AIR HANDLING UNITS

From the simplest equipment to the most powerful large-scale centralized air handling units, we offer precise solutions that ensure a perfectly balanced environment to control indoor air quality through processes such as filtering, ventilation, heating, cooling, humidification and dehumidification. We offer precise solutions that ensure a perfectly balanced environment to control indoor air quality through processes such as filtering, ventilation, heating, cooling, humidification and dehumidification to support fresh, healthy and comfortable environments for any type of building or specialized application.

This equipment is manufactured to maintain high performance and safety in specific applications such as Operating Rooms, Hospital Mixing Plants, Drug Manufacturing, Petrochemical or Electronic Components.

These equipments are equipped with Hepa Filters and depending on the industry or use they are equipped with chemical filter media such as activated carbon. Eliminating from pollen to volatile organic compounds (VOCs).

The manufacture of this equipment guarantees high energy efficiency and has heat recuperators that reduce consumption by up to 30%.

Unidad de tratamiento de aire (Pemex) — AIR TREATMENT UNIT (PEMEX)

The fans are responsible for driving air through the unit and into the ductwork.

Centrifugal fans are the most common for these applications
Plug fan fans (more efficient and silent)
AC or EC motor
Axial fans

Ventilador parte superior UTA — PLUG FAN

Criteria we consider when choosing a fan.

CRITERIA	CONSIDERATIONS
Air flow rate	How much air to move (m³/h or l/s)?
Static pressure	How resistant is the system (filters, ducts)?
Energy efficiency	Need to comply with efficiency regulations?
Permissible noise level	Are there requirements for acoustic comfort?
Speed control	Is real-time modulation required?
Maintenance required	How easy is access and repair?

Heat exchanger coils are used to heat or cool the air by means of hot/cold water or refrigerant:

Hot water coil (fed by boiler or heat pump)
Chilled water coil (fed by chiller or chiller)
Direct expansion: uses refrigerant gas directly

Recovery heat exchangers

They make it possible to recover part of the energy from the air extracted from the building, transferring it to the fresh air entering the building. This reduces energy consumption.

Rotary recuperators (enthalpy or sensitive rotor)
Plate recuperators

Humidifiers

They increase the humidity of the air when necessary, to avoid dry environments.

Steam humidifiers
Adiabatic humidifiers

Mixing gates and sections

They allow mixing outside air with the building's return air to achieve optimum air temperature and quality.

Types of Air Treatment Units, according to application.

Comfort AHUs: for offices, shopping centers, homes, etc.
Industrial AHUs: for factories, laboratories, clean rooms.
Hygienic AHUs: in hospitals, operating rooms and sterile areas. They have stricter standards (HEPA filters, anti-corrosion materials, etc.).

Related regulations

ASHRAE 62.1: Indoor air quality standards
UNE-EN 1886: Construction specifications for AHUs
RITE (Spain): Reglamento de Instalaciones Térmicas en los Edificios (Spanish Regulation on Thermal Installations in Buildings)

Unidad presurizadora de alto rendimiento — AIR TREATMENT UNIT (PRESSURIZER)

Sizing

With the sizing we define its characteristics and technical capabilities according to the specific needs of the space to be air-conditioned. It is not simply a matter of choosing a unit at random, but of designing a tailor-made solution that guarantees thermal comfort, air quality and energy efficiency.

First it is necessary to determine how much air needs to be moved, i.e. the air flow rate. This value can be calculated based on the number of people occupying the space, the use of the building or the internal thermal loads (from lighting, equipment, etc.). It is usually expressed in cubic meters per hour (m³/h) or liters per second (l/s). If the space has a high occupancy, such as in an office or classroom, a higher flow rate will be required to ensure good ventilation. If it is a technical space, the calculation may be based on thermal loads.

Another fundamental aspect of sizing is the thermal conditioning of the air. The unit must be able to heat or cool the air it introduces into the environment, and in some cases it must also modify its humidity level. For this purpose, the most suitable heating or cooling coils are selected, which can work with hot or cold water, or even with direct refrigerant. This step requires a good knowledge of the outdoor design conditions (temperature and humidity of the environment) and the desired indoor conditions (thermal comfort and relative humidity).

In addition to the flow rate and heat treatment, another parameter to be calculated is the total pressure drop of the system, i.e. the air flow resistance of the unit itself, together with filters, ducts, heat recovery units and other components. The higher this loss, the more powerful the fan selected should be. A common mistake in this step is to underestimate the losses generated by filters or long duct runs, which can lead to poor system performance.

In the end, what we are looking for is to balance three things:

The volume of air to be moved
The conditions to which the air must be conditioned
The ability to overcome the resistance of the system

All this without wasting energy and in compliance with current regulations. It is a technical job, yes, but also a strategic one, because the comfort, health and energy consumption of a building depend on it.

Air handling units

NEED	ELEMENT
Basic filtering	G4 Filters
Medium filtration	F7 Filters
Cold weather	Hot water battery
Warm climate	Cold water coil or direct expansion
High relative humidity	Dehumidifier or oversized cold battery
Low humidity	Steam or adiabatic humidifier
Energy recovery	Rotary or plate heat exchanger
Low noise	EC fan or Plug fan + mufflers

Parameters for design

Once the general sizing objective is understood, it is time to dive into the parameters that guide the design of an AHU. These parameters are the ones that will allow the correct selection of each of the components that will form the unit, from the fans to the thermal coils and filters.

The first and most important is the air flow rate, which refers to the amount of air that must circulate through the unit to meet the needs of the space. This value, as mentioned above, is usually expressed in m³/h or l/s and can be calculated in different ways. On the one hand, there is the criterion based on air renewal per person, which is applied in places where the main objective is to ensure good indoor air quality, such as offices, meeting rooms or classrooms. On the other hand, there are calculations based on thermal loads, where the aim is to maintain a stable indoor temperature in the face of external climatic changes or internal heat sources. In both cases, the aim is to ensure that the system ventilates sufficiently without being excessive, so as not to waste energy.

Another fundamental parameter is the total static pressure that the fan must overcome. This pressure is the sum of all the resistances encountered by the air from the moment it enters the unit until it reaches the interior space. This is influenced by elements such as air filters (which generate a resistance when passing through), air conditioning coils, heat recovery units, duct sections and even supply and return grilles. A poor estimation of these losses can result in the fan not having enough power to move the air, reducing the performance of the system and even generating annoying noises or points with low ventilation. Therefore, it is essential to carefully calculate the pressure drop and ensure that the selected fan can overcome it.

The outdoor climatic conditions and the desired indoor conditions must also be defined. The outdoor conditions are the starting point: for example, if in summer the air enters at 35°C with 60% humidity, the AHU must be equipped to cool and dehumidify it to comfort values (such as 22°C and 50% RH). The same is true in winter, where you may start from -5 °C and want to warm the air before introducing it into the space. These temperature and humidity differences will define what type of batteries the AHU needs, as well as their capacity in kilowatts.

Finally, it is necessary to consider the type of air conditioning required. Not all AHUs have to thermally condition the air; some simply filter it and introduce it at a temperature already treated by another system. However, in many cases, heating, cooling or even humidity control is required, which makes it necessary to include coils, humidifiers or heat recovery systems. In addition, depending on the use of the building, additional measures may be required, such as zoned temperature control systems or variable ventilation according to occupancy.

Together, these parameters make it possible to define an AHU that is not only suitable for its function, but also efficient, quiet and adaptable. Each design decision will influence the final performance of the system, the comfort of the occupants and the energy consumption of the building.

Component selection based on calculation

The next logical step is to select the specific components that will be part of the AHU. This is where the design becomes tangible: filters, fans, thermal coils, heat recovery units and other elements are combined into a configuration that must meet the previously calculated requirements.

The selection generally starts with the fan, since this component is the one that ensures the air movement. Depending on the flow rate and the calculated pressure loss, a fan capable of maintaining that constant flow efficiently is chosen. Nowadays it is very common to opt for EC (electronically commutated) fans, since they allow varying the motor speed with low energy consumption, besides being silent and more compact. Another alternative are plug fans, which offer great installation flexibility and efficiency when moderate pressure is required.

ventilador para unidad de tratamiento de aire — CENTRIFUGAL FAN

ventilador unidad presurizadora — CENTRIFUGAL FAN

After the fan, one of the most important items are the air filters. Their function is to retain particles such as dust, pollen, mold spores or industrial pollutants. In standard applications, G4 type filters are usually used for coarse particles, but when a higher level of air quality is required, F7 or even F9 filters are added, capable of retaining finer particles. In sensitive environments such as hospitals or laboratories, even HEPA filters can be used, which remove up to 99.97% of particles down to 0.3 microns.

Then, the air conditioning coils are selected, which can be heating or cooling coils, depending on the ambient conditions. These coils can operate with hot/cold water from boilers or chillers, or with direct expansion if connected to a refrigeration unit with refrigerant gas. The power of these coils must be calculated according to the thermal load, considering both the thermal jump (the difference between the air inlet and outlet temperature) and the flow rate. It is essential that these coils are correctly sized to avoid the air arriving too cold or too hot, or not reaching the desired conditions throughout the volume of the room.

Where precise humidity control is required - for example, in archives, museums or laboratories - a humidification or dehumidification system can be incorporated. This can be achieved by steam humidifiers, adiabatic humidifiers or by oversizing the cold coil to condense the humidity.

Another component that is becoming increasingly important is the heat recovery device, especially in buildings where energy efficiency is sought. These devices make it possible to take advantage of the heat from the extracted air to precondition the fresh air entering from outside. There are different types, such as plate heat exchangers, heat pipe heat exchangers or the most efficient, rotary heat exchangers, which allow a more complete transfer of heat and humidity.

Last but not least, the auxiliary elements are selected: acoustic silencers to reduce the noise of moving air, regulation or shut-off dampers, temperature and pressure sensors, drain pans and anti-freeze electric heaters in cold areas.

Each of these components must be selected not only for its individual function, but also for how it integrates with the rest of the system. The real challenge of AHU design lies in getting all these elements to work together in a coordinated, efficient and safe manner, adapting to load changes while maintaining interior comfort.

Software and tools useful for calculation

The design of an air handling unit, although it can be done with manual calculations, becomes much more accurate and efficient with the use of digital tools. Today, there are several programs and platforms that assist the engineer or designer in the various stages of sizing and selection of components of an AHU. From the calculation of thermal loads to the simulation of energy performance and the generation of complete technical data sheets, these tools are key to a professional design.

One of the first steps in the design process is to determine the thermal loads of the space to be air conditioned. To do this, specialized software such as HAP (Hourly Analysis Program) or Trane TRACE 3D Plus, both widely recognized in the industry, can be used. These programs allow you to enter detailed building parameters: orientation, building materials, occupancy, lighting, electrical equipment and more. With this information, they generate an hourly profile of thermal loads, both sensible and latent, which is essential to know what capacity the heating or cooling coils in the pressurizing unit should have.

Once the design conditions and thermal loads are known, the next step is to select the AHU as hardware, and here manufacturer-specific tools come into play. For example, programs such as Systemair Design, Swegon AHU Design, CIAT Select or AHU Selection allow complete AHUs to be configured according to project data. These platforms can be used to define the desired flow rate, air inlet and outlet conditions, type of filters, coils, fan type, maximum permissible sound levels, and even the physical dimensions of the unit.

These tools not only provide a technical and dimensional preview of the equipment, but also generate complete reports with performance curves, absorbed power, heat recovery efficiency, pressure drop per component, and even an estimate of annual energy consumption. This not only speeds up the design work, but also provides valuable documentation for tenders, energy certifications or technical work approvals.

For those who prefer more customized solutions, or for quick preliminary calculations, it is also possible to work with custom developed Excel templates. These spreadsheets can include formulas for determining flow rate based on volume or occupancy, estimating head losses by filter type or duct run, or sizing coils with defined thermal headroom. Although more limited, these tools are very useful in early design stages or for technical training.

Finally, we should not forget the usefulness of energy simulators and BIM tools (such as Revit or CYPE HVAC), which make it possible to integrate the AHU into the three-dimensional model of the building, verify physical interferences, and analyze the behavior of the system in conjunction with the rest of the installations.

The use of software is indispensable, not only facilitating the technical work, but also ensuring a more rigorous, efficient and adaptable design, improving project quality and reducing sizing risks or performance failures.