Zero carbon housing arrives in Australia

Designs have been released for the award winning Cape Paterson Ecovillage, Australia's first zero carbon housing development. Thirty-eight of 220 lots are available in the first section of the development.

The project takes sustainable house design, sustainable living and communities to an unprecedented level.

Starting from the ground up, the sub-division at the west end of the existing Cape Paterson village has been laid out such that all the sites have optimal solar access to the north. Excellent solar access is necessary for good quality, healthy and economic housing, a prime consideration of the Cape Paterson design team which is unfortunately lacking in most new housing estates.

Ecovillages aren't new; they exist in every state of Australia. Unfortunately they tend to fall down with either bland designs or ones that are too pricey – and they come with building envelopes and appliances that lack energy performance.

The Cape Paterson Ecovillage succeeds where others have fallen short as it has no fossil gas connection, instead its houses will utilise renewable ambient heat combined with electricity (to drive refrigeration pumps) for space and water heating.

Each house comes with a heat pump hot water unit and unless a buyer chooses to forgo them, one, two or three of the smallest reverse cycle air conditioners on the market (they're called heat pumps in Europe where they're mainly used for heating as they will be at Cape Paterson) as well as induction cooktops.

Cape Ecovillage houses will define our all electric future, with all electric appliances that will one day be powered from a 100 per cent renewable powered electricity grid. For now they’ll run on a combination of rooftop solar photovoltaic and certified Greenpower from the grid.

The most exciting aspect of the project is the use of passive solar design. There aren't many excellent examples of passive solar building in Australia – none exist site-wide across a large subdivision and not many are affordable. The houses come in modest to medium-large sizes.

To explain to you how the ecovillage houses will perform I have chosen a representative size for the houses on offer, which is 155 square metres (for example, one building on offer is a 132 square metre house and another  is 177 square metres), and the build costs are in the range of $1500-$2500 a square metre (including a bonus 20-40 square metres for the garage, landscaping and green options that normally aren't factored into an offer off the plan). The pricing is at the lower end for architecturally designed houses.

Each of the buildings' star ratings was completed by the team of Tony Isaacs (original developer of the FirstRate software), and Wayne Floyd (who runs one of Australia's largest energy rating practices and is the former chair of the Association of Building Sustainability Assessors board – one of the organisations who accredit energy rating assessors). Combined, they alone have over 50 years of experience in energy efficient building design and rating. Isaacs and Floyd worked closely with the design teams to produce the most cost effective ten 7.5 star houses to be sold off the plan. Some of the houses on offer are rating higher.

The ratings are rock solid and there is no easy way out for designers/builders. The star ratings are just for the building envelope and how it gains and loses heat. No concession is included in the rating for rainwater tanks or the heat pump hot water (better than solar hot water). It doesn't even have a concession for heavy curtains. 

So the 7.5 star rating is just passive heating and cooling of the building's interior space and keeping the space to the temperatures that a ‘typical’ household would find comfortable under the NATHERS model.

Achieving this rating and comfort level involves a tight building envelope with almost no air gaps, enough (summer) shaded glazing to the north and most importantly thermal mass located in the interior of the building. (A common mistake is for people to build with thermal mass located on the outside, where it is less effective or at worst counterproductive)

So if we check the star rating charts and we base the climate zone on Cape Otway Zone 64 (for the closest climatic likeness to Cape Paterson):

We find that for a house in zone (64) to achieve a 7.5 star rating, which is the mandated minimum for the Cape Paterson Ecovillage, a building (under the NATHERS model) is only allowed to consume 76 Megajoules of space heating and cooling energy per square metre for that zone. However, we have to adjust due to an area correction in star bands by a factor of 1.08. That's 22.8kWh per square metre per year.

So how does that look? Let’s take the average building size on offer for Cape Paterson at 155 square metres. (Ten building designs from five different architects have been independently rated and are available for people buying into the ecovillage off the plan).

For example not counting the garage, one house on offer is a 132 square metre building, the same size as my house in inner city Brunswick and the 1970s average building size. Another is a larger house at 177 square metres, again not including the garage.

Incidentally the 177 square metre house is $2000 a square metre and the 132 square metre building is $1500 a square metre, which represent very competitive prices for architecturally designed houses.

Building envelope

So what does 7.5 star mean for a typical householder on a site only hundreds of metres from the scenic but harsh southern coastline of Victoria?

At 22.8kWh energy use per square metre, an average 7.5 star rated 155 square metre ecovillage house will need 3,534kWh of thermal heating/cooling requirement per year. That is, of course, if you are a typical house that opens and closes the doors and windows as often as in the model and keep the house within the heat brackets that are defined as comfortable. It is most likely that most households would use their heater less than in the NATHERS star rating model, so think of the 3,534kWh heat requirement as the upper bound.

Heating with air-source heat pumps

Because the Cape Ecovillage houses are using the most efficient of heating devices available, namely heat pumps (reverse cycle air conditioners), the houses will use 95 per cent less energy to heat and cool (for the same comfort level) than average Victorian houses. The performance of the heat pump units would be comparable to a COP 5.5 Mitsubishi Heavy Industries SRK20ZJX-S, which (together if there is more than one in the house) will likely consume less than 642kWh of electricity annually to drive their motor and provide the entire heating requirement of the average 155 square metre ecovillage building.  

Again that's assuming behaviour in line with the NATHERS modelled building use behaviour in the living and bedroom areas and without curtains. Some buyers (who don't mind wearing thermals or a jumper for a few weeks of the year) will likely forgo having any heating appliance; in that case they will have to put up with the buildings hitting a high of at most 26C in the summer and an extreme low of 16C during the winter.

For most people it would be logical to add heavy set correctly installed curtains. That would effectively reduce the annual energy consumption per square metre from 22.8kWh (7.5 star) to 17.7kWh (8.0) star. Meaning the average building would only require at most 498kWh of electricity for running the heat pump heaters per year. So we're talking about heating for at most between $65 (off peak house with curtains) and $205 (peak rate no curtains) a year, but these houses come with a solar system which negates much of these heating costs (the heating season in Victoria is up to eight months long, the supplied 2.5kW solar photovoltaic system will produce 150kWh in June, 180kWh in July and 240kWh in August and 3,200kWh annually).

For just another $3000 the production over winter can be doubled (no need to double the inverter as winter production will not be significantly clipped with an oversized panel array) and annual production would still increase significantly to 5760kWh.

So what is a heat pump heater like? It's rated at 2.5kW delivered heat (450 watts of grid electrical energy), so about the same as a big oil-filled electric heater or the equivalent of a small gas wall heater. For the average sized ecovillage 7.5 star house with curtains, the heating requirement would be the equivalent of running one heat pump flat out for 48 days.

That is assuming you want to keep your house in line with the NATHERS star rating model, which specifies 20 degrees Celsius as a heating target in living areas heating from 7 am to midnight. In bedrooms heating is assumed to 18 C from 4pm to midnight, 15 C from midnight to 7am and 18 C from 7 am to midnight.

If your future home's living areas were allowed to dip to 18 C or 17 C at times, then the heating requirement would be considerably reduced.

Hot water – heating with air-source heat pumps

Heat pump hot water systems have been around for some time now. When selecting a unit we should note that the industry must move towards CO2 or hydrocarbon based refrigeration gasses. Sanden offers a CO2 model (GWP 1) (formerly Edson) and Siddons Solarstream offers a hydrocarbon option (GWP 3). The need to get away from HFC refrigeration gasses also applies to the refrigeration and reverse cycle air conditioner industries.

The other potential issue with hot water service heat pumps is whether they have a booster element for low temperature (less than 5 degrees Celsius) operation.

Although it is not in the specification, we trust that the ecovillage will specify a premium model that does not have this massive potential contributor to peak demand. Such models that operate properly with a meaningful C.O.P. (co-efficient of performance) at low temperatures include Siddons Solarstream, Stiebel Eltrom, Quantum and Sanden.

In regards to the hot water cost, an average house uses 4000kWh of heat for their hot water, but that house has an ordinary flow shower and an ordinary top loading washing machine. A house at the ecovillage with a AAA-rated mid-range 6.5 litre per minute shower head (saves 1433kWh) and a top-rated front loading washing machine (saves 1117kWh) will use no more than 1272kWh of hot water heating per year. But because a good heat pump hot water unit like the Siddons solar stream will achieve a seasonal average C.O.P. of 4.0, the annual demand for hot water heating will be around 318kWh. The hot water usage of home on this site is impressive at almost 90 per cent reduction when compared to the average Australian home.

Cooking – with induction cooktops

At less than half the energy demand of a gas cooker, an electric induction cooktop is efficient, responsive and fast. Used by top chefs the world over, induction cooktops bring precision to cooking. They are electric and will be running on renewable energy at the ecovillage.

The Cape Paterson Ecovillage is an exemplar of how houses can and must be built to address climate change and deal with energy poverty.

All new buildings across Australia should be built to a minimum (bare minimum) 7.5 star standard. And the government must set out a plan for upgrading the rest of the nation's stock to the same standard, starting with the most energy inefficient and costly housing first.

The average house in Victoria is using 6,000kWh of electricity per year and 17,000kWh for heating, usually with gas. A household in the Cape Paterson Ecovillage will easily get by with 2,000-3,000kWh of annual energy (not including transport) consumption. That's around 90 per cent less than an average house.