Air handling unit capacity calculation | DamaTajhiz HVAC Group

Air Handling Unit (AHU) is a standard air conditioning equipment used to control temperature and humidity and remove or reduce airborne pollutants in hot and cold seasons. The primary use of air conditioners is in industrial, commercial, residential, hospitals, meeting halls, hotels, halls, cinemas, and terminals, and according to the project's needs, they are manufactured and supplied in different capacities.

The capacity of the aerator expresses the aeration volume of the unit and is expressed in Cfm, which stands for cubic feet per minute or cubic feet per minute; for example, if the Air Handling Unit has a capacity of 4000 Cfm, it means that the unit is capable of transferring air flow of 4000 cubic feet per minute.

Correctly calculating the capacity of an Air Handling Unit requires knowledge, experience, and high precision. Choosing the wrong capacity of an Air Handling Unit, in addition to improper cooling and heating, will require spending a lot of money. Stay with us to learn how to calculate the air conditioning capacity.

Parameters used to calculate the capacity of the Air Handling Unit

Depending on several parameters, the capacity of the Air Handling Unit is calculated according to the cooling and thermal load of the desired room. These parameters, which directly and indirectly affect the Air Handling Unit capacity calculation, include the following.

• The dimensions of the room
• The geographical conditions of the area
• The angle of sunlight on the exposed walls
• The number and area of windows facing west, south, and east
• The presence of glass in the building's facade
• The presence of heating and lighting
• How many people live in the desired space, and how they move about
• The materials and insulation used in the building
• The environment's relative humidity
• Altitude above sea level
• The temperature of the incoming air
• Return air temperature
• Type of use (industrial, residential, office, commercial, etc.)
• Air transfer speed from the surface of the cooling and heating coil
• Pressure drop of air conditioner fan
• Pressure drop of air conditioning coils

Accurate and optimal AHU capacity calculation

The first step in calculating the capacity of the Air Handling Unit is the calculation of the cooling and thermal load of the desired space, which the installation engineers usually do with the help of software. You can contact the experts of Project Facilities or the air conditioning unit of the DamaTajhiz HVAC Group to accurately calculate the cooling and heating load of your desired space and get advice.

Q is the cooling load of the building in terms of Btu/ min, m is the airflow rate of the fan coil in terms of cubic meters per minute (cfm), cp is the specific heat of air at constant pressure (which is a number equivalent to 0.24 Btu/lb.F), and ΔT is the temperature difference between the inlet and outlet air of the fan coil in degrees Fahrenheit.

To calculate the airflow in cfm, the specific heat of the air must be multiplied by the density of the air (equivalent to 0.075 lb/ft3), the product of which is the BTU/ft3. ᵒF becomes 0.018.

According to the reports obtained from the software calculations, estimating the cooling load of the desired space is possible approximately. Roughly speaking, the cooling load per square meter is in the range of 300 to 900 BTU per hour and varies according to the expected climate; the following table has been prepared to facilitate the calculation of the approximate cooling load per square meter:

If the cooling load of a room is estimated at 45,000 BTU/hr, the CFMs or ventilation capacity of the air handling unit is calculated in the following way:

So an air conditioner with a capacity of 4000 Cfm will be suitable for this room. However, the capacity of the A/C unit is affected by other important factors, including the speed of the airflow from the surface of the unit's coil, the pressure drop of the unit's coil, the pressure drop of the A/C fan, the height of the unit above sea level, and the type and number of fins used in the unit's condenser.

Effect of fins on Air Handling Unit capacity calculation

As stated above, one of the influencing parameters in the design of air conditioning units and the calculation of the capacity of the Air Handling Unit is the type of fin or blade and its number per inch (FPIs) on the condensing coil of the unit. Fins are thin ribs that increase the heat transfer rate of cooling and heating coils by being installed in flat, undulating shapes on their surface. Fins are often made of aluminum and copper and are manufactured and supplied in wet and corrosive conditions with Bluefin and Goldfin coatings.

Fins per inch (FPI) indicates the number of fins per inch on the condenser coil; 12 to 14 fins per inch are for cooling coils, and eight are for heating coils.

Air Handling Unit fan and its effect on calculating Air Handling Unit capacity

The fan in the air conditioner is the most critical factor in delivering the desired amount of cool or warm air to the room. The air conditioner's performance is reduced if it is not selected correctly. The fan's pressure drop and the speed of the air passing over the surface of the cooling and heating coils depend on the type of fan used in the air conditioner.

Calculating the pressure drop in the A/C fan is also very important, and often, these calculations are made to comply with the A/C ducting principles; for this reason, the pressure drop of the A/C fan is calculated after ducting and with the ducting plan in hand.

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Final Speech

As you have seen, calculating the Air Handling Unit capacity is a relatively complex and challenging task and depends on many parameters; therefore, its calculation should be done carefully.

This article aims to provide valuable and practical information by trying to calculate or estimate the capacity of an air handling unit.

To view and compare different types of air conditioners of other brands and capacities, as well as to know the current price of the products, please refer to the international website of DamaTajhiz HVAC Group (the first and most reliable specialized collection in the field of equipment for building facilities and all Air Handling Unit devices since 2013 and has three valid business licenses); To accurately calculate the capacity of your air conditioner and also to get additional information during office hours, please get in touch with the phone number +98 21 88822550 and get advice from the air conditioning experts of DamaTajhiz HVAC Group.

Related Articles

For more information, you should read the "How to calculate Air Handling Unit Capacity" articles.

• Everything about the structure and use of AIR HANDLING UNITS (AHU)
• Difference between Fan Coil Unit and Air Handling Unit (AHU)
• What is an air handling unit (AHU)?
• Apartment Air Handling Unit (AUH)
• Hygienic air handling unit
• Application of air handling unit in the building
• The difference between an air washer and an air handling unit
• Comparison of types of AIR HANDLING UNIT (AHU)
• Household air conditioner electricity consumption

We await your call and look forward to meeting you in the DamaTajhiz HVAC Group.

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