[stevehull]

Thermal buffering is the sum of many thermal masses. The smallest thermal mass is the air mass. The most substantial are heavy dense things like stone counter tops and such. The resultant thermal mass sum is the aggregate of all the masses acting independently as the environmental temperature changes.

Turns out that just one or two IBC totes of potable water make a huge difference in a 100 meter square space. The problem DoD has (Afghanistan) is that nights are bitterly cold as the air is so dry.

The way temporary field structures are built allows totes to be placed first and then the structure dropped (or built) into place.

My initial experiment was with about 200, one gallon water jugs. The next experiment was with steel drums (42 gal). My wife was frankly not very pleased with 30 steel drums in the house and was VERY glad when the experiment was over.

Those notes are about 30+ years old, but I did some calculations and was amazed at the potential buffering. Turns out the reality was very close. The specific DoD stuff is, believe or not, classified.

Michigan winters have a typical low in the low teens (F). When Kathy was on call, I would put house temp to 70F, run the blowers to fully saturate all the thermal masses. This took about 12 hours. Then I would turn off the heat and record the temperature with an old style recorder (circular device with pen writing thermometer on graph paper). The house would drop rapidly in an exponential fashion to the mid 40's the next am. Then turn on heat so wife had a warm home to come back to!

Didn't take rocket science to do a semi log plot.

Then brought in barrels and filled with water. One problem was that ground water in Michigan is COLD so it took a while to heat up all this water to 70 F(a few days). This time the house did not drop much below the mid 50s.

The house was crappy in terms of air infiltration so I had to choose my nights carefully.

The DoD has huge (hanger size) environmental chambers (Natick, MA) where these concepts were done in a more elegant way.

When we built a later home, here in Oklahoma, I put in a lot of thermal mass. That allowed a smaller geothermal heat pump to work very efficiently as I was really just heating (or cooling) against the average outside temp and not the full extremes. Used lots of concrete . . . and built a large basement with insulation on the outside walls. Could keep that huge house cool with a 12 kBTU GT heat pump in summer in Oklahoma.

Back in the 1980's, I recall some people putting water jugs in walls, sealing them up. At first this is tempting - until you realize that the polyethylene is time unstable and tends to start cracking after a few years . . . .

There is another thread where a solar greenhouse with aquaponics uses water filled steel barrels to buffer air temperature changes. Same concept.

Bottom line is that thermal mass, constrained with the envelope, can be a huge help to minimize energy bills.


Steve