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In the past few years, a growing segment of construction professionals in North America has led the move into greener buildings. With more states and cities creating regulatory frameworks to support climate goals, it is becoming clear that most of the industry will soon join the trend, perhaps ramping up more quickly than before.
HVAC professionals have been reviewing the tools in their arsenal for designing net-zero energy buildings and seeking low-risk, proven technologies. For offices and institutions, radiant ceiling panels are receiving more attention, perhaps cemented by ASHRAE’s recent completion of its new headquarters in Georgia. It employs these devices for most of the cooling in the building.
Renovated ASHRAE Headquarters
The new headquarters is located near Atlanta in Peachtree Corners, Ga. (Climate Zone 3A). ASHRAE began renovations in January 2020 on an existing 66,700-square-foot double-wing, two-story building, originally constructed in 1978.
The recently completed retrofit is expected to achieve an Energy-Use Intensity (EUI) of about 19,000 BTUs/square foot/year. The objective was 24.1 EUI, the stretch goal was around 15, and after the HVAC system was designed, they were at about 17. Subsequent tweaks brought it up a little to 19. Members of the engineering team remained on site for months, optimizing the system through a thorough commissioning process.
It was a challenging project due to the existing building's constraints, the high profile of ASHRAE in the construction industry, and ambitious objectives from the planning committee. These included a net-zero energy requirement and formal or informal compliance with several certification guidelines.
With high-performance buildings, active HVAC systems must be assessed as part of an integrated, holistic strategy. The team reviewed the existing building’s performance baseline, the potential for on-site energy generation, the climate conditions, and the possible passive design and building envelope improvements. Only after that did it begin an analysis of active cooling, heating and ventilation options.
Mechanical design lead Stanton Stafford of Atlanta-based Integral Group says the design team narrowed numerous possible HVAC approaches down to two that could achieve the goals of the planning committee. The first involved an all-air-cooled system using thermodynamic-zoned packaged rooftop air-cooled heat pump systems, plus a dedicated outdoor air system.
This more-acknowledged route would have been less expensive from the first-cost point of view, however. “ASHRAE decided it wanted to show a forward-thinking approach to the industry — that we could put in a different system type, a more unconventional system for the U.S. market, perfectly viable and something we could use in warm, humid climates where there are a lot of naysayers saying these types of systems cannot be installed,” Stafford says.
Instead, the team went with the second option: an outdoor air-cooled modular heat pump, hot and cold buffer tanks, staged pumping, enthalpy heat recovery and demand-controlled ventilation using an air-cooled DOAS, decoupled from waterside systems. In most of the upstairs office areas, they used radiant ceiling panels for cooling and heating in exterior zones, cooling only in interior zones. Ceiling fans also were installed to induce cooling and improve environmental comfort.
On parts of the lower level, where the training center is located, they used water-source heat pumps for transient or potentially humid spaces.
Stafford says the radiant ceiling panels are arranged in “clouds” above the occupied spaces. They contain multipass, single-circuit coils with six-way valves, piping (two cold, two warm and one distribution) and valves or sensors to help with a higher level of zonal control. Panels can be piped in series for up to 64 square feet of active panel. They have quick disconnects for hoses, making installation and replacements easier.
Ventilation is cool/neutral temperature air delivered directly to the space and not directly responsible for temperature control within the zone. Duct distribution is for ventilation quantities only, at about 0.15 cubic feet/minute/square foot. It is at constant volume and delivered by fabric duct, reducing diffuser count and duct branches.
There are 120 high-volume, low-speed fans in the space, which expand the thermal comfort zone while still conserving energy. Occupants can switch them on or off, overriding the control system, which then makes appropriate adjustments.
The design accommodated most of the organization's goals and optimized the amount of rooftop solar that could be installed. Some consideration was given to a geo-exchange system using the adjacent lake, but it was not pursued in the end. The rooftop could supply about 17,000 of the required BTUs/square foot/year to hit net-zero, so some ground-mounted solar carports will supplement it in the parking lot.
Envelope improvements include exterior insulation, reducing the window-to-wall ratio from 70 percent to 40 percent, window shading, adding a roof to a large “hothouse” atrium between the two wings of the complex, and other measures.
“We wanted to demonstrate a replicable process for retrofitting a mid-century building to a high-performance building, and show that you can take a leaky building and get it to net zero,” Stafford explains. It looks like they’ve done it.
The Port of Portland: Lightweight Radiant
Another highly efficient building that incorporated a radiant system in the ceiling is a three-story, 205,500-square-foot port office at the Portland (Ore.) International Airport, which sits atop a seven-story parking complex. The weather conditions and unique architectural design, intended to suggest an airplane hull, both posed some challenges for Brad Wilson’s team at PAE Engineering in Portland (Climate Zone 4B).
They selected radiant panels partly because they are relatively light.
“With this architectural design, we could only install so much HVAC at the perimeter, and the panels offer a lot of cooling per square foot,” says Wilson, who wrote his thesis on radiant ceiling panels and now includes them in building designs. “We use a high-aspiration diffuser nozzle that ensures ventilation air gets to the occupants. And we blow some air across a radiant panel to get extra conditioning energy out of it.”
Beneath the building, two hundred geothermal wells reach 300 feet down, providing ground-source heating and cooling to the radiant system's heat pumps. “Ground-source temperatures work really well with radiant panels; it's a highly efficient way to go,” Wilson notes.
The building’s DOAS handles ventilation and dehumidification; it also recovers heat energy from building exhaust air. It uses 30 percent less energy than an office built to the Oregon code (ASHRAE 90.1).
Wilson says you must optimize efficiency and manage other considerations. “It’s tricky; it needs to be well-thought-out,” he explains. “You can’t have condensation and you don’t want thermal asymmetry, also known as ‘hot head syndrome.’ Design temperatures and applications are important with radiant panels.”
Also in Portland is one of the largest radiant ceiling panel retrofit projects in North America — The Edith Green-Wendell Wyatt Federal Building, built in 1974. Like ASHRAE’s headquarters, it recently underwent a deep retrofit; they were both gutted and structurally modified.
The 16-story federal building renovation called for about 107,000 square feet of radiant ceiling panels, plus 62,000 square feet of matching inactive panels. They contributed to a LEED Platinum certification and 55 percent in overall energy savings than a conventional building.
Sustainable Secondary Education
Considered one of the most beautiful study centers in the world, North Carolina State University’s award-winning 230,000-square-foot James B. Hunt Jr. Library in Raleigh (Climate Zone 4A) creates a vibrant research destination for students and faculty. With 40-foot windows, the building needed a reliable HVAC system. The design team decided to minimize heating and cooling energy losses by installing 13,280 square feet of radiant ceiling panels, an 80,000-square-foot torsion spring system and chilled beams.
University officials report that the system performs well, whether through a cold, wet winter or a hot, humid summer. The HVAC system conserved 31 percent of energy compared with a modeled all-air system alternative.
The product was Armstrong MetalWorks Airtite ceiling paneling. Hot or cold water circulates through concealed copper tubing on the back of the panels — for this project, a total of 32,000 linear feet of panel tubing. The building earned a LEED Silver certification.
Armstrong says that sustainability was a key client requirement for the building. They used 100 percent recycled cotton denim for insulation and about 90 percent recycled aluminum content in the ceiling panels.
A similar strategy was used for Millikan Hall at Pomona College in Claremont, Calif. (Climate Zone 3B). The mechanical designers used custom-designed, sloping radiant ceiling panels for about 60 percent of the 40,000-square-foot building. However, for the higher-load portion containing labs and machine shop, they used active chilled beams for cooling, with heating from a coil on the airside variable air volume box.
It seems to have worked well. Millikan Hall achieved 68 percent energy savings compared to its pre-retrofit consumption. The new system and other conservation measures result in very low energy use for this type of school laboratory facility.
Post-Pandemic Ventilation Strategies
Engineer Robert Monn, Armstrong’s manager of construction services, says interest in ceiling panels is increasing because radiant technologies don’t use forced air. Designers can combine it with fresh air ventilation rather than using recycled indoor air. The guidelines from ASHRAE and the Centers for Disease Control and Prevention suggest that this could be a better solution for preventing indoor airborne viruses. Armstrong also makes a UV-C filter for killing airborne viruses in indoor air.
“Eventually, people will return to the buildings and offices,” Monn says, adding that contrary to suggestions by some naysayers, radiant ceiling panels can efficiently condition a space even with 30 feet of glazing, such as at the Hunt Library. On the other hand, if office designers choose to move from open concepts to more controllable, compartmentalized spaces, the physical characteristics of radiant ceiling panels can help with that.
Monn points out that radiated heat is generally about 25 percent more efficient than forced air; thus, it works well in tandem with clean energy systems and modern low-load buildings.
“Climate change is the number one danger to our planet,” he says. “I feel fortunate to be working for a company that promotes energy-saving products. I want to be able to practice what I preach. I have two children. We have to make a better world for them.”
Interest in radiant ceiling panels is strong among project leaders working on offices and also among colleges and universities. Harvard, Yukon, Dartmouth and Pomona have all completed projects.
Another educational building with perhaps even more complicated lab equipment also uses radiant ceiling panels, heat recovery and demand-control ventilation in a place that has quite a different climate than the Los Angeles area — Canada. The project sought LEED Silver while requiring several high-tech spaces with nasty emissions, including a spray paint booth located at the roof level.
And like the ASHRAE building, there was reputational risk involved. It is the new engineering school facility at York University in North York, near Toronto (Climate Zone 5A or 6A). The mechanical systems are partly exposed as learning and teaching tools for engineering students and faculty.
The building includes a cleanroom rated at ISO Class 7, with an air-handling plant and three environmental chambers with individualized temperature control (-35 C to 85 C) for experiments. There also is a structurally isolated, heavily reinforced lab for materials destruction testing. These specialized labs include dedicated filtration exhaust and makeup air systems; in winter, they use 100 percent heat reclaimed from other parts of the building.
Most of the structure employs radiant ceiling panels, supplemented by perimeter trench heaters below the curved facade's double and triple-height glazing. Heat comes from the university’s central steam plant and campus chilled water plant via heat exchangers, with a dry cooler at roof level for data, electrical room and lab processes.
It looks as if the graduates from some of these institutions of higher learning will be well equipped, in both theory and practice, to help HVAC professionals with the low-carbon mechanical designs of the future. If you are not already using technologies such as radiant ceiling panels, maybe you should hire some smart young students to help you. Or you can study yourself on how to manage set points, humidity, condensation for radiant ceiling panel systems, and complementary technology.
One research company, marketwatch.com, says the global radiant ceiling panels market was valued at about US $900 million in 2020 and is expected to grow to $990 million in the next four years, with most of the action in North America and Europe. It may be that the universities, ASHRAE and other technology leaders described in this column are onto something.
As we hurtle ever more quickly into the green building era, we need more choices. Radiant ceiling panels offer flexibility in design, occupant comfort, quiet operation and energy savings. They could be a useful option.
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