Jerry - I don't think cmu's have any real strength without bond beams and corefills. While this is their strength it is also their greatest weakness because of human error and not understanding the importance of the reinforced concrete to the overall job. A good mason can make a good wall but they seem few and far between. What McFish is doing is filling everything. The cmus are just forms. Don't see why he wouldn't just use standard concrete forms and strip it. It would be cheaper. We just did 14' foot high walls for a dealership and the icf worked out slightly better in price than the three cmu bids and its a far superior product. Personally I don't see why anyone would use cmu anymore. Oh and we didn't have to hoard it in!

I find it interesting that interior mass makes it difficult to do nighttime thermostat setback (because it responds slowly) and setback typically saves more than any type of thermal mass (even none). ICF (or similar CMU with insulation on both sides) should facilitate setbacks more than interior mass. The ORNL study leaves lots of issues unexplained and unexplored.

Posted By jonr on 11 Apr 2011 11:40 AM

I find it interesting that interior mass makes it difficult to do nighttime thermostat setback (because it responds slowly) and setback typically saves more than any type of thermal mass (even none). ICF (or similar CMU with insulation on both sides) should facilitate setbacks more than interior mass. The ORNL study leaves lots of issues unexplained and unexplored.

I think you need to find some of the threads from the past re: thermal mass in walls. It can do a lot to reduce the overall heating/cooling load in a house because of the heat sink nature and resulting latency of it. Thermal mass works best with significant diurnal temp swings, exactly the same situation thermo setback works best.

From a comfort standpoint thermostat setback requires one significant equipment factor - the system has to be significantly oversized. If it's not, then you have a response speed problem, the same as you point out with thermal mass.

I seriously question whether thermo setback really saves much. I can tell you that in my ICF house with a Daikin heat pump thermo setback was a big time loser. Two reasons, the heat pump is not oversized by 50 to 100% like a hot air system might be. In fact it's not oversized at all. The thermal mass and resultant latency of all the furniture, frame walls, fixtures, the 2" concrete slab in the crawl space, etc., in the house is significant. My house is very comfortable, with no hot or cold drafts, with the thermo set at 74° day and night, year round.

{latency} can do a lot to reduce the overall heating/cooling load

If you are using an air source heat pump. No difference with nat gas.

Thermo setback doesn't benefit from diurnal temp swings - simply, less heating = less energy used

Depending on climate, thermal mass might save 6%. Setback almost always exceeds that.

Agreed, thermo setback requires excess capacity (or storage of the unused capacity during the setback period) and lower thermal mass. Agreed, a constant temperature can also be comfortable.