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Saving on Natatorium Energy Costs with Green Options

Photos courtesy Jarmel Kizel Architects and Engineers

Photos courtesy Jarmel Kizel Architects and Engineers

by Ralph Kittler, PE

When it comes to designing indoor swimming pool facilities, it is critical to ensure not only a healthy interior environment, but also energy efficiency. New technologies can provide both optimal natatorium environmental control and curtail utility consumption when specified.

Commercial dehumidifiers and 100 percent outside air ventilation system (OAVS) technology for indoor pools have significantly changed in the last decade. Consequently, a new or retrofitted natatorium HVAC system can potentially save millions of dollars in energy costs over the equipment’s 15 to 25-year lifecycle, depending on the sustainable options specified.

In short, today’s indoor pool HVAC equipment is not your parent’s dehumidifier. Current systems can come with:

  • reduced refrigerant charges of up to 85 percent;
  • lowered fan energy costs;
  • compressor heat recovery for ‘free’ pool-water-heating;
  • exhaust heat recovery for preheating outdoor air;
  • modulating controls for pinpoint temperature and humidity control;
  • glycol heat rejection to dry coolers; and
  • web-based microprocessor monitoring and alarms for maintaining daily pinpoint, real-time control by factory technicians.
In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifi er to keep glass shared by the aerobics and aquatic areas free of condensation.

In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifier to keep glass
shared by the aerobics and aquatic areas free of condensation.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.

 

 

 

 

 

 

 

 

The R-22 ban and dehumidifier retrofits
Thousands of units manufactured after the 1970s’ advent of the modern-day mechanical indoor pool dehumidifier will be reaching the end of their useful lifecycle within the next five years.

Most of these aging dehumidifiers operate using the hydrochlorofluorocarbon (HCFC) refrigerant R-22. According to the 1989 international treaty, Montreal Protocol on Substances that Deplete the Ozone Layer, this refrigerant has ozone-depleting potential. As a result of the treaty, R-22 is amid a world-wide manufacturing phase-out. The phase-out—which currently calls for 90 percent next year and 99 percent in 2020—has already spiked prices due to dwindling supplies. Price volatility is demonstrated by contractor charges ranging anywhere from $35 to more than $100 per pound of R-22.

Conventional natatorium dehumidifiers built during last 25 years can range from 45 kg (100 lb) to more than 317.5 kg (700 lb) of refrigerant. Therefore, a dehumidifier that leaks all, or even a substantial portion, of its R-22 refrigerant charge could represent significant cost for refrigerant replacement, not to mention damage the environment. This fact alone should get natatorium owners’ attention. However, the fact a refrigeration circuit will generally have at least one or two refrigerant leaks during its lifecycle should also be considered.

R-410A is the succeeding refrigerant to R-22. It is a less environmental-damaging hydrofluorocarbon (HFC)—due to its lack of chlorine—and used in most new dehumidifiers over the last five years, but it is also expecting a future phase-out and subsequent price increase.

Refrigerant price volatility, as well as the suspected danger to the environment, has prompted many HVAC manufacturers to look toward alternatives, such as substituting up to 85 percent of the refrigerant with glycol for heat rejection. Glycol is significantly less toxic to the environment. It operates under pump pressures versus the high pressures of compressors and refrigerants; thus, it is less likely to leak—when it does, glycol is not a vapor or ozone-depleting chemical.

The glycol-based units still have a small refrigerant charge of typically 10 to 20 percent of conventional dehumidifiers. These refrigeration circuits are necessary for dehumidification and optional natatorium space-cooling, however, they carry dramatically less leak liability and risk because they are ultra-compact and factory-sealed by expert technicians. The glycol is transported through polyvinyl chloride (PVC) piping to dry coolers for heat rejection. It also eliminates the potential of installation errors involving hundreds of pounds of refrigerant, expensive copper piping, and outdoor air-cooled condensers subject to contractor onsite workmanship.

In New Jersey, the new $24-million Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center Powered by the Giants, employs a 70-ton, 23,000-cfm dehumidifier that uses 80 percent less refrigerant to dehumidify its 743-m2 (8000-sf) aquatic space. The dehumidifier substitutes glycol for the estimated 312 kg (690 lb) of R-410A refrigerant used by a similar-sized conventional dehumidifier. Specified by consulting engineer firm, Jarmel-Kizel Architects and Engineers, the 10,405-m2 (112,000-sf) facility’s step toward refrigerant independence complemented HUMC’s sustainable programs, such as its in-house Dierdre Imus Environmental Health Center—a not-for-profit children’s advocacy group dedicated to identifying, controlling, and preventing environmental toxic exposure.

The HUMC’s dehumidifi er’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

The HUMC’s dehumidifier’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer ineffi ciencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer inefficiencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.

 

Retrofitting natatoriums
Whether it is an indoor pool for a small hotel or a large community center, specifiers should prepare for the coming deluge of the aforementioned dehumidifiers that will need replacement in the coming years.

A drop-in replacement with today’s technological improvements might appear feasible on paper, but the reality of mechanical room access may not accommodate a machine that is 2.4 x 3 x 9.1 m (8 x 10 x 30 ft) and arrives at the jobsite on a semi-truck flatbed trailer.

This was a situation confronting Ottawa-based consulting engineer firm, Goodkey Weedmark & Associates in nearby Kanata, Ont., during a $500,000-retrofit of the 25-year-old conventional indoor city recreation center into the new Kanata Leisure and Fitness Centre Wave Pool (KLFCWP).

The firm specified one large 2.6 x 3 x 7.3-m (8.5 x 10 x 24-ft) custom-manufactured unit, which was able to fit into a small mechanical room with no shipping door access thanks to a mechanical room’s mezzanine-level large exterior wall outdoor air louver. The dehumidifier manufacturer pre-planned the custom-built unit for breakdown into three 2.4-m (8-ft) long sections for shipping after the factory assembled and tested it under simulated natatorium operating conditions.

Mechanical contractor, T.P. Crawford (Gloucester, Ont.), rigged the three sections through the outdoor air louver, which was enlarged to 2.8 x 3-m (9.1 x 9.8-ft) for more access. The contractor then assembled and installed it inside the mechanical room. The louver’s opening then refitted for a new outdoor air damper/louver to comply with American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 62, Ventilation for Acceptable Indoor Air Quality—the standard’s outdoor air rates that had increased since the original building’s construction in 1986.

Instead of unit breakdown and assembly inside the mechanical room, a less-expensive and more reliable solution for cramped access and space in mechanical rooms has been developed. The solution is modular units designed to fit through 812-mm (32-in.) wide door frames. Once dollied into the mechanical room, the small horizontal footprint modular units are stacked and connections are quickly integrated to operate in tandem. Multiple pairs can equal the capacity of large units, but they consume considerably less floor space of large original dehumidifiers.

While they are mainly a logistics benefit and designed for retrofitting, the redundancy of two compressors, two coils, and two fans also offer energy-efficient staging that the larger unit with one compressor could never achieve. For example, during low-occupancy periods, staging off one of two small compressors instead of operating one large compressor sized for full occupancy can be a significant energy-savings.

Part of a retrofi t that netted the Wulf Recreation Center in Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

Part of a retrofit that netted the Wulf Recreation Center in
Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system
saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.

 

 

 

 

 

 

 

 

 

 

 

 

 

Considering outdoor air ventilation systems
Another sustainable consideration for either retrofits or new construction is an OAVS instead of a mechanical dehumidifier; however, the former is only viable in drier, cooler climates, such as mountainous regions or the northern United States. Using outdoor air in these geographical regions can reduce operating costs significantly, versus continually conditioning air with more energy-intensive compressor-based mechanical refrigeration circuits to maintain a natatorium’s desired 82 to 85 F (27.7 to 29.4 C) space temperature and 50 to 60 percent relative humidity (RH).

What make OAVS more conducive today versus a decade ago are many recent technology and control advancements combined with code changes mandating higher minimum amounts of outdoor air for indoor air quality (IAQ) reasons.

For example, today’s technological advancements were one of the reasons energy performance contractor, McKinstry in Seattle, Washington, was able to guarantee a 32-percent reduction as part of the retrofit of the 40-year-old Wulf Recreation Center in Evergreen, Colorado. The 3716-m2 (40,000-sf) center’s $540,000 retrofit—which included lighting, building envelope insulation, and digital controls—is saving the center $18,000 annually. New state-of-the-art indoor pool ventilation garners a significant portion of the savings. The two 6500-cfm outdoor air ventilation replacement systems for the 650-m2 (7000-sf) indoor pool is now saving a minimum of $4995 in operational savings and $12,704 in reduced therms annually, versus the former original gas-fired make-up air system, according to utility bills for the facility and an energy review McKinstry performed as part of its energy performance contract.

Integral to the savings are the two units’ heat recovery, direct drive fans, and an on-board microprocessor controller for pinpoint outdoor air modulation. Unlike the original supply/exhaust system, heat from the space’s exhaust air is now recovered via a glycol run around loop (GRAL) for pre-heating outdoor air. Using heat recovery helps raise outdoor air temperatures from –17.7 to 7.2 C (0 to 45 F) and reduces heating costs significantly.

As the Wulf Recreation Center demonstrates, an OAVS indoor swimming pool environment can be precisely controlled for much of the year, due partly to the technology advancements of outdoor air modulation controls.

While a well-designed OAVS can provide precise space conditions during drier, colder outdoor weather, this approach is not suitable for every facility. This is because there are periods when the space conditions may become warmer and more humid than desired, such as during mild weather and summer. For facilities where this period of time is short, or where the patrons would not mind elevated conditions during the warmer weather as a trade-off to the higher operating costs of running and maintaining a refrigeration circuit, OAVS is definitely a viable, sustainable option.

Whether an indoor pool is a prime candidate for the OAVS approach can be determined by software available from most dehumidifier manufacturers. The software calculates and models the expected space conditions throughout the course of a year, using local weather data input.

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The dehumidifi er industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifi er. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which signifi cantly reduces the environmental impact. Photo courtesy Seresco Technologies

The dehumidifier industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifier. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which significantly reduces the environmental impact. Photo courtesy Seresco Technologies

 

 

 

 

 

 

 

 

 

 

Specifying high technology
The real game-changer in indoor pool HVAC energy savings has come with technology such as exhaust-air heat-recovery, dedicated duty direct drive fans, and microprocessor operational control and monitoring.

Perhaps the most energy-saving air comfort and efficiency development has been the modulating outdoor air control. These controls monitor indoor and outdoor air conditions precisely and introduce only the amount of outdoor air required to maintain the best possible indoor air conditions. Before these precise controls were developed, natatoriums might have provided more outdoor air than needed during ultra-dry winter conditions that resulted in indoor relative humidity (RH) levels dropping too low below the desired 50-percent RH. Low RH levels create an uncomfortable chilling effect on wet skin and also raise operational costs. Bringing in more outdoor air than needed results in more outside air and pool water heating requirements.

Another option is pool water heating via heat recovery from the refrigeration circuit’s compressors. However, the ‘free’ pool water heating option is sometimes omitted during product specification, especially in value engineering requests. It is also sometimes missed during contractor installation.

There are dozens of dehumidifiers currently operating in natatoriums throughout North America where this energy-saving feature is mistakenly bypassed unbeknownst to the building owner. Consequently, the facility needlessly pays for pool water heating via a separate conventional gas-fired or electric pool water heater originally intended to back-up the dehumidifier’s pool water heating or expedite it during a dump-and-fill.

Selecting a mechanical dehumidifier with pool water heating through heat recovery might raise the upfront capital cost, but the benefit over the long-term will result in thousands of dollars saved in energy costs, depending on the facility size.

ASHRAE 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, has taken the energy recovery requirement a step further by mandating heat recovery or a pool cover. Many states have adopted the standard into local code requirements.

ASHRAE 90.1 calls for a pool cover for commercial indoor pools using conventional pool heaters unless “over 60 percent of the energy for heating comes from site-recovered energy.” The pool water heating option for a compressorized unit easily satisfies this requirement, but could also help satisfy a local code requirement and help eliminate the need for a pool cover.

Using exhaust air to pre-heat outdoor air
ASHRAE 62, Standards for Ventilation and Indoor Air Quality, recommends all commercial buildings bring a prescribed percentage of outdoor air as mandated by local building codes.

For the northern United States and Canadian indoor pools, wintertime heating of cold outdoor air to at least 26 C (80 F) to match the pool air temperature is costly. Fortunately for natatorium operators, their facilities’ humid and warm exhaust air is extremely energy rich and ideal for energy recovery. This recovered energy can be used to preheat the code-required outdoor air via heat-exchangers.

Preheating outdoor air using recovered heat from the exhaust air can cut outdoor air-heating costs by 50 to 75 percent. The payback for this kind of pool dehumidifier option is often only a few months (and rarely more than a few years), which makes it a cost-effective investment.

Remotely located exhaust fans can also be outfitted with heat transfer coils piped to the dehumidifier. Natatorium exhaust air is an energy source specifiers and operators should always consider for heat recovery. Aging dehumidifiers manufactured before this feature was available should be reviewed for a more energy-efficient replacement.

Direct drive plenum fans with VFD
Another example of a new energy savings technology is the introduction of dedicated duty direct-drive plenum fans with variable frequency drives (VFD). These plenum fans are a different style of fan that delivers air more efficiently than the traditional centrifugal-style typically seen in traditional dehumidifiers.

Compared to traditional belt-driven fans, a direct-drive plenum fan with a VFD can amount to as much as 15 percent in fan motor energy reduction. Considering a pool dehumidifier’s fans typically operate 24/7, the savings over the equipment’s lifecycle can be significant. The payback is instantaneous since direct-drive plenum fans with VFDs have comparable price to belt-driven systems.

Unlike belt-driven fans, the direct-drive concept connects the motor directly to the fan shaft. Thus, it eliminates friction, noise, maintenance, and power-transfer inefficiencies associated with belt drives.

Remote monitoring
All the aforementioned energy-saving technologies are worthless unless they stay well-tuned, maintained, and monitored. Unmonitored systems can limp along well below their intended optimal operating conditions, unbeknownst to the building owner.

Some dehumidifier manufacturers have solved this dilemma with the development of on-board monitor/control microprocessors that can send the entire unit’s vital operating statistics to the factory via the Internet. These programs sometimes offer a free daily monitoring service and even have smartphone applications where an authorized user can get e-mail alerts or access a unit from anywhere. The manufacturer can alert the facility manager of any issues and help the local service contractor troubleshoot, set up, or adjust the unit to ensure optimal performance. In the event of an alarm, troubleshooting can be assisted by a factory engineer, which ensures a quick resolution to any problem.

Conclusion
Many of the aforementioned advancements in indoor pool dehumidification over the past decade are manufacturers’ catalog items, but they also must be understood and specified by the consulting engineers and contractors. Once the building is operating, specifiers as well as building owners can rest assured the facility is operating at an optimal efficiency and is using the least amount of energy possible in providing IAQ.

Ralph Kittler, PE, is a co-founder and vice president of sales/marketing at Seresco Technologies, an Ottawa-based manufacturer of conventional and reduced-refrigerant natatorium dehumidifiers, and outdoor air ventilation system natatorium HVAC systems. He has 24 years of experience in the HVAC industry and a degree in mechanical engineering from Lakehead University (Thunder Bay, Ont.). Kittler is an American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) Distinguished Lecturer and sits on the association’s Technical Committee 9.8 and 8.10. He can be reached via e-mail at ralphkittler@serescodehumidifiers.com.

Seeing the Urban Forests for the Trees: Secondary benefits of our cities’ wood

Photo courtesy M MagazinePhoto courtesy M Magazine

by J. Gerard Capell, FCSI, AIA, CCS

A childhood treehouse, a place to hang a swing, or the support for a hammock in the cool shade—many of us can think back to these valuable memories that reflect the utility of trees in urban and suburban spaces. What if there were additional memories to be gained from the death and removal of those same trees? In a growing number of cities in the United States, urban forests are being recognized as a valuable, renewable resource for furnishings, paneling, flooring, or trim for residential or commercial spaces.

However, this transformation is neither straight forward nor simple. The process does not call for clear-cutting local parks—it involves the removal of trees that are diseased, storm-damaged, at the end of their natural lives, or need to be removed to make way for new development and street repairs.

Urban forestry is an industry resulting from the infestation of the emerald ash borer (EAB) that began in Michigan in 2002 and has now spread as far as Colorado, Georgia, and northeastern Canada. There are an estimated eight billion ash trees in the United States, and approximately 150 to 200 million have already died as a result of this invasive species.1 However, urban forestry is not limited to ash trees. In Milwaukee, the city cuts down and transports Norway maples, elms, honey locusts, basswood, and poplar—all of which are sent to a local mill for processing and are available for sale.

Emerald ash borers have been responsible for the felling of some 200 million trees. However, this wood could be repurposed in exciting ways. Photo © Leah Bauer, USDA Forest Service Northern Research Station

Emerald ash borers have been responsible for the felling of some 200 million trees. However, this wood
could be repurposed in exciting ways. Photo © Leah Bauer, USDA Forest Service Northern Research Station

City of Milwaukee workers loading a downed urban ash tree. Photo courtesy M Magazine

City of Milwaukee workers loading a downed urban ash tree. Photo courtesy M Magazine

 

 

 

 

 

 

 

 

Urban versus wilderness
Milwaukee is somewhat unique in that its department of forestry is responsible for cutting and trimming all city trees. The department can uniformly instruct the workers how to cut down the trees. The city also has a unique relationship with a local sawmill (Kettle Moraine Hardwoods), whose owner, Bob Wesp, has personally taught the workers how to look at a tree and keep in mind its usability as urban-cut lumber.

This might sound simple, but it is important to keep in mind the average city’s municipal employee is not a lumberjack from the Pacific Northwest with the skill and knowledge of how a mill will cut the tree into 1-by planks. For urban forestry, the first thing that needs to be done is to tell the workers the logs need to be as long as possible. Typically, tree service companies cut down trees into 915 to 1220-mm (3 to 4-ft) long logs that are small enough to fit into a Bobcat skip loader so they can be taken to the corporation yard where they will be ground into wood mulch. However, carpenters want trim that is at least 2.4 m (8 ft) long—preferably 3.1 to 3.7 m (10 to 12 ft) to eliminate mid-wall joints. Additionally, mills want a trunk or branch to be at least 254 to 305 mm (10 to 12 in.) in diameter for efficient sawing.

There are other things urban foresters must take into account. For example, by cutting too high up on the trunk or too close to the crotch of a pair of branches, one may unintentionally lose some really rich graining that will add a great deal of character to the planks. This is particularly the case for wood selected for furnishings where a unique grain pattern or coloration can make all the difference between just a piece of furniture and that special chair or table that can garner a higher price.

In regular forest-harvesting, the logs are placed on a 15 to 21-m (50 to 75-ft) tractor trailer. In urban forestry, a 25-m2 (30-cy) dumpster is the typical means of carrying the logs from the site to the mill, which means a log’s length is limited to a maximum length of about 7 m (21 ft) due to the dumpster’s length. The urban forester also needs a lift large enough to safely handle a 58 to 76-mm (20 to 30-in.) log that is 6.9 m (20 ft) long. Once the dumpster is full, it is transported to the mill.

tree crop

Emerald ash borer larvae scarring of the Cambrian layer. Photo courtesy  organicplantcarellc.com

Rough-sawn and planed urban ash board. Photos courtesy J. Gerard Capell

Rough-sawn and planed urban ash board. Photos courtesy J. Gerard Capell

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Meet the beetles
One of the first cities to undertake such efforts was Ann Arbor, Michigan, which was badly hit by the emerald ash borer. It is estimated that 7000 ash trees that lined its streets and yards were lost, and another 3000 were removed from the parks and surrounding nature areas, at a cost of at least $2 million. It is further estimated southeast Michigan lost upward of 30 million ash trees.2

EAB is believed to have come to the United States from Asia via packing crates and pallets. The beetle kills a tree by burrowing under the bark and depositing its larvae in the Cambrian layer, disrupting the tree’s ability to transport water from the roots to the leaves. Fortunately, the larvae do not damage the wood—this means if the tree is healthy and solid without rot or large splits, its lumber will be fine for higher-value uses.

The first method of EAB control was to clear-cut areas within 405 m (1320 ft) of the infested tree. Now, this radical surgery-management style is giving way to a controlled cut system such as that employed by Milwaukee in which insecticide is used to slow the EAB from destroying entire neighborhoods of trees, thereby giving the forestry department time to extend the devastation and tree replacement process out over a decade or more. The loss of so many trees within such a short time produced a significant volume of wood. Traditionally, such lumber was ground up for mulch, processed for bio-mass energy generation, or just sent to the landfill.

The Southeast Michigan Resource Conservation and Development Council (SEMIRCD) received a grant from the U.S. Department of Agriculture (USDA) to show there could be an economic benefit from the EAB problem and demonstrate markets for removed lumber.3 Through their efforts, numerous new markets for urban wood have been developed. For instance, an American Institute of Architects (AIA) Michigan award-winning project (Ann Arbor’s Traverwood Library) used reclaimed ash for flooring, wall panels, and ceilings. Structural columns utilized trees that were simply stripped and sealed leaving the scarred, rune-like patterns left by the chewing beetles.4 Similar efforts are now being employed in other cities, including Milwaukee.

Urban butternut (left) and urban red maple (right) sample panels.

Urban butternut (left) and urban red maple (right) sample panels.

Red Maple 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

From mill to shop
Once at the mill, a log may be set aside to dry, but because there might not be enough lumber to make up a pallet of one type, logs may have to wait until an adequate amount has accumulated. Unless there is a specific order for pieces of a specific size, a tree will be cut as ‘log-run,’ which is approximately 25 mm (1 in.)—or 4/4—thickness by random widths. This can be milled to 18-mm (3/4-in.) material that in turn can be used for most siding, flooring, and trim. Stair treads, mantels, and other special pieces need to be identified early so wider pieces with particularly good character can be cut at the same time. As this is log-run material, a pallet of lumber is not sorted or graded and the planks from a set of trees can range from FAS to No. 2 Common as defined by the National Hardwood Lumber Association (NHLA).

Another issue for urban lumber that is much more of a challenge is the greater likelihood that nails, wire, or bolts have been embedded in the tree. This means each log has to be magnetically scanned and cleared. Hitting even a small nail can ruin a blade, endanger workers, and result in downtime to make repairs. The mill operator in Milwaukee reported that from 30 to 35 percent of the urban trees it receives contain metal versus about two percent for trees coming from a standard forest preserve. They then have to pull those trees aside and search for the metal, and then remove it. If they cannot find the metal (or if there is too much of it), the tree may have to be discarded.

Once cut, hardwoods can take as long as 200 days to achieve 20 percent moisture content (MC) when just stacked with stickers (wood strips) between the planks. This is still a long way from the six to eight percent needed for interior use, so the wood must be put in a kiln, which takes two to four weeks to bring the wood to the desired moisture content. Then, the board can be shipped to a cabinet shop for fabrication.

If an owner or designer wants to use a particular stand of trees, the required time to turn those living trees into usable lumber for a carpenter or furniture-maker would be two to three months from the date of hewing the trees to have lumber stock ready to be milled into flooring, paneling, or trim. Most mills will have cut and dried urban lumber, but it is necessary to check to find out how much lumber is on hand so as not to delay the project.

Due to the need for a city to have a clear process to deliver its trees, most will probably have just one mill do the processing. Contractors and designers must connect with this firm, or work with another organization that has established a relationship with the mill to facilitate ordering and delivery. Groups such as Southeast Michigan Resource Conservation and Development Council in Michigan and Wudeward Urban Forest Products in southeast Wisconsin promote urban lumber use though education to the design and construction industry. More can be found on a state-by-state basis as businesses and cities look for an ecologically sound response to the losses in urban forests.

Once the lumber arrives at a cabinet shop, the real beauty of the wood emerges as the rough-sawn planks are trimmed, edged, and shaped into usable pieces. The hidden benefit of urban lumber starts to be realized at this time as richer colors and grain patterns emerge. However, since log-run lumber is not graded or sorted, splits, warping, and snapping at loose knots can easily claim upward of 50 percent of the lumber delivered from a pallet, adding to the cost to the fabricator in lost materials and time. The designer and owner may want to schedule a visit to the shop at this time to verify the design intent for the wood is being realized, especially when the piece is a feature element such as an entry wall or reception desk.

Urban ash trim at the University of Wisconsin–Milwaukee. Photographs courtesy Amy Hall

Urban ash trim at the University of Wisconsin–Milwaukee. Photographs courtesy Amy Hall

DSC_3235

 

 

 

 

 

 

 

 

The green forest
Another clear benefit of using urban lumber is the ability to gain credits from sustainability programs. With the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program, credits can be easily claimed for Materials and Resources (MR) Credit 5, Regional Material Use.

MR Credit 7, Certified Wood, is a more problematic credit to obtain. The difficulty arises in the lack of an established recognition by the Forest Stewardship Council (FSC) of urban wood. At press time, FSC had announced there will be a motion offered at its General Assembly to be held in Seville, Spain, in the fall to ‘capture’ urban wood as part of the supply stream. Many issues will have to be resolved to establish the type of recognition, but this is a positive event that was not expected by many in the urban wood community for at least another three years.

The designer’s role through this process is that of educator and facilitator. They need to ensure the contractor (and the related subcontractors) is aware of this special product and that additional care may be required during bidding and fabrication. They also need to make certain owners are aware this unique, sustainable resource is available and can be an asset to the completed project. As mentioned, the designer needs to be much more hands-on to facilitate the proper use of the urban lumber. It is akin to working with a fine marble slab—the goal is to capture as much of the intrinsic drama and beauty possible from a natural and non-uniform material.

Specifications
Specifiers have a key role in ensuring urban lumber is correctly specified and incorporated in the project. Typical sections that would be used are MasterFormat 06 20 00–Finish Carpentry, 06 41 00–Architectural Casework, and 09 64 00–Wood Flooring. A small but important addition to a standard master specification should be a brief definition such as:

Urban Lumber: Wood that is obtained from trees located in cities, towns or suburbs not harvested for their timber value, but removed because of insect, disease or circumstance.

This will help clarify the material, distinguishing it from salvaged lumber, which may be collected from an existing building, or from rivers and lakes.

This an example of urban ash stair treads.

This an example of urban ash stair treads.

Other key areas should be inserted into a specification section depending on the level of desired aesthetic control. They include:

  • samples of adequate size and length to show the range of acceptable color, grain, and acceptable flaws;
  • pre-fabrication meeting, where the designer, owner, contractor, and millworker meet to establish the quality of the finish work;
  • mockup approval of casework, paneling, or flooring to verify the desired quality level;
  • list of approved mills or suppliers that deal with urban wood near the project; and
  • clarification of the grade (or lack thereof) provided by the mill or supplier for the urban wood—NHLA grades are probably the best source for these, but there is no recognized grade for log-run material (it should be listed to give the cabinet shop an idea of what to expect).

Another important provision, especially for casework or stairs, is to use (AWI/AWMAC/WI) standards to define the expected quality standard of the completed work. These standards control the amount of grain and color-matching between members to ensure a uniform appearance is achieved (or not achieved, depending on the designer’s intent). This is especially the case when using wood such as ash that can have a broad variety of color and grain pattern within the same board.

When the designer is aware of the possibilities, a truly remarkable piece of casework or paneling can be achieved. By utilizing urban lumber, owners can attach a great story and add a unique component to any building.

Conclusion
From the disaster of emerald ash borer infestation emerges new opportunities to enrich urban spaces and provide new memories from city trees. Architects, contractors, and owners have the ability to use and promote this unique resource, but as with any ‘new product,’ the various parameters must be understood for its correct use to achieve the best results for all involved.

Provided design/construction professionals and urban forestry workers know the ideal criteria for board length, importance of identifying special cuts early, and the need to sort or grade material prior to delivery to fabricators to minimize waste results, urban lumber has great opportunity for richer character in the wood, making for a unique finish with a great back story.

Notes
1 This comes from Therese Poland and Deborah Therese’s April/May 2006 article in Journal of Forestry, “Emerald Ash Borer: Invasion of the Urban Forest and the Threat to North America’s Ash Resource.” (back to top)
2 See Marianne Rzepka’s August 22, 2010 article in the Ann Arbor Chronicle, “Seeds and Stems.” (back to top)
3 For more information, visit www.semircd.org. (back to top)
4 The project was profiled in Bradford McKee’s October 6, 2009 article, “Traverwood Branch Library,” which appeared in Architect. (back to top)

J. Gerard Capell, FCSI, AIA, CCS, is principal of Capell Design Associates in Milwaukee, Wisconsin, providing architectural design and specification writing services. His experience has broadly evolved from his work in California, Wisconsin, and Florence, Italy; this includes work as a rough and finish carpenter, architect, and specification writer on healthcare, education, civic, residential, senior living, retail, and industrial projects. Capell has served on CSI’s Certification Committee and Board, along with positions at the region and chapter level over his 28 years as a member. He can be reached at jgcapell@wi.rr.com.

Energy Efficiency and Building with Wood: Six Building Lifecycle Steps

Buildings have an impact on people and the environment throughout their entire lifecycle, starting with extracting resources from the earth to putting them back in the earth, or burning them, at the end of their lives. To evaluate the effect of buildings in this regard, everything from the energy they consume, the waste they generate, and the carbon dioxide (CO₂) they emit must be considered throughout the six major cycles below.

The combination of wood and the Passive House standard is a common-sense approach that can have a very positive lifecycle impact on the environment. In fact, according to a report from the U.S. Forest Service, wood in building products yields fewer greenhouse gases (GHG) than other common materials.*

1. Resource extraction
Everything in buildings comes from natural resources, some of which grow relatively quickly above the ground (e.g. wood), while others take millions of years to form below the ground (e.g. materials derived from fossil fuels). Taking a look at wood, the amount of heat, water, and pollution generated compared to extracting iron to produce steel, or extracting limestone to produce cement is significantly lower.**

The lifecycle of wood has a smaller impact. For example, the sun hits the tree, and the tree grows. It can be cut down with light machinery and a new tree is planted. It absorbs carbon, provides oxygen, and can be used in the future. In this context, it means a more sustainable production, compared to making concrete or steel, where digging for oil, coal, or natural gas and then burning it is a prerequisite to extracting the raw materials from the earth.

2. Manufacturing
The real ‘weight’ of a material—including resources, water, and energy used at the entry point of a manufacturing facility—compared to the material that comes out at the other end is referred to as the ‘ecological backpack.’ This measures the environmental impact of manufacturing products. Common sense suggests it requires less resources and energy to manufacture wood products compared to concrete and steel. Heavy timber and mass timber products can meet the same structural and fire requirements that also govern concrete and steel.

3. Off-site and onsite production
In many cases, the process of constructing buildings is antiquated, relying on manual and labor-intensive onsite processes. Other fields, such as manufacturing automobiles, have advanced considerably using automation and an industrialized system approach to designing and building, where the energy efficiency, in miles per gallon, can be guaranteed and the assembly occurs in a modern factory. Modern wood prefabrication processes can offer new opportunities and better working conditions. In this respect, building with wood can offer fast and efficient options for construction.

4. Operation
The natural resources needed to produce and deliver the energy consumed to heat and cool buildings for lighting, appliances, and water is the highest of all six lifecycle steps. While more efficient lighting and appliances can be specified, the only way to reduce long-term heating and cooling loads is to improve the building envelope. Airtightness is the most important element that has made the Passive House standard succeed. It can easily be achieved using modern wood carpentry, as discussed in this article.

5. Demolition
At the end of a building’s lifecycle, products are usually disposed of in landfills. Using a system approach to construction, buildings can be designed so they can be disassembled and separated for recycling. Design optimization, use of recovered wood, and specifying jobsite waste to be separated and taken to a local recovery center are all ways to reduce, reuse, and recycle.

6. Recycling
Wood from buildings can be recovered for use in other buildings or be employed to create furniture or other products. Even at the end of their second or third ‘life,’ wood products can be burned to generate energy or decompose naturally in the earth.

*See USDA Forest Service’s “Science Supporting the Economic and Environmental Benefits of Using Wood and Wood products in Green Building Construction.”
** For more, see the International Journal of Life Cycle Assessment article, “Wooden Building Products in Comparative LCA: A Literature Review,” by Frank Werner and Klaus Richter. Visit www.vhn.org/pdf/LCA-Wood-algemeen.pdf.

To read the full article, click here.

Energy Efficiency and Building with Wood

Photo © Norman A. Müller

Photo © Norman A. Müller

by Nabih Tahan, AIA

In creating energy-efficient buildings, one of the most important goals is to accurately predict during the design stage how a structure will perform when occupied—not only the natural resources used to produce it, but also the ongoing energy consumed for its regular operation. New opportunities combining modern carpentry techniques and the Passive House standard help achieve these goals.

There are three main ways to make a building energy-efficient—using less energy, generating more energy with renewable resources, or taking a combined approach of the two. In this author’s opinion, doing both is the best option. However, it is first important to eliminate heat losses due to design strategies and construction techniques.

In winter, heat in buildings is often needlessly lost due to conditioned air escaping through cracks in the envelope. To replace this heat, heaters are used. Eliminating air leakage and heat loss in buildings by making them airtight is the most important factor for making buildings energy-efficient.

New wood building systems have been developed to offer greater airtightness to minimize energy consumption. The building industry should focus on combining the two aspects of using renewable building materials and energy efficiency to achieve comfortable buildings, while optimizing indoor air quality (IAQ) and reversing the negative effect of climate change. (See “The Six Lifecycle Steps” to understand the advantages of combining wood and energy efficiency when specifying a building system.)

New building materials created through advanced versions of engineered wood are changing non-residential construction. With the right techniques, they can bring about improved energy effi ciency. Photo courtesy Nabih Tahan

New building materials created through advanced versions of engineered wood are changing  non-residential construction. With the right techniques, they can bring about improved energy efficiency. Photo courtesy Nabih Tahan

Europe is far ahead of North America when it comes to monitoring and reporting energy consumption of buildings and homes. This image comes from Ireland’s Building Energy Rating (BER) program for residences. Image courtesy Sustainable Energy Authority of Ireland

Europe is far ahead of North  America when it comes to  monitoring and reporting energy consumption of buildings and homes. This image comes from Ireland’s Building Energy Rating (BER) program for residences. Image courtesy Sustainable Energy Authority of Ireland

Using and measuring energy
It is not enough to design buildings using energy efficiency strategies—they must also be constructed accordingly and then meet the energy consumption goals of the design during operation. This is similar to a car manufacturer designing and producing a vehicle with a specific fuel economy, and then having the car actually meet that target. Everyone is familiar with comparing cars in terms of ‘miles per gallon,’ and now a similar unit of measurement for buildings is needed. At some point, this metric for energy consumption of a building or apartment might even be included in the Multiple Listing Service (MLS).

The European Union (EU) requires every building have an Energy Performance Certificate listing the energy consumption of space heating and cooling, water heating, lighting, and appliances. The certificate must be available to buyers and tenants when a building is constructed, sold, or leased. In Europe, the unit of measurement used for the certificate is kWh/m2/year.

In the United States, energy consumption in buildings is compared to the local energy code requirements in relative numbers as opposed to a consumption rate. Buildings are described as being a certain percentage better than the prevailing code, rather than having their actual consumption cited. As new energy code updates take effect, a similar unit of measurement comparable to the Energy Performance Certificate will be established. In the meantime, the Passive House standard is a good tool to measure and compare how much energy buildings are consuming.

For new-generation wood projects, walls are simply stood up and windows, siding, and trim are installed. Photo courtesy Nabih Tahan

For new-generation wood projects, walls are simply stood up and windows, siding, and trim are installed. Photo courtesy Nabih Tahan

Preparation for blower door test for LCT ONE—a Passive House-certifi ed, eight-story wood offi ce building in Austria. Photo courtesy Cree GmbH

Preparation for blower door test for LCT ONE—a
Passive House-certified,eight-story wood office
building in Austria. Photo courtesy Cree GmbH

 

 

 

 

 

 

 

 

 

 

Passive House and net-zero energy design
Passive House is a European-developed standard that has recently found its way to North America. The original German name ‘PassivHaus’ refers to both commercial and residential buildings. Rapidly gaining popularity in North America, the standard demands high-performing building envelope assemblies and airtightness.1

Passive House calculates energy consumption (in kWh/sf/year), and includes energy-use from space heating, cooling, and ventilation systems, along with water heating, lighting, and appliances. Under the standard, the maximum energy allowed for heating and cooling is 1.4 kWh/sf/year. The standard has become successful because it has proven it can accurately predict, during the design stages, the building’s eventual energy consumption. (This is comparable to a car company claiming a car will get 30 mpg and proving to be correct.) Predicting the energy consumption in the design stages is done with the Passive House Planning Package—an energy modeling tool.

The Passive House standard is a whole building strategy that harmonizes all aspects of a structure beginning with data on local weather and solar orientation and continuing with the design, layout, foundation, framing, and insulation systems to reduce, or even eliminate, thermal bridging. It also optimizes specification of the openings (i.e. doors, windows, and curtain walls), heating, cooling, and ventilation systems, along with lighting and appliances.

Specific to thermal properties, it is important to incorporate building materials that have low thermal conductivities, and design details that minimize thermal bridging. By nature, wood is ideal for this, made up of thousands of open cells that make it difficult to conduct heat. In fact, the thermal properties of wood products are 400 times better than steel and 10 times better than concrete.2

Most importantly, Passive House has a specific requirement for airtightness, which is where the biggest connection to modern wood carpentry is made. Airtightness is measured with a blower door test.3 Air is either pumped into or sucked out of a building to see how much air is leaked, in both pressurized and depressurized states. This is similar to fixing a leak in a bicycle inner tube. Air is pumped into the tube and placed in water and the leaks are found by following the bubbles. For buildings, smoke or other instruments are used to find leaks during a blower door test. If the test is performed before the building envelope is covered up, the leaks can be sealed to make the building airtight.

Lighting and all appliances (including ovens, cooktops, refrigerators, toasters, and computers), generate some heat. Instead of allowing this heat to escape through a leaky building envelope, it is trapped inside a tight building envelope. A mechanical ventilator, with a heat recovery component, brings in fresh air into the living spaces and removes the same amount of stale air from kitchens and bathrooms.

The heat in the outgoing stale air is transferred to the incoming fresh air inside the ventilator. This recycling (or ‘U-turn’) of ‘free’ heat’ that comes out of everyday appliances and lighting can dramatically reduce a building’s energy consumption. Future energy codes in North America will also be targeting a net-zero energy standard. A net-zero energy building is hooked up to the grid and draws electricity and natural gas from the grid. The building also has a source for generating renewable energy such as solar or wind energy. During a one-year period, the amount of energy a building draws from the grid has to equal the energy it generates from renewable resources. The easiest way to meet the net-zero energy standard is to consume less energy, which is where the strategy of Passive House, in combination with modern carpentry, becomes valuable.

To combine this strategy with the choice of materials and construction methods, use of modern engineered wood products—stable, cut accurately with computerized equipment, and assembled under a controlled environment—results in airtight buildings that are automatically energy-efficient.

Prefabrication and modular wood construction is helping building designers achieve this while increasing the speed of construction and reducing project cost. Energy-efficient design is also becoming more important in North America, as the U.S. Department of Environment (DOE) has a goal of all new commercial buildings being ‘net zero’ by 2025.

This photo shows framing lumber cut with computer numerical control (CNC) machinery. Photo courtesy Nabih Tahan

This photo shows framing lumber cut with computer numerical control (CNC) machinery. Photo courtesy Nabih Tahan

Wall elements are produced on tables. Photos courtesy Cree GmbH

Wall elements are produced on tables. Photos courtesy Cree GmbH

 

 

 

 

 

 

 

 

Wood technology
When talking about wood construction, the reference points are traditionally stick-frame, or light-frame residential construction. Modern wood construction falls under the category of heavy timber, using large-dimensioned posts and beams. A new category of mass timber includes cross-laminated timber (CLT)—sometimes referred to as ‘plywood on steroids.’4

The post-and-beam method of wood construction was prevalent in many cities at the beginning of the last century, before the industrial revolution introduced concrete and steel. Now, wood products are beginning to increase again in popularity due to awareness over some of the negative environmental effect of products extracted and manufactured with intensive use of fossil fuels. Of course, this is not to say one product type is always better than another—each material has special properties and they should be combined to make hybrid buildings.

Modern timber products for structural framing are referred to as engineered lumber. These members use smaller pieces of wood, eliminating the need to harvest large trees. The ends of these smaller pieces are finger-jointed and glued to make longer pieces. Several long pieces are laminated together to make large glued-laminated (glulam) post and beams. This lumber is stable and will not shrink or twist because it is dry, which is a great advantage for airtightness, performing much better than traditional stick frame wood with higher moisture content.

For fire safety, heavy timber is allowed under the 2012 International Building Code (IBC). Wood burns approximately 38 mm (1.5 in.) per hour. Therefore, the fire regulations allow the size of structural members to be increased by 38 mm per hour for each exposed member. If a member requires two-hour fire protection, 76 mm (3 in.) are added to the size required structurally. Light-frame construction is similar to kindling for a fire. Heavy timber construction cannot be ignited without kindling; like throwing a large log into a fire, heavy timber members will char, protecting their structural integrity and strength.5

The modern process of carpentry is based on digital, computerized information. The carpentry company receives the computer-aided design (CAD) drawings from the architect. They transfer the drawings to 3D-CAD/computer-aided manufacturing (CAM) program where the wood frame can be looked at in 3D and the structure can be optimized. This is called optimal value-engineered, or ‘smart,’ framing.

Every piece of wood is placed in an exact location and has a purpose. Unnecessary framing members are eliminated and replaced with insulation to optimize energy performance.

The material is then fed to a wood-cutting machine that uses the computer numerical control (CNC) data to precisely cut all the elements. The engineered lumber is stable and is cut precisely and eliminates waste since the members can be 12.1 to 18.2 m (40 to 60 ft) long. The individual pieces are assembled together in a facility, working on tables and prefabricated into wall, floor, and roof elements. These components can be quickly erected onsite in an airtight manner, ensuring energy-efficient construction.

Instead of asking carpenters to measure, cut, and assemble walls and floors onsite, employing labor-intensive processes, the carpenters are moved in a controlled environment, where they are given the drawings and pieces for each component to be assembled, making use of overhead cranes and forklifts to protect their bodies.

The advantage of this process is it optimizes the construction, guarantees stable material, and accurately cut pieces and assembled components that fit together tightly. Specifically designed tapes and gaskets are used at the intersection of panels to prevent air leakage. As proof of performance, the building can be tested for airtightness by a third party by administering a blower door test to meet the ≤ 0.6 air changes per hour @ 50 Pascal pressure—one of the main requirements of the Passive House standard.6

This wall element was craned in place. These types of components can be completed onsite in an airtight manner.

This wall element was craned in place. These types of components can be completed onsite in an airtight manner.

This is an example of precision cutting using CNC machinery. Photo courtesy Nabih Tahan

This is an example of precision cutting using CNC machinery. Photo courtesy Nabih Tahan

 

 

 

 

 

 

 

 

Conclusion
Combining modern wood technology and Passive House strategies helps save resources and achieves energy efficiency in buildings. The fundamentals of modern carpentry are based on:

  • optimizing the timber structure;
  • uses stable engineered lumber;
  • cutting the material accurately using industrial machinery;
  • prefabricating components under a controlled environment; and
  • assembling them quickly onsite to be cost-competitive, while automatically meeting airtightness requirements.

Using this construction process and modern carpentry skills, the building envelope’s thermal performance and airtightness can be predicted during the design stages. To prove the performance, the envelope is tested for airtightness with a blower door test after assembly. Similarly, the energy performance of a building can be predicted using the Passive House standard during the design stages—through the thousands of certified buildings in Europe, the actual energy consumption during occupancy has been shown to match the predicted values.

Overall, the use of new modern wood technologies can have a positive effect on construction industry from job creation to reduced environmental impact.

The design team, including architects and engineers, can collaborate to ensure wood-based building envelopes can meet these high-performance standards. In collaboration with the Passive House consultant, the design team can determine which layer in the wall/floor/roof assemblies prevent air leakage and include details on how to seal intersections and penetrations.7 They can model heat transfer effect in building components to eliminate or reduce thermal bridging and specify available products for taping and sealing joints proven to be durable and long-lasting.8

Notes
1 There have been dozens of certified projects in North America, and the numbers are growing fast. There are two competing U.S. organizations, and both of them have databases and listings for these projects. The North American Passive House Network (NAPHN)—www.naphnetwork.org—is directly affiliated with the Passive House Institute (PHI) in Germany, while the Passive House Institute US (PHIUS)—phius.org—was founded by someone who used to work with PHI, before branching off.
2 For more information, see Naturally Wood’s “Green Building with Wood–Module 3” at www.naturallywood.com/sites/default/files/Module-3-Energy-Conservation.pdf.
3 The Passive House Institute requires the test to meet the European Standard EN 13829, Thermal performance of buildings: Determination of air permeability of buildings, fan pressurization method. In the United States, ASTM E1927, Standard Guide for Conducting Subjective Pavement Ride Quality Ratings, and ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, would be used with Resnet Protocol Chapter 8, “Enclosure and Air Distribution Leakage Testing.”
4 The limitations of these types of wood assemblies are the current building codes or special approval by a jurisdiction for alternative means of design and construction. Obviously, it is not a one-for-one switch between wood and concrete—the architect and engineers have to run calculations for both materials to ensure the design meets the structural, seismic, acoustic, and thermal requirements. At the moment, the building codes limit wood buildings to 75 ft (i.e. 23 m). The wood industry is in the process of testing new wood products such as CLT for fire and seismic performance. This author’s company is in the process of negotiating a partnership/joint venture agreement to participate in an Expression of Interest for a 16 to 18-story student residence building utilizing advanced wood-based building system, physically demonstrating the applicability of wood in the tall building market.
5 For more on wood and fire resistance, see “Design of Fire-resistive Exposed Wood Members,” by Bradford Douglas, PE, and Jason Smart, PE, which appeared in the July 2014 issue of The Construction Specifier.
6 Visit www.passiv.de/en/02_informations/02_passive-house-requirements/02_passive-house-requirements.htm for more information.
7 This is a consultant that collaborates with the architect, and structural, mechanical, and electrical engineers. During the design stages, the passive house consultant begins the energy modeling in the Passive House Planning Package (PHPP) tool to determine the heating, cooling, and electrical loads. The PH consultant then submits the calculation to either PHI or PHIUS for pre-certification. The MEP engineers use these calculations to design the system, and the architect and structural engineers design the details to eliminate or reduce thermal bridging.
8 For more, see this author’s previous article, “LCT ONE–A Case Study of an Eight-story Wood Office Building,” in the March 2014 issue of The Construction Specifier.

Nabih Tahan, AIA, is an international architect, Passive House consultant, and CEO of Cree Buildings Inc. For more than 30 years, he has honed his knowledge in architecture, energy efficiency, and sustainable timber-based construction methods through work in Austria, Ireland, and the United States. Currently, Tahan is guiding Cree Buildings to establish a systems approach to design and construction, combining wood and energy efficiency strategies to build single-family and multi-family residential projects, along with office buildings. He can be contacted at nabih.tahan@creebuildings.com.

10 Key Questions about Exterior Shading

Photo © Richard Wilson. Photo courtesy Draper Inc.

Photo © Richard Wilson. Photo courtesy Draper Inc.

by Richard Wilson, B.Sc.

Over the last decade, exterior shading has become more popular in the U.S. construction market. However, many architects and building owners still have limited knowledge about these systems and why they should be considered part of the building design.

This article explores 10 frequently asked questions about exterior shading, while providing insight into available systems and how they can be an important part of the building’s environmental control.

1. What exterior shading systems are available?
A wide range of exterior shading systems are available, but they can be broken down into three broad categories of systems:

  • fixed louver;
  • adjustable louver; and
  • retractable.

Fixed louver systems include projecting sunshades generally installed at the head of the glazing (i.e. brise-soleil systems), as well as fixed vertical or horizontal louvers installed in front of the glazing. These systems are designed to remain in place at all times and need to be able to withstand all weather, including wind, ice, and snow. The shading performance varies depending on the system’s projection and the louver profile selected, as well as the angle of the louvers and the spacing between them. These items need to be evaluated during the design process to ensure the system provides sufficient shading during periods when solar gain is an issue.

Brise-soleil systems only address high sun angles and, as a result, they generally will only be effective on south or near south-facing elevations. They also only provide shading during the summer. During the winter months, the low sun angles mean these systems provide little or no shading.

The effectiveness of fixed horizontal or vertical louvers depends on louver size, angle, and spacing. These systems normally only shade higher sun angles in order to allow views to the exterior, and are most effective on south-facing elevations. They can be installed on east and west elevations, but will normally not protect occupants from the low sun in the early morning or late afternoon.

Vertical and horizontal adjustable louver systems can be motorized, allowing louver angles to be adjusted to give more responsive shading, particularly if they are connected to an automated control system. The systems do not retract—they will always remain in front of the glazing—but can be moved between the fully open and closed positions.

The method of control can range from switch operation, where occupants operate the system according to their needs, to a fully automated system that responds to the sun conditions and adjusts the louver angle to prevent any direct sun penetration. The systems are generally controlled independently of the interior lighting systems; ideally, levels are automatically adjusted to supplement natural daylight where required. Since the systems only operate from time-to-time, and only for a few seconds to adjust the louver angle, energy usage is not significant, particularly compared with the savings that can be achieved through a reduction in HVAC requirements.

This project features an exterior venetian blind assembly. Photo courtesy Draper Inc.

This project features an exterior venetian blind assembly. Photo courtesy Draper Inc.

This brise-soleil system was installed at the Southern Alberta Institute of Technology (SAIT) in Calgary, Alberta. Photo © Ralph Wilson. Photo courtesy Draper Inc.

This brise-soleil system was installed at the Southern Alberta Institute of Technology (SAIT)
in Calgary, Alberta. Photo © Ralph Wilson. Photo courtesy Draper Inc.

 

 

 

 

 

 

 

 

 

 

 

 

2. Why is an exterior system more effective than an interior one?
In broad terms, an exterior system is better than an interior one because it prevents a large part of the sun’s energy from reaching the glazing and entering the building. If the solar energy does not get into the building, it does not have to be dealt with.

Energy from the sun is short-wave and carries little heat. Heat is only produced when the solar energy is absorbed by a surface (e.g. carpeting, furniture, clothing, or skin) and is then radiated as long-wave infrared (IR) energy.

An interior shading system can:

  • allow solar energy to pass through;
  • absorb solar energy; and
  • reflect solar energy back through the glazing.

The reflected solar energy is not an issue—it remains short-wave and does not cause any heat gain. The transmitted energy is absorbed by surfaces in the building and is radiated as heat. The energy absorbed by the shading system is then radiated as heat and most of this heat is then trapped inside the building, particularly if low-emissivity (low-e) glazing is used.

An exterior system is similar to an interior one with regards to the transmittance, absorption, and reflection of solar energy. Anything absorbed by the shading system, however, is radiated as heat on the building’s exterior. Since glass is not transparent to long-wave energy, little of this radiated heat gets inside the building. Accordingly, an exterior system eliminates one of the two sources of heat gain, resulting in much greater reduction in solar gain inside the building.

Performance data is readily available for shading fabric. Consider a popular fabric in a grey-white color and a particular type of glazing (e.g. low-e, argon filled, double-glazed unit), the ‘g’ value is 0.13 when the fabric is installed on the exterior, but increases to 0.43 when installed on the interior. The ‘g’ value is the sum of the direct and secondary solar transmittance into the building. The secondary transmittance comprises the amount of solar radiation absorbed by the combination of glazing and shading system which is then convected or radiated into the building. In North America, the ‘g’ value is also known as the solar heat gain coefficient (SHGC).

Even with a white fabric, which has the highest level of reflectance, the comparison is 0.16 for an exterior installation compared with 0.36 for an interior one.

The message is therefore straightforward—for the most effective solar control, the shading system should, wherever possible, be installed on the exterior. There will be some situations where this is not practical—for example, high-rise buildings with 25 floors or more. In these cases, the use of a shading system inside a ventilated double façade is a potential approach, although shading is just one of many influencing factors when pursuing this type of façade construction.

3. What are the main benefits of an exterior shading system?
The primary benefit of an exterior shading system is a reduction in HVAC requirements. As discussed earlier in this article, exterior shading blocks a large part of the solar gain before it comes through the glazing and into the building. If there is less solar gain, then the size of the HVAC system can be reduced. This results in a saving in the initial capital cost—which can wholly or partly offset the shading system’s cost—as well as the ongoing running costs. The most effective shading systems, such as exterior venetian blinds, can block more than 90 percent of solar gain, having notable impact on reducing the HVAC requirements.

Some buildings, however, need to be cooled in the summer, while also have heating requirements in the winter. If a retractable exterior shading system is used, it can be turned off in the winter months, allowing the solar gain into the building and providing an element of free heating. During those months, glare and light control issues would be addressed with an interior shading system such as a roller shade.

Another benefit is natural daylighting. Exterior shade systems can help optimize the use of diffuse daylight to illuminate interiors, reducing the need for artificial lighting. More than 30 percent of the energy costs of an office building relate to artificial lighting, so if lighting needs can be reduced, significant savings can result.

A well-designed shading system also contributes to comfortable working conditions which can lead to increased productivity. A good shading system manages both heat and glare while providing access to outside views. Finally, using exterior shading systems can significantly contribute to a building’s appearance; it can become a design feature as well as one bolstering efficient building performance.

CS_October_2014_HR-44

The orientation of the glazing has a signifi cant impact on what solution works best. Shown above is the impact of orientation on incident solar radiation for a building in Indianapolis, Indiana.

The orientation of the glazing has a significant impact on what solution works best. Shown  above is the impact of orientation on incident solar radiation for a building in Indianapolis, Indiana.

 

 

 

 

 

4. Can exterior shading systems be used on both new and existing buildings?
It is always easier to apply exterior shading systems to a new building, as integration issues can be reviewed and connection details developed during the design phase. Fixed exterior louver systems can exert significant loads on the façade, and if they are being attached to the curtain wall, mullions might need to be reinforced to support them. Even with lighter, retractable systems, such as venetian blinds, it is helpful to be able to discuss attachments with the curtain wall contractor during the design phase so brackets can be specified to avoid problems such as cold bridging.

However, it is possible to apply external shading to existing buildings. While the original building design would not have anticipated exterior shading, structural elements can be incorporated as required, to allow installation onto the existing façade. The structure, rather than the façade, would then accommodate applied loads (i.e. wind, ice, snow) as well as the weight of the system itself.

If an operable system is going to be used with an existing building, it will be necessary to look at the electrical requirements and determine how conduit and electrical cabling can penetrate through the façade to allow connections to be made to the blinds or shades.

5. What are the common methods of attachment to the building façade (and what issues need to be considered)?
With both new and existing buildings, installation of an exterior shading system might involve attaching directly to the curtain wall mullions, to brick or concrete masonry units (CMUs), or through cladding to steel structure. It is probable different brackets will be required for each situation, and these will often be developed to meet the specific project requirements.

These louvers were designed for custom window shapes. Images courtesy Draper Inc.

These louvers were designed for custom window shapes. Images courtesy Draper Inc.

Exterior roller shades and venetian blinds are generally installed just above or at the top of the glazing. They are relatively lightweight and, because they are retracted when the wind speed exceeds a defined level, they do not apply significant loads to the façade. This means lighter aluminum brackets can normally be used to connect the head box to the façade. Pre-tensioned side guide wires are also generally used to prevent movement of the shading system under wind load (the other option is extruded side guides) and each of these will be tensioned to approximately 22.7 kgf (50 lbf).

Since exterior louver and brise-soleil systems remain fixed in place in all weather conditions, they apply more significant loads to the façade. The brackets for the system will therefore be designed in accordance with the loads defined in local building codes, and bolts or other fasteners will also be selected based on the maximum loads. If the systems are being connected to the curtain wall, it is possible the mullions will need to be reinforced with steel. This is particularly the case with brise-soleil systems, which project some distance from the façade and, as a result, generate significant turning moments and shear forces at the connection points. With these types of systems, structural calculations will always be undertaken to determine the applied loads and the impact on the façade design and building connections.

Other issues that need to be considered include separation of dissimilar metals, cold bridging, and water penetration, as well as relative expansion and contraction between the shading system and the façade. Given these issues, it is strongly recommended the shading requirements are reviewed and discussed during the early stages of the design process.

6. Will the building’s location and the glazing’s orientation influence the choice of exterior shading system?
There are many factors influencing the choice of an exterior shading system. Two significant ones are building location and glazing orientation.

As seen in Figure 1, the movement of the sun during the year (shown by the blue lines) is significantly different between two extremes in the United States—Miami, Florida, and Anchorage, Alaska.

In Miami, the sun angle is approximately 86 degrees, and almost vertical in the sky, at 12:00 p.m. on June 21. In Anchorage, the sun has a peak altitude angle of approximately 51 degrees, which is not much greater than the highest winter sun angle in Miami of 41 degrees. The sun also sets much further to the south in Anchorage during the winter compared to Miami.

Given the differences in sun movement, the optimal shading strategies will be different. In Miami, fixed projections will be effective; while in Anchorage, retractable and adjustable systems offer much more flexibility in controlling solar gain.

The glazing’s orientation will also have a significant impact on system choice. The graph in Figure 2 shows the incidental solar radiation on different orientations of glazing for a building in Indianapolis, Indiana. As expected, the solar radiation on the north elevation is the lowest as there is no direct sun. However, the background radiation is still reasonably significant, particularly in the summer.

The solar radiation on the east and west elevations is similar, with the maximum values occurring in the summer. Interestingly, the maximum solar radiation on the south elevation occurs during the colder months. In the middle of the summer, the high sun angles mean the incident radiation falls. The maximum exposure to solar radiation, however, occurs at the roof. Therefore, any skylights will potentially cause significant solar issues.

Given the variations by façade, fixed systems might work on the south elevation, but operable ones will be better east and west. Although vertical louvers might work on the east and west elevations, horizontal ones are generally better for controlling the solar gain and allowing views to the exterior.

This installation in Holland features solid-screen, ‘zip’ system installation. Photo © AVZ. Photo courtesy Draper Inc.

This installation in Holland features solid-screen, ‘zip’ system installation. Photo © AVZ. Photo courtesy Draper Inc.

7. How do exterior shading systems cope with adverse weather conditions?
As previously highlighted, fixed louver systems are designed to take account of the maximum applied loads. With brise-soleil systems, the loads at the attachment points might be significant, particularly if projections are substantial. If this is the case, diagonal brace rods might be incorporated into the design to allow the load to be shared between two attachment points. With fixed systems, ice buildup and the risk of falling ice must also be considered. Therefore, brise-soleil systems might be inappropriate for tall buildings in urban areas.

Retractable systems such as exterior roller shades and venetian blinds are more lightweight than fixed systems and are designed to retract when the wind speeds are high. Standard roller shades need to be retracted at relatively low wind speeds (up to a maximum of about 32 km/h [20 mph]) and will not be appropriate for windy locations or on tall buildings. There is, however, a generic version known as a ‘zip system,’ which allows the fabric to be locked into side tracks. This type can operate in wind speeds of up to 144 km/h (90 mph) and is suitable for tall buildings.

Ice is also a potential issue, but should not be a problem if the systems are protected in the raised position. Automated controls will ensure the systems are only deployed when there is sun. Temperature and humidity sensors can also be used to stop the blinds or shades from being operated when there is a risk of icing. In locations with a cold winter climate, buildings generally require heating in the winter months. It may be appropriate to leave the exterior shading systems in the retracted position during these periods and allow the solar gain into the building as a free source of heating.

8. What maintenance is required?
Most exterior shading systems require little or no maintenance. Fixed louver systems need to be cleaned periodically to maintain the warranty on the paint finish, but no other maintenance work is required.

Adjustable and retractable systems also require little or no maintenance. Nevertheless, it is recommended they be inspected on a periodic basis to check the systems are correctly operating, guide cables (where used) are adequately tensioned, and there is no evidence of damage or general wear and tear to components.

9. How can exterior shading contribute toward achieving LEED certification?
There are numerous areas where the use of exterior shading system can help achieve credits for Leadership in Energy and Environmental Design (LEED) certification. These include:

  • minimum energy performance: use of exterior shading systems can assist in achieving a five percent reduction in building performance compared with the baseline building (in many cases, the reduction achieved is substantially more);
  • optimize building performance: using exterior shading systems can help in achieving reductions beyond the minimum requirement;
  • thermal comfort: exterior shading systems can potentially assist in achieving the requirements of American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 55-2010, Thermal Comfort for Human Occupancy; and
  • daylight: to achieve this credit it is necessary to provide manual or automatic (with manual override) glare-control devices for all regularly occupied spaces (exterior shading systems—possibly in combination with interior ones—allow this to be achieved).

10. Do exterior shading systems make sense in terms of costs and benefits?
To justify using exterior shading systems, it needs to be demonstrated it makes economic sense to do so. Determining the cost of an exterior shading system is a straightforward exercise, but measuring the benefits can be more difficult. It is therefore important the shading system be considered in the context of the building as a whole, rather than as an isolated system, as it can impact several areas of building performance—notably lighting and the HVAC system.

This building in Erbendorf, Germany features an exterior venetian blind system. Photo © Faltenbacher. Photo courtesy Draper Inc.

This building in Erbendorf, Germany features an exterior venetian blind system. Photo © Faltenbacher. Photo courtesy Draper Inc.

In the past, it has often been the case the shading system’s performance was not taken into account when sizing the HVAC system. In this case, it is difficult to justify the use of exterior shading since the potential cost savings from reducing the size of the HVAC system will not be achieved. However, the mechanical consultants who deal with the heating and ventilation systems are now much more aware of the impact of effective shading, and are generally able to take this into account in their calculations.

Conclusion
The traditional approach to windows has been to use interior shading systems to control light and glare, and to address solar heat gain through the HVAC system. Increasing energy costs, requirements for improved façade performance, and greater environmental awareness are leading architects to look for alternative solutions.

Exterior shading systems will not be appropriate for all buildings; where they are used, however, they can make a significant contribution to the building’s performance as well as the building aesthetic. There is no question more architects are considering exterior shading, and, as understanding grows, exterior shading systems will become an important element in the design of high-performance buildings.

Richard Wilson, B.Sc., is a consultant to Draper Inc., and has been working with the company to introduce a range of exterior and specialty shading systems. He has been involved in the solar shading industry for more than 20 years. Wilson can be contacted by e-mail at rwilson@draperinc.com.