In-situ assessment of a Multifunctional Compact System (MCS) in a low energy residential test facility: A comparative study

Abstract. The assessment of thermal comfort (TC) and indoor air quality (IAQ) is closely linked to the systems integrated into buildings that ensure these conditions. These systems are major energy consumers and striking a balance between indoor air quality (IAQ), thermal comfort, and energy savings is one of the objectives of this study. This study presents an in-situ experimental evaluation of a compact multifunctional system (MCS) that integrates heating, ventilation, cooling, and domestic hot water (DHW) production into a single unit intended for use in residential buildings to address these conflicting requirements. These preliminary tests focused solely on the ventilation mode of MCS. The MCS incorporates a dual-flow ventilation architecture with static heat exchangers. This study aims to make a comparative analysis between the MCS prototype and a conventional single-flow ventilation system. A fuzzy logic controller is designed to maintain a set temperature of 22°C while responding to peaks in CO2 concentration. A 15-minute CO2 injection phase and a 120-minute ventilation period, both with and without room heating. The results showed that the MCS prototype outperformed the conventional system in terms of IAQ and thermal stability. The MCS prototype ensured a stable indoor environment with an RMSE of only 2.69 °C, on the other hand the single-flow fan struggled to compensate for the infiltration of cold outside air, resulting in significant temperature oscillations and an RMSE of 6.56 °C. Additionally, the tracer gas decay analysis revealed that the MCS achieved a more efficient air change rate (ACH), returning CO2 levels to background concentrations faster than the reference system. The first experimental tests on the ventilation function of the MCS showed good results compared to conventional systems. In conclusion, the incorporation of a static heat exchanger has improved control algorithms such as fuzzy logic, offering a reliable way to maintain high IAQ standards in low-energy residential buildings without sacrificing thermal comfort. In future studies, we will evaluate the system, but this time by performing ventilation and heating and comparing the results with those of this study in order to characterize the MCS under study and propose optimizations for the design of this type of system.