Domestic water heating futures

New Zealand’s approach to climate change will impact many aspects of our day-to-day lives. Rinnai looks at what changes we might expect for how we heat water in our homes.

The Government is in the process of deciding on policies following the Climate Change Commission’s (CCC) recommendations on how to tackle climate change and meet the requirements for carbon neutrality by 2050. This article looks at how these policies may impact the two main categories of domestic water heating: instantaneous gas and electric storage.

Instantaneous gas

Much has been talked of a ‘gas ban’. While the CCC’s advice does not advocate a total gas ban, they do recommend the Government sets a date on the halt of new gas connections once a national energy strategy is developed and there is greater clarity around the contribution future gases can make.

The gas industry is advocating that fuel gas transitions towards hydrogen and bioLPG over the next 10-20 years. This decarbonisation of gas has the same outcomes for New Zealand in terms of ‘carbon budgets’ as a halt on new connections proposed in the CCC recommendations.

The initial stage of decarbonised fuel gas would be the introduction of a blend of natural gas and up to 20% hydrogen. This percentage is used as it is the maximum you can realistically add to NZ natural gas whilst keeping the general characteristics of natural gas that current appliances run on.

When you consider a fuel change, it’s not just the current appliances being sold that will be impacted, but all the in-use connected appliances in homes, schools and businesses. At Rinnai, we have been doing some testing on our current appliances and we can report that these can operate perfectly well on a natural gas blend with 20-30% hydrogen.

We will shortly start testing water heating appliances that we have sold over the last 20 years to determine if they can operate on the proposed 20% blend. We don’t expect issues, but the correct thing to do is test and find out.

The work for bioLPG is also underway, and we will be running trials on some appliances shortly to see how they perform and operate.

Given the complexity of converting a natural gas or LPG appliance to 100% hydrogen, in future we are likely to see hydrogen-specific appliances where hydrogen combustion is factored in at the design stage.

Testing on current Rinnai appliances has shown that they can operate on a natural gas blend with 20-30% hydrogen. Rinnai will shortly start testing water heating appliances sold over the last 20 years to determine if they can do the same.

The move to 100% hydrogen

A current conversion from LPG to natural gas or vice versa is reasonably straightforward, but the same cannot be said for converting an existing natural gas or LPG appliance to hydrogen.

Hydrogen as a fuel gas has some unique challenges. It’s unlikely that a ‘conversion kit’ will be available to convert a current appliance to a hydrogen appliance.

Whilst you should never say never, here are some of the challenges that you might face in a water heater (in no particular order):

Noise and resonance.

Combusting hydrogen is a noisy business. This is due to the physical properties of the chemical reaction between hydrogen and oxygen. Hydrogen combusts with a popping noise, and this is far louder than current fuel gas combustion.

Safety systems. Current appliance safety systems like flame rectification do not work with 100% hydrogen.

Burner and aeration. Burner designs intended for natural gas and LPG are not necessarily suitable for hydrogen.

These factors make it difficult to convert a natural gas or LPG appliance to a 100% hydrogen appliance. Therefore, what we are likely to see is hydrogen-specific appliances or appliance designs where hydrogen combustion is factored in at the design stage and can operate on different gas types entering NZ’s market over time. Of course, the appliances will need a fuel source and gas companies are actively discussing the requirements for generation of hydrogen and how it will be distributed.

We are somewhat ahead of the curve here, as the current fuel gas standards will in time need to be updated to cover the new gas mixes as they become available.

Electric storage

Electricity as an energy source has a far lesser environmental impact in New Zealand than fossil fuels, as a large proportion of it is generated by renewable sources. Therefore, going forward, electricity will be an increasingly important energy source for water heating. NZ’s electricity generation capacity will have some challenges as it adjusts to cope with the electrification of transport and private car fleets.

How we manage our electricity resources and use electricity efficiently and wisely will become increasingly important. At Rinnai we recognise this and are working on numerous developments in the electric storage water heater space.

So, how might you improve the performance of electric storage?

You can use the electricity to heat water efficiently by increasing the insulation on cylinders. This helps retain heat in the cylinder, which in turn allows the cylinder to require less electrical power. Cylinders are already subject to regulation in the form of MEPS regulations on the amount of energy they can lose. Having a cylinder with very good insulation and heat loss that is far lower than the current MEPS regulations results in low energy consumption.

Most electric storage cylinders currently use a simple resistance element to heat the water. Using heat pump technology can deliver a more efficient use of electricity to heat the same volume of water. Whilst heat pump technology is currently available, it is often designed for an overseas market and not New Zealand. Coupling heat pump technology with a highly insulated cylinder makes for a high performing appliance that maximises the energy it’s supplied.

Rinnai are working on developments in the electric storage water heater space, as electricity will become an increasingly important energy source for water heating due to its lower environmental impact than fossil fuels.

About the author: John Swarbrick is Innovation & Technical Manager at Rinnai New Zealand. With qualifications in mechanical engineering, John has 18 years’ experience in the New Zealand gas industry and has been with Rinnai NZ for 10 years. He has previously chaired New Zealand’s Gas Equipment Supplier’s group and represented New Zealand’s gas industry on many appliance standards committees.