Solar air heat

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. [1] 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 of all solar technologies, especially in commercial and industrial applications, and it is the largest use of space heating and heating systems in the world.

Solar air collectors can be divided into two categories: [2]

  • Unglazed Air Collectors or Transpired Solar Collector (used primarily in air-conditioned heat in commercial, industrial, agriculture and process applications)
  • Glazed Solar Collectors (recirculating types that are usually used for space heating)

Collector types

Solar collectors for air heat can be classified by their air distribution paths or by their materials, such as glazed or unglazed. For example:

  • through-pass collectors
  • Front-pass
  • back pass
  • combination front and back pass collectors
  • unglazed
  • glazed

Unglazed air collectors and transpired solar collectors


The term “unglazed air collector” refers to a solar air heating system that consists of an absorbent of any glass or glazing over top. The most common type of unglazed collector on the market is the transpired solar collector. [3] This technology was invented and patented by John Hollick of Conservative Engineering Inc. in the 1990s, [4] who worked with the US Department of Energy ( NREL ) and Natural Resources Canada on the commercialization of technology around the world . [5] The technology has been extensively monitored by these government agencies, and Natural Resources Canada has developed the feasibility tool RETScreen [6]to the model of the solar energy savings. John Hollick and the transpired solar collector were honored by the American Society of Mechanical Engineers (ASME) in 2014 as being one of the best inventions of the industrialized age, by Thomas Edison, Henry Ford, the steam engine, and the Panama Canal. New York exhibition recognizing the best inventions, inventors and engineering feats of the past two centuries.

Several thousand transpired solar collector systems have been installed in a variety of commercial, industrial, institutional, agricultural, and process applications in over 35 countries around the world. [7] [8] The technology was originally used primarily in industrial applications, where it was produced in the United States. The first unglazed transpired collector in the world was installed by Ford Motor Company on their assembly plant in Oakville, Canada. [9]

High solar conversion (up to 500-600 thermal peak Watts / square meters), high solar conversion (up to 90%) ) and lower capital costs when compared against solar photovoltaic and solar water heating. [10]

Method of operation

Unglazed air collectors heat ambient (outside) air instead of recirculated building air. Transpired solar collectors are usually wall-mounted to the bottom of the sun and their optimum performance and return on investment (CFM per square foot) (72 to 144 m3 / h.m2) of collector area.

The exterior surface of a transparent solar collector consists of thousands of micro-perforations that allow the boundary layer of heat to be captured and uniformly drawn into an air cavity behind the exterior panels. This solar heating system is drawn into the building’s ventilation system from the air in the collector’s office and is then distributed in the building via a solar ducting system.

The extensive monitoring by Natural Resources Canada and NREL has shown that it is capable of reducing energy consumption by 10-50% of the RETScreen is a reliable predictor of system performance. [11]

Transpired solar collectors act as a rainscreen and they also capture heat loss from the building envelope which is collected in the collector’s air cavity and drawn back into the ventilation system. There is no need for solar heating and the expected lifespan is over 30 years. [12]

Variations of transparent solar collectors

Unglazed transpired collectors can also be adapted for other applications. A number of companies offer air-cooled roof-mounted air ducts and are designed for roof-mounted air ducts and connected to nearby fans and HVAC units.

Higher temperatures are also possible with greater amounts of heat, which can be configured to increase the temperature of the building. In a 2-stage system, the first stage is the typical unglazed transpired collector and the second stage The glazing allows for the first stage of the second stage of the second stage of solar heating.

Another innovation is to recover heat from the PV modules (which is often made by the PV module) by PV modules on the solar air system. In cases where there is a heating requirement, incorporating a solar component in the PV system provides two technical advantages; it removes the PV heat and permits the system of operation to its rated efficiency (which is 25 C); and it decreases the total energy cost associated with the combined heat and power system.

Glazed air systems

Functioning in a similar way as a forced air furnace, recirculating air-conditioned solar collectors . Through the use of an energy collector and the use of heat and air, it can be used for a variety of air conditioning and process applications.

SPF Solar Air Heat Collector

A simple solar collector consists of an absorbing material, sometimes having a selective surface , to capture heat from air conduction heat transfer. This heated air is then ducted to the space where the heating is used for space heating or process heating needs.

The pioneering figure for this type of system was George Löf , who built a solar system for a Boulder, Colorado, in 1945. He later included a gravel bed for heat storage. [13]

Through-air collector

In the through-pass configuration, air ducted on one side of the absorbent passes through a perforated or fibrous type of material and is heated from the conductive properties of the material and the convective properties of the moving air. Through-pass absorbers have the most surface area, which can cause greater fan power, and deterioration of some of the absorbing material. .

Back, front and combination passage collector

In-pass, front-pass, and combination type configurations are available on the front, or on both sides of the duct headers. Although it is possible to provide a greater surface area for conduction of heat transfer, . In cold climates, air loss will be greater because of greater heat loss, resulting in lower overall performance of the collector.

Solar air heat applications

A variety of applications can please use solar air heat technologies to Reduce the carbon footprint from use of conventional heat sources, Such As fossil fuels , to create a sustainable means clustering to Produce thermal energy. Applications such as space heating , greenhouse season extension, pre-heating ventilation, air-conditioning, or process heat can be addressed by solar air heat devices. [14] In the field of ‘solar co-generation’, solar thermal technologies are paired with photovoltaics (PV) to increase the efficiency of the solar panels. citation needed]

Space heating applications

Space heating for residential and commercial applications can be done through solar heating panels. This configuration operates by drawing air in the air by means of air collectors and by the means of air-conditioning. fan. In the older days, it would get hot inside buildings, during the day times, because of heat from the sun. Even in cars, the temperature inside can exceed 50 degrees Celsius, if the windows are up and there is no need to switch on the heater

Process heat applications

Solar air heat can also be used in processes such as drying laundry, crops (ie tea, corn, coffee) and other drying applications. Air heated through a solar collector and then passed over to an efficient way of delivering moisture.

Night cooling applications

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). We have clear night, a typical sky-facing surface at about 75 W / m2 (25 BTU / hr / ft2). Collectors can take advantage of this cooling phenomena. As warm night air hits the cooler surface of a collector, heat is transferred to the metal, radiated to the sky and the air is then drawn through the perforated surface. Cool air may be drawn into HVAC units. See also [9] [15] [16]

Ventilation applications

By drawing air through a properly designed air collector or air heater. Applications include transpired collectors preheating fresh air entering a heat recovery ventilator, or suction created by venting heated air out of some other solar chimney .

See also

  • Active solar
  • Passive solar building design
  • Heat recovery ventilation
  • Passive house
  • Low-energy house
  • Zero-energy building
  • List of low-energy building techniques
  • Sustainable architecture


  1. Jump up^ “Solar Thermal Collectors – Energy Explained, Your Guide To Energy Understanding – Energy Information Administration” . 2013-05-29 . Retrieved 2014-05-04 .
  2. Jump up^ “Advanced Manufacturing Office: Industrial Distributed Energy” . . Retrieved 2014-05-04 .
  3. Jump up^ “Survey of Active Solar Thermal Collectors, Industry and Markets in Canada” (PDF) . August 2010 . Retrieved 3 August 2011 .
  4. Jump up^ “SolarWall® Company Profile” . Conserval Engineering Inc . Retrieved May 3, 2014 .
  5. Jump up^ US patent 4899728 , HOLLICK JOHN C; PETER ROLF W, “Method and apparatus for air preheating ventilation for a building”, published 1998-07-17
  6. Jump up^ “RETScreen International Home” . Natural Resources Canada . Retrieved May 3, 2014 .
  7. Jump up^ “Solar Energy Use in US Agriculture Overview and Policy Issues” (PDF). United States Department of Agriculture . Retrieved 4 August 2011 .
  8. Jump up^ Siegele, Lindsey. SolarWall Solar Air Heating Technology . Mother Earth News . Retrieved 4 August 2011 .
  9. ^ Jump up to:b “Transpired Collector (Solar Preheaters for Outdoor Ventilation Air)”(PDF) . Federal Technology Alert . Federal Energy Management Program. National Renewable Energy Laboratory. April 1998. DOE / GO-10098-528 . Retrieved July 25, 2010 .
  10. Jump up^ Brown, David. “An Evaluation of Solar Air Heating at United States Air Force Installations” (PDF) . Air Force Institute Of Technology . Retrieved 4 August 2011 .
  11. Jump up^ “Solar-Heated Fresh Air Cuts Heating Costs” (PDF) . NREL. 1994 . Retrieved 4 August 2011 .
  12. Jump up^ “Solar Preheated Ventilation” (PDF) . Naval Facilities Engineering Service Center . Naval Facilities Engineering Service Center . Retrieved 3 August 2011 .
  13. Jump up^ Anthony Denzer, “George Löf: Denver’s Solar Pioneer” (PDF) , 2012 ASES National Solar Conference
  14. Jump up^ Rural Renewable Energy Alliance. “Solar Air Heat Basics” . Retrieved 05/07/2011 . Check date values ​​in:( help ) |access-date=
  15. Jump up^ “Solar Savings: An inside look at solar metal walls” . Metal Architecture Magazine . Retrieved 1 September 2011 .
  16. Jump up^ Lombardi, Candace. “Roof-mounted solar assists in cooling too” . CNET. Retrieved 1 September 2011 .

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