Solar domestic hot water systems can be classified in term of their means of protecting against freezing:
- Use an anti-freeze within the solar loop:
A very common system deployed within Canada, anti-freeze based solar hot water systems work well against freezing. The anti-freeze solution is a mix of food-grade propylene glycol and water. The anti-freeze solution usually requires changing every 3 years but the actual frequency depends on the system design.
- Empty the solar loop when freezing conditions occur:
Other common solar hot water system deployed in Canada are the drainback and seasonal systems. These solar hot water systems empty solar loop when freezing conditions occur. Both types use only water within the solar loop. The drainback system functions throughout the year and automatically empties the solar loop when freezing conditions occur. The typical annual maintenance consists of adding a cup of water to the solar loop to offset evaporative water loss. This type of system requires a very carefully install and is best suited when the solar panels and the mechanical room are vertically aligned. Seasonal systems are typical deployed in off-the-grid sites and are meant to be used only during the off-winter seasons. The system has to be manually emptied before the temperatures of the season reach freezing.
Vancouver Renewable Energy can install either anti-freeze or drainback solar domestic hot water systems.