I am working on a lab building near the coast where seawater is pumped into the building for use by researchers. The system gets complex, but essentially we are controlling these large "raw" seawater pumps with VFDs to maintain a specified seawater tank level. Additional "filtered" seawater supply pumps are specified with VFDs to maintain a system pressure setpoint near the point of use.
The similar size pumping systems of Appendix G (HHW and CHW) call for constant volume pumping riding the pump curve with a peak power in W/gpm. How would I show savings for our proposed system of variable speed pumping vs. constant speed pumping when a load profile is unknown? Has anyone had a similar building model?
Do I generate an assumed operation for the pumps, one as operating continuously (baseline) and one as partial energy consumption during off-hours (proposed)? What peak power should I use for the baseline pumping (same as proposed or a certain W/gpm)? Please advise, this also would apply to process cooling water pumping on variable frequency drives.
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
962 thumbs up
September 8, 2011 - 11:00 am
This is a building process load. For LEED, you should model that separately as an Exceptional Calculation Measure (ECM). Provide a narrative explaining your justification for the improvement. You'll need to estimate a load profile based on your best understanding of the use.
At first glance, I think probably you can't take credit for schedule differences, but can take credit for things like motor efficiency, and VFDs. You might want to put together a draft and submit to the reviewers as a LEED Interpretation.
The process cooling loop is different, and I think would be modeled as I indicated above.