Masonry Magazine April 1981 Page. 18
HEATED AIR
EXHAUSTED
OPEN VENT
OR LOUVERS
HEATED AIR
EXHAUSTED
OPEN VENTS OR LOUVERS
INSULATED ROOF
SUMMER SUNLIGHT
INSULATED
CEILING
INSULATED CEILING
SUMMER SUNLIGHT
SOUTH
FACING
OPEN VENT
TOP VENT OF THERMAL
STORAGE WALL CLOSED
MASSIVE BRICK
THERMAL
STORAGE
GLAZING
WALL
MASSIVE BRICK
THERMAL STORAGE WALL
EXTERIOR
AIR DRAWN
INTO THE
BUILDING
SOUTH
FACING
GLAZING
EXTERIOR AIR
DRAWN INTO
THE BUILDING
ENVELOPE
Cooling With the Vented Thermal
Storage Wall System
FIG. 3
itable space through the roof/ceiling component may
be used to increase the heat flow from the interior,
thereby drawing additional air into the building.
CONTROLS
These three basic passive solar heating systems, as modified for passive solar cooling, require controls to regulate internal heat gain and the level of comfort, "cooling", achieved. These controls may be automatically or manually operated vents, or registers. The controls should be such that the system can be totally "shut down" when it is not being effective, i.e., when exterior conditions are such that a comfortable effective temperature cannot be maintained inside the building. Shading devices are required as a means of controlling the amount of sunlight permitted to enter the structure for operation of the passive solar cooling system. These may also be automatic or manual devices, but are necessary to prevent overheating that can occur during the cooling season when the interior temperature, i.e., effective temperature, will no longer be within the comfort range. The entire system must be completely shut down before mechanical/refrigeration cooling systems are put into operation. Shading the south-facing glazing and closing openings are required for efficient use of any conventional cooling system. Anticipation of when overheating or a comfortable effective temperature will no longer be maintained is necessary so that the passive solar systems can be deactivated prior to creating additional cooling loads for the conventional cooling system. Obviously, operation is a critical factor in the performance of "passive solar cooling systems".
CAVITY WALL SYSTEM
A system which may be effectively used for cooling, with less consideration of the climatic conditions, is the cavity wall system, schematically represented in Fig. 4. The north and south walls of the structure are uninsulated cavity walls (see Technical Notes 21 Series).
OPEN VENT
DUCT WORK FOR
PRE-COOLING AND
DEHUMIDIFYING
EXTERIOR AIR
Cavity Wall System, Cooling Mode
FIG. 4
The south-facing wall, above grade, is an unvented thermal storage wall. The airspace in the thermal storage wall system is open at the bottom to the cavity of the basement or foundation wall, and at the top to the roof/ceiling. The cavity of the wall is open to ductwork extended in the north-south direction through the basement floor, or crawl space. As shown in Fig. 4, this provides an air passageway within the building envelope components. A ductwork system is provided from the base of the cavity to vents on the exterior. Exhaust vents are provided in the roof or gable ends.
With the cavity wall system, the south-facing glazing exposes the brick thermal storage wall to sunlight, which heats up and causes air to rise through the cavity. As the air rises, it is vented to the exterior from the top of the cavity, and exterior air is drawn into the cavity via the ductwork system and exterior vents. This provides a means of keeping the entire building envelope cooled. Since the surfaces warmed during the daytime hours retain heat, this continues through the evening hours, further cooling the building envelope. The cooled building envelope and interior require a longer time period to be heated up to uncomfortable temperatures during the daytime hours of the next day. The advantages of passive solar cooling with the cavity wall system are: (1) shutdown is not essential for conventional cooling to work effectively (the cooling systems are isolated from each other), and (2) since the exterior air for cooling is not brought into the habitable space, the effects of humidity (a major drawback in most passive solar cooling systems, depending on climate), may be reduced.
The east and west walls do not have to be uninsulated cavity walls. By keeping all walls cavity walls, the east and west walls may perform as a buffer zone between the north and south walls. This may increase the overall performance of the system.