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High-Temperature Cooling Systems for Sustainable Buildings Using Geothermal Energy

Holistic Assessment in the Mediterranean Climate

Time: Mon 2023-06-12 13.00

Location: D3, Lindstedtsvägen 5, Stockholm

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Language: English

Subject area: Civil and Architectural Engineering, Fluid and Climate Theory

Doctoral student: Henrikki Pieskä , Hållbara byggnader

Opponent: Professor Ambrose Dodoo, Linnéuniversitetet

Supervisor: Professor Johan Silfwerbrand, Betongbyggnad; Docent Adnan Ploskic, Byggteknik och design; PhD Qian Wang, Byggteknik och design; Professor emeritus Sture Holmberg, ; Docent Sasan Sadrizadeh, Byggteknik och design

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QC 20230522


Sustainable development is increasing its significance in both the scientific and political agenda. In light of this development, the United Nations have published 17 Sustainable development goals (SDGs). The SDGs relate to all aspects of sustainable development, the most significant for this thesis being energy decarbonisation and sustainable industry.

Space cooling is increasing in significance globally, on the one hand because of a global rise in temperatures due to climate change, on the other hand because of the rising living standards in developing countries mean more people will have access to cooling. Cooling has been linked to all 17 SDGs, and affects not only energy use but also health, well-being and productivity. Radiant cooling is gaining popularity as an alternative for conventional, air-based cooling systems. The main advantages of radiant cooling are lower energy requirement for transportation and the ability to use low-grade renewable energy resources such as geothermal cooling.

Building retrofitting is also a significant topic in sustainable development. Currently, while 75% of buildings in European Union (EU) are inefficient according to current building standards, 85-95% of these buildings are still predicted to be in use in 2050. This means retrofitting existing buildings to improve their energy efficiency is vital for reducing the EU's greenhouse gas emissions. Most of the work presented in this thesis relates to a European research project, Geofit, which sought to make retrofitting buildings with geothermal heating and cooling systems viable and cost-effective. Most of the work was done using building energy modelling, and focused on one of the project's pilot sites, in Sant Cugat, Spain. The pilot was selected for showcasing the potential of an innovative high-temperature radiant cooling system, supplied with geothermal energy.

The results showed that retrofitting the building with the radiant cooling system would achieve significant benefits in thermal comfort, reducing the highest temperature reached during the cooling season from 32 °C to 27.9 °C. The fraction of the cooling season, when indoor temperature exceeds 26 °C was reduced from 83% to 23%. The results also show that the radiant cooling system can achieve this improvement with higher efficiency and lower environmental impact than a conventional all-air cooling system.

It should be noted that in the hot and humid climate of Spain, the radiant cooling system has to contend with the risk of water condensing on the surfaces of the cooling panels. This risk can be mitigated in two ways: limiting the system's cooling capacity or dehumidifying the air entering the building. Limiting the cooling capacity leads to thermal discomfort, while dehumidification approximately doubles the system energy use. Therefore, the needs and requirements of the retrofit case need to be carefully evaluated and balanced when planning a retrofit project.