Calculator Inputs
Enter tower flow, temperature range, cycles, and loss factors.
Formula Used
Empirical method: E = K × R × ΔT. Here, E is evaporation in gpm. K is commonly 0.00085. R is circulation flow in gpm. ΔT is cooling range in °F.
Energy method: Q = ṁ × Cp × ΔT. Then E = Q / hfg. Water heat capacity is 4.186 kJ/kg·°C. Latent heat is entered in kJ/kg.
Water balance: B = E / (COC - 1). Makeup equals evaporation plus drift plus blowdown plus other losses. Drift can be credited against blowdown when selected.
How to Use This Calculator
- Enter the circulating water flow from tower records.
- Select the flow unit used by your plant system.
- Add hot water and cold water temperatures.
- Choose an empirical or energy balance method.
- Enter cycles, drift percent, and other losses.
- Press the calculate button to see results above the form.
- Download results as CSV or print them as PDF.
Example Data Table
| Flow | Hot Temp | Cold Temp | Cycles | Drift | Estimated Evaporation |
|---|---|---|---|---|---|
| 1000 gpm | 95 °F | 85 °F | 4 | 0.005% | 8.5 gpm |
| 650 gpm | 92 °F | 82 °F | 5 | 0.003% | 5.525 gpm |
| 250 m³/h | 35 °C | 29 °C | 4 | 0.004% | About 1.53 m³/h |
Cooling Tower Evaporation Planning Guide
Why Evaporation Matters
Cooling towers reject heat by evaporating a small water stream. That vapor carries latent heat away from the circulating loop. The process is efficient and common in plants. It also creates a steady demand for makeup water. A small error can become large over a season. This calculator helps estimate that demand with practical engineering inputs. It connects flow, range, heat load, drift, blowdown, and cost.
Understanding Range and Heat Load
Cooling range is the difference between hot and cold water. A wider range means more heat removal. More heat removal needs more evaporation. Flow also changes the answer. High circulation flow at the same range produces a larger heat duty. The tool converts common flow units before solving. It also shows heat load in kilowatts and Btu per hour.
Choosing the Method
The empirical method is fast for field checks. It uses the common factor for gpm and Fahrenheit range. It works best for approximate tower water balances. The energy balance method is more flexible. It uses heat capacity and latent heat. Choose it when water temperature, pressure, or site assumptions need closer control.
Cycles and Blowdown
Evaporation leaves dissolved minerals behind in the basin. Cycles of concentration describe that buildup. Higher cycles reduce blowdown. Lower cycles increase water discharge. The calculator uses cycles to estimate blowdown. Drift can also remove dissolved solids. The optional drift credit reduces blowdown when that plant rule applies.
Drift and Other Losses
Drift is liquid water carried out with exhaust air. Modern eliminators keep it low. Older towers may lose more water. Leaks, basin overflow, side stream filters, and cleaning drains can add extra losses. Enter those losses as other loss. Total makeup then becomes the full replacement water needed.
Cost and Operating Time
Water cost depends on the selected output unit. Add your local cost per unit. Enter expected hours and operating days. The calculator multiplies makeup rate by runtime. This gives a planning volume and estimated cost. Use the result for budgeting, audits, chemical planning, and water conservation reviews.
Calibration and Field Review
Use tower meters whenever possible. Compare calculated makeup with actual makeup records. Differences can reveal leaks, bypasses, valve issues, or sensor drift. Check readings during steady load periods. Avoid using startup or shutdown data. Record wet bulb, load, fans, and basin level. Repeat checks after cleaning or chemical changes. Trending improves confidence over time. It also supports permits, audits, and conservation projects. Keep assumptions with each saved result for clear future review. Document seasonal changes because tower performance changes with weather quickly.
Interpreting Results
The evaporation result should rise with flow and range. Blowdown should fall as cycles increase. Makeup should always exceed evaporation alone. If results seem unusual, check units first. Then review temperature readings and tower logs. Operators should compare estimates with meter data. This improves maintenance decisions and long term water control.
Frequently Asked Questions
What is cooling tower evaporation rate?
It is the water volume converted into vapor while rejecting heat. The rate depends on circulation flow, cooling range, and heat load.
Why does temperature range affect evaporation?
A larger range means the tower removes more heat. More heat removal usually needs more water evaporation to carry latent heat away.
What coefficient should I use?
The common field coefficient is 0.00085 for gpm and Fahrenheit range. Adjust it only when your plant standard requires another factor.
When should I use the energy method?
Use it when you want a thermodynamic estimate. It is useful when latent heat assumptions or metric inputs need tighter control.
What are cycles of concentration?
Cycles compare dissolved solids in tower water against makeup water. Higher cycles usually reduce blowdown, but treatment limits still matter.
Does drift count as blowdown?
Drift can remove dissolved solids. Some balances credit drift against blowdown. Use the checkbox only when that matches your site method.
What is makeup water?
Makeup water replaces evaporation, drift, blowdown, leaks, and other losses. It is the total new water added to the tower system.
Can this calculator estimate water cost?
Yes. Enter water cost per selected output unit. Add operating hours and days. The tool estimates total volume and cost.
Why is my blowdown zero?
It can become zero when drift credit exceeds calculated blowdown. Review drift percent, cycles, and the selected blowdown option.
Is wet bulb temperature required?
No. It is included to review tower approach. Evaporation is calculated from cooling range, flow, and selected method.
Can I use metric units?
Yes. The calculator accepts m³/h and L/s. It also accepts Celsius temperatures and converts them internally for calculation.