Smart solar control also enables the exchange pump to be used to transfer heat from the solar preheat to the water heater in periods of low DHW usage. This balancing is critical if the solar thermal system is to operate efficiently without wasting generated energy. The solar control will sense if the preheat tank reaches 70°C and, if the monitored after-heater temperature is less (60-65°C), the exchange pump will be activated forcing preheated water to the BFCs. The pump turns off once the pre-heat temperature drops to 60°C. This ensures that the solar energy is used most advantageously, effectively turning the IT tank into a combined solar preheat, extending the pre-heat volume and allowing efficient use of solar energy. Without this balancing, the thermal losses could be equivalent to turning off half of the building’s solar thermal collectors.
As well as the smart controls, the solar thermal system offers ongoing monitoring for improved management with a volt free alarm contact on the BFCs for general fault indication on the BMS. Each roof-mounted solar collector bank is also dedicated to one solar coil to allow uninterrupted drain back for stagnation protection. Should demand for DHW drop, solar thermal collectors can, unless drained, be prone to stagnation where the solar fluid overheats and takes on the consistency of tar within the collector. This requires a lengthy cleaning process and can cause considerable damage requiring costly repairs. At 100 Bishopsgate, when the preheat tank reaches 70°C, the solar pump stops, and the natural head of solar fluid flows in reverse back into the coil port and fills the drain back tank, emptying and protecting the solar collector.