Types of Cooling Towers in HVAC: Designs, Water Use, and Efficiency Considerations

Cooling towers are essential components in HVAC systems, particularly in large commercial, industrial, and district cooling applications. They remove heat from a building’s chilled water loop by rejecting it to the atmosphere via water evaporation or air movement. While their core function remains the same, cooling towers come in various designs — each with different space requirements, energy efficiency profiles, and water consumption characteristics.

This article explores the main cooling tower types, compares their performance, and highlights important considerations for water efficiency, use of recycled water, and energy optimisation.

1. Types of Cooling Towers in HVAC

Cooling towers can be broadly categorised based on airflow direction, heat exchange method, and construction.

A. By Airflow Configuration

1. Crossflow Cooling Towers

   • Air flows horizontally across the falling water stream.

   • Advantages: Lower fan power requirement, easier maintenance access, quieter operation.

   • Drawbacks: Larger footprint compared to counterflow designs, higher drift losses.

2. Counterflow Cooling Towers

   • Air moves vertically upward against the downward water flow.

   • Advantages: More compact footprint, higher thermal performance per unit area, lower drift losses.

   • Drawbacks: Higher fan energy use, more complex maintenance due to tighter internal space.

B. By Heat Exchange Method

1. Open Circuit (Direct Contact) Cooling Towers

   • Warm condenser water is sprayed over fill media while ambient air passes through, allowing direct contact and evaporation.

   • Advantages: High efficiency, simpler construction.

   • Drawbacks: Higher water losses, more susceptible to fouling and scaling.

2. Closed Circuit (Indirect) Cooling Towers / Fluid Coolers

   • Process water flows through a heat exchanger coil; spray water and airflow cool the coil indirectly.

   • Advantages: Reduced contamination risk, cleaner loop water.

   • Drawbacks: Slightly lower thermal efficiency, higher capital cost.

C. By Draft Type

1. Induced Draft

   • Fan pulls air through the tower; better airflow control and efficiency.

2. Forced Draft

   • Fan pushes air into the tower; simpler design but more prone to recirculation issues.

2. Comparison of Cooling Tower Types

Type	Space Requirement	Thermal Efficiency	Fan Power Use	Water Loss
Crossflow – Open Circuit	Large	High	Low	High
Counterflow – Open Circuit	Compact	Very High	Moderate	Moderate
Crossflow – Closed Circuit	Large	Moderate	Low	Moderate
Counterflow – Closed Circuit	Compact	High	Moderate	Low

3. Water Use and Efficiency Considerations

Cooling towers lose water through three main pathways:

• Evaporation (essential for cooling, ~0.8% of circulating flow per 5.5°C cooling range)

• Drift (small droplets carried away with exhaust air; reduced via drift eliminators)

• Blowdown (discharge of concentrated water to control scaling, corrosion, and biological growth)

Open circuit towers typically use more water due to direct evaporation and higher blowdown requirements. Closed circuit towers reduce water losses but still require water for the spray system.

Water efficiency measures include:

• High-efficiency drift eliminators (<0.001% drift loss)

• Optimised cycles of concentration (reducing blowdown)

• Automated water treatment controls

4. Using Non-Potable or Recycled Water in Cooling Towers

In water-scarce regions like the UAE, cooling towers can be designed to operate with treated sewage effluent (TSE), greywater, or other recycled sources. This reduces potable water demand but requires specific design and treatment considerations:

• Material Selection: Use corrosion-resistant materials (e.g., FRP, stainless steel 316) for structural components, basin, and fill media to withstand higher chloride and contaminant levels.

• Enhanced Filtration: Side-stream sand filters or multimedia filters to remove suspended solids.

• Advanced Water Treatment:

  • Biocides to control microbial growth (Legionella prevention)

  • Scale inhibitors tailored for higher hardness and alkalinity

  • Oxidation technologies (ozone, chlorine dioxide) for disinfection without excessive corrosion

• Instrumentation: Continuous monitoring of conductivity, pH, and ORP for automated chemical dosing.

Well-designed systems can run effectively on non-potable water without compromising efficiency or lifespan.

5. Improving Energy Efficiency of Cooling Towers

The performance of a cooling tower directly affects the energy use of connected chillers. A low approach temperature — the difference between cooling tower outlet water temperature and ambient wet-bulb temperature — enables the chiller to operate at a lower condenser water temperature, reducing compressor lift and improving kW/ton performance. Latest technologies allow approach temperatures as low as 1°C!

Ways to improve cooling tower energy efficiency:

• Variable frequency drives (VFDs) on fans to modulate speed with load and wet-bulb conditions

• High-efficiency fill media for better heat transfer

• Regular cleaning to prevent scaling and biofouling

• Optimised approach temperature settings for seasonal conditions

• Heat load management to avoid overdriving the tower unnecessarily

Result: A well-optimised cooling tower with a low approach can yield up to 5–8% chiller energy savings, translating into significant operational cost reductions over time.

In Summary:
Cooling tower design selection impacts not only thermal performance but also water and energy use. By carefully choosing the right type, optimising water treatment for the available source (including non-potable options), and improving operational efficiency, facility owners can significantly reduce operating costs and environmental impact — a win-win for sustainability and performance.