Solar space heating systems are simple. Typically they are designed to heat just a room or a part of the house by using solar air collectors, that is, solar panels that heats the air directly.
Typically, these space heating systems comprise one or two collectors in the sunny side of the house, and a blower or an electric fan to pull air from the room/house through the collector(s), where the air is heated, before being blown back into the room/house.
The collectors can be installed in a sunny wall of the house, or in the roof. In this last case (see image).
The solar collectors used in this type of systems are different from those used to heat water for bathing and cooking, or for baseboards and radiators. They use air as the heating medium.
Our video on Room Space Heating:
Transpired Heating Systems
Transpired systems belong to the same family of the solar air space heaters mentioned above. They just do not use conventional solar air collectors and work in conjunction with a mechanical ventilation system or are connected to the outdoor coil of a heat pump; their goal is to pre-heat the indoor air (boasting the efficiency of the heat pump).
These systems use perforated metal plates over a wall, to capture the sun’s heat, and to heat the air that is then pumped into the building.
The perforated metal plates are designed in dark color (to absorb the sun’s heat).
Like more common solar air space heaters, these systems also use blowers or fans to bring air from the building, which is heated while circulating in the space between the metal places and the wall, before being blown back. And they can be very effective at collecting great amounts of heat on sunny days, even when the outside air is very cold.
The problem with them is that it is difficult to control air circulation, and overheating problems in sunny days.
Simple active heating systems can use unglazed or glazed air flat-plate panels. .
Location and Pitching
Solar space heating systems using solar air collectors are very sensitive to the tilt angle and orientation of the panels to the sun. Shade can be a problem...
Installing the collectors on a vertical wall is an easy and common option: it prevents over-heating in summer (when the sun is higher) and provides good results in winter, when the sun is lower and the vertical position of the panels is favorable. For the same reasons, panels mounted on roofs should have a relatively high pitch.
Why do active solar systems have so little importance?
Three warnings about active solar space heating (using solar air panels)
» Without high levels of room insulation, it will not be effective
» It is not an off-the-shelf solution
» They are only advantageous for climates with good solar resources and long periods of cold temperatures.
To some extent, solar air space heating systems are the poor relation of the solar energy systems kingdom.
And we should ask, why? After all, they are simple and cheap to implement, and there are do-it-yourselfers implementing them.
Here are the answer:
- The results are poor in homes with low levels of insulation; solar air collectors do not provide great amounts of heat, and if the rooms aren't well insulated the heat will escape to other parts of the house and to the outside.
- Intermittency: the heat is often produced when people aren't in their homes, and the system may not produce significant amounts of heat during the periods when it is most needed:.
- The system has no storage means, or flexibility;
The Bottom Line
Active solar systems require very specific conditions to be useful and effective:
1) proper room insulation,
2) proper climate conditions (cold climates, or climates with long cold periods and sunny days),
3) good design and architecture...
4) whenever possible, floors or walls with high thermal mass, able to store the heat generated by the solar panels during the sunny part of the day and to release it slowly after the sun goes down (see: Thermal Mass and Low-Energy Strategies).