Fan coils are among the most common indoor unit types in offices, hotels, hospitals and shopping centers. Most come with a simple, washable coarse filter from the factory. With the growing importance of indoor air quality in recent years, we hear the question "if we fit a finer filter, will the fan coil be strained and will energy consumption rise?" more often. Nanofiber filters have an important place in the answer to this question.
What is a nanofiber filter?
A nanofiber filter is a filter material in which fibers usually thinner than 1 micron are laid in a web on top of a carrier layer. These fine fibers capture particles mainly by mechanical means, that is, by adhesion to the fiber and diffusion.
Some conventional synthetic fine filters get a large part of their efficiency from the electrostatic charge on their fibers. This charge declines over time with moisture and dust, and the filter's efficiency can fall during its service life. The mechanical capture property of the nanofiber layer offers a more stable efficiency. Because the fiber is so fine, the same efficiency can be reached with a more open structure that lets air pass more easily.
How does the filter affect a fan coil's energy consumption?
The filter affects a fan coil's energy consumption through its resistance to airflow, that is, its pressure drop. As pressure drop rises, the fan has to work harder to move the same air, or moves less air.
The fan type matters a great deal here. In a fan coil with a fixed-speed classic (AC) motor, fan power does not rise noticeably when resistance increases, but airflow falls. When airflow falls, the cooling and heating capacity drawn from the coil decreases, the room is conditioned late and the system runs longer. In fan coils with variable-speed EC motors and constant-airflow control, the fan raises its speed to maintain airflow; in that case the resistance is reflected directly in electricity consumption.
In short, the filter affects not only the fan's electricity but also the capacity the fan coil delivers, and therefore the load on the chiller or boiler. The assessment should not be made on a single item.
Does a nanofiber filter save energy?
A nanofiber filter can offer an advantage in fan energy and airflow because it can run with lower pressure drop than a conventional filter of the same filtration class. However, if a much finer class of filter is fitted in place of the existing coarse filter, the pressure drop may rise somewhat even if the filter is nanofiber.
The real energy gain often comes indirectly. Fine dust that passes through coarse filters builds up between the fins of the fan coil's coil over time and mats together. A dirty coil both makes it hard for air to pass and weakens heat transfer. Because a better filter keeps the coil clean for longer, the fan coil can run close to its design capacity. We described the scale of losses in neglected indoor units in our article neglected air conditioner and energy consumption.
It would not be right to give a general figure for the percentage saved. The result varies with the fan coil's fan type, whether it has duct connections, the class of the existing filter, the dust load of the environment and the maintenance frequency. The right method is to measure before and after the change.
How should the filter class be chosen in a fan coil?
The fan coil filter should be chosen to give the capture efficiency the space needs, within the pressure drop limit the fan can handle. Most fan coils work with low external static pressure and cannot handle filters with resistance as high as air handling units can.
Filters are now defined under the ISO 16890 standard in the ePM1, ePM2.5, ePM10 and coarse classes; classes such as G4 and F7 from the old EN 779 are still frequently used. In fan coils, the factory filter is usually in the coarse class. If moving to a finer class, the filter's initial pressure drop at the design airflow should be checked from manufacturer data and compared with the fan coil's fan curve. For choosing air handling unit filters and when to replace them, see our article when to replace air handling unit filters.
- The filter must sit in the fan coil filter slot with no gaps; air escaping at the edge cancels all of the filter's benefit.
- The initial and final pressure drop values must be provided by the manufacturer.
- Whether the filter is washable; some filters with a nanofiber layer are not suitable for washing.
- In humid environments, the moisture resistance of the filter material.
In which buildings does it make more difference?
Choose your fan coil filter by measurement
Let's measure airflow and pressure on sample units and recommend a suitable filter class and maintenance interval for your building.
A nanofiber filter makes the most difference in buildings that take in a lot of fine dust and particles from outside or that have high indoor air quality expectations. Offices near traffic, buildings around construction sites, hospitals, schools and hotels are at the top of this group.
In these buildings, fine dust that gets past coarse filters quickly fouls the coil; coil cleaning becomes more frequent and maintenance costs rise. When a better filter slows the rate at which the coil gets dirty, there is a gain on both the energy and the maintenance side. In buildings with little dust, where the fan coils run for short periods, the gain stays more limited and the payback takes longer.
How is the effect of the change measured?
The effect of a filter change is determined by measuring airflow, filter pressure drop and fan motor power on the same fan coil before and after the filter. Measurement on a few sample units provides enough data to decide for the whole building.
The measurement should be repeated not only on the first day but also after a few months. How quickly the pressure drop rises as the filter collects dust determines the replacement or cleaning interval. The rate at which the coil gets dirty can also be checked at the annual maintenance by eye and with differential pressure.
Taking these measurements and opening fan coil covers means working on a unit that has electrical connections and is located in the ceiling. The user may only remove and check the filter with the unit switched off, in the way the manufacturer allows; work on the motor, board and electrical connections is a job for a qualified technician.
The role of the filter in fan coil maintenance
Whichever filter is chosen, it gives no energy advantage unless it is checked regularly. A clogged nanofiber filter reduces airflow just as much as a clogged coarse filter.
Filter maintenance should be handled together with coil cleaning, drain pan checks, and fan motor and valve checks. You can find the details of these jobs in our article fan coil maintenance: filter, coil and drain. At YOİ Mühendislik, during fan coil maintenance, we measure airflow and pressure on sample units before a filter class change and share the result in a report.
Frequently asked questions
Can a nanofiber filter be washed?
It depends on the product. Some nanofiber filters are not suitable for washing, and washing can damage the fine fiber layer; the manufacturer's instructions should be followed.
Does fitting a finer filter in a fan coil strain the unit?
A filter with high pressure drop reduces airflow and lowers capacity. If the filter is chosen to suit the fan coil's fan curve and with low pressure drop, this effect stays limited.
How much energy does a nanofiber filter save?
It would not be right to give a definite figure. The gain depends on the fan type, the existing filter, the dust load of the environment and the maintenance frequency; the most accurate result is seen by measuring before and after the change.
How often should a fan coil filter be checked?
It varies with the environment, but checking every 1–3 months is recommended in heavily used areas. In dusty environments and in hospitals, more frequent checks may be needed.
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Detailed guide: Fan coil maintenance: intervals, checklist and maintenance form