Sustainable Houses

Operational energy/carbon

Operational energy (and the associated carbon emissions) refers to the energy needed for heating and cooling, cooking and hot water, as well as general power and lighting needs. In other words, it’s the energy required by occupants to live in their home.

Buildings that are ‘carbon neutral in operation’ do not cause any net emissions from direct fuel combustion and operational electricity use.

The first step to reducing operational carbon is to remove the need for gas. Traditionally, many homes in Australia have used gas for cooking, hot water and sometimes heating. Today, there are many all-electric alternatives that are much more efficient, as described below.

The ‘electrification’ of a building’s energy needs can be combined with a solar photovoltaic (PV) array and a connection to a 100% certified GreenPower retailer. This ensures that all electricity — whether generated through a PV array on the roof or purchased from the grid — comes from truly renewable sources.

Where carbon emissions may be unavoidable, they can be offset through an offsetting provider such as Greenfleet or a similar, reputable organisation.

Electricity and renewable energy

Installing a solar PV system is an easy way to reduce operational carbon emissions. The cost of solar PV systems has dropped dramatically in recent years, which means the purchase and installation cost can be recuperated over a shorter period of time.

Solar arrays are ideally placed on north-facing roofs to maximise exposure to sunlight. Some households — especially those without batteries — may also benefit from east- and west-facing panels to capture the sun’s energy during mornings and evenings, when electricity demands and grid tariffs are highest. Available roof area, overshadowing from nearby trees or other structures, and the building’s energy needs will determine the size of the array.

Naturally, most electricity is generated throughout the day when sunlight is abundant. If possible, energy-intensive devices that aren’t time critical, such as a dishwasher or a washing machine, should run during the day to make use of ‘free energy’. Excess electricity generated during the day can be stored in a battery to bridge gaps when there is insufficient sunlight, at night and on cloudy winter days.

Battery technology is quickly catching up with the advances made in solar technology, making them increasingly a practical, economically realistic option. Until batteries are appropriately sized and affordable, a connection to the grid is required to ensure uninterrupted electricity supply. A certified GreenPower retailer can provide renewable electricity.

Hydronic heating panels, like this one hidden under the window box of the living room, is keeping the Inside Out House warm during cooler days.

Heating and cooling

Thanks to good passive design, a sustainable house will maintain comfortable temperatures throughout much of the year. However, supplemental heating and cooling may be needed for the very hot or cold days, depending on the local climate.

Reverse-cycle air conditioning is a type of heat pump and the most energy efficient and popular system for both cooling down a space during summer and warming it up in winter. There are a variety of systems available, such as the common ‘split system’ (the heat pump is located outdoors, connected to an indoor, usually wall-mounted unit) and the ‘ducted system’ (the indoor unit is hidden away and air moves through a series of ducts and outlets). All reverse-cycle air conditioners put out hot or cool air to adjust indoor temperatures.

Hydronic heating systems also use an energy-efficient heat pump (see hot water below), but use water instead of air to adjust indoor temperatures. Hot water is pumped through wall-mounted units or an underfloor piping system that radiate heat.

Another option is a heat or energy recovery ventilation (HRV or ERV) system, which uses an integrated air-to-air heat exchanger that allows heat or energy to be transferred between incoming fresh outside air and exhausted stale air. This process minimises energy consumption associated with fresh air ventilation and produces significant seasonal energy savings.

Simple ceiling fans can also reduce temperatures by circulating air. They are the cheapest cooling option and have the lowest greenhouse impact.

No matter which option(s) for supplemental heating and cooling are used, they should be appropriately sized and positioned to minimise energy waste. A continuous thermal envelope is key in reducing the need and use of costly heating and cooling.

Hot water

Unlike gas-powered instant hot water systems, energy-efficient heat pumps use no fossil fuels when powered by renewable energy. These heat pumps essentially work like a reverse-cycle air conditioner, but they heat water instead of air. The heat pump is installed outside and connects to a well-insulated storage tank that can store large amounts of hot water for domestic use. This makes it possible to use cheap (or even free) solar energy during the day to heat water that is used during peak hours (morning or evening) when energy is expensive/less abundant.

Alternatively, a solar hot water system uses collectors/panels that are installed on the roof to expose and thereby heat the water through the sun’s energy. This system usually requires a ‘booster’ device to increase the water temperature on days with little or no direct sun exposure. It’s important to avoid gas-powered boosters to remove the need for fossil fuels and make the building carbon neutral in operation.

Lighting

Sunlight entering an indoor space through windows, doors and skylights provides natural light throughout the day. The size and placements of these openings will regulate how much light enters and at what times.

This is supplemented with artificial lighting: modern LEDs are long-lasting, energy efficient light sources. Timers, daylight controls and motion sensors can be used to turn lights on and off automatically, so lighting is provided only when and where it is required.

Appliances

Every appliance comes with an upfront cost and a running cost, and a heavy environmental impact throughout their lifecycle. Careful selection of appliances will save energy, water and money, and reduce associated carbon emissions.

New appliances should only be purchased if necessary and only require electricity (no gas) for their operation. Using an efficient induction cooktop, combined with an all-electric hot water system (see hot water above) means the building no longer requires a gas mains connection, saving the ongoing monthly metering fees.

When selecting appliances, energy efficiency ratings provide a useful indication of energy need and associated cost. In Australia, the official Energy Rating system and Water Efficiency Labelling and Standards (WELS) rate the energy and water consumption of new appliances. The higher the star rating, the more efficient the appliance.

Appliances should be appropriately sized for household needs. Principles of material reductionism apply: does a kitchen need a new, integrated refrigerator or will an existing refrigerator do just fine?

Brass tapware is used throughout the bathroom and shower of Double Life House.

Tapware

Water-efficient tapware reduces water use. In doing so, it can also save energy, since less water needs to be heated. The WELS rating (see appliances above) indicates flow rates in litres per minute. The higher the rating, the more efficient the tapware.

The chroming process of typical tapware involves a lot of toxic chemicals and top layers of chrome can peel off over time, requiring replacement or repair. Choosing tapware made from long-lasting, durable materials, such as brass or stainless steel, is free of toxic chemicals and ages more gracefully.

Rainwater

Water is a precious resource. Most homes use potable mains water for use throughout the house and even in the garden. Fortunately, most urban areas in Australia receive sufficient rainfall to significantly reduce the need for mains water. 

Rainwater can be channelled from the roof into a rainwater tank that is either placed next to the building or underground. Rainwater can then be used for toilets, laundry and garden irrigation, reducing mains water consumption and water bills.

Wastewater

There are two types of wastewater created in a home. Greywater is wastewater from showers, basins and taps. Blackwater is water that has been mixed with waste, such as from the toilet, kitchen sink or dishwasher.

Minimising wastewater helps cut down the amount of pollution going into waterways and thereby reduces pressure on our shared infrastructure for water supplies and wastewater treatment.

With small adjustments — such as using greywater-save soaps and shampoos only — greywater can be captured and reused for watering the garden, thereby saving potable water and reducing water bills. (Local council regulations will dictate whether greywater reuse is permitted.)

Stormwater

Stormwater is generated by rain runoff from a roof, driveway, footpath and other impervious or hard surfaces. As the water runs off, it collects soil, organic matter, litter, fertilisers and oil residues, which can pollute waterways. Using stormwater for garden watering (see above) saves potable water and reduces downstream environmental impacts.

Excavation and building should work with the topography, drainage patterns and vegetation of a site to help manage stormwater. Retaining vegetation and minimising impervious surfaces will help drain stormwater to vegetated areas. Paving and sealing off large outdoor areas, such as driveways or terraces, should be avoided. Instead, permeable paving options, like stone or brick paving with sand or grass between, helps cut down on stormwater runoff.