What is passive design?
If you simply googled it, there are multiple explanations for #passivedesign. Here we would like to offer our 2 cents worth of thought. Some defined it as providing thermal comfort for homes without the need for auxiliary cooling or heating (i.e., using active, energy-consuming, systems such as air-conditioning). We think this relatable perspective, though applicable, is slightly myopic.
Buildings are constructed to fulfil functions. Beyond residential and office buildings, logistic fulfilment centres, sports halls, data-centres and many others are just as necessary to adopt passive design. To fulfil the building’s purpose requires energy and passive design is any strategy that helps to achieve this with less or no energy. For example, in passive design for homes, there is often an emphasis on shading and insulation to keep the heat out and reduce energy consumption for cooling. The same strategy will be counter-productive when deployed for greenhouses in cold climate zones where maximum sunlight and heat penetration is desired for optimal plant growth (pardon our oversimplification to make a point here).
Passive design strategies
The Big Picture
Based on our definition, we can push our imagination further. Let us consider Microsoft’s testing of an undersea modular data centre. The system utilises a cooling system that pipes seawater directly through the heat exchangers of the server racks, dissipating the heat quickly out into the frigid surroundings [1]. This achieves (almost) free cooling and is the kind of mindset we want to adopt towards passive design. How do we sustainably ‘exploit’ freebies that mother nature has bestowed upon us? We hope businesses can seize opportunities during conceptualisation to push the boundaries and expand the frontiers of sustainable technology implementation.
Figure 1 Server Racks and cooling system checks before insertion into a container. Photo by Frank Betermin.
Good passive designs stem from the concept of ‘whole-building design’. We also subscribe to the design philosophy that sustainability considerations should be incorporated as early as possible to enjoy the maximum benefits at the lowest cost. This demand thinking using a ‘big to small’ approach. Let’s assume that you are ‘KapitaSoil’, a multi-national real estate company with the wealth and resources to invest in clusters of buildings worldwide. Site selection is one of the most important and necessary analysis. As the real estate mantra goes, the 3 most important things are “location, location, location”. Passive design is no different. Considering passive design provides an added layer of rigour that takes into account the shape, orientation and surroundings of the site of interest.
Site Selection for Passive Design
While site selection is a complex web of financial, regulatory and other considerations, for simplicity we focus on the technical sustainability perspective. To name a handful, brownfield redevelopment is typically less ecologically damaging. This type of revitalisation offer opportunities to improve the environment and economic potential of the area [2]. There is evidence to suggest that brownfield sites could support large biodiversity [3]. This implies that redevelopment should not just be a simple exercise of demolishing and rebuilding. Development in areas with access to sunny weather and coastal areas open doors to renewable energy adoption such as solar PV, wind turbines and tidal energy. We found a list of site selection considerations (The Los Alamos National Laboratory Sustainable Design Guide [4]), a great reference to kickstart your thought processes;
Figure 2 Considerations during siting. Los Alamos National Laboratory Sustainable Design Guide (pg 48)
The list is not exhaustive, and companies that want to adopt passive design should work with professionals to generate industry-specific key criteria. These criteria can be used as a communication tool to anchor the vision for a project.
Orientation and building form
In the context of Singapore, the sun path (roughly) stays in the middle of the sky throughout the year. As such, buildings are incentivised to be rectangular (see Figure 3.1) with the longer side parallel to the sun path to minimise building heat gain. Window facing the North and South are encouraged to harness natural #daylighting with less likelihood of glare occurring due to direct sunshine.
Figure 3.1 Long side parallel to the sun path.
Where the site does not allow for the preferred orientation, we can consider breaking up the building form to create multiple smaller blocks which individually demonstrate passive design sensitivity (see figure 3.2). Notice that the site area for the 2 configurations are the same, though the 2nd configuration will have better energy savings.
Figure 3.2 Forms that reflect sensitivity to passive design
When designing floor layout, heat gain reduction can be enhanced through the positioning of non-temperature sensitive and non-air-conditioned areas to the perimeters of the building, forming a temperature buffer zone to a temperature-sensitive core.
Figure 4 - 1 Hartford Building (Solar House History Blog).
Figure 4 - 2 Warrnambool Campus (Dianna Snape Photography).
Figure 4 - 3 Korean Industries Tower (Andrew Michler)
Consider the buildings above, the design exhibits self-shading, reducing the need for louvres and shading fins. In the case of Korean Industries Tower, self-shading design is integrated with BIPV, demonstrating clear intent towards sustainability. In an urban context, the shading effect from surrounding buildings, foliage and natural structures should also be considered. This can be done using various simulation software and is highly recommended.
Façade Design
As the most visible part of the building, the #façade is at the forefront of the interaction between the external and internal environments. There are multiple things to consider such as ‘Window to Wall Ratio’ (WWR), glass material and shading device selection. These and more are discussed at length in one of our previous articles;
Ventilation
Generally, for good cross-ventilation, we want to align our openings to the predominant wind direction of Singapore which is N & NE in the December to March period (corresponding to the NE monsoon season) and S & SE wind in the June to September period (corresponding to the SW Monsoon season) [5]. To achieve true cross ventilation, there should be openings for both air entry and exit. The same design principles can be used in reverse if strong winds are not preferred which may be the case if you stay in the 30th-floor apartment.
Figure 5 Visualisation for good cross ventilation (qnaguides.com, image source: Public Domain)
When considering ventilation, there is a need to consider surrounding buildings. Wind wall, wind tunnel, strategically placed pavilions and other architectural structures are options to generate low- and high-pressure zones to induce airflow. In future articles, we will showcase various examples that have done this masterfully.
Designing with regards to the surrounding buildings gets tricky because predicting how fluids (air) move is one of the greatest mathematical holy grails of the 21st century, one of the millennium problems [6]. Luckily engineers only need a good approximate, not a mathematical proof. We recommend you engage consultants that can conduct computational fluid dynamics (CFD) analysis.
Technologies for passive design
At a more granular level, we should consider wall materials, paints, window glazing and mechanisms for interfacing between window-wall and door-wall construct. Assuming that we want the internal environment to be a cool 24 °C through air-conditioning, we want to keep the higher temperature environment out and the cooler environment inside. In short, we are not a fan of the laws of thermodynamics (Think of The Martian but inverse). The concept is to minimise the pathways in which undesired heat exchange can take place. Commonly emphasized technologies include thermal bridges, wall insulation and airtight construction (supported with airtightness test).
Figure 6 Examples of a window with thermal bridge and types of insulation (Passipedia The Passive House Resource)
A wealth of information about passive design technologies can be found on the Passive House Institute website (https://passivehouse.com). Beyond the knowledge, there are also case studies from around the world [7]. The key to successful passive design is localisation, contextualisation and customisation. Every building and situation is different and clients should discuss sustainability aspirations with their consultants as early as possible to include the myriad of design, material specifications and technical analysis.
In the future articles of this series, we will showcase buildings that have demonstrated passive design elements. We hope this article has piqued your interest in passive design. If there are any topics mentioned that you would like to know more about, feel free to write to us and we might expand it into an article for this series as well!
[1] https://news.microsoft.com/features/under-the-sea-microsoft-tests-a-datacenter-thats-quick-to-deploy-could-provide-internet-connectivity-for-years/
[2] Dulić, Olivera & Krklješ, Milena. (2013). Brownfield Sites - Environmental Effects of Their Revitalization.
[3] Hunter P. (2014). Brown is the new green: brownfield sites often harbour a surprisingly large amount of biodiversity. EMBO reports, 15(12), 1238–1242. https://doi.org/10.15252/embr.201439736
[4] https://www.lanl.gov/orgs/eng/engstandards/esm/architectural/Sustainable.pdf
[5] Climate of Singapore, Meteorological Service Singapore (http://www.weather.gov.sg/climate-climate-of-singapore/)
[6] https://www.claymath.org/millennium-problems
[7] Passipedia - The Passive House Resource, https://passipedia.org