24 – Part 3: Solar water heater system installation – Boiler back-up heat exchanger connection
Boiler back-up heat exchanger connection
(VELUX solar water heating system with boiler back-up only)
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 fl ow 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 fl ow 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.
Pressure Drop
Solar Heat Exchanger / Boiler Back-Up
Contender Solar
0
2
4
6
8
10
12
14
Flow in GPM
Upper Coil
Feet of Fr
iction (Head)
Lower Coil
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Boiler loop control
Insert the boiler loop temperature sensor into the control well provided in the front of the water heater. Route the temperature
sensor cable to the solar system controller and connect to terminals S3. Route the circulator power cord to terminals R2.
