Buffer tanks play an important role in hydronic HVAC systems, enhancing efficiency and stability, but they are not utilized in every system. Understanding when and why to use a buffer tank is crucial for anyone looking to deepen their knowledge of hydronic HVAC systems. This blog will explore the function of buffer tanks, common applications, alternative solutions, and a straightforward method for calculating tank capacity.
Function in Hydronic Systems
Buffer tanks store heated or chilled water (thermal storage) to manage temperature changes and provide a steady supply of tempered water. They improve equipment efficiency by reducing frequent on/off cycling (short-cycling), which extends the lifespan of the equipment.
Buffer tanks provide a “buffer” between the heating or cooling source and the system load to ensure stable temperatures. This enhances the overall performance and reliability of the system, ultimately maintaining consistent building comfort.
Common Applications
Low System Volume: In systems with low water volume, the temperature can fluctuate rapidly because less water needs to be tempered. In this situation, equipment such as a boiler or chiller cannot run for an extended period because the temperature setpoints are reached quickly. Adding a buffer tank increases the volume of water to be tempered, allowing the equipment to run longer before reaching the setpoint.
Inadequate Turndown: When equipment can't reduce output capacity to meet the minimum load requirement of a system, it can use the buffer tank’s thermal storage instead. This prevents short cycling by not requiring the equipment to cycle on.
Variable Load Systems: Buffer tanks are useful in applications where the building load varies significantly throughout the day, such as office buildings or schools. Buffer tanks provide a thermal buffer that stabilizes the system against rapid changes in load, helping maintain precise control over the equipment output.
An Alternative Approach
Multi-purpose tanks (MPTs) offer an excellent alternative to traditional-style buffer tanks. MPTs combine the functions of a buffer tank, air/dirt separator, and hydraulic separator into a single piece of equipment.
Removal of Air & Dirt: MPTs have an integral automatic air vent and a 2” full port blow-down valve for removing air & dirt from the system.
Hydraulic Separation: A hydraulic separator decouples the primary and secondary loops in a hydronic system, allowing them to operate independently. A primary-secondary piping system may be designed perfectly, but improper field piping can hurt the functionality. You can mitigate this risk by utilizing MPTs for hydraulic separation.
Customizable Options: MPTs are available in various sizes, insulation options, and configurations - including a 90-degree connection option for greater installation flexibility.
Sizing Buffer Tanks
Taco’s Buffer Tank Sizing Wizard calculates the required tank volume based on system parameters. You can access the tool by clicking the picture to the right.
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