What we did:
We were tasked with designing and installing a small BMS system that controls the operation of a gas boiler and a biomass boiler. The Biomass boiler would always be the preferred source of heat but in the event that it fails then it would be required to automatically switch over to a backup heat source, in this case a gas boiler. This was critical as it was not only supplying the heating to the building but also heating a vat of wax that was used in the factory for production.
We designed a pump overrun into the system to remove any excess heat from the boiler before switching so that the biomass boiler wouldn’t just keep heating up while the fire burns out.