3.3.3 SPACE HEATING AND COOLING

3.3.3.1 Space Heating

Solar space heating represents a very large potential market, although it may have limited possibilities in existing multi-storeyed buildings in densely populated urban areas. The systems use air or a liquid that is heated in solar collectors and then transported by fans or pumps using a small amount of electricity. Air systems consist of collectors, fans, ductwork, and controls and can heat the air in a house without heat exchangers or thermal storage. Large air systems typically use thermal storage, such as a bin of small rocks. Liquid solar systems consist of collectors, storage tanks, pumps, pipes, heat exchangers (in closed loop systems) and controls.

Solar systems are usually designed to provide 40-80% of the annual heating needs of a house, but 50% may represent the most economical design because extra capacity is only used on the coldest days and would otherwise be idle. Heat not provided by the solar system must come from a backup system, usually a conventional furnace. The two systems can use common duct-work and heat delivery circuits, but the backup system should always be able to supply the total heating requirement for periods of cloudy weather, when little solar heat is available.

Source CRES-TRASOL CD-Rom

Figure 3.8 Solar radiant in-floor system
(P-1 to P-4 denote circulating pumps or fans)

The method of heat distribution most compatible with active systems is radiant slab heating, which uses plastic, rubber or copper pipes embedded in a concrete. When solar-heated water circulates through the pipes, the floor heats up and then radiates its heat to the room. In-floor heating systems (fig 3.7) use moderate water temperatures to keep from scalding bare feet. Typical inlet water temperatures range from 38 to 51.5 °C, which is precisely the range where active solar systems excel. Since the temperature difference between a radiant slab and the collector is greater than that for a water storage tank / collector system, the collectors are more efficient since they lose less heat to the cold outside air.

It is also possible to connect the solar system to small heat exchangers in individual rooms. These small heat exchangers are available as standard plumbing units in various sizes and contain their own blowers. The fluid temperature in a solar system reaches 32.5-50°C, whereas conventional systems heat water to 70-80°C. Therefore, if baseboards or radiators are used with solar heating, the surface area of the radiators should be significantly increased.