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Mainstreaming low carbon design

NATIONAL AUSTRALIA BANK OFFICE, MELBOURNE.
NAB, Melbourne. Photo: John Gollings

Low carbon design provides a cost-effective way of improving performance that can be adopted for all buildings. Now, clear guidance on how to achieve such designs is available in a series of free, technical guides.

The transition to net zero carbon is well underway and not a week seems to go by without the release of a new paper or publication making the case for net zero buildings. A number of early adopters, largely made up of institutional property funds and education institutions, are already leading the way.

However, if the building sector is going to play its part in the transition then widespread adoption of low carbon design is needed. 

Further, given that the buildings being designed or refurbished today will operate for many decades to come it is imperative that action is taken now to avoid locking in high emissions in the future.

What has been lacking to date is clear industry guidance setting out practical and proven low carbon design principles.

Cue the CRC Low Carbon Guides. The guides released by the CRC for Low Carbon Living (CRCLCL) draw on several years of research, and are combined with case studies that demystify and summarise best-practice, integrated low-carbon design principles.

The team behind the Guide to Low Carbon Commercial New Builds advise that “the fundamental purpose of the guides is to mainstream low carbon design and extend the knowledge base to build capacity across industry.

Low carbon design principles provide a cost-effective way of improving performance that can be adopted for all buildings and not just the few.”

Authors of the commercial building guide, Remy Augros (GHD), Ian Dixon (GHD) and Dr Philip Oldfield (UNSW), summarise their top low carbon design principles as follows:

The Cooperative Research Centre for Low Carbon Living is a national research and innovation hub linking leading Australian researchers and academics with private organisations working in the built environment.

It has undertaken more than 100 research projects and when it ceases at the end of 2019, it will leave a legacy of research outputs that will encourage best practice, innovation and enhance national industry capacity.

The Guide to Low Carbon Commercial New Builds is intended to be a practical reference for the design of high-performance, low-carbon commercial buildings for use by everyone involved in the creation of new buildings. It is one of several guides produced by the CRCLCL.”Low carbon design principles can be divided up into the following areas:

Form and typology

  1. Optimise commercial floor plate design for site, climate and occupant comfort. In particular, the service core can be located to shade office spaces from unwanted solar gain on the western or northern facades, thus reducing cooling loads.
  2. Embodied carbon can make up to 20 to 45 per cent of an office building’s total carbon footprint. If we decarbonise electricity supply in the future, it could be even higher.
  3. Usually, in commercial buildings the greatest contributor to this is the structural system. So, strategies to make the structure more efficient, such as structural optimisation, can cut costs and carbon, and increase net lettable floor area.
  4. When sustainably sourced, mass timber structures can contribute to significantly reduced embodied carbon in commercial buildings, compared with traditional steel and concrete structures. A timber structure can reduce embodied carbon by about 300 kg CO2-e per square metre.

Building Envelope

  1. Increasing the insulation and air-tightness of office facades can reduce cooling loads and improve thermal comfort in perimeter zones.
  2. However, for the best results, they need to be combined with other strategies to reduce internal heat gains, such as high-efficiency equipment (LED lighting, computers, etc.), and night purge ventilation.
  3. There is evidence to suggest that less glazing and a reduced window wall ratio (WWR) in Australian commercial buildings would cut carbon emissions.
  4. In particular, the use of insulated spandrel panels at low and higher levels would improve facade performance without reducing daylight or views.
  5. Facade design is an important contributor to low-carbon commercial buildings. In office buildings with large floorplates (>2,000 square metres), a high-performance facade may only have a small benefit on the total building carbon performance, since there is less exposed surface area per unit building volume.
  6. However, a high-performance facade with appropriate WWR, shading, U-value and air-tightness will always improve thermal comfort and reduce energy loads in perimeter occupied spaces.

Heating Cooling and Ventilation

  1. HVAC is usually the largest contributor to carbon emissions in office and commercial buildings. Specifying the most efficient systems and equipment for a project is an excellent way to reduce carbon emissions.
  2. For example, in the scenarios considered in the Guide to Low Carbon Commercial New Builds, improvements to motor, VSD and fan efficiencies resulted in an 11.4 to 28 per cent reduction in whole­building carbon emissions.
  3. Strategies to reduce fan static pressures can also reduce HVAC carbon emissions. Again, in the scenarios in the Guide to Low Carbon Commercial New Builds, reducing fan static pressures by 20 per cent resulted in total operating emissions reductions of 0.7-5.5 per cent.
  4. Allowing setpoints to vary beyond the standard 22.5°C ±1.5°C can reduce air-conditioning energy, with an increase of 1°C saving 6 per cent.
  5. Adopting an adaptive comfort model, where internal conditions change with the seasons, would provide more significant air-conditioning reductions, although it would likely require a work culture that allowed occupants to change their clothing and behaviors according to the seasons.
  6. Providing exposed ceiling-thermal mass, along with night purge ventilation, can reduce carbon emissions by reducing both the operating hours and load of HVAC plant.

On site low carbon energy generation

  1. Photovoltaic (PV) panels represent the best opportunity for on-site energy generation in commercial buildings in Australia.
  2. Roof-mounted PV panels are an excellent choice for many buildings because they can be tilted towards the sun. However, in taller commercial buildings, roof space is limited, so façade-mounted PVs may be used in tandem. These are usually more expensive and less efficient.
  3. Precinct level gas-fired trigeneration plants will likely not offer the lowest carbon emissions in the long term as decarbonisation of the electricity grid will mean electric systems are more carbon-efficient.

Integrated outcomes

As well as best practice, the guide includes case study simulations to quantify the impact of different strategies and technologies on carbon performance. These include simulations on a high-rise office building achieving NABERS 5.5 star, and a mid-rise office achieving NABERS 5 star. Both were simulated in Sydney, Brisbane and Melbourne.

The results indicate that making small changes to any one system or building characteristic on its own has limited carbon impact. Integrated strategies along with the installation of onsite solar PV offer the best outcomes.

Activity Systems

Reducing internal loads can have a significant impact on carbon emissions. A 40 per cent reduction in internal loads can provide up to 13.5 per cent reduction in carbon emissions.

Envelope Systems

Improvements to the building envelope alone often have a small impact on overall carbon emissions. Reducing the U-value is often only effective when combined with strategies to reduce internal loads.

In climates like those of Sydney and Brisbane decreasing U-value can trap heat in buildings, leading to increased cooling demand. Reducing solar gain through decreasing solar heat gain coefficient or shading is the most effective intervention.

HVAC

Targeting strategies to reduce air handling system energy is particularly effective. Reducing fan static pressures can lead to overall carbon savings of up to 5.5 per cent and improving motor and fan efficiencies up to 28 per cent.

As a single parameter, reducing air distribution energy offers the most significant carbon saving opportunity demonstrating the value of high-performance HVAC design in commercial buildings.

Improving chiller performance up to IPLV of 12 can lead to between 4.5 and 11 per cent carbon savings.

Combinations

The integration of strategies provides substantial opportunities for carbon emission reduction beyond current best practice.

In high-rise buildings, reductions to internal loads, improvements to building envelope, reduced air handling system static pressure and installation of a roof-based PV system could reduce emissions by 20 to 25 per cent. In a mid-rise building similar interventions could provide up to a 50 per cent reduction in carbon emissions.

Using more innovative technologies and strategies generated performance closer to carbon neutral. Using higher-performance façade systems, reduced internal heat gains, high efficiency HVAC and an extensive on-site PV system saw carbon reductions of 82 to 97 per cent across the scenarios – meaning effective carbon emissions of 2.29 – 10.23kgCO2-e/m²/annum.

These results are far better than those achieved by most high-performance buildings today, and demonstrate the potential of low carbon offices moving into the future.

Ian Dixon is technical director at GHD. GHD was involved in the preparation of industry guidance through the Low Carbon CRC, and co-authored the Guide to low carbon commercial buildings. 

Philip Oldfield is an Associate Professor and director of the Architecture Program at UNSW Sydney. Prior to joining UNSW, he was an Assistant Professor at the University of Nottingham where he co-led the Masters in Sustainable Tall Buildings – the world’s only course and qualification dedicated to the design and research of high-rise architecture.


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