Saving is Losing: Pumping Cost vs. GHG Emissions in Water Distribution Systems

Abstract

Global climate change has necessitated the reduction of GHG emissions. Water distribution system (WDS) pumping adds to these emissions and, therefore, should be reduced. Under electricity hourly cost tariffs, utilities are incentivized to pump during the nighttime hours. This can have a deleterious effect, however, on GHG emissions. To quantify this effect, a modeling study of twelve real WDSs was performed with an electricity tariff. The systems all had the typical tank-level-based pump controls but also time-based controls. Results show there can be a tradeoff between pumping cost and GHG emissions, depending on the pump schedule. If the pumps are forced to supply demand in a shorter time to take advantage of the lower cost during off-peak hours, then the flowrate must be higher with a concomitant increase in velocity and headloss, thereby adding to the GHG emissions. This effect was not found for all systems, however. Pumping over all the low-cost hours resulted in the pseudo-optimal solution of lowest combination of cost and GHG emissions for many systems. It might be worth it, however, to incur higher costs and reduce GHG emissions, given the severity of climate change occurring around the world.