Posted by gd on October 15, 2002 at 08:07:42:
In Reply to: double drywall as thermal mass posted by gd on October 15, 2002 at 06:27:16:
ok-- found this...
When is Mass-Enhanced R-Value Significant?
The mass effect is real. High-mass walls really can significantly outperform low-mass walls of comparable steady-state R-value--i.e., they can achieve a higher "mass-enhanced R-value." BUT (and this is an important "but"), this mass-enhanced R-value is only significant when the outdoor temperatures cycle above and below indoor temperatures within a 24-hour period. Thus, high-mass walls are most beneficial in moderate climates that have high diurnal (daily) temperature swings around the desired indoor setpoint.
Nearly all areas with significant cooling loads can benefit from thermal mass in exterior walls. The sunny Southwest, particularly high-elevation areas of Arizona, New Mexico and Colorado, benefit the most from the mass effect for heating. In northern climates, when the temperature during a 24-hour period in winter is always well below the indoor temperature, the mass effect offers almost no benefit, and the mass-enhanced R-value is nearly identical to the steady-state R-value. The ASHRAE Handbook of Fundamentals lists "mean daily temperature range" data for hundreds of U.S. climates in the chapter on climate data. These values can be helpful in figuring out how significant mass-enhanced R-value might be for a particular climate, but they do not tell the whole story; also significant is the percentage of days during the heating and cooling seasons when the outdoor temperature cycles above and below the indoor temperature
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