Indoor air quality and comfort have become one of the most important aspects of modern living. In office buildings, hospitals, shopping malls, or industrial facilities, maintaining the right temperature, humidity, and air cleanliness is essential. They act as the lungs of any HVAC system, ensuring that fresh, clean, and conditioned air is distributed throughout the building. In today’s blog, we will explore in detail the diagram, types, and working principle of AHUs.
What is an Air Handling Unit (AHU)?
An Air Handling Unit (AHU) is a large device used in heating, ventilation, and air-conditioning (HVAC) systems to regulate and circulate air. It is usually installed inside a building (mechanical room, rooftop, or basement) and is responsible for drawing in fresh air, cleaning it through filters, conditioning it (cooling or heating), and then distributing it to different zones via ductwork.
In simple terms, an AHU works like the “heart and lungs” of the HVAC system — it breathes in outdoor air, conditions it, and pumps it throughout the building to maintain a healthy and comfortable indoor environment. Depending on the building’s requirements, AHUs can be designed in different sizes and configurations, from compact packaged units to large modular systems used in hospitals or industrial plants.
Air Handling Unit Working Principle
- Air intake & mixing: Outside air and return air enter the mixing section. Dampers proportion the mix based on ventilation needs and economizer logic.
- Filtration: Mixed air passes through filters removing dust, pollen, and particulates. Clean air protects downstream components and improves indoor air quality.
- Cooling & Dehumidification: If the mixed air is warmer/humid, it flows over the cooling coil. The coil (supplied by chilled water or a DX system) cools the air and condenses moisture, reducing humidity. Condensate drains to a pan.
- Reheating (if required): To prevent overcooling when dehumidification is performed, a heating coil may reheat air to the desired supply temperature.
- Humidification (if required): In dry climates or specific process needs, a humidifier adds moisture to the supply air.
- Fan pressurization & distribution: The supply fan propels conditioned air through ducts to occupied spaces. Return fans draw air back to the AHU or exhaust it as required.
- Control & feedback: Sensors measure temperature, humidity, pressure, and sometimes CO₂. The AHU control panel or the building management system adjusts dampers, valve positions, fan speeds (via VFDs), and humidifiers to maintain setpoints efficiently.
Air Handling Unit Diagaram
A typical Air Handling Unit consists of several sections arranged in sequence to process air step by step. The ahu schematic diagram below shows a simplified layout of an AHU Drawing
AHU Diagram: Explanation
- Outside Air Intake & Dampers – Fresh air enters the AHU and is mixed with return air. Dampers control how much fresh air is allowed inside.
- Filters – The air passes through filters that remove dust, dirt, and pollutants to ensure healthy indoor air quality.
- Cooling Coil – Connected to chilled water or refrigerant, this coil cools down the air and removes excess humidity.
- Heating Coil – In winter or for reheat applications, the heating coil increases the air temperature to the desired level.
- Humidifier – Adds moisture if the indoor air is too dry.
- Supply Fan – Pushes the conditioned air through ducts and into the occupied spaces.
- Return Air & Exhaust System – Used air is partly returned for reconditioning and partly exhausted outside to maintain ventilation balance.
Ahu used to balance the temperature and filter the air flow, with the help of simple AHU Diagram, we will understand about the working of AHU parts.
Types of Air Handling Unit
1. Packaged AHU
These are factory-assembled units that come ready to install. They are compact, cost-effective, and widely used in small to medium commercial buildings where quick installation is required.
2. Modular / Custom-Built AHU
Designed in separate modules, these units can be customized as per airflow, filtration, and space requirements. They are ideal for hospitals, pharma plants, and industries with special needs.
3. Rooftop AHU
Specially designed with weatherproof casing, rooftop units are placed on building terraces or roof slabs. They save indoor space and are commonly seen in malls, offices, and multiplexes.
4. Make-Up Air Units (MAU)
These units supply 100% fresh air to replace exhausted air. Commonly used in commercial kitchens, industrial plants, or areas requiring continuous ventilation.
5. Constant Air Volume (CAV) AHU
A simple type of AHU that delivers a fixed amount of air all the time. The temperature is controlled by heating or cooling coils, making it suitable for smaller applications.
6. Variable Air Volume (VAV) AHU
More advanced than CAV, VAV AHUs adjust the airflow based on the cooling or heating demand of different zones. This makes them more energy efficient and comfortable for large buildings.
7. Heat Recovery AHU
Equipped with a heat recovery system (like plate heat exchangers or rotary wheels), these units save energy by transferring heat between exhaust air and fresh intake air.
8. Cleanroom / Healthcare AHU
Specially designed units with HEPA filtration, UV sterilization, and strict leakage control. They are used in hospitals, laboratories, and cleanrooms where air quality standards are critical.
Ahu Parts
These are the standard AHU parts name, but depending on project needs (hospital, data center, pharma, shopping mall), manufacturers like we can add customized components like UV germicidal lamps, heat recovery units, and high-efficiency particulate control systems.
- Casing – Insulated housing for all components.
- Air Intake & Dampers – Control fresh, return, and exhaust air.
- Filters – Remove dust and pollutants (Pre, Fine, HEPA).
- Cooling Coil – Lowers air temperature, dehumidifies.
- Heating Coil – Increases air temperature.
- Humidifier / Dehumidifier – Maintains proper humidity.
- Fans (Supply & Return) – Circulate and balance airflow.
- Mixing Chamber – Mixes fresh and return air.
- Drain Pan – Collects condensate water.
- Sound Attenuator – Reduces noise.
- Controls & Sensors – For automation and monitoring.
- Access Doors – For maintenance.
Benefits of AHU
- Improved indoor air quality through filtration and ventilation.
- Precise temperature and humidity control for occupant comfort or process stability.
- Energy savings with heat recovery and smart controls.
- Compliance with health and safety standards for sensitive environments.
- Scalability and customization to suit building-specific needs.
How to choose the right AHU
- Load assessment: Size for peak sensible and latent loads, not just floor area.
- Filtration needs: Healthcare, pharma, and cleanrooms require higher MERV/HEPA ratings.
- Energy efficiency: Consider heat recovery, VFDs on fans, EC motors, and optimized control sequences.
- Space & access: Modular designs allow transport through tight openings and easier maintenance.
- Noise & vibration: Select silencers and isolation for noise-sensitive environments.
- Local service & customization: A reliable manufacturer with local support ensures timely maintenance and spare parts.
Refcon Engineering, as a leading Air Handling Unit manufacturer, offers AHU solutions—from standard packaged units to highly customized systems with advanced filtration, heat recovery, and BMS integration—backed by local service expertise. We always prioritize the quality standard and durability, ensuring its perform efficiently at their applications.
