Air conditioning is set to become the greatest domestic energy consumer in the world, as average temperatures rise and more demand is created in developing countries. Air conditioning demands power during peak hours, when electricity is most in demand and most expensive. At the same time renewable energy production is increasing, creating less predictability in power networks which will drive an increase in the system capacity. Ice slurry has been used in Japan for more than a decade to smooth energy demands for cooling of commercial buildings, now is the right time to be considering its inclusion in both domestic and commercial new builds. In December 2016, the energy institute of the Netherlands published a report into this, recommending the pursuit of more business cases and more materials.

Energy storage systems are nothing new and they are becoming increasingly important as fluctuations in energy supply and demand both become more sporadic. The first systems were designed for smoothing the supply of a nation, such as the hydro pumped storage in Dinorwig, Wales, which was designed to smooth out the demand as everyone in the UK makes a cup of tea during half time of the World Cup. More recently there has been a trend towards personal smoothing, the best known being Tesla’s Powerwall (a personal battery to smooth out domestic solar supplies). We blogged about this trend late last year, looking at kinetic and chemical methods; ice slurry provides a different approach. Freezing a water mixture can provide a high-density heat sink to store ‘cold’, at the same time as being almost infinitely scalable and potentially very low cost.

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Overnight or during low cost energy periods an ice bank is partially frozen, then the ice bank is used during warmer hours, when energy is more expensive, to cool a building. As well as the smoothing of energy peaks, this provides two other significant benefits. Firstly, moving slurry around a building is easier than moving refrigerants and more efficient than moving cold air. Secondly, cooling takes place at a higher temperature than for refrigerants which results in less dehumidifying. The slurry makes transport of the cold simple and efficient while the latent heat of the melting ice gives the slurry its extremely high energy density.

It isn’t all simple though. The system still needs refrigeration, and pulling energy out at ~0°C is less efficient than if the source is at a higher temperature. But the thermal contact with the source is much, much better. You also need a tank of slurry to facilitate storage capacity, increasing the space taken up by the system, also including a means of preventing stratification of the slurry, which will inevitably require a pump.

I recently visited the 12th Annual Phase Change Materials conference in Orford, Quebec and it was clear that there is a lot of existing expertise on implementations of many different materials and systems. Whether water is the right phase change material is not yet clear, but the benefits to a broader energy ecosystem are increasingly important. The dawn of domestic PCM air conditioning is coming!

Author
Roger Burton
Senior Consultant

Roger is an expert in multi-phase fluids handling systems, having lead development of multiple consumer and medical products. He specialises in the application of technologies with harsh requirements and the integration of multiple engineering and design disciplines.