Solar Pool Heater Function
Residential solar swimming pool heaters are usually plumbed using the same size pvc pipe as the pool equipment, normally 2" or 1.5".
Notice in the typical arrangement shown in this schematic that filtered water flows through solar and then through the gas heater if there is one. Sometimes we reverse this order to put solar in a more favorable pressure environment. Less load on the pool pump means lower electricity costs.
The motorized valve sends water to solar when the roof sensor is warmer than the pool by a set differential of about 9 degrees C. If the pool is up to the setpoint temperature or insufficient solar radiation is available the motorized valve turns automatically so flow does not go to solar.
The vacuum breaker allows air to enter so that negative pressures cannot develop. Positive pressures can not be developed because the system is open to the pool. Air flushes through to the pool when solar starts up.