Warming to a better way

By Matthew Wright

Gas-fired cogeneration is often presented as a climate change solution for Australian households and commercial buildings. But before policymakers get carried away and encourage the mass deployment of decentralised gas electricity/heating plants, we should take a good look at the benefits of heat pumps.

Put simply, heat pumps employ highly efficient space-heating technology that uses much less energy and emits less greenhouse gas than almost any other, including their gas-fired competitors. Heating in Australia is predominantly provided by gas (government incentives allowed gas to propagate for water and space heating), but in Japan, it’s common for heating and cooling to be provided by heat pumps. With a focused policy, governments can move Australia towards the same technology widely used by the carbon-efficient Japanese.

Heat pumps can be either air-source, which are generally cheaper, or geo-source. Air-source heat pumps use the local atmospheric conditions as an energy source or sink to transfer heat/cool from outside to inside. Ground source heat pumps perform the same function but use the earth’s constant subsurface temperature to transfer heat. In Australia we mainly have air-source heat pumps, but they’re not called heat pumps – they’re marketed for air conditioning and are known as reverse cycle air conditioners. When we run our air conditioners, the inside gets cold and the outside of the unit gets hot; it is transferring energy via its refrigeration cycle. When run in reverse, they pump energy from outside, inside.

Air-source heat pumps harness the ambient energy contained in the air. This is what makes them so energy efficient. The ambient energy used by heat pumps can be considered a renewable energy resource as it is effectively another form of indirect solar energy, like wind power or biofuels.

A good quality split unit heat pump (say 2.5-3.5kW delivered in the heating cycle) will use one unit of today’s carbon-intensive electricity (to drive the pump motor) and harness five units of renewable ambient energy for heating and cooling. The net result is that reverse-cycle air conditioners use up to 80 per cent renewable energy sources.

Even when using electricity from non-renewable sources to heat spaces, heat pumps are less carbon-intensive than gas co- or tri-generation. Assuming that non-renewable grid electricity was being used producing approximately 0.9 kilogram of CO2 per kWh of electricity, with one unit of grid electricity and five units of renewable ambient energy you get heating at less than 190 grams of CO2 per kWh (delivered thermal energy) compared to 230 grams/kWh for gas, assuming an overall 80 per cent conversion efficiency. It takes gas heaters 3kW of energy to achieve the same performance as 1kW use by a heat pump. And, of course, if you run it on renewable electricity, then you’re getting zero-emissions heating. Fossil gas can never be zero-emissions.

There are three main advantages of using a heat pump. Firstly, in terms of efficiency and price, heat pumps cost less that standard electric bar radiators or oil filled heaters. Second, first mover households and businesses that purchase accredited green power can combine renewable electricity with the renewable ambient energy for climate-friendly heating. Third, households and businesses can avoid having their own mini-smoke stacks that pump out GHGs and other undesirable pollutants.

The bottom line is that we know we can have zero emissions electricity, but we can't have zero emissions gas. Contrary to the popularly held notion among some politicians and bureaucrats, which has unfortunately filtered down into some sections of the public, gas is no solution to climate change. Heat pumps work over a wide range of temperatures, and are a good option for climate-friendly heating in Australia. Government decision makers and bureaucrats take note.

Matthew Wright is director of Beyond Zero Emissions and 2010 Young Environmentalist of the Year. Beyond Zero Emissions a volunteer-based climate change and energy research organisation. It is now producing a second iteration of its Zero Carbon Australia Stationary Energy plan.