An In-Depth Look at Active Chilled Beams

August 12, 2016 by Chris Drake

All local MEP offices have one thing in common, and that is the challenge of determining the best and most efficient way to cool buildings and save its future occupants from the intolerable Texas heat. Active chilled beams offer a unique solution to this challenge with the potential to make a significant impact on the way engineers go about cooling buildings in Texas.

BIG RED DOG’s MEP Office in Austin has designed various kinds of Heating, Ventilation, and Cooling (HVAC) systems for all sorts of buildings. From retail spaces to offices to industrial projects, our expertise gives us the resources to make the smartest decisions regarding air conditioning and heating systems. We utilize different kinds of HVAC technology such as variable refrigerant flow systems, conventional direct expansion systems, heat pumps, and variable air volume systems depending on what each particular project requires as well as our client’s priorities. One technology that has been on the rise in the United States is the active chilled beam system. In the past, it has been primarily used in Europe and Australia, but in recent years it has slowly started to gain popularity in the United States.

What is an active chilled beam?

The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) defines an active chilled beam as: “an air induction and diffusion device that introduces and conditions air for the purpose of temperature and/or humidity control. Primary air is delivered through a series of nozzles, which induces and conditions secondary air through a unit-mounted coil” (Sipes, et al., 2).

How does an active chilled beam work?

Active chilled beams consist of a heat exchanger housed in a casing that is typically installed in the ceiling. Though they vary in size, active chilled beams usually take the place of standard ceiling air diffusers. The system provides primary air through nozzles, which then induce warm air from the space up and through the cooling coils and into the space. The beam itself only provides sensible cooling, and the coil within the beam contains chilled water that is maintained a few degrees above the space dew point to prevent condensation. The amount of primary air is determined by the latent load and ventilation requirements of the space, and it is typically 100% pretreated outside air.

chilled beams

Active chilled beams are suitable for various types of spaces including, but not limited to, “offices, schools, labs, computer rooms, and low-ceiling height building retrofits” (Alexander and O’Rourke 51).

Advantages of Active Chilled Beams

Active chilled beams are not the HVAC solution for every building. However, it does offer numerous advantages when compared to other HVAC technologies such as variable-air-volume (VAV) systems.

Energy Savings

Active chilled beams typically require as little as “99 cfm/ton to 250 cfm/ton (13 L/s per kW to 33.6 L/s per kW) of sensible cooling as it relates to the volume of primary air delivered to the beam plenum for dehumidification…for an office type building, this could translate into a reduction in the amount of total air processed at the air-handling unit to between 25% to 50% of that which is required by an all-air system” (Alexander and O’Rourke 51). “Most of the energy for chilled beam systems is distributed by chilled (or heated) water carried to the beams” instead of expending energy moving solely air (Sachs and Lin). This helps dramatically reduce both air-handling system size as well as reheat energy, because there is almost no need to reheat like a VAV system does. The amount of 100% outside air primary air delivered is based solely on the amount of air required for ventilation and latent load. A typical VAV system delivers mixed air to each space, often requiring it to deliver more air than needed to a space so the fraction of outside air is sufficient to meet the ventilation requirements of the space. This results in reheat to avoid overcooling the space.

Relatively Low Sound Levels

Active chilled beams are able to achieve relatively low sound levels due to the fact that there are no fans or compressors located in or near the occupied space.

Option to Integrate Additional Services

Many manufacturers now also give clients the option to integrate various services such as “cabling; and conduits for power; voice and data services; openings for sprinklers, smoke detectors, and public address system speakers; lighting control sensors; and closed-circuit television cameras” directly into the chilled beams (Roth et al. 86).

Controllability

Another unique advantage of active chilled beams is the controllability they offer. Designing a system so that the active chilled beams in each room or space inside of a building is controlled by its own exclusive thermostat is very feasible. This space-by-space controllability provides a high level of controlled comfort to the user.

Well Suited for Low Above Ceiling Clearance

Active chilled beams are particularly well suited for buildings with low above ceiling clearance space. There is much less ductwork required for these systems because they only use the amount of pre-treated outside air required for ventilation, or to treat the space latent load inside the space.

Design Considerations of Active Chilled Beams

Breakdown of the Perceived Higher Cost

Due to the somewhat limited market penetration in the United States, not as many contractors have worked with chilled beams. Their unfamiliarity with the equipment could contribute to a higher installation cost. Contractors may be unfamiliar with the installation of the beams themselves, or the process for balancing the air and water to each beam in the system. The field-installation of piping and control valves in order to ensure the delivery of chilled water to the beams in every space also contributes to a higher installation cost.

Nevertheless, as stated in the advantages, above ceiling space requirements for active chilled beams are quite modest when compared to VAV, constant air volume (CAV), and fan coil systems. In new construction, active chilled beams usually offer a reduction in clearance above the ceiling. They “can reduce per-story building height by 0.33 ft. to more than 1.3 ft. (0.1 m to 0.4 m) and the size of air-handling systems by 20% to 30%” (Roth et al. 86). This translates to lower construction costs thanks to the reduction in floor-to-floor building heights as well as in the ductwork. It is also important to factor in reduced operational costs due to energy and maintenance savings. Once all aspects of life cycle cost are considered, it is often concluded that chilled beam system are very cost competitive with other systems.

Require Chilled Water & Humidity Control

Not only do active chilled beam systems require chilled water, but they must also keep the chilled water temperature in the beam’s coil above the space dew point. This keeps moisture from condensing on the coil and subsequently dripping down into the space. This means that active chilled beams are not ideal for projects with leaky building envelopes or high latent loads, such as a gym or workout room. The ideal project will typically be a new construction, where a chilled water system is feasible within the budget.

Limited Heating Capacity

Historically, when buildings have used chilled beams for cooling, they also have had to incorporate a completely separate heating system. This is because it is difficult to deliver warm air at a speed fast enough to direct it downwards and into the occupied space despite flowing hot water through the coils. However, this isn’t that big of a limitation in the South, and heating with the chilled beams can work quite well in our region’s climate. Seeing as how our climate is one that consists of extremely hot summers where temperatures consistently reach over 90°F and mild winters with lows in the 40s, the cooling load is much greater than the heating load. In other words, a building is going to need an HVAC system that can cool significantly whereas the heating capacity is going to be much less in comparison. This is why active chilled beams are such a good fit for Austin’s climate—they pack a serious punch when used for cooling and still deliver enough of a blow to take care of the relatively low heating requirements we have in our region.

Blog post written by MEP Summer intern, Mariana Pérez-Lozano.

Experienced engineers are imperative to the process of determining the most compatible HVAC system for any building. At BIG RED DOG, we have the understanding and proficiency to thoughtfully assess your project’s needs and identify the best HVAC solution. Contact our MEP office today to learn more about how we can put our expertise to good use on your next project.

Sources

Alexander, Darren, and Mike O’Rourke. “Design Considerations For Active Chilled Beams.” ASHRAE Journal (2008): 50-58. Web. 13 July 2016.

Roth, Kurt, et al. “Chilled Beam Cooling.” ASHRAE Journal (2007): 84-86. Web. 14 July 2016.

Rumsey, Peter, and John Weale. “Chilled Beams in Labs.” ASHRAE Journal (2007): 18-25. Web. 14 July 2016.

Sachs, Harvey, and Wilson Lin. “Emerging Technology: Chilled Beam Cooling.” Air Conditioning, Heating & Refrigeration News 24 May 2010: n. pag. Web. 14 July 2016.

Sipes, Jerry M., et al. ANSI/ASHRAE Standard 200-2015, Methods of Testing Chilled Beams. Atlanta: ASHRAE, 2015. Print.

“Understanding Chilled Beam Systems.” Engineers Newsletter (Apr. 2011): 1-12. Trane. Web. 13 July 2016.

Written by Chris Drake

Chris Drake

Chris Drake is the Lead Plumbing Engineer at BIG RED DOG. He received a degree in Aeronautical Engineering from Rensselaer Polytechnic Institute in Troy, NY and is a registered P.E. His professional experience includes the design of plumbing and HVAC systems in the campus, institutional, sports, federal, and manufacturing markets. His is also experienced in design/build, construction administration, and is a member of ASHRAE and ASPE. Chris originally hails from the Finger Lakes region of upstate New York. Outside of work, Chris enjoys exploring Austin and the surrounding hill country, traveling, and supporting the Buffalo Bills.