Masonry Magazine October 1981 Page. 18
TABLE 1
Face Brick Thermal Storage Wall Calculation Summary for Washington, D.C. in January
| Wall Thickness (in.) | Tmax (°F) | Tmin (°F) | Vented Wall Time Lag (hr) | q (Btu/ft²/hr) | Tmax (°F) | Tmin (°F) | Unvented Wall Time Lag (hr) | q (Btu/ft²/hr) |
|---|---|---|---|---|---|---|---|---|
| 8 | 91.5 | 76.5 | 6 | 15.3 | 98.0 | 83.0 | 6 | 19.0 |
| 12 | 85.5 | 79.5 | 9 | 13.7 | 92.5 | 85.5 | 9 | 17.4 |
| 16 | 82.5 | 79.5 | 12 | 12.0 | 89.5 | 85.5 | 12 | 15.8 |
| 24 | 81.0 | 80.0 | 18 | 11.4 | 86.0 | 85.0 | 18 | 13.7 |
*Brown brick, α = 0.78
*q = q, for unvented walls.
where: V = Additional volume of brick masonry, in cu ft per sq ft of collector area.
V = Required volume of brick masonry, in cu ft per sq ft of collector area.
Vrw Volume of brick masonry in the thermal storage wall, in cu ft.
Using Equation 11, for the minimum requirement of one and one-half cubic feet of brick masonry for the unvented thermal storage wall, the additional brick masonry which should be located inside the building should be:
12-in. wall, V 1½ cu ft I cu ft = ½ cu ft per sq ft of collector area
16-in. wall, V 1½ cu ft 1/5 cu ft % cu ft per sq ft of collector area
Similarly, for the vented brick masonry thermal storage walls:
8-in. wall, V 1½ cu ft 75 cu ft % cu ft per sq ft of collector area
12-in. wall, V 1½ cu ft1 cu ft = ½ cu ft per sq ft of collector area
The empirical value for the minimum amount of brick masonry required in the building is applicable for buildings for which the passive solar energy system is supplying up to 40% of the total building heating load. This minimum requirement of 1½ cu ft of brick masonry per sq ft of collector area should be increased by no less than 4 cu ft of brick masonry per sq ft of collector area for every 10% increase in the percentage of the building heating load being supplied by the passive solar energy system.
If a 400-sq ft 12-in. thick brick thermal storage wall is supplying 70% of the total building heating load, the minimum amount of brick masonry required would be approximately 24 cu ft of brick masonry per sq ft of collector area. Using Equation 11, the amount of brick masonry needed on the interior of the building in addition to the thermal storage wall would be:
12-in. wall, V 24 cu ft 1 cu ft = 14 cu ft per sq ft of collector area
For the 400-sq ft collector, the interior brick masonry in addition to the thermal storage wall would be approximately 500 cu ft.
METRIC CONVERSION
Because of the possible confusion inherent in showing dual unit systems in the calculations, the metric (SI) units are not given in the examples. Table 13 of Technical Notes 4G provides metric (SI) conversion factors for the more commonly used heat transmission units.
SUMMARY
This Technical Notes provides information which may be used to assist the designer in the selection of vented thermal storage wall thicknesses, and to provide the designer with some basic information on how the wave of thermal energy travels through a thermal storage wall. The information presented is based on simplified heat transfer equations and the necessary assumptions so that the calculations may be performed by hand. The information is not intended to accurately predict actual performance but only to provide a comparison of performance so that the designer may more judiciously select the appropriate system type and vented thermal storage wall thickness. The decision to use the information and concepts presented in this Technical Notes is not within the purview of the Brick Institute of America, and must rest with the designer or owner of any specific project.
REFERENCE
1. ASHRAE Handbook and Product Directory, Fundamentals Volume 1977, American Society of Heating. Refrigerating and Air-Conditioning Engineers, New York City, New York.
2. Brick Masonry for Thermal Storage, by Stephen S.