Design Strategies for an Effective Implementation of Solar Harvesting Façades into Pre-Existing HVAC Systems in Buildings Renovation

Building renovation plays a key role on the path to low-carbon economy, yet the increasing complexity and cost of decarbonization strategies to reach nearly zero-energy buildings (NZEB) is a major challenge that hinders the potential of retrofitting the existing building stock. Multifunctional façade solutions appear as a feasible solution on this regard. This paper presents a novel methodology conceived to serve as a standardized approach for an effective implementation of solar harvesting-multifunctional façades into pre-existing HVAC systems in buildings renovation. The design strategies presented consider users' needs, different renovation scenarios and operation possibilities while ensuring an optimal use of renewable energy sources. The methodology is supported on building simulation and applied to a real case study, including pre-sizing and evaluation of different configurations to optimize the solar production and the thermal storage. The work shows a number of constraints and limitations that must be effectively addressed, ensuring the user's needs as well as the efficient operation of all systems, both existing and new. Main constrains encountered on the integration process are building geometry, user priorities, and the pre-existence of an HVAC system, being a central thermal storage system selected as the preferred solution for the integration with the pre-existing installation while optimizing solar fraction through an adequate building management strategy. The methodology is successfully applied in a demo-case on Tartu, demonstrating the capacity for integrating the solutions on existing HVAC configuration, with a potential reduction of up to 21 tons of annual GHG emissions.