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2.6 Passive systems.  NCEL has published a contract report, "Passive Solar
Design Procedures for Naval Installations" (see references) that is the
principal Navy reference on this subject.  It contains data and worksheets to
size passive so]ar designs at 200 geographical locations.  Over 100 different
passive designs can be considered and the method is applicable for single
family residences, family townhouses, dormitories (i.e. BEQ's), small
offices, and other concrete block buildings.  While the "Passive" report
should be consulted for detailed information and sizing, this section of the
Military Handbook is retained to provide an introduction and "rules of thumb"
for passive solar techniques.
A "passive" solar energy system is one which uses the building structure as a
collector, storage and transfer mechanism with a minimum amount of mechanical
equipment.  Some would include a thermosyphon, batch, and ISC systems in this
definition.  As a rule, passive systems are generally difficult to retrofit
Another disadvantage is that the owner or occupant may be required to perform
daily tasks, such as covering a south facing window at night, opening and
closing shutters, etc.  This is particularly significant in Navy housing
where the occupants are more transient and have less incentive to do these
maintenance items.  Although the specific arrangements vary, all of these
systems rely on direct solar heating of storage.  The storage then heats the
house.  A few examples are shown in Figure 2-19 (Barnaby et al., 1977).
Given the solar gain available on a vertical surface, the simplest and most
obvious means of solar heating is just to let the sun shine in through large,
south-facing windows.  In fact, in a house with any south-facing windows,
that is what is already happening to some degree.  But the sunshine through
the windows seldom heats the whole house.  There are two reasons for this.
First, most houses do not have enough south-facing glass.  Second, houses
lack enough storage to soak up the heat and keep it until night.  Even rooms
that overheat during the day cool off all too rapidly in the evening.
On many buildings it is possible to add south-facing windows or skylights to
increase direct solar heating.  However, the extra window area can cause a
"fry or freeze" situation unless storage and night window insulation is added
as well.  There must also be provisions for getting heat from the rooms
receiving sunlight to the rest of the house.  Providing such storage and
delivery of solar heat gained through windows is the basis of passive solar
As shown in Figure 2-19 the type of storage used and where it is located with
respect to the windows varies for different passive systems.  Tall metal or
fiberglass tubes can be used to hold water instead of drums.  Entire walls of
solid concrete or grout-filled masonry store solar heat well.  Slab floors
can absorb solar heat coming in through windows, skylights, or greenhouse
In each of these systems, the sunlight coming in through the glass must shine
directly on the storage.  If it does not the storage cannot absorb enough
solar heat to provide much warmth for the house.  Most passive systems
deliver heat to the rest of the house "naturally" - that is, the heat moves
by itself without use of pumps or fans.  There is some natural regulation of
how fast heat moves from the storage into the house - the colder the house
gets, the faster the heat is drawn out of the storage.  That is how the drum
wall works.

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