John Siegenthaler: Hydronics Workshop

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In 2024, the North American air-to-water heat pump market saw significant expansion, with nine new offerings introduced at the January AHR show by companies new to this category. By year's end, at least 18 companies either have or plan to offer these pumps in the U.S. Read the list of these companies as of mid-2024.

Air-to-water heat pumps and water-to-water geothermal heat pumps provide warm water for space heating, domestic water heating, and chilled water for cooling. Switching a hydronic heat pump system from space heating to cooling and vice versa seasonally is relatively simple. The system operating mode is changed at the thermostat or a dedicated system mode switch with heat, off, and cool settings.

I attended a conference hosted by the Building Performance Association and presented on air-to-water heat pump systems. Many professionals were interested in heat pumps, especially ductless air-to-air systems. One person mentioned the difficulty of finding qualified installers for air-to-water heat pumps and noted the higher cost compared to ductless air-to-air systems.

Flow direction is crucial in hydronic systems. Most designs have a fixed flow direction, but there are situations where reversals can occur. It's important to address these proactively to ensure smooth operations.

Primary/secondary piping is a way to achieve hydraulic separation by connecting multiple hydronic circuits with their own circulators to prevent interference. Using a pair of closely spaced tees is a common method to achieve this.

In rural upstate New York, residents harvest trees for firewood using chainsaws and hydraulic splitters. I burn about two face cords annually in my wood stove, enjoying its warmth during winter and relying on it during power outages caused by outdated utility lines.

I’ve written many PM columns discussing how air-to-water and geothermal water-to-water heat pumps can be combined with hydronic delivery systems to deliver efficiency AND superior comfort. This combination is a great solution for many consumers.

There is a growing interest in adding air-to-water heat pumps to existing hydronic heating systems. While I support their use, I do not recommend replacing a perfectly good cast-iron boiler that still has a long service life.

Find out about piping options for retrofitting an air-to-water heat pump into an existing hydronic system.

Hydronic-based heating and cooling systems stand ready to offer plenty of design and performance benefits. One of them is the potential for thermal storage.