Engineering fabric-covered buildings for true sustainability

September 11, 2017

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Photos courtesy Legacy Buildings Solutions Canada

By James Kumpula
Everyone wants ‘better’ things—better homes, better schools, and better quality of life—but defining what exactly constitutes an improvement is not always easy. The grass is not always greener on the other side of the fence, so attempts at making something better may not always yield the desired results. This is also true in design and construction.

For the most part, however, people agree the ‘green building’ movement is both desirable and necessary. Many building owners and operators are focused on the practical, daily advantages of green building, such as energy efficiency and reduction in operating costs. These factors make sustainability a priority for many people when building new structures, as it can provide an enhanced return on investment (ROI) of a capital project through lower energy costs and government incentives.

Natural green properties
Facilities can get a head start on achieving greater energy efficiency simply by altering the materials used to construct a building. For example, an increasing trend in industrial applications is to utilize engineered fabric. Polyvinyl chloride (PVC) fabrics generally offer high quality and durability, and the natural properties of these materials make them a highly effective alternative choice for building users seeking green improvements.

The most important characteristic of engineered fabric from a sustainability perspective is it provides high solar reflectance, which keeps the roof cooler and reduces the overall heat island effect by deflecting sunlight away from the structure. Fabric roofs also absorb less heat due to their high thermal emittance. During the summer, these properties contribute to keeping fabric roofs about 28 to 33 C (50 to 60 F) cooler than roofs built using conventional materials. The end result is a reduced need for air-conditioning or other cooling inside the building.

Although engineered-fabric roofs succesfully  reflect ultraviolet (UV) rays, some light diffusion does get through the material—and is highly beneficial. Fabric offers up to 12 per cent translucency, meaning natural light can flood the building interior, often providing more than enough working light during the daytime.

Direct sunlight produces approximately 10,000 foot-candles (fc) of illumination. Therefore, even a roof with just five per cent translucency would still allow around 500 fc to permeate the structure on a sunny day. This is significantly higher than the minimum 75 to 100 fc typically recommended to safely perform various industrial maintenance tasks.

Most buildings will still require artificial lighting for nighttime tasks, as well as to provide illumination when the sky is overcast. However, where fabric roofing is implemented, those artificial lights are rendered unnecessary during normal daylight hours. Simply by making use of the sun for natural daylighting, fabric roofs help building users take a big step toward lower electric bills and improved energy efficiency.

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The structural steel beams in a rigid-frame fabric building contain about 90 per cent recycled steel.

Sustainable engineering
While fabric itself has always offered a certain level of sustainability to facilities, the structural aspects of fabric buildings have not always been ideal. Fabric structures were traditionally erected using hollow-tube, open-web truss framing. This style was adequate, serving various industries well for many years, but it became clear these structures needed to evolve to be sturdier and more durable, as well as to adhere to new building codes and regulations. The traditional style was also limited in how well it could accommodate new green building features.

A key engineering upgrade was introduced several years ago, incorporating rigid-frame engineering into fabric structures. With this method, a fabric roof can be applied to the structural steel I-beams used in conventional construction projects. This concept allows for more design flexibility when customizing the fabric structure’s alignment and overall size, and allows users to incorporate features making the building more operationally and energy-efficient.

The old method with truss systems does not allow for a continuous liner with a thermal break on the interior, meaning it cannot reduce air leakage to a minimum. This type of system also comes only in standard sizes, unlike rigid frames, which allow users to specify exact dimensions for a custom build. Further, truss systems’ arch shape leaves unusable space on the curved sidewalls, while rigid frame is flexible enough to add features such as lean-tos, sidewall doors, and mezzanines, while also maximizing floor space.

Finally, rigid frame buildings offer greater strength than truss buildings, and can be designed specifically to accommodate hanging loads. This means energy-efficient options can be added to structures—for example, full solar racks can be added to the roof, as can energy-efficient HVAC, lighting, and air filtration.

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Recent engineering upgrades allow fabric roofs to be applied to conventional I-beam construction projects, thereby providing more design flexibility.

Solar panels
The rigid-frame method has contributed to excellent advancements in application of photovoltaic (PV) panels to roof systems. At a minimum, building operators can use this method to reduce their dependence on outside power, and it is even possible for them to become completely self-sufficient by supplying their own energy. Common solar options include traditional crystalline or silicon panels, although some industry manufacturers have also worked with a thin-filmed PV that adheres directly to the building’s fabric panels. Another, less-sophisticated system for solar heating during winter months utilizes perforated metal to capture hot air in a cavity and bring it into a structure.

Although current truss-style fabric structures are lightweight and less expensive to produce than a rigid-frame building, they do not adapt to additions to the roof, such as solar panels, or to any operational devices required in a building, such as conveyors or cranes. This means the life cycle cost of rigid-frame buildings will be considerably less than a standard truss and hoop system.

Interior environment
The design of a rigid-frame fabric building makes it relatively simple to add items such as interior fabric liners and insulation to the roof and sidewalls—a method allowing installers to achieve a certain level of temperature control. This combination of liners and insulation material can achieve insulation values of up to R-40, which is a rating that meets almost all applicable energy codes.

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Engineered fabric provides high solar reflectance, reducing the heat island effect by deflecting sunlight away from the building.

Rigid-framed fabric structures allow for the type of continuous liner that truss systems cannot accommodate. This means no matter what level of insulation is installed, this roofing style can provide a near-airtight building envelope, helping users save significantly on heating and cooling costs.

Certain insulation packages may require some of the building’s translucent fabric to be covered, but even structures demanding insulation and natural light can reap both benefits when a fabric skylight is included in the building design. For this to work, it is critical to reserve a large section of uninsulated fabric while still applying enough insulation to meet energy codes.

Another factor impacting a fabric building’s interior environment is ventilation. This can be addressed through passive or mechanical means. A rigid-frame structure can support mounted loads such as fans or heavy-duty ventilators if necessary, or a natural gravity ventilation system can be implemented.

This latter system relies on the simple movement of hot air. As warm air rises, it interacts with pressure intakes at the base of the building’s perimeter and with a gravity ventilator at the ridge, effectively creating circulation throughout the inside of the structure. By providing a natural intake for fresh air and an evacuation point for fumes without the need for powered equipment, users can further cut down energy consumption and operating costs.

Resources and results
On top of being naturally energy-efficient, tension-fabric buildings typically make responsible use of existing resources. For example, the structural steel I-beams in a rigid-frame fabric structure contain about 90 per cent recycled steel. Basic accessories such as gutters and downspouts to collect rain runoff into cisterns can also be applied to the building, allowing for onsite water management.

The number of building users who recognize the importance of energy and resource management is continuing to grow. Thus far, energy efficiency has mainly been a function of economics—applying logical green building principles reduces energy consumption and utility expenses. However, the environmental aspect of the equation matters, too (though building operators who need to be wary of the bottom line are understandably slower to adopt new technology for environmental benefits alone).

Whatever the motivation may be, committing to sustainability makes sense. The grass may not always be greener on the other side, but with the right approach, a building easily can be.

 SOARING OFF THE GRID
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The Solar Ship hangar roof includes 200 polycrystalline photovoltaic (PV) modules that collect enough energy for the building to run entirely off-grid.

Founded in 2006, Solar Ship set out to build aircraft capable of travelling anywhere to provide service to areas without roads or infrastructure. When planes, trucks, and ships cannot deliver critical cargo for disaster relief or haul supplies to remote locations, this company’s solarship can be designed and built to the requirements of the mission.

The solarship is a hybrid aircraft that gains lift from a combination of buoyant gas and aerodynamics. Its design allows for extreme short takeoff and landing (XSTOL), and a large surface area on its top allows it to collect solar electric power (thereby expanding its range). It can also be powered by traditional combustion, but the primary goal is to refine a new mode of transportation not dependent on fossil fuels or runways.

This forward-thinking aerospace technology came together with another industry—that of building design and construction—when Solar Ship contracted to have a new aircraft hangar built at the Brantford Municipal Airport in Southwest Ontario. The 3771-m2 (40,597-sf) aircraft manufacturing and storage facility had to be larger than normal to accommodate the significant size of the hybrid airships—a need met with rigid-frame engineering utilizing structural steel I-beams in a tension-fabric building.

This rigid-frame design allowed SolarShip to achieve its specified goal of 3716 m2 (40,000 sf) of unobstructured interior space, rooftop panels, and a bifolding hangar door. The lightweight nature of the fabric also meant an existing concrete pad could be used as the foundation—a feature saving both money and construction time.

The minimum dimension for the main hangar door was 51 x 18 m (169 x 59 ft). Positioned on an end wall of the 53- x 70-m (176- x 231-ft) clear-span building, the biparting opening allows access for crafts fitting the current portfolio of the company’s solarships, which have wingspans up to 30 m (98 ft). The design also anticipates the development of a prototype with a 50-m (164-ft) wingspan. With a roof peak of 25 m (82 ft) and an 18-m (60-ft) eave clearance, the hangar provides ample vertical space for manoeuvering the aircraft through the assembly process.

The robust structure of the building is also consistent with environmental values. For instance, the hangar’s roof features an array of solar panels.

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The dimensions of the Solar Ship facility were customized to provide space to maneuver new aircraft through the assembly process. The facility runs entirely off-grid.

Lewis Reford, partner at Solar Ship, says the design “incorporates a self-reliant photovoltaic power package that sits above the fabric roof, allowing our building operations to be entirely off-grid.”

The east- and west-facing sides of the roof each include 100 260-watt polycrystalline photovoltaic (PV) modules for a total 52-kilowatt array. Combiner boxes with full arc fault circuit interruption (AFCI) compliance are located between the array and the solar battery charge controllers. The arrangement also utilizes two energy storage systems.

Solar energy and a small generator supply power to the company’s onsite loads, including 24 high-bay, 300-watt light-emitting diode (LED) fixtures for nighttime work and electric operation to open and close the all-weather main hangar doors. Other loads requiring electricity include the energy storage systems, containerized office HVAC, fire system trace heating, small tool operations, video monitoring, electric vehicle (EV) charging, laptop and Wi-Fi power, and air blowers.

Based on estimated energy yield, which takes into account average insolation at the site and overall system efficiency, the solar assembly in place on the building will produce 62.4 megawatt hours of energy each year.

Facilitated by the strong load capacity of the rigid-steel framing and by the use of proven design principles, a series of I-beams runs parallel to the solar panels, reducing uplift beneath them and enhancing the structure’s stability. The pitch of the roof enables the PV panels to efficiently harvest solar energy, and is rated for 1.18 kPa rain-on-snow load and 0.42 kPa wind load.

Other aspects of the building also contribute to its sustainability profile. Mesh soffits and RV-3000 peak vents enhance passive ventilation, while the translucent polyethylene (PE) fabric cladding admits daylight to lower the facility’s reliance on artificial lighting.

In May 2016, the building was selected as the “Game Changer Project of the Year” by the Canadian Solar Industries Association (CanSIA). The award recognized the hangar for using a reliable and cost-effective system advancing the future of building-integrated distributed generation.

 

James Kumpula is in charge of business development, global operations, infrastructure implementation, and execution in his role as general manager of Legacy Building Solutions Canada. He works closely with staff in Canada and the United States to ensure projects are completed to clients’ demands. Over the course of more than 25 years, Kumpula has been responsible for more than $5 billion in projects, 3.5 million m2 (37.6 sf) of building installations, and staff of up to 1100. He is an innovative leader with a demonstrated ability to recruit, mentor, and motivate personnel to achieve corporate objectives while creating a cohesive team environment. Kumpula can be reached via e-mail at jkumpula@legacybuildingsolutions.com[7].

Endnotes:
  1. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_SolarShip_1-copy.jpg
  2. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_BuildingInstallation.jpg
  3. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_BioPlant-e1505157452671.jpg
  4. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_BioPlant_Aerial.jpg
  5. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_SolarShip_2.jpg
  6. [Image]: https://www.constructioncanada.net/wp-content/uploads/2017/09/Legacy_SolarShip_3.jpg
  7. jkumpula@legacybuildingsolutions.com: mailto:jkumpula@legacybuildingsolutions.com

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