I began writing about hydronics for Plumbing & Mechanical in July 1996. Back then, the hydronics market was expanding at a good pace, largely driven by growing interest in radiant panel heating. The market was searching for piping and control techniques for multiload/multitemperature systems that could incorporate a range of loads such as radiant panel heating, domestic water heating, higher-temperature heat emitters, snow melting and pool heating. Imagine trying to properly supply all those loads using the very limited design approaches that defined residential hydronics in North America back in the 1980s.
One technique that steadily gained acceptance was primary/secondary piping using a series primary loop. An example of such a system is shown in Figure 1.