November 2019

34 | Plant & Works Engineering www.pwemag.co.uk November 2019 Energy, the Environment & Water Focus on: HVAC 1 Cooling tower A cooling tower extracts waste heat into the atmosphere. Using a variable speed drive, instead of conventional direct-on-line or Star- Delta control, means the tower’s fan and pump speed can be adjusted. The pump, for instance, would only circulate the required water for the process while the fan can better regulate the output temperature. Using the drive this way achieves reduction in energy use between 20 to 60%. 2 Chiller A chiller reduces the temperature of water or other liquid to cool down and dehumidify the indoor air. A variable speed drive used with chillers is a proven way to optimise energy utilisation at full and part loads. Unlike a constant speed chiller, a variable speed drive inherently uses up to 30% less energy and reduces inrush currents on start-up. By soft starting the chiller controlling its speed, noise is significantly reduced, maintenance costs are lowered and overall plant life is extended. 3 Condenser water pump This pump circulates water between the cooling tower and the chiller. By adjusting the pump speed to the cooling load using a variable speed drive, energy savings can be achieved between 20 to 60%. 4 Chilled and hot water circulator pumps These pumps circulate water (or other liquid) between the heating coil and the boiler or cooling coil and chiller. The cooling and heating loads vary a lot over time. Variable speed-controlled circulation pumps make sure that an adequate amount of water or other liquid is distributed in the building. Soft start and stop of the pump reduces hydraulic stress, such as water hammer, on pipelines and valves. By installing drives energy savings of between 20 to 60% can be achieved effortlessly. 5 Boiler A boiler is deployed to heat up the water for building heating. The drive controls the burner fan to adjust the amount of combustion air to the heating load. 6 Air handling unit (AHU) An AHU circulates, mixes, cleans, humidifies/dehumidifies and heats/cools air. If Variable speed drives are used to control the speed of supply and return fans, then this eliminate mechanical stress of air duct system, avoids fan resonance speeds, controls the speed and efficiency of the rotary heat exchangers, controls the dampers and monitors AHU condition including filter clogging, fan belts and heating coil freeze. Variable speed drives should also be capable of operating in the event of a fire and have the option of an override mode, or fire mode, which secures drive operation in emergency situations. Savings of between 20 to 60% can be achieved by the installation of variable speed drives on these applications. Selecting the right motor Variable speed drives can be integrated with several types of AC motors, including induction, permanent magnet (PM) and even synchronous reluctance (SynRM) motors. The most cost- effective option can vary from application to Regardless of the season or external conditions, variable speed drives help make HVAC applications efficient, safe and informative while providing high levels of comfort, control and safety. ABB’s Carl Turbitt takes a tour around a typical plant and highlights the opportunities. Building efficiency, safety and comfort

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