Building conversations up with Pär Johansson

BUILDING CONVERSATIONS UP WITH...Pär Johansson, Associate Professor, Building Technology, Architecture and Civil Engineering (Chalmers University of Technology).
In this interview, we continue to dig into the important topic of sustainable cooling solutions, exploring how cooling can be integrated into buildings, what the latest developments in research into thermal storage are, phase change materials, and more... 

“The benefit of using latent thermal energy storage is the reduced volume and stable temperature from these materials during the phase transition” 

BUILD UP (BUP): How can cooling be integrated in buildings and how can it be optimised? 

Pär Johansson (PJ): Either small-scale decentralised thermal storage or large-scale centralised storage systems are possible. We have studied both options and found that the optimal solution is very much up to the system setup and the local conditions, such as available energy production and the local price scheme. In areas with district cooling available, centralised storage solutions are often beneficial over decentralised storage solutions. However, this is governed by the local price model for the district energy network. In areas where the cost of peak cooling power is high, decentralised storage becomes economically viable. The cost-benefit of these options, and many more parameters, was studied in the recent dissertation by Yichi Zhang.  

BUP: What materials could be used for thermal storage? What are the latest developments in research? 

PJ: The most used material is water in the tanks used for hot water storage. There are huge research efforts spent on different materials for latent thermal storage. The benefit of using latent thermal energy storage is the reduced volume and stable temperature from these materials during the phase transition. Ice storage is used for commercial purposes to store thermal energy at low temperatures. For higher temperatures, different phase change materials are being investigated. The most promising are different mixtures of eutectic solutions based on salts that can be optimised for different system temperatures.  

BUP: What are the benefits of thermal energy storage for cooling district networks? 

PJ: There is often a mismatch between the production of thermal energy and the demand in the system. In these cases, the thermal energy storage evens out the variations that would be needed at the production plant to reduce the design size of the production plant and distribution network. This can be done on different time scales, from hours, days, up to yearly variations, depending on the size of the storage. With the present increased variable renewable energy sources in the system, this demand is foreseen to increase.  

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