Maximising energy savings in variable-flow systems

In systems with variable-speed pumps and differential-pressure control valves, it is still very important to measure pressures at key points so that pump speeds can be optimised. Electronic manometers can accurately the high pressures that may be encountered.
Duncan Selby warns against placing too much reliance on differential-pressure control valves in variable-flow systems.As new Building Regulations take hold within the HVAC industry, we are seeing a concerted effort to show savings in pumping energy. One key method being exploited is the use of variable-speed pumps to modulate flow in systems. The use of variable-speed pumps combined with differential pressure control valves (DPC’s) offers considerable benefits. They include lower overall energy use, less complex control valve arrangements and simpler installation. Pump pressure The time taken to commission should also be reduced, as the need for proportional balancing reduces. However, commissioning engineers must be aware that consulting engineers will now demand more data than just flow rates to each terminal unit. As the use of DPCVs increases, so will the need to establish accurately the pressures controlled by these valves. It is too simple just to rely on DPCVs to control the pressure when the pressures generated by the pumps may be much greater than required. It is essential that when system is put to work the pumps generate only enough differential to do the job. Ensuring this requires that pressures are measured at key points around the building, so that pump speeds are adjusted to the optimum point. No longer will it be acceptable to simply measure the pressures at these key points and record that they are above the range of the instrument. Technology in the form of electronic manometers is now available to accurately measure key pressures across the system. The sooner we recognise the benefits of correctly ‘tuning’ the pump output to the requirements of the building and allowing sufficient time and resource for the process, the sooner we will exercise our duty to minimise our carbon footprint and achieve the lowest operating costs. Duncan Selby is with Comdronic Ltd
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