Sustainable Architecture Pillar 1: Thermal Comfort

Why are some houses always uncomfortably cold even with a heater turned on?

The reason is that the perception of temperature is more important to our comfort than the actual temperature – a concept known as Thermal Comfort.

This article will discuss Thermal Comfort and its importance as the first Pillar in Sustainable Architecture.

Note: If you haven’t already, it may be worthwhile reading Sustainable Architecture 101: Introduction before reading this article.

Sustainable Architecture Pillar 1: Thermal Comfort

What is Thermal Comfort?

Human Thermal Comfort describes the state of mind that expresses satisfaction with the surrounding environment.

Thermal Discomfort (an unpleasant sensation of being too hot or too cold) can distract people from their activities and disturb their well being.

Thermal Comfort is affected by six variable factors:

1. Air Temperature is the most common measure of Thermal Comfort and can easily be influenced with passive and mechanical heating and cooling.
2. Mean Radiant Temperature is the weighted average temperature of all exposed surfaces in a room. The greater the difference between air temperature and exposed surfaces, the greater the Relative Air Velocity.
3. Relative Air Velocity (‘wind chill factor’) is the apparent temperature felt on exposed skin due to wind.  For example, if cold air is leaking in from a window, the air temperature feels lower than the actual air temperature, hence the increased likelihood of feeling cold, even when the heater is on.
4. Humidity or relative humidity is the moisture content of the air. If the humidity is above 70% or below 30% it may cause discomfort.
5. Activity Levels can reduce the heating needs, as lower air temperature is acceptable when occupants have higher activity levels.
6. Thermal Resistance of clothing or warm blankets in a bedroom can reduce the need of heating.

The first four of these factors require an understanding of the environment and seasonal adjustments.

The last two factors require an understanding of the purpose and use of the building by occupants.

True Sustainable Architecture will take into account all six of these factors.

Thermal Comfort and Energy Ratings

Currently in Australia, all new houses and major renovations are required to pass 5 Star Energy Rating assessments.

While a step in the right direction, 5 Star Energy Ratings do not correlate to Thermal Comfort.

While Thermal Comfort may be inferred by attaining higher energy rating accreditation, it cannot be guaranteed.

This is because energy rating assessments in Australia are performed pre-construction.

This, of course, cannot take into account introduced air leakages caused by poor construction techniques, thus resulting in compromised Thermal Comfort.

In Europe, energy ratings are conducted post-construction with some countries even requiring airtight buildings. Such measures ensure that the goal of ensuring Thermal Comfort in the building at design time actually translates at build time.

Sustainable Architecture Pillar 1: Conclusion

The reason why some houses are always uncomfortably cold – even with a heater turned on – is because the perception of temperature is more important to our comfort than the actual temperature.

This perception of temperature is known as Thermal Comfort and is affected by six factors:

1. Air Temperature
2. Mean Radiant Temperature
3. Relative Air Velocity (‘wind chill factor’)
4. Humidity
5. Activity Levels
6. Thermal Resistance

A true Sustainable, Passive Solar House in Australia will require:

• A site specific Passive Solar design,
• An understanding that 5 Star Energy Ratings do not (and cannot) correlate to Thermal Comfort, and
• A builder who has proven experience in building for Passive Solar Energy Efficiency

The next article in this series will focus on Pillar 2 of Sustainable Architecture: Solar Access. To have this article automatically delivered to your email inbox, why not subscribe to our e-newsletter? Its free!

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Further Reading/References:

• Resource Smart Victoria on Passive Solar Design: Climate and Comfort (PDF)
• Sustainability Victoria on Sun, Climate and Comfort (PDF)
• Yourhome.gov.au Technical Manual on Thermal Comfort
• Health & Safety Executive UK – Thermal Comfort Checklist

Related posts:

1. Sustainable Architecture Pillar 5: Thermal Mass
2. Sustainable Architecture Pillar 3: Insulation
3. Sustainable Architecture 101: Introduction
4. Sustainable Architecture Pillar 4: Windows
5. Sustainable Architecture Pillar 2: Solar Access

Tagged as: Architecture + Design, Sustainability, sustainable architecture