There are a few important things to remember when using a chilled beam system in a building. For removing heat with chilled water, the water only removes sensible (dry) heat. This is primarily generated by lights, computers, electronics, etc. Fresh, and dry, air must still be supplied to the room to compensate for the latent (wet) heat gains and in order to supply fresh air to a room. Latent heat is generated by things like people and, in some regions, outside air directly entering a space. Condensation will occur on the beam if the dew point of a room rises beyond that of temperature of the water being supplied to the chilled beam. The water entering the chilled beam must be approximately 1 degree Fahrenheit above the dew point of the room. [2]. However, unlike where VAV systems require the air to be cool to around the mid 40s degrees Fahrenheit, the water in a chilled beam system only needs to be cooled to around the mid to upper 50s degrees Fahrenheit. This difference requires significant less energy. It also makes resources, like geothermal cooling, the use of water reservoirs, etc., viable options for cooling a modern commercial building. Reduced energy chillers are also viable, and are currently being used, as a solution in conjunction with chilled beams.
Types of Chilled Beams
Chilled ceilings were the original chilled beam system. They came out in the European market in the late 1970s. They work by a means of convection heat transfer, and induce air movement in the room of which they are placed in. Chilled ceiling have a very low profile. Their sensible cooling capacity is approximately 24 BTU per square foot of beam. Chilled ceilings lack the ability to control the humidity of a room and must be paired with a ventilation system [3]. Their low cooling capacity has kept them out of the Unites States (US) market. They are the most energy efficient of all three systems.
Passive beams are the second generation of chilled beams. They have an increased cooling and heating capacity, and they are the first to use a pipe surround by a coil in order to form a radiator system. Primarily they are used in conjunction with an under floor air distribution system. They are an extremely effective method of taking care of the solar heat load of a building and aforementioned sensible heat loads. Their cooling capacity is approximately 400 BTU per linear foot of beam. However, as with the chilled ceiling, they too have no method for maintaining the humidity of room, and must be paired with a ventilation system in order to maintain latent heat gains .
Active chilled beams came into the HVAC scene in the early 1990s. The third generation of chilled beams, they are the first in the series to offer a system of taking care of both the sensible and latent heat gains of a room in a single package. Like the generations before, they work by bringing chilled water into the room. The novel aspect of these beams is they couple with a ventilation system. An active chilled beam blows fresh air over the coil. This allows for the fresh air and the cooling to be taken care of at the same time. While the room still requires return air ducts, and the ventilation must be hooked up to the beam, all HVAC requirements can be handled in a single unit [5]. Active chilled beams can do approximately 600 BTU per linear foot of beam. Also, because they use forced air induction, active beams can heat as well as cool a room.
First brought to market by Trox in 1996, the next generation of chilled beam is the multiservice chilled beam. Either a passive or active chilled beam can be made into a multiservice chilled beam. A multiservice beam seeks to combine building operations into one unit. These beams can contain lighting fixed, sprinkler systems, smoke detectors, security sensors, motion detectors, intercoms, power distribution centers, fiber optic distribution centers, and much more. While over 10 years old in Europe, this system is new to the United States market. In both markets the demand for these systems has grown considerably .
Next Generation
Multiservice chilled beams can also offer some unexpected bonuses. That is, multiservice chilled beams can offer a decreased building construction time. By bundling basic building services, i.e. lighting, sprinklers, communication cables, etc, the contractor only has to install one unit instead of multiple items. In past jobs, contractors have typically found a decrease of 25% installation time of the bundled building components. On top of this, because multiservice chilled beams bundle all these different services they can reduce the ceiling space required for a floor. In fact, they can lower the space required between slabs by so much that in some cases building developers have been able to gain an extra floor for every 4 stories of a building [7]. That is to say, maintaining a ceiling height of 9' 6", five floors can be built at the same height of a standard four story building. This has been a considerable return on investment for buildings in areas with height restrictions, such as Washington, D.C. or Charleston, SC.
Current Applications
The use of chilled beam systems has been primarily in the commercial arena (e.g., office space, laboratories, schools, and a few applications in hotels). The residential market is a hard adaption for chilled beams. This is because of the level of humidity control required. In certain regions, if a window is left open in proximity to a chilled beam, condensation can form on the coil. Some example of Chilled Beams in operation include London Heathrow Terminal 5 and The Constitution Center, Washington D.C. [9]. According to BSEE, we can continue to see a rocketing sale of chilled beams long into the future .
The move away from VAV, variable air volume, systems to chilled beams is a fundamental shift in building construction. This shift is taking place under a perfect storm of pressure coming from rising energy costs, increase legislation pushing green building, consumer demand for cost saving space and LEED construction, and just a general focus on concern for the environment.
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