How Energy Savings are Acheived using AC Variable Speed Drives
Almost half of that power is used to drive variable torque loads such as fans, pumps and blowers. One problem with these applications is that a motor, is not an "Intelligent Device", and will at full speed irrespective of the demanded load. By utilising less energy to drive loads, we are able to improve motor efficiency, save energy and reduce cost.
Pump and fan applications offer the best oppurtunity for Energy Savings through the installation of an AC Variable Speed Drives (VSD's)
A 10% reduction in speed will give a 25% reduction in Energy consumption.
A 20% reduction in speed will give a 50% reduction in Energy consumption.
Actual Energy savings can be calculated using the formula below
Cost to run a motor at 100% speed = (kW) * (running time hrs) * (£/kWhr) = £___ (a)
Cost to run a motor with a VSD = (kW) * (% speed)³ * (running time hrs) * (£/kWhr) = £__ (b)
Energy Savings = (a) - (b)
Example
Lets look at an example of running a 75kW at full speed for 12 hours a day for 350 days a year, with an electrical cost of 5.5 pence per kW hour. If we take that same motor and reduce its speed by 20% using a variable speed drive, we will see substantial savings.
At 100% speed = 75kW * (1.00)³ * 12 hours * 350 days * £0.055 = £17 325
At 80% speed = 75kW * (0.80)³ * 12 hours * 350 days * £0.055 = £8 870
A saving of £8 455 per year or 48.8%
Saving = (reduction * reduction * reduction)