DXR Drainback
Page 5
THE WATER HEATER
The water heater used in this system is your existing standard water heater. This water heater is plumbed to
accommodate the solar interface. The water heater stores the heat energy generated by the solar system. As the
pumps circulate the fluids throughout the system, the fluids become hot and this heat energy is transferred to the
water in the water heater. This large volume of heated water is used as the hot water source for the fixtures in the
building/residence.
The backup water heating source is provided by a thermostatically controlled 4500 watt element in the water heater.
Refer to the water heater’s installation manual for specific installation/electrical requirements. It is recommended
that a water heater time switch be installed to limit backup heating by the electrical element. The time switch can be
automatically or manually activated and deactivated depending upon your additional water heating needs.
THE CIRCULATION PUMPS
The collector loop pump is selected for its head pumping characteristics. The potable loop pump circulates water
through the heat exchanger in the drainback reservoir and into the water heater. These pumps are very quiet,
efficient, and reliable. The collector loop pump is located below the drainback reservoir so that it has water pushing
into the suction side of the pump from above, and therefore will never run dry. If this pump needs to be replaced all
moving parts are contained inside a replaceable cartridge. The outer pump body may be removed by unbolting the
pump motor from the volute, and the inner cartridge may be replaced without having to disturb any of the plumbing.
THE DIFFERENTIAL CONTROL
A differential controller (and its accompanying sensors) is used to activate the pumps. The controller will be set by
the installation contractor to turn the pumps on and off at a specific temperature – usually on at 12°F difference
between the sensor at the water heater and the sensor at the collector, and usually off at a 5°F difference.
SYSTEM PROTECTION VALVES
The EagleSun drainback system is equipped with several thermal protection valves. A temperature and pressure
relief valve, on the water heater, insures that excessive temperatures and system pressure is adequately relieved as
needed. A pressure relief valve, on the drainback reservoir, insures the tank does not exceed the design pressure of
the system. Isolation valves are required to isolate the system when the system is need of maintenance or repair. A
tempering valve is required to insure that the water delivered to the fixtures is prevented from reaching scalding
temperatures.
FREEZE PROTECTION
The homeowner is not required to perform any actions to prevent freeze damage to the collectors. The system is
only circulating when the collectors are hotter than the storage. In freezing conditions this is not the case, therefore
there is no circulation and the water has drained from the collectors into the reservoir.
This system has a freeze tolerance limit of -60°F (60° below zero F), ambient air temperature. When conditions such
as these are present, during prime daylight hours, power to the controller should be disconnected by unplugging the
power cord to the controller.
“Freeze tolerance limits are based upon an assumed set of environmental conditions. Extended periods of
cold weather, including ambient air temperatures above the specified limit, may cause freezing in exposed
parts of the system. It is the owner’s responsibility to protect the system in accordance with the Supplier’s
instructions if the air temperature is anticipated to approach the specified freeze tolerance limit.”
OPERATING INDICATORS
The drainback system uses a sight glass, on the drainback reservoir, as an indicator that the system is working. As
the pumps are energized, the fluid level across the sight glass falls, thus indicating that the fluid is being removed
from the drainback reservoir. As the pumps are de-energized, the fluid level across the sight glass rises, thus
indicating the fluid in the solar loop is returning (draining) back into the reservoir. Additionally, the “Pump” lamp,
on the control face, will be illuminated when power to the pumps is available.
