Can You Use Solar Thermal for Hydronic Heating in Winter?

System Design and Sizing

When designing a solar thermal system for hydronic heating, it’s essential to consider the heating requirements of the space. A typical rule of thumb is to size the solar thermal system to provide 30% to 50% of the total heating load. For example, if a home requires 10,000 Btus of heat per hour, the solar thermal system should be sized to provide 3,000 to 5,000 Btus per hour. This ensures that the system can provide adequate heat input during winter months when solar radiation is lower.

Collector and Storage Selection

Selecting the right type of solar thermal collectors and storage tanks is crucial for a hydronic heating system. Flat plate collectors are suitable for most applications, but evacuated tube collectors can be more efficient in colder climates. For storage, a well-insulated tank with a capacity of 1,000 to 2,000 gallons is recommended to provide enough heat for a 24-hour period. The tank should be sized to store 50% to 75% of the total heating load.

System Operation and Controls

The solar thermal system should be designed to work in conjunction with a conventional boiler or heat pump to provide backup heat during periods of low solar radiation. A differential thermostat or a smart controller can be used to optimize system performance and ensure that the solar thermal system is operating efficiently. The system should also be equipped with a freeze protection system to prevent damage to the collectors and pipes during winter months.