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Buildings are at the heart of climate change mitigation and the rational use of energy. Aalto University’s Energy-Efficient and Resilient Buildings research group is working with all its might to enable energy use to rely on clean and flexible solutions that create a good indoor environment.

With the increasing use of renewable energy, buildings are both producers and users of energy. Their many interconnected systems further link buildings to electricity end energy distribution networks.

“We examine a building and its energy systems from many angles, combining a wide range of skills. In a recent study, we optimised an innovative plate heat exchanger with a special structure that improves the efficiency of a conventional plate heat exchanger by up to 21.4%,” says Andrea Ferrantelli, Assistant Professor leading the team.

Plate heat exchangers are used in a wide range of applications where efficient heat transfer between two different fluids is required. They are vital components in applications such as domestic hot water heating, heat recovery from ventilation, geothermal installations and many industrial processes.

The subject of examination was a plate heat exchanger where the waxy paraffin between the metal plates changes its phase with thermal variations. Ferrantelli's collaborators had previously demonstrated that this type of compact PHETES  (plate heat exchanger with thermal energy storage) structure improves the energy storage capacity of the heat exchanger by as much as 75%.

“However, this heat exchanger is sensitive to its design values such as the thickness of the metal plates and of the phase change material (PCM) or the inlet water temperature. We carried out a comprehensive and complete optimisation analysis to determine the optimal design values for different configurations.

Part of the heat pump and energy system

The results of the study, published in the prestigious Journal of Energy Storage, can be used to design and optimise the operation of the innovative PHETES heat exchanger.

“The device achieves maximum efficiency with a metal sheet thickness of 11.1 mm, a PCM material thickness of 5 mm, an initial device temperature of 70 degrees Celsius and an inlet water temperature of 23 degrees Celsius. Maximising energy storage capacity or minimising process time, for example, will lead to different calculated values. The design is a balancing act on how to optimise the heat exchangers performance.”

The results are currently being used in a follow-up study where the PHETES heat exchanger is being transferred to a heat pump to be installed in a building. The experiments help to optimise the sizing and operation of the heat pump.

“We then plan to integrate the PHETES heat pump into a heating plant or, for example, a domestic hot water heating system. This will allow us to optimise its use as part of an energy-efficient and flexible energy system."

Business cooperation to accelerate the energy transition

Ferrantelli's research team works closely with companies and universities. There is a clear need for research and development, as buildings consume 40% of all energy and are also a major source of emissions. There is plenty to do as the European Green Deal aims to achieve carbon neutrality by 2050. EU countries are set to cut greenhouse gases by 55% by 2030.

"Finland has a lot of companies involved in the energy transition. For example, we’re investigating the use of walls as heat storages using PCM material, the orientation of double-sided solar panels near water bodies, and the use of waste heat from data centres in a district heating network connected to a geothermal network.”

Energy and its related phenomena have always fascinated Ferrantelli. He did his undergraduate studies in theoretical physics at the University of Turin and his thesis was on particle energy fields and supergravity. His postgraduate studies in cosmology brought him to Finland, and his doctoral research at the University of Helsinki focused on the energy of the dark matter that holds galaxies together.

“In my studies, I have learnt about the energy density of the universe. In my current job, I'm helping to ensure that we use clean energy in buildings as efficiently and sustainably as possible.”

"We’re developing solutions to mitigate climate change. It's great to train new people who can contribute to sustainable development through their work. In my group, there are many students from outside Europe who have come to Finland because they’re finding it difficult in their own countries. I'm happy to help them progress in their careers too.”

Text: Marjukka Puolakka