New technology could cut energy costs significantly

The research was done at the University of Auckland. Photo / File

Cutting-edge thermal technology mixed with building materials could save Kiwi home owners on energy costs by up to 16 per cent each day, new research has found.

But phase change materials, or PCMs, won't become a reality for most New Zealand homes until its cost comes down, said the Auckland University researcher who used them in a just-published study.

PCMs, typically either paraffin or fatty acid esters, are materials capable of storing and releasing large amounts of energy by melting and solidifying at a given temperature.

When added into building materials, PCMs can substantially increase the thermal mass of the building materials without noticeably increasing their actual size.

"By having a large thermal mass, the temperature fluctuation inside the building can be significantly reduced, hence increasing the thermal comfort of the building, while also reducing the amount of electricity consumed for heating and cooling," said Professor Mohammed Farid, of Auckland University's Department of Chemical and Materials Engineering.

While solar energy was a form of energy often overlooked - the amount received by a typical residential building on a daily basis is many times more than its total daily energy requirement - this energy was largely wasted in most modern buildings due to the lack of heat storage capability.

"Being able to store solar energy as latent heat using the PCM during the day time in winter, the stored heat can then be released at night time upon solidification, which provides passive heating," Dr Farid said.

In summer, the PCM stored the coolness at night time and absorbs the heat during the day, hence providing cooling.

Realising that these materials needed to be encapsulated to prevent PCM from leaking out when melted, Dr Farid and his team developed its own microencapsulation technology allowing it to be mixed with building materials in an easy way.

In an experiment, the researchers built two small huts - one lined with the PCM technology and another without it - and observed the indoor temperatures.

They found that the temperature of the PCM hut took between three and five hours longer to drop down to 17C at night, because its boards were slowly releasing the heat they'd absorbed earlier earlier in the day.

In another test, a freezer was fitted with energy storage trays containing a eutectic solution of ammonium chloride, which had a melting point of minus 15C.

"For the freezer application, the objective was not to save energy but improve food storage especially in placed where regular power cut is experienced," Dr Farid said.

"However, in New Zealand cost saving will be related to being able not to use electricity when it is expensive."

Based on New Zealand electricity rates, savings of up to 16.5 per cent and 62.64 per cent per day were achieved for the freezer and building applications respectively.

"The benefits of applying PCM in buildings is not limited to capturing day solar heat in winter and night coolness in summer but also to create peak load shifting," Dr Farid said.

"When you have PCM in the walls of your homes you could switch your heating or air-conditioning for extended period without having the indoor changing significantly.

"This means you could use electricity at low peak period reducing your electricity bills and contribute to levelling electricity peak load."

Because of its mild weather, PCM could be ideal for countries like New Zealand - and some modern buildings were already benefiting from it.

But there was some way to go yet before it could become accessible to most people, he said.

"The cost of PCM needs to be reduced - and it must be used wisely to make it economical."

His findings have been published in the journal Energy.