SOLAR
THERMAL
MAKES A
COMEBACK
Active and passive solar systems
can supply domestic hot water,
space heating, or both
There was a time not
too long ago when
solar thermal systems
seemed like a relic of
the late 1970s. A er the
solar tax credits were
killed in the early 1980s,
the systems disappeared. ey started
reappearing, however, rst in Germany
in the late ’90s from manufacturers such
as Veissmann, in response to increasing energy prices in Europe. European
manufacturers remain among the leaders in the eld, with suppliers such as
Italy’s Cale and Germany’s Oventrop,
Rehau, and Schuco.
Solar thermal is making a comeback in the U.S. because of high energy
prices, and government and utility
incentives. Consequently, it behooves
green mechanical contractors to have
some elementary knowledge of solar
thermal systems.
Solar systems can be active or passive. A passive solar system depends
on hot water rising and cool water falling. The solar collector will have an
insulated storage tank above it, either
on the inside or outside of the house.
The solar storage tank is also piped
to a conventional water heater to
provide supplemental water heating.
The system depends on the thermosiphon e ect to move hot water from
the solar storage tank to the domestic
water heater.
An active solar system has a circulator. Almost all liquid-based solar
systems use either a flat-plate or an
evacuated-tube collector. A at-plate
collector has copper tubing attached to
a copper sheet. Both are painted black
to increase their ability to absorb solar
radiation. The collector is typically
housed in an aluminum enclosure, and
the underside is insulated to resist temperatures as high as 350°F. e copper
collector is usually covered with tempered glass.
An evacuated-tube collector has
tubes with concentric inner and outer
tubes that are evacuated like a thermos bottle. The inside tube contains
a heat-transfer fluid that vaporizes
from solar heat and rises into a heat-
