What is an air handling unit (AHU)?

The air handling unit is one of the most important types of equipment in the air conditioning or HVAC department, whose main task is to supply, transfer and move suitable air and refine it in the desired environment. For this purpose, this device is used in public places, companies, and commercial, industrial, etc. places to produce fresh air (ventilation), supply cool air (cooling), and provide hot air (heating).

In short, air handling units provide comfortable air by using the cold water flow of the central chiller to the air handler cooling coil in summer and the hot water flow of the engine room boiler to the air handler heating coil in winter.

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It should be noted that the word air handling unit is also called an air handler or air transfer unit.

Advantages of air conditioners

• High efficiency and performance
• Separate use and independence of ventilation of each complex unit
• Avoid occupying the space of the house by installing it on the roof
• Filtration and provision of suitable air quality
• It has a remote control.
• Easy installation and maintenance

Types of air conditioners

In general, air conditioners are produced and supplied in 4 types and in different applications, which are:

• an apartment
• industrial
• Hygienic
• Homemade

Any of the above types of air conditioners may be produced as variable volume air conditioners, variable temperature air conditioners, or variable air volume and temperature as full fresh air or return & fresh air based on the needs of the project, and the main goals of all these types of products can be mentioned the following:

• Temperature setting
• Air humidity adjustment
• air conditioner
• Fresh air supply

Hygienic air conditioner

Hygienic air conditioners are generally considered the most advanced type of air handling unit. These types of air conditioners are used for environments such as hospitals, laboratories, etc., due to having a filtration system and advanced internal equipment, whose main requirement is to have sterile and clean air that is free of any dust and pollutants. they take. Hygienic ventilators are mainly designed and manufactured based on specific and determined international standards, which are very important. These standards are:

• EN 1886 standard (ventilation system of buildings and its mechanical performance)
• VDI 3803 standards (technical and structural principles of air conditioning systems)
• VDI 6022 standards (hygienic air conditioning systems)
• EN 13053 standard (Rating and performance of various components and parts of the ventilation system)

Industrial air handling unit

The structure of industrial air conditioners, due to the fact that they are used in environments with larger dimensions and space than other types of air conditioners, they have a larger mechanism and structure. These air conditioners have different categories, the main ones are:

Classification based on the type of aeration

• Air conditioners with the fresh flow (Full Fresh)
  Air conditioners with return flow

Classification based on the amount of aeration

• Air conditioners with constant air flow (Constant Air Volume)
  Air conditioners with variable airflow (variable air volume)

Classification based on aeration area

• Multi-zone air conditioners
  Single-zone air conditioners

The places where this type of air conditioner is used to supply and produce comfortable air are factories and workshops of various industries, seminar and meeting halls, sports halls and clubs, etc.

Apartment air handling unit

This air handler is used in apartment environments when the conditions of its production and installation are fully met, because in some cases this device is combined with an air washer, and this not only does not have the desired efficiency and result but also causes the accumulation of bacteria. and pollution inside the air conditioner and then spread to the apartment environment.

Home air handler

Home air conditioners are used only to meet the cooling and heating needs of a unit. It should be noted here that air purifiers and air conditioners are different. Basically, air purifiers only purify the air and do not have any temperature effect on air heating or cooling.

The apartment air handling unit is one of the best options for ventilation and providing fresh air in low-area environments. This type of air conditioner, like other air conditioners, has the task of producing cold air in the summer season and warm air in the winter season, according to the capacity and power that are designed and built. Air purification by installing a suitable filter and removing the pollution in the air is another feature of this type of air conditioner.

Working principles and components of air handling unit

Despite their high efficiency, air conditioners have a straightforward structure. The air conditioner is used in four parts: cooling, heating, air purification, and humidity regulation. This system has various components, including hot and cold coils, fans, a number of air filters, humidifiers, channels, etc. The way the air conditioner works is that hot and cold water produced in devices such as chillers, boilers, and in the central engine room of the building is transferred to the air conditioner coil of the system. Then, several small fans or one big fan installed in the air conditioner blows the air from the hot and cold coils, and after cooling or heating the air, distributes it through the ducting in the desired location. In such a way that in hot seasons with the flow of cold water in the coils, the operation of the air conditioner is of the cooling type, and in the cold seasons with the flow of hot water of the engine room boiler inside the coils, the operation of the air conditioner is of the heating type.

The air conditioner is composed of different components according to the type of use and dimensions of the project spaces. The main and fixed components of this device are:

• Airtight and insulated body of the device
• Cooling and heating coil
• Air purifier filters (Filter)
• Electric motor and supply fan

Cooling and heating coil

As mentioned, the performance of air conditioners is such that they change the air temperature to produce and meet the heating and cooling needs of the project space. This temperature change is done by the coils that are in the airflow path. Also, cooling coils can be used as dehumidifiers (by reducing the air temperature below its dew point).

Air generator coils are designed and manufactured in two ways, considering the type of project:

Direct air handler coil

There are coils that directly use the cold flow of refrigerant (DX Coil) for cooling and the gases from fuel combustion (Fired Heater Coil) for heating. Heat pumps can also be used for direct cooling and heating in air conditioners. Another type of heating coil are electrical heaters that convert electrical energy into thermal energy by passing an electric current through the elements embedded in it and heating the passing air.

Indirect air handling unit coil

There are coils that use the flow of cold water produced by the chiller at a temperature of 7°C for cooling and the flow of hot water produced by the boiler at a temperature of 82°C for heating the ambient air. Hot water vapor can also be used in indirect heating coils.

Air handler filter

Filters are one of the most important components of air conditioners. So that having sufficient knowledge of the type of filter and choosing it correctly has a direct effect on the efficiency of the air conditioner. These filters, which usually have unique manufacturing technology and various types, are tested and classified based on certain standards, the most famous of which are:

ASHRAE American Standard

Abbreviation of the phrase (American Society of Heating, Refrigeration and Air-Conditioning Engineers)

EUROVENT European standard

which is coded with the EU and by which it is supplied throughout the European markets.

Different types of filters are used in air conditioners, which are:

• Olpa filter
• HEPA filter
• Fiberglass pre-filter
• Bag filter
• Metal pre-filter
• Pleated pre-filter (panel)

Supply Fan

Basically, the blower fan is called as the moving heart of the air-generating device. This is because the necessary energy for air flow inside the air channels of the building is provided by this department. This operation is done by creating a suitable pressure difference which is done by fans. Centrifugal fans and plug fans can be mentioned among the types of fans used in the air conditioner.

The most important thing to pay attention to here is that considering that fans are the main consumers of electricity in air conditioners, choosing the right fan with less energy loss has a direct impact on the efficiency and effectiveness of the device.

Air handling unit selection guide

As you know, as the humidity increases, the enthalpy of the environment also increases. In other words, the presence of high humidity causes the temperature to rise. On the other hand, due to the vastness and diversity of the climate and weather in our country, the percentage of air humidity is also different, so that in some climates the air humidity reaches over 95%! For this reason, before starting the calculations, the type of use and the installation location of the air conditioner should be examined in terms of the regional climate (humidity and temperature).

Another important point for choosing an air conditioner is its ventilation capacity. To calculate this characteristic, in addition to calculating the cooling and thermal load of the building, the type of use of the air conditioner should also be taken into account. For this reason, it should be determined at the beginning that the air conditioning device that we intend to choose will be used to meet the cooling and heating needs of the project, or the purpose of choosing and using it is only for fresh air conditioning. Therefore, the way to calculation of the aeration capacity is done in the following two ways:

Calculation of the ventilation capacity of the air conditioner to meet the cooling and heating needs of the project:

At this stage, the cooling and heating load of the project must be calculated by experts and experienced facility engineers. Basically, the amount of cold or heat that is wasted in a building through the walls, floor and ceiling, glass, seams, and other factors and must be compensated through cooling and heating devices such as air conditioners is the heating load or the cooling load of the building. They say. To calculate the cooling load, which is the first step in calculating the air conditioner capacity, you can use the BTU Calculator site, along with the advice and guidance of engineers and project installation experts, and the THERMO SOFT site to calculate the heating load.

We can also calculate the required aeration volume of the aerator through the following relationship:

A very important point in the above calculations is to consider the effect of the height of the location from the sea level on the relationship coefficients. This is because the air density decreases with increasing altitude. For example, for every 250 meters, 1% of air density is reduced and this number should be subtracted from the relationship coefficients.

Calculation of the aeration capacity of the aerator to supply fresh air:

To perform this calculation, various factors and criteria are used, including the use of the environment, square footage, number of people, number of air changes, and standards such as national building regulations. For example, in a room, 15 cfm per person, in corridors and halls of public places, 0.2 cfm of fresh air per square meter of floor area will be required.

What is cfm?

CFM stands for Cubic Feet per Minute (Cubic Feet per Minute), which is actually a unit of air displacement by air conditioning and air conditioning equipment. This means that when it is said that the air conditioner is 5000 cfm, it means that this air conditioner can move 5000 cubic feet of air per minute. The factors that affect the cfm of the air conditioner are:

• The height of the place of operation of the device above sea level
• Fan pressure drop, cooling, and heating coil
• The humidity of the installation site
• Air transfer speed over the coil

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Tips and guide for buying an air handling unit

• A detailed investigation of the static pressure drop that exists in the longest path of the channel or the static head of the aeration fan
• Accurate estimation of the volume of air passing through the air conditioner per unit of time
• Accurate calculation of cold and heat loads of the building

It should also be noted that if more than one air conditioner is used in the building, the contribution of each air conditioner to the total cooling and heating loads should be determined.

In addition to the above points, by referring to the product catalog, you can check all the features and specifications, including heat capacity, moisture capacity (which is usually 15 pounds per square inch), fan motor power, etc.

Air handler installation

For the installation and operation of air conditioners, one should pay attention to certain points and conditions, the most important of which are:

• Using a sewer pump with a reliable vent at the installation site of the air conditioner for periodic cleaning and service of the air conditioner
• Considering at least 1.5 meters of free space on one side for the possibility of service or possible replacement of the air conditioner coil
• Proper insulation of air channels exposed to the sun, heat, and cold to increase the efficiency and effectiveness of the device
• Installing an air conditioner in the right place to reduce the length of the ducting route and reduce costs

Final word

You can read the information on all types of air conditioners by referring to the website of DamaTajhiz, the air conditioning section and the air conditioner section, and get information about the updated prices of each of these products, or during office hours with the experts of the air conditioning equipment section in this collection.

In addition to a valid business license from the heating and air conditioning trade association, DamaTajhiz specialized collection has an electronic trust symbol and started its store site in 2013 in the head office of Tehran.

Related Articles

In order to get more information, it is recommended to read the articles related to the article "What is the air conditioner?"

• What is a fan coil?
• Difference between fan coil and air handling unit
• Everything about the structure and use of air handlers

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