Thermal labyrinths

[edit] Introduction

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.

[edit] Options

The labyrinth layout needs to balance optimum thermal storage with the air resistance of the system. Creating air turbulence, by increasing the roughness and incorporating bends, improves heat transfer. However, incorporating too many bends may increase the air resistance beyond the point where the system can be part of a passive or naturally ventilated scheme.

Thermal labyrinths are suited to new, mechanically-ventilated buildings with cooling demand that are located in climates with a large temperature difference between day and night.

[edit] Size and output

As labyrinths are often constructed directly beneath a building, only the sides and floor of the labyrinth are in contact with the earth and the top of the labyrinth is directly coupled with the building. This means that the labyrinth needs to be well insulated from the building to prevent heat transfer.

The earth contact of the labyrinth gives the benefit of steady ground temperatures, however, the undisturbed ground temperature cannot be used in calculations, as it will be affected by the presence of the building and the operation of the labyrinth. This means that optimisation of the design requires a complete thermal simulation of the system.

When the ambient air temperature can itself meet the cooling requirements of the building, the labyrinth can be bypassed so that its cooling potential is retained for use during peak conditions.

During the unoccupied period when the ambient air temperature is low, night cooling is used to ‘charge’ the labyrinth.

[edit] Running costs

Regular inspection and cleaning of the labyrinth are recommended, although thermal labyrinths are generally virtually maintenance free. The major cost that can be incurred is when fan power is required to supply air through the labyrinth.

[edit] Summary

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.

This article was created by --Buro Happold, 17 March 2013, based on a 2008 article in 'Patterns'.

[edit] Related articles on Designing Buildings Wiki

• Air source heat pumps.
• Dynamic thermal modelling of closed loop geothermal heat pump systems.
• Earth-to-air heat exchangers.
• Geothermal energy.
• Geothermal pile foundations.
• Ground energy options.
• Ground pre-conditioning of supply air.
• Ground source heat pumps.
• Thermal mass.
• Trombe wall.
• Types of ventilation.

[edit] External references

• Ingenia, Going underground September 2006.