Free Cooling Tower Approach & Range Calculator
Calculate cooling range, approach to ambient wet-bulb, heat rejection tons, thermal effectiveness, evaporation loss, and blowdown makeup water rates.
❄️ Thermal Conditions & Flow Rates
Thermal Effectiveness: 58.8% • Heat Rejection: 400 Cooling Tons
Makeup = Evaporation (9.6 GPM) + Blowdown (3.2 GPM)
The Wet-Bulb Physical Limit: A cooling tower can never cool water below the ambient outdoor wet-bulb temperature. The difference between cold basin water and wet-bulb is the Approach. Standard commercial cooling towers are engineered for a 6°F to 10°F approach.
Recommended Tools & Equipment
Tested hardware and components for high reliability
Cooling Tower Fundamentals: Range vs. Approach
Evaporative cooling towers reject waste heat from chillers, generators, and industrial processes by allowing a small fraction of circulating water to evaporate into an induced airstream:
- Cooling Range (ΔT): The temperature difference between the hot water entering the tower and the cooled water leaving the basin: $ ext{Range} = T_{hot_in} - T_{cold_out}$. The range is determined strictly by the heat load of the building or process, not the tower size!
- Cooling Approach: The temperature difference between the cold basin water leaving the tower and the ambient outdoor wet-bulb temperature ($T_{wb}$): $ ext{Approach} = T_{cold_out} - T_{wb}$. The approach is a direct measure of the tower's thermal capacity and heat-transfer surface area.
- Thermal Effectiveness: $eta = rac{ ext{Range}}{ ext{Range} + ext{Approach}} imes 100%$. Typical modern towers operate at 55% to 75% effectiveness.
Water Consumption: Evaporation, Blowdown & Makeup
Water loss occurs primarily through latent heat of vaporization (~1,000 BTU absorbed per pound of water evaporated):
Blowdown Bleed: B = E / (Cycles_of_Concentration - 1)
Total Makeup: M = E + B (plus minimal drift loss < 0.005%)
As pure water vaporizes into the atmosphere, dissolved mineral salts (calcium, silica) remain behind. If not periodically bled off via blowdown, scale rapidly coats condenser tubes, suffocating chiller efficiency.
Frequently Asked Questions
Why is 1 Cooling Tower Ton equal to 15,000 BTU/hr instead of 12,000 BTU/hr?
A refrigeration ton is 12,000 BTU/hr of cooling at the evaporator. However, the cooling tower must reject that evaporator heat PLUS the heat of compression from the chiller motor (~3,000 BTU/hr per ton), making 1 Cooling Tower Ton = 15,000 BTU/hr.
What happens if the ambient wet-bulb temperature rises?
If outdoor humidity and wet-bulb temperature rise (for example from 75°F to 82°F during a summer thunderstorm), the cold water sump temperature will rise in lockstep. The tower cannot cool water below ambient wet-bulb.
How do Cycles of Concentration (CoC) save water?
Increasing cycles from 2 to 4 cuts blowdown water waste by 66%! Above 5 or 6 cycles, however, diminishing returns set in and mineral saturation risks severe calcium scaling without heavy chemical scale inhibitor treatment.