"We have two different oils and need to determine which one is more energy efficient. What data should we collect? What parameters can help establish energy efficiency?"
Energy efficiency must be measured in terms of the reduction of energy consumption. More specifically, it is related to how much energy the machine consumes in order to operate. This principle applies to machines that convert one type of energy like chemical or electric to a mechanical one, such as electric motors and combustion engines. It is also applicable to machines that transmit mechanical energy, like gearboxes. In some cases, it may be evaluated in a powertrain such as a combination of a combustion engine and a transmission.
The energy saved is measured in terms of what is utilized to move or operate the machine. For example, for a combustion engine, the reduction in fuel consumption would be measured. For an electric motor and/or gearbox, the reduction of electric energy (voltage, current and power factor) would be measured.
The energy savings can also be measured indirectly by simply verifying a reduction in the operating temperature. This can be a practical method for electric motors, gearboxes and pillow block bearings. Although it likely will not reveal the amount of energy saved, there will be a clear indication of the reduced energy consumption.
For instance, a cement plant was able to achieve energy savings when it decided to switch from a lithium-thickened mineral grease to a synthetic lithium-complex-thickened grease. Previously, the plant was lubricating pillow blocks daily, with continual grease loss and operating temperatures near 80 degrees C. After the lubricant change, the relubrication intervals were extended to one or two per week, and the operating temperatures dropped about 20 degrees C. While an incorrect lubricant had been in use, the benefit of utilizing a better and more efficient grease was evident.
It is important to note that certain conditions must be kept consistent for the sake of comparison. These conditions would include using a similar amount of lubricant (the same oil level or regreasing amount), measuring the equipment in similar operating conditions (load and speed), and maintaining similar ambient or room temperatures. Preferably, the same instruments and methods should also be used to measure the energy consumption for both lubricants. Otherwise, similar or comparable instruments should be utilized. Finally, be sure to take several readings to minimize the impact of inevitable variations.