Holistic approach to environmentally friendly building.
The goal is to meet program objectives for the building while reducing the consumption of nonrenewable resources, minimizing waste and creating healthy, productive environments. However, the goal may be complicated by the requirements of building systems and issues--ventilation, air quality, energy usage--which are sometimes at odds with each other.
Successful environmental design takes a truly holistic view, where each component is reconciled with other components, and with the institution's goal and vision for environmentally responsible building design and construction.
Several not-for-profit organizations offer guides to assist in the design and construction of sustainable buildings including the Minnesota Sustainable Design Guide, the ASHRAE Green Guide and the Rocky Mountain Institute Primer on Sustainable Building.
The U.S. Green Building Council has codified the principles of "green design" in the Leadership in Energy and Environmental Design (LEED[TM]) rating system. LEED was created to define "green design", establishing a national standard of measurement that recognizes achievement in integrated, whole-building design practices by calculating performance points in five categories. Based upon total points earned, a building can attain LEED certification at one of four levels.
Ideally, certification is gained in a way that promotes a holistic approach.
The focus of sustainable design initiatives on many projects is often on energy usage and the use of green materials--but indoor environmental quality is also an important factor in designing and building high-performance buildings. Designers and planners at Cannon Design have found the key is to balance sustainable-design concepts in a way that optimizes user comfort, safety and productivity, in addition to using environmentally friendly materials and resource efficient systems.
LEED awards 15 points in its Indoor Environmental Quality category for: ventilation effectiveness, temperature/humidity control, the use of low-emitting materials and optimization of views and day lighting. To maximize success under LEED, owners, developers and their design teams must address multiple issues such as natural ventilation, polluted outdoor-air locations, air-distribution effectiveness, heat recovery/energy savings, humidity control and acoustic control. Looking at options in this area will result in selecting the best system for both current and future operating requirements.
Ventilation: Natural and Hybrid Systems
Natural ventilation is an option that allows occupants to breathe unfiltered outdoor air when outside conditions are optimal. This can result in a space with perceivably high indoor air quality with low energy costs. Take, for example, a dormitory project at Boston's Suffolk University, which uses a naturally ventilated 19-story atrium with glass on two sides. The atrium was designed to introduce outside air into the structure while also saving energy via recycled or rejected heat gain. Because of the high percentage of glazing in the space glare studies were conducted to identify the most appropriate design to optimize ambient lighting.
Lack of occupant control of ventilation systems is a problem experienced in many buildings. Hybrid ventilation systems give occupants control of their surroundings, as is the case with the Allegheny College Residence Hall in Meadville, PA. Students have the option of opening windows or using mechanical systems. On a 70[degrees]F day, in which the air conditioning might engage, occupants can shut off the HVAC system and open the windows. Student comfort is maximized as are energy savings.
In areas high in pollutants, including many downtown urban sites, air conditions are not optimal, therefore natural systems may not be healthy or improve indoor air quality. Chemical filtration is often overlooked, but it is an excellent option when intake locations cannot be located far enough away from exterior pollutant sources. Air is filtered chemically so that it is clean when it comes back through the air-handling system. The amount of outdoor air can actually be reduced utilizing this method of air filtration.
This is a worthwhile option where healthy outside air is not available. However, it is costlier because filters are expensive and must be changed periodically. A lifecycle cost and benefit analysis should be conducted to determine whether or not chemical filtration is an optimum solution.
Ventilation vs. Energy
To counter higher energy costs, energy-recovery equipment can be integrated into a ventilation design to provide an extremely cost-effective operating system. Separating the ventilation system from the heating and air-conditioning terminal unit system with the use of energy-recovery equipment can save energy and reduce capital costs while increasing a building's indoor environmental quality. The ductwork with this system is smaller and provides 100 percent outside air through an energy-recovery ventilator. The payback for selecting this option is usually less than two years.
Energy recovery can be utilized to provide 100 percent outside air to high-occupancy spaces as a good lifecycle cost measure. Heat-wheel units recover both latent and sensible heat and provide ventilation to the space, claiming 70 to 80 percent efficiency. Heat wheels can significantly reduce humidity control loads in the summer and during the winter. While there are other types of heat-recovery techniques, the use of the desiccant-coated heat wheel is the most efficient option for most applications unless cross contamination of air is a critical issue.
Energy recovery is frequently used in classroom projects where the air to the space is provided through an energy-recovery unit and fan-coil units serve the space to deal with the heating and cooling loads. However, acoustics in the space can be compromised with this type of system. The fan-coil units blowing the air to distribute the heat may in fact exceed the noise criteria for the space. Ventilation and air-distribution issues can arise with the use of this system with the two introductions of air to the space. It's a good way to maximize ventilation capacity in a space at a low first-cost, but designers need to be aware of the acoustic and air-distribution challenges.
In large classrooms and performance halls, displacement ventilation offers ideal indoor environment quality. Air supplies come into spaces at low levels, move slowly across the plane of the space in an upward direction, and return at high levels within the space. Users feel an even, once-through airflow rather than the traditional mixed air distribution systems that distribute air high across a room. Diffusers fit into a module on the floor and can be easily moved in many applications. Because velocities are much lower, acoustic issues are resolved, making it an ideal approach for performing-arts centers.
Finally, a holistic approach to addressing indoor air quality must also consider humidity. Providing a comfortable range for humidity is as important for comfort as it is temperature. Productivity as well as comfort are increased when relative humidity levels are maintained between 30 and 60% per ASHRAE Standard 55 "Thermal environmental conditions for human occupancy"
However, there can be significant energy-consumption and water consumption issues when incorporating steam or atomizer humidification. In some cases, dehumidification through re-heat and/or desiccant systems is necessary. This depends on the comfort criteria for a building's specific use. There are also operation and maintenance issues with humidity control systems that, when not properly attended to, can actually harm the indoor environmental quality of the space. When systems are not properly designed, installed and maintained, standing water or saturated duct liner can result in mold and bacteria growth in the supply air stream. As with all systems, a balance must be achieved between comfort and operational issues including maintenance and long-term operating costs.
Emphasizing one aspect of a building's sustainable design may cause other areas to suffer. A holistic approach to indoor environmental quality not only contributes to green design, it will help to achieve the highest comfort levels possible for end users.
A thorough evaluation of all systems, including comfort, maintenance and operating costs, will enable owners and operators to make the most appropriate choice based on current and future building requirements.
JOHN M. SWIFT, PE, LEED[R] VICE PRESIDENT, CANNON DESIGN
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|Title Annotation:||Special report: engineering|
|Author:||Swift, John M.|
|Publication:||Real Estate Weekly|
|Date:||Feb 16, 2005|
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