AS GREEN-BUILDING PRACTICES
become more important not only for environmental reasons but for also for cost savings and tax credits, new products supporting this philosophy are popping up everywhere. This wealth of product information can be tedious for a building professional to sort through. One product that is rising to the top and changing how sustainable products are used in the metal construction industry is the transpired solar collector.
The concept is simple: Perforated metal wall cladding is attached about 4 to 8 inches (102 to 203 mm) from a south-facing wall to a support grid of vertical and horizontal channels. The system may be applied vertically or horizontally over any noncombustible wall substrate; over or around existing wall openings. The grid system vertical channels are attached to the existing wall; the horizontal channels are attached to the vertical channels; and the perforated metal sheets are through fastened to the horizontal channels. The transpired solar collector wall may be mounted to a wall several different ways, depending on the volume of air required. In some cases, only a portion of the south wall is needed or even a penthouse wall is suitable.
The sun heats the metal panel, and the heated air is drawn through tiny holes in the panel into the cavity between the panel and wall by fans mounted at the top of the wall. The fans then distribute the heated air into the building through flexible ducts mounted from the ceiling or through standards ducts connected to the heating and ventilating system.
In the winter, the heated air removes a substantial load from the building's conventional heating system, saving considerable energy and money. In the summer, the panel is shading the inner wall, reducing the cooling demands of the building. When heating is not required, a controlled damper can be opened to allow air to bypass the solar collector, providing a continual supply of fresh air into the building. The transpired solar collector wall also is effective on cloudy days though at a reduced level.
The transpired solar collector wall may be mounted to a wall several different ways, depending on the volume of air required.
Using this preheated fresh-air system eliminates stratification of the air inside industrial buildings, where hot air rises to the ceiling and is lost through the roof or drawn out with exhaust fans. Because the air is constantly being replaced, the system is ideal for vehicle repair shops, machine shops, chemical storage plants and industrial applications where fumes are present. The system also provides positive pressure for the building. When a door or window is opened, the heat from indoors exists but the cold outside air does not rush in.
New ventilation codes specify minimum ventilation rates and indoor air quality, depending on the type of building and number of occupants. Inadequate fresh air leads to "sick building syndrome," which may result in headaches; eye, nose and throat irritations; fatigue; and difficulty in concentration for the workers inside. Everyone wants to avoid sick building syndrome, but constantly replacing air via a transpired solar collector is perfect for manufacturing plants, hazardous-waste storage buildings, gymnasiums, airplane hangars, schools, office buildings, apartment buildings and warehouses requiring ventilation. The system also provides process heat for agricultural or industrial purposes.
The system works for retrofit applications. Any existing noncombustible south-facing exterior wall in need of repair could be covered with the transpired solar collector wall panel. For a uniform appearance, the other exterior walls can be covered with a similar panel system in the same color. For variety and aesthetics, coordinating or contrasting colors may be used. Use of the perforated panels on a vertical, southern exposure wall is recommended to collect the most solar energy. A vertical surface will give more reflected radiation with no snow build-up and low wind loads.
Environmentally, the transpired solar collector is using natural energy that is clean, thus lowering the need for fossil-fuel heat and reducing production of greenhouse gases. Payback of the system is relatively short--generally within three years--and state and federal grants, as well as tax credits, are given as incentives for solar energy use. The installation may qualify for LEED points and credits. The cost of conventional energy can vary greatly depending on the area and season of the year. With soaring energy prices, the use of free solar heat reduces the need for conventional energy sources.
Research has proven that each square foot of panel will supply 150 to 200 BTU's per hour. Intake air is preheated by up to 65 F (18 C) above the ambient air temperature, reducing annual heating costs by $1 to $5 per square foot of collector wall, depending on the type of fuel displaced. U.S., Canadian and German governments have independently monitored installations of this type. The International Energy Agency Solar Heating and Cooling Programme (www.iea-shc.org), a coalition established in 1974 as an autonomous agency within the framework of the Organisation Economic Co-operation and Development to carry out a comprehensive program of energy cooperation among its 25 member countries and the Commission of the European Communities, reports efficiencies of more than 70 percent (according to its report SHC.T14.Air.1 9/99).
"Transpired collectors provide the most reliable, best performing, and lowest cost solar heating for commercial and industrial buildings available on the market today". --U.S. Department of Energy
The concept has received numerous honors and awards from the U.S. Department of Energy, ASHRAE (American Society of Heating, Refrigeration & Air Conditioning Engineers Inc.) and many others worldwide. DOE reported, "Transpired collectors provide the most reliable, best performing, and lowest cost solar heating for commercial and industrial buildings available on the market today" (DOE/GO-10098-558, 1998).
With testimonials like that in addition to cost and energy savings, as well as environmental reasons, why wouldn't you look into installing a transpired solar collector?