Passive design is the implementation of features into buildings that work in collaboration with and utilise natural processes for heating, ventilation and lighting, for the purposes of minimising energy consumption while providing comfortable living conditions. Active design involves the implementation of features that require energy input, such as electricity or gas.
Passive solar design is the use of solar energy to heat, cool, ventilate or light buildings, without the need for electricity or mechanics (Beggs, 2007, Ewers, 1977, Yudelson,
2007). Smith (2009) states that passive solar is design that maximises the ability of the building to gain energy from the sun and that building sites and design with solar exposure are preferable.
Passive design has specific implementation in heating, where it involves the utilisation of a building‟s structure to collect, store and transfer solar energy. This means the prevention of the summer sun gaining access to the building; the exposure of key areas of the building to the low hanging winter sun to capture and store solar energy; the insulation of the building to prevent unwanted heat loss or gains; and the orientation of the building to maximise solar exposure during the winter (Beggs, 2007, Ewers, 1977, Reardon et al., 2005, Smith, 2009, Yudelson, 2007). In many cases a house incorporating passive solar design principles does not look particularly different to buildings that ignore these principles. The primary differences come in the efficiency, running cost and levels of resident comfort (Crocombe, 2007, Reardon et al., 2005, Smith, 2009). This chapter will focus primarily on passive solar heating rather than passive cooling, as heating is considerably more relevant in temperate climates such as that found in Hobart.
3.3.1. How do passive and active design differ?
Many buildings are designed and constructed with little consideration of their surrounding climate, and create hostile internal environments that require considerable mechanical effort and electrical expenditure to maintain a habitable condition year round (Beggs, 2007). Active design in such a fashion is wasteful and represents an environmental failure in the building design.
While active solar design utilises complex electrical and mechanical systems such as: photovoltaic cells and water collector tanks with pumps; passive solar design utilises the processes of conduction, convection and radiation to transport heat energy (Beggs, 2007, Gnauck, 1985, Gray, 1997, Smith, 2009, Smith and Pitts, 1997, Yudelson, 2007). Passive design takes advantage of natural energy flows to ensure that a building remains thermally comfortable for the inhabitants (Beggs, 2007, Reardon et al., 2005, Smith, 2009).
Active solar design includes all heating systems where mechanical or electrical means are required to transfer or transport energy once it has been collected (Smith, 2009).
This includes such systems as photovoltaic panels, as well as systems where heat is collected in one area and pumped into another (Gray, 1997).
3.3.2. Importance of passive design – economic and social benefits
Many homes in Tasmania do not work in harmony with the local environment, rather they work against the climatic conditions, making them require unnecessary active heating to maintain adequate living conditions in colder months (Beggs, 2007, Gray, 1997, Reardon et al., 2005). Passive solar design can minimise the energy required to maintain a comfortable thermal environment, and in doing so reduce the energy expenditure and heating load of the building (Peterkin, 2008, Yudelson, 2007). Makaka et al. (2008) argue that even low cost buildings can implement a wide range of passive design features to improve thermal behaviour and ventilation efficiency.
Passive solar and energy-efficient features can be incorporated into buildings in temperate climates with little to no extra costs (Al-Azzawi, 1991, Ewers, 1977, Smith, 2009). Investigation by Roach (1979) showed that as early as the late 1970s passive solar designs could provide economic benefits. Schnieders and Hermelink (2004) showed that with an extra building cost of 10%, passive houses could reduce space heating demands by 15-20% and provide notable increases in thermal comfort. If considered early in the design phase, substantial savings could be garnered, in many cases, with no additional expenditure. This work also indicated a high level of user satisfaction with buildings implementing passive design features. Yakubu (2004) conducted a user satisfaction survey of people living in passive solar homes that also examined motivations behind a homeowners decision to design or purchase a passive designed home. The study determined that the primary motivating factor was the desire for high levels of thermal comfort with very little expenditure, followed closely by the desire for a house that was aesthetically appealing. The study also determined that passive designed homes have a high level of occupant satisfaction. The end result is that houses incorporating the principles of passive solar design yield significant financial and health benefits for the inhabitants, as well as reducing the building‟s impact on the environment.
3.3.3. Environmental benefits of passive design
The average Australian home produces over 15 tonnes of greenhouse gas per year. With over seven million residences in Australia, this means that homes emit more than
20% of the Australia‟s greenhouse gas emissions (Reardon et al., 2005). Tasmania is now part of the national electricty grid, and with 85% of Australian energy produced by the coal fired power stations, reductions in electricity consumption mean significant reductions in greenhouse gas emissions (Jordan, 2009). Passive solar design mitigates the environmental impacts of the building by reducing the need for unnecessary expenditure on electrical heating, gas consumption, and the use of wood fired heaters.
3.3.4. Possible negative impacts of passive design?
Nutt (1994) suggests that while there are many claimed benefits of passive design, there are also several potential risks that must be considered and managed. These risks include:
increased purchased energy consumption through inappropriate use;
seasonal overheating;
unacceptable temperature fluctuations;
poor air quality and condensation;
unacceptable lighting variation and glare;
temperature stratification;
thermal fatigue and fracture of materials; and
winter survival of plants.
While these risks are, potentially real, all of them can be mitigated or managed effectively through intelligent and informed building design. As noted by Nutt (1994) the correct education of occupants on the operation and performance of the building‟s passive design features can mitigate these risks.
3.3.5. The purpose of the modern building
It is important to consider what functions a dwelling serves in the design process.This is a concept that can be overlooked in the creation of ostentatious modern buildings designed to garner attention and prestige with little consideration of their comfort or environmental impact. The fundamental purpose of modern buildings is to protect the occupant from elements of the environment outside which are deemed undesirable,
environment that is not only comfortable but promotes the good health and wellbeing of the occupants.