BCIT Thesis and other Required Graduate Degree Works | BCIT Institutional Repository

BCIT Thesis and other Required Graduate Degree Works

Assessment of natural ventilation using whole building simulation methodological framework
Natural ventilation is a passive alternative to provide both indoor air quality and thermal comfort for the building’s occupants with low energy use. But at the same time, it is challenging for the building designers to implement natural ventilation strategies due to its complexity and highly dynamic behaviour, especially when it is compared with the mechanically ventilated buildings. Nevertheless, the use of naturally ventilated buildings is increasing along with the use of passive strategies, but depending on the complexity of the project, the designer still use rules of thumb for the implementation of natural ventilation strategies instead of a more comprehensive simulation-based approach. In theory, whole building simulation models (WBSM) are becoming viable tools to support natural ventilation design, particularly in the early stages of the project where the impacts of measures to implement a natural ventilation strategy are magnified. However, the only “evidence” of such level of support comes from individual case-study projects. Nevertheless, there is a lack of validation through measurement of the effectiveness of natural ventilation design in real buildings. This research will shed light into the “inner-workings” of natural ventilation models in WBSM to answer fundamental questions such as the following: How is wind data processed? How are envelope openings characterized? How are internal openings modelled? When and how is air buoyancy modelled in spaces? How are the coupled thermal and fluid mass transfers modelled to reflect the dynamic thermal responses of constructions and airflows? Therefore, a methodological framework is developed in order to provide the necessary knowledge for natural ventilation assessment. This framework is based on simulation (WBSM) and field testing. The proposed framework is tested in an existing landmark building in Vancouver. A WBSM of that building is developed, calibrated, and used to analyze how different factors that compose an integrated natural ventilation strategy (like the building shape, window shading, thermal mass, indoor spaces functionality and connectivity, and local climate) influence the thermal comfort of its occupants., Natural ventilation, Thermal comfort, Adaptive model, Whole building simulation models (WBSM)
Model-based coupling of air and hydronic system operation in a high performance academic building
This research is motivated from preliminary teamwork on analyzing the “Performance Gap” of three high-performance buildings, which are currently under operation. All three buildings are facing operational challenges that are not unusual considering the complexity of their systems. However, evidence from design documents, an existing energy model, and operational data suggests that their performance is not entirely reflecting the design intent. This research follows the premise that there is a need to design buildings as systems-of-systems to be able to understand, interpret, quantify, design, and fine-tune the dynamic couplings between systems. This research was dedicated to a high-performance academic building (HPAB) – one of the above three buildings – as a case-study to gain understanding on the complexities of systems coupling, and learn and apply dynamic simulation-based systems coupling tools and methods. The main focus of the study is the classrooms because of the existing evidence on the significant impact of indoor environmental comfort on student performance in academic facilities. The HPAB case-study building incorporates, at the source side, ground-coupled water-to-water heat pumps (WWHP) and solar-thermal as primary means of heating, with boiler used as a backup source. Cooling is provided by the cold side of the WWHP system. On the demand side, heating and cooling are delivered via thermally active radiant floors; while air handling systems take care of the ventilation and de/humidification needs, and provide supplementary heating and cooling. The building was initially designed to rely on natural ventilation for summer cooling; however, designers realized that natural ventilation alone was not able to meet the building cooling demands in the summer. Nevertheless, the building has operable windows and a central atrium that seems to be collecting the air from the individual spaces and exhausting it after some heat recovery. The thermally active building is not adequately meeting the demands from some critical zones. Furthermore, the operation is not consistent with the reduced hours of summer operation of an academic building. These and other observations on the building indicate that the air and radiant systems are not operating in synergy. Existing industry practices in building controls systems, and the research literature show limited evidence of efforts to attempt to harmonize these two complementary systems. Simulation was used to re-create the HPAB building’s mechanical system response in two levels: a classroom-level model, and a Whole Building Energy Model (WBEM). The implementation was in EnergyPlus modeling software. Design documents, and historic operational data from the building automation system (BAS) were used for calibration. In this work, various features of Energy Management System (EMS) module of EnergyPlus has been utilized to create a responsive mechanical system control within the simulation. In the end, the typical responses of the building spaces could be accurately recreated in the simulation for both models. In the next step, testing different controls approaches – labelled as Strategies – and comparing them with defined comfort and stability metrics showed that harmonizing the air and radiant systems, in addition to increasing the consistency of the radiant system operation, results in improvement to the system operation without sacrificing the comfort. This research explores the challenges of employing a WBEM to assist building design decisions by accounting for the building dynamics and enabling the coupling and tuning of systems parameters and control strategies through simulation. The research demonstrates the benefits of improved operational control sequences that are more in tune with the building’s design intent.