Developed in Norway in the mid-1970s, chilled-beam systems have been used effectively in Europe for more than 30 years in the construction and renovation industries. They’ve also been appearing more frequently in U.S. applications as an alternative to conventional variable-air-volume systems. There are two different types of chilled-beam systems: passive and active. Each system has a cooling coil, and supplies cooling by means of circulating cool water through the coils and inducing room air across the cooled coils. But that’s where the similarities end.
A passive system runs above the ceiling and goes to individual beams that are either 2 feet by 4 feet or 2 feet by 6 feet in length. Inside the beam unit, there’s a series of fins or coils that look similar to a radiator. Chilled water runs through the beam units so that when the cold surfaces come into contact with the warm air, it creates cool air that falls while the warm air rises, therein removing heat from the room air by convection without the assistance of devices such as fans and pumps.
On the other hand, an active system relies on forced convection, which means that primary air is blown through the unit to induce air from the space up across the coils, resulting in a larger cooling capacity than you would see with a passive system. Whereas you may have needed many feet of beam coil for a passive system, an active system generally requires one to two square feet of active beam coil.
Active chilled-beam systems can either be recessed in the ceiling or out in the open, below the ceiling level. All moisture is taken out of the air at a central ventilation unit, and the primary airflow helps deliver required amounts of outdoor air to ventilated space.
“People don’t often make the distinction between passive and active chilled-beam systems when talking about this subject, but they mean active chilled beams,” says Peter Rumsey, managing director at Integral Group in Oakland, Calif. “We are seeing a lot more installations of the active system today.”
A chilled-beam system can achieve relatively low sound levels, since there are no moving parts such as fans, compressors, or pumps to raise the noise level. “There’s a central air-handling unit that provides the primary air, but the induction of airflow at the chilled beam itself happens from a combination of the primary airflow and the induction of air across the chilled water coil,” explains John Swift Jr., a principal at Cannon Design in Boston. Another advantage is the energy savings, since large fans take more energy to run and therefore cost more than smaller fans. Floor-to-ceiling heights also can be reduced because chilled beams don’t require a boiler room or large ductwork.
“I think the biggest advantage is [that] you can make your mechanical equipment much smaller because you aren’t pushing big volumes of air around the building to cool the space,” explains Jonathan Baron, AIA, architect at Shepley Bulfinch in Boston. “Instead, you are distributing ventilation air. So it is smaller fans, smaller ductwork, and smaller mechanical units.”
Considerations and Challenges
Even in hot and humid climates, a chilled-beam system can work effectively if some concerns are addressed. “As long as you pretreat the outside air before you deliver it to the space, the chilled-beam system is still a good system,” Swift says. More challenging environments for the systems include buildings with center atriums and operable windows, data centers that generate a high level of energy, and retail structures where customers are constantly going in and out. In addition, a building needs to have a tight envelope in order to be able to handle the right humidity-level requirements.
As for new versus existing structures, are there any winners or losers? “Buildings can be retrofitted if there is a full change out of the HVAC,” Rumsey says. “One of the most significant chilled-beam projects in this country is an office building in Washington, D.C., that occupies 1 million square feet. And it’s a renovation.”
Condensation can be a major problem for buildings that use chilled beams. “Humid air can condense on cold water pipes,” Baron says. “But a fail-safe sensor can be installed into the system to stop the water flow in the pipes if humidity rises too high.” The system is reactivated once the humidity drops to normal levels.
Chilled beams take care of heating and cooling requirements so that large air handlers on the roof can be replaced with smaller ventilation air handlers that are typically 75 percent smaller than standard air-conditioning units. Other considerations include integrated sprinkler heads and lighting. As Rumsey explains, using the chilled-beam system has no apparent impact on the lighting, fire-protection, or sprinkler system. In fact, the compact systems afford more room in ceiling cavities for easier distribution of sprinkler pipes and allow most of the ceiling to remain free for lighting solutions.
With any innovative system there are challenges for clients, manufacturers, and for those who will have to work with them. Swift says that the lack of knowledge about how a chilled-beam system operates is the biggest challenge that he and his company face. He says the first concern the client is likely to bring up is condensation, but he notes that there is no condensation when properly applied. “Then, sometimes the client thinks it will be more expensive, but the installed cost is the same if you make sure the chilled-beam system is designed and installed correctly,” Swift says.
Baron agrees, and points out similar difficulties when working with subcontractors who are unfamiliar with the technology, as well as manufacturers. “Since it’s a fairly new system, manufacturers want to start out with a small product line as they’re not sure what will sell,” Baron says. “On one project, it took months to iron out the programming, but this client was committed to energy savings. We did the work that was necessary to get the kinks out.”
Structures that would be suitable to employ chilled-beam systems include classrooms, laboratories, schools, and universities because the systems allow a space’s ventilation system to be decoupled from the equipment that handles cooling loads. Rumsey has several projects in the works that incorporate chilled beams. One is a 175,000-square-foot building with classrooms and a teaching lab at California Polytechnic State University in San Luis Obispo. Another is two 500,000-square-foot buildings for Infosys, a software company in India.
Baron says that one of his company’s current projects is evolving at Princeton University in New Jersey where Shepley Bulfinch is working on the Firestone Library, a 420,000-square-foot existing structure. “We are using chilled beams throughout the library with a very aggressive energy target as part of a strategy to reduce energy use in the existing building by half.” Installed in one temporary, 2,000-square-foot space and a small stack area, the chilled beams are performing well and the administration has been pleased with the product.
In a library, there may be concerns about condensation dripping onto the books below, however that should not be an issue if the proper precautions are taken. “We need to make sure that everything is working together, like temperature sensors, the dew point, [temperature at which the air becomes saturated], and humidity sensors,” Baron says. “If the temperature is too close to the dew point, it turns the system off so the cold water isn’t running through the pipes.”
The lesson: To establish if chilled beams are the right system for the job, architects, designers, and engineers must understand the payback and challenges of a particular project. With an increased awareness and growing enthusiasm, chilled-beam systems are here to stay.
Judith A. Stock writes about design, green building, and remodeling from Los Angeles.