heating and cooling with solar (thermal) chimneys

Thermal (or solar) chimneys promote natural ventilation. They suck the hot air inside the living space, expelling it through their vents. They are mostly used in hot climates for cooling purposes, though they may also be used as heating systems.

The basic idea

Solar chimneys demands outdoor fresh air, coming from breezes or a shaded side of the building, and involves a well known natural mechanism: hotter air tends to rise and to escape through upper overtures, if they exist.

Solar Thermal Chimney That fact makes the heated air inside the solar chimney to rise and to escape through their venting system, sucking the air inside the home into the chimney (the chimney is built to communicate with the living space); that, by its turn, causes fresher outdoor air to enter into the home - through windows or other vents at lower levels. See image, from Australia Sustainability Victoria, explaining the mechanism.

Heating with a solar chimney

In cold weather conditions, the solar chimney role can be reversed. Instead of promoting ventilation and cooling, the solar chimney vents are closed. Instead of going out, the heated air is forced - through fans, or other equivalent system -to drop into the living space of the building...

Thermal chimneys configuration and materials

The basic architectural features of the thermal chimneys are rather simple to implement.

A thermal chimney… is like an ordinary chimney (narrow and located at the top of the building) built with a glazed front and heat absorbing (high thermal) materials, to generate high temperatures.

The walls of this structure should be particularly well insulated to avoid unwanted leaks.

Location

The solar chimney should be located in order to get enough sun and as much heat gains as possible. The chimney bottom should terminate above the home’s roof level.

The chimney should be protected from winds and breezes. These can interfere with the working of the system, namely the exhausting of the heated air… An alternative is to use a rotating metal scoop (opening opposite to the wind) at the top vent, in order to allow heated air to exhaust without being overcome by wind.

Vents

The solar chimney includes a vent at its top, which exhausts the heated air and provides a suction mechanism to the ventilation system associated with the chimney.

Other elements of the solar chimney system

Solar chimneys should be integrated into a wider home design. Often, they communicate with open stairwells or atria.

Limitations and drawbacks

Solar chimneys should be properly designed and can be very effective, specially in hotter climates with sufficiently favorable breezes and buildings with landscapes involving suitable differences of temperatures. They complement other cooling (or mechanical) heating and cooling strategies.

Obviously, they demand properly insulated structures. Otherwise they will cause heat losses or cold air infiltration in harsh winter conditions...