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Building energy efficiency scope
The building is a complicated system with massive different components. The building energy efficiency potentials can be identified from many of the building components. Taking residential building as an example. A set of building components pertaining to different functionalities and manifesting energy efficiency potentials are illustrated in Fig. 1.1.
Some components pertain to the power generation. Apart from the main grid power supply, several supplementary power supply or renewable energy resources can be incorporated into the building system, e.g., the diesel generator, fuel cell, photovoltaic (PV) system, wind generator, biomass, etc.
The supplementary power supplies improve the cost effectiveness and reliability subject to the occupant energy demands and energy prices. For example, in South Africa, the time-of-use (TOU) tariffs are applied by Eskom. Consequently, the scheduling of alternative power sources result in the improvement of cost effectiveness [3]. Furthermore, in South Africa, off-grid applications are required in the rural sites, where the combination of several supplementary power supplies including the battery system are implemented [4]. Although the battery storage system is too expensive to provide full supply back up at the current stage, it is however the most effective and promising solution at present to improve the supply reliability against the risk of main grid failures and intermittent renewable energy sources.
A recent article [5] introduces a trend of rapidly falling costs of battery packs for electric vehicles. There is a reason to believe that the battery systems can become affordable component for domestic buildings.
The building materials and envelope comprise another important category of components. The building envelope delivers a significant impact to the energy consumptions of building heating ventilation and air conditioning (HVAC) system. A large proportion of the HVAC system workload comes from the heat transmission between the interior and exterior of the building. The transmission rate is greatly influenced by the building materials and envelope, e.g., the insulations and windows. Improving building materials and envelope can reduce the building HVAC system workload and corresponding energy consumptions [6]. In this way, the materials and envelope also influence the occupant thermal comfort [7, 8, 9]. Some building envelop studies also take into account the building orientation [10, 11, 12] and corporate with the geographic information system (GIS) platform [13, 14]. The orientation of the building can be taken into account to maximise the effectiveness of heating and PV generation. The GIS platform provides further energy efficiency opportunities via the ‘geospatial awareness’, i.e., the integration of energy and GIS modelling. The geographic information is incorporated into the building modelling and data analysis and energy optimisation. Thereafter, the building envelop design can be assisted by the GIS platform to better identify the impacts to building energy efficiency. In summary, although the building materials and envelope do not consume any energy, they still manifest significant energy efficiency potentials.
The appliances are energy-consuming components pertaining to various functionalities and energy efficiency opportunities. Generally, we categorise the appliances into four classes according to the functionalities: the lighting, HVAC, water heating and plug devices. The existing studies reveal that appliance energy efficiency can be improved from developing more energy-efficient equipment. For example, with the development of lighting technologies, new efficient lamps have been developed, e.g., the compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs). Significant energy savings can be achieved by replacing inefficient lamps with efficient ones [15, 16]. Similar strategies can be applied to the water heaters. The inefficient resistive element water heaters can be replaced with the heat pump water heaters, which are identified to have approximately two thirds less consumption [17].
The plug devices, e.g., the TV, refrigerator and microwave oven can be replaced with efficient ones with high energy rating as well. Apart from developing efficient equipment, employing advanced control strategies can also improve the appliance energy efficiency. A series of studies where energy efficiency control strategies are employed to facilitate the air conditioner energy efficiency can be found from [18, 19, 20].
Further building energy efficiency can be achieved by incorporating the water energy nexus, which is receiving increasing attentions [21]. The water-energy nexus brings a series of direct and indirect benefits to the domestic dwellers, including the water savings, energy savings from water purification, utility pumping and carbon emission reduction [22]. Given that South Africa is a water-scarce country, the energy efficiency impact from water-energy nexus deserves more attention.
One or several aforementioned components can comprise a subsystem in buildings, which provides additional and enhanced functionality to the building. Many such subsystems can be identified in the building context, each brings in a number of energy efficiency opportunities. For example, an air conditioning system comprises a subsystem in the building that adjusts the indoor thermal comfort, where the control of the air conditioner components bring in energy efficiency potentials; several supplementary power sources can also comprise a subsystem that increases the reliability and costeffectiveness of the power supply, where the energy balancing offers additional energy efficiency opportunities; the supplementary power sources and appliances, e.g., the heat pump water heater, can be combined to simultaneously take into account the supply side and demand side energy efficiency.
These subsystems define the scope of building energy efficiency, and the subsystem modelling is the foundation of building energy efficiency studies. Various studies have been conducted with focuses on different subsystems, where massive energy efficiency issues have been identified. These energy efficiency issues involve different time scales, from ms level to year level, due to different focused subsystems. According to the multiple time scales, we categorise the energy efficiency opportunities into four levels. A hierarchical building energy efficiency framework is thereby proposed.
Hierarchical building energy efficiency framework
There are four layers in the building energy efficiency framework, including the power electronics layer, smart appliance layer, energy flow layer and planning layer. Each layer corresponds to a different subsystem category and energy efficiency perspective. Generally, the four layers are distinguished by the following criteria. The power electronics layer involves energy optimisations that focus on maintaining and improving the power quality where the control intervals can be very small, e.g., several ms . The smart appliance layer involves bringing energy efficiency intelligence to the appliances, where the control intervals range from a few minutes to half an hour. The energy flow layer involves energy balances for grid-connected or off-grid systems that aim at different objectives, where the control intervals are often several hours. The planning layer involves organising and managing an energy efficiency project with limited capital investment and manpower. The decisions are made via evaluating performances over a long time period, e.g., 5-10 years. More detailed explanations are introduced as following:
The power electronics layer pays attention to maintain the power quality, i.e., the electricity quality in buildings. Specifically, a satisfying power quality can be characterised as a power supply with 1) steady voltage within a predefined range; 2) steady alternating current (A.C) frequency and 3) smooth voltage curve waveform [23]. The power quality is a traditional topic for the power system, as low quality power supply, e.g., unstable voltage or A.C frequency can damage the equipment, including the power generator, power consumer and power line. According to the definition, the major concerns of maintaining power quality is the voltage, frequency and AC phase [24]. From the energy efficiency viewpoint, the power quality also plays an important role. This is because the damaged equipment results in deterioration of energy efficiency. For example, the lighting, air conditioner and refrigerator are the most common appliances in domestic environment. If the power quality cannot sustain, these equipment can either consume more energy or become malfunctioning, i.e., the energy performances deteriorate due to the worse working state. In this way, the power quality is essential to building energy efficiency. In South Africa, the power quality is generally well maintained, however the capacity of the main grid is not very satisfying comparing with the growing demands. In 2014 and 2015, a major coal supply incident in South Africa resulted in continuous load shedding: Eskom shed load for the first time in six years for 14 hours on 6 March 2014, and three more load shedding events occurred during June 2014 due to multiple unit trips, as well as a constrained power system in meeting demand [25]. The shortage of supply capacity encouraged the deployment of supplementary power supplies such as renewable energy facilities, especially in the rural sites [4]. As a result, new power quality challenges are brought in. Firstly, the electricity generated from supplementary power supplies, especially from the renewable energy sources, must be processed to meet the service level power quality requirement. Secondly, for grid-tied systems, the generated electricity must further meet the power quality standard from the grid. Given the distributed nature of the renewable energy system, additional building energy efficiency opportunities are revealed at the power electronics layer. In domestic context, the inverter is the main method to adjust the power quality. A number of studies have been conducted with the focus on inverter control. Abo-Al-Ez et al. [26] proposes the design of a dual-loop model predictive controller for voltage source inverter operation in smart microgrids. Liu et al. [27] proposes a control strategy for microgrid inverters based on adaptive three-order sliding mode and optimised droop controls. Wilson et al. [28] proposes a non-linear power flow control design that regulates renewable energy sources, loads and identifies energy storage requirements for an AC inverter based microgrid system. Mokgonyana et al. [29] investigates daily volt/var control in distributed networks, where the proposed approach determines the most suitable substation secondary bus reference voltage and dispatch sequences to minimise daily voltage deviations and total loss over 24h. There are many other studies contributing to similar topics [30, 31, 32, 33]. The switch interval of inverters can be as small as ms level and control actions usually take place every hundreds of ms. Such intervals are much smaller than the control problems at the other layers.
CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW
1.1 BACKGROUND
1.2 BUILDING ENERGY EFFICIENCY FRAMEWORK
1.3 ENERGY RETROFITTING IN BUILDINGS: STATE OF THE ART
1.4 A CONTROL SYSTEM FRAMEWORK
1.5 RESEARCH CONTRIBUTIONS AND LAYOUT OF THE DISSERTATION
CHAPTER 2 OPTIMAL RETROFITTING PLANNING WITH LIFE-CYCLE COST ANALYSIS
2.1 INTRODUCTION
2.2 MULTI-OBJECTIVE OPTIMISATION MODELLING
2.3 RESULTS AND ANALYSIS
2.4 CONCLUSION
CHAPTER 3 MAINTENANCE PLAN OPTIMISATION
3.1 INTRODUCTION
3.2 MULTI-OBJECTIVE BRCMP
3.3 CONTROL SYSTEM APPROACH WITH UNCERTAINTIES
3.4 SIMULATION AND VERIFICATION
3.5 CONCLUSION
CHAPTER 4 MAINTENANCE PLANNING WITH INTERACTING ENERGY EFFECTS
4.1 INTRODUCTION
4.2 PROBLEM FORMULATION
4.3 SIMULATION AND VERIFICATION
4.4 CONCLUSION
CHAPTER 5 MULTI-STATE BASED MAINTENANCE PLAN OPTIMISATION
5.1 INTRODUCTION
5.2 CONTROL SYSTEM MODELLING
5.3 CONTROLLER DESIGN
5.4 SIMULATION AND VERIFICATION
5.5 CONCLUSION
CHAPTER 6 MAINTENANCE INSTANTS AND INTENSITIES OPTIMISATION
6.1 INTRODUCTION
6.2 Control Problem Formulation
6.3 Simulation and Analysis
6.4 CONCLUSIONS AND FUTURE WORKS
CHAPTER 7 GROUPING ROBUSTNESS ANALYSIS
7.1 INTRODUCTION
7.2 Mathematical description of item grouping
7.3 Robustness of grouping in building retrofitting context
7.4 Conclusion
CHAPTER 8 CONCLUSION AND FUTUREWORKS
8.1 CONCLUSIONS
8.2 FUTURE WORKS
REFERENCES
