Articles by John Siegenthaler, P.E.

A 20°F temperature drop has long been treated as a hydronic design standard, but there’s nothing inherently ideal about that number. John Siegenthaler explains how varying Delta T can reduce flow rates, pipe sizes and circulator power without compromising performance.

Improper piping sends heated fluid backward through an idle boiler in this hybrid hydronic system.

Two identical air-to-water heat pumps deliver nearly twice the expected output when operating together, but when either unit runs alone, its measured output falls well below its rating. What’s causing the performance drop, and how can the system be corrected?

Non-pressurized storage systems have advantages and limitations. In applications where cost per gallon of storage is critical, or where it’s otherwise impractical to bring in one or more pressure-rated tanks, a non-pressurized tank combined with the piping and control concepts discussed represents a viable solution to leverage the combination of time-of-use electrical rates, heat pumps, and the unsurpassed comfort made possible by modern hydronics technology.

Many air-to-water heat pumps are combined with boilers. In retrofit projects, it’s likely an existing boiler; in new projects, it’s likely a mod/con boiler. The boiler can provide supplemental heat during very cold weather. It can also serve as a backup heat source should the heat pump become inoperable.

Upcoming DOE regulations and rising energy costs are creating new opportunities to improve hydronic distribution efficiency through smarter circulator strategies.

As utilities and building owners look for new energy storage solutions, hydronic thermal storage presents an efficient alternative to batteries in many applications.

Air-to-water heat pumps are different from boilers. As the outdoor air temperature decreases, their heating output decreases. That’s a characteristic of all air-source heat pumps, and it runs opposite to how heating load changes with decreasing outdoor temperature.