Free tools / Chiller diagnostics

Chillers in the Dark · Guided field assessment

Find the cause.
Not just the symptom.

Validate the readings, follow the evidence, and leave with a defensible next step. A guided chiller evaluation based on Jim Green’s field method.

THE METHOD

Compare the machine to itself. Close the heat balance first. Confirm before recommending.

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Method, calculation basis & limitations

Based on Chillers in the Dark

Jim Green, Principal Consultant, Industrial Water Advisory. The workflow implements the supplied paper’s Figures 1–6 and Appendix A. Tier 1 screens baseline deviations; Tier 2 follows the diagnostic trees; Tier 3 computes thermal state and documents confirmation. A calibrated physical model or digital twin is a separate engineering escalation, not a capability claimed by this calculator.

Transparent calculation basis

  • Water heat rate: Q = 500 × GPM × positive water ΔT, in Btu/h. Evaporator ΔT = entering − leaving; condenser ΔT = leaving − entering.
  • Heat-balance variance = 100 × (Qcond − Qevap − 3,412 × compressor kW) / Qcond. The gate passes at an absolute variance ≤5%.
  • Cooling load = GPM × evaporator ΔT / 24. kW/ton = compressor kW / cooling tons. COP = evaporator Btu/h / (3,412 × compressor kW).
  • Condenser approach = saturated condensing temperature − leaving condenser water. Evaporator approach = leaving chilled water − saturated evaporating temperature.
  • Expected ΔP = baseline ΔP × (current flow / baseline flow)². Tube velocity = 0.4085 × GPM × passes / (active tube count × inside diameter²), in ft/s with diameter in inches.
  • LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2); equal terminal differences use their common value. U = Q / (outside area × LMTD). Rd = 1/Ucurrent − 1/Uclean.
  • Paper allowance comparison: condenser 0.000250 and evaporator 0.000100 h·ft²·°F/Btu. These are rating references, not tube-integrity or cleaning acceptance criteria.
  • Nitrogen conversion: NO₂ × 0.304 and NO₃ × 0.226 when reported as full ions; values already reported as N are not converted again.
  • Coupon rate = 534 × loss (mg) / [density (g/cm³) × area (in²) × time (h)]. Use proper coupon cleaning, alloy-specific closed-loop interpretation and morphology; no universal corrosion limit is assigned.
  • Energy cost = (current − baseline kW/ton) × current tons × annual hours × rate. A constant representative operating condition is assumed; no demand charges, load-bin integration or guaranteed savings.

The paper provides a ±5% heat-balance gate but no universal numeric cutoffs for “flat,” “elevated” or “matched.” Default screening settings are editable: 0.5°F approach, 5 load percentage points, 5% flow, 10% ΔP, 10% chemistry/ΔT trends and 1°F superheat/subcooling. They are implementation assumptions, not OEM limits. Tighten or widen them only using sensor uncertainty and site evidence.

Use panel-reported saturation temperatures or temperatures obtained from an appropriate OEM refrigerant P–T reference. This tool does not convert shell pressure or assume a refrigerant. The simple water heat balance is not valid for glycol/brine or absorption machines. Follow site safety procedures; pressure-vessel, refrigerant, electrical and chemical work belongs to qualified personnel.