©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 9, September 2012.
By Steven P. Brzezenski, P.E., Associate Member ASHRAE
About the Author
Steven P. Brzezenski, P.E., is mechanical project manager at Kibart, Inc., Towson, Md.
Wake Forest Biotech Place is a converted historic warehouse and machine repair facility that was retrofitted into labs and offices that use a chilled beam mechanical system. The building will use 37% less water over the EPAct 1992 and ASME A112.18.1-2005 standards, as well as save 31.5% in energy cost over ASHRAE/IES Standard 90.1-2007. The building anticipates LEED Gold certification.
The 242,000 ft2 (22 482 m2) building contains a five-story section (89,000 ft2 [8270 m2]) and a three-story section (153,000 ft2 [14 212 m2]). The five-story section was originally built in the 1930s and over time, the original glass block envelope began to deteriorate. The National Park Service standards for preservation and guidelines for preserving historic buildings did not allow a full replacement of this existing glass block with a higher efficiency glass envelope. All the glass blocks were removed; damaged blocks were replaced with blocks found in building storage and were reinstalled with new grouting in an effort to reduce infiltration.
The three-story section was all brick and built as an addition in the 1950s. There are no historical envelope requirements on the three-story section that allowed us to replace the insulation and add high-efficiency windows for better visibility to the outside.
The chilled beam system provides the advantage of decoupling the ventilation and load conditioning requirements, which saves energy. The ventilation system provides a year-round neutral air temperature of 66°F (18.8°C) to all spaces. A combination of cooling-only and cooling/heating beams was used throughout the building, depending on space requirements. To maintain space conditions, the thermostat controls the valve to provide either cooling or heating from the chilled beam. Space loads are conditioned without the need to increase air movement and reheat is eliminated.
The chilled beams provide only sensible cooling and have a limited capacity. They are not a good application for spaces with high latent loads, such as the glass block perimeter where infiltration moisture could condense on the beam. Chilled beams should also be avoided in equipment rooms such as freezer rooms, where load densities are high enough that there would not be enough ceiling area for the required quantity of beams.
The majority of lab spaces are research-oriented non-production wet labs with equipment heat gains varying between 5 and 15 W/ft2 (53.8 and 161.5 W/m2). Chilled beams work well in these areas because of a high sensible heat load ratio. To plan for inconsistent latent loads within the labs, such as where water is boiled directly below a chilled beam, all central station air-handling units include a dehumidification energy recovery wheel, in addition to a total energy recovery wheel, to provide dry air to the spaces. We also have included two systems to detect conditions that could cause condensate to form on the chilled beams.
Humidity sensors are provided adjacent to each thermostat. Upon high humidity level detection the chilled water control valve serving the beams within the control zone would close, and cool dry airflow from the central station units will increase to the room.
Condensate sensors are installed on the beam chilled water supply piping at the chilled beam connection. When moisture is detected, a similar sequence to the humidity sensor is followed.
In a building served by a chilled beam system, the air-handling unit no longer provides primary load conditioning; it provides only the air required for beam activation and ventilation. The internal loads are conditioned by the chilled beam, which make standard return air unnecessary. General laboratory, office, and toilet room air is ducted back to the air-handling unit for total energy recovery then exhausted. The air-handling units are 100% outside air.
Citation: ASHRAE Journal, vol. 54, no. 9, September 2012
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