Multi-Zone Air Handlers vs. Single-Zone AHUs

Generally, when deciding which type of air handling unit (AHU, also known as Air Handler) to choose—based on air delivery capacity, cooling and heating capacity, horizontal or vertical layout, and more—we usually come across two main types: Multi-Zone and Single-Zone AHUs. Here, this question comes to mind: What is the difference between a Multi-Zone and a Single-Zone air handler? And, depending on the specific requirements, which one is more suitable for our project? This article answers that question by explaining the features and applications of these two types of air handling units.

single zone air handling unit vs multi zone ahu

Single-Zone Air Handling Unit

A single-zone AHU is a centralized unit typically installed outside the building. It treats the entire building—or any area composed of multiple sections connected by ductwork-as one single zone. The unit supplies a consistent flow of air with controlled temperature and humidity to all sections equally.
Since single-zone units are not capable of delivering air at different temperatures to individual zones, they are less commonly used—unless we have a large, open, and uniform space such as a hall or warehouse, where a uniform air condition across the whole area is required.

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Multi-Zone Air Handling Unit

If we want to have independent temperature control for each part of a building, we should use a Multi-Zone Air Handling Unit (AHU). In a multi-zone system, each section of the building is connected to the AHU through a main duct and several branch ducts.
Before the air exits into the branch ducts, a terminal box (also known as a unit box) is installed. Each of these boxes is responsible for controlling the temperature of different building zones. Every terminal box includes a secondary cooling and heating coil, a 3-way motorized valve, an automatic air damper, and countless branch ducts (one for each room or section).
In multi-zone AHUs, the air from the main duct enters the terminal box, and its temperature is adjusted using the secondary coil based on the specific needs of each area. The secondary coil, connected to the chilled and hot water circuits of the chiller and boiler via a 3-way motorized valve, is activated when users request warmer or cooler air, adjusting the temperature accordingly.

multi-zone air handler

After the air is cooled or heated by the secondary coil, the airflow rate to each zone is controlled by the automatic motorized damper within the terminal box. The air is then distributed through the branch ducts into each room or space, allowing each area to maintain its desired temperature independently.
Typically, multi-zone AHUs use variable-speed motors (inverters) to maintain the temperature of the primary coils constant while adjusting the airflow rate as needed (especially when only one main duct is used). Another method for regulating incoming air temperature to each zone is by using a secondary coil with a 3-way motorized valve inside each terminal box, while keeping the fan speed fixed.
The automatic motorized damper and the secondary coil in the terminal box are both controlled automatically by a thermostat installed in each room. This allows for automatic adjustment of both the air volume and temperature in each area based on user demand.

Multi-Zone AHU vs. Single-Zone Air Handler in Brief

One of the key differences between Single-Zone and Multi-Zone AHUs is the ability to deliver customized air to each area. As mentioned, a Single-Zone AHU can only provide a uniform type of air throughout the entire building. However, if different zones require different air conditions, separate Single-Zone units would be needed for each section.
In contrast, Multi-Zone AHUs can meet the needs of different areas using a single unit by distributing various airflows through separate ducts connected to each zone, making them a more efficient solution.
Thanks to this capability, Multi-Zone AHUs can significantly reduce electricity consumption compared to Single-Zone systems. Moreover, the overall cost of purchasing and operating multiple AHUs is minimized.

DamaTajhiz: The Best Prices and Brands for HVAC Equipment

In this article, we aimed to explain what Multi-Zone and Single-Zone AHUs are and how they differ. As discussed, the choice between a single or multi-zone system depends on whether you require separate air conditioning for different parts of your building or if a uniform environment will suffice. You can make your selection based on these differences.
To compare various models of Single-Zone and Multi-Zone AHUs by brand and capacity, and to view updated prices, visit the specialized DamaTajhiz air handlers (the first and most trusted HVAC platform in Iran since 2004, with three certified business licenses). For further information and expert advice, please feel free to contact our HVAC consultants during business hours.

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