Fan coil capacity calculation

Complete tutorial on calculating fan coil capacity using accurate engineering methods and rule of thumb methods. Calculating refrigeration load, fan coil cfm, Q=MC∆T formula with numerical and practical examples.

Calculating fan coil capacity is simple but time-consuming, and many parameters such as altitude above sea level, fan coil inlet and outlet air temperatures, fan coil inlet and outlet water temperatures, ambient relative humidity, etc. are influential in determining its capacity.

Fan coil capacity can be obtained by two methods: exact calculations and rough calculations. In the accurate calculation method, all physical characteristics of the building and the indoor and outdoor air must be available. Specifications such as the material of the walls, doors, windows, their thermal conductivity, the use of the building, the number of people, the type of activity of people in the environment, heat-generating equipment installed in the environment, etc., are practically difficult to access for all this information for old buildings without engineering documentation. For this reason, in these buildings, the calculation of fan coil capacity is done as an approximate calculation.

Accurate calculation method:

For this purpose, the cooling load of the building must first be calculated. This is usually done by mechanical engineering consultants. Having the cooling load of the building, the ventilation volume of the fan coil is calculated. 
For this purpose, the following formula is used:

Q=M.Cp.∆T 
 

Q: Building cooling load in Btu/min 
M: Fan coil air flow rate in cubic feet per minute (cfm) 
Cp: Specific heat of air at constant pressure, which is a constant number equal to 0.24Btu/Lb.°F. 
∆T: Temperature difference between fan coil inlet and outlet air in degrees Fahrenheit (°F)

To calculate the air flow rate in cfm, we must multiply the specific heat of the air by the volumetric mass of the air. (The volumetric mass of air is 0.075 Lb/ft3. Therefore, the product is equal to 0.018 Btu/ft3.°F.) 
Therefore, the above formula can be simplified as follows:

M[cfm] =    

For example: The calculation of fan coil capacity for a space with a cooling load of 9700Btu/h is as follows:

Air supply the fan coil 86 degrees Fahrenheit 
Air exhaust the fan coil 64.4 degrees Fahrenheit 
Residential building located in Tehran.

M= = 415cfm 

Therefore, the appropriate fan coil for this space has a capacity of 400cfm.

Approximate calculation method:

In this method, to obtain the fan coil capacity, we must also have the cooling load of the building. However, since the calculation of the fan coil capacity is an approximate calculation, the cooling load can also be calculated by the rule of thumb.

In these calculations, for cities with similar climatic conditions to Tehran and for residential and office uses with low population, a cooling load of about 400 Btu/h is usually considered per square meter of building area. To calculate the desired fan coil capacity in these spaces, it is sufficient to divide the cooling capacity in terms of Btu/h by 26.

For example: The fan coil capacity for a residential space in Tehran with an area of ​​100 square meters is calculated as follows:

Q = 100 (m2) 400 (Btu/h) = 40.000 (Btu/h)

Required fan coil capacity =   = 1538cfm

The fan coil required for this space is a device with a capacity of 1600cfm.

The above calculated capacity may be provided by one or more units. The number and type of fan coils in a space depends on the piping system, number of branches, and the type of architecture of the spaces.

Ultimately, selecting the appropriate fan coil unit is not solely dependent on capacity. Other critical factors such as the number of units required, installation location, piping configuration, and architectural layout also play a significant role in the final decision. Applying the proper calculation method leads to optimized HVAC system performance, improved energy efficiency, and extended equipment lifespan.

If you're unsure about choosing the right fan coil unit for your project, don't hesitate to contact Green's technical experts or use the online fan coil capacity calculator available on our website.

Ultimately, choosing the right fan coil does not only depend on capacity, but other factors such as the number of units, installation location, type of piping system, and space architecture also play a role in the final selection. Using the right method for calculation will optimize the performance of the ventilation system, save energy, and extend the life of the equipment.

If you are unsure about choosing the right fan coil for your project, contact Green's experts now or use the online fan coil capacity calculation tool on the site.