Solar Space Heating Systems

Solar air-space heating can be a a very simple system based on solar heated air, directly pumped into the rooms by fans or through a forced air system.

Other space heating options involve more complex systems, based on solar heated hot water and radiant heating, that is, involving radiators, or radiant floor systems, or boilers...

See:

Solar powered radiant floors
Solar Space Heating & Radiators
Solar & Boilers).

Solar space heating systems are auxiliary systems

Solar space heating systems are typically auxiliary space heaters. They have limitations, demand reasonable or high solar resources, are pricey than solar water heaters and depend a lot on the implemented configurations. You should carefully consider its limitations and constraints, before adopting such a system.

Solar space heating systems aren't designed to replace other heating systems entirely, or to provide all the home's heating needs. It would demand a too complex, large and expensive system, and also very favorable climate conditions...

Designs

Solar space heating systems aren't standard and well defined systems. Large manufacturers do not present pre-packaged, kits or well integrated solutions for solar space heating. Solutions for solar space heating are often designed by professional solar installers, taking into account local conditions and adapting the systems and the designs of solar hot-water systems.

Since solar space heating systems are more demanding in terms of collectors, storage capacity (and more complex and expensive than solar hot water systems) they can be designed to provide both solar water heating and home space heating.

Simple solar space heating systems Limitations

Space heating systems based on direct pumping of heated air, present strong limitations in most climates. Since these systems don’t use storage equipment or activation-deactivation controllers, they may easily inject too much hot air into the house. And since they are used just for house space heating, they are useless during a large part or most of the year in many climates.

Required weather conditions

Simpler solar space heating systems should only be implemented in climates where long and cold winters coexist with many sunny days; they are a typical solution to solve specific problems of ventilation or seasonal coldness in a room (they are commonly used in commercial and industrial applications, namely those demanding outdoor ventilation like warehouses and hangars…

More complex solar heating systems and the Storage Space Issue

Systems with a more complex design use a large collector area and a large storage space (much larger than that needed in solar water heating systems).

Intermediate systems (in terms of complexity) use separate thermostatic control to regulate the temperature. They may also use a photovoltaic panel to power the fan inside the unit.

Solar space heating & Forced air ventilation

Solar space heating systems can use forced air ventilation and ductwork. In a common design, air is drawn from inside the room through the bottom of the collector, where it is heated and blown out through a duct located in the top, linked to other ductwork and to the forced air ventilation.

Though systems can be directly based on solar heated air, they may also use a liquid medium. In these cases, the solar heated water in the storage tank is pumped into a coil, which will heat the indoor air in the forced air ventilation system, whenever needed and possible (this type of systems use sensors and a thermostat that calls for heat and allows the pumping whenever the temperature of the solar heated water is sufficiently high).

Collectors type

The simpler solar air-space heating systems are often based on unglazed air flat-plate collectors, but glazed flat-plate collectors are also common and the more efficient evacuated tube collectors may also be used in colder climates.

See: Types of solar collectors (thermal uses)

Location & Solar collectors pitching

Solar space heating systems are more sensitive to the solar collectors tilt and orientation than solar water heaters. So, make sure that trees, buildings or other landscape elements do not shade the collectors area.

Collectors should be oriented within 15 degrees of true South (or North, in the southern hemisphere). When located in a roof, space heating collectors should be placed at a steeper pitch (to catch more sun in winter, and to help prevent overheating in the summer).

Mounting the collectors on a vertical wall is a good solution in space heating, since that may prevent over-heating in summer (when the sun is higher in the horizon) without loosing efficiency in winter (when the sun is lower and the collectors may benefit from a lower winter sun).

Sizing a solar space heating system

Space heating systems require a larger area for collecting solar energy than solar water heating systems.

In the glazed flat-plate collectors case, a sizing rule of thumb is 2 square feet of collector for each 10 square feet of the footprint of the building. But that doesn't represent much. It all depends on climate conditions and on the efficiency of the chosen collectors, their type and the type of system.

Working with a good solar professional is the best way to size a solar thermal system.