32 – Part 3: Solar water heater system installation
Boiler back-up heat exchanger connection
(VELUX solar water heating system with boiler back-up only)
For installation and operation instructions, refer to the Installation/Operation manual provided with your solar storage tank.
The Installation/Operation manual for your water heater must be kept with this manual at all times.
The boiler heat exchanger connections are located in the front of the solar storage tank. Use a minimum 1” nominal tube size,
wherever you are using zone valves or circulators. The inlet of the circulator is to be connected to the hot outlet side of the
boiler. Be sure the direction of the arrow on the circulator is facing toward the flow direction from the boiler to the boiler heat
exchanger inlet of the water heater. On the water heater, the boiler return is to be connected to the return side of the boiler.
The return from heating loop should have a flow check or swing check valve installed before the return pipe from the boiler
heat exchanger.
Boiler loop
circulator sizing
The boiler back-up
circulator pump must
be sized for the related
piping and pressure drop
of the heat exchanger. The
following graph represents
the pressure drop of
the solar back-up heat
exchanger. Select a 115
volt circulator pump with a
maximum current draw of
1 amp.
Charging the potable water system
Solar storage tank
Fill the solar tank with water. Do this by opening the cold water isolation ball valve to the solar tank. Inspect all fittings for
leaks. Purge all air from the potable water system by turning on several hot and cold faucets and running water for several
minutes. Air is purged when water runs continuously for 1-2 minutes without air discharge.
After the water and electrical connections have been made, the tank has been filled with water, and all air has been purged
from the tank, turn on power to heater. The heater is now operational.
Freeze protection
The propylene glycol heat transfer fluid provided acts as a freeze protection fluid and must be used to protect the system from
freezing. The VELUX propylene glycol provided is rated as nontoxic. A 40% propylene glycol/60% water mixture should be
used, however, you must use a mixture most appropriate for your climate. Do not use a higher glycol to water concentration
than necessary, as this will adversely impact heat transfer efficiency. See the propylene glycol Data Sheet in the back of this
manual for recommended concentrations. A copy of the MSDS sheet must be left with the end user of the solar system. See
“Propylene glycol emergency overview” as part of the propylene glycol Data Sheet in the back of this manual. The collector
loop must be charged with a mixture of heat transfer fluid and distilled or deionized water. The use of regular tap water as a
mixing agent is prohibited. Scheduled maintenance must be established to monitor and maintain the proper PH level of the
heat transfer fluid in the system to protect the heat exchanger and other components in the system.
