Efficiency Starts at the Envelope

Want to get the best energy performance from a building? Work from the outside in

By Karen Kroll  

Much of the talk about energy efficiency revolves around energy-using systems like lighting and HVAC. That’s not surprising. After all, lighting and indoor climate control consumed 59 percent of primary energy used by the commercial sector in 2002, according to the Center for Sustainable Systems at the University of Michigan.

But when a new building is being designed, the interior is the wrong place to start looking for energy-saving opportunities. Instead, energy should be foremost in facility executives’ minds when the building envelope is being planned.

“You start with the envelope, and try to conserve as much as you can before you start spending on the mechanicals,” says Tom Hootman, director of sustainability with RNL in Denver.

Of course, that’s easier said than done. In a traditional design and construction process, aesthetics is the primary consideration when the exterior is being planned, with energy efficiency as an afterthought. But to a significant extent, the exterior determines the heating and cooling loads, as well as the amount of electrical lighting that will be needed. So if the design of the building envelope neglects energy considerations, the building will use more energy than it might have, even if the facility executive invests in the most energy-efficient HVAC and lighting systems available.

Today, a growing number of projects reflect the energy benefits of paying careful attention to the building exterior. One reason is greater concern for energy and green buildings. But the emergence of computer applications that can reliably model estimated energy use under a range of scenarios is making it easier to create energy-efficient exteriors.

Technology is also playing a role. For example, the quality of energy-efficient materials, such as high-performance window glass, has improved. And a simple understanding of the role of the exterior has led to increased use of measures such as reflective roofs — an energy-saving technology that may add nothing to the cost of a new building.

Building codes in a growing number of states and municipalities are also leading facility executives to pay more attention to the building exterior. In some cases, that’s because codes mandate steps like the use of reflective roofs. Beyond those specific requirements, tighter code limits on overall building energy use are leading facility executives to pay more attention to the exterior as an opportunity to reduce the amount of energy the building consumes.

Civic and Justice Center

A first step toward energy efficiency is orienting a building so that heating and cooling by the building systems can be minimized, Hootman says. That strategy was used for the Civic and Justice Center for Commerce City, Colo. Within the constraints of the plot available, the design minimized the portion of the building that would be exposed to the west and thus vulnerable to solar heat gain. Due to the shape of the lot and the activities that occur inside the 90,000 square foot facility, which opened in 2007, it contains some western exposure.

To compensate, a dozen different glazings were used on the Center’s windows; the glazing chosen varied with the heat gain a window received, as well as the space behind that window. For example, the upper portion of windows that lead into office spaces contain daylight glass that disperses sunlight across the ceiling, rather than letting it pour directly down to occupants’ desktops. On the other hand, the lower portions of the office windows are made of high performance glass that lets in light, but not heat. Sun shades were incorporated into all south-facing windows to reduce heat gain and glare.

To further reduce energy consumption, the Center installed more insulation than required by code. For instance, the insulation value of the roof is R30, or about twice the code mandate, Hootman says. In addition, the roof membrane is white, and reflects heat — preventing it from entering the building.

These measures, along with the use of energy-efficient building systems and lights, have cut energy use by about 33 percent, for annual savings of more than $50,000 when compared to ASHRAE 90.1-2004, Hootman says. These figures are based on energy models, as the Center has not been operating long enough to provide meaningful energy use statistics.

Sweetwater Creek State Park Visitors Center, Lithia Springs, Georgia

The energy efficiency measures incorporated into the Sweetwater Creek State Park Visitors Center also started with the placement and design of the building, says Dan Gerding, managing principal with Gerding Collaborative. The 8,700 square foot building, which is built into a south-facing slope, captures the sun’s rays in the winter, while avoiding most of its heat in the summer.

Two bands of windows are carved into the south side of the building, Gerding says. A sun shade protects the lower band from the sun’s strongest rays. At the same time, light shelves installed inside the building, extending 18 to 24 inches below the upper band of windows, reflect the light coming in, causing it to bounce deeper into the interior.

One-third of the roof is vegetated, Gerding says. This helps keep the building at a constant temperature. The roof is constructed of steel bar joists and metal decking; the roof membrane sits on top of this. The insulation is located on top of the membrane, protecting it from UV radiation. Above the insulation is a layer of short (about one half inch deep) plastic cups that act as a reservoir and slow the rate at which rain water runs off the roof. On top of this is the root barrier and about 10 inches of engineered soil that is less vulnerable to compacting.

The remaining two-thirds of the roof is constructed of high-reflectance, high-emissivity metal roofing.

Software models indicate that energy consumption at the Visitor Center is estimated to be about half that of a comparable building that lacks these and the other energy saving measures implemented, Gerding says. What’s more, construction costs for the building, which earned LEED Platinum certification, came to about $175 per square foot – competitive with most non-green buildings.

The Brewery Blocks

The Brewery Blocks project in Portland, Ore., is a mixed-use project covering about 1.7 million square feet. The facility, developed by Gerding Edlen Development, consists of two residential and three office buildings, as well as a performing arts center. “We understand the effect of the building’s façade on the mechanical system,” says Bruce Brown, principal with GBD Architects.

The window glass in the Brewery Blocks varies depending on the solar exposure of the window. In addition, some of the windows can be opened several inches. When an occupant opens a window, he or she also can shut off the mechanical system near the window. That way, the building gets fresh air, but heating or cooling isn’t wasted. “We have a temperate climate, so natural ventilation strategies can be pretty successful,” says Renee Worme, spokesperson with GBD.

Several eco-friendly features are found on the project’s rooftops. Brewery Block Four, for instance, sports photovoltaic panels that will generate enough electricity to save about $1,500 per year. A portion of the fourth floor roof setback is planted with vegetation native to the area. In addition to enhancing the green image of the project, the “eco-roof” will attenuate storm water run-off. The roof will handle about 320,000 gallons of water each year, according to GBD.

The rooftop garden is an integral design element of the building, Brown says. Many town homes look down over the eco-roof, giving occupants a much more aesthetically pleasing view than a black or ballasted roof would have.

Construction costs for Block Four’s eco-friendly features boosted overall costs by about one percent. However, energy models show that the high-performance building envelope, along with energy efficient HVAC systems, should cut energy costs by $58,000 annually, for a payback period of about 8.5 years, GBD says. Block Four received certification by the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) program.

Visitor Center, Fullerton Arboretum

The Visitor Center at the Fullerton Arboretum, at California State University — Fullerton, is designed to take advantage of the westerly breezes that blow in from the ocean and across campus, says Brian Dougherty, project architect and partner with Dougherty & Dougherty. To accomplish this, the windows and roof on the west side of the building are lower, while those on the east side are higher. “It’s like an airplane wing,” Dougherty says. “Air goes over the roof and creates a vacuum that draws hot air out of the classes, and then draws in cool air.”

Double-pane windows further boost the energy efficiency of the 8,500-square-foot-building, which opened in March 2006. The use of two-by-eight beams, rather than two-by-fours, allowed for more insulation, says Michael Craig Smith, director of design and construction with the university.

Between these design elements and the variable speed ceiling fans installed in the Arboretum’s classrooms, air conditioning and heating is needed only on very hot or cold days. “It’s very comfortable without HVAC,” says Smith.

New Haven School District

Even small energy savings add up quickly when they’re multiplied by 40 or more facilities. That’s one reason the New Haven School District, New Haven, Conn., began implementing energy efficiency measures in its elementary, middle and high schools, says Thomas Roger, vice president and project executive with Gilbane Building Company, the program manager for the $1.05 billion rebuilding effort. “If the buildings are not built to operate efficiently, you won’t have money to run them,” he says.

The program, which is scheduled for completion in 2012, will provide the city with 37 renovated and six new school buildings. As of early 2007, five of the high-performance buildings were operating, and another 10 were in the pipeline.

The district is using conventional construction techniques, while dramatically boosting its use of materials that can conserve energy, Roger says. “The roofs and walls far exceed ASHRAE standards.” The district is using R15 wall insulation, compared to the R7 value called for by ASHRAE. Similarly, the roof insulation is 12 inches, versus the more conventional 6 inches. The windows are made with glass that features U-values of .3, versus the .75 U-value allowed by ASHRAE.

Energy use within the renovated buildings has dropped to less than half what it was before the upgrades — including insulation and windows — were put in place. An analysis of utility bills shows that the average building in the district previously used 250 BTUs per square foot; that compares to less than 100 BTUs per square foot in the energy-efficient buildings now. The insulation contributes about 20 percent of the savings, Roger estimates.

Valley National Bank, Wayne, New Jersey

When management at Valley National Bank decided to replace the bank’s roof, they also considered installing solar panels. However, given the significantly higher cost of a solar panel roof – the jump in the price tag ran into six figures – the design team had to justify the additional expense, says Scott Watkowski, former vice president of facilities management with the bank and now a senior real estate manager with CB Richard Ellis. “We had to justify the up charge from standard roof panels to solar.”

To install the system, the old roof was removed. Then the construction crew installed a base-ply and cap-ply membrane. On top of this, the crew applied an epoxy resign and adhered the solar panels. Each solar panel fits within a roof panel, Watkowski says. That will make it easier to do any roof repairs that may be needed down the road.

While the solar panel roof wasn’t cheap, Watkowski estimates that the bank will recoup its investment in about four years. The return comes from energy savings, as well as from New Jersey renewable energy credits.

Envelope Challenges

While incorporating energy efficient designs and materials into a project can reduce energy use, it also creates challenges. Brown, the architect behind the Brewery Blocks project, notes that using elements such as photovoltaic panels requires incorporating them into the overall design of a facility. “You have to integrate it so that they don’t look like a TV antenna plopped on the building.”

Completing an energy-efficient building also requires an integrated effort between the designers, engineers, contractors and others involved in the project. For example, if any particular aspect of the design is new for the designers and engineers, it’s critical to discuss the challenges during project meetings. This will allow team members from other areas to offer their perspectives and keep the project on track and moving forward.

Some projects require working with local officials. When management at a New Jersey bank installed a solar roof, they had to address the fire marshall’s concern that, if a firefighter needed to cut through a panel during a fire, the electricity generated by the panel would cause a shock. That’s not the case, as each panel individually generates a small amount of electricity, and the firefighters’ saws are insulated against higher electrical voltage.

As more energy-efficient buildings get up and running, and more builders, inspectors and others involved in the process become familiar with them, these issues are likely to occur less frequently.

Down the road, the focus will shift from designing buildings that are energy efficient to creating buildings that actually help the environment by, using less energy than they generate, says Dougherty. “We’re talking beyond green,” he says.

Tax Breaks for Energy Efficiency

The Energy Policy Act (EPAct) of 2005 provides opportunities for tax deductions for energy efficient building envelopes that achieve at least a 16.67 percent energy cost reduction compared to envelopes designed to meet ASHRAE 90.1-2001.

For tax purposes, the term building envelope covers all of the perimeter surfaces of a building, including roofs, slabs, walls, windows and doors. Facility executives can take a variety of measures to improve the energy efficiency of the building envelope.

  • Roofs, slabs and walls can use insulation to reduce heating and cooling loads. "Cool roofs" reflect, rather than absorb, sunlight and heat; they are being required in some jurisdictions. Windows can use coatings and films and solar shades to control heating and cooling loads. Doors can also use glazing.
  • Walls can incorporate vapor barrier and moisture systems that enable a building to use energy more efficiently.
  • Skylights, particularly in large retail buildings, distribution centers and warehouses, can substantially reduce the need for conventional lighting. Under California's Title 24 energy codes, certain large footprint buildings are required to have skylights.

To qualify for the building envelope tax deductions, energy cost savings have to be confirmed or supported by energy modeling software that has been approved by the Internal Revenue Service (IRS). To date, IRS has approved five software models: Trane Trace 700, Energy Plus, Carrier HAP, Visual DOE and EnergyGauge. It is likely that other modeling software will be submitted to IRS for approval.

Because of the cost of energy modeling, it is rare for buildings to be modeled strictly to justify a tax deduction. But an energy model has other potential benefits. For example, modeling can help to evaluate the efficiency of building design options. Modeling is also required for certification under the U.S. Green Building Council’s Leadership in Energy and Environmental Design for New Construction (LEED-NC) program and may be needed to qualify for rebates. Facility executives should be aware that the EPAct modeling approach for the building envelope is different from the one used for LEED and should ensure that the engineer doing the modeling understands EPAct modeling requirements.

Facility executives should also investigate whether rebates are available to reimburse some or all modeling costs. Generally, these rebates must be obtained before the modeling is done; in most cases it is not possible to obtain a rebate for modeling after it has been done.

Karen Kroll, a contributing editor for Building Operating Management, is a freelance writer who has written extensively about real estate and facility issues.

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  posted on 7/1/2007   Article Use Policy

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