I too, am an advocate of the large thermal mass inside lots of insulation and I am considering straw bale construction with clay/lime rendering both sides.

I would imagine that straw in compression had good decrement delay and its insulation value is also high but leaving asside the internal walls and floor does straw/clay/lime constitute high thermal mass?

Joe

Posted By: ChrisEnglandby adjusting the phasing of the passage of exterior warmth/coolth into the interior

That's only the classic, well-known illustrative use of decrement , suitable for Arizona (blistering hot days, v cold nights). Other uses aren't so at-a-glance simple to understand, but believe me, decrement is happening all the time in every building, whether you build it into your calcs or not. I don't fully understand decrement yet but when I do, am sure it's an understanding that can be wonderously exploited in e.g. any kind of heat storage (whether in the structural elements, or remote). Understanding of decrement can also avoid unexpected and unwelcome temp swings even in simple state-of-art Passivhaus-type interiors, where the sun comes in thro windows and is expected to be soaked up (preventing overheating), stored and released by the heavy surfaces the radiation falls on.

Anyone know of any plain-language texts that explain decrement (not just its promised effect, but how it works) without resorting to equations and calculus?

Chris, planning for decrement delay is definitely most worthwhile where the average indoor temperature is similar to the average outdoor temperature, as in fostertom's Arizona or as (I suspect) in Adnams warehouse. And it is sometimes oversold as a benefit of particular build systems for houses in predominantly heating climates, so it gets a confused reputation. I've read elsewhere that the time constant in typical passivhaus-type interiors tends to be several days - i.e. there's already a huge 'decrement' of temperature variations. Uncontrolled solar gain is the big problematic exception.

Water has high thermal mass and can move large quantities of heat around (by convective or pumped motion rather than by conductivity). It can be a pretty good alternative to concrete if you want added thermal mass.

Tom, I'm not sure what kind of explanation you're looking for. Heat is vibration of atoms. Heat moves by these vibrations being passed on from one atom to another. The passing on takes time, depending on what atoms are involved and how they're connected together (think of a Newton's cradle toy, for example) and there's a constant averaging, smearing of temperature differences goes on because the vibrations spread in all directions from everywhere. So there's a delay and the variation is decremented.

Cheers, Dave

PS As an aside, the term 'decrement delay' is two words and they both have a point. The delay obviously refers to the time it takes heat to pass through walls etc. The decrement refers to the fact that the amplitude of external temperature oscillations is reduced inside the building. So I think decrement delay is quite a good name for the phenomena.

Posted By: djhthe term 'decrement delay' is two words and they both have a point. The delay obviously refers to the time it takes heat to pass through walls etc. The decrement refers to the fact that the amplitude of external temperature oscillations is reduced inside the building. So I think decrement delay is quite a good name for the phenomena

I agree - will do, from now on.

sinnerboy - re your excel query - there's an error in cell C28:- =(1.38*C29)*(SQRT(C30*C31)/(3.6*C32)). The bracket left of the SQRT should be to the right of it thus:- =(1.38*C29)*SQRT((C30*C31)/(3.6*C32))

Apart from that, the 3.6 figure is the difference between the two formulae. That's probably due to a combination of using seconds in one place versus hours in the other and a factor of 1000 somewhere in the units. Brain fade took over at this point.

Just located this programme which

"Draws a detail of wall or roof sections, calculates U-value, Time Lag, and Decrement Factor. It plots temperature drop through the section. Draws 2-D daily and 3-D annual plots of Outdoor and Sol-Air Temperatures, Normal and Total Surface Radiation, and Heat Flow through the envelope. It was originally called SOLAR-3. Unzip the download and install OPAQUE by clicking on SETUP.EXE, and to see the Users Manual open Manual.txt"

http://www.energy-design-tools.aud.ucla.edu/tools/opaque2-1.zip

here

http://www.energy-design-tools.aud.ucla.edu/

Note that if the above is right, the delay is proportional to the square of the thickness - ie. double the thickness and you quadruple the delay. Seems important.

(Re the formulae first quoted - I wonder if there wasn't just a mis-transcription somewhere along the way, squareroot instead of squared. That would account for the difference)