What is a Zero Carbon Building?

What does “Zero Carbon” mean?  We thought we’d post this for clarity, when eTool make a claim about one of our subscriber’s (or client’s) buildings we aren’t cutting corners. When we use phrases like “Zero Carbon”, “Low Carbon” etc we’re talking about the Life Cycle Emissions of the buildings.  The normal scope is summarised in the following system boundary diagram (which also works pretty well for infrastructure as well).

 

eToolLCD System Boundary

eToolLCD System Boundary

There’s a number of varying definitions for “Zero Carbon” in use.  In Europe (including the UK) it’s generally only inclusive of module B6 in the above diagram (that’s integrated equipment energy use in the building) which is very limited.  Some more detail on the varied definitions is available from these two downloads (there are a host more such studies / reports / articles on the internet, this is just a sample):

What is a “Carbon Neutral” Building? Light House Sustainable Building Centre Defining Zero Carbon Buildings – ASBEC

Defining Zero Carbon Buildings – ASBEC

 

One Brighton Life Cycle Assessment Report

eTool completed a post construction Life Cycle Assessment of the One Brighton development the report can be found below.  The assessment provided some interesting results and lessons surrounding materials choice and centralised biomass heating.

BioRegional One Brighton Lifecycle assessment report final

Project: One Brighton

Client: Bioregional

Benchmarking Best Practice Residential Green Buildings

Executive Summary

How green are green buildings?  The question is very subjective but if we approach it purely scientifically there’s a way to (kind of) answer this.  The method was to measure the environmental savings of best practice conceptual green buildings against EN15978:Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method.

The results are summarised in the below chart showing Global Warming Potential (GWP) performance (more indicators shown in the report).

Summary Chart 2

The main findings were:

  • Green buildings that focus entirely on non-greenhouse gas (GHG) related credits within rating tools (as far as is possible) achieved a 28-29% greenhouse gas saving against the benchmark
  • Those that focus entirely on GHG related credits will save between 65 and 77%
  • The large range in values was surprising but reflects the many green building credits that don’t relate to GHG savings in the EN15978 scope
  • The taller the building the more difficult it is to get large savings due to space limitations for onsite renewable generation
  • There were no significant poor trade offs in the Low Carbon focussed green buildings when other environmental indicators were analysed
  • The scope of EN15978 doesn’t include the below items which may also have a significant impact on overall GWP performance of the development, all of which can be influenced to some extent by building design (and some green building credits aim to do this):
    • Occupant transport
    • Occupant food and consumable goods consumption
    • Occupant waste generation

Introduction

The green building movement has been very successful globally.  Uptake is incredible particularly considering most of these rating systems are voluntary for developers.  eTool is in awe at how the Green Building Councils motivated the industry to do better and in some sectors has totally redefined what is considered “normal”, significantly lifting sustainable design standards.   And it’s not only buildings that have benefited.  A whole generation of green building professionals have spawned from the design improvement requirements that the rating systems demand.  The green building movement has been an incredible success.

Despite this success there’s an underlying question that many people are now answering and that is “how green are green buildings?”.  Answering this question historically has largely been achieved by arguing relative values of different “green” credentials but with internationally recognised standards now available that measure the environmental performance of buildings, there’s actually a scientific approach to measuring greenness.

But care must be taken as greenness isn’t just about the planet, at least not anymore.  Typical green building rating tools now also look at social and economic sustainability, not just environmental performance.  In this post we are purely looking at environmental performance.  More specifically we will be focussing on Greenhouse Gas emissions (GHG) but also report performance against a number of other environmental indicators.

Purpose

The aim of this exercise is to determine how much GHG emissions are avoided for best-practice green buildings compared to business-as-normal buildings.  eTool decided to conduct this research  to prevent any poor environmental trade offs associated with an organisations decide between a rating system and environmental impact targets.

Background

It’s very difficult to compare rating systems, and perhaps impossible to do this in a fair manner.  It’s important to note that what follows is not a holistic benchmarking exercise, but rather just seeks to understand the environmental performance of green buildings.  Although this should be a simple process there are some complexities that warrant discussion.

The Rating Tools

Each major green building rating tool attempts to define environmental, social and/or economic performance (or all three).  At first glance most of the major tools look very similar.  They have criteria that leads to a scoring system that leads to some kind of recognisable rating.  On closer inspection however, depending on why, how and when each tool was set up, the weightings applied to different areas of sustainability vary significantly.  The illustration below shows how the weighting varies between the predominant rating tool in Australia and Germany.  The Australian “Green Star” system has a much higher environmental weighting and largely skips any direct credit for economic sustainability.  This is typical of most most green building rating tools around the world.  The DGNB system on the other hand gives equal weighting to each of the three areas (economic, social and environmental).

DGNB v Green Star

Having established these differences there is generally a bit of a convergence in the language when the final rating is communicated.  In the case of Green Star, the highest rating of six stars equates to world leadership and this seems to be goal of each rating system’s top rating, to recognise excellence on a global scale.

The Standards

Since 2005 the European Committee for Standardisation has been tackling the job of measuring building sustainability.  The work is being conducted by Technical Committee 350.  Specifically their task is to establish standardized methods for the assessment of the sustainability aspects of new and existing construction works and for creating standards for the environmental product declaration of construction products.  At the building level they are writing (or have written) standards to measure the performance of buildings in the following areas:

  • Environmental
  • Economic
  • Social

In this post we’ll be drawing on the environmental performance standards, specifically EN15978:Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method.  Note that the standard is very building design focussed, the system boundary, shown below, doesn’t include building occupant transport, occupant food consumption, or occupant waste generation.  eTool have attempted to expand the scope as much as possible within the limits of the standard by including non-integrated operational energy use.

NewSystemBoundaryDiagram

Building Characteristics

Different buildings inherently perform differently when looking at life cycle impacts.  The key factors are:

  • Energy intensity of the building use per unit of floor area (for example office verse residential use)
  • The site and building geometry characteristics that dictate renewable energy capture (mainly solar)
  • Climate zone which effects heating and cooling loads, natural daylight, available solar radiation and mains water inlet temperature

To account for these anomalies we’re modelling a range of characteristics to understand how they effect results.  Initially however we’ve restricted the climate zone to residential buildings, Building Codes of Australia climate zone 5 (Sydney, Perth), which we will likely expand, get in touch if you’re interested in seeing these results.

Methodology

The basic methodology was to create a conceptual “standard” apartment building which represented “business as normal” delivery of apartment dwellings in Australia.  The quality of the construction including energy efficiency etc was to match construction code compliance levels.  This set a baseline for performance (this is different from the benchmark as it’s more location and geometrically representative).  This basic apartment building model was then upgraded by applying changes in eToolLCD to reflect changes that would need to be made to achieve a best practice green building rating.

We have chosen the Green Building Council of Australia’s Green Star rating tool as our case study as it’s local to eTool, very transparent and is fairly well aligned with other leading global rating systems.  Because we want to understand what world leadership means in terms of life cycle GHG savings, we are modelling theoretical buildings which would achieve a 6 star rating in the Green Star system.

Due to the range of credit criteria that span non-GHG related issues as well as those that relate directly to reduced GHG we have modelled the extremes.  The process to achieve this was:

  • Identify how the rating tool credits relate to GHG savings within the scope of EN15978 and categorise as follows:
    1. have a direct relationship on GHG reduction
    2. are partially or indirectly related to GHG reduction
    3. are largely unrelated to GHG reduction
  • Based on the building characteristics we determine the feasible limit of points that may be practically obtained for each credit * (see note)
  • To determine the “best case” GHG performance we model credits category 1 (direct GHG relationship), followed by 2 and lastly 3 (unrelated to GHG relationship) until we have achieved the required points for the top rating (Green Star 6 Star).
  • To determine the “worst case” GHG performance we model the credits in category 3 first, then 2 and lastly 1 until we have achieved the top rating.

For each building modelled this provides a range of possible GHG performance outcomes for the top rating.  The details on how we categorised the credits is found in a table in the appendices.

*NOTE: In some cases all available credits in a given category could not be feasibly achieved.  For example, for some buildings it’s not feasible to achieve a 100% reduction in operational energy related GHG emissions (worth over 20% of the Green Star rating).  In this case we estimated the maximum possible energy demand reduction and the maximum possible on-site renewable generation and determined the operational GHG savings based on this.

The buildings we chose to model are:

  • 5 Story
    • 25% of roof area lost to set backs or landscaping (unusual but possible best case solar capture potential)
    • 50% of roof area lost to set backs or landscaping (typical)
  • 15 Story
    • 25% of roof area lost to set backs or landscaping (unusual but possible best case solar capture potential)
    • 50% of roof area lost to set backs or landscaping (typical)
  • 25 Story
    • 25% of roof area lost to set backs or landscaping (unusual but possible best case solar capture potential)
    • 50% of roof area lost to set backs or landscaping (typical)
  • The benchmark buildings we chose to measure the GHG savings against are the eTool International Developed Country benchmarks.

Pitfalls

No methodology is flawless so we wanted to highlight the potential pit falls in the below list:

  • eTool may not be aware of technologies or approaches that enable an increase in the number of points that can be achieved for a particular credit over and above our “feasible limit”.
  • We have had to make assumptions on building use profiles
  • This is building design and hence predictive approach rather than an empirical approach to measuring actual building performance
  • The Green Star tool has an “Innovation” category which accounts for up to 10% of the rating score. This category is quite flexible in how the points are awarded and may effectively increase or decrease the GHG savings.
  • The scope of EN15978 is very building centric, it doesn’t include for example occupant transport which is going to have a large effect on the GHG (if improved through better building design).  Depending on the savings facilitated by applying the green building transport related credits, the overall saving in GHG per person per year may be substantially different and the comparison may change between designs.

Residential

The code compliant apartment building represented an 18-19% saving compared to the international benchmark.  The taller building had a slightly better saving than the shorter building mainly due to some efficiencies in shared spaces.  The main differences between the benchmark and this baseline apartment building were that the base line building had:

  • Less heating loads (Benchmark includes regions like North America, Europe etc where as Australian climate is much, much milder)
  • Longer design life (Benchmark has a mix of densities which average less than the baseline)
  • Larger floor plate per occupant (particularly car parks, common areas, outdoor areas) and hence more operational energy to light and ventilate the building per occupant

Green buildings that focus entirely on non-GHG related credits (as far as is possible) achieved a 28-29% greenhouse gas saving against the benchmark.  Those that focus entirely on GHG related credits will save between 65 and 77%.  The large range in values was surprising but reflects the Green Building credits that don’t relate to GHG savings in the EN15978 scope.  The taller the building the more difficult it is to get large savings due to space limitations for onsite renewable generation.  A summary of the results is given in the below chart:

Summary Chart 2

 

It should be noted that the GHG focussed Green Building  is very aspirational and includes such strategies as biomass boilers for hot water and space heating, 9 or 10 star NatHERS performance and 20% reduction in the car park size.  The full list of strategies that were modelled that produced these results are given in the appendices.

Other Environmental Impact Results

To help determine if there were any poor trade-offs environmentally a host of other indicators were also predicted in the LCA.  These other environmental indicators are not as robust as the GHG figures due to less research effort and hence lower quality background LCI data.  They do however provide some basis for understanding relative impacts between designs.  Interestingly the results for other environmental indicators support the strategy of focusing on GHG savings as there’s generally a positive outcome.  The only poor trade off was a very slight increase in POCP due to combustion of timber as a low carbon heat source (for domestic hot water and space heating).  The 5 storey and 15 storey apartment building results are both very similar.

15 Storey Apartment Building LCA Impact Assessment for Multiple environmental Indicators

 2015.06.08 15 Storey Apartment Building, Multi Indicator Radar Chart  Green Star 6 Star GHG Savings Focussed (Standard Roof)

 

5 Storey Apartment Building LCA Impact Assessment for Multiple environmental Indicators

2015.06.08 5 Storey Apartment Building, Multi Indicator Radar Chart  Green Star 6 Star GHG Savings Focussed (Standard Roof)

The higher ecotoxicity result is due to increased copper use in the Green Star buildings.  This is an unexpected result but may be a reflection of poor background data (copper is by far the dominant ecotoxicity effect).  The reason for the higher copper in the Green Building models is replacement of PVC with copper and higher churn (longer building design life) for some copper in equipment.  This result could be seen as noise rather than a significant feature of the LCA impact assessment.

Conclusions

The main findings were:

  • Green buildings that focus entirely on non-greenhouse gas (GHG) related credits within rating tools (as far as is possible) achieved a 28-29% greenhouse gas saving against the benchmark
  • Those that focus entirely on GHG related credits will save between 65 and 77%
  • The large range in values was surprising but reflects the many green building credits that don’t relate to GHG savings in the EN15978 scope
  • The taller the building the more difficult it is to get large savings due to space limitations for onsite renewable generation
  • There were no significant poor trade offs in the Low Carbon focused green buildings when other environmental indicators were analysed
  • The scope of EN15978 doesn’t include the below items which may also have a significant impact on overall GWP performance of the development, all of which can be influenced to some extent by building design (and some green building credits aim to do this):
    • Occupant transport
    • Occupant food and consumable goods consumption
    • Occupant waste generation

Appendices

Building Use Assumptions:

ABS Stats used to determine occupancy per bedroom in residential apartments

Assumed occupancy density of 15m2 / workstation in office buildings

Green Star Credit List and how each credit was applied to the LCA Model

Green Star Credits and Relationship to EN15978 Savings

More About the Conceptual Green Buildings:

The following strategies were modelled in eToolLCD software to determine the life cycle impacts of the conceptual green buildings:

  • Behavioural Change Initiatives Leading to a 5% reduction in building operational energy use through the application of the following credits:
    • Commissioning and tuning:
      • Services and Maintainability Review
      • Building Commissioning
      • Building Systems Tuning
      • Independent Commissioning Agent
    • Building Information:
      • Building Operations and Maintenance Information
      • Building User Information
      • Environmental Building Reporting
    • Commitment to Performance:
      • Environmental Building Reporting
  • Increase in end of life recycling recovery rates to 100% and where possible allocate waste to down cycling processes (rather than landfill, eg concrete recycling) through the application of the following credit:
    • Commitment to Performance, End of Life Waste Management
  • 100% reduction in potable water use via efficiency, rainwater collection and water recycling through the application of the following credits:.
    • Potable Water (This would require water recycling infrastructure and large rain water tanks etc to achieve which are modelled).
  • Energy monitoring upgrades lead to an additional 5% reduction in building operational energy use through the application of the following credits:
    • Metering and Monitoring:
      • Monitoring strategy
  • 50% reduction of construction waste through the application of the following credits:
    • Construction Environmental Management:
      • Formalised Environmental Management System
    • Construction and Demolition Waste:
      • Reduction of Construction and Demolition Waste
  • 20% Reduction in car park size through the application of the following credits:
    • Sustainable Transport:
      • Modelled pathway (reduction in number of car spaces and provision of alternative transport methods)
  • 100% recycled content steel through the application of the following credit:
    • Sustainable Products
  • Reduction in operational GHG through to the practical limit through application of the Green House Gas Emissions credit.  See section below on how this is applied.
  • Refrigerant change to CO2 which essentially negates any refrigerant impacts through the application of the following credit:
    • Refrigerant Impacts

Operational GHG Detail:

Operational GHG scope for residential buildings is all integrated loads in addition to the below items.  Also included in the below list is the maximum efficiency energy saving based on the most efficient MEPS rated products for each appliance:
  • Fridge / freezer (40% energy saving achievable for 10 years)
  • Dishwasher (35% energy saving achievable for 10 years)
  • Clothes washer (80% energy saving achievable for 5 years)
  • Clothes dryer (56% energy saving achievable for 5 years)
Individual strategies that were applied to achieve the lowest possible operational GHG savings:
  • Reduced fridge space (10.3% drop in average refrigerator energy use for primary refrigerator)
  • Improved fridge ventilation (See Basix requirements, 12.5% saving in refrigerator energy assumed)
  • 9 or 10 star NatHERS rating.  Cooling supplimented with ceiling fans and heating conducted with biomass (effectively zero carbon)
  • Water heating supplied with biomass and/or waste heat
  • Common area and car park lighting on 1 minute delay motion sensors and also automatically shut down when required lux levels are achieved by other light sources (natural or other artificial light)
  • Lighting Coefficient of utilisation improved due to colour scheme in building areas:
    • 0.6 Achieved in car park with white concrete or painted white floors and walls
    • 0.8 Achieved in apartments
  • High efficiency lamps, ballasts and fittings installed throughout
  • Regenerative drive elevators with auto shut down of controls and lighting when not in use
  • Cooking energy supplied by gas (stove and oven)
  • Engineered CFD modelled car park vent solution saving 70% of energy8
The efficiency improvements associated with these items is only applied over the life of the first product installed.  Other strategies (such as refrigerator space and ventilation) are assumed permanent over the building’s life.

The “Peak Electricity Demand Reduction” credit is likely to effect EN15978 results depending on how it is achieved.  If batteries are utilised it would likely increase the net impacts of the buildings.  For this reason the credit has not been modelled to ensure the results reflect the performance of the Green Building positively.