Where to now for hot water?

It’s a conundrum. A really tough question for architects and engineers. And it’s a question that is going to be asked more and more in the near future. What do we do about hot water?

By John Greaves (NZCE- Mech) Senior Design Engineer - Black Diamond Technologies

It’s Gas Now, But This Can’t Last

Many have already seen the writing on the wall. Despite soothing noises from several gas industry suppliers there is huge uncertainty that gas, traditionally the go-to for heating hot water, is going to play any significant part in future water heating solutions - especially in larger scale commercial buildings.

A few quick checks will tell you that NZ as a whole consumes about 2 Petajoules of gas per annum, and our current gas stocks total around 20 Petajoules.

So, unless we find new gas supplies (which is currently off limits) then NZ will run out of gas in around 10 years. What’s more topical is that burning fossil fuels for heating is an unpalatable option for many building owners and occupiers. There is now a strong groundswell for more environmentally friendly, future proofed solutions – and this particularly applies to hot water as it affects essentially every building.

So we need a new answer for hot water. There is a plethora of options, each with its own pitfalls and foibles. The key is understanding the limitations of each early in the design process to allow selection of the best solution. So what are some of the alternatives?

Historically the Alternative is Direct Electric – Do We Go Back to the Future?

Outside of gas, the hot water solution used most historically has been electric, or more precisely, electric immersion resistance heating. This solution was commonly installed in houses for many years prior to the rise and rise of instantaneous gas hot water.

While electric immersion is well proven it should really only be considered for small scale hot water, and even then there are probably better solutions available.

Electric immersion hot water is VERY energy hungry, and so will always require substantial electrical infrastructure to support it.

New or retrofit electric water heating will almost always require mains upgrades, which may not only involve local rewiring it may also trigger upgrades to street cables and transformers – which is expensive.

And that’s if you can get them, there are many anecdotal stories floating around of commercial sites in cities having restrictions placed on them by electricity infrastructure providers.

There simply isn’t enough power supply around to waste it like this.

From a carbon footprint point of view this option is poor. It doesn’t tick boxes for any building owner or tenant looking to do the right thing. So in the vast majority of cases this means a direct electric water heating solution is dead in the water, pardon the pun.

Solar is green – but is it New Zealand’s Alternative to Gas?

Solar hot water is a solution that’s been around for quite a while and due to current pressures is seeing a bit of resurgence. There is no doubt that this is a very green solution – what could be better than

Read the full article in the Industry Journal, December 2022 issue