At last year’s Gulf Construction Conference Week, John Lightfoot of the UK-based Marstair Limited presented a paper on how the environmentally-friendly concept of active chilled beams – popular in Europe – can now be used to provide air-conditioning in the Middle East. Excerpts:

01 April 2004

With the Kyoto Treaty calling for means of reducing CO2 emissions in air-conditioning units, European manufacturers have been urged to consider developing new air-conditioning systems to meet the demands being pressed on them by building owners and legislation.

In the UK, it has led to a change in the country’s building regulations. To construct a building in the UK requires builders to ensure the design is such that it does not use more energy than prescribed by the regulations.
This has forced designers of building services to look at alternative methods of cooling buildings, especially very large commercial/office development where air-conditioning is essential to attract tenants.

Passive chilled beams
One system that is increasingly appealing to building owners and designers alike is the passive chilled beam concept, which originated in Scandinavia, where outside temperatures do not reach the levels they do in the Middle East.
Buildings that have large auditoriums with very high ceilings such as museums, theatres and stadiums are the most difficult to air-condition.
The Scandinavians came up with a very simple solution the passive chilled beam. It uses a very large diameter pipe around the area to be cooled at high level.
Water is then passed through this pipe at about 16 deg C and allowed a two deg C temperature rise upon its return to the chiller. The large surface area of the pipe provides a significant cooling effect and since the water temperature is maintained above the dew point of the room air, no condensation is caused.
This system has many advantages: it is very quiet and does not require the movement of large volumes of air around the building, which could otherwise consume a significant amount of energy and cause unnecessary noise.
In northern Europe, in particular, another significant advantage is that by simply passing the chilled water through an outside coil, with ambient air being blown over it, a very energy-efficient method of heat rejection is produced. The energy savings of this method of cooling are obviously significant when compared to those of cooling by using a refrigeration circuit.
When ambient temperatures rise to the extent that little or no cooling can take place, the water is diverted and cooled by chillers.
In Northern Europe a significant percentage of the operational year will require only the free cooling to take place. In the Middle East one would not gain much benefit from free cooling, but considerable benefit could still be achieved from the higher coefficient of performance due to the relatively high chilled water temperature of 16 deg C.
There is however one drawback to this system – if the surface of the beam is 16 deg C and the temperature and humidity rises to a point where the air’s dew point becomes 16 deg C, water vapour will start to condense on the surface of the beam.
In Northern Europe this is likely to happen on so few occasions that with careful design, the risk can be considered worthwhile.
If this should occur, the chilled water temperature is simply increased until it is above the dew point of the air. In effect this means that just when the building’s occupants need increased cooling the system actually starts to reduce the cooling capacity.
However, the benefits offered by the system in terms of reduced energy costs, lack of noise and lack of complaints due to cold drafts far outweighs this disadvantage.
Given the significant energy savings designers began to look for methods of introducing this type of system into a commercial office environment. Clearly having large diameter pipes running around in areas with restricted height would not be appropriate.

Active chilled beams
The next development therefore was to utilise horizontal coils, much like those used in fan coils, although normally with much larger fin spacing and between two and three metres long, positioned at high level.
The coil is positioned parallel to the floor allowing the warm room air to rise and pass over the cooling coil.
The fresh air is ducted above the coil and discharged through a series of nozzles. The air jet from these nozzles causes a negative pressure to be formed just above the cooling coil inducing the warm room air through the coil, causing the air to cool and then mix with the fresh air before being passed back into the conditioned space.
Given that building regulations in several European states call for the provision of ventilated fresh air to areas where natural ventilation is not possible, the energy used to distribute the fresh air would in any case have to be consumed, thus this system manages to provide cooling with the minimum of energy required.
This system therefore has considerable advantages over many other air-conditioning systems. To illustrate this advantage the system can be compared to say a fan coil system.
Starting with the main disadvantage of chilled beams:

• Capital costs – active chilled beams, which tend to be between two and three metres long, are larger than the equivalent fan coil and therefore tend to be more expensive per kW, (or Btu) than fan coils.

The advantages:

• Installation costs can be less – whilst the active chilled beams are larger and therefore take more time to install, they do not require wired adjacent electrical spurs to be installed.
• They do not require ductwork and diffusers to be supplied and fitted and their cost can also be offset by the fact that the fresh air diffusers do not need to be supplied or fitted;
• The capital cost of the chillers will normally be less with a chilled beam system compared to a fan coil system. A smaller chiller is required to cool the water to 16 deg C rather than 5 deg C, thus lowering the capital costs;
• The running cost is considerably less, no local terminal consumption (that is, the fan motor in the fan coil) reduced energy requirements because of the higher coefficient of performance from the chiller and reduced energy requirements because of the option of free cooling (using the ambient air to chill the water);
• The service costs are also considerably cheaper;
• No filters to clean every four to eight weeks; and
• No moving parts, therefore minimal servicing.

Because of the cheaper lifetime costs, better air distribution, and lower sound levels, the popularity of these systems have increased considerably especially in high specification buildings.

Multi-service chilled beams
The development of the active chilled beam did not stop there. Lights, fire sprinklers, smoke alarms, and lighting can all be incorporated into the beam. This enables all the components of a multi-service active beam to be incorporated in a factory where it is far easier to maintain and test to high standards, compared to trying to carry out the same tests to the same standards on site.
This type of beam is also used to great effect in refurbishments where headroom is such that false ceilings are not possible.

Active chilled beams cassette
Now probably for the first time since their introduction, active chilled beams can be applied to warmer climates, thanks to an innovation by a UK-based company – Marstair.
Early this year, Marstair launched the Active Chilled Beam Cassette that will allow builders to adapt the chilled building systems in the hotter climes of the Middle East by incorporating an innovative solution to the problem of condensate that would have otherwise have been difficult to deal with. 
The product combines many of the advantages of the fan coil and the active chilled beam. As seen in the diagram 1, the warm air rises from the room into the body of the unit, the fresh air is feed into a plenum at the top of the unit, which is designed to equalise the pressure within the plenum so that each nozzle delivers the same air volume at strategic positions around the coil.
This air jet causes a negative pressure on the outside face of the coil causing room air to be induced through the cooling coil and mixing with the treated fresh air. This product also has the advantage of only being 600 mm square, which enables it to be easily accommodated by the architect within the ceiling grid.
The most important difference, however, especially for warmer climates, is the presence of a condensate-removal drain, meaning for the first time that chilled beam technology can be applied in hot and humid climates to provide a better energy and environmental air conditioning solution.
* Gulf Construction Conference Week’s Annual Heating, Ventilation and Air-Conditioning Conference will be held this year in Dubai during November 23 and 24. The Conference Week extends from November 20 to 25.

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