John Siegenthaler: Hydronics Workshop

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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.

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.

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.

Last month, we started with an air-to-water heat pump for space heating and added an auxiliary heat source and chilled water cooling. This month, we’re adding domestic water heating, similar to last month’s setup.

Standardized piping layouts for air-to-water heat pumps can improve acceptance by facilitating a basic heating system that uses a monobloc heat pump with a 30% propylene glycol solution for freeze protection.

Hydronically-heated concrete floor slabs offer comfort but can be slow to warm up. A proposed solution uses a heat pump and variable-speed circulators to provide rapid heating through air handlers, ensuring quick warmth during cool days while maintaining energy efficiency.

In 1986, I installed a 1.5-ton geothermal heat pump in my home using two 500-foot horizontal HDPE earth loops. After digging a trench, I connected the loops to the pump and opted for a 2 HP swimming pool pump to fill and flush the system, as a garden hose couldn't provide the needed flow rate.

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.