دانلود رایگان مقاله انگلیسی بهینه سازی عملکرد سیستم تهویه کنترل شده تقاضا توسط نظارت بلند مدت - الزویر 2018

abstract

The thermo-hygrometric treatment related to the air change in buildings requires a relevant quota of the total energy demand of HVAC systems, especially when the ventilation demand is significant. A correct energy saving strategy therefore should always focus on the use of suitable techniques to reduce this energy consumption. As proved by the modern theories on comfort, less strict values can be accepted for the internal humidity set points without compromising indoor comfort conditions. In addition, Demand Controlled Ventilation (DCV) gives the opportunity to reduce energy requirements. This paper investigates the opportunities offered by the installation of a DCV system and a Building Management System (BMS) able to perform long term monitoring of the HVAC system in a real case study. This refers to a historic building in Venice in the area of the harbour and recently transformed into a modern university facility. Starting from the experimental data recorded by BMS, an optimization of the control strategies and simple tuning actions of the DCV controller were possible. Results validate the use of more flexible set points of indoor relative humidity and long term on-line tuning even in absence of self-learning control systems, as well as they highlight the achievement of remarkable energy savings thanks to these actions. The research demonstrates the fundamental contribution of successive control performance assessments by long term monitoring to individuate possible weaknesses in DCV system management.

4. Conclusions

The real amount of energy savings achievable through suitable control strategies in a university facility was assessed by means of a long term monitoring. Simultaneously, the maintenance of adequate internal comfort conditions was verified. In detail, the measurements indicate as CO2-based DCV has provided a reduction in the energy requirement equal to 31% for thermal energy demand during winter period and 40% for fan electricity consumption compared with a traditional system with constant ventilation air flow rate. The reduction of ventilation air amount was 26%. Nevertheless, the experimental data also drew attention to the peculiarity of the control of the indoor CO2 concentration and the difficult achievement of a fine control. Maximum attention is required by an on-line specific tuning of the control system parameters to optimize DCV operation for each application case. Unlike the usual, control performance tests should be extended to the whole operation life of HVAC system. Monitoring results showed significant improvements even by simple interventions of manual tuning. The frequency of the overruns above 900 ppm limit for CO2 concentration was reduced under 2%.

Furthermore, the experimental analysis validates the possibility to combine DCV with a flexible humidity control strategy. Additional consistent reduction in energy demand regarding air treatment was assessed as a consequence of less strict humidity set points. During winter the latent energy requirement share was reduced from 46% to 14% of the total heat demand in the roof-top AHU South thanks to 35% RH set point instead of 50%. In summer 65% RH set point versus 50% permitted a cooling load reduction between 11% and 34% for the internal AHUs Therefore greater flexibility should be promoted more effectively against the widespread use of rigid design set points.