IN-91-13-3 --Thermal Mass Credits Relating to Building Envelope Energy Standards ✓ Most Recent

Refers to the results of the DOE thermal mass research, which showed that if all building parameters remain constant, exterior wall mass improves or maintains the annual thermal performance of buildings. Thermal mass in the exterior walls does not save energy if the building load is continuously a gain or a loss for all hours of the day. An insulated mass wall is most effective with the insulation outside the mass. BLAST, DOE-2.1, and DEROB can simulate mass effect tendencies. More than 100 comparisons of model predictions with measured experimental data were made. The periods of comparison varied from one day to two weeks. The cumulative comparison of all test periods, test houses, and models predicted 1.5% above the measured loads, and 88% of these comparisons fell within plus or minus 25% of the measured loads. Several simplified thermal mass prediction techniques were developed, based on calibrated whole-building simulation models and empirical regression equations that predict delta loads of single-family residences with different mass loadings and identical R-value walls. The R-value difference between an insulated massive wall and insulated frame wall that provides the same annual thermal performance is typically between zero and 5 ft2.deg F/Btu, less than one inch of most foam-board insulations. These results do not accurately portray passive solar buildings with managed south-facing windows and large quantities of mass exposed to the inside air and insulated externally.

KEYWORDS: calculating, buildings, walls, research, heat flow, thermal properties, insulated housing, performance, thermal resistance, computer programs, measuring, comparing, thermal inertia, housing, mass solar walls, solar walls