In a hydronic system with multiple circuits, which circuit is used to calculate the total equivalent length (TEL)?

In a hydronic system, the longest circuit is used to calculate the total equivalent length (TEL) because it typically represents the highest system resistance due to its greater distance and the associated friction loss along the piping. When designing or analyzing hydronic systems, the longest circuit will usually dictate the sizing of the pump and the overall performance of the system. This is necessary because the flow rate and pressure drop experienced by the fluid will be influenced by the circuit with the most significant resistance, which is inherently linked to its length. Hence, the longest circuit is critical for ensuring that the system operates efficiently and provides adequate flow and heat transfer across all circuits.

Other options, while they may represent important factors in system dynamics, do not serve the primary purpose of establishing a baseline for total equivalent length calculation in the context of a hydronic system.