# Development and Application of a Novel Non-Iterative Balancing Method for Hydronic Systems
## Appendix D Test Rig Description  
The circuit consists of 8 terminals distributed two by two over 4 branches derived from a main collector, as shown in Figure 14.  
Branches are named A, B, C, D, and terminal are referred to by branches and numbers (A\({}_{1}\),A\({}_{2}\),B\({}_{1}\),B\({}_{2}\),C\({}_{1}\),C\({}_{2}\),D\({}_{1}\),D\({}_{2}\)). Figure 15 shows the layout and the position of the components. The test rig has been realized on a vertical panel; the supply and return sections of the main manifold are positioned vertically and are connected at the top by a bypass which has been kept closed during the tests. The pressure drops of the simulated terminals are replicated by calibrated valves set to be representative of the selected user types (i.e., radiators, fan coils units, air handling unit coils). The system is equipped with balancing devices on each user; these are motorized balancing valves (MBV) coupled with an ultrasonic flow meter integrated in a device normally used for flow control in variable volume systems (Belimo mod. EP015R); the opening position of each valve is digitally controlled via the bus and its actual position is transmitted back to the operator panel. Branch balancing valves (BBV) are manual calibrated valves whose position is clearly indicated by the multi-turn graduated handwheel and whose flow measurement feature is only used if/when required by the TAB method being used. The accurate position detection of all the valve types is useful to compare the balancing configurations achieved by the tested balancing method. The set-up is completed by the adoption of a pump speed control combined with an adjustable bypass for more precise volume modulation. With regard to the measuring points, the two methods to be compared involve different detections: the Ratio Method requires flow measurements at each terminal, whereas the PFM method only requires instrumenting the reference terminal of each of the four zones (A,B,C;D) with pressure taps and a single flow meter at the pump. The ultrasonic flow meters at the terminals (MBV) present declared accuracy of 6% of the reading value ranging from 25% to 100% of the measuring range of 0-1200 L/h. The control point at the pump is instrumented with two rotameters (Both Frank mod. M350, different size, declared accuracy of 8% of measured value for flow rates between 20% and 100% of measuring range according to VDE/DIN 3531), the two instruments are placed in parallel as shown in Figure A7. According to general criteria for centralized measuring discussed in Section 3.3 of the paper, the two rotameters have a measuring range, respectively, of 50 \(\div\) 500 L/h and 300 \(\div\) 3000 L/h. In this way, managing and running only the appropriate instrument, the flow rate can be measured with the accuracy, range and the resolution required at each step of the PFM procedure. Figure A7 also shows the bypass branch provided for easier maintenance operations. Finally, the calibrated valves installed to simulate the terminals' drop losses are provided with pressure taps. The taps were connected to pressure probes (Thermokon mod. DPL1V, declared accuracy 1%, resolution 0.2 kPa) to be used as reference when required by PFM procedure. All active probes and electrically controlled actuators are managed by a bus control system capable of PID logics and data acquisition/elaboration. A large display shows actual operating parameters and values (i.e., the current flow rate values, pressure drops, motorized valves position, total pump flow rate, electric consumption, pump speed). The construction drawing is shown in Figure A8. The pipework and pump are sized for a total flow rate of 0.833 L/s (3000 L/h), the pipes are sized according to a speed range of 1 \(\div\) 1.5 m/s, maximum terminals' pressure drop is 30 kPa (consistent to the typical drop values of fan coil units, AHU coils or an underfloor heating/cooling system).