Liquid solar thermal heating systems are best for central heating in the home. The solar collectors use either water or a non-toxic glycol antifreeze to absorb the thermal energy. With the help of a controller, a circulating pump moves the fluid through the collector. The liquid flows quickly through the collector, resulting in an increase in temperature of 10°–20°F (5.6°–11°C).
The warm liquid flows to a storage tank or a heat exchanger. The heat is then spread through the home via one of the methods described below.
Heated liquid from the solar collector travels through pipes in a concrete slab flooring, usually covered with tiles. The heat radiates to the room.
This kind of solar home heating system can work without a heat storage tank, although a tank is needed to control the temperature.
These systems take longer to warm up but, once operating, provide a consistent temperature. Carpets and rugs will reduce the effectiveness of radiant floors.
Hot Water Baseboards or Radiators
These need water heated between 160° and 180°F (71° and 82°C). However, flat-plate solar collectors – the most common type of collector – heat liquid to a lower temperature. In this case, the liquid from the collectors needs to be heated more by the backup system, or that a higher temperature collector be used (such as an evacuated tube collector).
Central Forced-Air System
This kind of system works through a heat exchanger in the air duct. As air from inside the home passes over the heat exchanger, the liquid inside heats the air. The coil must be big enough to transfer enough heat to the air at the collector’s lowest operating temperature.