بهینه سازی عملکرد سیستم تهویه کنترل شده تقاضا توسط نظارت بلند مدت Performance optimization of a demand controlled ventilation system by long term monitoring

1. Introduction In the recent past the environmental emergencies focused the efforts towards the fundamental goal to achieve NZEB condition especially in the refurbishment of existing building. But nowadays, the necessity to combine energy saving with the increasing interest for better indoor comfort and air quality is become a very relevant topic [1,2]. In Europe, people stay in indoor environments about 90% of the day [3]. Air pollution has such a concentration in indoor environments that causes adverse health effects especially in case of long exposure periods as shown in [4] and [5]. Indoor air quality (IAQ) is an important public health problem causing social and economic consequences as proved in [6,7]. This is especially true in school buildings [8]. As a consequence standards about IAQ have become increasingly strict [9], corresponding to higher ventilation flow rates. [10]. On the other hand in modern buildings the envelope is highly insulated and airtight, thus leading to the reduction of natural ventilation flow rates [11]. Therefore the use of mechanical ventilation, ensuring appropriate air change rates, is spreading. Consequently the energy demand for ventilation air handling grows and often becomes the prevailing share in the total energy ∗ Corresponding author. E-mail address: luigi.schibuola@iuav.it (L. Schibuola). required by heating, ventilation and air conditioning (HVAC) systems [12]. Therefore, especially in buildings characterized by highly variable attendance as in the case of educational buildings considered in this study, a precise information about the actual occupancy patterns permits to elaborate ventilation strategies [13] and operational tools [14] to achieve significant energy savings. The exigency to optimize energy requirement for ventilation becomes even more strategic in the case of historical buildings subject to preservation order. Here the impossibility to modify the envelope obliges the designer to reduce energy consumption by focusing on ventilation and HVAC system management in order to achieve an energy saving retrofit . Otherwise the refurbishment of historical buildings for modern uses would be difficult to accept in terms of energy consumption and operating cost [15–17]. Therefore, a suitable building management system (BMS) becomes fundamental to achieve the lowest energy consumption without compromising indoor comfort conditions, as noted in [18] and [19], especially when operating by means of demand controlled ventilation (DCV) [20]. In particular, CO2-based DCV [21] may enable easy real time adaption to current occupancy especially when characterized by strong variability, as proved in [22–24]. In this context, this paper focuses on the new potentialities offered by modern BMS today easily able to collect a great data flow for long periods to help energy/facility managers to redesign strategies in each application case. Adopting a case study approach, this study investigates the ability of this method to individuate specific shortcomings in a DCV system and to resolve them by simple tuning actions usually undervalued in traditional HVAC control system. In detail, the paper treats the actual issue of the optimization of ventilation systems [25] by using the approach of the demand side management (DSM) [26–28]. In this case by CO2-based DCV and satisfaction index evaluation with a particular care to the possibility of a performance improvement by using long term monitoring to optimize control parameters The outcomes are based on a monitoring campaign carried on in the context of the energy retrofit of an historical building in Venice. The acquired experimental data allowed the authors to optimize the use of the DCV system by: i) analysis of the operative mode, ii) control performance verification and consequent tuning intervention, iii) test of more flexible humidity control strategies by assessing the effect on energy demand of different set points, both in winter and summer. In spite of its potentiality, this technique is still poorly used in practice, because it lacks of experimental verifications in different application contexts. In this scenario a case study is here presented to provide a contribution to spread awareness of the advantages resulting from its systematic application.