Providing fresh air inside a building requires more than an opening connected to the outside; outdoor air may be hot and laden with dust and humidity, and it needs treatment suited to the conditions of the site.
This is where the air handling unit comes in; it can be equipped to draw in outdoor air, filter it and cool it before distributing it through the ductwork.
In this article, we review the system shown in episode 8, and how fresh air treatment is integrated with the conditioning of interior spaces.
What is an air handling unit (AHU)?
AHU stands for Air Handling Unit. It contains equipment selected according to the system’s function, such as the fan, filters, and cooling or heating coils, and it may include additional sections.
These units come in different configurations to meet airflow and treatment requirements; therefore, the name AHU alone does not tell you its function within the project.
It may treat return air from the building, a mixture of return and outdoor air, or entirely outdoor air.
What is the difference between AHU and FAHU?
AHU is a general name for an air handling unit. FAHU, meaning Fresh Air Handling Unit, is typically used for a unit dedicated to treating outdoor air and supplying it to the building.
Manufacturers state that fresh air units draw in outdoor air and treat it to meet ventilation needs.
What matters when reviewing the project is knowing the source of the air, its quantity and required conditions, then confirming that the unit’s configuration meets these requirements.
How does the system shown in the episode work?
The episode shows an outdoor air treatment unit connected to an outdoor unit via refrigerant pipes. This arrangement treats the air before sending it to the interior spaces.
Commercial solutions exist that combine an air handling unit with an outdoor unit using direct expansion (DX), along with suitable connection and control components.
In this type of application, the air passes through stages including:
- Drawn in from a suitable outdoor air intake.
- Filtered according to the specified filter level.
- Passed through the cooling coil to be treated thermally and for humidity according to the design.
- Pushed by the fan into the duct network.
- Distributed to the zones in the required quantities.
Does an air handling unit always work with VRV or VRF?
Not all AHUs are connected to VRV or VRF systems. They may use chilled water coils, or connect to compatible direct expansion units, depending on equipment selection and system design.
When connecting to an outdoor unit, the compatibility of the coil, capacities, pipe lengths, control components and approved operating conditions must be verified.
Therefore, the unit’s shape or the presence of copper pipes alone is not enough to define the system’s details.
How does it integrate with room air conditioning?
In some designs, one unit may be dedicated to treating fresh air, while other indoor units handle the air conditioning of rooms and spaces.
However, the division of responsibility between the two systems must be clear: What is the quantity of outdoor air? At what temperature and humidity does it arrive? And what load remains for the room units?
This review helps avoid introducing air that is insufficiently treated, or selecting capacities that do not match the actual loads.
Does this solution save 30 or 40 percent of electricity?
A fixed percentage cannot be adopted without a study.
The comparison depends on equipment efficiency, the quantity of outdoor air, climate, operating hours, controls, the potential for energy recovery, and maintenance cost.
Any saving percentage should be linked to a specific alternative and similar operating conditions, while comparing solutions that meet the same cooling and ventilation requirements.
What should be verified before approving the system?
- The fresh air quantity required for each zone.
- The design outdoor air conditions.
- The required supply air temperature and humidity.
- The efficiency of the filters and their accessibility for maintenance.
- The fan’s ability to overcome network resistance.
- The compatibility of the cooling and control equipment.
- Condensate drainage and the location of the air intake.
- Measurement and balancing of airflows during operation.
Frequently asked questions
Does having an AHU mean the air is completely fresh?
The unit’s design and air source must be reviewed; it may operate on return air, a mixture, or entirely outdoor air.
Does fresh air eliminate the need for room air conditioning?
This depends on the design and the selected capacities; it should not be assumed that the ventilation system covers all of the air conditioning loads.
Can this solution be used in villas?
It can be studied for villas and other buildings, according to ventilation needs, available space, budget and operating requirements.