FANS
potential of the fan laws (power is proportional to rotary speed cubed: P N3). This delivers a reduction in energy costs throughout the equipment’s lifecycle. Installations employing this approach to date indicate that fan energy consumption can be reduced by around 45%. Secondly, the damper blade position will be between 40% and 100% open at this lower pressure point. This facilitates better control of the VAV units themselves, at the same time as improving the system’s acoustic performance. Lastly, the ability to control fan speed via the positioning of the damper blade, rather than a pressure transducer, removes complexity from the commissioning process. It removes the difficulties associated with determining where to position the pressure transducer within the duct to obtain the required data. The utilisation of damper blade position therefore provides a more stable control circuit on which to design and operate the system.
Control options
Of course, controls capable of monitoring and acting upon the damper blade position data are necessary for this methodology. One obvious option is to use the central Building Management System (BMS) to fulfil this responsibility. This, however, can involve complex and expensive bespoke programming, whereas a simpler and more cost-effective option would be to harness the digital control capability already resident in the VAV systems themselves. A number of standard TROX products and solutions, for example, have integrated control technology capable of fan speed optimisation without the need for bespoke BMS programming. Examples include TROX's X-CUBE air handling unit, which incorporates the option for fan speed optimisation via damper blade positioning as standard. The X-CUBE connects to centralised BMS via Modbus, TCP, Ethernet or BACnet, and facilitates room-by-room air management, adjusting fan speeds automatically in line with changing requirements.
Another example is TROX's X-AIRCONTROL system. Its main focus is the individual, demand- based control of air volume flow rate on a room- by-room, or even a zone-by-zone basis, with fan speed being controlled based on the damper blade positioning within the VAV terminal units as standard.
To conclude, the latest generation of digital VAV systems allow fan speed and pressure to fall together when demand reduces. The system can therefore become much more efficient, delivering valuable improvements in environmental performance.
www.acr-news.com January 2021 11
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