Range, Flow, and Heat Load in Cooling Tower: The Fundamental Relationship
These three parameters are mathematically linked and form the core of cooling tower thermal design and performance analysis. Understanding their relationship is essential for sizing, operating, and troubleshooting.
1. The Three Variables Defined
A. Range (ΔT)
- Definition: The temperature drop of the water through the tower
- Formula: Range = Hot Water Temperature (HWT) – Cold Water Temperature (CWT)
- Units: °F or °C
- What it indicates: The amount of cooling being accomplished. Primarily driven by the heat load.
B. Water Flow Rate (GPM or m³/hr)
- Definition: The volumetric rate of water circulating through the tower
- Typical Symbol: Q or GPM
- Units: Gallons per minute (GPM), cubic meters per hour (m³/hr)
- What it indicates: The quantity of water being cooled.
C. Heat Load (BTU/hr or kW)
- Definition: The amount of heat energy being rejected to the atmosphere
- Typical Symbol: H
- Units: BTU/hour, Tons of Refrigeration (1 TR = 12,000 BTU/hr), kilowatts (kW)
What it indicates: The total thermal duty of the system
. The Fundamental Relationship
The Governing Equation (Heat Balance)
text
Heat Load = Water Flow × Range × Specific Heat Constant
Or:
text
H = Q × R × C
Where:
- H = Heat Load (BTU/hr or kW)
- Q = Water Flow Rate (GPM or m³/hr)
- R = Range (°F or °C)
- C = Specific Heat Constant
In Common Units:
| System | Formula | Constants & Notes |
| Imperial (US) | H (BTU/hr) = GPM × Range (°F) × 500 | 500 = 8.34 lb/gal × 60 min/hr × 1 BTU/lb·°F |
| Metric | H (kW) = m³/hr × Range (°C) × 1.163 | 1.163 = Specific heat of water / 3.6 |
| Refrigeration Tons | Tons = (GPM × Range (°F)) / 24 | 24 = 12,000 BTU/ton ÷ 500 |