ERD Efficiency: What System Builders and Consultants Need to Know

Executive Summary

This White Paper addresses the impact of ERDs on the energy consumption of the RO process using an objective and fully transparent criteria. The analysis shows that published ERD efficiency data has virtually no correlation to the actual energy consumption of the RO system.

There is no standard definition of efficiency for energy recovery devices (ERDs). Each supplier is free to create their own definition that (not surprisingly) often favors their particular technology.

Two new factors are presented, transfer efficiency and field efficiency that allow a more accurate characterization of ERDs in realistic field operation. The impact of various ERDs on energy consumption of a hypothetical 20,000 m3/day SWRO train is presented.

In large scale systems, the analysis clearly indicates turbochargers provide the same or better energy consumption than all other ERDs including Isobaric Chambers.

In particular, isobaric chambers, that purport to have a 97% efficiency have, in fact, an efficiency in range of 83-85% in most field applications. An unfortunate consequence is that efficiency requirements of 95+% are often included in project specifications precluding other ERDs that can offer a significantly lower cost of permeate through comparable energy consumption and reduced CAPEX and OPEX.

It is time to open project specification to all field-proven ERDs and let the market decide the winner