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238214 Chilled Beams

By David P. Rebhuhn, PE (GA PE#32928), NCEES (#18079), CSI Member

Description  

Chilled beams are generally viewed as an alternative to a traditional, fan-driven, HVAC system. They are a convective cooling and/or heating device (2-pipe or 4-pipe) constructed of copper tubing and bonded to aluminum fins, housed in a sheet metal enclosure, and usually installed at ceiling level.  There are 3 variations:              

History

The application of chilled beam technology is relatively new in the United States, even though it has been applied in Europe and Australia for over 20 years. Today, chilled beams are one of the most common HVAC systems installed in Europe. It has only been within the last decade the technology has seen some application in North America. As of 2007, chilled beam HVAC systems were more widely used in Australia and Europe than in the United States. Acceptance in the USA has steadily been increasing since 2007.

Noteworthy Project Locations                                               

In Australia, the system was first used in "30 THE BOND", Sydney, which received a 5 Star Australian Building Greenhouse Rating benchmark, which is the approximate equivalent of a Gold LEED greenhouse certification level. Chilled beam HVAC systems have been used at London Heathrow Terminal 5 in England and the Constitution Center which is the largest private office building in Washington, D.C. The system has also been installed at Harvard Business School, Wellesley College, and the American headquarters of the pharmaceutical company AstraZeneca. The multiservice beam was first installed at the Barclaycard building in Northampton, England, and has since been installed in the headquarters of Lloyd's Register (London), Airbus UK (Bristol), and the Greater London Authority; Riverside House (London); Empress State Building (London); 55 Baker Street (London); and 101 New Cavendish Street (London).                                    

Advantages                                                                       

Disadvantages                                             

Suitable Applications                                        

These systems are better suited for projects where the HVAC system is primarily based on heating and sensible cooling space loads rather than ventilation loads. Buildings with a high heat gain from equipment, solar radiation, etc. are excellent candidates. If the ventilation system is so large that it could simultaneously handle the heating and cooling loads, then chilled beams probably are not a viable application. In spaces where thermal comfort is important, chilled beams can work well. Entrance lobbies would not be a good application. Specific examples of suitable installations include K-12 and post-secondary educational facilities, office buildings, LEED and Green buildings, data centers, television studios, and load driven laboratories.

A discussion of chilled beams would not be complete without mentioning the opportunity for their use in the retrofit of older, existing induction unit installations. Back in the 1950's and 1960's, induction units were used in large buildings where space was at a premium and the small primary air ductwork used with these systems was advantageous in reducing floor heights and mechanical space requirements. These units were usually mounted on the floor against an exterior wall, concealed under custom built enclosures. Induction units became very unpopular during the energy crisis of the 1970's because of their high inlet static pressure requirement which elevated the fan horsepower requirement. These units exhibited higher noise levels along with compromised air distribution patterns. Unit controls were based on pneumatics requiring a high level of maintenance while unable to produce acceptable levels of comfort and efficiencies as compared to present day DDC systems. A wholesale renovation of the existing HVAC system in these older buildings to a more traditional, fan-driven HVAC system may be cost prohibitive due to the existing low floor-to-floor heights, HVAC piping, and small, high velocity fresh air risers. It could be more cost effective to abandon the existing building in favor of new construction. Retrofitting the building with chilled beam technology rather than replacing the old induction units could be the solution to budget and improved comfort concerns. The existing infrastructure such as ductwork, HVAC piping, etc. could be reused in support of the retrofit to chilled beams.       

Installation Considerations                                       

Maintenance                                           

Applications in Hot Humid Climates                              

Passive chilled beams have limited application in hot and humid climates, although they can be used when needed to supplement the load requirement where an active beam falls short. Humidity becomes an issue if the surface temperature of any cooling coil or unit panel falls below the dew point of the surrounding air resulting in the formation of condensate. This is can be prevented by making sure the primary air supplied to the beam is dry and adequate to handle the space latent loads and will limit the indoor dew point temperature to below 55F. How dry this air must be will depend on the CFM and the space load. Chilled water supplied to the beam to handle space sensible loads, should be provided at temperatures above the local dew point to avoid the formation of condensate. Chilled water temperatures delivered at 58-60 F should keep the beam surface temperature above the local dew point. The physical shape of the beam may provide relief in situations where the surface may momentarily dip below the local dew point temperature. Moisture will begin to accumulate on the surface of the coil or panel. This is a very slow process and due to the size of the beam, there is a limited amount of condensate that can form. This can be prevented by sound design and implementation of the correct control strategy as follows:                      

Monitoring of the space temperature, dew point, moisture on CHWS piping, and outdoor conditions can be accomplished with traditional sensing devices available from major controls manufacturers. A variety of high-performance sensors are available when more demanding requirements are presented. These include impedance dew point sensors, chilled mirror sensors, and instrumentation utilizing dark spot optical hydrocarbon dew point detection.