MIL-HDBK-1003/19
TAPs have thermal storage requirements similar to those of direct gain
and radiant panel systems. Generally speaking, the best performance will be
obtained from passive solar systems associated with high heat capacity
structures. Although a backflow TAP performs slightly better than a
comparable system in the frontflow configuration, the difference is not
significant and construction costs should govern any choice between the two.
Both TAP configurations outperform radiant panels and direct gain systems
with comparable glazings and thermal storage mass. This performance edge is
due to the low aperture conductance of TAPs, which can be insulated to
arbitrary levels, thereby limiting night time heat loss.
4.1.5 Thermal storage walls. A thermal storage wall is a passive solar
heating system in which the primary thermal storage medium is placed
directly behind the glazings of the solar aperture, as illustrated in figure
5. The outer surface of the massive wall is painted a dark color or coated
with a selective surface to promote absorption of solar radiation. Solar
radiation absorbed on the outer surface of the wall is converted to heat and
conducted (or convected in the case of the water walls) to the inner surface
where it is radiated and convected to the living space. Heat transfer to
the living space is sometimes augmented by the addition of circulation vents
placed at the top and bottom of the mass wall. These vents function in the
same manner as the vents in a TAP system except that only a portion of the
solar heat delivered by the system passes through the vents.
A thermal storage wall provides an effective buffer between outside
ambient conditions and the building interior; night time heat losses are
reduced during the cold winter months, and during the summer, unwanted heat
gains are limited. This moderating effect generally enables thermal storage
walls to outperform direct gain systems. There are many types of thermal
storage walls distinguished by the type of storage medium employed. The
options included in the design procedures are reviewed in the following
subsections.
4.1.5.1 Trombe wall. A Trombe wall is a thermal storage wall that
employs solid, high density masonry as the primary thermal storage medium.
Appropriate thicknesses range from 6 to 18 inches depending on the solar
availability at the building site. Sunny climates require relatively
thicker walls due to the increased thermal storage requirements. The wall
may be vented or unvented. A vented wall is slightly more efficient and
provides a quicker warm up in the morning but may overheat buildings
containing little secondary thermal storage mass in the living space.
4.1.5.2 Concrete block wall. Ordinarily, a thermal storage wall would
not be constructed of concrete building blocks, because solid masonry walls
have a higher heat capacity and yield better performance. However, concrete
block buildings are very common in the Navy and offer many excellent
opportunities for passive solar retrofits. The south facing wall of a
concrete block building can be converted to a thermal storage wall by simply
painting the block a dark color and covering it with one or more layers of
glazing. Walls receiving this treatment yield a net heat gain to the
building that usually covers the retrofit costs rather quickly. The
relatively low heat capacity of concrete block walls is offset somewhat by
the large amount of secondary thermal storage mass usually available in
these buildings. Concrete floor slabs and massive partitions between zones
help prevent overheating and otherwise improve the performance of concrete
block thermal storage walls.
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