- Close control of indoor air temperature
- Controlled flow of chilled water to the air handling units
- Output down to 45% of the maximum pump speed
- Drives interfaced with BMS
- Less downtime
|The National Gallery in Trafalgar Square, London, houses a permanent collection of over 2,300 paintings by many of the world’s most famous artists.Chilled water was being continuously re-circulated with the pumps running at full speed, resulting in considerable waste of energy.||Eight variable speed drives were fitted to the system, two at 3kW, four at 4kW and two at 15kW. These were installed to control the flow of chilled water to the air handling units, ensuring that the temperature stays within +- 1oC of the set point. Stable temperature and humidity levels are required for the conservation of the pictures.|
Equipment : Two 3kW, four 4kW and two 15kW drives
Saving P.A. : £70,000
Variable Speed Drive Benefits
Now output varies with demand, down to 45% of the maximum pump speed. The new drive system gives a closer control of each individual area of the Gallery. It is interface to a Trend Building Management System, which controls the speed of the pumps by giving the variable speed drive a 0-10 volt signal.
The drives are controlling the air temperature throughout the Gallery’s West Wing, protecting the work of artists such as Michelangelo, El Greco, Titian and Vernoese.
“Variable speed drives are extremely accurate devices and so are ideal for applications where close control is required.” explains Mike Carman, UK Sales Manager HVAC at ABB. “They are extremely versatile when it comes to receiving input from feedback devices and immediately adjusts the fan or pump speed to the required output. In addition, it causes less wear and downtime on mechanical components than the continuous stopping and starting of traditional on-off control”.
Variable speed drives are more efficient than traditional control devices because they control output by regulating the motor speed, rather than running the motor at full speed and using restrictions to reduce flow. The reason that the difference in consumption is so staggering is that to increase the speed of a centrifugal load, such as a pump or a fan, requires a power increase which is the cube of the speed increase. This means that to double the flow, the power input required is the cube of the desired flow increase, 23=8 times the power; to treble the speed takes 33=27 times the power. Conversely, this also means that a small reduction in the flow results in a large cut in the energy consumption; for instance, reducing the flow to 80% cuts the energy consumption by half.