Abstract

Urban building energy efficiency has been a focus on urban building layout design. To improve the urban energy saving, this study conducted a work by urban energy simulation through urban layout design. One campus-area building model and real energy datasets are applied to validate the different rule-based design strategies and their energy efficiencies. The results show that the design strategy with space coefficient of 0.8 and south low north high layout can save more energy of about 1.5% compared to original energy use.

Abstract

NH4-N-loaded steam-activated biochar (BC) is found to be a suitable candidate for soil amendment and fertilization. Compared with four other char-based sorbents, H2O-activated BC adsorbed the highest amount of NH4-N (1440 mgNH4−N. kgBC −1) sourced from a high nitrogen wastewater sample, and showed a limited desorption of 19.6 % under acidic conditions. In comparison, neat BC and activated carbon (AC) achieved lower adsorption capabilities, with theoretical maxima of 1028 mgNH4−N. kgBC −1 and 733 mgNH4−N. kgAC −1, respectively. While neat AC obtained a lower desorption of 19.5 %, neat BC showed similar desorption capabilities to that of the H2O-activated BC. Oxidative treatment using 10 % H2O2 reduced adsorption for BC (520 mgNH4−N. kgBC −1) and AC (545 mgNH4−N. kgAC −1) and increased desorption to 47.9 % and 41.9 %, respectively. From these results, H2O-activated biochar clearly is the most suitable for soil amendment that is resistant to leaching, is environmentally-friendly, and is an energyefficient nitrogen adjunct. A simplified version of an adsorption process simulated in AspenTech predicts that NH4-N may be recovered at an energy cost lower than that of the Haber-Bosch process for AC yields of below 19.5 %. A more in-depth investigation still needs to be completed to evaluate the techno-economic feasibility for this class of loaded sorbents, and whether this means of nitrogen capture from wastewater is a suitable replacement of the costly Haber Bosch process.

Abstract

Optical fiber daylighting system is a promising alternative for indoor illumination, which provides not only comfortable and safe lighting but also environmental benefits. Economic analysis results show that, total cost of traditional fluorescent lighting system is higher than that of hybrid optical fiber daylighting system after 7 years of operation. In addition, results of environmental benefits for the studied case show that, an annual average 39410kg of CO2 emission can be reduced when traditional lighting system is replaced by the hybrid daylight system. The potential of applying the hybrid optical fiber daylighting system to save energy and protect environment is promising.

Abstract

Hourly energy readings from heat billing meters are valuable data source for energy performance assessment of district heating substations and the buildings they serve. The quality of such analyses is bounded by the accuracy of the hourly readings. Thus, assessing the accuracy of the hourly heat meter readings is a necessary (but often overlooked) first step to ensure qualitative subsequent analyses. Due to often limited bandwidth capacity hourly readings are quantized before transmission, which can cause severe information loss. In this paper we study 266 Swedish heat meters and assess the quantization effect by information entropy ranking. Further, a detailed comparison is conducted with three heat meters with typically occurring quantization errors. Uncertainty due to the quantization effect is compared with the uncertainty due to typical accuracy of the meter instrumentation. A method to conflate information from both energy readings and energy calculated from flow and temperature readings is developed. The developed conflation method is shown to be able to decrease uncertainty for heat meters with severely quantized energy readings. However, it is concluded that a preferable approach is to work with the heat meter infrastructure to ensure future recorded readings holds high enough quality to be useful for energy performance assessments with hourly or subhourly readings.

Abstract

This study is part of an investigation on the influences of future energy demand and increased application of renewable resources on production planning of a regional energy system in the central part of Sweden. The study addresses the impacts of power supply from rooftop solar cells, increased application of heat pumps and penetration of electric passenger cars. Optimization results imply that use of heat pumps to replace district heating affects the demand side and reduces the heat production from energy plants. However, the power imports increase by 22%, compared with the reference system. By contrast, 100% penetration of electric vehicles in the transportation system only increases the power imports, without substantial effects on the energy plants performance.

Abstract

Use of a cheap, non-edible feedstock would reduce the biodiesel production cost and make the process economically viable. This study investigated the production of fatty acid methyl ester (FAME) using both acid (sulfuric acid, H2SO4) and base (sodium hydroxide, NaOH) catalysts. Techno-economic analysis was performed to assess the commercial feasibilities of acidcatalysed biodiesel production from waste shark liver oil (WSLO) and alkali-catalysed biodiesel production from refined vegetable oil in Oman. Historically, the discarded WSLO was used to proof wooden boats, but now these applications are no longer required as modern boats are made of fiberglass. Hence,the excess WSLO derived from these discarded shark livers in the fishing industry could instead be utilised for biodiesel production. This would be environmentally beneficial as it converts a waste into a product. Aspen HYSYS-V9 was used to simulate both production types at plant capacity of 12,000 te/y and lifespan of 20 years. Net present values (NPVs) of US $34.8 and US $4.9 million were obtained for the acidcatalysed process using WSLO and the alkali-catalysed process using refined vegetable oil, respectively. The internal rate of return (IRR) was calculated to be 260% for the acid-catalysed process and 56% for the alkalicatalysed process. Sensitivity analysis was also conducted to show the effect of certain variables on the NPV of both biodiesel production types. It was concluded that the biodiesel selling price has more effect on the NPV than the glycerol variation price, whereas the triglyceride feedstock purchase prices have the largest influence on the NPV of the two processes.

Abstract

Flue gas quench (FGQ) at advanced combined heat and power (CHP) plays a vital role by linking flue gas (FG) cleaning and wastewater treatment. In this paper, we have performed a detailed mass balance of pollutants in the flue gas and the process water with and without FGQ at a CHP plant. The results show that the system with FGQ puts less wastewater load (about 74 tonnes/day) together with less pollutant load on the municipal wastewater treatment plant (MWWTP) than the system without FGQ. Meanwhile, it results in fewer burdens on the external water use.

Abstract

This study deals with the investigating of the potential of employing two energy storage technologies., i.e. battery storage and pumped hydro storage (PHS), for PV powered supply system on a small island in Sweden. The optimal design of two hybrid PV-Battery and PV-PHS systems are compared and analyzed. Genetic Algorithm (NSGA-II) is employed as the optimization algorithm. Investment cost and loss of power supply probability are considered as objective functions. Number of PV modules and battery capacity are considered as design variables for PV-Battery system and a wide range of design variables including number of PV modules, turbine capacity, pump capacity, volume, installation height and depth to diameter ratio of reservoir, pipes diameters constitute for PV-PHS system. As a result, a hybrid pareto front is proposed for case study, that means, regarding objective functions, designer can decide that which of two systems are more suitable for current case study. The results show that pareto fronts of two hybrid systems intersect each other at a point. In this case, PV-PHS led to the lower pareto front for LPSPs up to about 6.94% and for LPSPs higher than 6.94%, pareto front of PV-PHS system lies above that of PVBattery system. This implies that under LPSPs range of 0- 6.94%, the PV-PHS system resulted in the lower initial cost, therefore, it is better option for the current case study. In contrast, for LPSPs higher than 6.94%, for the same LPSP, PV-Battery system led to the lower investment cost in comparison with PV-PHS, so it can be chosen as a better option regarding designer’s priorities. Also, results show that the proposed strategy can reach a design with the full satisfaction of fluctuating demand and system constraints. In this case, for the yearly average demand of 16.3 kW, the investment cost is obtained to be 2.1M$ and 1.87 M$ for the PV-battery and PV-PHS, respectively. The paper compares in detail the optimal designs and operations obtained for the two hybrid PV-Battery and PV-PHS systems.

Abstract

Increasing the share of renewable energy in buildings sector is essential. While the dynamic nature of the renewables is an obstacle for improving its efficiency. In this context, thermal energy storage technologies are to store the renewables and supply it to meet building’s demand. Thermochemical energy storage stands out in advantages including high energy storage density and low thermal loss. However, for a thermochemical energy storage system, the thermochemical reactor is critical. To tackle drawbacks of the reactor, this paper proposes an innovative three-phase thermochemical reactor and investigates its performance through an experimentally validated numerical model. The reactor is integrated with fins and air gaps to enhance heat and mass transfer. Key parameters and the related heat and mass transfer efficiency of the reactor in both charging and discharging processes have been investigated. According to the analysis, the integration of fins has increased the reactor performance by 129% in charging and by 77% for COP in discharging. The effect of fin pitch has been examined and the results show that reducing the fin pitch can increase the reactor performance by up to 14% in charging and 7.5% in discharging. However, the enhancement is not sensitive for fin pitch lower than 30 mm. Additionally, increase the gap size can enhance the charging performance but may reduce discharging efficiency and the optimal gap size range is 3 mm to 5 mm.

Abstract

Ultra-high heat flux cooling has become a research hotspot owing to its wide application in thermal engineering fields. Only by exploring its internal physical mechanism and calculating the CHF (critical heat flux) of different surfaces, can the necessary theoretical basis be provided for the design and optimization of pool boiling heat exchange in engineering applications. Previous models cannot accurately predict CHF value due to the limitations of their physical models. In this paper, a new theoretical physical model was obtained to predict CHF value of pure liquid on a heated surface. The theoretical model proposed a new CHF trigger mechanism based on the bubble behavior near the heater surface. A three-dimensional force balance of a separated bubble was analyzed at CHF condition to derive the analytical correlation for CHF value. The correlation considers the effect of hydraulic pressure, surface tension, liquid properties as well as the contact angle of the heater surface. The predicted values of CHF value on heated surfaces obtained from the present model were found in agreement with existing experimental data within a wide range. It is shown that CHF is mainly affected by factors of adhesion force and hydraulic pressure.