14 June 2002
Freeze Protection. The propylene glycol mixture used in the closed-loop
system provides freeze protection. Direct circulation is used only in non-freezing
climates. Because the direct circulation system is more or less a special type of closed-
loop system, its control strategy is the same.
Over-Temperature Protection. Over-temperature protection of the
collector loop in the event of stagnation is provided through expansion tank sizing (refer
to Chapter 4). The pressure-temperature relief valve located on the storage tank
supplies over-temperature protection of the storage loop. If a direct circulating system
is supplying water for domestic use, it is required that users be protected against the
possibility of live steam being issued from taps or showerheads. This protection is
provided through the proper use of relief and mixing valves.
Auxiliary Pump Switches. The use of auxiliary high- and low-
temperature switches that will trip the pumps as a backup to the differential controller
are not recommended. These switches are as prone to failure as the controller, and
have been the cause of many solar system failures.
Location of Controls. Whenever possible, electronic displays and visual
pressure and temperature gauges should be panel-mounted together in the mechanical
room. Temperature sensors, which are located on the collector manifolds and on the
storage tank, should be easily accessible for calibration and servicing. A common
problem is sources of electromagnetic interference with the sensor wiring. This
problem can be avoided by making the sensor wiring path as short as possible and by
using conduit separate from AC power wiring. It may be desirable to include extra
conductors for future expansion or maintenance needs.
COORDINATION. The system designer is responsible for ensuring that all
essential information is provided to the architect and structural engineer, so that the
building plan can accommodate the solar system requirements.
Roof Requirements. The most important requirement for the architect, with
regard to the solar energy system, is to provide adequate unshaded roof area and
proper orientation for the system. Other architectural requirements for roof design
include providing roof penetrations near the array for collector supply and return lines;
designing the array support structure; allowing adequate access to the array for
maintenance; including access to the roof for personnel (and equipment); including
walkways around the array; and locating the collector array above or near an area that
can be used for pipe chases.
Location. The equipment room for the solar energy system hardware will