Design for climate

Design for climate

Design for climate
Design for climate requires that homes be designed or modified to ensure that the occupants remain thermally comfortable with minimal auxiliary heating or cooling in the climate where they are built. Passive design — working with the climate, not against it — is an important component, as are energy efficient heating and cooling systems, and smart behaviour by the occupants.
Approximately 40% of household energy is used for heating and cooling to achieve thermal comfort. This rate could be cut to almost zero in a new housing through sound climate responsive design and, indeed, should be our aspirational goal. Taking into account current consumer preferences and industry practices, halving the rate to 20% is highly achievable in the short term.

The 40% of the household energy used for heating and cooling to achieve thermal comfort could be cut to almost zero in a new housing through sound climate responsive design.

Reducing or eliminating heating and cooling needs in existing homes is a significant challenge, particularly those designed and built before building energy efficiency standards were introduced when appliances were effective but inefficient. Based on 1.5% annual renewal rates, at least 50% of our current housing stock will still be in service in 30 years’ time.

New homes built now will be in service in future times when we expect to see significant changes in the climate. Designing for today’s climate is important; ensuring that those designs can be just as efficient after 30 years of climate change would certainly be desirable.
Affordability is often cited as the main barrier to greater efficiency but increasing energy costs are rapidly shifting the affordability focus from initial or upfront cost to ongoing or operational cost. With this shift, high levels of thermal performance are becoming increasingly valuable and the payback or amortisation period for thermal performance upgrades is diminishing rapidly.

This introductory overview of key design objectives and responses to creating thermally comfortable homes in each main climate zone in Australia needs to be further refined and customised to your individual site, locality and design brief. Use this overview, and the references to other articles, to access more detailed information as you proceed through the various stages of designing, purchasing or altering your home.

Human thermal comfort
Humans are comfortable only within a very narrow range of conditions. Our body temperature is about 37°C, despite the fact that the body generates heat even while at rest: we must lose heat at the same rate it is produced and gain heat at the same rate it is lost. The diagram below shows the various ways by which our bodies achieve this.
Source: Steve Szokolay
Human thermal comfort has two components: psychological and physiological. Both are governed by the processes in the diagram but reach the brain and trigger responses by very different pathways. Both needs must be met before we feel truly comfortable.
The main factors influencing both physical and psychological human comfort are:
  • temperature
  • humidity
  • air movement (breeze or draught)
  • exposure to radiant heat sources
  • exposure to cool surfaces to radiate, or conduct to, for cooling.
Thermal simulation software can model with great accuracy the amount of heating or cooling energy required to achieve physiological comfort; it is unable to model highly variable human perceptions of comfort. Sound building envelope design based on modelling delivers an environment that addresses all the physical factors necessary for comfort (except humidity) but can’t always meet our psychological comfort needs.
Important triggers for psychological discomfort are radiation, air movement and conduction. Although they are less effective physiologically, they trigger innate self-preservation responses that override our ability to perceive physical comfort. Until they are met, we don’t feel thermally comfortable and our behaviour can render the best of design solutions ineffective. Acclimatisation is a critical component of psychological comfort.
Psychological thermal discomfort can make us set the thermostat on heating or cooling systems well beyond levels required for comfort. For every 1°C change in thermostat setting, it is estimated that our heating or cooling bill rises by around 10%. In other words, failure to address psychological comfort can increase heating and cooling energy use by up to 50% (Australian Greenhouse Office 2005).

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