Centralized vs de-centralized ventilation

Centralized vs de-centralized ventilation. Every time you are working on a new HVAC project for a new construction, or even for a retrofit project, you are in front of an important decision. It is the kind of decisions that can have a huge impact on the success of the project you are following.

Are you going to centralize or decentralize the buildings’ ventilation system?

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Centralized ventilation systems

They usually involve the use of fewer but larger air handling units (AHU) located outdoor on the rooftop of the building, or indoor in a technical room. That means there would be a single location accommodating the equipment. That equipment, then, would ventilate the whole building through a network ducts and grills. That means there would be a single location for future AHU maintenance.

Also, large buildings with centralized ventilation systems require long duct to deliver air to occupied spaces, and that is an important aspect to consider when designing a ventilation system for a building. In fact, ductwork resistance to airflow (External Static Pressure or ESP) increases with increasing duct length, forcing AHU fans to work harder, thus making the system less efficient. Increasing the ducts diameter, helps solving the issue, but ceiling or shaft space isn’t always available to accommodate big ducts. The same ducts, then, should also be sealed to avoid leakages, since leaking prevent air from reaching its destination, causing thermal and moisture control issues and efficiency issue.

De-centralized ventilation systems

They use a greater number of smaller Air Handling Units or HRU (Heat Recovery Units). Decentralization could mean one AHU per apartment in a multi-family residential project, for instance, or an AHU per office in a multi-storey office building. A project like that could then require different utility hook-ups, also requiring to schedule maintenance on different AHUs installed in different locations.

This solution doesn’t require AHUs fans to do any extra effort to overcome ductwork resistance to airflow, because of the short ducts used, which allow to save energy. Also, small AHUs like Daikin Modular L, designed to be implemented in de-centralized ventilation systems, offer great compactness. In fact, Daikin Modula L can be installed in false ceilings. That helps saving floor space, which is important for applications where floor space is important.

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Flexibility, then, is another relevant aspect in de-centralized ventilation. In fact, some buildings might not require air conditioning in a specific time of the day. De-centralized systems allow to have a better control on the different areas of the building.

Those are a few of the main differences between the two systems, but there is more to consider.

Centralized vs de-centralized ventilation: what is the best solution?

The answer is: it really depends on the project. But we also need to understand that few buildings are built purely centralized or decentralized in terms of ventilation. Usually, buildings need a solution somewhere in between. Sometimes would be ideal to employ the best of each concept to best satisfy budget, energy and comfort goals. Consultants can only achieve that through a study specifically made to determine the right degree of centralization for a project.

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