Passive design refers to a design approach that uses natural elements, such as sunlight and wind, to heat, cool, or light a building. Passive solar or passive cooling designs take advantage of the sun’s energy to maximize heating or cooling based on a building’s sun exposure and the local prevailing wind condition. Systems that employ passive design require very little maintenance and reduce a building’s energy consumption by minimizing or eliminating mechanical systems used to regulate indoor temperature and lighting.
The passive design approach can include the structure of the building itself, including building orientation, window placement, skylight installation, insulation and building materials, or specific elements of a building, such as windows and window shades.
In ZCB, the various passive design measures lead to 20% energy saving compared to a similar building of the current standard design.
Cross ventilation refers to the movement of air from one side of a building or room and out of the other side.
Cross ventilation is the most important environmental design strategy to counter the humidity of the summer months. The façade facing southeast maximizes the capture of the breeze.
Wind catcher is a device that ventilates a building by the use of wind. A small tower on the roof contains an opening that faces the prevailing wind, which is at a cooler temperature than the interior of the building. Because the wind velocity at this opening is greater than it is at the lower windows of the building, air in the shaft of the tower is forced down the shaft to cool the building.
Wind catchers improve ventilation in areas furthest from the windows. The dampers can be controlled by the Building Management System or manually to regulate the fresh air intake. It can improve the local air speed by about 25%.
Earth Cooling Tube
Earth cooling tube is a pipe buried underground and connects the fresh air intake to the air conditioning system.
Making use of the naturally lower temperature underground, the earth cooling tube provides naturally pre-cooled air for the building to reduce energy use. Air is drawn in from a landscaped area northeast of the ZCB and it is cooled as it is drawn through the buried pipe.
High Performance Glazing
High performance glazing, by definition, performs better than normal glazing in terms of thermal insulation and solar heat control.
The high performance glass wall system offers good thermal and optical performance to lower cooling load, reduces the reliance on artificial lighting and hence reduce energy consumption. The reflecting shade inside the glazing achieves this by reflecting heat and reducing heat gain
Ultra-Low Thermal Transfer
Along with glazing, a high-performance envelope provided by deep overhang over the south façade, external shading fins in the north facade, heat minimized east and west facades/windows, and shaded and insulated roof, all contribute to the ultra-low overall thermal transfer value (OTTV) of 11 W/m2 (over 80% lower than the maximum value required under the current statutory control).
OTTV is the quantity of heat transferred per unit of temperature difference into a building through its walls or roof, due to solar heat gain and outdoor indoor temperature difference. The lower the OTTV of a building, the higher would be the building energy efficiency.
The tapered built form of the ZCB not only draws stronger airflow across the building, but also reduces exposure to solar heat gain from the south façade and increases daylight from the north façade.
Light shelves are a system based on sun path geometry used to bounce light off a ceiling, project light deeper into a space, distribute light from above, and diffuse it to produce a uniform light level below.
At an angle of about 20 degrees, light shelves in the ZCB are strategically positioned to reflect light to the centre of the building, distributing light to areas further away from the windows. The light also bounces off the ceiling to the floor area.
Light pipes are highly reflective tubes that capture light from domes on the roof. They help bring light to windowless areas inside the building.
Heat Reflecting Shade
Heat reflecting shade comprises a metalized polyethylene sheet that reflects solar heat gain back through windows when required. The shade with an aluminum sheet on one side, only emits 3% to 5% of radiant heat absorbed due to its low emissivity, while appearing translucent. It reflects heat out in summer and reduces heat loss in winter. It blocks 92% of UV rays and reduces solar heat gain by 8%.
Cool paint reflects and emits the sun’s heat back to the sky, reduces surface temperature by up to 5°C, lowers heat transfer to interior and mitigates heat island effect.
Optimised Window to Wall Ratio (WWR)
The following WWR adopted effectively reduces the solar heat gain and the cooling load for air-conditioning while maximise natural ventilation and good views:
- High WWR (>65%) for the north-west façade, coupled with fritted glass and external shade, with high transparency to enhance view and north light
- High WWR (>70%) for the south-east façade, coupled with the deep overhang, for good views and large openable windows for cross ventilation
- Low WWR for south-west facade (about 10%) and north-east facade (<25%) to minimize heat gain
Following external shading effectively reduces solar heat gain and glare:
- Deep overhang projection on the south-east facade to block high-angled sun
- Trellises providing additional shade on the south-east facade
- Vertical shading fins on the north-west facade block the low angle sun in the late afternoon
- Light-coloured external shading reduces the risk of glare
Clerestory for Daylighting
Light reflection by light shelf onto light-coloured and angled ceiling soffit improves daylight distribution. The use of natural light reduces the electricity demand and the cooling load from artificial lighting.