Hydronic Chilled Beam System Regulates Military Environment
Wet Heat Technology Brings Comfort to Air Force Base
Weldin Construction’s Mechanical Division has successfully completed multiple hydronic installations throughout the Joint Base Elmendorf-Richardson (JBER) Air Force base near Anchorage, Alaska. As the base constructed its Emergency Operations Center (EOC), Weldin’s was on the top of the list to handle the HVACR installation work.
Highly classified and on the cutting-edge, some of the world’s most advanced military technology is housed within the EOC. Though only 8,000 square feet in size, the facility has computers and work stations for more than 100 officers and is tasked with operating as a strategic central command in case of emergency. With all of the high-tech equipment inside the building, the facility requires substantial cooling, even during an Alaskan winter.
Headquartered in Palmer, Alaska, Weldin faced some challenges with this install; one of which was the amount of overhead clearance that was available. The main facility’s floor is built on top of a 12-inch plenum that acts as a conduit for the maze of necessary electric and communications wires. This left no vertical space to spare. During the design process, it became apparent that there would be no room for ductwork either. The solution: Weldin opted for a hydronic chilled beam system.
Early Adopter Concerns
According to Weldin, hydronic chilled beam technology had not been specified to heat and cool a facility before. The technology is relevantly new to the U.S. market and government managers were wary to install this technology, but, trusting Weldin’s knowledge and on-base experience, they elected to move ahead with the idea.
“Weldin has a fab shop and a one-acre yard on base,” said Steve Nazaroff, mechanical division manager at Weldin Construction. “As general and mechanical contractors, we’ve had projects going on within the base continuously since 2001. The EOC is the third project that has incorporated engineering from Taco Inc. In 2010, we built an F-22 fighter jet flight-simulator building, and a training facility. Ironically, those two buildings also use a new and emerging hydronic recipe — LoadMatch — and they’ve performed flawlessly. That’s the sort of track record we needed for involvement on this project.”
Weldin’s earlier JBER projects put hybrid, single-pipe, and primary-secondary hydronic technology to work with mechanical-system designs chosen because of their operational efficiency, yet unproven in the U.S. on a broad scale. A similar project on base — albeit from an entirely different engineer, installer, and manufacturer — had failed in the 1980s.
Concerns that the new chilled beam system wouldn’t operate as planned were quickly settled; the Weldin team gained full approval within the hard-to-impress military community.
“We have a good relationship with government managers here,” said Nazaroff. “They knew we could be trusted to handle the EOC project, and we weren’t planning to let them down.”
Chilled Beam Debut
Chilled beam technology is a method of delivering heating and cooling with what Nazaroff describes as “off-the-charts efficiency.”
Visually, contractors should picture a flat, low-profile fin tube radiator mounted inside a sheet metal box suspended from the ceiling.
The hybrid system sometimes uses forced convection, which makes it an active chilled beam unit. Other times, air circulation is left to natural convection, making it a passive chilled beam system. These types of systems can approach 150 Btuh per square foot for passive operation and 400 Btuh per square foot for active systems.
Because chilled beams are ceiling-mounted and do not require the use of drain pans, chilled water-supply temperatures must be above the ambient dew point. As a result, dehumidification, or latent cooling, is usually handled by a separate, dedicated outdoor air system (or DOAS), supplying dry, conditioned air to the space.
Passive chilled beam systems supply the DOAS airflow through a separate diffuser or grille in the room. An active chilled beam supplies the DOAS airflow through the chilled beam, thereby increasing the capacity of the cooling coil through forced convection.
“What makes chilled beam 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. “Another key advantage is that a chilled beam system requires very little ceiling space and height.”
To help with the pump energy demand from this system, Weldin specified Taco’s pre-packaged LOFlo injection mixing system. It consists of a variable-speed injection circulator on the chiller side of the mixing block, and a constant-speed zone circulator on the beam side. According to the company, the use of LOFlo mixing blocks eliminates the need for a separate chiller or air conditioning system to handle the latent load.
“With a LOFlo system, we’re able to use one chiller,” said Cunniff. “Water comes out of the chiller at 45˚F. It supplies the DOAS coil for latent cooling, and goes to the mixing blocks where it’s mixed to the exact temperature needed in the chilled beams. Return water is generally around 60˚.”
In this manner, a 20-ton Aaon chiller supplies water to 32 Price chilled beam fixtures, each measuring 2 feet by 4 feet.”
All or Nothing
The hydronic system at the EOC rarely coasts at the half-load mark. Either the facility will be empty, or an exercise will be underway, with 100 or more occupants, each served by one or more computers. When the EOC is occupied, the cooling load is 140,000 Btuh — nearly three times that of the heating load.
When this occurs, the LOFlo mixing blocks run at a steady, half-gallon per minute rate on the beam-side. Five of the mixing blocks are used and six or seven chilled beam units pull water from each of the mixing blocks.
“The system resets the chilled-water temperatures as the latent load increases,” said Nazaroff. “Under normal load conditions, chilled water-supply temperatures hover around 59˚, about two degrees above the room’s dew point. In the summer, the target temperature for the room is 68˚.”
Three 5-ton Data Aire chiller systems handle the heavy load caused by computer infrastructure in some smaller rooms. The uninterruptible power supply (UPS) room and critical telecommunications room need extra cooling capacity to keep equipment functioning properly.
In the winter, and especially when unoccupied, the EOC calls for heat, even though it’s mostly underground. Design temperature for the long heating season is 68˚. A Taco 2400 circulator moves 180˚ heating-supply water to satisfy the 52,000-Btuh heating load for the 16-room facility. Heat comes from a standalone steam boiler.
“Security is always a challenge that we encounter when working at JBER, and that’s to be expected,” said Nazaroff. “The challenge didn’t last long though.”
Weldin’s trucks were identified, background checks on technicians were completed, and ID tags were issued. “Like you’d expect with any job involving new technology, we had a few bugs to work out,” said Nazaroff. “But now, after two exercises in the EOC, the personnel in the facility are completely unaware of the heating and cooling system, just as it should be. I like to refer to it as a stealth comfort system.”
Publication date: 3/4/2013