John Seigenthaler: Renewable Heating Design

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Multiple boiler systems have been used for decades. They allow full heating capacity to be delivered when necessary, while also retaining high efficiency under partial load conditions compared to a single large boiler.

When a fixed output heat pump supplies a highly zoned heating or cooling distribution system, a buffer tank is typically used to prevent the heat pump from short-cycling under very low load conditions.   

ades of dealing with hydronic systems, I’ve confirmed two characteristics that always govern their operation. Both are rooted in the tenants of thermodynamics. Neither should be thought of as mysterious. 

Those who evaluate the performance of HVAC source equipment such as boilers, furnaces and heat pumps have to work with a wide variety of acronyms. Some of them were spawned by government bureaucrats, mostly the U.S. Department of Energy (DOE). Others were created through a consensus process based on input from manufacturers and other industry stakeholders.

Over the years I’ve had opportunities to work with several architects. They’re interesting people who have the ability to meld art with building technology. Sometimes the result is more “art,” and sometimes it’s more “building.” In either case, their designs typically get handed off to engineers with the simple request: Figure out how to heat my creation…

Given the current upward trend and volatility of fossil fuel pricing, there’s renewed interest in heating using wood pellets. Federal incentives that currently cover 26% of some qualified equipment adds enticement toward purchasing pellet-burning stoves.

When designing hydronic circuits, most engineers focus on what’s necessary for that circuit to absorb thermal energy at a heat source, carry it along like a conveyor belt and drop it off at one or more heat emitters.

In 2012 the price of #2 fuel oil in upstate New York was approaching a previously unheard of $4 per gallon. This spurred many pending heating system projects to consider the use of cordwood or wood pellets.

As with most things hydronic, there are multiple approaches, and the “best” approach for each installation has to consider cost, aesthetics, access to the existing piping, available wall space and the goal of how the overall system will operate based on existing or newly created zones.

What characteristic do solar thermal collectors, hydronic heat pumps and thermal storage tanks supplied by biomass boilers have in common?