Do’s and Don’ts related to
Pressure Independent Control Valves, PICVs
By Christina Cohr, CCO, M.Eng (Export), FlowCon International ApS, Denmark
Why use a 2-port valve?
Historically, it was common years back to have the system control performed by 2-way control valves. But as indicated by the name, these would only control and not balance. To achieve reasonable system balance with a conventional 2-way control valve, it would require the addition of a balancing valve with each control valve and a DPCV on the zone. Working with more valves per terminal unit instead of only 1 (PICV), obviously affects to overall installation cost and actual pressure drop, but also the commissioning practice. To ensure design flow for each terminal unit the commissioning process would include numerous adjustments of each DRV's flow setting. Every flow adjust must be followed by verification of flows and differential pressures in the zone and if necessary, re-adjusted to achieve balance. Unfortunately, long-lasting system balance was rarely obtained.
Also, a 3-valve-solution will most likely result in an internal authority conflict. Control valves within the system attempt to regulate flow- or control conditions simultaneously and their interaction would affect one another, and the numerical estimate would consequently take longer time. Such conflict results in inefficient or inconsistent system operation, which potentially would lead to temperature imbalances, energy waste, and reduced comfort. When using true PICVs, you will obtain 100% authority and no conflicting as each PICV will have full control over its regulation. With a pressure independent solution, you will achieve the most energy efficient solution which benefits not only your wallet (the energy usage is lower), but also the environment (as carbon footprint is reduced).
What is the difference between a pressure dependent and a pressure independent control valve?
It is important to know whether the control and balancing functions chosen work pressure dependent or pressure independent. The conventional 2-port control valve is a pressure dependent valve. And the balancing valve mentioned in the earlier section can be either a static balancing valve or a dynamic balancing valve. A static valve – also known as manual DRV – is a pressure dependent valve and therefore flow output will change if system pressure changes. The dynamic balancing valve works pressure independently and will secure that flow output remains constant even if changes occur in the system pressure. But again, separating balancing and control over two valves will result in an authority conflict and high pressure drops, and therefore our recommendation is a PICV-solution.
Need more Information….?
Contact FlowCon and gain knowledge from our expertise with Pressure Independent Control Valves and reach out for further details or guidance in choosing the proper PICV. All our PICV solutions are 3rd party tested according to BSRIA BTS 01 standard which includes Pressure Independency, Accuracy, Repeatability, Control Characteristics and Seat Leakage.