Chiller action

zoom

zoom

The function and mode of operation of a passive chilled beam system in an office.

With the demand for more energy efficient air conditioning systems rising, new technologies are entering the market. Thomas Michaelsen and Ian Leake outline the benefits of multi-service chilled beams.

When it comes to ensuring thermal comfort conditions in offices, conference rooms and meeting rooms as well as the best air quality possible, architects and specialist planners are provided with a wide range of ventilation and air conditioning systems to choose from. Among these, air-water systems are continuously growing in importance.

Chilled beams are particularly suitable for installation in new buildings and modernisation projects due to their compact design, the minimal investment and operating costs involved and their adaptability to the wishes of architects and building owners.

Passive or active systems?

First, a distinction can be made between the various designs and features of chilled beams in passive and active systems. The term passive means that the secondary air is cooled convectively ie it is unforced.

Active systems, on the other hand, use fans to bring pre-conditioned outside air into the room and cool the secondary air by means of induction. The induced air is guided through the chilled water coils in the beam.

For Middle East applications, passive chilled beams are unlikely to be suitable due to the high capacities needed. Active chilled beams should be considered for applications as these can take care of higher loads.

There are two fundamental differences between active and passive chilled beams. Firstly, active chilled beams are specifically used to induce a defined amount of conditioned outside air into the room.

Secondly, in active chilled beams the warm ambient air no longer flows into the beam from above as is the case in passive chilled beams. Rather, the warm air is absorbed into the beam through the bottom of the unit.

In a central ventilation device, filtered outside air is delivered as primary air to the active chilled beam via an air duct system. The primary air flows under high pressure into the chilled beam through a number of nozzles in the left and right air chambers.

The high velocity of this primary air results in negative pressure in the central chamber of the chilled beam, which ensures that warm ambient air is absorbed (induction) into the chilled beam through the bottom of the device (see figure 2, opposite).

This secondary air flows through the heat exchangers arranged on the left and right and is thereby cooled. The cool secondary air is subsequently mixed with the primary air, which is then discharged into the room with a direction of airflow that is nearly parallel to the ceiling.

As such, depending on the size of the nozzles chosen, the device has an induction ratio of approximately 1:4, which means that for every 1m3 of primary air, approximately 4m3 of ambient air is induced into and cooled within the chilled beam.

Because active chilled beams absorb secondary air from below, they can also be installed in suspended ceilings. This is particularly advantageous for modernisation and retrofit projects that already have suspended ceilings.

Chilled beams in application

Because of the effects described above, the use of active chilled beams can also establish a desired and stable room airflow that is significantly less sensitive to thermal disturbances in comparison to passive chilled beams.

The dimensions of an active chilled beam have a significant influence on its overall cooling capacity. The standard width of chilled beams ranges from 300 to 700mm, with an overall height of 120 to approximately 300mm.

Supply air volume flow rates ranging from 80 to 400m³/h per metre of beam length result in cooling capacities of up to 185W/m2 depending on the layout and spacing.

This also provides for adequate fresh air quantities to ensure a pleasant working environment.

To adjust the cooling capacity and the supply air volume flow rate to meet the current requirements in the room, two parameters control the performance of an active chilled beam:

• water-side control, which modifies the flow and temperature of the chilled water;

• air-side control, which modifies the volume of primary air. This in turn controls the amount of induced secondary air.

Chilled beams can be designed for a specific project and tailor-made to meet the needs of the building owner and architect.

There has been a noticeable trend towards multi-service chilled beams, the objective being to integrate functions such as lighting, sprinkler systems, electrical cabling, smoke detectors and presence detectors, along with ventilation and cooling functions.

Middle East application

While chilled beam technology is a relatively new concept in the Middle East, it has been successfully used for many years throughout the world, including countries that have aggressive climates with high temperatures and humidity.

A common concern is that of condensation occurrence and possible subsequent water damage. It should be remembered that the system is designed to run dry, as opposed to say a fan coil system, which is deliberately designed to run wet.

The design of a chilled beam system is such that several safeguards are built-in to ensure that condensation problems do not occur.

Print | Email | Discuss this article

| Share |

READERS' COMMENTS

Click here to post a comment

Add your Comment All posts are sent to the administrator for review and are published only after approval. ArabianBusiness.com reserves the right to remove any comment at any time for any reason. Please keep your responses appropriate and on topic. Arabian Business would like to point out that only comments relevant to the story will be published. Any containing personal insults or inappropriate language will not be approved.
Name *
Remember me on this computer
Email *	(Your email address will not be published)
City
Country
Subject *
Comment *
Notify me of further comments
Enter the words above *
Please click post only once - your comment will not be published immediately.

MORE FROM ARABIANBUSINESS.COM