Solar Air Heating Systems
Table of Contents
This infosheet provides farmers and rural residents with information on how solar air heating works, on current technology and on whether a solar air heating system is right for you.
Description of Solar Air Heating Technology
Solar air heating technologies use only free, renewable, and clean energy, and can help defray the rising cost of conventional energy. Solar air heating systems absorb thermal energy from direct sunlight to heat air; this heated air can then be circulated through buildings to provide heat.
Active Solar Heating
Active solar air heating systems, a more recent development, use fans to draw in, circulate, and exhaust air. The perforated cladding system (Figure 1) is a bare plate solar collector that uses fans to draw air through thousands of tiny holes in a layer of unglazed dark metal plating, which acts as the solar absorber. Replacing siding on a wall, the absorber, when exposed to direct sunlight, transfers heat to the air as it passes into the building. Working on similar principles, a glazed panel air heating system (Figure 2) consists of a metal case in which dark metal tubes, covered by a layer of clear plexi-glass, absorbs heat from direct sunlight. Fans draw fresh air into the tubes, which emerges heated and proceeds through the ventilation system or directly into the building.
Figure 1. Perforated cladding detail, typical installation. Courtesy of Conserval Engineering Inc.
In the winter, the sun is lower in the sky and the glazed panel receives more direct sunlight than in the summer. This keeps the temperature increase in the summer to a minimum; active systems can also have summer bypasses installed that cut off the flow of heated air.
Figure 2. Glazed panel. Courtesy of Cansolair.
Passive Solar Heating
Passive solar collection can be as simple as allowing sunlight into a heated space through south facing windows. The heat energy is then stored in the building materials inside the space. Passive solar collectors (Figure 3 and Figure 4) use the natural convective movement of heated air to transfer heat from the solar collector into the building. When the sunlight is sufficiently intense, the air between the clear glazing and the dark metal absorber is warmed and rises. This hot air exits into the building through a slot at the top of the wall into the building. A slot near the bottom of the wall allows cool building air into the solar collector to start its cycle again.
Figure 3. Passive solar collector wall.
When the sunlight intensity decreases, this type of collector ceases to function. A check valve is needed on the top opening to prevent back-siphoning of heated air from the building out to the solar collector. When the sun shines you collect heat. When it's dark or dreary outside you don't.
A passive solar wall requires no fans or controls to work year round, day and night. The wall produces heat late fall, winter and early spring when the sun shines. Even on bright days when the sun is not visible, the solar wall collects heat. During night-time hours, a check valve prevents reverse flow of warm building air from flowing back into the collector. The solar wall is totally self-regulating, starting and stopping without personal attention (Figure 5).
Glazing materials selected for solar collectors should be transparent and durable. Choose materials that require minimum routine maintenance. Glazing that is held too rigidly in the collector can buckle or crack. Corrugated glazing allows for some expansion of the material across the corrugations.
Corrugated polyvinyl chloride (corrugated PVC) is the preferred glazing material for passive solar walls. This material weathers well with no maintenance required. Corrugated fibreglass reinforced plastic (corrugated FPR) requires renewed applications of the Tedlar coating to protect the FRP sheets from ultraviolet deterioration every 3 to 5 years.
Figure 4. Passive solar collector-on large workshop door.
State of the Industry
Active and passive solar air heating technologies, starting in the 1970's, were mainly built by farmers, using free plans distributed by the Canadian Plan Service (Figure 5).
In the past several years, the market for active solar air heating systems has greatly expanded, with Canadian companies playing a prominent role in the manufacturing and distribution of perforated cladding and panel systems.
Figure 5. Passive solar wall. Courtesy of Canadian Plan Service.
Is a Solar Air Heating System Right for Me?
Like all solar energy technologies deployed in Ontario, solar air heating systems should face within 30° of true south to maximize their exposure to the sun. In barns and outbuildings where ventilation is important, an active solar heating system that uses perforated metal cladding can guarantee an inflow of heated fresh air (Figure 6), improving indoor air quality. It can be easily incorporated into plans for a new building or retrofitted onto an older building, replacing the normal cladding.
In warmer climates, solar air heating can be used for more intense work, like drying crops. In Ontario, it is more viable as a means of preheating the air for barns and other buildings, reducing the amount of energy expended for space heating. Apart from the upfront costs, solar air heating requires only routine maintenancethe energy it generates is free. According to a study by the Integration of Renewable Energy on Farms (IReF) website, the average payback period for a solar air heating system is 2 to 5 years.
Installing a Solar Air Heating System
The easiest and least expensive way to install a solar air heating system is to incorporate it into plans for a new building.
Retrofitting an existing building requires that the air collector of the solar heating system be connected to the building's existing ventilation system, a task best performed by a professional contractor.
Once the system is installed, it requires only routine maintenance to the fans. The cost of a solar air heating system can vary: a simple panel system can cost around $3,500 with installation, whereas a perforated cladding system can cost up to $250 per square metre, installed.
Passive solar walls can be added to an existing insulated building with slight modifications. The building requires a good southern exposure to consider any type of solar heating.
For all approved commercial solar air heating systems, the Province of Ontario is offering a full PST rebate of those installed and purchased before January 1, 2010.
For commercial enterprises, the federal and provincial governments offer joint incentives for adopting active solar thermal air heating, reimbursing farms up to 50 per cent of the total cost of a solar water heating system. For the federal ecoEnergy Renewable Heat Program, the incentive is up to $80,000 and is proportional to the "Performance Factor" assigned to the individual system, the "Incentive Rate" assigned to the general type of system, and the "Area (square metres) of the solar collector" installed. The Ontario Solar Thermal Heating Incentive (OSTHI) is linked to the federal program, matching the federal funding. The Ontario Soil Crop Improvement Association through the Canada-Ontario Farm Stewardship Program, offers to pay 30 per cent of the costs, up to $5,000 of a solar air heating system for a farm.
For the RA 240 Solar Max, a panel collector from Cansolair Inc., the incentive payout would be about $1,300 on an installed price of about $3,500, or approximately 36 per cent. For the Solar Wall, a perforated cladding collector from Conserval Engineering Inc., the incentive payout for a 100m2 installation would be $19,000 on an installed cost of $25,300, which in this case the incentive payout is around 75 per cent.
This is an example only. Incentives are available for other approved solar system vendors which can be found at www.ecoaction.gc.ca
Figure 6. Perforated cladding active solar air heating system. Courtesy of SolarWall.
Incentives for Farms
Exacon Inc. (Agricultural Distributor for SolarWall in Ontario)
Companies are listed only for example purposes. This list is not meant to exclude other qualified vendors offering this technology and service throughout Ontario. See a complete list of accepted solar collectors at www.ecoaction.gc.ca.
A special thank you to Graham Juneau for all of his hard work in creating this infosheet.
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