Adiabatic pre-cooling can be used to reduce the summer cooling load of existing air-handling units. During peak summer temperatures, the cooling duty of an air-handling unit is determined not only by the building’s internal heat load. The warm outdoor air drawn in through the fresh-air intake must also be cooled to the required supply-air condition. The greater the required airflow and the higher the outdoor temperature, the greater the load on the cooling section of the air-handling unit.
This can be particularly significant in manufacturing plants, warehouses and logistics facilities with high fresh-air demand. During the hottest periods, the air-handling unit may operate close to its design capacity, while the energy demand and operating cost of cooling also increase.
Replacing the entire air-handling unit or expanding conventional cooling capacity, however, is not always the most technically and economically favourable solution. Another approach is to reduce the temperature of the outdoor air before it enters the existing air-handling unit.
The BoostAir® Type I was developed for this purpose: it connects to the fresh-air intake of an existing air-handling unit and uses adiabatic pre-cooling to reduce the temperature of the incoming outdoor air.
The BoostAir® Type I is an adiabatic pre-cooling unit designed for connection to the fresh-air intake of existing air-handling units.
Outdoor air also represents a cooling load
During summer operation, the air flowing through the fresh-air intake continuously introduces heat into the system. If, for example, the outdoor air temperature is 35 °C while the required supply-air temperature is significantly lower, the cooling system must bridge this temperature difference.
At high airflow rates, even a difference of a few degrees Celsius can represent a significant cooling load. The required cooling capacity is primarily determined by:
- the volume of air handled per hour;
- the temperature difference between the outdoor air and the required supply-air condition;
- the actual moisture content of the outdoor air;
- the final supply-air condition to be provided by the air-handling unit.
The load on the system can therefore be reduced not only by installing a larger or more efficient cooling unit. The condition of the air reaching the existing cooling section can itself be an important engineering intervention point.
Why does the air temperature entering the air-handling unit matter?
If the outdoor air is cooled before entering the air-handling unit, the cooling section has a smaller temperature difference to overcome. This can reduce the peak load on the conventional cooling system and, depending on the system design, can also lower its cooling energy demand.
Pre-cooling can be particularly valuable when the outdoor temperature is high and the existing system is already operating close to its capacity limit. In such cases, an entirely new cooling system may not be necessary: improving the condition of the entering air can itself provide a meaningful reduction in cooling duty.
This approach is particularly suitable for retrofit applications in existing industrial systems where retaining the current equipment and minimising the extent of system modifications are important considerations.
How does adiabatic pre-cooling work?
Adiabatic, or evaporative, cooling uses the heat absorbed during the evaporation of water. Outdoor air passes through a wetted evaporative medium, from whose surface water evaporates.
The energy required for evaporation is drawn from the heat content of the air. As a result, the dry-bulb temperature of the air decreases while its moisture content increases. The higher the outdoor temperature and the lower the relative humidity, the greater the temperature reduction that can be achieved.
The technology is therefore typically most effective during hot, dry summer periods, when the cooling load on the air-handling unit is also at its highest. Under favourable outdoor air conditions, the BoostAir® Type I can reduce the temperature of the passing air by up to 10–14 °C.
The water distribution system evenly wets the evaporative medium, reducing the temperature of the outdoor air as it passes through.
The intensive contact between the passing air and the wetted surface enables evaporation and the resulting heat absorption.
For more information on the physical principle of the technology, see our article What is adiabatic cooling?
Adiabatic pre-cooling for an existing air-handling unit
The BoostAir® Type I is not a standalone air-handling unit. It is an industrial pre-cooling unit designed for connection to the fresh-air intake of an existing air-handling unit.
The unit first filters the outdoor air and, depending on the outdoor air conditions and cooling demand, automatically switches to pre-cooling mode when required. The pre-cooled air then enters the existing air-handling unit, where the subsequent air-conditioning processes can be carried out.
The Type I does not contain a separate air-moving fan. Air is drawn through the pre-cooling unit by the existing air-handling unit’s own fan. Operation requires a start signal from the air-handling unit, without the need for fundamental modification of the existing unit.
The electrical connections are made using pre-assembled industrial plug-and-play cables. This reduces on-site cabling and installation work and supports faster system integration.
The plug-and-play industrial connections simplify the on-site electrical installation and commissioning of the BoostAir® Type I.
During system design, the available static pressure reserve of the existing fan, the feasibility of the air-duct connection and the required airflow must always be checked. The effective operation of the pre-cooling unit can only be assessed as part of the complete air-handling system.
The BoostAir® Type I pre-cools the outdoor air before it enters the existing air-handling unit.
Warm outdoor air flows directly into the Type I unit. Following adiabatic pre-cooling, air at a lower temperature enters the existing air-handling unit, reducing the temperature reduction that must be provided by its cooling section.
The possibilities for system integration are also influenced by the installation environment. Rooftop or ground-level installation should therefore be assessed according to the available space, the existing air-handling system and the specific site conditions.
What can pre-cooling achieve in practice?
The BoostAir® Type I has a nominal airflow of 25,000 m³/h. At an outdoor temperature of 35 °C and 30% relative humidity, its cooling capacity is 100 kW at an airflow rate of 25,000 m³/h.
This value represents the cooling capacity resulting from the temperature reduction achieved by the adiabatic process. It does not mean a 100 kW reduction in electrical power consumption, nor should it be considered a constant value under all weather or operating conditions.
The achievable pre-cooling effect is primarily determined by the outdoor air temperature and relative humidity, the actual airflow rate and the final supply-air condition required from the air-handling unit. Drier outdoor air allows a greater temperature reduction, while higher outdoor humidity reduces the available evaporative cooling potential.
Evaporation draws the required heat from the air: the temperature decreases while the moisture content increases.
During operation, the warm outdoor air passes through the evenly wetted evaporative medium. Water evaporating from the surface of the medium absorbs heat from the air, so the air leaves the unit at a lower temperature but with a higher moisture content.
The complete air condition must therefore be considered when assessing adiabatic pre-cooling. If an application requires tight humidity control or active dehumidification, the associated load must also be included in the calculation. The expected cooling capacity and reduction in energy demand can be determined by psychrometric and energy analysis.
Performance data and further technical parameters of the unit are available in the BoostAir® Type I technical datasheet.
Cost-effective upgrading without replacing the entire air-handling unit
The economic advantage of the Type I stems primarily from the way it is integrated into the system. The existing air-handling unit and its fan can remain in operation, while the pre-cooling unit is installed upstream of the fresh-air intake. In many cases, this can require less investment and system integration work than replacing the complete air-handling unit or significantly expanding conventional cooling capacity.
One central control unit can manage up to four Type I pre-cooling units. Control signals and the electrical power supply for the units are routed through the central controller, so a single central power feed may be sufficient.
The expected payback period is always project-specific. It should be determined by considering the airflow rate, summer operating hours, typical outdoor air conditions, the efficiency of the existing cooling system and energy costs together.
Automated water management and hygienic operation
In industrial applications of water-based cooling technologies, water quality and hygienic operation are just as important as cooling performance.
The BoostAir® Type I automatically controls humidification and water management. It monitors the quality of the water used for operation and, when required, performs an automatic water replacement or drying cycle. The unit operates with potable water.
Based on the operating parameters and water temperature, the control system completely dries the surface of the evaporative medium at least once per day. This reduces the risk of persistently wet surfaces and supports operation in accordance with the hygiene requirements of VDI 6022.
When should the use of BoostAir® Type I be considered?
Adiabatic pre-cooling can be a suitable option for existing systems where:
- large volumes of outdoor fresh air must be handled;
- the air-handling unit operates under high cooling load in summer, sometimes close to its capacity limit;
- retaining the existing air-handling unit is a priority;
- a connection can be created at the fresh-air intake and the fan has sufficient available pressure reserve;
- reducing investment and operating costs is an important consideration.
Typical applications include manufacturing plants, warehouses and logistics facilities where large volumes of outdoor air must continuously be supplied through the air-handling system to meet ventilation requirements.
The decision should always be based on the technical condition of the existing air-handling unit, the available installation space, outdoor air conditions and the required indoor climate parameters.
Part of the cooling load can be addressed before the air-handling unit
The BoostAir® Type I does not replace the existing air-handling unit; it supports its operation. By reducing the outdoor air temperature before the air enters the air-handling unit, it can reduce both the load and the energy demand of the cooling section.
The actual cooling capacity, reduction in energy demand and expected payback can be determined from the air-handling and energy data of the specific system. Properly sized adiabatic pre-cooling therefore represents a targeted engineering optimisation of the existing air-handling system.
Would you like to find out whether adiabatic pre-cooling can be applied to your existing air-handling unit?
Autent Solutions specialists can assess the airflow rate, outdoor air conditions, technical parameters of the air-handling unit and operational requirements to determine a technically and economically appropriate system configuration.