Toward s Zero m Carbon Buildings

lntegrated RE systems central to design approach

T he most successful complex sys-

tems in the world are simple bio- logical organisms like bacteria,

which work on äght closed cycles of ener-

gy and nutrients. Collection, storage and

use are linked by complex feedback cydes,

constantly fine tuning to maximise the

emciency of the system. This is how the

buildings of the future will function.

Energy is the essential nutrient of modern

civilisation and we must learn to extract it

sparingly from the ambient sources

around us. But this is not a futurist's

dream: with the ingenious combination of good design and technology, zero-carbon and autonomous buildings are becoming a reality today. Robert Webb, Robert Webb Associates, UK provides an archi- tect's perspective of how buildings may weil look in the not too distant future.

When we were asked to create the Zero-

Energy Research Building (ZERB) for

Renue, an environmental community

organisation based in south-west London, UK the brief was to use both the design process and the building itself to expand understanding of energy, and demonstrate some of the upcoming technologies to a wide audience stretching from the local community to decision-makers in govern- ment and business. Making a zero-carbon buitding was not enough - we also had to

show how it was done. The key to respon- sive bioclimatic design is to understand the

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invisibles. Just as trees on a wind-swept hillside teil the story of the prevailing wind, and as their root-structures reach

out towards sources of nutrient and water, so next generation buildings must use their form and structure to efficiently accom- modate the many layers of human activity, air movement, structure, and the capture and efficient use of ambient energy and

water.

Concept design Just like bacteria, zero-carbon buildings achieve eßciency through feedback - in both design and use, feedback loops ensure that energy &mand is minimised and bal- anced to meet what is available, which in turn is informed by the relationship between building and site and the ambient

energies available. At ZERB the site means that the main

driver is solar energy collection through both active and passive means. W i n d energy and some hydro-power from the neighbouring small river are also incorporated, but these will only be small contribu- tors to the total. The basic response was therefore to cre- a t e a simple building enve- lope with a Iong fagade ori- ented south (which also cre- ates an enclosed urban square to the north). The sequence of sketches shows the devel- opment of this form. 'Pushing over' the arch puts the majority of the faßade within 5 ° of the opt imum solar collection angle for the site, while streamlining the form to generate suction for natural ventilation. Analysis showed that the output from photovoltaic (PV) panels on the facade is increased by 50% compared to a vertical faßade, and 35% compared to " a horizontal roof. It also cre- ates an ideal form for passive solar collection through the transparent patts of the faßade.

Technology review Design for eftqciency should be supplemented by efficient energy product ion, and a

tial technologies has been carried out to inform the design. In this case scale and cost mitigated against biomass-powered combined heat and power (though a near- by development is incorporating a gasiflca- tion system by B9 Energy Biomass), and

we have developed a simple biomass heat- ing system using local urban street tree thinnings. We will also incorporate some small wind turbines, potentially using the increased wind speed at the building apex. Small wind is something we are campaign- ing for, as it is an option orten overlooked in the urban environment (though it can produce double the output than PV for the same collection area)•

In PV technology, we are excited by new techniques for mass-deposition of poly- crystalline and amorphous silicone on sub- strates, and also by the development of Dye-Solar cells which will in due course

coat all building windows. And most of all,

we are looking to demonstrate a total energy storage hydrogen system using elec- trolysis and a fuel cell. Total autonomy is a

misleading goal for urban buildings where the grid can be rauch more efficiently used

For storage. However fuel cells will soon be seen in the home as micro-CHP units run- ning on natural gas, and in due course at remote locations.

Design for comfort and quality of life Sustainable design must alm to achieve a high quality of life with min imum use of

resources - we cannot skimp on comfort to

reduce environmental impact, and in the

ZERB we alm to show how this can be done.

The twentieth century invented a static-

engineering approach to building design,

where the building was seen as a sealed box

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100% 80% 60% 40% 20% 20% 40% 60% 80% 100°6 North South

Diagram showing the sun's energy from different inclinations for 51 .TN - the RENUE building profile overlaid

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complete review of the poren- Schematic ofrenewable ene*~ Œte,rls.

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F E A T U R E T O W A R D S Z E R O - C A R B O N B U I L D I N G S

which could be manipulated to achieve

constant comfort conditions (typically 22

°C +1 and, for example a uniform 400 lux

of light across the working plane). In tem-

perate climates we now know that people

are tolerant of a wide rande of conditions

and will in fact greatly enjoy variety in

temperatures and light levels in the work-

ing environment. Design in response to

this more sophisticated understanding of

comfort requires understanding of temper-

ature contours or changing [ight levels over

the day and year - requiring the latest too[s

of physical and computer model[ing now

available to us we can design low-energy

buildings in response to a detailed dynam-

ic understanding of the 'invisibles ', to

achieve high comfort levels with [ow ener-

gy use.

Integrated design analysis At ZERB we have invested considerable effort in integrated design analysis in order

to i[[ustrate the richness that can be achieved in this design process - and how

the analysis can contribute both to the architecture and to the understanding of building function, as weil as reducing energy use. Computer and physical mode[- ling techniques that we emp[oyed include: computer modelling of the PV outpuc computer simulation of daylighting;

dynamic thermal ana[ysis of the building fabric and thermal conditions; and CFD

modelling, in conjunction with wind tun- nel testing to understand both internal and external air flow, essential where natural

ventilation is part of the passive cooling strategy.

At the same time the team also built a spreadsheet modal of the electrical demand within the bui[ding. This helped the dient to understand how day-m-day demand cou[d be managed, via a large-scale projec- tion of the current bui[ding status com- pared to both the current and the average weather conditions. One way to do this is

via a daily 'energy budget' based on yester- day's weather conditions, and the next step would be to incorporate automatic con- crols varying energy use to match - non- essential background and external lighting,

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PV afe monocrystaltine cells mounted in glass-tedlar frameless units /

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"~-Internal board

Joints between unlts are leff open er stlicone sealeo aepenalng or angle and explosure of roof

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Ve ntilallon intake / mesn screen '~,

exc~udes insects

Structural e l e m e n t s : rare;hai- eg llrnDer or plywooa

Rooling system Gart De made off-site and craned into place

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B Structural ply skin

Waterproof mernbrane , /

L.--- Ventilated air gap

Cutaway drawing shows PV as ventilated rainscreen system over

stressed-skin timber panels.

- The system can be used as part of urban • regeneration and densification schemes

to provide lightweight residentJal acco- modation on currently unused rooffops

close to city centre facilities.

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The principles and applications of the rainscreen PV ctadding system

for example, can be varied between speci- fled maximum and minimum levels, creat- ing a varied night-time environment in response to varied daytime weather condi- tions!

Initial electrica[ demand estimates began at about 25,000 kWh/yr for the 480m 2 building, with the expected out- put from the PV reaching 16,500 kWh/yr and about 800 kWh/yr from wind and micro-hydro. By the end of the design process the two figures had practically swapped over - we had succeeded in reducing the demand to 19,000 kWh/yr while the PV area had been increased in response to fine tuning of the day lighting strategy, and in the ~nal design generates around 26,000 kWh/yr from monocrys- talline panels.

Detailed design - the rainscreen approach The PV dadding is seen to be an 'armature' wrapping over the southern fagade and peeling back where required to provide day- light, views and routes in and out of the buiiding. At detailed design stage it became clear that a rainscreen was the best physcial interpretation of this princip[e as weil as offering great advantages in other respects. The concept of a rainscreen otters many advantages and fits weil with the panel con- struction method and construction sequence, as welt as offering many practical advantages. RWA received first prize in the International Energy Agency's PV Products in Buildings Competition for an early ver- sion of the concept, which also showed how the system can be applied to arange ofcon- struction types and inclinations but is par- ticu[arly appropriate for 'lightweight 'con- struction.

PV can be integrated in a variety ofways but the rainscreen approach has particular value as it achieves the following: • Separation of cladding functions reduc-

ing likelihood of failure (UV protection and weather barrier separated from water barrier).

• Venti[ation to rear of PV panels ensuring low temperatures and good efficiency.

• Wiring is outside building, not accessib[e to users to maintain safety, and can be gathered to achieve fewer penetrations of waterproof membrane.

• Panels can be easily removed and upgrad- ed in the future. No framing system is required, reducing the amount of material required (curtain-

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CFD analysis showing air velocity and pressure, driving the ventilation

Daylight rnodelling image

wall systems usually use complicated alu- rainium extrusions made of high-energy virgin aluminium). This also dramatically improves the appearance and elegance of the system.

• PV rainscreen cladding can accommodate a variety of forms and play a part in dynamic architectural expression. A further advantage to this approach is

the fact that the air gap improves the envi- ronmental performance of the bui[ding (particu[arly in lightweight construction) by removing radiant solar heat in summer and providing an extra insulation layer in winter. The former strategy is quite weil understood and used widely in hot coun- tries (solar radiation on a roof surface can be very high in the summer), while the lat- ter may depend for optimum performance on having controllable openings to limit air movement in winter.

Conclusions One can draw many conclusions from this work, not least that good architecture and cutting-edge energy design are not incom- patible. Our work is aimed at finding prac- tical solutions which increase the speed of change towards sustainability and we are pleased to have shown that achieving build- ings which are zero-carbon in-use is possible and practical with today 's design knowl- edge and current technologies. In fact we would argue that design for zero-carbon in- use should become a commonly-accepted target for dients and design teams. This puts a maximum premium on energy effi- ciency, but it also allows the building to be designed to grow towards zero-carbon ener- gy. The active design measures and addi- tional technology at ZERB adds about 30%more to the building cost compared to the 'bare ' building. While current energy prices may not support this extra invest- ment in every case, they most certainly will in the future, and a truly future-proof building will be designed to accommodate later renewable technology additions.

Model of a section through the building showing PV panels and air flow

Contact: RWA, 1-3 Leonard Street, London EC2A 4AQ, UK Tel:+44 20 7689 6345. Email: info@rw-a.co.uk; www.rw-a.co.uk. A detailed animation of the rainscreen construction can be seen at www.xco2.com

Note: This work is based on a report sponsored by the New and Renewable Energy programme of ETSU,UK.

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