John Siegenthaler, P.E.

What happens if there’s a simultaneous call for domestic water heating and cooling?

Fortunately, our industry is at a point where the question "But what do I do about cooling?" can be answered, with confidence, and by the same hydronics professional offering heating.

When the system was operated, the owner complained of flow problems. The heat emitters in any given zone were only marginally warmed when their associated zone circulator was operating. The owner questioned if another circulator should be installed.

As electrification reshapes the HVAC market, hydronic-based heating and cooling systems stand ready to offer many design and performance benefits. One of them is the potential for thermal storage. After all, water is one of the best materials on earth for storing sensible heat.

Last month, we discussed direct-to-load hydronic heat pump systems. These systems use a variable-speed compressor and circulator to adjust heat output and flow, eliminating the need for a buffer tank or hydraulic separator.

When only the air handler is operating the heat pump is able to supply the 120 ºF water. However, when the floor heating zone and the air handler are operating at the same time and the outdoor air temperature is below 24 ºF the fluid temperature leaving the heat pump can’t climb above 103 ºF. Why is this happening, and what can be done?

The availability of heat pumps allows designers and installers of hydronic heating to include cooling. A simple method involves using a single air handler with a chilled water coil for a ducted distribution system, providing single zone cooling that can complement multi-zone hydronic heating in average houses.

Can you spot several details that are either incorrect or missing? Can you propose an alternative design that would accomplish the same goals using less hardware?

A recent design approach for air-to-water and water-to-water heat pumps is "direct-to-load" piping. This method utilizes an inverter-driven scroll compressor, which operates across a wide range of speeds and can handle on/off cycling without the high inrush current typically seen in fixed-speed compressors.

Most heat pumps in North America extract heat from outside air to warm interiors, which is why we call them "air-to-air" heat pumps. However, this term is incomplete, as heat pumps can also provide comfort without relying on forced air delivery.