The Passive and Mitigative Building Approach

Global environment is under pressure due to the high waste in natural resources and the unreasonable proportion of energy consumption compared to that really needed.

Cities are the engine of our world [1] but a polluting one: 78% of the Greenhouse Gas (GHG) emissions produced worldwide are actually produced in, by or for cities.

The world has started consuming resources and energy. This process has been driven by powerful commercial stakeholders, including the energy, construction, and banking industries, which have addressed cities as agglomerations of assets rather than “living organisms” [3].

Not only have natural processes been excluded, but also its consequences of this exclusion have been, and largely still are, ignored.

As a consequence, especially in urban areas, the built environment and the energy processes have affected 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, health and increasing buildings’ energy consumption [2].

The microclimatic modifications in the urban environment are produced by the interaction of the causes of Climate Change with specific urban issues that are particularly complex to be solved, as their causes and effects are interrelated generating a negative loop in the city.


The urban situation: the Negative Loop

Not all the urban green house gases are related to the negative loop, but those wasted because of it are elevated and mainly caused by the consequences of manmade landscape modifications:

  • substitution of vegetation with buildings and streets
  • density of buildings and distribution of functions or intended use
  • reduced surface reflectivity due to the generally dark colours of horizontal surfaces of cities that are highly insulated in summer but not in winter increased re-absorption of the reflected radiation by the urban fabric within urban canyons
  • high thermal storage properties of the urban fabric such as street and facades reduced air movement due to urban obstructions
  • local green house effect caused by urban pollution
  • poor building fabrics and buildings designed against the climate
  • waste heat from mechanical and thermal processes of transportation, boilers and HVAC
  • human behaviour that generally is highly energy consuming

To reduce pollution and avoid the use of mechanical cooling, air quality for natural ventilation must be improved and alternative forms of mobility must be enhanced by offering better opportunities and conditions for the uptake of alternative transportation modes (e.g., walking, cycling, and low-emission public transport).

At the same time, buildings use enormous amounts of energy for space heating because they and the surrounding city are not design to maximise the benefits coming from the energy of the sun as a source of free and clean energy.

Buildings and cities are usually designed exactly the contrary of how they should be, and the consequences of this attitude are numerous, detrimental and now well documented.


Negative aspects of the Negative Loop: microclimate matters

The context described has a number of consequences on citizen health, urban sustainability, equality and economy.

The “negative loop” reduces the use and enjoyment of open spaces that are extremely relevant for urban prosperity and economic growth in both developed and developing countries [5].

In general, high urban temperatures have a serious impact on the quality of life of urban citizens and affect the local economy by also reducing productivity.

It also affects the health of the inhabitants, by raising the concentration of specific urban pollutants that provoke respiratory diseases, and increasing the risk for the vulnerable urban population during periods of extreme heat [5,8,9].

Moreover, microclimatic changes of large urban environments modify the pattern of the local weather. As the urban microclimate amplifies the magnitude of heat waves making cities and their inhabitants more vulnerable, it can also intensify other weather events such as precipitation patterns and storms.

The negative loop, above all, makes buildings consume more energy.
Its impact is particularly crucial during summer when the increment of ambient temperature in cities can go up 10K more when compared to the countryside. The benefits deriving from the consequences of the negative loop in winter are negligible compared to the disadvantages of the summer.

Bioclimatic strategies – e.g., natural ventilation and passive cooling for summer or passive solar heating for winter – could avoid or drastically reduce the use of mechanical systems, in most climatic regions.


Current actions to contrast “the urban situation”: the gap

Future projections estimate further growth of global urban population, with 70% living in cities by 2050 [16]. This will put even more pressure on current urban environments and infrastructures and will create a greater demand for space and energy.

Yet, while the building scale policies have imposed minimum thermal conditions for building elements and share of energy from renewable sources, a large proportion of their energy performance will be influenced by and will be influencing the urban environment, for which no policies exist [17].

Efficiency is a milestone against green house gas emissions but it is not sufficient to tackle urban issues and eradicate the causes and effects of the “negative loop” that are happening in cities and it is often not a feasible pathway for emerging, and developing countries especially due to high costs.

This gap in policies between the building and the urban scale is mirrored by a lack of recognition of the strategic importance of the outdoor design as a microclimate modifier in itself, and therefore of its mitigative potential.

Moreover, very little attention is given to the impact that buildings, their form, position, fabric, colour, etc. have on surroundings.

Also, no attention is given to the energy savings potential coming from the implementation of bioclimatic strategies for space heating and cooling for which no energy is required.


Avenues for the future architecture and cities: The New Paradigm

In order to reverse the negative loop a great effort to change a consolidated mindset must be done by public and private realm.
The public realm has large responsibility on local climate change through the choice of pavement materials, urban planning, transportation, street design, green infrastructures and more.

Nevertheless, buildings and districts cover large portions of the urban landscape and consequently their choices greatly influence the urban microclimate.

If the synergy between public and private realms is the strongest route to move towards sustainable cities [18,19], buildings should be considered for the impact they have on the urban environment both when retrofitting and especially when new districts are planned.

Thus, based on the existing research and experimentation on the urban microclimate, we advocate a new paradigm for building: Passive and Mitigative Buildings.

Mitigative: buildings will fine-tune the surrounding microclimate in order to improve health, extend the use of passive strategies, reduce energy demand and enhance users’ indoor and outdoor comfort.

Passive: modernity in architecture is about providing buildings with the ability of not consuming energy by utilizing natural elements and what is offered by the surrounding while providing them with the ability of tuning the microclimate with the users’ need to reduce their energy dependency.

The level of technological readiness of strategies and techniques now available on the market to help improve urban microclimatic conditions and the level of advancement in performance analysis of outdoor spaces have made possible the design and delivery of Mitigative and Passive Buildings.

The Passive and Mitigative Building Approach

There is no valid universal solution for Mitigative Building paradigm: every case will be specific for climate, microclimate context, culture etc.
Yet, the approach to be followed, holistic and innovative, is universal.

The optimization of the master-planning and outdoor design, included the external part of the building fabric is the first step in order to tune the surrounding microclimate to the building needs and to make the most out of passive strategies for indoor comfort.
Through the massing of the volumes, the penetration or not of the solar radiation, the surfaces exposure or not to the sun, the reduction or enhancement of wind driven air movement, the use of vegetation, water or only by the choices of materials and colours the majority of the energy flows through the city can be controlled and favourable condition for the implementation of effective passive strategies can be designed.

Shading and self-shading can be the most effective strategy in summer in most climates while allowing sun to hit horizontal and vertical facades can be beneficial in winter.

Darker colours will be preferred on the surfaces hit by the sun in winter while light and cool colours will be chosen for the irradiated parts in summer: the surface temperature can be 20K cooler or warmer according to the colour chosen.

The use of vegetation in those parts of the building or district hit by the sun in summer can help in generating shadows and in cooling the air through processes of evapo-transpiration.

The same process can be used to cool the air through the design of water bodies or fountains or water spray.

The mitigated microclimate and the other optimization offer the opportunity to step back from an “active system” based approach for indoor comfort in favour of a low energy model based on maximization of passive strategies that are nowadays mature and innovative at the same time.

Heating through the sun or the containment of the internal heat gain, cooling through ventilation and materials properties, light up a space, a desk or an office through the manipulation of the visible solar radiation it’s not obsolete, but the real innovation that clients and users should require to designers in order to enhance comfort, health and productivity while moving to a sustainable built environment.


Benefits of Passive Mitigative and Buildings

Mitigative and Passive Buildings will consume negligible amount of energy compared to the traditional low energy architecture. This will be done at a lower price, but above all they won’t have the negative impact that other buildings have on the surroundings.

The mitigation and tuning of the urban microclimate to the energy and comfort needs will translate into a reduction of building energy demand in the first place.

Moreover, active systems, as traditional heat pumps, will consume less energy due to the fact that they will be able to work at higher efficiency.
The tuning of the microclimate will translate into the possibility of integration of low-tech/low-cost bioclimatic strategies which will reduce or avoid the energy demand for comfort.

Cities will become more liveable both in winter and summer, streets and space between buildings will become a catalyst for urban economy and interaction. They will return to be an attractive part of neighbourhoods where new experiences can take place.

Thus a key benefit of the new paradigm is its potential to allow people’s behavioural shift: the short-term improvements coming from the application of Mitigative Building in the urban environment can potentially have the benefit of connecting public awareness directly to the issues of local climate change and, indirectly, to that of global climate change.

Hence the 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.

Benefits from this transition could be much higher for low income citizens and other vulnerable groups due to the poorer conditions of their housing, the lower affordability of high efficiency goods and lower level of health care they can afford – helping in reducing social disparities and energy poverty.
Also the UN recognizes that “a more suitable strategy for these countries is the use of ‘passive’ technologies that combine flexibility, accessible know-how and traditional knowledge […]. Urban areas might want to consider combining such ‘passive’ methods with some features of modern technology taking advantage of their declining cost in recent years (solar photovoltaic/thermal energy, water harvesting, etc.).”

Having showed the importance of the urban environment under so many aspects, it is necessary to find an international agreement on its value as a social good [21] and to integrate this concept within the discussion on public spaces and on their quality.

The innovative potential of this concept lies in a new and more holistic way of conceiving urban environments and buildings as microclimate modifiers. The associated innovation potential of the proposed new paradigm is also found in the almost universal relevance of its message.

The new paradigm will shape the future of our cities. A paradigm that acknowledges and respects the weak balance of our world system and transforms buildings into thermodynamic systems in harmony with the climate.

Filippo Weber, MArch | Dr. Rosa Schiano-Phan, PhD

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