heating systems. 95/5 tin/antimony is normally used on most joints. 96/4 tin/silver
is recommended for joints involving bronze to avoid leaching the zinc from fittings.
In loops containing fresh water (e.g., potable water), copper, brass, bronze or
stainless steel are normally the only appropriate materials. If galvanized piping
already exists, it is necessary to use dielectric unions to isolate different metals.
In loops containing non-freezing solar fluids, or water which is never exposed to
oxygen (e.g., the collector loops or closed-loop and drainback systems), small
amounts of cast iron or steel can be part of a copper piping system. These are
normally the wetted components of pumps, expansion tanks, etc.
Aluminum should never be piped into a system with copper, but if it is, special steps
such as dielectrics and getter columns must be used.
2.7.4 Solar Fluids, The best fluid available for moving the heat from solar
collectors is water. Unfortunately, when water is exposed to freezing temperatures it
becomes solid and expands, two undesirable characteristics.
Special non-freezing fluids have been developed for solar applications. The three
types typically used are:
o Glycol/Water mixtures
o Synthetic oils
o Silicone oils
These materials have different characteristics, but they all have one thing in
common, their specific heats and thermal conductivities are lower than water. This
results in higher pump and heat exchanger requirements and costs.
Once a system has been filled with a particular type of solar fluid, it
should always be recharged with the same material.
Glycols are either ethylene glycol or propylene glycol, usually in a 50/50 mixture with
distilled or demineralized water. Special inhibitors are added to help prevent the
fluid from becoming corrosive.
2.7 COMPONENT OPERATION