Thermal Labyrinths

Hidden from view, Melbourne’s Federation Square has a  1.4km long thermal labyrinth located below the civic square in the middle of the 3.8 hectare site. The labyrinth plays dual roles – that of a structural support to the public plaza above, as well as delivering energy- efficient cooling to the large atrium, and pre-chilled air to the refrigerated systems serving other buildings on the site. It acts as a heating, ventilation and air conditioning system (HVAC).


A thermal labyrinth decouples thermal mass from the occupied space, usually by creating a high thermal mass concrete undercroft with a large surface area. Decoupling the thermal mass means it can be cooled to a lower temperature than if it was in the occupied space.

This stored ‘coolth’ can be used to condition the space in hot periods.

Thermal Labyrinth Diagram

Thermal Labyrinth Diagram


The basic design and operation of Federation Square’s thermal labyrinth follows the rules of decoupled thermal mass. At night, fans draw the cool ambient air from outside through vents placed along the southern edge of the development, close to the Yarra’s riverside. These fans move the air through the 1,600 sq m labyrinth, cooling – or charging – the zigzag of 3m high corrugated pre-cast concrete walls to the lowest night-time temperature.

During the day, the warmer ambient air is then drawn through the labyrinth by the fans and is cooled as it comes into contact with the chilled (charged) walls. This air is then distributed into Federation Square’s large atrium via a displacement system at floor level.

A glass-walled, high-volume structure approximately 18m high, the Atrium covers a floor area of approximately 2,040 sq m. The warmer air in this space is displaced and evacuated through vents in the ceiling.

The use of the labyrinth generally produces a 10–12°C temperature differential between the daytime external temperature and that of the internal Atrium temperature. This significantly reduces the amount of energy required to cool surrounding office spaces.

A structural thermal labyrinth - Federation Square, Australia. Source: Pinterest

A structural thermal labyrinth – Federation Square, Australia. Source: Pinterest


There are a wide range of strategies being adopted around thermal labyrinths, both within Australia and around the world. These include rock-store labyrinths, earth (or Canadian) tubes, earth-mounted concrete culverts, zigzag labyrinths and channel labyrinths. Thermal labyrinths have been used as key ESD elements with increasing uptake in Australia and abroad.

Federation Square. Source: Design Milk

Federation Square. Source: Design Milk

Thermal labyrinths can be integrated into a building’s structure to provide free cooling in the summer and pre-heating of air in the winter. They can have high capital costs, but over the life of a building, can yield substantial savings by reducing peak demand for cooling and heating.

Source: Bates, D., Ecolibrium, July 2013

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