Radiant & Hydronics

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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.

A heating contractor is installing two air-to-water heat pumps as the primary heat source in a large home's hydronic system, keeping the existing boiler as backup. However, problems like heat migration into off zones and corrosion of the vent connector suggest design flaws that need to be addressed.

Last month's column discussed piping for air-to-water heat pumps. A 2-pipe system allows staging but not simultaneous heating and cooling, while a 4-pipe system with motorized valves enables both modes of operation.

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.

An emergency call led a team to a school with a leaking boiler, which was shut down due to safety concerns. After clarifying the need for urgent repairs, the executive director approved the work. Complications arose from snow and transport challenges, but a friend connected them with a group of young workers willing to help, easing manpower concerns.