Fan coil units
www.heatingandventilating.net Winds of change
Fan coil units remain some of the most popular air conditioning systems available. However, says Tim Mitchell, sales and marketing director of Klima-Therm, to maintain their popularity, these ubiquitous units have had to embrace significant technological changes
F
an coil units (FCUs) are well-established, well- liked terminal systems for controlling room temperatures because they are relatively
simple and have a reputation for consistent and dependable performance. In addition, if the base design is done right,
FCUs are flexible in terms of air change rates and alterations in office layouts. Moreover, because they can be positioned in a false ceiling, there is plenty of latitude in terms of where you can place the partitioning and this appeals to property developers who want to offer space flexibility. Fan coils can also deal with a wide range of
cooling and heating loads. For example, if you have a meeting room that must accommodate a sudden influx of people, a fan coil can respond quickly; not only is it perceived to be more responsive than the alternatives such as chilled beams, but they can also offer a broader operating range – a particularly important consideration in COVID-19 times, as office occupancies have become so unpredictable. But there’s a hitch. With a conventional constant
volume fan coil system, the motors always run at the same speed and the fan continues to operate at the design speed whether the room needs to be cooled, heated or is at the right temperature. This is an appalling waste of energy. The good news, however, is that it does not have to be this way. By employing variable speed fan
Preventing airborne transmission with FCUs
Accessories for FCUs such as filters, ultraviolet (UV) lighting and air purifying ionization technology, can help to alleviate the problems associated with the airborne transmission of bacteria and viruses.
High-efficiency particulate air
(HEPA) filters comprise a mat of very fine fibres, typically glass fibre. These filters can stop viruses and bacteria. However, because they have a higher resistance to air passing through than regular
air filters, upgrading a ventilation system to HEPA filters necessitates a review of the fan and motor capabilities, noise limits and energy efficiency limitations. Using UV light to kill micro-organisms can also be problematic. Dan Arnold, who works for UV Light
Technology, a company that provides disinfecting equipment, told the BBC that only one type of UV can reliably deactivate Covid-19, for example – and it’s dangerous if misapplied. “You would literally be frying people,” he said. Arguably, a more practical method of purifying the air – and one that can easily be retrofitted to a typical HVAC system – is bipolar ionization.
motors, it is possible to control the FCU fan speed to closely match demand or occupancy. This must be combined with diffusers that can handle the varying supply volumes without creating drafts, e.g. high induction swirl diffusers. When done properly, energy consumption can be reduced dramatically, especially with modern electronically commutated (EC) fan motors. A speed reduction of just 20%, for example, can
effectively halve the energy usage from the fan motor, significantly reducing operational carbon emissions. Variable speed fan motors, therefore, are perhaps the most important money-saving and, arguably, planet-saving development in the sphere of FCU design. But it’s not the only one. Combining high efficiency heat recovery and filtration with the ability to further heat or cool using integral heat pumps, delivers year-round comfort in areas not served by other central plant. Integral controls make fan coils especially simple
to install and heat recovery ensures that they are even more energy efficient. Meanwhile, heat recovery (HR) units decrease heat loss in systems that bring in external air. They
22 February 2022
do this by ensuring that heat from internal air is transferred to the fresh air brought in from outside. In other words, with HR technology, the exhaust air is used to pre-heat or pre-cool the incoming fresh air supply without the two air streams mingling. This enables the recovery of up to 90% of the heat that would otherwise be ejected from the building. FCUs come in three main types:
• Exposed units – where the units remain visible. These are typically slim, low height ‘designer’ elements, installed as hi-wall or low-wall units. • Concealed/chassis/ducted units – suited to applications where the units are hidden in ceiling, floor, or service voids, built into wall cavities, or hidden behind wardrobes or airing cupboards. • Cassette – combining the fan coil unit with the air distribution function, like a VRF cassette, such that no extra ductwork is necessarily required, these units are for applications where installation space is limited or where simplicity is paramount. All types come in horizontal and vertical versions, with integral controls and, nowadays, electronically commutated (EC) variable speed motors to further boost efficiency.
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