When should a water utility run its lake pump, and how much of the saving is the tariff?
research/infra-pumpsched
Pump scheduling on EPANET's Net3 (WNTR): running the lake pump 21 h from 01:00 cuts pumping energy 52 % at a flat tariff because it idles the booster pump; the time-of-use tariff adds 3 to 16 % of cost at a ratio of 3 or less, and hourly on/off schedules (21,806 simulated, plus a GA) add almost nothing beyond one window once tank drawdown is priced (simulated, assumed tariff shapes).
What it found
WNTR simulates Net3 for three days with pump 10 (the lake source) on a repeating 24-hour schedule, scoring the last day on pump energy (Net3’s 75 % efficiency) and time-of-use cost under three assumed tariff shapes with the peak/off-peak ratio swept 1.5–10. Feasible schedules keep the tanks in range and the daily balance within 1 %; pressure and tank range never bind. At a flat tariff the best window (01:00, 21 h) uses 1,307 kWh a day against 2,728 as shipped, 52 % less, because Net3’s river supply is mostly gravity and the booster pump 335 only runs when tank 1 is low, so more lake pumping idles it: a saving that needs no tariff. Beyond that, knowing the tariff adds 3.3 % of shipped cost at ratio 1.5, 15.8 % at 3 and 95 % at 10 for a 16:00–21:00 peak, and 3.1/12.1/39.2 % for a daytime peak. An exhaustive search of all 21,806 schedules with at most two on-runs a day finds a second window worth 0–0.02 % of cost for 8 of 10 tariffs (9.5 % and 1.2 % for the other two); a genetic algorithm and a local search over all 224 hourly schedules beat that by up to 4 points, but most of it is tank drawdown within the 1 % tolerance, and priced it falls to about 0–1.3 points. A first version mis-simulated windows that cross midnight; corrected here. One network, assumed tariffs (none sourced), no demand charge, a 1 % mass-balance gap not traced.
A figure from its own output
Paper, code and results
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.