Updated: Sep 19, 2020
#Buildingfacade is the face of the building, and it is the most visible part of the building.
Building facade allows architects and facade designers to "paint" it with innovative and creative ideas. Building facade functions as the building’s skin, it protects the building from any external environmental impacts, it also creates a controlled condition inside the building.
This article discusses the sustainability elements for building facades. There are many possibilities and opportunities to bring the sustainability concepts in the facade design, from the material, to shading design, to innovative technologies.
Facade heat transfer
The facade is like the building’s skin, it blocks the heat, pollution and rain water from the external environment. The facade must be designed to allow the connection between internal and external allowing the best views and the access to the natural environment.
From the sustainability point of view, one of the common focus is the facade heat transfer. Minimise heat transfer is the most effective way to save energy when building is operated by air conditioning and heating system (#HVACsystem). Imagine, HVAC systems are using energy to bring the external air to the comfortable temperature suitable for living, the less heat transfer from the outside, the less "work" required for the systems, hence saving energy.
The following ways help to reduce the heat transfer (taking tropical climate as an example when outside air is hot and humid):
Effective external facade shading design to cut the direct sunlight
Good thermal performance facade walls and window glasses
Good facade insulation to reduce air infiltration (air leakage)
Coatings / cool paints to reflect more heat back to the external environment instead of transferring to the internal environment (note that the paint must be applied at external side of facade to block the heat transfer, I have saw some projects put the paint and coating inside the building which serves no purpose because it already allowed the heat to transfer in through the glass).
Optimised building orientation to avoid direct sunlight during the hottest season and the hottest time of the day
To measure the facade heat transfer, we use #ETTV (Envelop Thermal Transfer Value) or OTTV (Overall thermal Transfer Value) at unit of Watt/m2 K. Generally ETTV is more stringent than OTTV. The ETTV calculation takes consideration of building orientation, wall material, glass material and external shading devices. It's noticeable that glass material and the shading devices have the most effective impact to the ETTV.
Manual calculation is only possible when building shape and design is simple, for more complicated design, the project is encouraged to use computer simulation to calculate the ETTV.
Facade shading design
Building shade is the most effective way to block the heat and reduce glare. Before we discuss the types and functions of shading, let's review the pattern of sun movement:
The knowledge of sun path during different seasons and different times of the day helps the designers understand the effectiveness of shading design.
Imagine you are standing on the earth's equator, you see the sun at your North during the summer solstice (around 21 Jun), at your South during the Winter solstice (around 21 Dec), and the sun is right on your top during Spring and Fall (Equinox, around 21 Mar/21 Sep). In a day, you see the sun at East side in the morning, and at West side in the evening, the sun is on top of you during noon time.
Buildings should have shades during the hot season to prevent heat enter into the internal space, however, shade should not be used for winter because the heat is more than welcomes to contribute to a warmer internal space (unless shade is for the purpose of preventing glare).
There are horizontal and vertical or mixed types of shadings.
Horizontal shade is useful to block the heat in seasonal aspect, for example, north horizontal shades prevent heat during summer. The length of the sun shade should be calculated according to the sun angle of the building location. Vertical shade is effective in daily aspect, for example, vertical shade at the west edge prevents heat from the afternoon sun. Project may also consider the combination of horizontal and vertical shade for the best result.
Shadings are also effective to cut the glare. Glare is not pleasant in working space because it causes eye fatigue and reduce productivity. Glare is usually caused by too much sunlight or high contrast, and it can be adjusted by internal blind, colour/shade of the window or adjust the workplace layout. Glare is commonly simulated or measured by daylight factor, useful daylight index, or unified glare rating. There are other tools and measurements used for different softwares as well to simulate the potential of glare.
#Innovative facade designs
Building facade defines a building, and make it more uniquely identifiable. When the creativity art meets the design function, it makes a high performance and innovative facade. JOS is sharing some new, trendy and innovative facade designs with you, however, creativity never limits itself in any lists.
A moving facade is usually designed to react according to the sun angle, to effectively block the sunlight, and more importantly, to open up the good view during the low sunlight time.
#Rotatingfacade be designed with a timer to precisely set the facade movement algorithm according to the sunlight simulation, however, this cannot be optimised during a raining day or a cloudy day.
The best functional design for the rotating facade is to design with daylight sensors. It opens up the fin during the low daylight time, and shade the correct place during the sunny day.
One key note for this rotating facade is the motor maintenance, especially in the place with high dust, as sensors must be placed in the individual spot to receive daylight data. The design must take consideration of the system sensitivity and potential sound impact.
Self cleaning facade
We used to see spider men climbing on skyscrapers, just to make the glasses more shiny. How nice it could be, when the facade can be cleaned by itself. #selfcleaningfacade
Research shows that Titanium dioxide is considered as one of materials that has a high photo-catalytic activates when illuminated with UV light. The self cleaning facade will significantly reduce the manpower cost to clean the facade, and reduce the risk for workers.
Algae is known as superfood and fertiliser, it is also a super CO2 scrubber. Algae bioreactor is 400 times more effective at capturing carbon than trees in the same unit area.
#Algae facade is an extra layer and provides natural shade to the facade, the harvested algae is can also be sent to create by products. The building may also consider to pump the exhaust air into this algae tube/panels, serving both purposes of reducing CO2 emission and feeding Algae.
#Waterfacade makes the building more dynamic and energetic. The element of water also hints the sense of life, dynamic and natural flow. The layer of water provides the natural cooling effect to the building.
For the building use such features, the project needs to pay attention of the moving reflection from the water to the internal space, and avoid any disturbance or glare.
Building Integrated Photovoltaic Facade (BIPV)
This is a solution to turn the building into a powerhouse, with #photovoltaic (PV) panels wrapped around the building to maximise the renewable energy production.
The PV panels are meant to replace the facade glass and wall panels, to reduce the initial investment cost. It's true that BIPV is less productive than putting PV on the roof (#BIPV usually generates half of the power as it was generated by the roof with the same area), however, with limited space around the building, it's still a good choice to maximise the renewable energy production potential. Project also has the options to choose different colours and patterns to decorate the facade design with some compromisation of the PV panel efficiency.
The "Talking" building - digital facade
Building facade can "talk" to its users by sharing the performance data and its "health condition".
Basically, a #digital facade made it possible to send any message. A digital facade may change colour to indicate whether the building energy is performing within the design target; A digital facade may change its colour in response to the external thermal condition; A digital facade may even become an education hub to engage the users and visitors.
Digital facade allows the building to be programmed easily without any physical renovation.
The sustainability design solution for the facade is one of the most important elements of a green building. Sustainable design on the facade is also the best opportunity to showcase the project's innovation, thanks to the visibility and large applied area on facade. Facade, being part of the total building element, should also design to synchronise with the building performance systems. Being the external "#sensor" and "skin" of the building, there are great sustainability potentials for the facade!