Pierre Hollmuller is a senior research scientist at the Energy Group, Institute of Environmental Science, University of Geneva. Over the years, he has carried out energy and economic analysis of in-situ innovative energy systems in the built environment. His international experience ranges from research and academia to consultancy and grass-roots NGO work. He has developed guidelines and thumb rules for engineers and architects that are widely used. For many years, his research has focused on the design and implementation of earth air tunnels for heating and cooling purposes. His work is based on diverse complementary approaches, such as monitoring and evaluation of real-scale installations, mathematical modeling, numerical simulation, and system analysis.