roar of 20kW fans turning at full speed is no longer much in
evidence in and around the flight simulator cells at British
Airways’ Flight Training Centre at Heathrow Airport. Thanks to the
site’s Trend building energy management system and the variable
speed drives they control, the powerful air handling unit fans now
tend to rotate at a much more leisurely pace – with the result that
their power consumption has fallen considerably. There have been
significant savings too on the energy used by the centre’s chillers
and boilers, and on air handler plant maintenance.
Moreover, the BEMS provides highly stable control of temperature within the cells, which is vital if the simulators are to function correctly.
At Heathrow, BA boasts one of the UK’s largest civil aviation training centres, a facility that is used both by its own crews and those of other airlines. It is equipped with 15 full flight simulators located in self-contained bays. In almost all of these cells the environmental conditions are regulated by Trend IQ controllers and there is variable speed control of the air handler supply and extract fan motors. The controllers form part of the centre’s extensive building energy management system, which incorporates some 30 networked IQs.
The air conditioning in a number of the cells has had IQ controls and variable speed drives for over twenty years. The plant serving other cells has acquired them only recently, with six days being converted since the end of 2007. The impact of this work is clearly seen in the annual energy consumption figures for the centre, which is one of BA’s heaviest power users at Heathrow. From 2004 to 07, consumption remained more or less constant, but in the 12 months to January 09 it fell by 11.8% (degree day corrected) compared with 2006/07 - a combined saving on electricity and gas of 3466MWh. In the year to December 09 it was down 16.4%, equivalent to 4817MWh.
When a cell’s space temperature is within +/- 0.5oC of setpoint and air quality requirements are satisfied, the fans are run at a pre-set minimum speed (though in the latest cell to be converted they are shut down completely). Should temperature begin to go out of tolerance, the IQ controller initially attempts to correct it - if outside temperatures permit - by modulating the AHU’s dampers to make maximum use of ‘free’ heating or cooling. If demand continues to rise, the IQ slowly ramps up the fan speed and opens the AHU’s heating or cooling battery valves. The greater the difference between actual and setpoint temperature the faster the fans run.
If air quality deteriorates beyond a certain limit, the AHU dampers are positioned to admit more fresh air and it may also be necessary to increase fan speed. The IQ calculates and compares the respective speed settings that are needed for temperature and air quality control and applies whichever is the higher. Regulating fan speed on the basis of air quality (CO2) measurements has eliminated unnecessary air changes, which has had major impact on energy usage.
Fan electrical usage has generally fallen by 80 – 90% and in some instances by 95%. Fewer air changes and energy efficient control of the AHUs have also meant less demand for chilled and hot water, which has in turn meant savings on chiller electricity usage and gas consumed by the boilers.
With the fans running at much reduced speed, there is far less wear and tear on motor bearings, drive shafts and belts. The AHU filters – which cost around £100 each – also need replacing less frequently. Previously, they had to be renewed every three months, whereas now they generally last for a year. BA is also benefiting from improved control of environmental conditions within the cells. The IQs have proved capable of consistently maintaining the space temperature to within +/- 1oC of setpoint. This is important because temperature fluctuations can actually cause distortion of the visual images seen within the simulator. They do so by disrupting the vacuum that holds a thin layer of Mylar on the surface of the curved mirror onto which the images are projected.
Other facilities at the centre include a number of fixed base simulators for cabin crew training. These are housed in a large, high-roofed hall, the air handling plant for which has long been Trend controlled. Here there is also an IQ controlling the hydraulic motion system on two cabin evacuation trainers. Previously, each of these had its own hydraulic rig, both operating 24hrs a day. Now, one rig serves both trainers and is controlled according to demand by the IQ and a VSD. As a result, power consumption has dropped from 360kWh per day to just 21kWh. The motion system for one of the flight simulators is similarly controlled, with an IQ and VSDs regulating the speed of the hydraulic pumps to exactly match demand. This has produced an annual electricity saving of 260MWh.
Owing to the scale of the savings made in the simulator cells, BA has in some cases been recouping its investment in Trend and VSD control in less than 6 months. There is scope too for extending the Trend BEMS to more of the centre’s office areas. It is already controlling the site’s boilers, chillers and heating and chilled water circuits.
System monitored data and control settings are accessed via Trend ‘963’ supervisors. One is used by BA’s maintenance contractor EMCOR, which has personnel permanently on site, and another by BA’s own engineers. Through these it is possible to view the operational status and performance of any of the plant – including any fan. The whole BEMS is linked via an Ethernet network to all BA’s other Trend controlled buildings at Heathrow – of which there are over 100. This enables centralised monitoring by the maintenance contractor.
E-mail Trend Control Systems