Hard to believe the energy saving from Schneider Altivar 212?

If you are not a motor engineer it can be hard to believe the energy saving from Schneider Electric UK Altivar 212. The Altivar 212 (ATV212) is a variable speed drive (VSD) for three phase asynchronous motors from 0.75 kW to 75 kW. Its operating characteristics are matched  specifically to the most commonly encountered fluid management applications in buildings (HVAC): heating, ventilation, air conditioning and pumping.  Schneider Electric  has engineered the drive for HVAC duty, and to deliver energy savings of up to 70% compared to a traditional control system.

Variable speed drives also contribute to the building’s overall comfort level by optimising and regulating air flow and temperature into the building’s occupant space. Unlike a fan that runs either full speed or off, a variable speed drive can run at all speeds in between, allowing facilities managers and building occupants more control to adjust the temperature.

Hard to believe the savings?

Many plant owners are confused how variable speed drives (inverters) save them money: if they are that clever, why aren’t they installed as standard.  The primary reason is that they costs money to install, but they only save money for the user of the building.  The other most frequent challenge is “What’s the difference between using inverter drives and my ventilation fans being thermostatically controlled?”  The answer here relates to how they work.

How do VSD’s use less energy?

A VSD reduces the speed of the motor controlling the fan or pump when full flow is not required, thereby reducing the power and the electrical energy used.  Without a speed controller, motors are stopped or running at full speed, and airflow or water flow are controlled by valves of vanes.  What is not understood by many facilities managers is why reducing the speed by say 10% reduces the energy consumption by 27% and not 10%.

Cube Law

It’s obvious that reducing the speed of a motor reduces the power consumed by the motor.   As motor speed falls, the reduction in electrical energy required to drive the motor is determined by the cube law.  Simply put, reducing the motor speed by 10% reduces the power required by the motor to 90% x 90% x 90% =72.9% of full speed: a saving of 27.1%.  By the same law, if you reduce the motor speed to 60% then 60% x 60% x 60% = 21.6% or a reduction of 78.4%.

Payback time

Now consider a typical installed 22kW IE2 (91.6% efficient) motor running at full load for 10 hours a day 250 days a year.  This will use 22 x 10 x 250/91.6% = 60,000kW of electricity in a year.  Assume £0.10 per kW that’s a running cost of about £6,000.  From the previous paragraph, by running it at 90% of full speed you save 27.1% of your energy consumption or £1626 a year for as long as the motor runs.  The cost of a 22kW inverter is around the same price, so the payback calculation is relatively straightforward too.

Although AC drives from most manufactures have provided similar rates of energy savings, the Altivar 212 has been optimised for efficiency to provide additional savings in buildings.  The ATV212 provides no so hard to believe the energy saving from Schneider Altivar 212

Contact us at 999 Automation to see how we can provide you with guidance for your energy savings.