Solar air heat is a type of energy collector in which the energy from the sun, solar 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.

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

  • glazed (recirculating types)
  • unglazed (ambient air heaters -transpired type)

Glazed air systemsEdit

Functioning in a similar manner as a conventional forced air furnace, systems provide heat by recirculating conditioned building air through solar collectors - Solar thermal collectors. [3]. 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.

SPF Solar Air Heat Collector

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.

Collector typesEdit

Due to varying air-ducting methods, collectors are commonly classified as one of three types:

  • a) through-pass collectors,
  • b) front-pass,
  • c) back pass,
  • d) combination front and back pass collectors.

Through-pass air collectorEdit

In the through-pass configuration, air ducted onto one side of the absorber passes through a perforated or fibrous type 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 enables relatively high conductive heat transfer rates, but significant pressure drop can require greater fan power, and deterioration of certain absorber material after many years of solar radiation exposure can additionally create problems with air quality and performance.

Combination passage air collectorEdit

In back-pass, front-pass, and combination type configurations the air is directed on either the back, the front, or on both sides of the absorber to be heated from the return to the supply ducting headers. Although passing the air on both sides of the absorber will provide a greater surface area for conductive heat transfer, issues with dust (fouling) can arise from passing air on the front side of the absorber which reduces absorber efficiency by limiting the amount of sunlight received. In cold climates, air passing next to the glazing will additionally cause greater heat loss, resulting in lower overall performance of the collector.

Air heat applicationsEdit

A variety of applications can utilize solar air heat technologies to reduce the carbon footprint from use of conventional heat sources, such as fossil fuels, to create a sustainable means to produce thermal energy. Applications such as space heating, pre-heating ventilation makeup air, or process heat can be addressed by solar air heat devices. Further strides are being made in the field of ‘solar co-generation’ where solar thermal technologies are being paired with photovoltaics[4] (PV) which increases the efficiency of a typical PV system by generating additional useful energy in the form of both electricity and heat.

Space heating applicationsEdit

Space heating for residential and commercial applications can be done through the use of solar air heating panels. This configuration operates by drawing air from the building envelope or from the outdoor environment and passes it through the collector where the air warms from conduction of the absorber and is then supplied to the living or working space by either passive means or with the assistance of a fan.

Ventilation, fresh air or makeup air is required in most commercial, industrial and institutional buildings to meet code requirements. By drawing air through a properly designed unglazed transpired air collector or an air heater (such as an energy and heat recovery ventilators ERV/HRV]), the solar heated fresh air can reduce the heating load during daytime operation. Many applications are now being installed where the transpired collector preheats the fresh air entering a heat recovery ventilator to reduce the defrost time of HRV's.

Process heat applicationsEdit

Solar air heat can also be used in process applications such as drying laundry, crops (i.e. tea, corn, coffee) and other drying applications. Air heated through a solar collector and then passed over a medium to be dried can provide an efficient means by which to reduce the moisture content of the material.

Unglazed air systemsEdit

Transpired air collectorEdit

Transpired air collectors are becoming the most popular type of solar air heating system in North America. These unglazed solar collectors are low cost and primarily used to heat ambient air and not building air. Transpired collectors only require one penetration into the building, or if existing fan inlets are used, then no additional penetrations are necessary. The transpired air collectors are generally wall mounted to capture the lower sun angles in the winter months, additional sun reflection off the snow and they also capture heat loss escaping from the building envelope which is collected in the SolarWall air cavity and drawn back into the ventilation system. As of 2009, there are over 1500 transpired collector installations with over 300,000 square meters of collector surface.

Solar heating efficiency Edit

The efficiency of a solar air collector is highest when the temperature of the air entering the solar panel equals ambient temperature. This occurs with the transpired collector (SolarWall type) since outside air always enters the panels. In space heating designs, building return air enters a solar panel to be heated above room temperature. On cold, overcast days, there may be insufficient energy to achieve this, whereas, with the ambient air heater any heat gain, whether it be a rise of two degrees or twenty degrees, is useful energy.

See alsoEdit

References Edit

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