Energy saving made easy: Pluck low hanging fruit

Submitted by digital on Thu, 04/07/2016 - 15:08
{"version":"0.3.0","atoms":[],"cards":[],"markups":[["a",["href","http:\/\/\/documents\/insights\/bsi-006-can-fully-glazed-curtainwalls-be-green","target","_new"]],["a",["href","http:\/\/\/globalassets\/modern-steel\/archives\/2012\/03\/2012v03_thermal_bridging.pdf","target","_new"]],["strong"],["em"]],"sections":[[1,"p",[[0,[],0,"At the AIA Convention in Atlanta, President Clinton, when asked about his advice to architects, replied that we should go after the \u201clow hanging fruit.\u201d "]]],[1,"p",[[0,[],0,"I think in many ways he is right. Our profession sometimes tends to want to jump to the sophisticated, complicated and highly technological solutions while we may be overlooking the very simple measures. In fact, missing the simple measures may be undermining those more advanced solution. "]]],[1,"p",[[0,[],0,"Literally every building can incorporate simple features of energy efficient enclosure design. Once you reduce the heating and cooling loads with a better enclosure, all of the MEP systems go down in size. Just reducing energy results in large reductions in water consumption at the utility level, an added benefit."]]],[1,"p",[[0,[],0,"First and foremost, proper green or sustainable design must include substantial reductions in the energy required to operate the building. I suggest 30 percent better than current ASHRAE 90.1 values as a starting target. Hypothetically, is a building with an average enclosure performance of R-5 (very common), but has been certified as LEED Silver by using locally sourced materials with high recycled content, actually helping to save our planet? I think not much, but they are presented as successful examples all the time. "]]],[1,"p",[[0,[],0,"The building would be much more \u201cgreen\u201d if it were full of petroleum-based products from around the globe, with full faucets and no bike racks, but delivered an average enclosure thermal performance of R-20. The energy saved during the 25 to 50 year life of the building will offset the carbon cost of the construction many times over. Of course, if you can do the R-20 building with the other sustainable features, all the better."]]],[1,"p",[[0,[],0,"Contrary to a relatively common perception, energy saving features are fairly easy to incorporate into your design. You don\u2019t need LEED, GreenGlobes, HERS or PassiveHaus. Those rating systems have their place, but you don\u2019t need to follow them to create more energy efficient buildings. In fact, following these low-hanging fruit recommendations will feed directly into the energy savings criteria of those systems. "]]],[1,"p",[[0,[],0,"You don\u2019t need to research the recycled content or local sourcing. Those may also be important, but the carbon impact from recycling and transport are tiny compared to operational energy. You don\u2019t need earthtubes, green roofs, double facades, solar chimneys, electrochromic glass, phase-change materials, or other supposed high performance materials. You don\u2019t need biomimicry, deconstruction, EPDs or HPDs. or other fads. In fact, all of those efforts just get in the way if they distract you from the basics (which appears to be the general case)."]]],[1,"p",[[0,[],0,"To identify the low-hanging fruit, we will look at the major determinates of energy consumption in a typical commercial building. The following lists problem areas and means to address them in a more or less descending order of importance. Note that energy savings are determined more by glazing and air infiltration than by just adding insulation."]]],[1,"h3",[[0,[],0,"Glass and Glazing"]]],[1,"p",[[0,[],0,"The primary energy determinate in typical commercial buildings is the area of glass in relationship to the opaque assemblies. This is followed closely by the amount of glass. Rounding out the top three determinates is the over-use of glass. I hope that you are getting the point. Glazed areas, even with supposed high performance glass and advanced thermally broken aluminum frames, perform at around R-2.5 or worse! Glass doors may be lower than R-1. "]]],[1,"p",[[0,[],0,"Measuring fenestration products using u-factors instead of R-values tends to mask the exceptionally poor thermal performance of windows, curtain wall and storefront. Making the energy equation even worse is the extreme amount of solar heat gain through the glass. Remember in the 1970s when we used dark-colored and mirrored glass to reduce heat gain. Now we have an incredible selection of low-e coatings, so we can have beautiful clear glass and energy performance. "]]],[1,"p",[[0,[],0,"The rotten truth of this low hanging fruit is that modern low-e clear glass performs at about the same SHGC level as the old-fashioned dark tinted or mirrored glass. Heat pours through fenestration at an incredible rate, so much so that over-glazed buildings require air conditioning on cold sunny days. (See "],[0,[0],1,"BSI-006: Can Highly Glazed Building Fa\u00e7ades Be Green? "],[0,[],0,"by John Straube of BSC.) Note that the prescriptive compliance method in the IECC and ASHRAE 90.1 limits glazing to 30%."]]],[3,"ul",[[[0,[],0,"LHF #1: Limit glass areas to around 30 percent or 40 percent of the wall area and less than 5 percent of the roof area for skylights, and use a higher SHGC."]]]],[1,"p",[[0,[],0,"Following glass, spandrel areas of aluminum-framed fenestration systems are the next common source of energy consumption. The aluminum framing systems still transfer huge amounts of energy. In a typical spandrel area with R-20 insulation, the average system performance can easily be only R-5. When you are trying to make the opaque areas good enough to make up for the glass, spandrel areas just aren\u2019t very effective."]]],[3,"ul",[[[0,[],0,"LHF #2: Limit the use of insulated spandrel areas in aluminum-framed systems for an opaque wall. Count the spandrel as part of the glass area when computing the glass-to-wall ratio. Better yet, use a well-insulated wall assembly as described below for opaque portions of the wall."]],[[0,[],0,"LHF #3: Avoid building designs with the majority of the enclosure composed of aluminum-framed curtain wall, storefront or window wall."]]]],[1,"h3",[[0,[],0,"Air infiltration"]]],[1,"p",[[0,[],0,"Air infiltration is the next big waster of energy. While it is not as easy to quantify as the code requirements for insulation, there are some research papers that show substantial energy loss through uncontrolled air infiltration, perhaps as high as 40 percent of the load."]]],[3,"ul",[[[0,[],0,"LHF #4: Air-tighten the exterior walls with a heavy-duty commercial self-adhered membrane or fluid-applied membrane applied over the backup wall of a drained cavity assembly. A general rule of thumb is that thicker membranes are better. The drained cavity assembly provides a surface with the least interruptions and has the added benefit of allowing for continuous insulation. "]]]],[1,"p",[[0,[],0,"The following is a list of common areas of air infiltration and a method to control:"]]],[3,"ul",[[[0,[],0,"The interface of windows, doors, and edges of curtain wall and storefront provides miles of crack; make sure this joint is sealed to the AB with a membrane flashing or sealant. This also provides an added level of protection against water infiltration."]],[[0,[],0,"Elevator and stair shafts, especially those that connect to non-conditioned or semi-conditioned spaces at the top or bottom of the buildings. Make sure louvers at the top of elevator shafts are closed with gasketed dampers. Separate elevator shafts from the building with lobbies with gasketed doors. Add weatherstripping to doors into stair shafts, especially when the doors open to conditioned or semi-conditioned spaces."]],[[0,[],0,"Seals between the wall above and the foundation are often left unsealed, which allows not only air infiltration but also water leaks. Either extend the foundation waterproofing up the wall or extend the air barrier on the wall down over the foundation."]],[[0,[],0,"As at the foundation, seals to the roofing or to an airtight ceiling are commonly left out. Connect the AB to the roofing membrane, a vapor barrier in the roofing or to an airtight GWB ceiling."]],[[0,[],0,"Soffits and porticoes are often shown with vents through the air barrier layer, somewhat of a holdover from previous practices. Make sure that any vents, if required, only vent the outer cavity and do not penetrate through the air control layer. Make sure the ceiling space over a portico is separated from the interior with an air control layer."]],[[0,[],0,"Hollow metal doors, aluminum entrances, and especially all-glass entrances tend to leak huge amounts of air. Specify a double layer of high quality weather-stripping on the perimeter of all exterior doors. Better yet, use a door assembly that has been tested for better air infiltration resistance, such as an aluminum terrace door. As an added benefit, terrace doors are much more resistant to water infiltration."]],[[0,[],0,"Vestibules are usually only provided at the main entrance, but current energy codes require vestibules at many doors. Use vestibules as often as possible, but at least where required by code, to supplement the weather-stripping on the doors."]],[[0,[],0,"Loading docks are commonly open, and even when the roll-up doors are closed they leak huge amounts of air. Detail the interior walls and doors of a loading dock to be airtight to stop the spread of the air leaking through the doors. "]]]],[1,"h3",[[0,[],0,"Insulation"]]],[1,"p",[[0,[],0,"Incorrect assumptions about the actual thermal performance of the opaque assemblies are a common point of error in determining energy savings. The thermal performance of the entire assembly is not to be confused with the R-values printed on the insulation stuffed into the wall. In many commercial buildings with opaque walls of cold-formed metal framing, the effectiveness of the insulation is cut in half or worse because of the heat transfer through the highly conductive thermal framing. "]]],[1,"p",[[0,[],0,"Continuous insulation applied over the framing will make a big difference if properly detailed (see below). Otherwise, be aware that R-19 batt insulation probably provides only R-9 performance in the assembly. Likewise, R-11 batts will drop to R-5 for the whole assembly."]]],[3,"ul",[[[0,[],0,"LHF #5: Use project-specific r-values for assemblies rather than the values printed on the insulation to understand performance. Better yet, add continuous insulation."]]]],[1,"p",[[0,[],0,"Continuous insulation (ci) when properly installed substantially reduces the heat transfer across a wall assembly, especially those framed with metal. For the continuous insulation to perform, it must be free of major thermal short-circuits; 1 percent is sometimes the value given for maximum cross-sectional area of metal through the ci."]]],[3,"ul",[[[0,[],0,"LHF #6: Add continuous insulation inside of the air cavity of a drained cavity wall assembly with minimal thermal short-circuits."]]]],[1,"p",[[0,[],0,"Perhaps the most common method for the support of cladding over ci is to install continuous metal zee girts, which essentially defeats the intent. The use of these girts will reduce the effectiveness of the R-value of the ci by approximately 50%. The following are some suggestions to avoid this loss."]]],[3,"ul",[[[0,[],0,"Use proprietary clip systems or proprietary sub-framing systems, typically made of non-conductive materials or of metals with thermal breaks where they penetrate the ci."]],[[0,[],0,"Use zee-girts of non-conductive materials ,such as pulltruded fiberglass."]],[[0,[],0,"Apply furring over the ci, fastening through into framing. "]],[[0,[],0,"Design a system with small stainless steel clips (less conductive) on a large grid; approximately 4 by 4 ft. to support a network of girts beyond the ci. "]]]],[1,"h3",[[0,[],0,"Thermal short-circuits"]]],[1,"p",[[0,[],0,"It is impossible to detail a building with no thermal short-circuits through the ci and\/or exterior enclosure assembly. There are always items that must be structurally connected back to the main building structure through the assembly. There are methods to decrease the number of these short-circuits and their impact."]]],[3,"ul",[[[0,[],0,"LHF #7: Reduce short-circuits through the enclosure assemblies by covering all surfaces of the structure with ci and adding thermal breaks."]]]],[1,"p",[[0,[],0,"Following is a list of common thermal short-circuits and how to avoid them:"]]],[3,"ul",[[[0,[],0,"Masonry shelf angles provide a continuous thermal break at every floor level and are therefore a significant detail. Space the shelf angle off the wall with clips spaced 24 to 32\u201d apart and extend the ci behind the shelf angle. There are also proprietary systems. At a minimum, introduce a thermal-break structural shim between the angle and the support. See "],[0,[1],1,"Thermal Bridging Solutions"],[0,[],0,", published by AISC for more information."]],[[0,[],0,"The edges of concrete slabs at the grade line are often left uninsulated. The large thermal short-circuit resulting from this is not only an energy loss but also can cause condensation on interior finishes. Extend the ci down the face of the concrete slab and connect into the insulation that protects the foundation. Cover with stainless steel flashing or troweled finish."]],[[0,[],0,"While now a bit less common, sometime the edge of the floor slabs are extended through the exterior wall assemblies for visual accent and\/or to support a masonry veneer. The further the slab projects, the more heat transfer. Hold the slab edge in line with the face of the backup wall and extend the ci past to cover. Create any projecting visual expression in the cladding."]],[[0,[],0,"The extreme version (and unfortunately too common) of the exposed slab-edge is the cantilevered concrete balcony. These projecting concrete slabs are essentially acting as radiator fins. Provide a thermal break using proprietary structural joints including insulation or separately support the balcony."]],[[0,[],0,"Parapets are a challenge because they require structural support to cantilever up. Frequently the best solution is to wrap the entire parapet with insulation including the top. Extend the ci up the exterior face and extend roofing insulation up the interior face. Be very careful to control infiltration of interior air into the parapet to avoid condensation problems."]],[[0,[],0,"Structural framing for canopies and roof screens. These items are a bit less important because they will typically make up an extremely small percentage of the area of the enclosure assemblies. However, it is relatively easy to add structural thermal break shims to isolate the exterior framing from the interior. "]]]],[1,"p",[[0,[2],1,"About the Author"]]],[1,"p",[[0,[3],1,"David Altenhofen, AIA, is an Associate Principle and Technical Director at the Philadelphia office of Hillier Architecture."]]]]}
Learn about the most direct ways to improve energy efficiency in the structures we design, and pitfalls to avoid.
Members Only
Tile Sizes
Use on Homepage
Temp Draft