Before getting into the nitty gritty, it’s important to understand the purpose of the eTool benchmarks, which is:
- Establish a common measuring stick against which all projects are assessed so that any report is comparable to another (for the same type of project).
- Create a starting point, or “average, business as usual case” from which to measure improvements.
The benchmarks are not an average of existing stock but rather an average of new stock. Hence any efficiency requirements etc in the Building Codes etc are taken into account. When comparing to the benchmark, the target is pretty simple. Effectively Australia has to drop it’s GHG emissions by about 90-95% on a per capita basis for us to become sustainable global citizens. With this in mind, what we should be trying to do is drop our building’s emissions by 95% against the benchmark to ensure the building is stabilising the climate.
Creating the business as usual benchmark is pretty complex. For residential buildings in Australia there is a broad density mix from detached through to apartments. This is the latest breakdown of the new dwellings density mix in Australia (from ABS) over the last two years:
|Detached||Semi Detached||Low Rise Apartments||High Rise Apartments|
|Proportion of New Dwellings||61%||13%||7%||19%|
For each of these density types, eTool have formulated a BCA code compliant building. We have then created a nominal statistical mix of floor areas to match the average new dwelling size in Australia (214m2). In this way we come up with a “dwelling” that is a mix of densities and matches the size of the average Australian dwelling.
A similar approach is taken for operational energy. In this case we first research the most up to date residential energy estimates for Australia. This data comes from ABARE Energy in Australia 2012. It gives us guidance on the total energy used per household (existing housing stock) in Australia and also the fuel mix split (electricity, gas, wood etc). We then use other end use percentage estimates to determine where this energy is being used in the dwellings. The most commonly quoted breakdown of household energy use in Australia is from the “Your Home Technical Manual” which is actually a reference to the “Energy Use in the Australian Residential Sector, 2008”. This report is commonly referred to as the “Base line report”. This report itself actually states:
The study identified a paucity of end-use data for residential energy use in Australia, particularly in regional areas. Some of the appliance energy consumption estimates used in this study rely on research that is 15 years old or, alternatively, on work undertaken in New Zealand.
The study recommends an comprehensive end use energy monitoring program which we believe is being undertaken. Until the results are out we’re a feeling our way in the dark a little. Not withstanding this, the study is useful to guide the decisions about where we’re using our energy. To verify the Base Line Report figures we also took some state government studies (eg Sustainable Energy Development Office in WA) and statistics from other countries (notably the BRANZ HEET study and also stats from the US). The largest unexplained discrepancy seems to be in the estimates for heating demand.
The Base Line Report suggests that 38% of total end use energy in Australia homes is dedicated to heating and cooling purposes. This seems very high given the following facts:
- The comprehensive HEET study from BRANZ in New Zealand (a much colder climate, and one dominated by heating requirements) only calculated 34% of end use energy dedicated to thermal performance.
- The WA SEDO estimate for thermal comfort energy demand is also much less, hence it’s hard to believe the additional demand is due to cooling.
- A large percentage of Australia’s population (Perth, Sydney and Brisbane) all live in quite mild or warm climates where heating would not make up more than 50% of the thermal control energy demand (and less still of the actual end use energy demand)
- Heating is the most end use energy intensive thermal comfort mode as cooling typically utilises either apparent cooling methods (evaporative or fans) or heat pumps, both of which have effective Coefficient’s of Performance of 2.5 or more. This means for every one unit of energy input, 2.5 units (or more) of heat is dissipated of pumped from the dwelling when cooling. Heating on the other hand requires more energy than the actual heat load demand theoretically required to heat a space (or at least the same amount). This is mainly due to flue losses.
The high estimate in the Base Line Report may be linked back to the ABARE Energy stats which are also questionable. The Energy in Australia 2012 document from ABARE gives a biomass figure for residential energy use that equates to 6280MJ / household /annum. When this is calculated in terms of mass of wood, it works out at 400kg of timber per household in Australia. Even if one in every 5 houses (studies suggest it’s more like one in every 10) is using a wood heater that was their primary source of heat, that’s 2t of wood per annum they would need to be burning in order for the ABARE data to reconcile. To give you an idea, an average small box trailer full of wood is about 250kg. We’re not convinced there’s 2 million households in Australia receiving 8 trailers of wood per annum to heat their homes. The BRANZ HEET study further supports the proposition that ABARE have overestimated biomass consumption in the Australian residential sector. BRANZ calculated that each wood heater uses 4,500kWh (one tonne) of wood per annum.
Without making any adjustments to either the end use demand figures, or the top down supply figures the numbers don’t reconcile very well. For example, trying to “fit” the biomass, gas and LPG energy into the end use break down “squeezes” electricity out of the hot water and space heating categories. There simply isn’t enough low grade heat requirements in dwellings to account for all the biomass. However, when we aligned the biomass use predictions with BRANZ, and adjusted the demand figures to better match some of the competing studies we got good reconciliation.
This also supports the total residential demand estimate in the Base Line Report which is quite a bit lower than the ABARE stats.
Once we knew the amount of energy the existing housing stock were using, we then determine how this would differ in new dwellings. Some energy use would remain pretty static (eg appliance use and refrigeration). Lighting, hot water and heating and cooling have relatively new BCA code requirements focussed on energy efficiency. For these end categories appropriate adjustments were made to account for the newer technologies and associated demand.
Heating and Cooling (Thermal Control)
The heating and cooling energy requirements are the most complex, as there are very few stats on what equipment is being deployed in new houses. The NatHERS system does help this situation and we make an estimate of the deployment of heating and cooling technologies in the current housing stock as follows:
- Estimate the heating verse cooling loads for buildings in the top 20 populous NatHERs climate zones (85% of Australia’s population). This works out to be 60% heating and 40% cooling.
- Estimate the efficiency of each type of heating and cooling technology
- Estimate the deployment of each type of heating and cooling technology
- Adjust estimates such that total energy consumption matches our adjusted ABARE figures and the split in thermal demand matches the NatHERs weighted average for Australia
This then informs our decisions about what people are likely to choose for new houses. The summary is found in the following tables:
|Electric Heat Pump||Electric Fans or Evaporative Coolers|
|Existing Stock Cooling Demand||50%||50%|
|New Housing Stock Cooling Demand||60%||40%|
|Electric Heat Pump||Electric Radiators||Gas Flued||Gas Internal Heater||Wood Heaters|
|Existing Stock Heating Demand||20%||10%||17%||51%||2%|
|New Housing Stock Heating Demand||35%||0%||20%||40%||5%|
For each major BCA climate zone or population centre then simply divide the NatHERs energy demand estimates for a 6 star dwelling for the building between these categories and apply appropriate efficiency or COP figures to determine what the end use energy demand will be.
The building codes have now banned the use of electric resistance storage hot water systems in all residential buildings apart from class 2 building (strata buildings). Some state governments also discourage the use of electric heaters in class 2 buildings. This has led to a huge shift from electric storage hot water heaters to gas, solar, and heat pump units. This is a great thing for reducing the carbon intensity of the delivered hot water to dwellings (see more explanation on hot water fuel types here).
Using the same reconciling procedure between the end use energy estimates and the adjusted ABARE data we get the following mix of fuel uses for meeting demand in Australian existing housing stock:
|Fuel Contribution to Water Heating Demand of Existing Stock||Fuel Contribution to Assumed Water Heating Demand of New Stock|
|Natural Gas and LPG||77%||79%|
Note, this doesn’t imply that 77% of water heaters are gas fired, it implies that 77% of energy used by water heaters is gas. The difference is that gas water heaters have lower efficiencies than electric resistance heaters (99%) or heat pumps (approximately 270%). With a gas water heater, depending on the age of the heater, it may be as low as 50%, and won’t get much better than 85%. So the mix of heaters installed in existing buildings is actually more slanted towards electric.
New buildings will tend more towards gas due to the current BCA requirements. With this in mind, we’ve used the figures in the right hand column for the split in fuel use for new dwellings.