Solar Swimming Pool Heater: Wiring the Collector Solar Swimming Pool Heater: Wiring the Collector

A solar swimming pool heater uses renewable energy to warm up water and extend the pool season. Solar pool heaters are relatively expensive but pay back quickly. Designing the system requires an appreciation of structural, plumbing, and electrical considerations. The collectors will cover a large surface area of the roof with heavy water; the frame must be strong enough to bear the load. The typical control kit includes the differential controller, a 3-way valve, two temperature sensors (or thermistors), and a motorized actuator. The controller senses the temperature of the pool water and the solar collectors. When it detects a potential heat gain, it opens a valve to the solar loop. This valve is located after the check valve from the pool filter. When the collector is cold, the controller opens a bypass valve and the solar loop is skipped. The most common differential controller is the GL-235.

Safety Precautions

Kill the circuit breaker before wiring the controller. Some controllers can be wired for either 110 volt or 220 volt alternating current. Choose what works best for you but don't connect live voltage to the wrong terminal. You may also have to choose between 12 volt or 24 volt current for the actuator motor.

High Voltage Wiring

The main input for the controller is high voltage. There may also be high voltage outputs for booster pumps or timer overrides. Wire these connections according to the National Electric Code and local building codes. Run a separate ground conductor to the ground terminal of the pool service panel. Hire a licensed electrician if necessary.

Low Voltage Wiring

The wiring between the controller and the actuator will be 24 volts with newer equipment or 12 volts with older equipment. Connect the two components using the color coded 3-position terminal block on older equipment, or the newer 3-pin connectors. If the valve opens the wrong way, reverse the polarity of the connection.

Sensor Wiring

One temperature sensor is installed in the same location as the solar collector. It should be exposed to the same conditions of insolation and solar flux. The easiest approach is to attach it to the side of the panel with a screw or silicone caulk. The sensor is housed in a black plastic casing which approximates the thermal conductivity of the collector panel. Run a wire between this sensor and its corresponding input terminal on the controller. Use the manufacturer's recommended wire gauge and type. In most cases, you can fasten the wire directly to the water pipes.

The other controller measures the temperature of the water intended for swimming. Avoid placing it in the pool, where it can be damaged or shaded. Place this sensor inside of a pipe or in the pump strainer basket. The best pipe to put the sensor in is located after the check valve, near the controller. Drill a small hole in the empty pipe. Feed the tip of the sensor through, then seal around with an o-ring and silicone caulk. To avoid electromagnetic interference, do not run the sensor wire in the same conduit as any other wire.

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