Passive and Mitigative Buildings and Districts
Filippo Weber, MArch | Dr. Rosa Schiano-Phan, PhD
The global environment is under pressure due to the high waste in natural resources and the extremely high proportion of energy used compared to that really needed.
Cities play a fundamental role in the development of the global economy’s sustainability and in the effectiveness of Climate Change (CC) actions. Historically, they are the engine of our world (Glaeser, 2013) but a polluting one: 78% of the Green House Gas (GHG) emissions produced worldwide are actually produced in, by or for cities. Of this proportion 45% are produced by buildings and 60% of this is for “comfort” – mainly space heating, cooling and lighting. Hence, “comfort” accounts for approximately 30% of the total GHG emissions produced by cities and 20 % of the total GHG produced in the world. These figures are even more outstanding if it is considered that cities represent only 2% of the earth’s surface (Stone, 2012).
In order to mitigate CC, the European energy policy has placed great attention on buildings’ energy efficiency due to its substantial savings’ potential. This has led to improvements in the efficiency of services, components and appliances to the point that today technology has theoretically arrived to a level of maturity which allows to reach “a suitable target for nearly zero-energy buildings” and beyond (Hermelink, 2013).
However, the focus on efficiency has created a disjointed approach between the design of the building as an envelope and that of its environmental control systems as mechanical add-ons, leading to considering buildings as isolated systems or standalone entities.
But, especially in urban areas, the built environment and the energy processes highly affect the microclimate to the extent that today’s cities are at the forefront of the most rapid environmental and climatic changes ever experienced by mankind, causing reduction in comfort and health and increasing buildings energy consumption (Stone, 2012).
While the building scale policies have imposed minimum thermal conditions for building elements and energy standards, a large proportion of their energy performance will be influenced by and will influence the urban environment to which little attention has been given. The paper will show how actions to mitigate and fine-tune the urban microclimate are one of the most effective vehicles towards CC mitigation and adaptation, and will highlight how buildings (especially when new districts are planned) can contribute to positive microclimates, hence proposing an innovative take on buildings and urban environments.
- From global to local
The complex phenomena characterising urban environments and microclimates have been studied as part of the Urban Heat Island (UHI) effect. It relates to the relative higher warming of the cities’ core compared to the rural surroundings and to the warming of global climate. The temperature in city streets can be 6 degrees or more, higher than the surrounding countryside and this will also exaggerate the impact of changes in weather patterns due to CC. The microclimatic modifications in the urban environment are produced by the interaction of the causes of CC with specific urban issues. This generates what we could also call a local CC. The ‘street section’ (Schiano-Phan, Weber, Santamouris, 2015) is the physical and metaphorical backdrop of these complex interactions such as reduction in evaporative cooling potential caused by the substitution of vegetation with buildings and streets; reduced surface reflectivity due to the generally dark colours of cities (red, black, grey); increased re-absorption of the reflected radiation by the urban fabric within urban canyons; high thermal storage properties of the urban fabric; reduced air movement due to urban obstructions; local Green House effect caused by urban pollution (exhausts from gas, coal or fuel); waste heat from mechanical and thermal processes of transportation, boilers and HVAC; human behaviour that generally is highly energy consuming (i.e. A/C or private cars).
2.2 Penalties of local CC
These urban issues have a number of crucial consequences, which are reviewed below.
On the energy penalties of local CC. Since the global climatic changes in urban environments are nowadays overlapped to the local climatic changes, the greater energy penalties of the current situation occur for cooling demand. These penalties happen along three dimensions: 1. use of mechanical systems also in climatic regions where their use should be avoided and instead passive strategies implemented – cities have been experiencing an exponential increase of A/C systems also at northern latitudes; 2. extension of the cooling season to the extent that paradoxically mechanical systems for cooling are used in those spaces with high internal gains such as offices and commercial spaces also in winter at high latitudes; 3. especially at lower latitudes, reduced efficiency of the mechanical systems due to the outdoor temperatures very close to the upper tolerance range of the equipment.
Studies have quantified the increase in energy demand for comfort due to the urban heat island in summer: 1°K increase of temperature produces 8% increase in energy demand (Santamouris, 2014). Consequently, being the urban temperatures 5 to 10 K higher than the countryside, the same building in a city uses 40 to 80% more energy for cooling compared to the same building in the countryside.
On urban inhabitant’s comfort. Direct consequence of the causes that lead to local Climate Change is that cities are uncomfortable both in winter and summer. Outdoor discomfort leads to two main issues: reduced attractiveness of the open spaces which has impacts on pedestrian and cycling mobility and also on the urban economies and on indoor comfort: during extremely hot periods the severe conditions of urban environments translates in the body’s inability to adapt the seasonal changes. As a consequence indoor spaces are experienced as a mean to escape from the outdoor and it has to generate unnatural microclimates that have to create alternative conditions to the outdoor.
Other consequences related to indoor and outdoor discomfort are reduced productivity, health and excess deaths, quality of life and biodiversity. As an example, studies correlating temperature and hospital admissions have shown that during heat waves, the latter increased for heat related diseases. These first studies indicate that the indoor and outdoor environment may play an important role on people’s health (Santamouris, 2011), especially when the excess heat is related to lack of cool shelters.
On missed opportunities. It is clear that the current situation of cities prevents substantially the use of passive strategies for cooling that could be a very effective way to cut off GHG for comfort in cities and avoid the associated waste heat. As evidence, output of previous European projects (e.g. Altener Cluster 9 and other FP7 projects) have identified the poor quality of urban environments and microclimates as one of the main barriers to the implementation of bioclimatic strategies in cities, which are fundamental for the reduction of energy demand and cost.
- The need for a new paradigm
The surrounding environment plays a major role on buildings’ performances and human comfort, health and productivity. Yet its improvement is not usually considered when designing a building or better a new district. Nevertheless the strategies to mitigate the urban microclimate are well known and have been proven by many researches and case studies.
As an example the University of Athens has participated to the bioclimatic rehabilitation of a small central district of Athens where many bioclimatic strategies to improve the ‘street section’s negative loop’ where applied: light colour materials, vegetation, water bodies, air to soil heat exchanger, pedestrian streets, street and building shading and others. The rehabilitation has shown a crucial aspect: also a local intervention can decrease the peak of urban temperatures between 2.3 and 3.4 °K (Santamouris, 2014) and consequently energy demand while improving outdoor comfort.
The public realm has large responsibility on local CC through the choice of pavement’s materials, urban planning, transportation, street design, green infrastructures and others. Nevertheless buildings and districts choices greatly contribute to the urban microclimate: massing and master planning, functions distribution, geometry, materiality, environmental (mechanical) control systems and others. These equally important responsibilities make the traditional dichotomy between urban action to mitigate local CC and building action to reduce energy consumption outdated. If the synergy between public and private realms should be the strongest route to move towards sustainable cities (Schiano-Phan, Weber, Santamouris, 2015), buildings should be considered for their impact on the urban environment both when retrofitting and especially when new districts are planned.
Hence, based on the existing research and experimentation at urban microclimatic level, this paper advocates a new paradigm of building: the Mitigative Building; a building (or group of buildings) that considers the impact that buildings, space in between buildings and users have on each other in order to mitigate and fine-tune the surrounding microclimate and consequently extend the use of passive strategies, enhance users’ indoor and outdoor
comfort, improve health and reduce energy demand. The new paradigm moves along four principal dimensions: 1. optimization of the master-planning (massing and functional distribution) and outdoor design not only to improve but also to fine-tune the microclimate in order to extend the seasonal passive strategies for indoor and outdoor, 2. optimization of the passive strategies for indoor and outdoor users’ adaptive comfort, 3. evaluation of human comfort, behaviour and interaction with the building, 4. fulfilment of the residual energy demand with onsite renewable energy production. These dimensions translate into a design process that looks at the ‘whole system’ which is formed by the surrounding, the building and the users and by the interactions that they have with each other: the adaptive comfort approach helps us in this aspect, as it works with many attributes of the system. The outdoor climate, the building’s context, its form, services and occupants as well as the seasons and times of day (Nicol, 2012). The whole system thinking will consider improvements both at microclimatic, building and human behavioural level, which go beyond addressing the problem of UHI and summer comfort but that extend to year round outdoor and indoor comfort. The emphasis on the mitigative aspects of the external interface of buildings is not only beneficial to address problems related to overheating of cities but, where required, can also improve comfort in winter through the harnessing of climatic potential, urban morphology, building geometry, materiality and the adoption of an adaptive comfort approach. The microclimatic improvements range from strategies for the heating season such as enhanced solar access, prevailing wind barriers, solar energy “collectors”, to strategies for the cooling season such as prevailing wind access, cool pavements, cool facades and cool roofs, misting devices, soil to air heat exchanger, shading, vegetation. Similarly, building strategies build upon on a non-prescriptive approach that has been widely adopted in the low-energy architectural field and which includes a combination of passive solar and back-up systems during the heating season and natural ventilation, passive cooling and alternative hybrid system during the cooling season. The overarching premise for the success of these well-known strategies is a greater and alternative inclusion of perhaps the most important factor: users’ behaviour and adaptation. This is an area much talked about but certainly not fully exploited yet and passible to further interdisciplinary research and experimentation. Existing pioneering examples of buildings, also in urban environments, that try to implement bioclimatic strategies and improve the surrounding microclimate can be found in the CH2 Building in Melbourne and in the Sony HD in Tokyo. Their design concept and the advantages of their approach has been extensively studied (Newman, 2009; Yamanshi, 2011). However, these are few and discrete examples which are not integrated into a policy framework or a broader discourse on the potential of buildings to fine-tune the urban microclimate with the need for comfort and energy demand reduction.
3.1 Benefits of the new paradigm
The advantage of moving towards a new paradigm of Mitigative Building is threefold.
On the energy consumption. The mitigation and attuning of the urban microclimate to the energy and comfort needs will translate in a reduction of building energy demand in the first place, (reducing the difference in temperature to be covered by active systems both in the heating and cooling season and increasing the efficacy of the systems) and, even more importantly, allowing the integration of low-tech/low-cost bioclimatic strategies which will reduce or avoid the energy demand for comfort.
On the societal behavioural shift. Initial studies and experimentations indicate that actions at street, neighbourhood and district scale would yield significant, and more important, immediate benefits in improving the local microclimate around buildings.
The short-term improvements of the urban environments have potentially the benefit of connecting public awareness directly to the issues of local CC and, indirectly, to that of global CC. In fact, the decoupling of CC from the geography and timescale of people’s lives, produced by the global scale of the issue and the difficulty for some to grasp the importance of energy and CO2 savings, produces a considerable impediment to behavioural change (Stone, 2012). Hence he implementation of the new paradigm will be more likely to produce the behavioural changes required for the radical transformations needed to enable the transition to a clean, low-carbon, sustainable and resilient society. In fact, changes in behavioural choices, which are also “strongly influenced by changes in the built environment” (Wilhite, 2008), have been agreed as one of the main strategies towards mitigation of CC, with a potential reduction in energy consumption by up to 20% (EEA, 2013). Hence focusing on mitigation of the urban environment will have a more immediate and tangible impact not only on cost reduction and improved performances of building but also on societal behaviour.
Other benefits. The impact of heat waves on health and of heat islands on local weather patterns has been documented in several studies (Loughnan, 2010; Phi, 2007). The direct improvements that mitigating large portions of urban environments can have on these aspects are obvious but what is interesting to emphasize is the indirect benefits that these can potentially have on society. The energy demand increase, health issues, death risks and other consequences can potentially be much higher for low income and more vulnerable groups of society due to the poorer condition of their housing, to the lower affordability of high efficiency goods and to the usually denser and overheated zones of cities where they live – further emphasizing social disparities and energy poverty. Urban heat island highly affects indoor comfort conditions in low income housing. Studies performed in different parts of the world have shown indoor comfort conditions during heat waves exceeded highly the set threshold limits for health and well-being (Sakka, 2012; Lomas, 2013).
From a review of the well-studied problems and opportunities facing our built environments globally and locally, it is apparent that there are a number of strategies applicable at urban and building scale in order to attune the local microclimate to the inhabitants need for health and comfort and consequently reduce energy consumption. Nevertheless the dichotomy between urban scale policies, yet slow and often ineffective, and building scale interventions based mainly on improvements in efficiency, has highlighted a gap in policies and interventions. In order to move towards more climate change responsive cities, the buildings’ role in the urban environment must be reconsidered. A new paradigm of building and urban environment is proposed based on the unexploited potential of considering urban environments, buildings and users as part of the same systems working in balance between them. A whole-system thinking is advocated to yield significant improvements in terms of energy, comfort and behavioural shift. Given the technological maturity of present times, most of the strategies and techniques needed to mitigate the microclimate, and which are referred to in this paper, are well known and available. Their discrete application and some small scale demonstrations have occurred and concepts and outcomes have been discussed broadly at many levels. Moreover barriers to the full implementation of the strategies to fulfil the new paradigm of mitigative buildings and urban environments are found in the lack of policies at the appropriate scale and in inevitable societal value gap between the public and private realms. So far the public nature of the urban environment has implied that if mitigative strategies to improve the microclimate need to be applied, these are mainly responsibility of the public authorities, while the private stakeholders mainly focus on aspects related to the improvement of their private assets (such as efficiency of buildings, products, appliances, etc.). However, the concept of mitigative building places emphasis on the contribution and responsibility that also private buildings have on the public and shared space, and on their impact on the urban microclimate, with benefits not only for the outdoor shared comfort but also for the indoor private comfort due to the extension of the applicability of passive strategies.
The Authors acknowledge the individuals that have directly or indirectly contributed to the development of the ideas described in this paper. Especially to: Prof. David Dernie, Prof. Mat Santamouris and Prof. Joanna Goncalves.
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