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

BCIT Thesis and other Required Graduate Degree Works

Assessment of natural ventilation design and efficacy in a net-zero energy house
Achieving acceptable indoor environmental quality and thermal comfort in buildings can be difficult without relying on energy intensive mechanical equipment. When the climate conditions permit, natural ventilation could potentially help minimize the reliance on mechanically conditioned air; however, natural ventilation is rarely engineered. Houses are typically designed as fully enclosed climate systems in which the connection with the outdoor environment is rarely planned. Unlike in commercial or specialized buildings, houses are not designed with many energy conservation measures in mind. Reconnecting them with the outdoors has a great potential to increase thermal comfort and reduce reliance on mechanical systems. With such a connection to the dynamic weather conditions of the outdoors, it is difficult for architects to choose beneficial design elements to be included in the construction of their houses. Knowing which elements work and to what extent under particular conditions can potentially achieve increased thermal comfort using little or no energy. This research aims to offer a thorough assessment of a case study house and determine the effects of the design choices made by the architect of the house. This research may help architects know the risk factors affecting natural ventilation design in a systematic manner; and in doing so, enable quantifying the benefits of natural ventilation to meet the design goals of maintaining satisfactory indoor conditions without the use of air conditioning, particularly in the summer. A constructed net-zero case study house located in the Pacific marine climate of Canada was used to develop the proposed research. The house had been designed by an architect to rely solely on natural ventilation for cooling during the summer and much of the spring and fall. The house was instrumented and its indoor environment was monitored for a period of several months in 2014 to collect data to evaluate the effectiveness of design choices made, including the effect of a large atrium and the air flow characteristics of the windows intended by the architect to deliver most of the ventilation. Recorded data showed the house performed commendably and this was confirmed through evidence from the home owners. To aid in the understanding of the dynamics of the Harmony House, whole-building, multizone air flow network modeling and computational fluid dynamics (CFD) modeling of the house was developed and calibrated with monitored data and testing. The models were used to assess the indoor air quality and further quantify the natural ventilation of the house, as well as test hypothetical situations that were once considered for the house. Simulations revealed some additional insight into the design choices that were implemented in the house and showed that further technologies intended to increase ventilation were unnecessary and some instead, reduced ventilation through the house.
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.