If you’ve ever designed a hydronic system, you’re probably familiar with the struggle of balancing simplicity and flexibility. Because hydronic systems use a closed system of pipes to circulate water through a building for heating or cooling, keeping the equipment used to power a hydronic system simple can help lower project costs. On the other hand, keeping residents comfortable across a spectrum of temperature and humidity conditions is a struggle with any system. So, is it worth it? Here’s a quick summary of considerations before you decide.
Ultimately, hydronic heating and cooling systems are significant initial investments—which makes funding a major short-term concern for building owners and managers. Engineers, however, focus on the long term. When they design a building’s HVAC system, they’re inclined to choose the most efficient equipment and layout that meets the facility’s budget.
Funding, for building and facility managers, is the ultimate struggle with a long-term capital investment like a hydronic heating system. For the specifying engineer, there are substantial benefits to using the most efficient boilers, multiple zones, and centrally controlled valves in terms of minimizing energy usage and maximizing occupant comfort.
Unfortunately, while it can be easy to map out the payback period for certain upgrades to an existing system, there is still the maximum budget to work with. This is particularly important when the specifying engineer may only be coming in after the project owner has agreed on initial budget constraints.
Currently, boilers for commercial operation face some of the least stringent efficiency requirements among HVAC systems on the market. The most common metric is annual fuel utilization efficiency (AFUE), and government regulations require a minimum AFUE of 80‒84 percent depending on whether the system uses steam or hot water and whether the system uses natural gas or heating oil. Note, some building codes require a new facility to meet ASHRAE 90.1 standards. If required, hydronic heating systems must have a return hot water temperature of 120 F or less. For boilers to accept 120 F return water, they must be of the condensing type. Condensing boilers are more efficient than non-condensing boilers.
There are obvious benefits to going with higher efficiency boilers, but to do so requires leveraging some different technologies. Condensing technology basically acts like a turbocharger in a car engine and uses exhaust heat to increase efficiency. With an AFUE of 93 percent or better, these are clearly more attractive on a lifecycle basis but are sometimes more expensive than standard or non-condensing options.
The heart of the hydronic heating system is the boiler but so much of the system’s energy consumption and first cost is contingent upon the selection and design of the building’s heating and air distribution strategy as well as the building envelope and purpose.
Building use, purpose, and physical constraints: When designing a hydronic system, one must consider how the heat is getting into the space. Will occupants be exposed to warm forced air, or will they be in line of sight with heating elements (radiators or radiant heating panels)? Both systems use heat exchangers where hot water is run through pipes in the building that feed heat transfer coils. These heat transfer coils must be sized to transfer enough BTUs to the space while allowing the return water temperature to be approximately 120 F or lower.
Older heating systems were designed so that the return hot water temperature was above 140 degrees Fahrenheit. The lower the return water temperature, the greater physical space required by the heating coil. If the building’s configuration or purpose cannot accommodate the space, then condensing operation will be challenging.
Hydronic system boilers and terminal devices: Hydronic heating equipment selection is a key part of the overall design. Installation, maintenance, and operating costs are all impacted by where the equipment can be installed. If it is inside a building, contractors should consider where in the building it will be located, and if it will be exposed or integrated into the building. As a rule, the more hidden the equipment, the more expensive the equipment.
Here at Windy City Representatives, we work with leading names in HVAC equipment. We understand how complex the planning, development, design, and construction of a hydronic system is for commercial buildings. Contact us today at 630-590-6933 for support.
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