Cooling Tower Test Matrix

Reference engine: Two layers of evidence: (a) 72 analytical CogenS gates over the part-load and curve space, with curve coefficients byte-identical to the EnergyPlus 26.1 example library; (b) 12 EnergyPlus-coupled hourly cross-validation cases run on a coupled chiller + cooling tower plant. ASHRAE Guideline 14-2023 scoring on layer (b).

Reference engine: Real multi-tower EnergyPlus topology: N parallel CoolingTower:VariableSpeed objects under one PlantEquipmentList with SequentialLoad distribution + PlantEquipmentOperation:CoolingLoad, coupled to Chiller:Electric:EIR on a shared CondenserLoop. Each EP CT is sized to 1/N of the aggregate water / air flow and fan power so the plant-level nameplate matches the CogenS multi-unit configuration. Two layers: Layer A — hourly staging-decision regression of the CogenS engine against the analytical band-fit predictor at zero hourly mismatches (the engine implements the documented rule consistently). Layer B — ASHRAE Guideline 14-2023 cross-engine on plant-aggregate fan electric, supply temperature, heat rejection, and makeup water against the multi-tower EnergyPlus reference, July full-month Chicago TMY3 weather with sinusoidal cooling load.

Reference engine: Two layers: Layer A — hourly free-cooling mode-classification regression of the CogenS engine against the analytical predictor (Mode 0 when supply > 10 C, Mode 1 full FC when cooling load ≤ qecomax + supply ≤ 10 C, Mode 2 partial FC when cooling load > qecomax + supply ≤ 10 C) at zero hourly mismatches. Layer B — real EnergyPlus cross-engine on the chiller + CT plant at Chicago January TMY3 (744 hourly steps). Both engines exercise the cold-ambient regime: CogenS FCYES_FCDESIGN config activates internal FC for 369 hours; EP runs the same chiller + CT topology with its supply-temp setpoint manager naturally tracking the cold WB. The supply temperature delta agrees to 0.06 K (essentially exact); the makeup water gate passes Tier 2 (115%); the fan electric gate passes Tier 2 (32%). The cogens FC HX bypass control logic is verified internally (Layer A); the underlying physics (low fan, low evaporation, low supply temperature) is cross-validated against EnergyPlus (Layer B).

Reference engine: Two-layer evidence pack. Layer A: cogens internal self-consistency on chiller energy balance (Q_rej = Q_cool + W_elec) + multi-pass orchestration convergence (|Pass3 - Pass1| / Pass1) — REGRESSION TEST on the cogens iterative orchestration, NOT a cross-engine validation. Layer B: ASHRAE Guideline 14-2023 cross-engine on chiller electric (annual / NMBE / CV(RMSE)) + CT supply temperature + chiller condenser inlet temperature, against EnergyPlus Chiller:Electric:EIR coupled to CoolingTower:VariableSpeed on a CondenserLoop with SetpointManager:Scheduled at 30 C CW supply. Topology mirrors the PlantApplicationsGuide_Example1 reference plant.

Reference engine: EnergyPlus LifeCycleCost (NIST Handbook 135 reference implementation) for the operating present value. Independent polynomial-root IRR solver, direct NPV recompute, and published IRS Publication 946 MACRS GDS schedules for the investment KPIs.

Reference engine: EnergyPlus 26.1 FluidCooler:SingleSpeed and FluidCooler:TwoSpeed — a dry, sensible-only, dry-bulb-driven fluid cooler, which is a different machine from the evaporative wet tower in Stages 1–5. Each CogenS fan-control strategy is scored against its MATCHING EnergyPlus device; scoring one against the other would measure the control strategy rather than the model. Both objects run with Performance Input Method = UFactorTimesAreaAndDesignWaterFlowRate, so EnergyPlus is handed the same heat-exchanger UA the CogenS engine derives from its own design point (and, for Two-Speed, the same low-speed UA) rather than autosizing its own — the two engines solve the same exchanger. Both are driven by one shared hourly duty file (EnergyPlus reads it via Schedule:File) and one shared TMY3 weather file, with the hourly outdoor dry bulb verified identical to 0.00000 °C.