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FRENGER Systems - Chilled Beam Cooling & Heating Effects

Thermal Comfort - Passive Beam - Fan Coil Units - 'Coanda' Effect

Thermal Comfort Principles

How we experience the thermal indoor climate depends primarily on our overall heat exchange with the surroundings. A person's thermal comfort is affected by the following:

  • air temperature
  • air velocity
  • radiant temperature
  • activity
  • relative humidity
  • clothing

Thermal comfort is realised when a person feels in thermal balance, i.e. they are neither too hot nor too cold. In addition, there should be no unwanted heating or cooling of individual exposed body areas (draughts around the neck or the ankles). We primarily exchange heat to our surroundings via ‘Convection’ and ‘Radiation’.

These two methods of transferring heat are approximately equal with normal air movement in a room. Therefore, we are affected just as much by the room’s surface temperatures as we are by the air temperature.

If the temperature of the room’s surface is decreased, fully or in part, the air temperature can be increased by an amount corresponding to the decrease in the room surface’s mean temperature. Therefore, when we cool an environment with a radiant cooling device, the desired operative temperature can be slightly higher. Visa versa when we heat an environment with a radiant heating device, the desired operative temperature can be slightly lower thus energy savings are available.

Thermal Comfort is also affected by the velocity and temperature of any air movement within the space. As a rule of thumb when cooling an indoor environment with a room temperature of 24°C, the air movement within the space should not exceed 0.25 m/s. Excessive air speeds cause (draughts) discomfort which is measured by the Percentage People Dissatisfied (‘PPD’). The European standard for such matters is BS EN ISO 7730 the “Ergonomies of the indoor Environment”.

Frenger always design and selects its product solutions with Thermal Comfort as a fundamental starting position before meeting the required cooling and / or heating loads of the indoor environment. Some companies just design / select their products to meet the cooling and / or heating loads with little regard for thermal comfort which can lead to occupancy complaints even though the environment may be at the design temperature. Usually this is due to high air velocities below the cooling device ‘if passive’ or in-between cooling devices ‘if active’.

Frenger avoid such situations of high air velocities for passive chilled beam solutions by having 40% of their cooling by ‘Radiant’ absorption and the remaining 60% by convection (“X-Wing”). The radiant quotation provides cooling without any air movement, hence the total cooling air movement is approximately 35% lower air velocities than that of a convective only passive chilled beam (fin coil batteries are 95% convective). Also, Frenger limit their total cooing capacities to 315 watts / linear meter for ‘Radiant’ passive chilled beams and 200 watts / linear meter if convective only fin coil battery element, both of which when concealed behind a perforated metal fascia and / or ceiling.

Frenger avoid such situations for high air velocities for active chilled beam solutions by limiting the supply air discharge to not exceed 23 ltrs / sec / meter for a two way discharge unit and through patented registered designs to create “Coanda” effect within the casing of the product by means of a smooth (non faceted) discharge curve and air management discharge veins ‘AMDM’ mounted within the air chamber at the point of discharge for a short fan shaped distribution pattern.

This short fan shaped distribution with “Coanda” effect is particularly useful when two or more active beams are positioned closer together than 3m centres with supply air at the upper limits, as without such product features care must be taken to avoid converging air streams / turbulence intensity.

Frenger take thermal comfort so seriously they have invested millions of pounds in their UK Technical Facility (Pride Park, Derby) to equip themselves with 3 x Climatic Test Laboratories, 2 x Photometric lighting labs and 1 x Acoustic sound laboratory to not only enable their R&D (research and development) to be one step ahead of the competition but also to extensively test all disciplines (heating, cooling, lighting and sound) of what products they develop and in-house manufacture. Furthermore, Frenger also gain secondary validation by using independent laboratories for each discipline periodically. All of Frenger’s Chilled Beam product performance have also been independently tested and “Accredited” by the EuroVent Certification Scheme.

Frenger Passive Beam Features

40% Radiant Absorption / 60% Convective Passive System.
Can be concealed behind micro perforated ceiling systems or within an MSCB or fully exposed.
Requires minimal control.
75 W/m² – 135 W/m² cooling capacity when concealed behind a ceiling or up to 315 W/linear meter as part of an MSCB.

Frenger Active Beam Features

Fresh air introduced via the fascia / underplate.
Room air induced through fin coil cooling batteries.
High cooling capacity of up to 1000 W/m. Heating capacity 500 W/m.
Can integrate lighting and other services including controls within an architectural metal casing “MSCB” (Multiservice Chilled Beam).

Running Cost / Energy Use – Chilled Beams

There are several aspects of an active chilled beam system that promotes a more energy efficient operation than air based systems such as fan coil units and VAV. Typically, the chilled water is distributed to the chilled beams at 14-17ºC to minimise the risk of condensation, whereas fan coil units operate typically at 6-12ºC. Elevated chilled water temperatures offer two principal benefits in terms of energy efficiency:

By operating the chiller plant at elevated temperatures its co-efficient of performance (COP) is increased and energy consumption reduced. The efficiency of the compressor can be increased by using a dry cooling system (inlet water 14ºC instead of 7ºC) with a percentage increase in COP of typically 22%.

Elevated temperatures enable a significant increase in the opportunity to avail free cooling from sources such as outdoor air or ground water heat sinks. That is an annual increase from 800 hours to 2000 hours for a 12 hour day and 2100 to 5200 hours for 24 hour operation.

Fan coil unit and VAV systems rely on a fan assisted cooling distribution; that is each fan coil unit incorporates a fan. Chilled beam systems utilise a centralised fan that can be sized to deliver the amount of air to meet respiratory requirements (not additional air to compensate for cooling loads); with a consequent reduction in capital cost, electricity consumption and maintenance cost.

Maintenance Costs – Chilled Beams Vs. Fan Coil Units

There are no moving parts in chilled beams and therefore maintenance requirements are very low. An active chilled beam will require the cleaning of the batteries – using a vacuum cleaner and brush attachment – at intervals of 3-4 years by simply wiping the surfaces with a damp cloth. The chilled beam itself requires no further maintenance and can be expected to last the life of the building; however water quality must be appropriate and associated control valves and flexible hoses will require frequent inspection / replacement.

The maintenance and replacement cost is taken from REHVA’s Chilled Beam Application Guidebook issued 2005.

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Thermal Comfort

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Frenger Systems Limited
Riverside Road
Pride Park
Derby
Derbyshire
DE24 8HY

Frenger Systems Limited is an FTF Group Company

Email Frenger Systems

Tel: 01332 295678
Fax: 01332 381054

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