Masonry Magazine February 1981 Page. 31
Technical Notes on Brick Construction
Brick Institute of America 1750 Old Meadow Road, McLean, Virginia 22102
43A
July/Aug
1979
INTRODUCTION
BRICK PASSIVE SOLAR HEATING SYSTEMS
PART II-SIZING SYSTEMS
The general concepts and requirements for brick passive solar heating systems are discussed in Technical Notes 43. Technical Notes 43B provides performance calculation methodologies for direct gain and thermal storage wall systems. This Technical Notes provides an empirical method for sizing the solar collector for both direct gain and thermal storage wall systems. The methods are straightforward and are based on steady-state heat transmission methodologies as set forth in the ASHRAE Handbook of Fundamentals. The methods set forth in this Technical Notes allow the designer to quickly and easily size the system. To determine the performance of the system and the amount of auxiliary heating to be provided, the methods set forth in Technical Notes 43B should be used.
The numerical values in this Technical Notes are expressed as U.S. Customary Units. See Table i of Technical Notes 4E for conversion to Metric (SI) Units.
SYSTEM SIZING
The size of the system refers to the surface area of the collector, which is usually south-facing glazing. The size of passive solar heating systems may first be approximated by empirical sizing techniques. The size is determined from the amount of heat required in the building and is expressed as a ratio of solar collector area to the floor area of the building to be heated by the passive solar system. This empirically estimated size may then be used in the initial performance calculations to determine the amount of energy supplied by the passive system and the auxiliary heating furnished by a backup system. The size of the passive solar system may then be adjusted with the results of the passive solar heating system performance calculations.
Direct Gain Systems
Direct gain systems are usually designed to prevent overheating of the interior spaces of the building. Spaces as used in this Technical Notes refer to the habitable interior heated areas of the building. In well designed direct gain spaces temperature fluctuations from 15° F to as little as 10° F below interior design temperatures may be expected. These temperature fluctuations occur because the direct gain systems are designed so that overheating does not occur. Larger systems may be used to increase the solar energy absorbed by the direct gain system but provisions should be made to prevent the occurrence of overheating. Overheating may be prevented by using shading devices to reduce solar heat gain or by venting the system to exhaust excess heat. Venting may be achieved either by opening windows or by using an exhaust fan.
In the space using a direct gain heating system, brick floors and walls should be exposed to direct sunlight. These walls and floors should be at least 4 in. thick. The areas of the walls not used for thermal storage exposed to direct sunlight should be a light color to reflect sunlight to the brick masonry floors and walls.
The size of the south-facing glazing required in a direct gain heating system to maintain average interior temperatures between 68° and 70° F on clear winter days is given in Table I as a ratio of the solar collector area to the floor area of the passive solar heated space. Table 1 provides values to determine the size of the direct gain heating system for 36° to 48° North Latitude and average clear day exterior temperatures from 20° to 45° F. Average clear day exterior temperatures should be used to reduce the possibility of overheating when estimating the size of the systems. The values in Table 1 are for December and January which are usually the coldest months and apply to building designs which have a total heat loss of approximately 8 Btu/ day/F/ft of floor area. If the space heat loss is greater or less than 8 Btu/day/°F/ft² of floor area, the values in Table 1 should be adjusted accordingly. This is done by multiplying the value in Table I by the ratio of the estimated building design heat loss in Btu/day/F/ft² of floor area and 8 Btu/day/F/ft² of floor area. If night insulation having a thermal resistance of R 8 is added to the direct gain system, the values in Table I may be decreased by 15 per cent to prevent overheating.
Example. Consider a 50 by 30-ft residential structure with the long dimension on the East-West axis in Washington, D.C. The structure is assumed to have: a roof ceiling component with an area of 1500 ft and a U