5.2.5 Heat Exchangers,
Always confirm that a double wall heat exchanger is used whenever a
toxic solar fluid is used, particularly with DHW systems. This
information should be available from the nameplate. If a single wall
heat exchanger is present, replace the toxic fluid with a non-toxic
Water with a high dissolved mineral content, "hard" water, will deposit scale on
heated surfaces. This usually occurs in loops filled with "city" or well water, such as
DHW systems. The water passageways of heat exchangers can be descaled to
remove this material.
Some heat exchangerscan be mechanically descaled with brushes. This process
requires draining and opening the heat exchanger and running the brush through
each tube several times. After brushing, flush the heat exchanger with plenty of
water to avoid allowing small pieces of scale to get stuck in system components.
In many cases, the scale cannot be removed mechanically. The heat exchanger
may not be built for it, or the scale deposits may be too hard or thick. In these
cases, chemical descaling, using various types of acid is necessary.
If the water being heated is potable (used for drinking, cooking or
bathing), the descaling solution should not be toxic! If this is not
possible, be sure to completely flush the heat exchanger with fresh
water after descaling.
One acceptable descaling solution is phosphoric acid, sold by Stewart Hall as
"ScalestripTM." Another choice is lntech 52TM, which is shipped as a dry powder,
and is mixed with water just before use.
5.2 REPAIR PROCEDURES