Articles by John Siegenthaler, P.E.

Nearly all closed-loop hydronic heating and cooling systems are supposed to be filled with water or a mixture of water and antifreeze. The only intentional air in the system is that contained in the expansion tank.

All hydronic systems designed around renewable energy heat sources — as well as those designed around conventional boilers — have at least one controller that measures and responds to temperature. Common examples are temperature setpoint controllers, outdoor reset controllers, mixing controllers and differential temperature controllers. Complex systems that operate in multiple modes, or use multiple heat sources, often have several temperature-based controllers.

As global energy planning moves away from fossil fuels and toward electricity, an increasing number of hydronic heating systems are being supplied by heat pumps. Some use water-to-water heat pumps supplied by geothermal earth loops. Others use air-to-water heat pumps.

As residential building codes and energy conservation standards continue to evolve, many are requiring proof of high quality air sealing.

Heated floor slabs, without floor coverings, have one of the lowest supply water temperature requirements of any radiant panel system. This makes them well-suited for use with renewable energy heat sources such as air-to-water heat pumps, water-to-water geothermal heat pumps, biomass boilers and solar thermal collectors.

Over the last few years, I’ve written several columns describing how air-to-water heat pumps can provide heating, cooling and domestic hot water for homes. Many of the systems involve buffer tanks to help stabilize heat transfer from the heat pump to a zoned distribution system.

This month I want to deviate a bit from a purely renewable energy topic to one that’s important across the entire spectrum of hydronics technology. It’s a topic that likely gets exercised on a daily basis in any engineering office where water-based HVAC systems are conceived.

Aside from the fact that they are all used in hydronic heating systems, what do the following items have in common?

As interest and incentives build to transition space heating and domestic water heating systems away from fossil fuels and toward electricity, a somewhat predictable but only marginally quantified problem is developing. Two words describe it: Peak demand.