Theses for Architecture and Sustainable Built Environment

Permanent URI for this collection

https://bspace.buid.ac.ae/handle/1234/1178

Browse

Browsing Theses for Architecture and Sustainable Built Environment by Subject "energy consumption"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Heating, Ventilation and Air Conditioning Multivariable Control System with Least Energy Dissipation
    (The British University in Dubai (BUiD), 2019-03) Touqan, Basim
    The highest energy consumption in building sector is caused by building's services such as lighting units and thermal comfort systems. Heated Ventilated Air Conditioning (HVAC) system consumes approximately 50% of the total building energy bill. Many measures have been proposed to achieve energy efficient buildings. Accurate HVAC mathematical models, as well as suitable HVAC control system that leads to optimised energy consumption and improved system performance are part of the engineering efforts to achieve greater efficiency. This study is part of such engineering efforts. It concentrates on employing a ready developed reliable HVAC system mathematical model, namely hybrid distributed-lumped parameter model which handles HVAC as spatially and dimensional dispersed systems for specific HVAC components such as ventilated volume. Other components, such as fan motors, inlet and exit impedances, have physical properties that treated as concentrated lumped mass elements without compromising on the accuracy. Applying an appropriate automatic control strategy to achieve improved HVAC system performance associated with least control energy consumption is one of the major research objectives. This objective has been achieved by adopting and applying a multivariable Least Effort (LE) control technique to regulate a multivariable three inputs-three outputs HVAC system model that employs output feedback, passive compensators and proportional gains, avoiding employment of active integrators. Direct Nyquist Array (DNA), as an alternative multivariable control technique, was employed to compare with the LE performance in terms of system performance and proportional control energy cost. Contrasting the straightforward procedure used to decouple the interaction between the outputs in the LE controller, the identification of decoupling matrix in the DNA controller was based on a trial and error approach, which was very time consuming. After decoupling the plant transfer function matrix, the DNA controller was able to regulate and control the HVAC multivariable system based on using PID loop control, but on the price of consuming higher proportional control energy cost which contravenes with global efforts to minimize energy consumption inside buildings. The ratios of proportional control energy cost between LE and DNA at the time 900 seconds following disturbance unity changes on the system outputs are , and for three different disturbance scenarios. LE controller has shown also better system performance than DNA which at the end makes it superior to the DNA control solution based on the consideration of the simplicity of each controller, the system behaviour under closed loop control and the control energy dissipation.
  • Thumbnail Image
    Item
    Urban Geometry: The Effect of Height Diversity and Buildings Configuration on Thermal Performance and Cooling Load at Urban Scale. A Case Study in Dubai / UAE
    (The British University in Dubai (BUiD), 2018-05) SHAREEF, SUNDUS LUAY
    Urban geometry and buildings morphology are important factors that affect both thermal behaviour of the spatial environment as well as a building’s energy performance. This research aims to explore the effect of the urban block with different building configurations on energy performance at the urban level. For this aim, a literature review was conducted to identify the previous and recent studies relevant to this research topic. It has been proven that the compactness element is a key urban geometry variable that controls the desired thermal performance of the built environment in hot climates. However, the previous studies have primarily focused on traditional methods of increasing the shading effect, such as by increasing buildings height / canyon width H/W ratio to provide the required compactness for desired solar access and energy saving target. This research attempts to provide alternative methods to achieving the required compactness and increase the shading effect by adapting building height variations and configurations in urban block design. As observed in the previous literature, the energy consumption assessment and the strategies that can be adopted to reduce this consumption are generally implemented and evaluated on the scale of individual buildings. Therefore, further investigation of both the diversity in building heights and the effect of this on the energy performance, and the evaluation of the energy consumption at the urban scale is required to fill the gap identified in previous literatures. This study utilised two software packages to simulate a base case urban configuration and evaluate this case against the proposed suggested scenarios of different configurations. The proposed scenarios depending on the urban configuration sustainable strategies were implemented and simulated to find the effect of adopting these strategies on the building’s total energy performance within the case study area, i.e., the Dubai / UAE local context and weather characteristics. Three groups with 56 proposed scenarios were simulated, where in different ratios of building height variation were implemented in the first two groups, and different building configurations were adopted for the third group. The research found that a significant variation in building height reduces the cooling load more than a gradual height variation, and consequently offers more energy saving. The variation along the short direction of the urban block has a greater positive effect and the saving in cooling energy consumption reaches 4.6 %. The significant variation in building height along the short axis of the urban block provides more shading to the canyons and the adjacent buildings compared to the base case. This over shading reduces the air temperature by 1.1 ͦ C within the canyon and directly reduces the conduction heat gain through the buildings envelop. This is in addition to the other effect represented by reducing the direct solar access to the building surfaces and decreases the solar energy gained by the buildings envelop through direct radiation. Furthermore, building orientation plays a significant role in the thermal performance of the urban block, and it contributes to the total cooling load energy saving of the urban block by 6.6 % at the peak time of cooling demand. Moreover, the research found that the variation in building heights will increase the wind velocity by up to 23 %, and this improvement in air flow affects the outdoor air temperature positively. This positive effect of the height variation on the outdoor air temperature of the urban canyons reduces the conduction heat gain through the buildings envelop by 4 %, and consequently reduces the energy required for cooling purpose. In addition, the alternative arrangement of the buildings within the block is another geometrical variable that affects the thermal performance of the built environment. It has been found that the alternative, or stagger arrangement, provides more shading effect on both canyon and building surfaces. However, this arrangement reduces the wind speed due to the obstruction created by the buildings mass and decreases the air velocity in the canyons. On the other hand, this type of configuration improves the distribution of the air around the buildings block and consequently enhances the outdoor thermal comfort around most of the buildings within the urban block. The reduction of 1.9 ͦ C in outdoor air temperature, and 4.9 % in cooling load is achieved by increasing the H/W ratio of the main canyons from 0.96 to 1.2. Therefore, designing the urban block with a significant diversity in building heights, or gradual height variation will have the potential of a shading effect and wind speed increase to enhance the thermal performance of the urban block. Finally, adopting the rectangular shape of the urban block, creating diversity in building heights and alternative building morphology are some of passive urban design strategies that can be followed for the optimised urban block configuration, with high efficient morphology and less environmental impact. This prototype is recommended for the new urban development in the UAE and other areas of the same climate zone.