黑洞社区

On the gleaming, corporate skyline of Canary Wharf, the partially clad office block that鈥檚 taking shape on one of the last remaining sites around Canada Square doesn鈥檛 look out of the ordinary. The steel skeleton that has now topped out at the 14th floor is gradually being wrapped in familiar glass curtain walling. But number 15 Canada Square marks a turning point for the Canary Wharf Group (CWG), and is a glimpse of the future of Part L of the 黑洞社区 Regulations.

All of CWG鈥檚 developments must meet a BREEAM 鈥淓xcellent鈥� rating, but this building goes one step further. The client, accountancy firm KPMG, set itself a target of reducing carbon dioxide emissions by 50% from its new building compared with the requirements set out in the 2002 Part L. This is equivalent to constructing an office to what is likely to be the CO2 reduction target in the 2010 revision of Part L.

If this sounds challenging, the design teams had the added burden of ensuring that the building complied with Canary Wharf鈥檚 commercial office criteria 鈥� above those of the British Council of Offices 鈥� in terms of cooling loads, occupancy densities and air supplies, as well as making sure that it met market expectations in case the firm ever decided to sublet floors or sell it on. In other words, it needed to have solid commercial appeal, so couldn鈥檛 be too wacky.

The impetus for the tough environmental credentials came from KPMG, and is the toughest yet out of Canary Wharf鈥檚 14 million ft2 portfolio, which includes 33 office buildings. 鈥淭his was the first negotiation we were involved with where there were specific requirements for environmental issues,鈥� says David Hodge, associate director of M&E at CWG. 鈥淚t was very detailed and it had to be an integral part of the design, construction and operation of the building.鈥� The 50% reduction in CO2 emissions wasn鈥檛 an arbitrary figure but had been worked out over six months with a number of bodies including BRE and the Carbon Trust to establish an achievable target in a changing legislative environment.

We could generate better performance by investing in the building services than by spending the money on the facade.

David Hodge, CWG

The design concept evolved over a number of months. CWG is responsible for the shell and core but KPMG will do its own fit-out. With the site largely determining the building鈥檚 footprint and orientation and a conventional structure of concrete cores with a steel frame, thoughts turned to the facade. According to Paul Katz, principal with architect Kohn Pedersen Fox, while a lot of buildings in Canary Wharf are very opaque and inward looking, KPMG wanted a transparent and open building, which translates as glass. A 14-storey atrium open to the office floors fronts the building, with mini three-storey stacked atriums at the corners.

Such heavily glazed facades don鈥檛 exactly cry out as energy efficient. In-depth studies were carried out to explore the potential of using a double-skinned facade with automated venting and external shading. 鈥淜PMG was very open to innovation as long as it delivered performance benefits and could be justified on cost grounds,鈥� says Robert Phelan, project executive with CWG. It quickly became apparent that an active facade couldn鈥檛. Compared with the high-performance double-glazed curtain walling, the improvement in terms of heat losses and gains of an active facade when balanced with cost was relatively low. 鈥淚t was felt we could generate better performance by investing in the building services than by spending the money on the facade,鈥� says Hodge.

If you鈥檙e expecting a building dotted with renewables, think again. Solar hot water heating and photovoltaics were both dismissed after a cost analysis. There simply wasn鈥檛 a business case; the solar thermal water system demonstrated a CO2 saving equivalent to 10 return flights to Berlin, something that could be more effectively achieved by introducing video conferencing.

The design team went back to basics and started analysing each system to see where improvements in energy efficiency could be found. The tradition for cooling offices at Canary Wharf over the years has been to install variable air volume (VAV) systems, which vary the amount of cooled air delivered to the space depending on the heat loads. The current Part L limits fan power, and VAV systems struggle to meet these requirements, so a switch to fan coil systems or active chilled beams has become the norm.

55 - the reduction on CO2 emissions expected on 2002 part L (taking trigeneration into account)

It鈥檚 the latter that KPMG has opted for. Fresh air will be delivered onto the office floors via the beams. This will induce the room air to circulate across the cooling coil in the beam, which effectively increases the cooling capacity of the beams. 鈥淵our main ventilation system fan power goes up slightly but you immediately eliminate all the fans in the terminal units that you would have had with a fan coil system,鈥� says Hodge. 鈥淪o you make an immediate saving and you can still get equivalent cooling capacities of fan coil units. The more even air distribution also allows for higher air temperature deliveries.鈥�

Of the four buildings CWG is currently constructing, two use fan coil systems and two chilled beams. 鈥淎 few years ago the perception of active chilled beams was not that great but we鈥檝e now seen a shift in their use in high density offices,鈥� he says.

The chilled water system employs more efficient water-cooled chillers rather than the air-cooled systems previously used for smaller developments by CWG. The design team also explored the idea of using the dock water as a source of cool water to raise the efficiency of the chillers further. The calculations eventually showed this wouldn鈥檛 be needed, which was something of a relief. 鈥淭he proposal for constructing the Crossrail project is to drain the dock to construct the new station. If we had relied on that to achieve the targets it would have meant for the duration of the construction of Crossrail we wouldn鈥檛 have been able to use it.鈥�

But by far the biggest contributor to CO2 reduction will be the installation of a trigeneration set (see box, opposite) as part of the shell and core construction. Under the Greater London Authority鈥檚鈥檚 London Plan, trigeneration is being promoted as one of the technologies to meet the 20% target for on-site renewables. According to Hodge, the building already had planning approval in place and didn鈥檛 need to comply with the measures set down in the London Plan but the trigeneration kit made sense. Taking into account the expected usage and building loads it is expected to account for 9% of the 22% reduction in CO2 emissions beyond the current Part L requirements.

22 - the reduction on co2 emissions expected beyond current part L Requirements.

As the trigeneration plant is only efficient when it is working at 50% capacity or higher it has been sized to meet the building鈥檚 24-hour base load. During the working day it will ramp up to meet the additional requirements such as cooling and small power items such as computers and printers. The waste heat will be fed back into the building鈥檚 heat system when there is a heating demand or else used to serve an absorption chiller.

Elsewhere, around a 5% saving is achieved with the lighting system. Daylight level and people movement sensors will ensure that the lighting on the office floors is switched off when it is not needed.

One of the green technologies that did make it through cost analysis was grey water recycling.

Although this doesn鈥檛 contribute directly to the building鈥檚 CO2 emissions it was one of KPMG鈥檚 targets. It is expected to cut water consumption by over 30% and the water distribution system in the building has been configured so that KPMG can install a grey water system at the fit-out stage. The WCs and urinals are fed from separate risers to the wash basins, which means they can easily be connected to the water treatment and recycling plant at basement level. Water meters at each floor will allow water reduction to be more easily targeted.

30 - the minimum expected cut in water consumption

KPMG is aiming to occupy 15 Canada Square in the summer of 2010. The latest Part L assessment of the building, incorporating the detail fit-out design (see graph) shows that the CO2 emissions for the building should be 39.5kgCO2/m2 per year, a 44.3% reduction on the CO2 emissions over 2002 Part L. 鈥淭his includes the fit-out with the daylight control and chilled beams and a rather conservative assessment of daylight linking,鈥� says Hodge. 鈥淚n reality there should be further improvements on this number.鈥�

One area that will be targeted for improvement is the cooling system. Plans are being made to trial higher room temperatures of 25脼C 鈥� based on the rule of thumb that allowing air temperatures to drift up by 1脼C can result in energy savings of 6-8%. If there is no effect on occupant comfort this will be rolled out on each floor.

With the trigeneration system taken into account, the CO2 reduction rises to 54.6%, taking it beyond the proposed requirements for the 2010 regulations. Which all adds up to show that meeting the next round of Part L doesn鈥檛 mean radically redesigning office spaces, or reconsidering comfort levels.