14 June 2002
solar storage tank where it then passes through the collector array (if activated) or on to
the conventional water heater.
Water Supply. Due to their inability to withstand freezing temperatures,
there is a relatively small market for direct circulation systems within the military.
However, because of their simplicity and straightforward operation, they have proven
superior when used at the proper location. An overwhelming consideration for the
success of these systems is the quality of the local water supply. Water is circulated
directly through the collectors, so that corrosion and scale buildup can be a major cause
of failure in these systems. In many regions where the water supply is of poor quality, it
is necessary to treat the incoming water supply so that it is within the prescribed quality
SYSTEM SELECTION. The standard systems described represent proven
designs that are both simple and reliable. System selection is largely based on the site
location, with the number of freezing days being the critical factor. Also important are
the estimated load size and the water quality at the site. Use APPENDIX B to estimate
average hot water loads for various facilities. Use APPENDIX C to evaluate the water
quality for various locations and water sources. Figure 3-3 is a flowchart to facilitate the
system selection process. This figure allows only service water preheating applications
to be chosen.
SYSTEM LAYOUT. The system layout phase identifies the solar energy system
requirements that will impose certain constraints on the building design. The architect
and structural engineer must be notified of these requirements early in the design stage
of the project. These requirements include proper orientation of the building,
identification of available roof area and structural criteria, and proper design and
location of the equipment room. Once these requirements are met and the necessary
building parameters are fixed, the solar system design can be completed.
Representative Solar Collectors. Many flat-plate solar collector (refer to
Figure 3-4) sizes are available. Typical collectors range in size from about 16 to 47 ft
(1.5 to 4.4 m2) of net aperture area, with corresponding gross dimensions of 3 by 6 ft
(914 by 1829 mm), to 4 by 13 ft (1219 by 3962 mm). Two standard sizes are
considered to be about 30 and 40 ft (2.8 and 3.7 m ), with gross dimensions of 4 by 8
ft (1219 by 2348 mm) and 4 by 10 ft (1219 by 3048 mm), respectively. Single-glazed
collectors filled with liquid weigh approximately 4 to 5 lbs/ ft2 (192 to 239 Pa).
Recommended flow rates vary over a wide range, but most fall between 0.01 to 0.05
gals/min-ft2 (0.007 to 0.034 L/sec-m2).