Masonry Magazine February 1981 Page. 36
The required thermal storage wall area is then:
0.236 x 1500 ft of floor area = 354 ft²
and the heat supplied on a clear winter day would be more than required to maintain interior temperatures of 68° to 70° F when R-8 night insulation is added to the thermal storage wall system.
It is important to realize that these values are conservative as compared to actual performance of the thermal storage wall system because average maximum monthly temperatures were used and not specifically clear day exterior temperatures. However in specific applications, the designer may wish to use larger sizes to compensate for when the temperatures are below average or when it is cloudy. When this is done provisions for exhausting excess heat from the space are recommended.
Combined Systems
Estimating the size of combined direct gain and thermal storage wall systems is a simple procedure. Approximately 1 ft of direct gain provides about the same amount of heat as 2 ft of thermal storage wall. Thus, continuing with the same example without R-8 night insulation, consider that 50 per cent of the heat is to be supplied by the direct gain system and 50 per cent by the thermal storage wall system.
Example. It was found in the direct gain example that 311 ft of south-facing glazing was required to supply 100 per cent of the required heat on clear winter days to maintain interior temperatures of 68° to 70° F. Since 50 per cent of the required heat is to be supplied by the direct gain system, one-half the size, 311 ft², is approximately 156 ft. The size to provide 50 per cent of the required heat by the thermal storage wall system is simply twice the area required by the direct gain system supplying 50 per cent or 311 ft. Since this combination, 467 ft², exceeds the area of the south wall, 400 ft², it is not realistic.
However, if 200 ft of the south-facing wall is used for direct gain and 200 ft² is a thermal storage wall, this system would supply close to 100 per cent of the required heating to maintain interior temperatures of 68° to 70° F on a clear winter day, with less interior temperature fluctuations than achieved by the direct gain system alone.
As previously discussed, this value may be attained by considering that I ft of direct gain system supplies as much heat as 2 ft² of thermal storage wall system. The 200 ft of thermal storage wall system may be represented by 100 ft of direct gain system. Then 300 ft of direct gain system, nearly equal to the required 311 ft² shown in previous calculations, supplies most of the heat required to maintain interior temperatures of 68° to 70° F on clear winter days.
SUMMARY
This Technical Notes provides an empirical method for sizing both direct gain and thermal storage wall passive solar heating systems. It also provides a means for sizing combined systems made up of direct gain and thermal storage wall systems. Also provided are methods to size the systems both with and without added nighttime insulation.
This methodology is in a very simplified form and does not consider climatological and environmental factors which may have an effect on the performance of the system. The energy savings and dollar savings of a passive heating system may be almost negated if it is not shaded from direct summertime sunlight. This can be accomplished by deciduous vegetation, fixed shading devices such as overhangs and moveable shading devices. Due to prolonged natural cloud cover, the passive solar systems may not provide sufficient heat. Therefore, an adequate backup system should be provided.
The decision to use these methods and the performance of the systems is not within the purview of the Brick Institute of America and must rest with the project designer or owner, or both.
ACKNOWLEDGMENTS
The Brick Institute of America greatly appreciates the assistance and cooperation of Edward Mazria in developing this publication.
REFERENCES
1. The Passive Solar Energy Book, Expanded Professional Edition, by Edward Mazria, Rodale Press, Emmaus, Pennsylvania, 1979.
2. Proceedings of the 1978 Annual Meeting in Denver Colorado of the American Section of the International Solar Energy Society, Inc.. Volume 2.2, Passive Systems, Plysics, Socio-economics, Solar Radiation, Wind, published by the Publishing Offices of AS/ISES. Inc., University of Delaware. Newark. Delaware 19711. 1978.
3. Proceedings of the 2nd National Passive Solar Conference. Volume 2. Components. Simulation and Testing, published by the Publishing Office of the American Section of the International Solar Energy Society, Inc.. McDowell Hall. University of Delaware, Newark, Delaware 19711, 1978.
4. The ASHRAE Handbook of Fundamentals. American Society of Heating. Refrigerating, and Air-Conditioning Engineers, Inc., 1977.
5. Input Data for Solar Systems, prepared for the U.S. Dept. of Energy, by B. Cinquemani, J. R. Owenby, Jr., and R. G. Baldwin of the Dept. of Commerce. National Oceanic and Atmospheric Administration. Environmental Data and Information Service. National Climatic Center, Asheville, N.C., 1978.