Types of Air Handling Units
Mohamed Khaled
Calibration and Qualification Engineer | ISO 17020 Certified | Equipment and Utilities Validation | ISO 17025 Calibration Expertise | MBA E-JUST University
In this article, we will focus on the various types of Air Handling Units (AHUs), providing clear and straightforward explanations to enhance your understanding of each type.
Before diving in, it is highly recommended to review the following articles to build a foundational knowledge that will aid in comprehending the specifics discussed here.
Standard Air Handling Units
Description
Designed for general applications, these units are versatile and can be used in various settings including office buildings, schools, and commercial spaces.
Features
Typically equipped with standard components such as filters, fans, and coils.
Application
Suitable for most HVAC needs, providing efficient air circulation and conditioning.
Fresh Air Handling Units (FAHUs)
Description
Specifically designed to intake and condition outdoor air.
Purpose
Ideal for buildings requiring high ventilation levels, such as schools and hospitals.
Benefits
Improves indoor air quality by replacing stale indoor air with fresh outdoor air.
Hygienic Air Handling Units
Description
Engineered for environments where cleanliness and air quality are paramount.
Applications
Commonly used in hospitals, laboratories, and food processing facilities.
Features
Incorporate advanced filtration systems and sanitation technologies to ensure uncontaminated air supply.
Packaged Hygienic Air Handling Units
Description
These units provide the same cleanliness standards as hygienic AHUs but come pre-assembled in a compact package.
Advantages
Simplifies installation and maintenance, making them suitable for spaces with limited room.
Use Cases
Ideal for facilities that need high hygiene levels without extensive installation efforts.
Heat Recovery Air Handling Units
Description
Designed to capture and reuse heat from exhaust air.
Energy Efficiency
Reduces the demand on heating systems, improving energy efficiency.
Ideal Conditions
Particularly beneficial in climates with extreme temperatures, offering significant energy savings.
Energy Recovery AHUs
Description
Similar to heat recovery AHUs but designed to recover both heat and moisture from exhaust air.
Ideal Use
Perfect for buildings in hot and humid climates, where maintaining indoor air quality while reducing energy costs is essential.
Pool Dehumidifiers AHUs
Description
A specialized type of AHU designed for indoor swimming pool areas.
Function
Controls humidity levels and prevents condensation, maintaining a comfortable environment.
Protection
Helps protect building materials from moisture damage caused by high humidity.
Chilled Water Air Handler Units
Description
Utilizes chilled water as a cooling medium to dehumidify and cool the air.
Components
Consists of a cooling coil, supply fan, filters, dampers, and sometimes a heating coil.
Operation
The chilled water coil removes heat from the air while the supply fan circulates the conditioned air throughout the building.
Direct Expansion (DX) Air Handler Units
Description
Self-contained HVAC systems commonly found in commercial buildings, also referred to as rooftop units (RTUs).
Components
Include a compressor, evaporator coil, condenser coil, supply fan, filters, and optional heating elements.
Functionality
Provide both cooling and heating, using refrigerant as the cooling medium.
Cleanroom AHUs
Description
Designed for environments where air quality is crucial, such as pharmaceutical labs and research facilities.
Features
Equipped with HEPA filters capable of removing airborne particles as small as 0.3 microns.
Environment Control
Maintains a high level of air cleanliness and a controlled environment.
Outdoor AHUs
Description
Built to withstand harsh outdoor conditions, suitable for industrial applications.
Durability
Often constructed from heavy-duty materials like stainless steel or aluminum to endure extreme weather.
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Applications
Commonly used in industrial plants, wastewater treatment facilities, and power generation plants.
Dual Duct Air Handling Unit
Functionality
This unit provides both cold and warm air, distributing them through two separate main supply ducts to dual-duct Variable Air Volume (VAV) mixing boxes.
Operation
After passing through the mixing box, the air combines in a common duct, achieving the desired temperature setting for the space.
Multi-Zone Air Handling Unit
Configuration
Each zone has its own hot and cold deck damper, differing from the dual duct system.
Air Distribution
Each zone is equipped with separate supply air dampers for heating and cooling coils, allowing for tailored temperature control in different areas.
Multi-Zone Dual-Duct Air Handling Unit
Mixing Capability
Features a mixing box that allows return air and outside air to blend.
Ventilation Control
The outside air damper modulates to maintain the minimum required ventilation air as mandated by code. CO sensors can optimize outside air intake for energy conservation.
Multi-Zone Air Handling Unit with In-Duct Reheat
Design
Similar to the multi-zone unit, but this configuration utilizes only a cooling coil.
Heating Provision
Heating is supplied by an in-duct reheat coil when necessary.
Variable Air Volume (VAV) Air Handling Unit
Typical Usage
Commonly mounted on rooftops, VAV units are prevalent in medium to large commercial buildings.
Functionality
These systems adjust airflow based on the temperature requirements of different zones, enhancing energy efficiency.
Typical Custom Air Handling Unit
Structure
Begins with a return air section, passes through return air fans, and enters an economizer that can exhaust air or redirect it back into the system.
Dampers Operation
Outside air dampers work with the economizer to meet ventilation needs, automatically adjusting to maintain balance with exhaust dampers.
Types of Air Handling Units (AHUs) Based on Size and Component Arrangements
Air Handling Units (AHUs) can be classified in other ways, particularly based on their size and the arrangement of their components. This classification helps in understanding how different units are designed to meet specific HVAC needs. Below are some of the primary types based on size and component configurations.
Size
Small AHUs
These are used in localized spaces and have minimal components (fan or blower, heat transfer coil, filters). They are referred to as fan coil units (FCUs) or blower coil units (BCUs), serving single zones such as loading docks or stairwells.
Larger AHUs
Packaged units or rooftop units (RTUs) are used outdoors, featuring additional control dampers and serving larger areas or multiple zones.
Fan
Suction Fan (Draw Through)
The fan pulls air between the coils and the mixing box, directing it into the distribution channels.
They are available in both horizontal and vertical configurations.
Due to the fan's suction, the area before the fan operates under negative pressure.
Blower Fan (Blow Through)
The fan blows air between the coils, creating positive pressure in the section after the fan.
It Requires careful positioning of the fan relative to the coils to optimize airflow.
Generally has a longer design and is slightly more expensive than suction types.
The airflow can be more turbulent, causing greater temperature variation across the coil surface.
Material Type
Frame Construction
Materials that are used can be made from steel, stainless steel, galvanized steel, or aluminum, based on the application and required strength.
Fan Motor Type
Electric Motors
Their Motors can be standard or inverter motors, with inverter motors offering reduced energy consumption.
The Connection Methods can be direct coupling, belt drive, or gearbox connections are typical.
Arrangement of Components
Horizontal Units
All components are positioned at the same horizontal level.
Air enters from the inlet, is conditioned as it passes through each component, and exits through the outlet.
It requires more floor space for installation due to the need for separate areas for each component.
Proper management of vibration and noise is also necessary.
Vertical Units
The components are stacked on top of one another, making them more compact.
It requires less floor space than horizontal units and is typically installed in AHU or fan rooms.
Recap
Air Handling Units (AHUs) are vital components of HVAC systems, responsible for regulating indoor air quality, temperature, and humidity. They can be classified in several ways:
By understanding these classifications, users can select the right AHU to ensure a comfortable and efficient indoor environment.
Check these two below videos for better understanding.
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Calibration and Qualification Engineer | ISO 17020 Certified | Equipment and Utilities Validation | ISO 17025 Calibration Expertise | MBA E-JUST University
1 个月We encourage you to actively participate in this discussion by asking questions, providing comments, and sharing additional information that can benefit all members of this community.