Masonry Magazine April 1981 Page. 16
Passive Solar Cooling Systems
Passive solar cooling systems use natural phenomena to cool buildings. These systems rely on the principles of convection, radiation, and evaporation to remove heat from a building without using mechanical equipment. The basic components of a passive solar cooling system include: south-facing glazing, thermal storage media, and controlled openings. The south-facing glazing allows sunlight to enter the building and heat the thermal storage media. The thermal storage media, such as brick masonry, absorbs and stores the heat. The controlled openings allow for the exhaust of heated air and the intake of exterior air. The openings for exhausting heated air are typically located at the highest points of the structure, preferably in the roof/ceiling, or gable. Control of the openings may be provided with operable vents, or registers. Similar openings can be placed at the low points of the structure for intaking exterior air. The openings for intaking exterior air may be the windows or doors of the structure. The operation of each of these systems is very similar in the cooling mode: (1) sunlight strikes the south-facing glazing, (2) solar energy is transmitted through the south-facing glazing to the brick masonry thermal storage media, (3) the brick masonry absorbs and stores the heat, (4) radiant heat from the surface of the brick masonry rises, (5) the heated air is exhausted through the controlled openings at the top of the structure, (6) as the heat is exhausted, exterior air is drawn into the structure, and (7) the air movement created by exhausting and intaking air through the structure creates the effect of cooling and provides more comfortable interior conditions.
Direct Gain System
The direct gain system, when applied as passive solar cooling, is the most economical, but probably the least effective. The minimum 4-in. (100 mm) thick brick masonry floors and walls on the interior are exposed to direct sunlight to absorb and store heat.
The interior brick masonry should be dark to absorb most of the heat and radiate and reflect only a small portion during the day. The gradual release of radiant heat through the night draws the cool night air into the structure and cools the structure.
The system is only advantageous when the nighttime temperatures consistently fall below the interior design temperature and when internal solar heat gain can be adequately controlled to prevent overheating in the daytime.
A major problem with using a direct gain system is that the interior space used to store heat is also an integral part of the habitable space of the building.
Attached Sunspace
Using the attached sunspace for passive solar cooling is probably more effective but less economical than direct gain cooling. In the attached sunspace, the heat storage element is not usually part of the space that is to be cooled. The system schematic is shown in Fig. 2. Although the intent in many applications is to use the attached sunspace as a greenhouse, this is not advantageous in most applications because the greenhouse will be vented to the interior and the humidity from watering plants may result in uncomfortable interior conditions and condensation problems. The major disadvantage of this system is the cost of the additional floor area which has limited use.
The system consists of minimum 4-in. (100 mm) thick brick masonry floors, south-facing glazing and preferably a 10 to 18-in. (250 to 450 mm) thick vented brick masonry thermal storage wall between the sunspace and the habitable portion of the building.
In the cooling mode, the top vents of the brick masonry storage wall are closed and the bottom vents are open. The air in the sunspace is heated by radiant heat from the brick masonry. The heated air rises through operable openings in the roof of the sunspace, drawing air from the habitable spaces through the bottom vents of the brick masonry thermal storage wall. The air drawn from the habitable space is replaced by exterior air drawn in through operable windows or doors.
Thermal Storage Wall System
One of the most economical and effective passive solar cooling systems is the vented thermal storage wall, shown schematically in Fig. 3. The greatest advantage of the thermal storage wall is that the heat used for the passive solar cooling does not directly enter the interior spaces of the habitable portion of the building.
The system consists of exterior glazing 2 to 4 in. (50 to 100 mm) in front of a 10 to 18-in. (250 to 450 mm) thick vented brick masonry wall used for storing heat. Operation is similar to that of the attached sunspace. The operable openings for exhausting the heated air may be located at the top of the exterior glazing. The exhaust system may also be operable vents at the top of the airspace from which the air may be exhausted through additional vents in the roof. When using the latter exhaust system, additional vents from the hal