Solar air heating is a solar thermal technology in which the energy from the sun, insolation, is captured by an absorbing medium and used to heat air. Solar air heating is a renewable energy heating technology used to heat or condition air for buildings or process heat applications. It is typically the most cost-effective out of all the solar technologies, especially in commercial and industrial applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating.
Solar air collectors can be commonly divided into two categories
- Unglazed Air Collectors or Transpired Solar Collector (used primarily to heat ambient air in commercial, industrial, agriculture and process applications)
- Glazed Solar Collectors (recalculating types that are usually used for space heating)
Unglazed air collectors
They heat ambient (outside) air instead of recirculated building air. Transpired solar collectors are usually wall-mounted to capture the lower sun angle in the winter heating months as well as sun reflection off the snow and achieve their optimum performance and return on investment when operating at flow rates of between 4 and 8 CFM per square foot (72 to 144 m3/h.m2) of collector area.
The exterior surface of a transpired solar collector consists of thousands of tiny micro-perforations that allow the boundary layer of heat to be captured and uniformly drawn into an air cavity behind the exterior panels. This heated ventilation air is drawn under negative pressure into the building’s ventilation system where it is then distributed via conventional means or using a solar ducting system.
Hot air that may enter an HVAC system connected to a transpired collector that has air outlets positioned along the top of the collector, particularly if the collector is west facing. To counter this problem, Matrix Energy has patented a transpired collector with a lower air outlet position and perforated cavity framing to perpetrate increased air turbluence behind the perforated absorber for increased performance.
The extensive monitoring by Natural Resources Canada and NREL has shown that transpired solar collector systems reduce between 10-50% of the conventional heating load and that RETScreen is an accurate predictor of system performance.
Transpired solar collectors act as a rainscreen and they also capture heat loss escaping from the building envelope which is collected in the collector air cavity and drawn back into the ventilation system. There is no maintenance required with solar air heating systems and the expected lifespan is over 30 years.
Night Time Cooling
Radiation cooling to the night sky is based on the principle of heat loss by long-wave radiation from a warm surface (roof) to another body at a lower temperature (sky). On a clear night, a typical sky-facing surface can cool at a rate of about 75 W/m2 (25 BTU/hr/ft2) This means that a metal roof facing the sky will be colder than the surrounding air temperature. A modified transpired collector can take advantage of this previously ignored cooling phenomena. As warm night air touches the cooler surface of the transpired collector, the heat is transferred to the metal, radiated to the sky and the cooled air is then drawn in through the perforated surface. The cool air is then drawn into the economizer cycle typically found on newer HVAC units.
Glazed air systems
Functioning in a similar manner as a conventional forced air furnace, systems provide heat by recirculating conditioned building air through solar collectors. Through the use of an energy collecting surface to absorb the sun’s thermal energy, and ducting air to come in contact with it, a simple and effective collector can be made for a variety of air conditioning and process applications.
Solar Air Heat Collector, Flat Plate Air Collector, Solar Powered Furnace, installed on a vertical wall on the house for optimum winter performance and minimize summer performance to prevent over-heating.
A simple solar air collector consists of an absorber material, sometimes having a selective surface, to capture radiation from the sun and transfers this thermal energy to air via conduction heat transfer. This heated air is then ducted to the building space or to the process area where the heated air is used for space heating or process heating needs.
