CH2 6 stars, but how does it work? Su-fern Tan of Advanced Environmental outlines the “green” approaches and systems explored in Melbourne City Council’s demonstration project, CH2.
Design objectives and strategies
The environmental design behind the Melbourne City Council building CH2 is one of the most comprehensive internationally. The choice of airconditioning system, the energy and water strategies, the solar-powered shading devices and the choice of building materials – all these decisions endeavour to be world’s best practice. The building is the first to achieve a six-star office design rating, the highest rating possible certified by the Green Building Council of Australia. (Interestingly, CH2 was designed before the existence of Green Star.) A green building is one that is sustainable and healthy for both its occupants and the natural environment. Although many perceive green buildings to be purely environmental, this is a fundamental misunderstanding – it is about the people, too. If it were only about energy, we would all be working in windowless offices with recycled air. The focus in CH2 has been to give priority to the environment and to its occupants. This means that, in addition to the need for the building to be economically viable and provide decent payback periods, the building’s design needs can be split into two. Occupant needs address fresh air, water, light and wellbeing, while environmental needs address reduction of energy consumption, greenhouse gas emissions and water consumption, reduced demand on public infrastructure and reduced dependence on energy and water providers.
The approach was to minimize the building’s energy and water consumption (at no expense to occupant wellbeing), and then to design low energy and water solutions that satisfy those needs.
This explains, for example, why even though the recirculation of exhausted or relief air would have reduced energy consumption even further, it was not adopted – occupant wellbeing came first.
An integrated design approach was taken from the beginning. For us, as environmental consultants, working closely with Mick Pearce, DesignInc and Lincolne Scott made all the difference.
From CH2’s first design workshop, the target was a carbon-neutral building that had no reliance on public infrastructure for water or energy. Although it will achieve carbon-neutral status through investment in renewable energies, the ten-storey office building does connect to public energy and water services – in essence, the self-sustaining building was not achieved. What is achieved, however, is a building that, compared to the existing Council House of a similar 8,900-metre net lettable area, consumes 85 percent less electricity, 87 percent less gas and 72 percent less potable mains water. CH2 will emit approximately 60 percent less CO2 than a five-star (highest) base building rating under the Australian Building Greenhouse Rating Scheme.
A building’s airconditioning system is typically responsible for half the base building’s energy consumption. The other half typically includes services such as common area lighting, domestic hot water, lifts, and so on. As such, any reduction in airconditioning energy consumption or efficient energy utilization offers significant savings in total building energy consumption and carbon emissions.
No real new technologies have been incorporated in CH2, with the exception of phase change materials for the storage of coolness.
The chilled technology cooling system, gas co-generation and water recycling, for example, are already used in Australian buildings. The concepts of thermal mass, wind turbines, night ventilation and exhaust plenums have existed for centuries.
Cooling and Heating The chilled ceiling airconditioning system, evenly spread around the workspaces, provides low-energy cooling. Gentle radiant and convective cooling effects fall freely from the chilled ceiling at comfortable temperatures of around 18°C–19°C, without the use of fans. At the perimeter, with its higher heat loads, chilled beams are used. A traditional overhead air or VAV system uses fans to blow air at around 13°C directly at occupants, which is not beneficial from an energy consumption or an occupant comfort point of view.
Heating is managed through convective heating fins sitting below floor level. These form a warm air barrier around the perimeters, protecting the office areas from the cold. This warm air rises into the space naturally, using buoyancy, not fans.
Natural ventilation will be used to cool the building down during unoccupied hours at night and on weekends. Night purging uses thermal mass benefits to store the coolness from the night air in the exposed concrete ceilings. This helps to reduce loads on the airconditioning system by up to 14 percent in summer. Night air flows into the building through north and south windows, cooling the concrete ceilings which then radiate this coolness to the occupants during the day.
The building has been operating since early spring of 2006. So far, the combination of fresh air supply and cool concrete ceilings has kept the fully occupied offices cool, without the need to turn on the chilled ceilings/beams. The building is being closely monitored via a building management system and thorough commissioning.
Fresh Air The building’s fresh-air displacement ventilation system far exceeds conventional practice. Firstly, because CH2’s fresh air rates, at 22.5 litres per second per person, are about three times the minimum prescribed in the Australian Standard. Secondly, exhaust or relief air, once it exits the occupied zone, is not recirculated back into the occupied space. This warm, contaminated air is completely flushed out, with the air in each workspace being fully replaced with fresh air every half hour. Together these factors mean that the occupants are constantly breathing high-quality non-recycled air.
The displacement ventilation system introduces this fresh air at a low velocity below floor level.
Buoyancy enables the formation of thermal layers from floor to ceiling, which separates clean cool air from contaminated warm air. Warm air from heat sources lifts up through occupied zones and is relieved through vents in the ceiling. This air is drawn from the space by exhaust air shafts located on the building’s north facade. A wind extract turbine at the top of each shaft ensures that air is continually exhausted through passive means.
The floor-fed fresh air works in parallel with chilled ceilings and beams. This is a popular system in Europe. When fresh air from the floor hits a heat source, for example an occupant, it rises and mostly overcomes the radiant and convective forces from the chilled elements. Negatively pressured exhaust plenums in ceilings also ensure that warm air completely exits the plenum through the turbineassisted exhaust ducts.
Energy The design of the energy systems behind the heating/cooling and fresh air system is innovative and extensive. The water running through the chilled ceilings is cooled by passing through a phase change material store, which stores coolness. Water runs around in a closed loop – it leaves the phase change material as cool water, passes through the chilled ceilings, cools the space, runs back into the phase change material store to be cooled and is ready to run through the chilled ceilings again. During short periods in summer, when the phase change material storage cannot provide enough cool storage, the chilled ceilings |will be supplemented by an electric chiller.
The coolness for the phase change store is produced by water that has passed through shower towers (and cooling towers). Water moving through the shower towers and cooling towers at night will be cooled and stored by the phase change material tank. This achieves “free cooling”, whereby cool water is generated by utilizing night temperatures with low dew points and without running a chiller.
Shower towers are not only beneficial for cooling water, they also ventilate the retail space below the office levels. Outside air is drawn in from high levels (eight metres or more above street level) and induced into the space. As this air falls within the shower tower, it is cooled through the evaporation of water.
Fresh air for occupants is provided at 19°C and needs to be heated or cooled and dehumidified before entering the workspace. This heating/cooling of fresh air will not be powered by a traditional system of gas boiler and electric chiller, but instead by a co-generation plant and a heat recovery system.
A gas-fired co-generation plant will provide 60kW of electricity, meeting about 40 percent of the building’s electricity with much lower carbon emissions. Waste heat from the co-generation plant will be recycled to provide 40 percent of the building’s fresh air heating and cooling load via direct heating and an absorption chiller.
Approximately 60 percent of CH2’s domestic water heating needs will be met by 48 square metres of hot water solar panels on the roof. For days with little solar heat gain, a gas boiler will be used.
Another initiative that harnesses the sun’s energy is the 26 square metres of photovoltaic cells which will generate about 3.5kW of electricity from the sun. This will power the sun-responsive shading devices on the western facade.
Light Natural light is admitted into the office spaces through light shelves that reflect the indirect sunlight that enters the building via clear or non-tinted performance facade glass. This glass was selected after extensive thermal and daylight modelling by Advanced Environmental.
As well as incorporating zone switching, the artificial lighting system utilizes automatic perimeter-zone dimming, which responds to daylight levels via sensors. The artificial lighting system is a two-component system whereby energy-efficient T5 fittings provide lower ambient lighting levels and each workstation has its own task or desk lamps.
This solution not only provides occupants with more control over their working environment, it also consumes 65 percent less energy than the existing Council House lighting system.
Shading on the north, east and west facades contributes to visual comfort, and also provides a huge thermal benefit, with regard to energy consumption, peak airconditioning loads and occupant comfort.
Water Like the energy strategy, low consumption measures were implemented before a reuse strategy was considered. Fittings with a minimum 4A rating have been installed for all water fixtures.
The water reuse strategy involves a multi-water reuse plant which is a non-biological and non-chemical process for extracting (not treating) grey water and black water. Approximately 90 percent of sewage is clean water, and this is extracted by the plant for the building’s irrigation requirements, cooling towers and toilet flushing.
The sewage loading by the building will be reduced by about 80 percent, which significantly reduces the pressure on the public sewer system.
This also means that 100 percent of non-potable water needs will be met by water harvesting.
Wellbeing Occupant wellbeing is not usually considered a priority in environmental design, however, with this project, an investment in the health of Melbourne City Council workers was a serious consideration.
Several initiatives were adopted to promote the health and wellbeing of council staff. They include the provision of balconies on each floor, which allow occupants to “break out” of their indoor office environment; the provision of vegetation on these balconies to give occupants a connection with nature; a roof garden – another breakout space; individual control of fresh air vents; individual control of the task lighting system; increased fresh air rates through the airconditioning system; and the elimination of any recycled or recirculated air back into the occupied space.
All in all, CH2’s base building cost about 30 million dollars, with an additional 11 million dollars worth of sustainability features, calculated at an estimated payback of 10 years.
Council House 2 leaves its older, similarly sized sister, Council House 1, far behind, consuming 15 percent of the energy and emitting only 13 percent of the emissions of its counterpart – which sadly still represents a majority of buildings in the commercial marketplace today. However, it is encouraging to see that more and more property industry players are seeing the light, and realizing that those dollars for green buildings do make sense.
So let us hope that in the future, CH2 is one of many bright lights on the green building stage.
Green Building Council and Green Star
Developed by the Green Building Council of Australia, this is the outcome of several other assessment methods, including LEED, BREEAM and the Melbourne Docklands ESD Guide. Rating tools and technical manuals can be downloaded from the website, as well as information on project certification. Case studies of certified projects, industry news, training and accreditation programmes, and policy statements are also included.
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World Green Building Council
The WorldGBC provides a federated “union” of national Green Building Councils whose common goal is the sustainable transformation of the global property industry.