Ventilation Strategies

In addition to providing opportunities for personal controls, architects are using ventilation strategies to assure fresh air in buildings in the eventuality of mechanical failure. The principles for designing appropriate air flow strategies from operable windows include an understanding of the microclimate surrounding the building.

 

Ethylene tetrafluoroethylene is a film that can substitute for glass. An operable roof optimizes ventilation to this long span structure. Photo courtesy of OpenAire Inc.

 

 

Exterior wind flow patterns are important factors when determining how to cool a building or how to provide relief from vapor pressure when it is humid. Exterior wind flow can be modulated through landscaping or through the manipulation of positive air flow on a building. New design solutions to modulate temperature and humidity include the design of multi-layered glass enclosures and vegetated screens.

 

Integrated Design - Blue Hill Club

Low voltage controls, an operable roof and high-performance glazing reduce the use of mechanical equipment and provide energy savings. Photo courtesy of OpenAire Inc. In 2007, The Boys and Girls Clubs of Boston renovated its Blue Hill Club, located on the corner of Blue Hill Avenue and Talbot Avenue in Dorchester. This project included the retrofit and updating of the swimming pool. By using an enclosure with a retractable roof and sliding doors, ventilation strategies were documented as reducing this project's carbon footprint by 31 percent in electrical savings. Energy savings result from turning off cooling and dehumidification of the pool area in the warmer months when the roof is open to allow solar gain in the winter, which eliminates  most artificial lighting throughout the entire year.  "BGCB strives to have each of its Clubs be a beacon of hope to the at-risk youth and families who need them most," said Daphne Griffin, Executive Director of the Blue Hill Club.  "Our Club was outdated and undersized given the community need. Creating a year-round aquatic program was an essential part of the renovation project, and adding a retractable roof enclosure created a special play space where youth can learn essential skills and have fun doing it." This client invited an independent company to assess the energy consumption of this operable enclosure, as compared to a traditional brick and mortar type of building using the same typical pool and space loads. The analysis showed a 31 percent annual savings in electricity and an overall 27 percent savings in annual energy consumption, with a net total utilities cost savings of over $9,000 a year.

 

 

Air flow strategies include an understanding of the convective loop. Hot air rises and is lighter than cold air, creating a convective loop that can be manipulated by designers to draw air through a building. A "stack effect" can be created by opening the lower windows in the room to the windward side of a building and providing an outlet in the upper windows of the room on the opposite side. To be successful, each room should be modeled to determine if there are obstructions to air flow, such as room dividers. Vertical shafts can also be used to draw air through a building, however, a vertical shaft used to provide an exhaust pathway must meet fire codes. Designers need to manipulate and measure the following elements of indoor air flow:

• Interior wind flow patterns with respect to interior partitions- designing for multi-zone air-flow
• Air stratification principles, such as the location and size of inlet openings
• The effect of overhangs over windows, including exterior or interior blinds and shading devices
• Types of window openings, such as awnings, casements, pivots, and sliders

Many of these strategies can be tested by designers through building integrated modeling and evaluated by mechanical engineers throughout the entire design and construction process. The size of a building, its orientation and location can also determine the success or failure of ventilation strategies.

Window Mechanics

A window system in a wall, roof or door should open easily in order to function properly. Windows can be opened manually by   individuals or low voltage controls can be provided by window manufacturers to automate the integration of window openings. Ideally, a window will open to meet the demands of changing weather patterns. Each window type has unique locking and operating characteristics.

Double-hung windows are opened by releasing the  locks and pulling on the lift and should be measured by the ease of operations. Rollers should be equipped with vents and nylon roller housings containing 2 acetal nylon rollers each. The lock should be a self-aligning, cam-action lock designed for its ease of opening, locking and unlocking.

Awning windows are often chosen by green designers to channel air flow through buildings. Some of the components of an energy-efficient fully automated awning window, or roof enclosure system include:

• Low voltage electric remote controls - U.L.I.-listed and C.S.A.-approved rain sensors
• Compatibility with frame profiles and crank mechanisms
• Computer operated controls with the ability to monitor off-site
• Temperature controls that can be set to an LED display
• Optional manual controls or interruptible power supply
• Personal controls through infrared sensors
• Safety mechanisms, which include motor reverse systems and screen interlocks
• Maintenance guarantees for durability and replacement

Window Hardware and Automated Controls

The Construction Specification Institute (CSI) provides standards for automated controls, as well as for window hardware. Designers should choose hardware that will not compromise energy efficiency through heat loss and thermal bridging. Components should be rated for ease of use and the performance values should match those of the window class for operability.

Views to Nature - Operable Glass Walls

Expansion of interior space to include exterior rooms can be challenging for energy conscious designers. In her  Not So Big House books, architect Sarah Susanka, AIA, has shown designers how to expand small spaces by using a variety of visual tools. Operable glass walls can be effective as a means to remove the visual and physical barriers to the outdoors, increasing the sense of space and dimension of smaller building footprints.

An effective glass wall is weather-resistant and has water penetration ratings proving its ability to prevent leaks and meets or exceeds The American Society of Testing and Materials Standards (ASTM). ASTM E-283 is the "Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls and Doors Under Specified Pressure Differences." ASTM E-547 is the "Standard Test Method for Determining Water Penetration of Exterior Windows, Curtain Walls, and Doors by Cyclic Static Air Pressure." Occupants should not feel drafts as they sit adjacent to the windows that have large glass openings.

 

Many of these systems use recycled aluminum and other recycled materials in the frame construction. Some manufacturers supply options to designers to choose wood that is certified by the Forest Stewardship Council (FSC). The FSC is the only non-profit organization recognized by the U.S. Green Building Council as providing certified chain-of-custody for sustainable wood products, as well as requiring worldwide sustainable forestry practices. As with a high-performance window, the leading glass wall systems provide designers with the options to choose window glass with high-energy performance ratings, as well as good acoustic properties.

Sunshine: Natural Light

Whether the building occupant looks out on a parking lot, a busy street or a forest, windows allow a view to the sky and to natural light. Humans respond to the biological effects of daylight; that is, we respond to the circadian rhythm that affects behavior and productivity. The primary tool for designers who wish to maximize daylight into a building is to understand building orientation and solar access. Studies have proven that solar energy, radiation, warmth and light can provide environmental savings.

The components of natural sunlight include visible light, ultraviolet radiation, and infrared radiation. Visible light can cause glare on a work surface particularly in the late evening and early morning when the sun is low in the sky and if the building faces east or west. Ultraviolet rays add heat to a room. In passive solar design, an architect can store this heat as needed, particularly in a colder climate and may choose a clear glass to allow for greater solar gain. Infrared radiation is the component of sunlight which causes interior finishes to fade. Intelligent solar design includes the ability to moderate visible light while preventing glare, fading and excess heat into the design space.

In the Northern Hemisphere, as the sun moves across the sky in an east−west axis, solar radiation varies across the face of a building. The south building façade will be the warmest throughout the year. The east and west façades will be colder in the winter and warmer in the summer. The north façade of a building will not receive any direct sunlight, only diffused daylight. The amount of solar energy available to heat a building varies throughout these natural cycles. In addition, in the summer, the angle of the sun is higher in the sky than it is in the winter. These solar angles can be calculated to determine how much daylight will be allowed into interior spaces. An easier procedure is to use one of the many solar calculators available in most computer software programs, which can show a variety of options depending on the latitude and longitude coordinates of the project.