Get Up To Speed With VSD Energy Savings

Worldwide, electric motors account for around 70% of all electricity consumed – in European industry alone, electric motors consume in excess of 1,000,000,000,000 Kw/h annually, which generates over 400,000,000 tonnes of CO2. Global bodies have been working to set new standards for electric motor performances, and the EU has introduced the MEPS (Minimum Efficiency Performance Standards) EU directive 2005/32/EG. This directive is being introduced in three steps: Step 1 – from 16 Jun 2011 all new electric induction motors between 0.75Kw & 375Kw must meet the IE2 standard, equivalent to the old EFF1 high efficiency standard Step 2 – from 1 Jan 2015 all new electric induction motors between 7.5Kw & 375Kw must meet the IE2 standard and be used along with a variable speed drive, or meet a new IE3 premium efficiency standard (new permanent magnet motor technologies etc) Step 3 – from 1 Jan 2017 all new electric induction motors between 0.75Kw & 375Kw must meet the IE2 standard and be used along with a variable speed drive, or meet a new IE3 premium efficiency standard (new permanent magnet motor technologies etc) The use of variable speed drives (VSDs) gives a potential saving of 20-30%, and the projected savings in Europe by 2020 is estimated at 135,000,000 Kw/h per annum. Variable speed drive design has improved with the use of high performance semiconductor switching devices and the efficiencies of VSDs have now reached 96% or better. GAMBICA, the manufacturers steering body, have recently published a “Guide to Measuring Efficiency” with the aim of ensuring that all manufacturers present their efficiency figures in the same format to enable accurate comparisons. In building services, electric motors are mainly used for running pumps and fans. These applications generally have the most potential for energy savings and can have quite short payback periods for the capital investment involved. Traditionally on a ventilation system the motor operated at a fixed speed and the airflow was controlled by the use of dampers either on the input or output to the fan. Using a variable speed drive to control the speed of the fan allows the dampers to be fully opened therefore removing any restriction to airflow. A centrifugal fan has a cube law relationship between speed and power consumed i.e. a fan running at 40Hz instead of 50Hz is operating at 80% of its nominal speed and the power consumed is (0.80 x 0.80 x 0.80) 51.2% – therefore we have a general rule of thumb that a fan running at 40Hz consumes approximately 50% of the energy required to run at 50Hz. In practice if a 11Kw fan was operating for 12 hours a day, seven days a week, and the Kw/h cost was 15p a unit, that fan would cost £7220 per annum to run. However, if a variable speed drive was fitted and the speed could be reduced to 40Hz, the fan would cost £3610 per annum to run. A typical 11Kw variable speed drive would have a capital investment of around £1300, meaning the payback would take around four months. The energy saving potential of variable speed drives is enormous, but this is dependant on the running hours and the duty required. If a fan or pump is required to operate at full speed, there is no advantage to using a variable speed drive. This means it is essential that an energy survey is carried out first to assess the potential savings. To encourage the retrofitting of variable speed drives and high efficiency motors, a grant scheme exists in Northern Ireland, operated by Energia, which can cover between 20-40% of the equipment cost for an approved scheme. For further information contact Janine Brady at Energia on 0845 073 0099 or speak with Ian Atkinson at Greenville Electrical on 028 9064 5060.