If you’re in this industry, you’ve probably heard the terms AHU and HVAC mentioned. Are they interchangeable, or do they represent different concepts? Although they might sound different, there’s some overlap between an Air Handling Unit (AHU) and a Heating, Ventilation, and Air Conditioning (HVAC) system. This can be not very clear.
Starting with the basics:
HVAC System
The HVAC system aims to ensure environmental comfort. HVAC systems are generally large installations that condition the atmosphere in residential and commercial buildings using principles of fluid mechanics, thermodynamics, and heat transfer.
An AHU, or Air Handling Unit, is a part of an HVAC system designed to handle and condition the air processed within the HVAC system.
HVAC
HVAC is responsible for heating and cooling buildings. It also provides ventilation to remove moisture. HVAC systems come in various shapes and sizes but typically require a dedicated room or outdoor space. An HVAC installation may include a combination of:
– Boilers
– Air conditioners
– Ducts
– Dehumidifiers
– Furnace
Panda Home Comfort commented that not all HVAC systems will have all these components. Instead, it’s a broad term referring to interconnected and interdependent air control systems.
AHU (Air Handling Unit)
The purpose of an AHU is to ensure better indoor air quality. An AHU consists of a combination of the following elements:
Air Filters
Air filters are used to remove common pollutants from the atmosphere, such as particles and gases. The most common type of filtration used in AHUs is mechanical filtration, which removes particles like dust, pollen, and pet dander from the air and traps them on a fibrous filter.
Filters help keep the AHU clean and free from materials that could clog the mechanism. They also reduce the likelihood of harmful bacteria breeding inside the unit.
Some jobs may require additional filters. AHUs used in kitchens to remove grease and odors often need extra filters. Workshops that regularly use certain types of harmful chemicals might also need additional filters to remove potentially dangerous molecules from the atmosphere.
To be most effective, filters need to be installed as securely as possible without air leaks through the AHU casing or filter frame gaps.
Energy Recovery Components
The performance of an AHU often depends on the climate. For most of the year, the outdoor air temperature will differ from the required supply air conditions. Thermal treatment is a way to manage air temperature; however, because controlling and managing it is crucial, methods minimizing energy consumption are often used, such as an Energy Recovery System (ERS). In fact, the installation of an ERS has been mandatory in the European Union since the Ecodesign Regulation (EU) No 1253/2014 came into effect. Similarly, in the US, there are energy recovery requirements set by ASHRAE standards, and in Canada, the National Energy Code includes guidelines for energy recovery systems.
Heating and Cooling Components
It’s unlikely that one ERS system will be enough to meet a building’s temperature needs. In this case, additional components for thermal treatment are necessary. Compact water-to-air heat exchangers are commonly used. These systems connect to the building’s central heating and cooling system. A heat exchanger can also be integrated into the AHU to act as an evaporator or condenser for the refrigerant circuit, cooling or heating the air being processed.
For heating, an electric heater can be used, and for cooling, a cooling coil can be adapted to also perform a dehumidifying function in addition to its primary purpose.
Fans
Fans are vital parts of the AHU system, responsible for directing air to various parts of a building. Both single fans and assemblies of fans can be used.
There are several types of fans:
– Forward curved
– Backward curved
– Aerofoil
– Backward inclined
Software is often used to assess the static pressure and air volume in the AHU to determine the right quantity and type of fan to use.
Sound Attenuators
Noise can be an unwanted and disruptive by-product of the AHU system. Therefore, they are often equipped with attenuators to reduce the noise produced by fans or other loud parts of the system.
Humidifiers/Dehumidifiers
AHU systems can also be used to add or remove moisture from the air. Humidity is controlled and maintained within specific ranges to create the ideal environment.
Steam or liquid water is used for adding humidity, while dehumidification is achieved using a cooling coil that causes the water in the air to condense.
Mixing Section
In the mixing chamber, inside and outside air is combined to achieve the ideal mix for conditioning, minimizing the thermal treatment requirements by precisely achieving the required air conditions.
Difference Between AHU and HVAC
The simplest way to distinguish between AHU and HVAC is to remember that an AHU is a part of an HVAC system, adding extra utility to the setup.
Simply put, the Heating, Ventilation, and Air Conditioning (HVAC) system is the complete system, of which the Air Handling Unit (AHU) is an integral part.
