In order to better understand the real-life thermal performance of Solar domestic hot water (SDHW) systems, SDHW systems installed in dormitories in a university were selected for on-line monitoring. There are 50 dormitory buildings in this university, and each building contains around 430 students. A SDHW system is installed in each building, using the glass evacuated solar tube collector, with an average collector area of 260 m2 . Air source heat pumps are used as auxiliary heat sources in the collector side. All SDHW systems were equipped with data logging system and remotely monitored with online data. Thermal performance analysis and economic analysis of SDHW systems were presented in this paper. The results show that the thermal performance and economy of SDHW systems for dormitory buildings are very good because the domestic hot water demand of student dormitories is relatively concentrated in time and space. Therefore, SDHW systems has a good application prospect in dormitory buildings.
In this study, we aim to find an optimally sized battery that can be installed to an existing grid-tied solar home system without a prior energy storage system, in order to maximize the user’s financial benefits while maintaining reliable power supply to the home. To solve this optimization problem, we formulate the objective function as the net present value of the investment on the battery. Solution to the optimization problem returns the optimal battery size, power flows and battery age status during a 10-year evaluation period. In order to identify the most favorable solution to the user, we apply the proposed optimization algorithm to five typical photovoltaic (PV) generation and home load levels, and find that the optimal battery size is very sensitive to the level of PV power generation and the home load. In addition, it is more financially viable to have the battery when the daily PV power generation is less than the home load.
Energy consumption in cities can be a great environmental burden. Renewable energy and waste-to- energy technologies are promising methods to assist the transition of energy- and carbon-intensive urban environment towards low carbon cities. This study aims to investigate the economic and environmental feasibility of renewable energy and waste-to-energy technologies in cities for low carbon transition. Being a well-known city-state, Singapore is taken as an example for the case study. An optimization-based decision support framework is used to estimate the optimum energy mix that minimizes the greenhouse gas emissions of the urban energy system while meeting the energy demand of Singapore. It is found by incorporating solar PV and waste-to-energy facilities to the current natural gas dominating energy system, a 9-10% of renewable energy penetration is achievable in Singapore.
In order to reduce the impact of fouling on the efficiency of central air conditioning chillers, and thus improve the energy efficiency of buildings, we propose a new type of special online water treatment technology (SOWTT). The effects of SOWTT were evaluated by tracking and calculating the operating efficiency, annual electricity consumption, annual electricity expenditure, and carbon dioxide emission reduction of dozens of chillers in Xiamen. The results show that compared with the mechanical cleaning technology, the SOWTT not only reduces the annual power consumption of the refrigeration unit, but also increases the emission reduction of carbon dioxide. At the same time, the COP of the chiller is also greatly improved, and the comprehensive benefits are remarkable.
Bioenergy with carbon capture and storage (BECCS), as a negative emissions technology, plays an increasingly vital role in the low-carbon energy systems. Urban wastes are the fastest-growing bioenergy resources in recent years. This study aims to provide a high-resolution spatial assessment of GHG mitigation potentials for using urban wastes as the resource for BECCS in China towards 2030. For this evaluation, the domestic urban wastes potential in a 2017 baseline year and three waste to energy (WTE) processes are calculated and proposed. Results show that the collectable potential of urban wastes in 2017 was 1026.53 PJ and its utilizable potential would reach 2191.98 PJ in 2030. If this utilizable potential would be fully realized to displace fossil energy, approximately 151.82 Mt CO 2 e of GHG emissions could be reduced. Moreover, WTE process coupled with carbon capture and storage (WTE-CCS) would result in extra negative emissions of 1.83 Mt CO 2 e in 2030. Spatially, higher urban wastes potential leads to larger GHG mitigation potentials of WTE-CCS. Compared with less developed regions (e.g. Tibet, Qinghai and Ningxia), the regions with higher densities of population and economy activity (e.g. Guangdong, Jiangsu and Shandong) would have larger GHG mitigation potentials. Our study could provide geographically targeted information on the deployment of WTE-CCS in China.
Faced with ever-increasing environmental pollution and public concerns about energy security, urban energy systems (UESs) need to be constructed to improve the efficiency and reliability of energy utilization. However, due to significant impacts of extreme weather on the operation of UESs, it is important to develop a model to evaluate the resilience of UESs. In this paper, a synthetic model is proposed to quantify the impacts of windstorms on the resilience of UESs. Firstly, the optimization model of UESs under contingency states is developed to determine the generation re-dispatch and load shedding. Moreover, considering the effects of high winds, the line fragility model is utilized to calculate the unavailability of power lines according to the surrounding wind speeds. On the basis, the simulation framework for the resilience evaluation of UESs is developed utilizing Monte Carlo Simulation (MCS) technique to quantify the impacts of high winds on the UESs. Finally, the proposed methods are validated using the urban energy test systems.
natural gas system (IEGS), operating reserve and gas storage are both useful support to cope with contingencies in IEGS. This paper proposes a day-ahead SCUC model for the IEGS to schedule the operating reserve and gas storage simultaneously. The multi-state models for generating units and gas wells are firstly established. Based on the multi-state models, the expected unserved energy cost (EUEC) criterion is proposed based on probabilistic methods considering random failures of generating units and gas wells. Then, the EUEC criterion is incorporated into the day-ahead SCUC model, which is nonconvex and mathematically transformed into a solvable mixed integer linear programming (MILP) problem. The proposed model is studied using a 6-bus-6-node IEGS with natural gas storage.
A mathematical model has been developed to theoretically investigate the heat and moisture transfer between water and air in a hollow fiber membrane- based evaporative cooling module. We validated the model by comparing its outlet air dry bulb temperature and relative humidity against experimental data acquired from literature sources. The numerical model showed good agreement with the experimental findings with maximum discrepancy of 7%. The validated model was employed to investigate the influences of the inlet air velocity, inlet air dry-bulb temperature, inlet air relative humidity and geometric parameters on the cooling effect of the evaporative cooling module. The simulation results have been employed to propose optimization suggestions for the design of the hollow fiber membrane-based evaporative cooling module.
This paper proposes an investment model to analyze the economic feasibility of WtE projects in the Philippines. Applying the real options approach (ROA) under uncertainty, we compare the option values of investing in WtE technologies over continue dumping waste into the landfill. The optimization results find that incineration is the best option followed by gasification and pyrolysis considering the energy production, investment costs, and emission rates. At the current price of electricity, it is more optimal to postpone investment in pyrolysis, otherwise, the tipping should be increased to make pyrolysis a more viable option than continue the landfill. On the other hand, it is a more optimal decision to invest immediately in either incineration or gasification as waiting to invest incurs opportunity losses from generating electricity from these technologies. The paper suggests that the government must support WtE program as it will significantly contribute in solving the problems of the environment, particularly air quality, waste management, and energy security and sustainability.
Building layout is one of the most important factors of residential outdoor wind environment. Existing researches on the impact of building layout mainly focus on a certain layout or an actual case, which lacks comparisons and analysis of different typical models. Three typical residential models with different layouts are established in this paper. Based on the meteorological data in Shanghai, the influences of different layouts in different seasons are analyzed through the numerical simulation. The study helps to provide a reference for architecture design.