Council House 2 - Design

Design

CH₂ is meant to be a ‘lighthouse project’ for new building developments, aiming to influence future design to be more sustainable and efficient. Some objectives when designing the building were to be greenhouse neutral and improve the overall employee wellbeing. Different strategies were used when doing this but all were focused around a sustainability aspect.

Biomimicry was a large component in designing the building. The building's principal design architect, Mick Pearce, incorporated a system previously and successfully used in the Eastgate Centre in Harare. The heating, ventilating, and cooling system (hvac) is designed with strategies taken from a termite mound. In the termite mound, the cool wind is drawn into the base of the mound, via channels and the ‘coolth’ is stored using we soil. As the air warms, it flows upwards and out of the mound via vents. This gives the mound the ability to keep a stable temperature. CH₂ uses similar strategies with its system by effectively using natural convection, ventilation stacks, thermal mass, phase change material, and water for cooling. Another strategy used taken from nature is the skin system. The façade is composed of an epidermis (outer skin) and dermis (inner skin). The ‘dermis’ of the building consists of the outside zone to house the stairs, lifts, ducts, balconies, sunscreens and foliage with the inner line defining the extent of the ‘fire compartment’. The dermis was designed with lightweight constructing using a steel frame. The epidermis provides the micro-environment including the primary sun and glare control for the building while creating a semi enclosed micro-environment.

Ventilation stacks are implemented on the north and south façades of the building. These stacks are used to channel air. The north stacks receive more sun so they are black to absorb heat, which in turn encourages the warm air from the building to rise up out of the stacks. The south stacks are used to channel down cold air through the vents. These stacks also offer shading for office windows.

The ceilings are made from pre-cast concrete, with a ‘wavy’ shape, to optimize surface area, which allows for an increase in thermal mass capacity. The thermal mass in the concrete is flushed at night, through a night purge, absorbing ‘coolth’ form the night air and allowing it to absorb heat from the space during the day. With the ‘wavy’ design, heated air is collected at ceiling height, and then channeled out of the building and into the ventilation stacks. Radiant cooling is also a strategy used by running chilled water through beams and ceiling panels. Chilled panels cool the rising warm air, which then drops, creating a natural convection current. Phase change material is used to cool the water for the chilled beams and panels. It efficiently helps to keep the water circulating through the beams and panels at a desired temperature. The phase change material is often referred to as the ‘battery’ of the building because of its purpose of storing the ‘coolth’.

Natural day lighting was a difficult task for the CH₂ team due to the building's orientation and position in relation to surrounding buildings, and the requirement for a deep open plan office space. The best design techniques for CH₂ to allow the most natural light included a synergy between windows size and air ducts, light shelves to reflect light into the office area, vaulted ceilings to allow further light penetration, shading on north, west, and east façades, and finally timber louvres to control light penetration from the afternoon western sun. The light shelves were place on the north façade which in turn will create a soft indirect light on the roof space. These light shelves are placed externally and made of fabric in a steel frame. The vaulted ceilings allow for more natural light filtering to the deeper parts of the office space. Locating the windows at the highest point of the curve improved this technique. The east facing façade uses a perforated metal system for shading that also acts like a thermal chimney. Heat rises pulling air through the eastern part of the building allowing it to be naturally ventilated. The north facing façade is composed of steel trellises and balconies supporting vertical gardens nine stories high. The foliage protects the building from the sun and also filters sunlight for a reduction of indoor glares. Light shelves are used to provide shading as well as reflect natural light into the building. These light shelves are placed externally and made of fabric in a steel frame. The west facing façade is covered with a system of timber louvres that pivot to optimize the penetration of natural light and views. These louvres also protect the façade from the harsh western sun. The louvres open and close depending on the amount of sun that is hitting the western façade. The louvres are made from untreated recycled timber and are moved by a computer-controlled hydraulic system. The building also uses artificial lighting throughout to provide a sufficient amount of light when natural light is not available. These lights use the low-energy T5 luminaries which achieve a lighting power density of less than 2.5 watts/m² per 100 lux.

Shower towers are used on the southern façade. These towers draw outside air from above street level and cool the air by evaporation to form the shower of water. The cool air is then supplied to the retail spaces and the cool water is used to pre-cool the water coming from the chilled water panels. The towers are made from tubes of lightweight fabric 1.4 meters in diameter. Testing from these towers has shown a temperature reduction of 4 to 13 degrees Celsius from the top of the tower to the bottom of the tower.

The designers also used an innovative concept of design by using the same amount of foliage on the building as would have been present if the site was still in its original natural vegetated state. This is accomplished by using a roof garden, which also serves as a breakout and recreation space for staff. The northern façade also incorporates planter boxes situated east and west of each northern balcony.