Sustainable Architecture Pillar 5: Thermal Mass

If you have experienced Europe in winter you may have noticed that despite the extreme cold outside, rooms inside are unexpectedly warm and cozy.

In Australia, however, its not uncommon to experience headaches, nausea, dehydration and cold draughts indoors when a heater is turned on in winter.

What’s the difference?

Sustainable Architecture Pillar 5: Thermal Mass

Over and above the heating obtained from solar energy:

  • Australian homes are mainly heated using Convective heat. eg. Split System Air Conditioners, Ducted Heating
  • European homes are mainly heated using Radiant heat. eg. Hydronic Heating, Open Fire

The key difference is that:

  • Convective heaters warm the air in a room. The room is warm when the heater is on and cold when it is off.
  • Radiant heaters warm the material in a room. The room stays warm even when the heater is turned off.

The reason why Radiant heaters in European homes are more effective is because Europeans integrate radiant heating with Thermal Mass.

Thermal Mass

In the context of Sustainable Architecture, Thermal Mass refers to a material that has the ability to absorb and store heat from warmer surroundings and release it slowly when the surroundings become cooler, thus helping to retain a constant indoor temperature.

It is the most effective way to maintain Thermal Comfort in a building and plays an essential role in saving energy.

Generally speaking, the heavier a material the better its ability to act as Thermal Mass. For example:

  • Concrete, brick, sandstone, rammed earth, mud brick and water have good thermal storage capacity
  • Timber and insulation have poor thermal storage capacity

In addition, dark colours and dark materials tend to absorb more heat which is good for Thermal Mass.

Thermal Mass in Australia

In Australia we don’t suffer from a lack of Thermal Mass, as evidenced by:

  • The abundance of Thermal Mass on building exteriors (eg. the classic Brick Veneer home)
  • The abundance of Thermal Mass downstairs (while using cheaper, lightweight construction upstairs).

We do however, suffer from inefficient use of Thermal Mass, because:

  • Thermal Mass should be placed on the interior. This allows the Thermal Mass to absorb and release heat inside – where it matters.
  • Thermal Mass should also be situated upstairs. This is even more important for multi-storey buildings because hot air rises and therefore upper rooms tend to overheat easily. Having Thermal Mass upstairs will absorb excess heat during the day, leaving upstairs rooms cooler.

The following is series of cross sections of different types of construction.

Unfortunately the first two types of construction, weatherboard and brick veneer, are the most common in Victoria and and also the most ineffective uses of Thermal Mass.

Although the above are only a few examples of missed opportunities to capitalise on the energy saving properties of Thermal Mass, it demonstrates that the biggest obstacle to Sustainable Architecture in Australia isn’t availability of materials, but of design + build tradition.

Integrating Radiant heat and Thermal Mass properly is a condition for Passive Solar Design and is a very real and available heating and cooling alternative to our traditional Split System Air Conditioners and Ducted Heating.

The results will be better for the environment, for your wallet and for your health.

Sustainable Architecture Thermal Mass Conclusion

The reason why Europeans experience greater Thermal Comfort indoors is that they use radiant heat combined with Thermal Mass to heat their homes.

Thermal Mass is a material that can absorb and store heat from warmer surroundings and release it slowly when the surroundings become cooler, thus helping to retain a constant indoor temperature.

In Australia we don’t suffer from a lack of Thermal Mass but we do suffer from its inefficient use handed down from past design + build traditions.

Integrating radiant heat and Thermal Mass properly is a condition for Passive Solar Design and is a very real and available heating and cooling alternative to our traditional Split System Air Conditioners and Ducted Heating.

The results will be better for the environment, for your wallet and for your health.

The next article in this series will focus on Sustainable Architecture Pillar 6: Thermal Bridges.

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