Market Warms to Chilled Beams
May 3, 2010
For many years, chilled beam systems have provided space conditioning to buildings throughout Europe and Australia, but the technology has been slow to catch on in the United States. Given the move to everything green that may soon change as chilled beams have many compelling benefits, according to the Environmental Protection Agency (EPA). These benefits include high cooling capacities, excellent performance, and dramatic energy savings for little or no additional costs over conventional systems.
Most mechanical contractors in the United States are not yet familiar with chilled beam technology, so there will be a learning curve involved when initially designing and constructing these systems. However, contractors who spend the time educating themselves about chilled beams now will likely be rewarded, especially as more owners explore this energy saving technology for their buildings.
CHILLED BEAM BENEFITSSerious energy savings due to reduced fan horsepower is the primary advantage to using chilled beam systems, said Mark Ford, product manager, Carrier Commercial Applied Products. “The volume of air that the air-handling units are required to move is greatly reduced compared to an all air system. Since the sensible loads are handled by the cooling coil at the beam, the air-handling unit only has to move enough air to meet the ventilation requirements. The pressure of the delivered air is relatively low, thus resulting in a quiet operation.”
Indeed, quiet operation is one of the advantages of using chilled beam systems, as they make little or no noise, which makes them a perfect fit in auditoriums, theaters, and classrooms. An additional benefit of the technology results from the constant volume air distribution, said Ford.
“The ventilation air is delivered at a constant volume; therefore, air circulation and direction is always the same, as opposed to the minimum and maximum air variations in a VAV system. The water temperature delivered to the beams is higher than traditional systems, so there could also be energy savings at the chiller or from water-side economizing.”
A reduction in duct size compared with conventional VAV systems is yet another benefit to using chilled beam technology, said Vladimir M. Petrovic, founder - Dadanco; vice president - Dadanco-Mestek JV. “This enables construction costs to be reduced significantly as floor-to-floor space can be reduced by up to 1.5 to 3 feet. On a multi-story building, costs savings are significant. In addition, chilled beams require minimal maintenance.”
While the advantages to using chilled beam technology are many, there are also a few disadvantages, including the need for chilled water to be piped to each and every unit, noted Petrovic. In addition, “The perception of condensation is also present, but a thorough engineering design approach and solution easily resolves this issue fairly early in the design stage. In my opinion, the biggest disadvantage is that the system is fairly new in the United States, and it usually takes more than five years to have a reasonable number of case studies in place in order for the system to become more popular.”
Even though chilled beam systems can be used in both new and retrofit construction, they may not be suitable for certain applications, added Ford, especially if the latent to sensible load ratio is very high, such as in a locker room. “Additionally, areas that have untreated air infiltrations, such as vestibules or a retrofit building that is not sealed well, would not be good applications.”
HOW THEY WORKA chilled beam system is made up of three primary components: the beams, which are located in the space; a central air source, which pre-treats outside air; and a chilled water loop, which supplies water to the beams. The general differentiation of a chilled beam system compared to others is that the ventilation air is decoupled from the sensible cooling, explained Ford.
“One hundred percent outside air is treated at the central air-handling unit and delivered to the beams to provide both ventilation and latent load requirements in the zone. The ducted air is delivered to the beam under a small amount of pressure and is discharged along the length of the beam through small openings or nozzles. The movement of this supply air causes room air to get induced through a heat exchange coil and then mixed with the supply air to get discharged into the room.”
A thermostat opens and closes a water valve connected to the beam to supply the cool water as necessary to meet the dry bulb set point, said Ford. If the zone rises above the set point, the thermostat opens the valve. One thermostat and one valve can be applied to each beam, or one valve can control a number of beams piped in parallel, as would be typical in a cubicle office space.
The water temperature to the beams is higher than that used in a traditional VAV system, and typically should be a degree or two higher than the dew point, noted Ford. “The chilled beam water loop is either separate or secondary to the water being supplied to the dedicated outside air unit or other HVAC equipment that may be in the building,” added Ford. “The secondary water loop may have its own dedicated chiller or be conditioned with a three-way mixing valve or heat exchanger from the primary water loop.”
There are two different types of chilled beam systems, explained Petrovic - active and passive. A passive chilled beam does not have fresh air supplied to it, and it is essentially just a cooling coil located in the ceiling. It requires a separate air distribution system to supply fresh air to each of the rooms. Active chilled beams incorporate nozzles, which deliver fresh air into each of the units. “Assuming there is minimal fresh air delivery to the space, both active and passive beams will be equally effective. If comparing energy efficiency as well as the amount of comfort delivered, active chilled beams would be more beneficial as well as more cost effective.”
Another difference between active and passive chilled beams is that active chilled beams can also provide heat through the use of a four-pipe unit and a heating coil. Similar to the cooling side, milder hot water temperatures - typically less than 120°F - should be used in the heating coil, noted Ford. Heating with passive beams is not possible and would require a separate heating system.
Each chilled beam can be controlled individually, however, for economic reasons they can be connected to cover exactly the same floor areas as VAV systems (approximately 1,000 square feet per control point), said Petrovic. “Additional control sensors may be required for dew point temperature, so the system can ‘understand’ if the room conditions approach a temperature that may cause condensation on the chilled beams.”
Chilled beam systems are typically connected to a dedicated outside air source, so the amount of outside air being delivered to the zone can be easily controlled.
“The outside air is preconditioned by the dedicated air-handling unit to account for all latent loads; thus humidity is controlled even at part loads,” said Ford. “Since the preconditioned air supply is constant and part loads are met by shutting off the water valve, the space humidity is always being treated by the supply air even if there is very little sensible load.”
EMBRACING NEW TECHNOLOGYGiven their recent introduction to the U.S. market and the relatively small number of systems currently being installed, the first cost of chilled beams can be up to 15 percent more than a conventional system. However, as engineers become more familiar with the systems, the designs will become more cost effective; that, combined with increased sales volume, will lead to the decline of first costs.
First cost should only be part of the consideration, though, said Petrovic, as overall construction costs can be significantly reduced if chilled beams are taken into consideration when designing a building. That’s because a building using chilled beams can utilize smaller ducts and risers, as well as smaller air-handling units, which could result in a reduction of building height due to less room needed for ductwork.
“I have been involved in buildings where we have been able to reduce the building height, which reduces the heating and cooling loads, which in turn reduces the size of the HVAC equipment,” said Petrovic. “In addition, the size of the vertical infrastructure is reduced, creating a smaller hole in the ground, as well as significantly reducing the area of the façade. All of this, when deployed at the early stage, basically offsets the overall cost of air conditioning. This is how the construction industry in the U.S. will get a new lease on life.”
Ford agreed that the future is very bright for chilled beam systems in the United States, thanks to the potential energy savings this technology can provide. “Projects that plan to obtain Leadership in Energy and Environmental Design (LEED®) certification are looking at chilled beam systems with greater interest. It is just a matter of the different parties becoming familiar and comfortable with the technology for chilled beam usage to greatly increase.”
Contractors who learn about the technology now and become familiar with its benefits will be on the cutting edge of the green market, which is a good place to be these days.
Publication date: 05/03/2010