Novel thermally activated building system with bi-metal heat pipes as reinforcement for optimal passive heat transport

Heating and cooling of non-residential buildings account for a significant share of primary energy use in the European Union. Thus, reducing the ecological footprint of the building sector is vital to reach the European Green Deal. Thermally activated buildings systems (TABS) are widely used for cooling. In TABS coolant flows through long pipes integrated in concrete ceilings. This implies several limitations as e.g. coolant warm-up along the pipe resulting in temperature gradients at the ceiling‘s surface. This reduces thermal comfort and limits the maximum cooling capacity as the temperature should not drop below the dew point. Moreover, the length of the pipes introduces hydraulic resistances and the necessity of powerful circulation pumps. Furthermore, the pipes are commonly made of plastic, which increases the thermal resistance while lowering the cooling efficiency. Hence in this study, a novel concept is investigated where the hydronic piping system is replaced by highly efficient heat pipes to mitigate the aforementioned disadvantages. Heat pipes allow passive heat transfer at high transport rates and do not require circulation pumps. Additionally, they provide a uniform ceiling temperature increasing thermal comfort and cooling capacity. Already the prototype without any optimisations shows a very good equivalent heat transfer coefficient of 6.1 W m − 2 K − 1 . Another advantage of the novel system is the use of heat pipes for the load bearing capacity as concrete reinforcement. This reduces the overall material consumption and CO 2 footprint. Moreover, the study investigates an environmentally sustainable working fluid. The excellent performance is demonstrated in a full-scale experiment representing a two-person office.