Air conditioning Fan coils/chilled beams
satisfied with them that they are becoming the system of choice for the right reasons – they are a high-quality, energy-efficient system.’ For Lees, it is a mistake to look at the design only
in terms of the terminal devices: ‘You cannot make a poor-quality building energy-efficient by simply adding chilled beams – these are one of the components in an energy-efficient building, but they are not what make it an energy-efficient building.’ Linden Shuttleworth, UK sales manager – Flakt
Water-based cooling using chilled beams provides a more energy- efficient solution, says Halton Products
> And Chris Pinn, national sales manager of Dunham-
Bush, adds: ‘With the market going through a “lick and stick” phase due to current uncertainty, fan coils are still pushing forward within the refurbishment sector. I do, though, see the chilled beam market picking up when the new Part L comes in and the SFP [specific fan power] and carbon emission reductions take effect.’ Ian Lees, sales director of Krantz Systems UK, agrees
that fan coils are putting up a brave fight: ‘Consultants that have used fan coils before without problems are likely to use them again. However, you also get consultants who are keen to use the next new thing and enough people have used chilled beams and been
System Products, sees a boost in refurbishment in the coming two years: ‘And, with the needs of lower energy targets with the European Energy Performance of Buildings Directive in mind, both fan coil unit and chilled beam systems will go into “demand controlled ventilation” designs, with sensors within the space varying air volume from the main plant for chilled beams and from the room fans in fan coil units.’ Many consultants, he says, have accepted the need
for ‘load lopping’ or ‘peak clipping’, whereby they ‘stop adding in their traditional 10% safety margins and not designing on ridiculously high ambient temperatures of 35 deg C’. On top of this, he adds, clients are demanding lower
cooling loads on the system by tracking the internal and external temperatures and using ‘load shifting’ (saving cooling energy by cooling storage with exposed masses and night time cooling). As a result, ‘chilled beam use will increase as the running costs on the fans and chillers fall significantly’. l
Pros and cons of the two systems The most
significant issue in the short term is the change of fan coil specific fan power under the 2010 version of Part L – Ian Thomas
50 CIBSE Journal July 2010
Chilled beams A chilled beam is a building cooling device that circulates air using the principles of natural heat convection. Typically mounted overhead near or within a ceiling, the beam is a type of radiator, chilled by an external source such as recirculated water. It cools the space below it by acting as a heat sink for the naturally rising warm air of the space. Once cooled, the air naturally drops back to the floor where the cycle begins again. Advantages • Typically more energy efficient than fan coil units • Quieter because they have no moving parts • Require little maintenance • No need for condensate drainage pump and pipework Disadvantages • Requires a good external structure to the building to maintain effective humidity control
• Chilled beams are generally unsuitable for ceilings higher than 4.5m
• They respond relatively slowly to varying cooling loads Cooling capacity • Chilled beams assisted with displacement ventilation: 70 to 120 W/sq m; active chilled beams: 120 W/sq m
Fan coil units A fan coil unit is placed at each place which needs to be heated or cooled. A central plant delivers hot or cold water to fan coil units. The fan draws air from the room, blows it over the water coil and returns it to the room. Dehumidified air from a central plant or fresh air from outside may also be used by a fan coil system Advantages • Building zones can be individually controlled, allowing unoccupied areas to be isolated and shut down
• Central equipment may be sized smaller by taking advantage of building heating and cooling diversity
• Electrical wiring and water pipes are simpler to install than ducts, making retrofitting easier
• Fan coil units do not require humidity control Disadvantages • Require more maintenance than chilled beam systems • Condensate must be drained from each individual unit • Noisier and require more maintenance than chilled beams
• Typically require more complex control systems Cooling capacity • This can range between 3kW and 14kW
Sources: Pros and cons – contributing companies. System descriptions – CIBSE. For more detailed information, see CIBSE Guide B, Heating Ventilation Air Conditioning and Refrigeration, available from
www.cibse.org/bookshop
www.cibsejournal.com
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