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www.fueloilnews.com | FUEL OIL NEWS | March 2014 45 in temperature has been measured by the room or zone thermostat or sensor, so there is a delayed reaction," Boss continued. "For example, at low-load conditions when only a small amount of hot supply water is required, the actuator in the temperature control valve will partially close to limit flow to that specific CUBO unit. Consequently, the pressure in the rest of the system increases, which increases flow to the other units. The standard temperature control valve compensates to decrease flow, which increases system differential pressure to start the cycle over again. The back-and-forth cycling behavior of overflow and underflow — known as "valve hunting" — decreases system efficiency and stability, while increasing temperature swings. The frequent open- closed cycling also reduces the valve's lifespan." Tweaking manual balancing valves in the field to balance the system cannot compensate for constant differential pressure fluctuations. "You need PICV function that can absorb system pressure fluctuations to maintain the desired flow rate to the coil at all times," Boss notes. "The AB-QM valve in itself does the balancing dynamically to prevent cycling and hunting. It exactly matches flow to load regardless of pres- sure changes. You always get the proper flow rate." True PICV FunCTIon PerForms PreCIsely aT low loads and Flow The AB-QM valve combines the best of two technologies in one unit: it acts as a modulating temperature control valve and as a dif- ferential pressure controller containing an integrated membrane. This enables the control valve to do double duty: to provide water at the required flow The AB-QM valve acts as a modulating temperature control valve and as a differential pressure controller containing an integrated membrane. This enables the control valve to do double duty: to provide water at the required flow rate to the CUBO coil and to maintain that exact flow by eliminating the effects of pressure fluctua- tions on the valve as system loads change. Regardless of how much flow each temperature control actuator is calling for, the differential pressure within the AB-QM valve remains stable. When a temperature control valve is unaffected by system differential pressure changes throughout its entire range it is said to have "100 percent valve authority," something that was only possible in laboratory conditions until recently. Aungst noted that "with the AB-QM valve, neither pressure nor balancing affects the individual circuits. In other words, each AB-QM valve lets each single CUBO circuit act independently of the system. The AB-QM valves and the variable speed drive pump work in har- mony. Redundant pumps powered by Danfoss drives simply circulate the hot water to the circuits. The AB-QM valve matches the flow to the exact load. And at lower loads, the pump reduces speed to save electric- ity. The pump only needs to produce the minimum required differential pressure for the valves to operate. Each AB-QM valve is outfitted with an optional 4-20ma actuator. The actuator is controlled by a propor- tional integral- derivative loop in a programmable logic control system configured by Total Energy Solutions that uses inputs from a thermistor located in each zone. The control network runs over Ethernet. Local control can be done on the PLC's color touch-screen. The system can also be monitored remotely from the comfort of Zimmerman's home, combining convenience and reliability. PreCIse TemPeraTure/Flow soluTIon For CuBo sysTems "The full PICV function of the AB-QM valve is perfect for our CUBO system," Aungst emphasized. "The area zones are PID con- trolled, so every zone is at a different state of modulation. The valves moderate water flow precisely compared to the surging that can occur with open-close type controls. Any one valve may be wide open, closed or partly closed to match the exact flow required for that individual coil. They operate independently and smoothly through the entire range regardless of system pressure. Plus, they are self flushing, so they also operate cleanly. "The AB-QM valve is very precise. Across a 22,500-square-foot floor area, the readouts on the eight thermistors are all within one degree F." For Earl Ray Zimmerman, getting temperatures that consistent over an area about half the size of a football field is impressive. "The chicks like an even temperature," he said. " I'm very happy with how things are working." HVAC/ HydroniCs l F o n