Masonry Magazine January 1980 Page.18
In the direct gain system, the south-facing glazing permits sunlight to strike the dark brick masonry construction. The brick masonry, because of its color and mass, provides the thermal storage for the system. The dark brick masonry absorbs the thermal energy from the sunlight striking its surface. The heat, which is stored during the daylight hours, is released gradually. The heat that is reflected from the dark brick masonry provides heat to the habitable space during the daylight hours. The light-colored surfaces provide continuous reflection of the heat reflected or radiated from the dark brick masonry to the air and surroundings in the habitable space.
Direct gain systems provide rapid temperature increases in the habitable space and may have large temperature fluctuations. This is because such systems often must be designed to prevent overheating. The systems may have limited amounts of brick masonry exposed to the winter sunlight. This is especially true in the lower latitudes where the winter sun has a higher altitude. This may be overcome by providing clerestories to obtain solar radiation on the north wall, as shown in Fig. 5.
Ultraviolet degradation is of the greatest concern in the direct gain systems. Materials affected by the ultraviolet degradation should not be exposed to direct sunlight. This may become an inconvenience in the living areas heated by direct gain. The walls and floors exposed to the sunlight and used for thermal storage should not be covered. Wall hangings and carpet greatly decrease the performance of the system.
THERMAL STORAGE WALL SYSTEMS
The thermal storage wall system, often referred to as a Trombe Wall System, is schematically represented in Fig. 6. The interior of the thermal storage wall is shown on the right of Fig. 2. It consists of glazing spaced 2 to 4 in. on the exterior of a south-facing wall, constructed of brick masonry, usually ranging in thickness from 10 to 18 in. The massive brick wall may be loadbearing, or non-loadbearing.
The winter sunlight penetrating the south glazing heats the dark brick, the heat slowly penetrates the brick wall and warms the interior. Thermal storage walls may have storage of sufficient capacity to maintain comfortable temperatures in buildings for periods up to three completely overcast days. The thermal storage wall systems have considerably less temperature fluctuation than do direct gain systems, but usually do not achieve the same high initial interior temperatures.
The massive brick thermal storage wall prevents ultraviolet degradation of materials contained in the living space. The performance may be substantially increased by providing vents at the top and bottom of the brick wall to provide convection in addition to the heat radiated from the interior face of the wall. This will decrease the temperature fluctuations and increase the maximum temperature achieved in the living space.
Figure 1. shows a vented thermal storage wall under construction. A schematic of a vented thermal storage wall system is shown in Fig. 7. When venting the storage wall system, vents with automatic or manual closures should be used so that the system does not reverse at night, creating a heat loss.
If controlled vents are not installed on the vented thermal storage wall systems, night insulation is essential to prevent heat losses at night. Night insulation is