Resilient Buildings that Bounce Back
Combined Heat and Power Capabilities
The ability to generate both heat and power on-site is attractive in a number of situations both for normal operations and in terms of resilience. Such combined heat and power (CHP) systems can use a propane or natural gas engine, heat exchanger, and generator to create electricity that powers the building. Simultaneously, the heat from the unit is captured by the heat exchanger and used to channel thermal energy to applications like space heating, domestic water heating, dehumidification, or other loads such as swimming pool heat. Utilizing both the electrical and thermal output of the propane CHP system achieves system efficiencies as high as 75 percent, while typical stand-alone electric generation from the grid is only about 30 to 50 percent efficient.
In commercial settings, CHP systems can greatly improve energy efficiency when compared with traditional systems. These systems are most effective in buildings with significant and steady thermal demands, which could include heavy domestic hot water needs (e.g., hotels, hospitals, car washes), swimming pool heating, or space heating through a hydronic system. CHP systems can also be ideal for retrofit situations when existing water heating equipment needs replacement, electric rates are increasing, or on-site power generation is an increasing priority. From a resiliency standpoint, most CHP systems can be used for standby power during grid-based power outages.
In many states it is even possible to sell extra electricity produced by the CHP system back to the energy grid. Where this “net metering” is permitted, these programs allow utilities to issue kilowatt-hour credits to customers, who can use them to offset any electricity consumed from the grid. In most cases, the transfer is accomplished through a bidirectional meter. The meter turns backward as excess electricity is sold to the utility. Optimized CHP systems can synchronize with utilities to operate when electric rates are highest, maximizing cost savings.
Overall, propane has been used and viewed favorably by design professionals and others as a fuel choice. Dan Weber is an architect at Anacapa in Santa Barbara, California. He notes “In rural residential projects, [propane] is just the status quo. Everyone uses propane because it’s really reliable and the cost is low. I was surprised that it was really not that expensive to do a subterranean propane tank." Related to resilience, Alex Wilson, founder of BuildingGreen and the Resilient Design Institute has stated "Propane is a good option for backup generators and offers the prospect of resilience.” Whether used as a stand-alone fuel with lower emissions than some other options or an auxiliary to clean, renewable systems, propane is a viable option.
Conclusion
Strategies have been presented for achieving better resilience in buildings. Doors that are designed and fabricated to withstand wind, flooding, and blasts help protect people on the other side of them. Properly designed and installed expansion joints and cover systems allow buildings to move and be fully operational following thermal, wind, or seismic events. On-site power generation such as can be provided by propane offers continuity in operations during utility service interruptions. Taken all together, these strategies help form an overall, holistic approach to building resilience.
RESILIENT DOORS CASE STUDY
Project: Davis Barracks
Location: U.S. Military Academy, West Point, New York
Architect/Engineer: Clark Nexsen
The Project: Originally established in 1802 as a fort set high above New York’s Hudson River, today’s U.S. Military Academy at West Point is renowned as one of the most elite institutions in the country. As the 4,000 students study and train on the campus, they can’t help but absorb the academy’s storied past. Indeed, the entire central campus is a national landmark, home to buildings and monuments that honor and celebrate U.S. military history.
In 2017, the busy academy opened an impressive new barracks built to house 650 cadets. The six-story Davis Barracks was designed to provide modern amenities for the cadets while respecting West Point’s designation as a National Historic Landmark campus. It also had to be resistant to attack. The door manufacturer became involved in the early stages of the project, working closely with the project architect to design and fabricate the entranceway’s blast-resistant door and frame assembly calculated to keep cadets safe in the event of an emergency such as a bomb blast. They also provided 14 smaller openings throughout the building.
The Door Design: Because the building was designed in a military gothic style, the architects at Clark Nexsen were resolute that Davis Barracks have an imposing entranceway with gracious curves and detailed recessed panels. Eight panels of insulated glass with muntin bars running both vertically and horizontally completed the look. That geometry made it an intricate custom design. Adding in the fact that this door needed to structurally withstand blast loads, it became more complicated.
The manufacturer’s engineers and technicians had to match craftsmanship with precise specifications to ensure the steel entrance doors met the government’s stringent antiterrorism/force protection (ATFP) blast criteria. Given that the Gothic-style entranceway is 16 feet high and 17 feet wide, it was a technical challenge to fashion a complex internal structure and blast frame, all while maintaining the striking design envisioned by the architect. Because the recessed door panels were so intricate, the architect provided a detailed cross section of exactly how they wanted them to look. The manufacturer then took that design and prototyped it in the factory to make sure they could match the desired appearance while still meeting the blast standards. Its size meant the frame had to be fabricated in two mirrored sections, then shipped to the site where it was assembled according to meticulous instructions — directives that considered both the integrity of the main door structure, as well as the anchoring system into the surrounding wall.
Combining Design and Performance: Once the team was satisfied the panel profile was perfect, they turned their attention to the next challenge. Because the architect designed the door to include eight glass panels, the final piece of the puzzle was making sure that, given the various sizes and shape of glass, it would meet blast loads (the glass is allowed to travel just 3.3 feet from the inside face of the door). Fortunately, the manufacturer’s in-house engineering staff was able to make those calculations, analyzing glazing in response to blast loads and engineering the appropriate supporting structures to retain the glass.
From the outside, the design looks like a typical custom door, but the appropriate structures needed to be fit inside the panels to make them blast resistant. Furthermore, the outer arch of the entranceway, though impressive to the eye, was, for engineers, another test of their ingenuity. Everything has an arch — the outer frame, the panels, and the glazing beads. That meant each piece had to be uniquely curved to match exacting dimensions and templates, making sure that both sides of the frame matched the structural wall and formed a precise mirror image. Having two frames presented another test - they had to treat the door as two separate blast-resistant frames, then run their computer models accordingly. After being transported to the site, the two frames were welded together and then painted.
Overall, everything came together beautifully; it’s impossible to tell that the structure is actually two frames. It is also impossible to see the blast frame that ensures the door holds its ground in the event of a surge of pressure generated by a blast. While it simply looks as if the door sits in the center of an attractive stone facade, the door apparatus is actually securely anchored into a structurally reinforced poured concrete wall (which is finished with decorative stone cladding).
The Results: Although every job presents different complexities, this one for the Davis Barracks project was quite involved. The full project has gone on to win a number of prestigious awards, including two for engineering excellence from the American Council of Engineering Companies (ACEC). As 650 cadets rush through the noble entranceway each day, they’re passing through a door that embodies West Point’s long military history — and is carefully engineered to keep them safe.
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