HXV Series Operation Modes & Water-Saving Strategies

Based on the CTI-certified FXV closed-circuit cooling tower platform, the HXV series integrates BAC’s patented hybrid flow technology. A dry finned coil section is added at the discharge area, delivering enhanced heat transfer efficiency with lower fan energy consumption.

Three Modes of Operation – HXV

Maximize Water Savings

Hybrid Wet/Dry Mode
In this mode, the process fluid first flows through the dry finned coil for initial cooling and then enters the main evaporative coil section for further cooling. Spray water is pumped from the cold water basin to the top of the evaporative coil. As the water flows over the coil surface, evaporative cooling occurs. The water then falls onto the fill layer beneath, where it is further cooled by the airflow before returning to the basin.
The air that flows through the coil and fill surfaces absorbs heat and moisture, becoming saturated. However, the discharge air remains relatively cool, allowing the finned coil located above the fan to extract additional heat from the process fluid.
By combining sensible heat transfer in the dry coil with latent heat exchange in the evaporative section, this mode dramatically reduces visible plume formation—even under peak operating conditions—while significantly saving water compared to conventional evaporative systems.

As thermal load and/or ambient temperature decrease, the evaporative demand and water usage naturally decline. This is controlled by an automatic bypass valve that modulates the fluid flow to the evaporative coil, maintaining the required leaving fluid temperature.

The control strategy ensures that the dry coil is used to its fullest capacity before increasing evaporative load, minimizing water consumption and reducing visible plume by heating discharge air through the dry coil section.

Adiabatic Mode

In adiabatic mode, the process fluid completely bypasses the evaporative coil—no heat transfer occurs within the wet coil section. Instead, spray water is used solely to saturate the incoming air, pre-cooling it through adiabatic cooling.
Even in most climates, ambient air has enough capacity to absorb moisture, and the resulting pre-cooled air significantly enhances the sensible heat transfer rate in the dry coil.
Compared to traditional evaporative systems, adiabatic mode drastically reduces both water consumption and visible plume, while maintaining the required fluid temperature and maximizing system efficiency.

Dry Mode

In dry mode, the spray water system is turned off, saving pump energy. The process fluid flows in series through both the dry finned coil and the evaporative coil, with the control valve fully open to ensure the full heat transfer surface is utilized.
This mode eliminates both evaporation and visible plume entirely.
HXV units can be configured to switch to dry operation at dry bulb temperatures between 50°F (10°C) and 60°F (15°C) or higher, depending on the project’s specific needs.

If dry mode is expected to run for extended periods, it is recommended to drain the cold water basin, eliminating the need for antifreeze protection and water treatment.

HXV Hybrid Coolers

BAC’s patented HXV design combines the advantages of evaporative and dry cooling technologies to deliver a highly efficient, compact, and water-saving solution. This hybrid operation concept has earned multiple patents and innovation awards in North America and Europe.
HXV is engineered to meet the demanding requirements of critical projects.

Eliminate Visible Plume

Visible water vapor discharge caused by saturated air leaving conventional cooling towers can create safety concerns, especially in sensitive areas like airports and traffic zones. The HXV operates in a hybrid mode that combines sensible, adiabatic, and evaporative heat transfer, significantly reducing or even eliminating visible plume formation.
During the coldest periods of the year—when plume potential is highest—the HXV can run in 100% dry mode, completely eliminating visible vapor emissions.

Maximize Water Savings

The HXV can operate in three different modes throughout the year to reduce water consumption. Under peak thermal load or extreme weather conditions, much of the heat is removed through sensible cooling in the dry section, greatly reducing evaporation losses compared to traditional evaporative systems.
As thermal load or ambient temperature decreases, water consumption further drops—especially during adiabatic mode—and eventually ceases entirely in dry mode. Compared to conventional evaporative coolers, water savings can reach up to 70%, all while maintaining efficient fluid cooling. In many regions, the water savings alone can offset the equipment investment within two years.
For projects with limited water supply, the HXV is an ideal solution.

High-Temperature Fluid Cooling Capability

For fluid temperatures above 82°C (180°F), pre-cooling is achieved in the dry section before reaching the evaporative coil. Even under peak summer conditions, HXV systems deliver lower fluid temperatures with minimal fan energy, thanks to the synergy between dry and evaporative heat transfer—all within a compact footprint.

Superior Economic Value

Reduced Capital Investment
Heat exchanger selection is typically based on peak dry bulb conditions, which often result in larger and more expensive dry cooling systems. In contrast, evaporative systems like the HXV are selected based on wet bulb conditions, providing greater temperature driving force and allowing for lower system design temperatures.
This advantage translates into smaller heat exchange surfaces and lower equipment costs.
During peak loads, HXV uses evaporative cooling, enabling reduced unit size, lower fan horsepower, and minimized structural and cabling costs.
Unlike dry coolers that require water spray during extreme days—causing corrosion and scaling—the HXV’s hybrid design avoids these risks.
Its low scaling tendency allows for lower fluid temperatures and reduces the size and cost of downstream equipment (e.g., chillers, compressors). It also eliminates the need for plume abatement accessories.

Lower Operating Costs
Thanks to its hybrid cooling concept and water-saving design, the HXV offers clear operational cost advantages.
In peak summer, a significant portion of the heat is removed via the dry coil, reducing evaporation, blowdown, and chemical treatment costs. In adiabatic mode, only a small amount of water is evaporated to pre-cool the air, minimizing blowdown.
In low ambient conditions, dry mode eliminates both water and pump energy consumption.
Depending on local water costs and availability, the HXV can reduce water consumption by up to 70% or more, delivering ROI through savings on water, treatment chemicals, blowdown disposal, and improved energy efficiency—often within two years.

In addition, the HXV’s closed-loop system and advanced coil design prevent fouling and scaling common in open-circuit cooling towers, ensuring long-term efficient operation. The entire product line exceeds ASHRAE 90.1 energy efficiency requirements.
Axial fan designs also consume less power than centrifugal fans used in conventional systems.

Low Installation & Maintenance Costs

The HXV is modularized into three sections to reduce hoisting weight and overall unit size. Fewer interconnecting pipes are required, enabling the use of smaller and more affordable lifting equipment.

Maintenance-Friendly Design
The hinged access doors are integrated into the casing and allow direct entry into the internal space, which includes a standard internal walkway. The spacious interior enables easy inspection of the cold water basin, drift eliminators, fan drive system, and coil surfaces.
Air and spray water flow in the same direction, and the spray system is located above the coil section, allowing for maintenance of the coil top even during operation.

Typical Construction and Available Options

Corrosion-Resistant Structure

• Constructed with heavy-duty imported G-235 hot-dip galvanized steel panels

• Dual protection with galvanized coating and optional corrosion-resistant paint

Power Transmission System

• High-efficiency motors rated for cooling tower duty and compatible with VFD operation

• 3-year warranty on motor and drive system

• Corrosion-resistant cast aluminum pulleys

• Premium-grade bearings with L10 life ≥ 80,000 hours

• High-quality solid-core multi-groove belts

• Low-horsepower axial fans for quiet, efficient operation

• Vibration cut-off switch for abnormal vibration protection

Water Distribution System

• Large-diameter, non-clog spray nozzles

• 360° overlapping spray pattern ensures full coil coverage

• Accessible for inspection and maintenance during operation

Hybrid Coil (Wet/Dry Coils)

• Continuous serpentine steel tubing

• Entire coil assembly hot-dip galvanized after fabrication (HDGAF)

• 2.5 MPa air pressure leak test

• Sloped coil layout allows easy drainage of process fluid

Dry Fin Coils

• Copper or stainless steel tubing with high-efficiency aluminum fins

• 2.2 MPa air pressure leak test

• Sloped layout for fluid drainage

• Optional flow control system:

  • Temperature sensors

  • Three-way flow control valve

  • Complete piping connections

BACross® PVC Heat Exchange Fill & Integral Drift Eliminators

• High-efficiency heat transfer surface

• Made of recyclable PVC

• Corrosion-, UV-, aging- and bio-resistant

• Flame spread rating compliant with ASTM E84 (flame spread index: 5)

• Mounted above cold water basin for easy cleaning

Inlet Air Screens

• Corrosion-resistant and UV-resistant

• Easy to maintain

Recirculation Spray Water Pump

• Close-coupled centrifugal pump with bronze impeller

• Totally enclosed, fan-cooled motor

• Drain line from pump to overflow point, controlled by metering valve

Access Door

• Wide internal maintenance corridor

• Inward-opening access door for easy internal inspection and servicing