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Down to Zero

15 November 2009

From 2016, all new build homes, schools and colleges must be ‘zero carbon’, and other buildings in the public sector by 2018 and in the private sector by 2019. It is a challenge but already achieved at Defra’s new offices in Alnwick, as Nigel Banks explains

IN OUR EXPERIENCE there are four key stages to delivering a zero carbon building in reality rather than on a computer screen – Briefing, Design, Construction and Operation. Failure to deliver at each stage or sufficiently communicate between stages will lead to a poor performing building which will either fail to achieve its aspirations or achieve them at high cost. Although these apply to the design of new buildings, the issues considered at each stage are still highly pertinent to the planned upgrade or refurbishment and operation of existing buildings.
Briefing: Setting out clear minimum standards and aspirations in terms of actual end results such as a DEC rating of ‘A’ or reducing metered energy use by 30 percent and CO2 emissions by 100 percent give the design team clear focus. On the Defra Alnwick offices, all the various Defra policy requirements were pulled together into a single sustainability charter. All items in the charter which were then ring fenced through later value engineering processes.
Design: Four key design aspects which need to be considered if very low or zero carbon buildings are to be achieved:
Passive design: With clear client aspirations towards a low energy and low carbon building, AECOM worked with Frederick Gibberd architects to develop the form of the new building. One critical aspect was the orientation of the new building, which has long north and south facades which are easy to shade with overhangs in summer and allow useful winter sun though in winter. The building has no windows on its East and West facades to prevent low angle summer solar gain and maximum heat retention in winter.
The windowless West elevation also has the added benefit of buffering occupants from noise created by the three 15kW wind turbines on the site. The Northern elevations of the 13.5m deep open plan office wings are designed to capture as much natural daylight as possible to reduce power consumption from artificial lighting while on the South side a photovoltaic (PV) array is orientated towards the sun’s path for most of the year with solar shading provided to reduce glare and heat gain in summer. If the building was rotated by 90 degrees the impact on energy use would be dramatic as heat demand would rise by 20 percent and cooling would have been required (cooling requirement would rise by 40 percent to maintain 25°C).
● Energy efficiency: With a good building envelope the development of an ultra efficient
mechanical and electrical design is made easier. High levels of insulation and the use of mechanical ventilation with heat recovery in winter nearly eradicates the need for local space heating and issues of cold draughts. Narrow floorplates allow excellent natural daylight penetration which enables daylight dimming, motion sensing, high efficiency light fittings to only be on when really required. Lighting is only provided to 300lux on the working plane with desk lamps provided if necessary. Narrow floorplates also allows natural cross ventilation when outside temperatures rise above 14°C. The need for cooling is eradicated (in all but the server room) through orientation and shading, low energy computing and lighting and exposed, night cooled thermal mass. Should cooling be required in future this can be easily incorporated by adding a cooling coil to space left in the AHU.
Hot water demand is reduced through low flow showers and taps with IR controls. Variable frequency drives control pumps and the AHU’s fans according to return air CO2 concentration.
● Clean power generation: All this great work on energy efficiency and passive design can only reduce energy use and CO2 emissions so much. In order get to very or net zero carbon emissions you need to provide your energy from low or zero carbon sources on site. In order to assess the viability of technologies, AECOM undertook a detailed feasibility study to assess their technical and economic viability. This resulted in three 15kW wind turbines being installed (a single larger turbine was rejected by planners), 120sq m of high efficiency PV solar shading arrays being installed, a small solar thermal array provides hot water for showers and taps and a biomass boiler provides the majority of the heating with a gas back-up. All the technologies were expected to
have less than a 25 year simple payback.
● Occupants: Getting the occupants of a building on board with saving energy is key to achieving a low carbon building in reality. As a result it was decided that high level control would be provided but occupants would be engaged through local controls to adjust in their own comfort and as a result their energy use. Also, building occupants are informed of their impacts through a display in the building’s reception and through workshops held with them.
● Construction: Clearly the building has to be constructed and commissioned to the standards expected during design. The building achieved an impressive 3.84m_/hr/m_ at 50Pa in its air pressure test and metered heating energy use shows the thermal envelope performs superbly. As with (nearly) all buildings, there were teething problems and these have mostly been resolved in the first year’s use and through seasonal re-commissioning.
● Operation: AECOM have recently been reviewing the first year’s operation of the office complex and have started reviewing the second year in more detail. The sub-metering of equipment has enabled areas of poor performance to be identified and proposals put in place to rectify them. The new building replaces an existing single-glazed, 1960s office building on the same site which housed the same staff and equipment as now in the new office. This provided a great comparison. In the buildings first year of operation, without the benefits of the wind turbines and biomass boiler for most of the year (they were only built once the old building was demolished), the building achieved an 84 percent reduction in its operational carbon emissions compared to the old building.
So, what has worked and where can further improvements be made?
1. Heat demand in year one was near zero and much lower than predicted. The back-up gas boiler went down before the biomass boiler was installed and temperatures remained above 19°C for 3 days! This low heat demand is suspected to be due to the higher than expected electrical energy use which is effectively electrically heating the building.
2. As a result, the biomass boiler has not had to fire as much as expected but is still providing the remaining heat demand effectively.
3. The solar thermal hot water array installed was smaller than originally expected due to the low usage expected from the low flow fittings, but is performing well.
4. The wind turbines have been operational since January 2008 and are generating a considerable amount of electricity. A full analysis of the performance of the turbines will be undertaken when twelve months of data is available.
5. The PV arrays are slightly exceeding expectations so far and are consistently generating electricity during the day which matches demand well.
6. Two thirds of the water used to flush toilets and urinals is rainwater that has been collected and filtered in the rainwater harvesting system, which contributes positively towards Government targets.
This Defra occupied building proves that zero carbon buildings are within reach. They are achievable on sites where zero carbon electricity can be generated and very low carbon buildings are achievable on nearly all sites. Facilities managers and occupants of buildings hold the key to delivering upon low carbon aspirations in reality and their role should never be underestimated.
Nigel Banks is an Associate Director at AECOM. AECOM (formerly Faber Maunsell) undertook the M&E, Civil and Structural, Sustainability and BREEAM, and Specialisms for this New Lion House project for the client, Defra. Other project team members were Appleyards (Project Manager), Frederick Gibberd Partnership (Architect), and Davis Langdon (Quantity Surveyor). The Contractor team comprised Kier Northern (Main Contractor), Frank Shaw Associates (Architect), Haden Young (M&E Sub-contractor) and 3 Planets (BREEAM).
The FM contractor is Interserve.

What is Zero Carbon
There are currently three ‘official’ definitions in use:
1. Energy Performance Certificate (EPC): EPCs in England and Wales are based on a CO2 index calculated via computer simulation of the building’s regulated emissions (heating, cooling, hot water, ventilation and lighting) with a score of less than 0 shown as ‘net zero CO2 emissions’.
2. Current BREEAM ‘true zero carbon’: BREEAM 2008 requires non-regulated energy such as small power loads to also be included in the simulation (process loads are still excluded) and that these total emissions should be zero or less to be ‘true zero carbon’.
3. Zero carbon homes definition: The 2016 target for new homes has been recently
confirmed by the Government; it requires a 70 percent reduction of regulated CO2 emissions through on site measures with the remaining 30 percent of regulated plus unregulated cooking and appliances needing to be being ‘offset’ through ‘allowable solutions’. These include off-site renewable electricity connected via direct physical connection, exports of low carbon or renewable heat to surrounding developments,  section 106 Planning Obligations, retrofitting of existing buildings in the locality or investments in LZC energy infrastructure.
* All these definitions are currently based on computer simulation estimations of building CO2 emissions only and exclude embodied emissions from construction and other emissions associated with ongoing transport, waste, water, etc. It is expected that the 2019 non-domestic definition will be further consulted upon later this year.

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