Thermally activated building systems (TABS): Energy efficiency as a function of control strategy, hydronic circuit topology and (cold) generation system

By integrating the building structure as thermal energy storage into the building services concept, thermally activated building systems (TABS) have proven to be economically viable for the heating and cooling of buildings. Having already developed an integrated design method and various control concepts in the past, in the present paper the impact of different aspects of TABS regarding the energetic performance of such systems is analyzed. Based on a simulation case study for a typical Central European office building, the following conclusions can be drawn. The energy efficiency of TABS is significantly influenced by the hydronic circuit topology used. With separate zone return pipes energy savings of approximately 15–25 kW h/m2 a, or 20–30% of heating as well as cooling demand, can be achieved, compared to common zone return pipes, where energy losses occur due to mixing of return water. A strong impact on energy efficiency can also be observed for the control strategy. Thus, by intermittent operation of the system using pulse width modulation control (PWM), the electricity demand for the water circulation pumps can be reduced by more than 50% compared to continuous operation. Concerning cold generation for TABS, it is shown that free cooling with a wet cooling tower is most efficient, if the cold source is the outside air. Variants with mechanical chillers exhibit 30–50% higher electricity demands for cold generation and distribution, even though their runtimes are much shorter compared to the cooling tower runtimes. In conclusion, the results show that significant energy savings can be achieved using adapted system topologies and applying appropriate control solutions for TABS.