Summary
There are millions of existing hydronic heating systems in North America. The vast majority of them were designed around boilers operating on fossil fuel and capable of providing relatively high water temperatures.
As energy markets trend toward electrically powered HVAC systems, heat pumps (both air-to-water and geothermal water-to-water) will play an increasingly important role within the hydronics industry. There will be many situations where an existing system, supplied by a boiler, will be examined for possible inclusion of a heat pump, either as a replacement for the boiler or as the primary heat source in a dual fuel system.
Having a procedure for evaluating the thermal performance of an existing hydronic distribution system for possible operation at lower water temperatures is crucial in deciding how best to integrate the heat pump and what its expected performance will be.
This issue of idronics has presented a method for on-site testing of existing hydronic heating circuits, as well as a way to use the results of that testing to infer the performance of those circuits at different — typically lower — supply temperatures. It has also provided guidance on how to configure a modified system to avoid issues that cause unstable operation, corrosion or zones with widely different supply temperatures.