Miscellaneous Tests (cont.)
National Bureau of Standards, NBSIR 81-
2199, "Wind, Earthquake, Snow, and Hail
Loads on Solar Collectors" Jan 1981; and
NBSIR 82-2487, "Hail Impact Testing Proce-
dures for Solar Collector Covers" Apr 1982
National Bureau of Standards, NBSIR78-
(See also HUD Report 4930.2)
1532, "Environmental and Safety
Considerations for Solar Heating and
Certified Test Labs
National Bureau of Standards, NBSIR
78-1535, "Laboratories Technically
Qualified to Test Solar Collectors in
Accordance with ASHRAE Standard 93-77" Nov
In addition to these standards, there are plumbing standards published
by The International Association of Mechanical and Plumbing Officials
(IAMPO), and various state building codes.
1.3 Solar energy.
1.3.1 Solar radiation. Energy from the sun is received by the earth as
Tropic of Cancer (23 deg. N latitude), the sun makes a daily arc across the
southern sky from east to west as shown in Figure 1-1. For a typical
location at 32 deg. N latitude the sun would be 81.5 deg. above the southern
horizon or nearly overhead at noon (solar time) on June 21 while on December
21 it would be only 34.6 deg. above the horizon (Barnaby et al., 1977).
Solar insolation (I) is measured in Langleys (L) or Btu/ft2. One Langley
equals 3.688 Btu/ft2. The amount of solar energy that exists outside the
atmosphere, often called the solar constant, is 116.4 L/hr or 429.2
Btu/ft2-hr. At most 70% to 80% of this amount will strike the earth's
surface, the remainder being absorbed or reflected in the atmosphere.
Monthly average and yearly average daily insolation data for numerous
locations are given in Table 1-1. In general, the higher the latitude, the
less insolation is received on a horizontal surface.
1.3.2 Collecting solar energy. Collection of solar energy is based on the
very high absorption of radiant energy by dull, black surfaces and on the
"greenhouse effect." The latter refers to the ability of glass to transmit
visible radiation but prevent the loss of heat from the collector plate which
radiates at longer wavelengths (infrared frequencies). Glass (or plastic)
cover plates are generally used over flat absorber plates to reduce heat loss
(see Figure 1-2). The heated absorber plate may have a fluid (water, air or
other) pass over it or through tubes attached to the plate. The fluid thus
heated may be used to heat potable water, heat spaces, or drive an absorption
or Rankine power cycle air conditioner.