The Mean Heat Transmission Coefficient as a New Parameter to Control Heat Transmission and Mold Growth in Building Refurbishment

In refurbishment of existing buildings energy need reduction and avoiding mold growth risks are very important. Heat transfer by transmission and ventilation can be minimized acting on the building envelope energy need. Since ventilation of existing buildings is generally natural, the simple widespread action of changing windows determines a better insulation, but the lower "involuntary" ventilation due to better airtight increases the risk of mold growth. The purpose of the present paper is to research possible values for a unified parameter which can, at the same time, take into account both energy consumption reduction needs and mold growth risk. The evaluation method follows the methodology indicated in European Union technical rules, integrated and developed by the authors with superficial mold grow risk and steady state heat transfer theories applied to buildings. The discussion aims to determinate a possible range of values for the mean heat transmission coefficient in order to satisfy both goals to increase energy saving and, meanwhile, avoid mold growth. The present application case study pertains to insulation actions in existing buildings, made step by step according to maintenance plans, which regard from 25% to 100% of the whole exchange surface and are carried out over some years.