Journal of Energy Engineering

Increasing interest is being paid to the exploitation of wind power to supply stable electricity for the microgrid. The microgrid system coupled with wind turbines is available to generate power for local residents, especially in isolated areas. Being suitable for a microgrid, a 30-kW compressed air energy storage (CAES) system directly driven by a vertical axis wind turbine (VAWT) is presented in this paper. A high-pressure storage tank was used to store the compressed air in order to guarantee continuous operation. In addition, a control strategy was designed for the system to make full use of wind energy and enhance system stability. Moreover, a mathematical model was established to simulate the system with hourly wind speed data, which were randomly selected from Zibo in the Shandong province of China. Variations in gas turbine temperature, operation pressure, and the mass flow rate of compressed air with wind speed over two weeks in winter and two weeks in summer are shown in the paper. The results indicate that the adoption of the VAWT control strategy enables the round-trip efficiency to increase by 5.21% and the number of hours in the protection mode to decrease by 22 h in four weeks. Moreover, the system absorbed zthe fluctuant wind power and generated stable output (30 kW) for consumption.

Ethanol extracted from cellulose has attracted considerable attention and previous studies have shown that hydrolysis is a key process for extraction of hexose from cellulose. This study describes the effects of solid-liquid ratio of cellulose/water on production of fermentable hexose by hydrolyzing microcrystalline cellulose in supercritical water (400°C) at different reaction times (6, 7, and 8 min). Thermal property of microcrystalline cellulose was characterized by thermogravimetric (TG) analysis. The concentration of fermentable hexose (glucose and fructose) was determined by using high-performance liquid chromatography (HPLC). Scanning electron microscopy (SEM) was carried out to observe the morphology of the hydrolysis residues. The results demonstrate that the concentration of hexose produced increased with increasing the solid-liquid ratio of cellulose/water in the hydrolysis process. The maximum concentration of fermentable hexose ($37.98\mathrm{g}/\mathrm{L}$), corresponding to a hexose yield of 11.39%, was achieved at the solid-liquid ratio of cellulose/water of 250 ($\mathrm{g}/\mathrm{L}$) at 6 min. Various holes and spherical particles were observed on the surface of hydrolyzed cellulose, which suggests that the dissolving ability of supercritical water was restricted. The results show that many chars were produced as residues, which results in a low-hydrolysis yield but a high-hexose concentration. This study provides an important guide of producing high-concentration solution of hexose from cellulose for fermentation.

The solution MDEA/PZEA [methyldiethanolamine/2-(1-piperazinyl)-ethylamine] was used as a new absorbent in membrane gas absorption technology. In the present work, a two-dimensional (2D) mathematical model was developed to describe the behavior of ${\mathrm{CO}}_2$ absorption from flue gas in a hollow fiber membrane contactor under a nonwetted condition. The modeling predictions were in good agreement with the literature data. Meanwhile, the simulation results indicated that the decrease in gas velocity, gas temperature and ${\mathrm{CO}}_2$ concentration in the feed gas, and the increase in those of the liquid phase promoted the ${\mathrm{CO}}_2$ removal effect. Additionally, adding an activator into the MDEA solutions dramatically improved the absorption performance. It was found that the optimum blend concentration was when $\beta$ was equal to 1 considering the costs and comprehensive separation performance. Therefore, MDEA/PZEA could be a good alternative to alkanolamines for ${\mathrm{CO}}_2$ membrane separation.

Indoor air quality (IAQ) and energy consumption are becoming increasingly important in the HVAC field. This paper examines the potential of improving demand-controlled ventilation (DCV) performed under an occupant based ventilation standard. ${\mathrm{CO}}_2$-based DCV and radio frequency identification–based DCV methods are simulated in an office building model served by a dedicated outdoor air system combined with a fan-coil system. A numerical model for estimating real-time occupancy is developed. Simulations are conducted with current Chinese ventilation standard as an example. Results show that the current standard causes severe fluctuations under a ${\mathrm{CO}}_2$-based DCV strategy. It is concluded that the current standard defines the ventilation rate as a function only related to the occupancy number, which makes DCV control unstable. As an improvement, the current Chinese ventilation standard is modified to a form similar to the standard of the American Society of Heating, Refrigerating and Air-Conditioning Engineers that considers the occupant and the building separately. The modified standard is applicable to various DCV approaches and can maintain an acceptable formaldehyde concentration. This modification significantly improves the applicability of the current Chinese ventilation standard to ${\mathrm{CO}}_2$-based DCV and can be easily extended to similar ventilation standards.

In order to reduce weight on a building roof and save electrical energy for water circulation, a solar water heater with a built-in thermal water pump was introduced. However, such a system still does not have high enough effectiveness. The target of this study was to improve the efficiency of the solar water heater by eliminating critical losses such as vapor and head losses. Consequently, a new system of ${1.58\mathrm{m}}^2$ flat plate solar collectors, an overhead tank placed at the peak level, a larger water storage tank without a heat exchanger at the lower level, a new vent tube and a one-way valve for water circulation control were constructed. The discharge head was reduced to be 0.5 m. A pump was powered by steam and air and operated at a solar collector temperature of about 70–80.2°C and gauge pressure of 2.2–6.3 kPa. The stored hot water of the solar water heater ranged between 25 and $89.9\mathrm{L}/\mathrm{day}$. Furthermore, the max water temperature in the storage tank was roughly 64.6°C. The max daily pump efficiency was about 0.0012%. For the 0.5 m h discharge head, the solar water heater had daily max thermal efficiency of about 41.2% compared to 17.4% for a previous system of the same type. The system simulation gave a reasonable agreement with the experimental results (error of less than $\pm 10\%$). Long-term performance and economic analysis were included.

To improve the accuracy of short-term load forecasting, a least-squares support vector machine (LSSVM) method based on improved imperialist competitive algorithm through differential evolution algorithm (ICADE) is proposed in this paper. Optimizing the regularization parameter and kernel parameter of the LSSVM through ICADE, a short-term load forecasting model that can take load-affected factors such as meteorology, weather, and date types into account is built. The proposed method is proved by implementing short-term load forecasting on the real historical data of the Yangquan power system in China. The result shows the proposed method improves the least-squares support vector machine capacity and overcomes the traditional imperialist competitive algorithm and least-squares support vector machine that exist in some of the shortcomings. The mean absolute percentage error is less than 1.5%, which demonstrates that the proposed model can be used in the short-term forecasting of the power system more efficiently.

A series of the $\mathrm{Cu}/\mathrm{MnMgAl}$ mixed oxides were prepared by using the acid-processed gelatin method, characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) techniques and applied as sulfur transfer catalysts under conditions similar to those of fluid catalytic cracking (FCC) units. The analysis of the ${\mathrm{SO}}_2$ abatement curves as a function of the copper content indicates that the reaction mechanism of ${\mathrm{SO}}_2$ uptake depends on two reversible surface processes (the chemisorptions of ${\mathrm{SO}}_2$ and its oxidation by copper ions) and a nearly irreversible process (bulk diffusion of the sulphate species). The results also show that the mixed oxides catalysts achieve the highest oxidative rate when they contain 11.1% (mol) copper (sample $10\mathrm{Cu}/\mathrm{MnMgAl}$).

High-rate algae ponds (HRAPs) are widely used in increasing biofuel production because of their effective design in terms of cost and power consumption. Using modeling and simulation techniques is an economical approach for improving the design of raceways. Previous modeling studies reported the use of a flat velocity profile, thus failing to depict the real phenomena involved. However, in practice, the rotating paddle wheel in HRAPs produces a pulsating velocity that is necessary for culture growth. In this study, the hydrodynamic characteristics of algal ponds were investigated using a coupling algorithm to map the effects of a two-dimensional paddle wheel on a three-dimensional raceway model. HRAPs with and without paddle wheels were compared in terms of hydrodynamic mixing, dead zones, and power consumption. The results revealed that compared with a flat velocity at the inlet, the pulsating velocity of a paddle wheel produced a large dead zone volume with reduced power consumption, shear stress, and turbulence. A few pond design modifications were tested with this realistic situation and an additional recirculation zone was found near the paddle wheel. This zone needs to be addressed in future pond designs.

China’s wind power is primarily distributed in West China which is far away from the load center. Power from these wind farms is difficult to consume, so it needs to be transmitted to East China to extend its consumption area. To coordinate interregional power construction and to make full use of the interregional power generation resources, especially the wind electricity, a joint plan for an interregional power source and power grid construction is necessary. A mixed integer programming model of interregional electric power investment dynamic optimization is established for many reasons. The most important reasons are the optimal operating costs of power generation and the factors involved in interregional power planning. Such factors include load and electricity demand constraints, fuel cost volatility, installation cost changes of clean energy, carbon emissions price growth, and installed capacity constraints. The results simulated by general algebraic modeling system (GAMS) show that on the economic level, interregional power investment optimization could reduce the economic input of electric power construction. On an environmental level, interregional power investment optimization achieves ${\mathrm{CO}}_2$ emission reduction benefits. With interregional planning, wind power will gain more in development and reach a greater percentage in power resources. The introduction of carbon emission trading will promote low-carbon construction in China’s power industry and guide the interregional utilization of clean energy.

Driven by architectural trends and the need to maximize daylight, commercial building façades have become more transparent. High-performance façades include spectrally selective glazing systems, dynamic elements and insulated spandrel sections. Nevertheless, it is generally accepted that, compared to standard, traditional opaque construction, modern transparent envelopes result in increased overall energy use in these buildings. In this paper, the building façade is treated as a part of the building perimeter zone, which also includes electric lighting controls, shading attachments, HVAC components, and indoor environmental controls. Consequently, the objective is to balance the need for daylighting and view versus the need for controlling of solar gains and maintaining human comfort, while reducing energy demand for air conditioning and lighting. Key parameters in solving this problem are (1) technological advancements in glazing products, (2) utilization of dynamic building envelope components, and (3) lighting and HVAC controls. In order to demonstrate the potential of high-performance façades, a typical office building with large perimeter zones is used as an example. The basic model consists of standard brick exterior walls with 20% punched windows. Then, a comparative analysis is performed for a more transparent envelope with dynamic systems including shading and electric lighting controls, for the climates of Chicago and Rome. An integrated thermal-lighting model with flexible dynamic system controls, verified with commercial software, is expanded to simulate more complex façade controls for reducing glare problems while maximizing useful daylight. The results show the advantages of transparent façades with active systems, compared to traditional building envelopes. The more transparent building results in lower operational costs and source energy use, although total site energy use can be higher for heating-dominated climates.

For better understanding of the thermodynamic characteristics of natural gas, this paper experimentally investigated the attaching characteristics of the natural gas jet flame on a partially premixed coflow burner, and the effects of velocities and equivalence ratios are considered. Based on the experiment results, the instantaneous height and attaching velocity of the tribrachial flame base obviously vary for different jet velocities at a small (approximately 7) fuel equivalence ratio. With the increase in fuel equivalence ratio, a critical velocity exists and the attaching characteristics become significantly different. For the tip of the tribrachial flame, due to the Kelvin-Helmholtz instability, oscillation is observed and its level is quantified. According to the quantified results, the attaching characteristics of the flame tip can be divided into two regimes: stable and oscillation. Furthermore, the increase in jet velocity and/or fuel equivalence ratio induces the flicker phenomenon and/or boarding of the attaching velocity range of the flame tip. Based on the results, empirical fitted formulas for the attaching velocities of the flame base and tip are established for further investigations.

The purpose of this paper is to investigate the effects of injection parameters on combustion and emission characteristics of a six-cylinder diesel-piloted direct-injection natural gas engine at idle conditions. The tests were conducted at three injection pressures (15, 18, and 24 MPa), two different injection intervals (0.7 and 1.0 ms), and start of natural gas injection in the range of 4–13° before top dead center (BTDC). The experimental results revealed that in terms of cylinder pressure and heat release rate, the maximum cylinder pressure and the maximum heat release rate were substantially higher at the injection pressure of 24 MPa and increased gradually with advanced injection timing, while only slightly influenced by injection interval. In terms of combustion parameters, the ignition delay was reduced by adoption of higher injection pressure and the rapid combustion duration was extended more evidently with the advance of injection timing. In terms of emissions, application of relatively lower injection pressure of 15 and 18 MPa had benefits in reduction of CO, HC, and ${\mathrm{NO}}_{\mathrm{x}}$ emissions; CO emissions were higher with advanced injection timing and could be improved with shorter injection interval at the injection pressure of 15 and 18 MPa, while ${\mathrm{NO}}_{\mathrm{x}}$ emissions exhibited the same trend for all injection pressures.

Geothermal energy pile foundations are sustainable, cost-effective alternative energy systems for heating and cooling needs of buildings. This paper presents the thermal modeling of two different configurations of energy pile foundations used for seasonal energy storage. Several two-dimensional (2D) transient analyses were carried out to find the optimum pile configuration and to obtain preliminary information about the heat exchange between the ground and the building. Two scenarios were modeled. In Scenario 1, a combination of long and short piles was simulated, while in Scenario 2 only long piles were considered. Long piles are structural piles and work as a heat exchanger throughout the year, while the nonstructural short piles operate only in the summer months to inject surplus solar energy into the ground. Simulation results show that in Scenario 1 the vertical temperature distribution was uneven, resulted in high temperatures at shallow depths (0–10 m) and near-freezing temperatures at greater depths. In contrast, Scenario 2 yielded a more uniform temperature distribution throughout the depth. More importantly, in Scenario 2, the temperature inside the storage system was maintained well above the freezing temperature.

Groundwater aquifers are key sources of water in arid and semiarid regions. Fossil fuels are commonly used to power water-well pumps. The adverse effects of greenhouse gas emissions from fossil fuel use have led to the search for alternative clean energy sources to extract groundwater. A key factor in assessing the viability of wind energy use in groundwater extraction is the safe yield of groundwater production that can be derived by using windmills to power water wells. This paper presents and tests simulation and optimization models developed to estimate the safe yield of groundwater production derivable from the joint application of wind energy to water extraction and water storage for irrigation.

This paper presents an experimental investigation of a new use of phase change materials (PCM) as a coating material on concrete and hollow brick walls. Its aim is to study the influence of the integration of PCM on the thermal behaviour of cells and on the improvement of thermal comfort in buildings under the Algerian climate. Tests of the flexural strength, compressive strength, bond strength, and hardness were performed at seven days of age on composite plaster/PCM materials. Different percentages of phase change material were used in the designs of composition (plaster/PCM). In situ measurements of air and walls temperatures were made in three cells. The first one was built with traditional materials and the other two with a composite material plaster/PCM. The cells are located in the Algiers region. The measurement results show that the use of a gypsum plaster incorporating 30% PCM contributes to a reduction of the amplitude of indoor temperature of the cell by 4°C in the summer. The use of PCM has also improved thermal comfort and increased the maximum cell temperature by 2°C during winter.

The effect of phase change material (PCM) integration in buildings is investigated in mild climates for the entirety of the hot season. The incorporation of PCMs in building materials is particularly interesting because it allows for the thermal storage to become a part of the building structure while being completely passive. Simulations in a typical single-family home are carried out, and the effect of incorporating PCMs in different building components is analyzed. Results show an important reduction in cooling energy. No explicit relation was found for a unique PCM optimum switch temperature; however, clearly it is closely related to the local climatic conditions and construction systems rather than indoor temperature. Because the walls and ceiling do not operate at the same temperature, some targeting strategies for selecting PCMs are tested and the best choice is found to be differentiating PCMs with different switch temperature for the walls and the ceiling.

This study deals with the thermal performance of a solar-assisted heating system for the Jordan University of Science and Technology indoor Olympic swimming pool. Solar heating is accomplished by using hot water generated by heat exchange with the solar evacuated tube collector working fluid. A transient analytical approach has been adopted for developing an explicit expression for the pool temperature, including all thermal losses. Detailed computations have been made from the beginning of September until the end of May. The effect of relevant parameters such as collector area, heat removal factors, collector heat loss coefficient, and evaporation losses on the performance of the proposed systems is investigated. The effect of covering the pool has been manifested in the analysis to reduce heat losses. The percentage of primary energy savings is used to measure the performance of the system. It is found that using a collector area equal to 53% of the pool surface results in 100% savings in primary energy for both pool heating and domestic hot water; for a collector area of 40% of the pool surface, 87% of primary energy savings results; and for a collector area of 26.6% of the pool surface, the energy saving is 59%. Financial analysis reveals that utilizing a $200\text{-}{\mathrm{m}}^2$ collector area has the lowest energy production cost among the considered alternatives ($\$0.011/\mathrm{kW}·\mathrm{h}$).

For the development of a double-stage metal hydride–based heat transformer (DS-MHHT), three metal hydrides, namely, A, B, and C, with different thermo-physical properties are required. Hydrides A and B together act as a hydrogen compressor, and hydride C upgrades the heat input quality. In the present paper, the performance tests of a double-stage metal hydride–based hydrogen compressor (DS-MHHC) employed in the development of metal hydride–based heat transformer are presented. The metal hydrides chosen for the present study are ${\mathrm{LaNi}}_5$ and ${\mathrm{La}}_{0.35}{\mathrm{Ce}}_{0.45}{\mathrm{Ca}}_{0.2}{\mathrm{Ni}}_{4.95}{\mathrm{Al}}_{0.05}$. The effects of supply pressure and heat source (desorption) temperature on the delivery pressure, amount of hydrogen compressed, and isentropic efficiency of the hydrogen compressor were investigated. It is observed that an increase in supply pressure up to 10 bar significantly increases the delivery pressure, which reduces the compressor efficiency significantly. A maximum compression ratio of 22 was obtained when the DS-MHHC operated at 2 bar supply pressure and 140°C heat source temperature. At supply conditions of 10 bar supply pressure and 140°C heat source temperature, the maximum delivery pressure achieved was 74 bar.

Organic Rankine cycle (ORC) has been examined as an effective way to recovery waste heat from industrial manufacture. The effects of internal heat exchanger (IHE) and superheat degree on the thermoeconomic performance of ORC are presented in this paper. Zeotropic mixtures are employed in the simulation and six indicators are used to evaluate the system performance, as follows: (1) net power output, (2) thermal efficiency, (3) exergy efficiency, (4) cost per net power output (CPNPO), (5) area of the heat changers per net power output (APNPO), and (6) energy saving and emission reduction performance (ESERP). The results indicate that the more volatile pure component has a higher increasing rate of net power output when IHE is equipped. The IHE has a greater impact on thermal efficiency and exergy efficiency of the ORC with zeotropic mixtures than that of the ORC with pure fluid. For the ORC with both mixtures and pure component, the rising superheat degree results to the decline of the net power output but increase of the thermal efficiency, and exergy efficiency at the constant turbine inlet pressure. Both the basic ORC and regenerative ORC with zeotropic mixtures have a better economic performance than that with pure fluid. In addition, superheat degree has a negative effect on the economic performance of ORC with more volatile component mixtures.

In this paper, a thermodynamic equilibrium analysis coupled with experimentation for the hydrogen production from dimethyl ether is performed by total Gibbs free energy minimization method. Heat requirement from the process can be achieved from the exhaust gas of the engine. The effects of temperature of exhaust gas (250–400)°C and ratio of steam to Dimethyl ether (DME) (1.5–5) on the equilibrium compositions, yield of hydrogen and energy efficiency of the system are analyzed. In this way, the most thermodynamic favorable operating conditions have been identified. Experimental study is implemented on a self-designed equipment. Experimental results over the $\mathrm{Cu}\text{-}\mathrm{ZnO}\text{-}{\mathrm{Al}}_2{\mathrm{O}}_3\text{-}{\mathrm{SiO}}_2$ catalyst are compared against the results obtained from thermodynamic analysis.

In view of the sensitivity to the wind conditions, the architecture of the air-cooled steam condenser (ACSC) always affects the characteristics of the whole power plant. As a result, it is important to structure a reasonable ACSC for better comprehensive performance in the power plant. This paper uses an existing numerical model to discuss the impact mechanisms from the inner walkway on the performance of the ACSC, and the relevant characteristics of the power plant at different inner walkways is also studied. It is found that the performance of the ACSC as well as the power plant is improved by extending the length extending of the inner walkway, thus shrinking the negative pressure regions around the fan surfaces. Finally, the net power and the thermal efficiency are improved by an amplitude of 1.2 and 0.3% from $L_w=0$ to 2 m, respectively, for the inner walkway based on the relevant value at the design wind speed case. It is concluded that an appropriate inner walkway should be chosen during the design period of the air-cooled power plant.

Cavitation is a destructive phenomenon in industrial needle-type control valves. In order to reduce the damaging effects of cavitation, a circular row of vanes is used at the end section of the needle valve. By changing the path of flow at the end section of the valve and generating a spiral movement in fluid, these vanes increase the near-wall pressure; thus, cavitation intensity is reduced and the bubbles move away from the walls. In this study, the effect of vane camber angle on cavitation intensity and formation location has been investigated. The results show that by increasing the vane camber angle from 10° to 70°, the spiral movement of flow increases and cavitation intensity diminishes mildly; however, as the camber angle increases beyond 70°, the spiral flow movement increases considerably and there is a significant reduction in cavitation intensity. It should be mentioned that at camber angles less than 70°, the flow coefficient remains almost constant; but at angles greater than 70°, the flow coefficient diminishes, resulting in an increase of energy supply cost.

An experimental study on a pump-driven loop heat pipe (PLHP) charged with R22 for cooling a data center is reported in this paper. The PLHP had five tube-fin heat exchangers as evaporators and three tube-fin heat exchangers as condensers, a liquid reservoir, and a canned motor pump. The coefficient of performance of the unit was 3.75 when the indoor-outdoor temperature difference was 10°C, then increased to 9.37 when the temperature difference was 25°C. The mass flow rates of R22 increased from 200 to $\mathrm{1,100}\mathrm{kg}/\mathrm{h}$ with one evaporator and one condenser of the PLHP, and the heat transfer rates first increased and then decreased. When the vapor quality of R22 at the evaporator outlet was between 0.3 and 0.6, the mass flow rate affected the heat transfer rate slightly. As the increase of mass flow rate in the PLHP, the temperature difference between the evaporator inlet and outlet, and the sensible heat ratio were both rising. When the mass flow rate was about $\mathrm{1,400}\mathrm{kg}/\mathrm{h}$ and the indoor-outdoor temperature difference increased from 10 to 30°C, the relationship between the heat transfer rate and the temperature difference was linear.

Piezoelectric materials have proven their efficacy for both energy harvesting and structural health monitoring (SHM) individually. Piezoelectric ceramic (PZT) patches, operating in $d_{31}$-mode, are considered best for SHM. However, for energy harvesting, built up configurations such as stack actuators are more preferred. The proposed study in this paper provides a proof-of-concept experimental demonstration of achieving both energy harvesting and structural health monitoring from the same PZT patch in the form of concrete vibration sensor (CVS), designed specifically for RC structures. This packaged sensor (CVS), composite in nature, has better compatibility with surrounding concrete and can withstand the harsh conditions encountered during construction. The paper covers experiments carried out in the laboratory environment to measure the voltage and the power generated by a CVS embedded in a life-sized simply-supported RC beam subjected to harmonic excitations. An analytical model is developed to compute the power output from the embedded CVS, duly considering the effect of the shear lag associated with the bonding layers between the encapsulated PZT sensor and the surrounding concrete. The performance of the CVS is compared with the surface-bonded PZT patch. Utilization of the same patch for SHM through a combination of the global vibration and the local electro-mechanical impedance (EMI) techniques is also covered. Harvesting potential of vibration energy by PZT sensors during idle time is experimentally demonstrated and extended to real-life structures based on the validated analytical model.

In this study, the relationship between manufacturing plant areas and the plant’s overhead energy was investigated and analyzed. The physical information about five industrial facilities, which included blueprints, plant layout, plant area, and machine configuration, was collected and in-plant measurements were made. The goal of this research is to measure, in actual manufacturing plants, the area distributions and their relationship to the basic machine area footprint (where the product manufacturing occurs) across a wide range of machine types. A six-categorization system (A to F) was developed for the different plant areas and can be used easily by other researchers. A linear relationship of decreasing total plant area (A to F) with decreasing machine size (A) was found. Thus, the allocated total plant area (TPA) is determined as A to F and can be estimated for a single machine operating at a manufacturing rate of $x$ products or workpieces per hour. The nonprocess energy, then, is $\mathrm{TPA}\times$ ($30\mathrm{W}/{\mathrm{m}}^2$ or $3.6\mathrm{kJ}/{\mathrm{h}\mathrm{m}}^2$) for manufacturing building nonprocess energy intensity. Then, total nonprocess energy for the manufacturing machine ($\mathrm{kJ}/\mathrm{h}$) divided by the production rate $x$ $\mathrm{products}/\mathrm{h}$ gives the nonprocess energy per product ($\mathrm{kJ}/\mathrm{product}$). This research has contributed further to the life cycle of products by estimating the nonprocess energy per product, which then can be added to the direct process manufacturing energy to give a total energy per product.

A commonly used data assimilation (DA) algorithm, Kalman filter, is integrated with the seasonal autoregressive integrated moving average (SARIMA) model to make a one-step forecast of monthly municipal solid waste (MSW) generation in Seattle. The DA solves the problem that parameters of the forecasting model need to be updated in every forecasting process. The performances of prediction models are compared using mean absolute percentage error (MAPE), root-mean-square-error (RMSE), and 95% confidence interval. The MAPE of the SARIMA model with DA is 0.0422, whereas the MAPE of the SARIMA without DA is 0.0914. A 95% confidence interval of SARIMA without DA keeps increasing, whereas SARIMA with DA remains constant, which means DA raises the stability of SARIMA as time progresses. Results show that DA enables the same MSW prediction model with more accurate and more robust forecast results. The SARIMA parameter updating cycle can be prolonged, which saves time and effort.

China has been vigorously developing natural gas-based urban district heating (UDH) for years to reduce severe air pollution. In this paper, energy and exergy analysis methods are applied to distributed combined heating and power with heat pump heating for peak shaving (DCHP + HPH) in five representative UDH cities in China. Effects of a peak shaving ratio (a ratio of the maximum heating load undertaken by heat pump heating to the maximum design heat load of the UDH system) on gas turbine load rate, primary energy ratio and exergy efficiency of the DCHP + HPH are investigated. The analysis results show that when the peak shaving ratios are in the range of 0.3–0.4, the average exergy loss of gas turbine can be reduced by approximately 25%, and the maximum average exergy efficiencies of the DCHP + on-demand HPHs in the five representative UDH cities reach approximately 50–51.4%. This optimal natural gas-based UDH should be promoted in China instead of natural gas-fired heating boilers to replace coal-based UDH.