John Siegenthaler, PE

While it’s true geothermal heat pumps do offer excellent opportunities in combination with low-temperature hydronic distribution systems, they are not the only viable way to combine the heat-leveraging ability of heat pumps with the unsurpassed comfort offered by modern hydronic distribution systems.

Long before Americans had access to natural gas, propane, fuel oil, or electricity, and long before there were automatically controlled central heating systems, wood was the most commonly used heating fuel.

My objective is not to dissuade you from designing around 20° delta T at design load. It’s to assure you the sun will come up tomorrow if you happen to pick a different value.

The combined cost of hydronic radiant panel heating, along with a separate central cooling system, often strains the construction budget to a point where something has to go, and that something is usually the radiant heating option. It gets trumped by a lower-cost forced-air system that delivers both heating and cooling, albeit often at reduced comfort.

Having the proper air-side pre-pressurization prevents system water from entering the expansion tank, until the water begins expanding due to heating. 

Last fall, I taught my first online course dealing with designing hydronic heating systems. The course was titled “Mastering Hydronic System Design.” It was a collaborative effort between HeatSpring Learning Institute, BNP Media’s CE Campus, and myself.

If you’re using a calculator, spreadsheet, or other computational tool, you should use the most accurate numbers possible. It’s just part of being a professional.

The following formula has been around the North American hydronics industry for a long time: Btuh = 500 x gpm x delta T. It can be used to estimate the rate of heat transfer into or out of a device that has a stream of water flowing through it at a known flow rate, and with a measured temperature change between the inlet and outlet of that water stream.

In newer modulating/condensing boilers, many of their heat exchangers had to sacrifice two very desirable qualities in the interest of being small and light.

A cool concrete slab is like a black hole for Btus. It gobbles up any heat that dares to get close. The solution is to install a mixing assembly operated by a controller that measures the boiler’s inlet temperature, as well as the water temperature supplied to the distribution system.