Masonry Magazine October 1981 Page. 13
BIA Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road, McLean. Virginia 22102
43F
Jan/Feb
1981
PASSIVE SOLAR HEATING WITH BRICK MASONRY
VENTED THERMAL STORAGE WALLS-PART VI
Abstract: The thickness of thermal storage components for passive solar energy systems have typically been determined by empirical methods. This empirical approach is usually sufficient. The modified rational approach used to select unvented thermal storage wall thicknesses may also be used to select vented thermal storage wall thickness. In addition, it will give the designer a better understanding of how the wave of thermal energy permeates a vented thermal storage wall.
Key Words: Absorptivity, bricks, emissivity, energy, masonry, passive solar heating systems, thermal conductivity, thermal diffusivity, vented thermal storage wall systems.
INTRODUCTION
The thickness of most thermal storage components for passive solar energy systems is currently determined by empirical methods. Guidelines for empirically sizing and selecting the required thickness of passive solar energy system thermal storage components are provided in Technical Notes 43A. These provisions are for the thermal storage components exposed directly to sunlight; however, as discussed in Technical Notes 43E, there should be at least one and one-half cubic feet of brick masonry within the building assisted by passive solar heating for every square foot of glazing area used as a collector. This empirical minimum amount of brick masonry includes the brick masonry exposed and unexposed to direct sunlight which may not be sufficient to provide an adequate thermal flywheel for vented thermal storage wall systems. Three cubic feet or more of brick masonry for one square foot of collector area may be required to adequately decrease interior temperature fluctuations for vented thermal storage wall systems. This is because of the increased thermal energy available during daytime hours when the convective loop through the thermal storage wall vents is taking place.
Modifications to account for the radiant energy released from the wall due to the convective loop through the vents of the thermal storage wall may be applied to the simplified heat transfer equations for unvented thermal storage wall systems as discussed in Technical Notes 43E. These modified equations may be used to aid the designer in selecting vented thermal storage wall thicknesses. They may also be used to give the designer a better understanding of how the wave of thermal energy permeates the thermal storage wall and the amount of heat available to the interior by radiation and convection. These equations are based on average temperatures, sinusoidal heat flow in one direction, and steady-state heat loss. Precise analysis cannot be easily achieved by hand calculation methods because it would require complex hour-by-hour calculations. Even precise computer analysis is only feasible for locations where hourly solar radiation and temperature data is available.
VENTED THERMAL STORAGE WALL
# General
The thickness of a vented thermal storage wall may be found using the same procedure as for unvented thermal storage walls except that the energy balance equations are now more complex due to the addition of the convective loop through the vents in the wall. The consideration of the convective loop requires revision of the maximum and minimum exterior surface temperatures.
# Exterior Surface Temperatures
The maximum and minimum exterior surface temperatures of a vented thermal storage wall require an hour-by-hour energy balance to be adequately predicted. This is generally not feasible for most passive solar energy system designs, and maximum and minimum exterior surface temperatures need to be approximated.
Maximum. Maintaining the assumption that on a clear winter day the average maximum exterior surface temperature of an unvented black thermal storage wall, having an absorptivity of 0.98, behind glass will be about 160°F, the maximum exterior surface temperature of a vented thermal storage wall may be approximated. The 160°F maximum exterior surface temperature is an average value which may be used when more precise information is not available. The correction factor for adjusting the maximum exterior surface temperature may be determined by an hour-by-hour energy balance considering all of the conductive, convective and radiant heat losses. Such an approach is beyond the scope of this Technical Notes and thus a Jan/Feb 1981
Brick Institute of America
0000
4d
BRICK
MASONRY
1 ENERGY
GENERAL DATA
ENERGY CONSERVATION
13d
TOTAL ENERGY SYSTEMS
SPECIAL CONSTRUCTION