I entered the HVAC field in 1978 fresh out of college. My first job was as a junior engineer with Revere Solar & Architectural Products in Rome, N.Y. Our group manufactured flat plate solar energy collectors and designed both space heating and domestic water heating systems around them. Revere Solar was where I cut my teeth on hydronic system design. It also was where I began seeing the difference between wild theoretical heating concepts and what really worked in the field. It was an invaluable time of learning under the guidance of some very good mentors.
It probably doesn't surprise you that one of the systems I designed and installed in our house was an active solar energy system for supplying domestic hot water and some space heating. After considering many design options, I settled on the concept of a closed-loop gravity "drainback" system. This type of system uses a simple means of preventing water from freezing in the collectors and exposed piping. As soon as the collector pump turns off, gravity, a very reliable commodity, causes all water to drain from the collectors and pitched piping and back to a storage tank in heated space.