Solar Hot Air Systems

Table of Contents

  1. Description of the Technology
  2. State of the Industry
  3. Is a Solar Hot Air System Right for Me?
  4. Basic Numbers
  5. Benefits and Drawbacks
  6. Planning Issues and Regulations
  7. Setting Up and Operating a Solar Hot Air System
  8. Additional Resources

Description of the Technology

There are many types of systems that use air to capture solar energy and many applications for that heated air, from providing space heating or ventilation to drying crops.

Simplest of all is passive solar design, which uses the strategic placement of windows and thick, heat-absorbing walls to capture the sun's energy during the day and gradually release it.

Active systems rely on fans to circulate the heated air. A basic hot air heating system consists of a panel that absorbs heat and transfers it to air-filled tubes that pass through the panel. A fan system then draws that warmed air into the building through ductwork.

Perforated-plate solar collectors are large sheets of heat-absorbing dark metal that double as exterior cladding attached to an outside wall. The metal heats the air between the cladding and the wall. As the air warms, it rises into a ventilation system at the top that then distributes it into the building's interior. It is replaced by fresh air drawn behind the cladding through small holes punched in the metal.

Meanwhile, crop drying systems and food dehydrators can range from simple boxes to entire barns that use either passive airflow or fans to create movement of warm air across the material to be dried.

State of the Industry

Solar air heating was commercially introduced in the 1990s, while solar drying systems have been around since the 1970s.

Is a Solar Hot Air System Right for Me?

For maximum efficiency, a solar hot air system should face more or less south.

Perforated-plate solar collectors are an excellent option in barns and outbuildings where ventilation is important. They are easy to incorporate into plans for new buildings and can also be retrofitted onto an existing building, given a reasonable expanse of south-facing wall.

With a wide range of models available, solar drying systems are a viable option in most agricultural settings.

Basic Numbers

According to the Integration of Renewable Energy on Farms website, the average payback period for a hot air heating system is 2 to 5 years, with costs ranging from $100 to $250/m2 for the collector and $0-$100/m2 for the ventilation system.

The cost of drying systems varies depending on the design and size, but payback periods are quite short: typically less than 5 years.

Benefits and Drawbacks

Solar Air Heating Systems

Benefits:

  • Reduces heating costs
  • Requires minimal maintenance
  • Reduces the stratification of air that leaves cold air at floor level and hot air higher up
  • In the case of perforated-plate systems, provides fresh air that improves indoor air quality

Drawbacks:

  • Performance decreases substantially at night and on cloudy days
  • Supplementary systems will probably be necessary
  • Active systems require electricity

Solar Drying Systems

Benefits:

  • Reduces energy costs
  • Requires minimal maintenance
  • Reduces the risk of burning or damaging the material to be dried

Drawbacks:

  • Performance decreases substantially at night and on cloudy days
  • Supplementary systems may be necessary
  • Active systems require electricity

Planning Issues and Regulations

Contact your municipality to find out about any local approvals or permits required. An active system may need to be inspected by the Electrical Safety Authority.

Setting Up and Operating a Solar Hot Air System

Installing a perforated-plate hot air system requires skills in construction, electrical systems and heating and ventilation systems, so consider hiring a qualified contractor. Panel-based systems may be simpler to install, but they will still require basic carpentry and electrical skills.

All solar hot air systems are extremely simple maintain. Passive systems require absolutely no maintenance, while the ventilation system of active systems should be cleaned and checked periodically.

Additional Resources

Publications and Websites

Natural Resources Canada's Heating Your Building with Solar Energy, OMAFRA's Solar Air Heating Systems and the Ontario Sustainable Energy Association's Solar Thermal Community Action Manual are both excellent resources on solar hot air systems.

As well, you'll find good information on solar air heating and solar drying at the Integration of Renewable Energy on Farms website.

For a fee, you can order Canada Mortgage and Housing Corporation's Tap the Sun: Passive Solar Techniques and Home Designs.

Online Maps and Tools

Natural Resources Canada offers solar resource maps as well as Swift, a software program that models how a SolarWall® perforated-plate system can heat a building.

Associations


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 22 April 2009
Last Reviewed: 22 January 2014