黑洞社区

If you wanted to find the world鈥檚 greenest office building, Melbourne in Australia is probably not the first place you鈥檇 look. Consider the figures. About 95% of the nation鈥檚 electricity derives from coal, putting Australia sixth in the league of global greenhouse gas emitters. The country kicks out 20.2 tonnes of CO2 per person each year, compared with the UK figure of 9.55 tonnes. Emissions grew 43% between 1995 and 2005, against the UK鈥檚 4%. All this from a nation of just 20 million people.

What the figures don鈥檛 reveal is Australia鈥檚 determination to change its poor environmental record. It started by ejecting the biggest environmental problem from office: prime minister John Howard not only lost the general election last November but his seat as well, only the second premier in Australian history to do so. His successor, Kevin Rudd, signed the Kyoto Protocol just a few weeks after taking office, at the stroke of a pen reversing years of climate change denial.

The new political atmosphere caught the mood of the nation. For, despite Australia鈥檚 dismal environmental performance, the property industry has been quietly and effectively greening itself. And nowhere is this more evident than in downtown Melbourne, where the city council has built what may be Australia鈥檚 鈥� and possibly the world鈥檚 鈥� first truly ultra-low-energy, city centre office block. This building, known as Council House 2 (CH2), has been awarded six stars under the Green 黑洞社区 Council of Australia鈥檚 Green Star design rating scheme (see box, page 38) and won the title of 黑洞社区 of the Year at BSj鈥檚 Sustainable 黑洞社区 Services Awards 2007.

CH2 came about when the city council ran out of office space and decided to build a green exempla. Construction started in early 2004 and the building was occupied in late 2006. Compared with Council House 1, a typical 1970s office block across the road, CH2 is intended to use 85% less electrical power, consume 87% less gas and 72% less mains water, and achieve a 13% reduction in C02 emissions. All this equates to a target saving of 330kWh/m2 a year.

The business case for the building was based on a 4.9% actual increase in staff productivity arising from the improved facilities, which is predicted to save the council up to 拢500,000 a year.

The council is still commissioning and fine-tuning the building, although it has been in use for more than a year, which hints at a range of issues still to be resolved. Indeed, there have been many adjustments and improvements since the 540 staff moved in, particularly to the lighting.

Design issues

CH2 is a building defined by its constrained site. The streets adjacent to the main thoroughfare of Little Collins Street are narrow, with neighbouring buildings only 6m away. This created a number of challenges for the architect, Mick Pearce, notably natural light penetration for the lower floors of the 10-storey scheme.

鈥淭he site designed the building,鈥� Pearce says, 鈥渁nd that gave us the 21m-deep floorplate. But at the same time everyone agreed that each elevation should be totally different, designed around what it faced, therefore the elements are all different colours, sizes and shapes. Normally, when you design a building like this, you spend a lot of time on one floor, and then just multiply it by nine. Here, we had to make each elevation and every floorplan different.鈥�

The extended commissioning period for the building is wise given that it has phase-change refrigeration, absorption cooling, co-generation, exposed concrete mass, chilled ceilings, photovoltaics, solar panels, night cooling and 鈥� last but not least 鈥� a sewer mining system. The latter takes black water from Melbourne鈥檚 sewers and turns it into grey water for toilet flushing and irrigation.

The concrete-framed building has 9373尘虏 of net lettable area. The ground floor has retail outlets (yet to be let) plus the main reception. The nine floors above are largely open-plan offices, topped by a roof garden and a plantroom for air-handling units and the gas-fired co-generation plant. Car parking and cycle racks occupy the basement, beneath which are the primary plantrooms for the chillers, phase-change tanks and sewer mining system.

The south-facing facade comprises ducts that channel fresh air from the roof air-handling units. The conditioned supply air is injected into a floor plenum and introduced to the occupied space from adjustable swirl diffusers. During the summer months, a night-cooling strategy is used to discharge heat from the concrete structure.

Extract air is drawn up through shafts on the north facade by stack effect (the vertical axis wind turbines on top of the ducts were intended to pull through the air, but have not proved successful). The ducts get larger in cross-section as they climb the building, while the window area in between reduces in proportion.

The double-skinned west elevation houses three glazed electro-mechanical lifts, enclosed glazed lobbies on each floor, and external stairwells. All this is shaded by a motorised louvre system 鈥� made from recycled timber 鈥� that tracks the sun鈥檚 path.

Floor separation is formed by precast waveform concrete slabs. The unpainted concrete (sand-blasted to create a rougher surface for heat transfer) is exposed to obtain the radiant and heat storage benefits of thermal mass, and to support bespoke chilled ceiling panels. The design of the profiled slabs was inspired by ideas about increasing surface area for thermal transfer, radiant cooling, acoustic control and aiding air flow at BRE鈥檚 energy-efficient model Environmental 黑洞社区 at Garston, designed by Hopkins Architects.

The raised floor is a plenum for the air supply. Occupants are able to control the flow of the 100% fresh air by adjusting the floor vents. Cooling in the occupied space comes primarily from the thermal mass and the chilled ceiling panels. However, the supply air is also chilled, and being a mixing system rather than a displacement one, the ventilation plays a greater role in conditioning the offices than would otherwise be the case.

Lighting relies on low-energy fluorescents throughout, with the installation aiming for only 140 lux at desk level. The idea was to do the rest with high quality task lights.

Energy systems

A 60kW gas-fired co-generation plant is used to generate 60kVA of electricity and 120-160kW of heat, reducing the building鈥檚 reliance on grid energy by about 30%. The heat can be used directly for heating or, via an absorption chiller, for cooling. The designers expect the co-generation plant to satisfy 80% of the fresh air heating/cooling requirements through waste heat alone. Heat is recovered from the building鈥檚 extract air. CH2 relies on a single-pass ventilation, with air supplied into the occupied spaces at 18掳C.

About 60% of the hot water supply will be provided by 48m2 of solar panels on the roof, with a gas boiler as back-up. CH2 has about 26m2 of photovoltaics, which the design team hopes will generate about 3.5kW of electricity to power the timber solar-shading system on the west facade. Six 3.5m-high wind turbines were intended to extract the air from the offices via ducts on the north facade. This, however, has not happened, except on a few hot, windy days.

There are five 鈥渟hower towers鈥� on the east facade. These 3.5-storey transparent plastic tubes carry both the supply air to the retail spaces on the ground floor and water spray to cool the air by direct evaporation. The water is part of the chilled water circuit for the phase-change system, which augments the mechanical refrigeration system.

The chilled water circuit charges the phase-change spheres overnight, with the energy released into the chilled water circuit during the day. In the mid-seasons, the phase-change system is run until it鈥檚 exhausted (early afternoon), after which the chillers take over.

The water, cooled by the chiller serving the shower towers, also travels through a heat-exchanger to help to freeze the phase-change material. A separate water loop passes through the tank to be chilled, and then to the chilled ceiling panels and chilled beams, the latter installed by the windows along with trench heating.

For the sewer-mining system, CH2 has equipment to extract about 100,000 litres of raw sewage from the sewer in Little Collins Street. This sewage, along with that generated on-site, is run through ceramic filters and non-chemical water treatment to remove 95% of the water. The solids are returned to the sewer.

The objective is to create A-grade clean water 鈥� a potable standard in Australia 鈥� to meet the building鈥檚 water cooling, plant watering and toilet flushing needs. The water will also be used in other council buildings, fountains and plant-pots, and to charge street-cleaning machines. More water will be saved by recycling from the sprinkler system and from recovering rainwater.

In-use performance

黑洞社区 manager Shane Power has been monitoring, modifying and fine-tuning CH2 since occupation. Energy consumption has been monitored only since June, but early results indicate electricity consumption is already about 55% less than at Council House 1.

Given that CH2 has so much passive cooling capacity, it was interesting that the management decided to try to maintain comfort setpoints more typical of a conventional air-conditioned building (read the designer鈥檚 perspective, page 40). The design capacity of the chilled ceilings and the operational characteristics of the phase-change thermal storage are predicated on maintaining an environmental temperature of less than 23.5潞C.

Consequently, the thermal mass of the building (cooled overnight to 21潞C) runs out of cooling capacity at about midday, at which point the phase-change tanks supply chilled water to the chilled ceiling panels until 4.30pm when they are exhausted, whereupon the chillers kick in to finish the day (see figure 1).

For a typical warm day, mid-season, with a maximum daytime external temperature of about 24潞C, the thermal mass is able to maintain a steady space temperature without any mechanical refrigeration.

In winter, almost all cooling is achieved by off-peak refrigeration through the phase-change system. But for hot summer days when 40潞C is not uncommon, the thermal mass only manages about an hour of occupied time before the phase-change tanks and chilled ceilings are needed. Some floors require cooling sooner as they are home to the city council鈥檚 CAD engineering department.

鈥淲e have discussed running the building with wider parameters, say five or six degrees centigrade, so that the supply air isn鈥檛 conditioned, but that would require people to take jumpers on and off,鈥� Power says. 鈥淲e would need to prepare people for that, then try it for a month to see what would happen. Lots of people want us to do it.鈥�

The environmental systems are demanding in terms of management, maintenance and automation because they comprise three or four layers of technology, much of it inter-connected. One wonders how much would be needed if the environmental parameters were relaxed to the wider range typical of UK low-energy buildings.

As it is, CH2 can operate in what Power calls 鈥渘eutral mode鈥� for five months a year, with just night purge and phase-change refrigeration to keep the building comfortable. 鈥淚n January 2007 it was more than 40潞C for four days in a row,鈥� he says. 鈥淲e came in on a Monday morning after two of those days to find that the chillers hadn鈥檛 been working for some trifling reason, and the building started to heat up.

鈥淏ut it only rose to 26-27潞C and no one got stressed out about it. We fixed the chillers, pumped air though at 13潞C for a few hours, and cooled down the building really quickly, except for level 1 which took two weeks to discharge its heat from the slab.鈥�

The low-velocity floor supply, hard sound-reflecting surfaces and open-plan offices inevitably led to complaints about sound privacy. This was solved by the installation of a white-noise system.

The electric lighting has not been a total success, with possibly too much emphasis on feature lighting to the detriment of task illumination. Council staff previously worked in a building with 500 lux lighting, so the 140 lux target was a bit of a shock to them. Mick Pearce, the architect, believes a combination of dark furniture and carpeting and partitioning has increased perceptions of lack of light.

There was a disinclination to paint the exposed concrete slabs white, primarily because of the expense but also because of concern about getting an even coat and a feeling that the paint would significantly reduce the slab鈥檚 thermal contribution.

The gloom is lifted to some extent by the high-spec Swedish task lights. 鈥淧eople feel that task lights give them intimacy,鈥� says Pearce, 鈥渁 camp-fire effect.鈥� It was nonetheless decided that insufficient light was being produced in the highest points of the waveform slabs, so additional T5 strip lighting has been suspended beneath those areas. Some of the bespoke light fittings have also been repositioned, achieved by sliding them up and down the slots between the slabs.

鈥淚t鈥檚 taken a while to get the addressable lighting system updated to suit the new lighting layout,鈥� Power admits, 鈥渂ut now we can control the lighting to do what we want. Also, we have turned off the perimeter wall-washers. They were good in theory but didn鈥檛 add much.鈥�

Assessment

One year on, the building鈥檚 management admits CH2 isn鈥檛 finished. 鈥満诙瓷缜鴖 like this need a full 12 months鈥� commissioning, and many elements required fine-tuning and seasonal adjustment,鈥� Power says. Immediately after occupation, CH2 went into summer mode, a very high energy period. Unfortunately, the micro-turbine co-generation plant was not operating effectively. Also, trend monitoring on the building automation system was not fully in place until June 2007.

While CH2 is a remarkable building, you wonder what parts of its complex specification are truly contributing to its performance and what is merely green gesture. The council admits the wind turbines have not done their job; there鈥檚 simply not enough air movement to get them turning, so their role is mainly symbolic.

Then there鈥檚 the motorised timber shuttering system. There鈥檚 no doubt that office buildings in Melbourne have a significant problem with sunlight, but the shuttering on the west elevation merely shades the enclosed lift lobbies. Daylight penetration to the office areas from the shuttered elevation is practically non-existent. This begs the question of whether a cheaper, simpler shading system would have been more than adequate.

Inevitably, public perception of what is green about the building and what is really helping its environmental performance are different things. For this the architectural ostentation is to blame. What鈥檚 the point? Especially for a building that is, fundamentally, very good.

It鈥檚 a pity design attention has been focused on the wrong things. Had they not been sidetracked, the environmental engineers might have been able to cope with the high relative humidity, typical of Melbourne, which forced them to adopt a mixing ventilation system.

The scheme鈥檚 environmental designer, Ch茅 Wall of Lincolne Scott, says moisture rises during night purging, and a displacement system, would not have been able to shed this moisture fast enough. This is a pity, as a displacement approach could have reduced the refrigeration load and fan energy.

And then there鈥檚 the comfort setpoint of 23.5潞C. Why doesn鈥檛 CH2鈥檚 management relax that? The slab would work for longer, the phase-change system would cope on its own for more days a year, and the mechanical refrigeration could be held off for a greater time. It could even obviate the need for so many chilled ceiling panels.

The reason, according to Wall, is that building innovation is running ahead of institutional norms. Admittedly, chilled ceilings are a system new to Australia, and CH2鈥檚 management would need to change the expectation of the occupants, but surely it could be done.

So, the overall response to CH2 conjures up the words brilliant, bravura, amazing and awesome. But, also, it is overcomplicated and finicky, and very demanding of highly skilled premises management. It鈥檚 no wonder some Melburnians have dubbed it 鈥済reen bling鈥�.

Given the design team鈥檚 attention to detail, and the love and energy devoted to it by the facilities team, the building will probably meet its environmental targets. But without some of the 鈥済reen bling鈥�, with simplified systems and more relaxed occupational comfort setpoints, it could probably shatter those targets.

Given all this, CH2 is arguably not the ultimate in low-energy office design 鈥� it鈥檚 a work in progress. But if this is what Australia can produce today, what will its property developers be delivering in five years鈥� time?