Having been involved in the renewables business since 1985 I’m perplexed that solar air heating systems for non-residential applications have not eked out a greater share of the industry’s attention, or government funding dollar.
Commercial buildings alone in the United States including stores, offices, schools, churches, hospitals, warehouses and jails accounted for nearly 20% of all energy use in the United States in 2008 according the U.S. Energy Information Administration’s 2008 Annual Energy Review. Within this sector alone space heating and ventilation accounted for nearly 20% of the energy end use derived from natural gas and petroleum. Currently available unglazed transpired solar collectors and some high efficiency, backpass solar air heating systems now operate at near 70% efficiency resulting in remarkably high returns on investment. (Show close-up of perforated cladding)
The most cost effective and efficient solar air heating system commercially available is the unglazed, transpired solar collector (UTC) that was developed in conjunction some years ago with the National Renewable Energy Laboratory in Colorado. The U.S. Department of Energy calls such systems the most reliable, best-performing, and lowest-cost solar heating method for commercial and industrial buildings available on the market today. These solar fresh air heating systems are demonstrating operating efficiencies upwards of 70% and show payback’s within five years on most new buildings.
According to the April 2009 edition of the Solar Heat Worldwide newsletter article entitled Solar Thermal Capacity in Operation Worldwide, the global installed solar thermal capacity at the end of 2007 equaled 146.8 GWth or 209.7 million square meters. The breakdown by collector type is as follows:
• 120.5 GWth – flat-plate and evacuated tube collectors
• 25.1 GWth – unglazed plastic collectors
• 1.2 GWth – air collectors
Clearly solar air collectors are far from their market potential!
The energy savings and carbon emissions reduction potential of solar air heating systems should not be overlooked for the commercial or industrial buildings sector. According to the EPA’s 2007 Inventory of U.S. Greenhouse Gas Emissions and Sinks, the combustion of fossil fuels in the commercial sector alone resulted in the emission of 277 million metric tons of carbon equivalents in 2005, or roughly 17% of all U.S. carbon dioxide emissions for that year. Independent performance results of transpired collectors such as MatrixAir™ solar air heating systems demonstrate that each 1 m2 of MatrixAir™ cladding can produce 2.1 GJ or 583 kWh of thermal energy per year. Such energy transformation results in the avoidance of 55 tonnes of CO2 being emitted versus natural gas; 131 tonnes of CO2 versus oil; 164 tonnes of CO2 versus coal; or 102 tonnes of CO2 versus propane.
Apart from the energy savings benefits the health benefits of fresh air are well known. According to the University of Michigan’s Centre for Sustainable Systems, volatile organic compounds (VOC) are found in concentrations of up to five times greater than naturally found in the environment. The typical means of reducing VOC’s to improve indoor air quality is the introduction of fresh ventilation air, the heating of which in cold climates can be achieved cost effectively using a transpired or high-efficiency backpass solar collector.
Commercially available products, marketed under the MatrixAir™ brand are straightforward, simple and efficient. Perforated metal cladding is used to draw in heated fresh air off the surface of south-facing walls, where it can then be distributed throughout the building as pre-heated ventilation air. The genius of this system is in the cladding and overall systems’ fundamental simplicity: solar energy is used to heat fresh air, which is then brought into the building via a conventional make-up air or ventilation system.
While simple in their function and appearance similar to that of conventional metal siding proper system sizing and design will ensure that the solar air heating collector will produce the anticipated energy savings. (insert visualization) A general rule of thumb suggests that each square foot of installed transpired collector area will cost effectively yield 5 – 7 CFM of preheated fresh air. The following table demonstrates the average increase in air temperature versus the incoming fresh air flow through the collector. (insert temp rise vs flow table) As can be expected the lower the air flow through the collector the higher the temperature rise. Such low flow applications are ideally suited for buildings with reduced fresh air requirements where the space heating load exceeds that of the demand for fresh air, process heat or other high temperature applications. Greater operating efficiencies and lower installed costs per unit area are typically achieved for preheating of make-up air or ventilation air systems where air flow will reach up to 9 CFM/ft2 of façade mounted collectors or as high as 12.5 CFM/ft2 on roof mounted, modular solar air heating systems such as the MatrixAir™ Delta.
Apart from the commercial and institutional applications other excellent applications for solar air heating include combustion air pre-heating and make-up air preheating for garages, or any manufacturing plant where high volumes of fresh air are required throughout the work day.
