Every day we are hearing “energy saving” expressions but what does it really mean, specifically in the industrial automation field?
- How much savings we can have?
- Is it a fixed value or calculable?
- What are the different criteria that effect this concept?
- In what kind of applications is it valid?
- Are there any tools/software to take care of this task?
To give you a clearer picture, I will first try to explain what “energy savings” is not…
No, it is not energy efficiency
The first thing that comes to mind is the energy efficiency chart when I want to purchase home appliances or a muscle car, with G level for fun we don’t care, but this is not the case for different automation products (PLC, HMI, VSD…) that uses some energy for supplying/running internal circuits and it could be different from brand to brand and also product to product.
No, it is not mechanical life cycle
Although we are increasing the life cycle of gears, bearings, welding… by using Variable Speed Drives or Soft Start-Soft Stop units and prevent the mechanical shocks and vibration during start up and stop, it is difficult to have precise mechanical life time calculation and related saving.
No, it is not Telemetry or web-Visualization
Even though by remote connection to the automation products which are located in the field we can save some money (travel, fuel… costs) and time by handling debugging and monitoring from far distances via different medias.
No, it is not Reactive Power (Q, kvar)
Although by using Variable Speed Drive we can improve the Power Factor (Cosɸ) close to 1 by internal capacitors of Variable Speed Drive and automatic regulation and consequently power factor correction by capacitor bank is not needed any more.
In variable torque applications such as Fans or Pumps that nominal torque at startup is not needed and the resistive torque applies to the asynchronous motor’s shaft gradually, in parallel we can decrease the driven torque/active power when it is not needed in this way saving some energy that is active power is possible.
Yes, it is calculable
Based on load profile, number of working days per year and hours, cost of electricity (kWh)… we can calculate it; let’s have a look at a practical example:
How to calculate Energy Saving
A 37kW Fan needs to supply air during 10h/day for 250 days per year with the price of the power at 0,164€/kWh
- The cost of running that Fan at full speed will be 15170€
37kW x 250days x 10h x 0,164€/kWh = 15170€
If the Fan only runs:
20% of the time at 100% of full load means 20%*2500 h= 500 h
The cost: 37 kW x 500 h x 0,164 €/kWh = 3034€
50% of the time at 80% of full load means 20%*2500 h= 1250 h
The Cost: 37 kW x 1250 h x(0,8)^3 x 0,164 €/kWh = 3883,5€
30% of the time at 60% of full load means 30%*2500 h= 750 h
The Cost: 37 kW x 750 h x(0,6)^3 x 0,164 €/kWh = 983 €
- Total Costs: 3034€ + 3883,5€+ 983€ = 7900,5€
- The cost of running that Fan with a VSD will be 7900,50€
52% in Saving
Eergy Saving = 15170-7900.5=7269,5 €
- Energy savings means active power savings and consequently affects the Apparent power (S) as S= √ (P^2+Q^2)
- The level of savings related to the working time and load profile, cost of electricity (kWh), cost of the product & installation so, it is not fix value.
- In variable torque applications like fan & pump that reduce the duty cycle it is possible to implement the energy saving concept, but in constant torque applications that nominal torque at asynchronous motor at start-up is needed… this concept is not feasible.
- Less foot print by reducing CO2 emission
- The Variable Speed Drive suppliers usually providing such software that is very nice in case of fast calculation and reporting for management level to make investment decisions.
I hope now you have a clearer picture of what is the basics of Energy Savings calculation software in industrial automation field.