Designing & Commissioning Variable Flow Hydronic Systems

Direct return Variable Flow Hydronic Systems (VFHS) must be designed to be self-balancing. However, in practice many design engineers will use customary pipe sizing routines, piping detail drawings, and specifications that apply to more familiar constant flow systems. Substituting a 2-way valve in place of a 3-way valve and bypass pipe, while retaining the balancing valve and balancing specification ultimately creates control problems and energy waste. The use of balancing valves on VFHS is detrimental to the performance of the system because it reduces the authority of the control valve and adds a permanent restriction in every branch (References 1 & 2). This restriction increases the pumping costs for the life of the building.