John Seigenthaler: Renewable Heating Design

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The homerun system is a simple technique for connecting multiple heat emitters using two runs of small flexible tubing (such as PEX) for supply and return. In North America, the standard size is 1/2-inch, but 3/8-inch tubing can be used with proper design and compatible fittings.

Many of the ratios used in the HVAC industry are just some “desirable output” quantity divided by the “necessary input” quantity. One example is the coefficient of performance (COP) of a heat pump. The desirable output quantity is Btu/hr of heat output. The necessary input quantity is the electrical input power needed to operate the heat pump. The latter is typically measured in watts or kilowatts.

Some hydronic heating systems use slab-on-grade floor heating combined with an air handler or fan-coils in other areas of a building. This approach is also used for heated basement floors combined with a “hydro-air” delivery system for the main living areas.

Zoning has always been a premier benefit of hydronic heating and cooling systems. There are many zoning configurations capable of delivering heat (or cooling effect) when and where it’s needed in a building, with minimal effect on the temperature in other parts of the building. Some methods use circulators to create flow in each zone; others use either motorized or thermostatic valves to regulate flow.

While I admit to not being fully informed on the latest things from Google, Apple, Chat GPT, or social media, I’m confident that I can still pass along advice to those who are new to the hydronic industry, especially those involved with designing systems

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.

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.

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.

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.