ACTC helps estimate VSD energy savings and RoI

The Applied Control Technology Consortium was asked by one of its member companies, a leading paper mill, to provide help in identifying and quantifying potential energy savings
The ACTC Helps Estimate Energy Savings and Return on Investment The Applied Control Technology Consortium (ACTC) was asked by one of its member companies, a leading paper mill, to provide help in quantifying potential energy savings. The replacement of fixed-speed drives of fans and pumps by variable-speed drives (VSDs) can lead to significant power and energy savings under partial-load conditions. In many systems, this means most of the time! The payback time of the installation of a VSD depends on the relative savings in energy costs against the investment cost of the VSD.

ACTC engineers worked with plant staff to establish the standard operating conditions, and how these affected current and projected energy use.

The ACTC investigated two scenarios in a case study: an air fan and a thick stock pump.

On the air fan, the projected energy savings were 30-40%, depending on the actual load conditions.

This is likely to be sufficient to justify the investment in a VSD, with a payback time of 2-3 years.

The thick stock pump was found to be running at nearly full load most of the time, meaning that the energy savings with a VSD would be very small.

The study thus saved the paper mill from potentially making an uneconomical investment.

However, the fact that the pump usually runs at full load also indicates that it is a bottleneck in the production process.

If production capacity were extended and the pump drive replaced, a VSD is likely to provide sufficient energy savings to justify its installation.

Comparison of the results of the study against the results of a tool provided by a VSD supplier showed lower projected savings in the ACTC study.

Checking the data requirements of the two methods against each other showed that the supplier tool ignored certain essential characteristics of the process in its calculation of the projected energy savings.

The study therefore showed that this supplier tool, and others like it, should only be used with great care in the interpretation of their results.