Both EPDM and silicone rubbers have been found adequate for use as gasket
materials. Silicone sealants have exceptional weathering resistance and have
received widespread use for many years.
2.1.7 Collector fluids - corrosion and freeze protection. The choice of
which collector fluid to use is important because this is the life-blood of
the system. The cheapest, most readily obtainable, and thermally efficient
fluid to use is ordinary water. However, water suffers from two serious
drawbacks - it freezes and it can cause corrosion. Therefore, the choice of
collector fluid is closely linked to the type of solar system, the choice of
components, future maintenance, and several other factors which will be
discussed in this section. Implicit in this discussion is the use of a fluid
other than air as the collector fluid. As explained in Table 2-1 an air
solar system does not suffer from corrosion or freezing effects, but its low
density and heat capacity require the use of fans and large ducts, large
storage volumes, and is generally not suitable for domestic water heating.
The remainder of this section applies to liquid solar heating systems.
A list of standards has been prepared for heat transfer fluids and can be
found in the reference, "Intermediate Minimum Property Standards" (see
Section 6.0). Generally the standards state that the heat transfer fluid
must be nonionic, high dielectric, nonreactive, noncorrosive, nonflammable
and stable with temperature and time. If the fluid is toxic it may be used
only in systems specially designed for it as will be explained later.
The National Bureau of Standards (1980), Ref - DOE Solar Heating Materials
Handbook, has proposed the following criteria to reduce the risk of fire in
the use of solar heat transfer fluids:
The flash point of the liquid heat transfer fluid shall equal or exceed
the highest temperature determined from (a), (b), and (c) below:
A temperature of 50 deg. above the design maximum flow temperature
of the fluid in the solar system; or
A temperature 200 deg. F below the design maximum no-flow
temperature of the fluid attained in the collector provided
the collector manifold assembly is located outside of the
building and exposed to the weather and provided that relief
valves located adjacent to the collector or collector manifold
do not discharge directly or indirectly into the building and
such discharge is directed away from flames and ignition
The design maximum no-flow temperature of the fluid in all
other manifold and relief valve configurations;
100 deg. F.