs of active thermal storage can be pretty high- it works, but wouldn't necessarily be cost-effective, even if it reduced the output requirements of the heat pumps & boilers by half.  Most ICF buildings are sufficiently massive that the sizing of mechanical systems can be downsized somewhat, but that's not guaranteed by any means. It CAN be guaranteed by design though, even in buildings with low-mass walls.  Most of the example buildings in the ASHRAE documents have very sophisticated envelope and mechanical system designs to ensure getting best efficiency out of them.

Hitting the same structural capacity with CMU as with poured concrete gets complicated, but at least the thermal mass of the interior masonry is fully accessible.  I'm not sure there's a great case for CMU being more durable than poured concrete (quite the contrary).  Making CMU air tight also requires more detailing than with ICF.  But there are clear energy-use and comfort benefits to having the thermal mass fully inside the conditioned space rather than isolated by R8 or more on the interior.  For the same amount of material, a poured concrete wall with all of the insulation on the exterior is a superior performer to an ICF type stackup (always.)

The Warren County schools (in the ASHRAE 50% K-12 document) seem to have tipped toward ICF for construction scheduling reasons, where the higher initial costs over CMU construction are made back by the relative speed and simplicity of construction- it's just easier to manage.  (That's the strongest case for ICF I can find in the document.)   It would usually be simple to add interior mass elsewhere in the building where modeling indicates sufficient additional benefit. 

I would think that building schools with SCIPs would be better than ICFs or CMUs.  Mass is in the correct location with the foam being in the middle.  The mass walls can withstand more abuse than drywall or CMU.  SCIPs have a much higher compressive PSI than CMUs.  Thicker SCIP walls use more insulation and no more concrete than thinner SCIP walls.

I realize I am posting in an ICF forum but what is to keep an ICF contractor from learning how to do SCIPs.  I know the entry barrier fee will be much higher in equipment and learing curve just like it is for CIP concrete walls with Western aluminum forms.

Dana1,

 

Your comments in bold.

 

But there are clear energy-use and comfort benefits to having the thermal mass fully inside the conditioned space rather than isolated by R8 or more on the interior.  For the same amount of material, a poured concrete wall with all of the insulation on the exterior is a superior performer to an ICF type stackup (always.)

 

I like the words “for the same amount of material” and “all the insulation on the exterior” because many misquote this advantage to apply to systems that either don’t exist or systems that have mass to the inside but are not technically even mass walls – e.g. heat capacity less than 7 Btu/sqft F.    For example, some AAC is not classified (at least by this document) as a mass wall since it’s generally under 7 Btu/sqft F. 

 

So Dana1, where can I find some data on exactly what happens to a covered mass that is more slowly “communicating” with the interior space through the foam?   I haven’t found this anywhere and don’t know how to model it.  Please don’t send me to that old ORNL report.   All that report says is that there is a very minor improvement to interior mass --- given equivalent mass and R-value – therefore, the insulated mass is still working and I would bet better in some climates since the mass effect is dampened by the foam.  Furthermore, the ease of installation of electrical and plumbing may outweigh this small advantage.

The Warren County schools (in the ASHRAE 50% K-12 document) seem to have tipped toward ICF for construction scheduling reasons, where the higher initial costs over CMU construction are made back by the relative speed and simplicity of construction- it's just easier to manage.  (That's the strongest case for ICF I can find in the document.)   It would usually be simple to add interior mass elsewhere in the building where modeling indicates sufficient additional benefit. 

 

What you are saying about speed is true,  however, section EN5 states that they originally chose ICF as a thermal performance upgrade… and it has subsequently been used in approximately 50 schools across the state.

 

 

The presumption that the CMU-built Warren County schools in KY all meet the ASHRAE definition of a mass wall (or even that the schools listed are CMU) is to assume facts not in evidence.

 

This is not a presumption of any kind.  I am sure about this.  All of the schools I listed as CMU are CMU and yes they meet the 7 Btu/sqft F minimum heat capacity criteria.  I know several people directly involved in the construction of these schools (including the CMU ones Iisted).

The stellar performance of Richardsville was due to the fact that it was designed as a Net Zero building (with a large grant not typical for most school construction budgets) and apparently modeled extensively for daylighting & passive solar heating as part of the design process. The stated reasons for using ICF was thermal performance, enhanced air tightness, and construction speed- all good reasons for supporting use of ICF, but neither prescriptive nor necessary. To ascribe the energy performance of this building to wall construction type would be over-reaching beyond merely ridiculous. (But clearly use of ICF didn't get in the way of the performance goals.)

 

This one’s a bit comical.  Yes, Richardsville is the first Net Zero school in the U.S. and has extensive modeling of daylighting, passive solar, geo etc. etc.   The problem with bringing the grant discussion into is that the key is that it has nothing to do with the consumption.   The 17 kBtu/sqft/year is he key --- and thus having a reasonable PV budget.   Net Zero is easy with enough money – getting below 20 kBtu/sqft/year is not.  And I must repeat yet again.  No one (including me) has tried to say that the synergies of these technologies revolve around the walls. Only, that the majority of the best performing schools in the US are mass wall systems and that the best performing school today is ICF.   

The Alvaton school was also ICF, but uses more than 2x the energy pf the Richardsville school, and more than the Plano school, the wall construction of which is not described. Nor is the construction of the Henry Moss Middle School, Drakes Creek Middle School, or the Warren East Middle School described in the ASHRAE document. From website of the engineers & architects who built them it's clear that they have brick cladding, but the mass and structure behind it is not at all clear: http://www.cmtaegrs.com/?page_id=87

 

Again, all of these schools I said were ICF were ICF and all of the schools I said were CMU were CMU. If you look at the dates you will see the evolution of the design team through various stages of insulated mass from CMU to more insulated CMU to ICF.    Of course other evolution such as distributed pumping and tackling kitchen efficiency, etc. were critical and also took place.

And yes, DOE2 models will show increasing energy use on buildings of this type with increasing wall-R beyond some optimum value (yup, I'm reluctantly going there, but only because the facts lead me there), but that penalty is small, and not a reason to rule out ICF, given how small a role wall-R plays in the bigger picture. In residential applications there is no such thing as too much R- despite diminishing returns it never reaches the point of negative returns. But that point exists with schools & commercial buildings. (Some have erroneously used the commercial building case to argue against going high R on single family homes in cooling dominated climates.

 

I would be interested learning more about this.  This is new to me.  Particularly the part about ICFs having too much R-value.  Diminishing return is one thing but too much is another thing entirely.   Whatever you can point to regarding ICFs or other building systems having too much R-value would be appreciated.

BTW: Where is the target BTU/ft listed for the Marin County CA? The target mentioned in the ASHRAE document was 40% below California Title 24 standards, but it would take some digging to find out what that is for the California state specified climate zone for Marin County. Speculating "...high 30s..." is devoid of actual data to support that. The ASHRAE specified target for US climate zone 3C (which includes Marin county) is 27KBTU/ft for primary schools, 28K for secondary schools. Title 24 compliant buildings are already well below the national averages, so 40% below Title 24 that could easily (or even likely) meet or beat the ASHRAE target. (Searching the http://www.energy.ca.gov website does not quickly come up with simple numbers for comparison.) Given the very temperate climate (including very low latent AC loads) I'd be very surprised if any LEEDs platinum school hit the"high-30s"- a number that could probably be met at Title 24 code min with a bit of care with site design & building shape. (Corte Madera CA design temps are 35F heating, 88F cooling- nothing too tough.)

 

 

As you know, one needs to remember this is total consumption and involves much more than the envelope.   You can guess at this one and say they might have been this or that but the even 40% below energy star is in the mid 30s.

 

Here is title 24 link: http://www.cmacn.org/energy/documents/standards.pdf

 

Knock yourself out.  As you know Marin County is metal stud and not a mass wall.   I looked at it for while and instead of not including Marin since for whatever reason they didn’t report their results I kept them in with the estimate that I thought was generous.  I would imagine they didn’t make it or they would have reported it – California title 24 has kBTU/sqft/year targets but it looks to me like they are based entirely on modeling and the other schools primarily reported empirical data.  Perhaps all the schools that didn’t report shouldn’t be in the list.  This would virtually all the non-mass schools from the list and I knew you wouldn’t like that either.   Regards.