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ABSTRACT HEADING

Variable speed pumps in hydronic circuits are often controlled to sustain a constant differential pressure across two points in the circuit. However, this strategy is not energy-efficient in part-load conditions. Instead, pump speed can be controlled to maintain at least one control valve nearly fully open. Thorough comparisons between the two methods are rarely seen in the literature. Moreover, it is difficult to find discussions addressing and quantifying the impacts of selecting different pressure sensor locations. In order to address these points simulations are run for a simplified chilled water circuit using Flownex SE software, a numerical tool able to model thermal-hydraulic circuits. The results show that controlling pump speed to maintain at least one control valve nearly fully open is more energy-efficient (in part-load conditions) than using a constant differential pressure across two points in the circuit. The pressure sensor location is relevant when the pressure set point is kept constant. Generally, placing them away from the pump reduces energy consumption, as the set point is smaller. However, this might lead to starving coils in certain circuits and operating conditions. The results corroborate ASHRAE's recommendations (see, for instance, Standard 90.1) - controlling pump speed to maintain at least one control valve nearly fully open is strongly advised for systems working frequently in part-load conditions.