Hydronic cooling
Chilled beams turned out to be a Chilled beam technology practical solution for cooling. offers efficient cooling for commercial buildings By John Vastyan
Editor’s note: This is part one of a two-part article about chilled beams, a fast- emerging technology about efficient hydronic cooling for commercial spaces. Part 2 will appear in our next issue.
Chilled beam systems offer a relatively new and efficient way to cool commer- cial buildings. An alternative to conventional variable air volume (VAV) systems, chilled beams separate the functions of ventilation and dehumidification. The business end of chilled beam systems are made of copper tubing bonded to aluminum fins. The “beam” is housed in a sheet metal enclosure that’s typically placed at ceiling level. Some have called the convective cooling systems “a fan coil without a fan.” “What makes this technology so interesting is its broad applicability for commercial structures, and extreme energy and thermal efficiency,” said Greg Cunniff, P.E., application engineering manager for Taco, Inc., Cranston, Rhode Island. “A key advantage is that a chilled beam system requires very little ceiling space and height.” Another advantage is that water, the main transporter of thermal energy, permits very high energy carrying capacity via pipes – a big advantage over larger, far less efficient, forced air conveyance. A forced air system is, by its very nature, greatly less efficient because of the inherently low density of air and requires large ducts to transport BTUs.
Chilly in Chicago Before we look at greater depth into the theory and technology of chilled beams, I’d like to explore a recent application, one that took place in Chicago where 635 active chilled beams were installed. 250 S. Wacker is a 15-story, multi-tenant office tower with retail space on the first floor. The first and top floors had dedicated HVAC systems separate from A total of 635 chilled systems serving the second through 14th floors. beams were installed These intermediate floors had a floor-mounted in this renovated induction perimeter system and a constant volume- office building. Please see ‘Beams’ on page 31 www.plumbingandhvac.ca May/June 2011 – Plumbing & HVAC 29 ■ Refrigeration
Fig. 1: A radiant cooling/chilled beam system can reduce electrical energy demand by al- Fig. 2: Flow rates are in the range of 4.5 to six gpm per ton compared to most 25 percent. conventional chilled water systems of two to three gpm per ton.
Beams reduce space requirement
Continued from page 29 mounted overhead. professionals keenly interested in chilled beam, thereby increasing the According to Jim Wilson of Windy studying the system’s function, have been capacity of the cooling coil through variable temperature interior system. City Representatives – a manufacturer’s conducted. One trip to the building forced convection. Each of the floors has about 14,300 sq. rep – there were many advantages, happened when ambient temperatures “The amount of outside air required ft. of rentable floor area (215,000 sq. ft. beginning with unobstructed visibility were at -12°F, yet visitors were very to operate a typical chilled beam system total). through the floor-to-ceiling windows comfortable sitting next to exterior is much less than that needed for a forced In 2006, a major renovation of the along all exterior walls. Also, there are windows with no hint of downdraft. air system,” added Cunniff. building began which included no downdrafts, floor space is gained, Building owners are now seeking LEED “A chilled beam system typically needs removal of the building’s exterior and the cost of custom enclosures for certification for the structure. only one air change per hour, using walls and glass, and gutting of the floor-mount units was avoided. Finally, outside air to pressurize the space to structure down to the concrete. fan energy and noise levels were greatly Design considerations prevent the infiltration of outside air. Building owners concluded that the reduced. There are number of design With a forced air system, that need grows existing induction units and The next year, the developer considerations that building and HVAC to 8 to 10 air changes of recirculated (and enclosures would have to be replaced. approved the installation of 635 active professionals need to keep in mind. fresh) air to cool a space.” Naturally, with the circulation of cold Also reduced is the ceiling space fluids, they’re quick to see the need to typically required for ductwork. The avoid dew point/condensation issues. amount of air circulated by the central But there are other needs to consider system is also dramatically reduced, often when designing and installing chilled 80-90 percent less than with conventional, Passive chilled beams employ beams that circulate chilled water all-air systems. Of course, this also through tubing embedded in a metal dramatically reduces the horsepower to natural convection while active chilled ceiling fixture to wick away heat. circulate air within interior spaces. Because chilled beams are ceiling- “The net result is lower energy mounted and do not use drain pans, the consumption and operating costs,” beams employ forced convection. chilled water supply temperatures must be continued Cunniff. above the ambient dew point. As a result dehumidification, or latent cooling, is Reduced electrical load handled by a separate 100-percent Studies have shown – in typical The building’s renovation involved chilled beams which now consume dedicated outdoor system (or DOAS) commercial buildings – that fan energy a change to 100-percent, low-e exterior only 30 percent of the fan and pump supplying dry, conditioned air to the space. is often second only to lighting in glass, which significantly reduced the power of a fan-powered VAV system, Passive chilled beams employ natural energy consumption. With active building’s heating and cooling loads. assuming that the average cooling convection while active chilled beams chilled ceiling and chilled beam systems, Heat losses along the perimeter were loads are 70 percent of the full design employ forced convection. Passive energy to operate fans is dramatically reduced to less than 200 BTU per lineal cooling load. chilled beam systems supply the DOAS reduced due to the relatively small foot, which made it possible to provide The building’s chilled beams have airflow through a separate diffuser or amount and low pressure of the primary comfort conditioning of interior now been successfully operational for grille in the room. An active chilled beam spaces with active chilled beams two years. Many visits to the site, with supplies the DOAS airflow through the Please see ‘Lighter’ on page 33 www.plumbingandhvac.ca May/June 2011 – Plumbing & HVAC 31 ■ Refrigeration Lighter fan load
transfer from a chilled panel is radiant, ceilings is therefore approximately double Cooled air drops down and 40-50 percent is convective (as that of conventional chilled water systems. through ceiling grills. shown in Figure 1). Even with higher flow rates, “The chilled water temperature must the capacity of radiant chilled panels be above dew point to prevent and ceilings is relatively low, in the condensation from forming on the range of 20 to 40 Btu/h per sq. ft. underside of the panels,” said Cunniff. While this is within the range of This is typically in the range of 55º to cooling loads for interior spaces, it may 60ºF. The driving force or temperature not be adequate for interior spaces with difference between the chilled water exterior walls. For the European and a room at 75ºF is therefore experience in the 1980s, some cooling reduced, falling within the range of 15 was better than none. ✚ to 20ºF as opposed to a conventional º chilled water system using 40 to 45 F John Vastyan, a º chilled water and a range of 30 to 35 F journalist whose temperature difference. work focuses on the “As a result, higher chilled water flow plumbing and rates are required to achieve reasonable mechanical, HVAC, capacities,” continued Cunniff. geothermal, solar Continued from page 31 Beam me up, Scotty These flow rates are in the range of 4.5 and radiant heat Sounds futuristic; many trade to six gpm per ton using chilled water industries, owns º º air being circulated by the central system. professionals are surprised to learn that delta Ts of 4 to 5 F as opposed to Common Ground, a trade Figure 1 shows that a radiant chilled beam technology is relatively conventional chilled water systems of two communications firm based in º cooling/chilled beam system can reduce simple and straightforward. to three gpm per ton using delta-Ts of 8 Manheim, Pennsylvania. He can be º electrical energy demand by almost 25 In a radiant chilled ceiling system, to 12 F as shown in Figure 2. The chilled reached at [email protected]. percent. about 50 to 60 percent of the heat water flow rate for chilled panels and
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