Example data table
A realistic operating point for checking your numbers.
| Cooling load (TR) | Chiller kW | Pumps kW | Towers kW | Aux kW | Total kW | Plant kW/ton | Plant COP | Annual kWh (2000 h) | Annual cost (@0.12) |
|---|---|---|---|---|---|---|---|---|---|
| 500 | 300 | 40 | 35 | 10 | 385 | 0.770 | 4.57 | 770,000 | 92,400.00 |
Formula used
- Total plant power (kW) = Chiller kW + Pump kW + Tower kW + Auxiliary kW.
- Plant efficiency (kW/ton) = Total plant kW ÷ Cooling load (TR).
- Cooling capacity (kW) = TR × 3.517.
- Plant COP = Cooling kW ÷ Total plant kW.
- EER (Btu/W-hr) = (TR × 12,000) ÷ (Total kW × 1,000).
- From flow (water): TR = (gpm × ΔT°F) ÷ 24 or TR = (1.163 × m³/h × ΔT°C) ÷ 3.517.
- Annual energy (kWh) = Total kW × Operating hours.
- Annual cost = Annual kWh × Rate, and CO2 (kg) = Annual kWh × Emission factor.
Note: Flow equations assume water and typical density/heat capacity. For glycol mixes, use corrected constants from your design data.
How to use this calculator
- Choose how you know the load: enter TR or calculate from chilled water flow and ΔT.
- Enter chiller power directly, or enter COP to estimate chiller kW.
- Add pump, cooling tower fan, and auxiliary loads measured at the same time.
- Press Calculate efficiency to view results above the form.
- Optional: add a baseline kW/ton to estimate improvement percentage.
- Download a CSV or PDF to attach to submittals or site reports.
For construction commissioning: capture several operating points (different loads and ambient conditions) and compare trends, not just a single value.
Plant efficiency metrics that matter
Plant kW/ton is the most practical site KPI because it captures chillers, pumps, towers, and auxiliary loads together. It also translates cleanly to COP and EER. Many well-tuned plants operate around 0.55–0.75 kW/ton at design conditions, while values above 1.10 kW/ton often indicate control, flow, or heat-rejection issues.
Load and lift drive most variation
A single kW/ton value changes with load and condenser lift. At low load, fixed-speed pumps and fans can dominate total kW and depress plant COP. At high wet-bulb temperatures, tower approach widens and condenser temperature rises, increasing compressor power. Capture multiple operating points to see whether kW/ton improves as load increases.
Where the energy usually goes
In many plants, chillers contribute roughly 70–85% of total kW, with pumps and tower fans making up most of the balance. If non-chiller loads exceed 0.20 kW/ton, investigate oversized flows, bypasses, constant-speed operation, or poor sequencing. Variable speed drives, differential-pressure reset, and optimized tower staging commonly deliver measurable reductions without changing equipment.
Commissioning checks for construction teams
Verify sensor locations, calibration, and trending intervals before concluding performance. Confirm chilled-water ΔT is stable, valves are not short-circuiting return water, and pump curves match installed impellers. On the heat-rejection side, confirm tower cells stage correctly and condenser-water flow is not excessive for the load. A stable operating point with 10–15 minutes of averaged data improves repeatability.
Using results for reporting and upgrades
Use the annualized kWh, cost, and CO2 outputs to rank corrective actions. For example, improving plant efficiency by 0.10 kW/ton on a 500 TR load saves about 50 kW at that point; at 2,000 hours per year, that is about 100,000 kWh. If your rate is 0.12 per kWh, that is about 12,000 per year. Pair the calculator’s CSV/PDF exports with trend logs and baseline comparisons to support submittals for project teams and closeout documentation.
FAQs
1) What does plant kW/ton represent?
It is total plant input power divided by delivered cooling in tons. It includes chillers, pumps, tower fans, and auxiliaries, so it reflects how the whole system performs at a specific operating point.
2) Which load method should I use?
Use known TR if you have a reliable load or meter. Use flow and ΔT when TR is unavailable. Keep readings synchronized, and avoid mixed units unless you also enter matching unit selections.
3) Why is my kW/ton high at low load?
Fixed-speed pumps and fans can become a larger share of total kW when cooling load drops. Poor sequencing, bypass flow, or low ΔT also reduces effective tons, pushing kW/ton higher.
4) How do I estimate savings from an improvement?
Multiply the kW/ton reduction by the operating tons to get kW saved. Then multiply by annual hours for kWh, and by your energy rate for cost savings. Use the baseline field for quick percent improvement.
5) What emission factor should I enter?
Enter your local grid factor in kg CO2 per kWh if available. If you do not know it, use a published utility or national average. The CO2 result scales linearly with this value.
6) Is this suitable for glycol or seawater systems?
The flow-to-load formulas assume water properties. For glycol mixes or nonstandard fluids, adjust the constants using your fluid specific heat and density, or enter the cooling load directly in TR.