A typical application of Circuit Setters is in the balancing of flow rates to heat exchangers in a closed loop cooling water system with fairly constant heat transfer loads. Many of these types of systems have a very large number of loops and users. Due to the steady state nature of the thermal loads in these systems, controlling the flow rates to each user with a fully automated control valve is not economically justifiable. Instead, the flow rates are set by establishing appropriate differential pressures across branches, headers, and loops by setting the Circuit Setters to fixed positions.
The process of determining the fixed positions of the Circuit Setters to balance the system is iterative and very time consuming when done in the field. However, modeling the system in PIPE-FLO® Professional with Circuit Setters, and using the process described by the Bell & Gossett Instruction Manual (V1000187C), to determine the valve position of each Circuit Setter is a quick and accurate process.
While PIPE-FLO® does not have a native device for a Circuit Setter,which is commonly used in many cooling water systems, it is still possible to simulate and balance Circuit Setter operation in the program. To balance these types of systems, PIPE-FLO® users should model the system using the Control Valve device for circuit setters, riser balancing valves, and the triple duty valve by obtaining the Cv profile from the performance curves.
The hydraulic performance data may be in the form of a Flow Coefficient vs. Valve Position data table or a Flow Rate vs. Head Loss (or Pressure Drop) curve. For example, the hydraulic performance curve of Flow Rate vs. Head Loss for a 4″ Bell & Gossett Circuit Setter Plus balancing valve is shown in Figure 1.
Figure 1: 4″ Bell & Gossett Circuit Setter Plus® balancing valve performance curves.
The Cv data for each valve position can be read from the curve by reading across the Cv line which is drawn at 2.31 feet (1 psi pressure drop across the valve). The value of the flow rate at the intersection of the valve position line is the value of the Flow Coefficient (Cv) at that position, which can be seen by using Equation 1 for SG=1 and dP=1.