Journal of Energy Engineering

Wind energy has become one of the leading sources of renewable energy, but faults and unscheduled shutdowns of wind turbines are costly. As the size and number of wind turbines continue to rise, monitoring for faults has become increasingly important for companies to remain competitive. This paper presents a three-phase methodology to detect emerging faults and to possibly reduce the number of unscheduled shutdowns. The first phase monitors the wind turbine online by constructing residual control charts for the turbine’s power curve. Type I errors or type II errors are identified in this phase to avoid false warnings if an unusually high number of observations outside the control limits are present. Given the control charts, the second phase uses autoassociative neural networks (AANNs) to detect anomalous components by comparing the mean square errors (MSEs) of the components. The third phase generates a schedule chart consisting of an anomalous schedule, a preventive schedule, and an ideal schedule. The objective of the schedule chart is to enhance the turbine’s productivity by reducing the number of unexpected shutdowns, with the aim to eventually eliminate them.

A ground source heat pump system can cause the fluctuation of the underground temperature field in the working process. If this system is used for a long time, the “heat accumulation” phenomenon will occur, the unit coefficient of performance (COP) value will be reduced, and the system energy consumption will be increased. In order to solve this problem, a new type of heat storage of solar and ground source heat pump coupling system was developed in this paper. The solar collector system can achieve high quality heating seasonal storage, i.e., high quality heating in winter and high quality cooling in summer. The falling film evaporation process was adopted to obtain efficient refrigeration. The experimental results show that the buried tube heat exchanger and the intermittent heat storage tank can operate well in the system. In addition, the COP value of the system is 6.96, which demonstrates that the working efficiency of the designed solar ground source heat pump system is high. The working efficiency and service life of the ground source heat pump were improved. Therefore, the new system has remarkable economic benefit.

The main objective of this research was to study a hybrid energy thermal water pump (HBWP) in order to produce hot water from a shallow well in Thailand. The pump was powered by air-steam which was produced from a flat-plate solar collector (SC) coupled with a supplementary heat source. The HBWP system with 9 L capacity comprised an SC, an overhead tank (OT), a storage tank (ST), a heat source tank (HST), a liquid piston tank (LT), and a one-way valve. A one-meter discharge head and 1–3 m suction heads were tested. The LT was initially filled with 10% air and 90% water. The pump could run automatically. It was found that for suction heads of 1 and 3 m, the total pump efficiency was around 0.012–0.027%, and the thermal efficiency was around 32.5–36.3%. The pump could suck around 7–8 L/cycle. The average temperature of pumped water was around 42.9–46.7°C, which is sufficiently high for residential use. It was concluded that the suction heads affected the pump efficiency. Increasing air amount in the system could reduce some energy consumption. Moreover, a heat source thermal water pump (HSWP) was tested. The pump capacity was expanded to 240 L. The energy input was taken from only one heat source. System operation was controlled by hand. Suction heads of 1, 3, and 5 m were tested. It was found that the pump could suck around $192.2–218.8\mathrm{L}/\mathrm{cycle}$ and had more pump efficiency than the smaller pump with hybrid energy. However, the HSWP is more essential for agriculture in the rural area.

This paper proposes a two-diode model to represent the photovoltaic cell. This model requires only three parameters (photocurrent, diffusion, and recombination of the dark current). The analytical resolution of continuity equations in each region of a crystalline solar cell enabled the determination of the expressions of diffusion and recombination of dark currents. New relationships are proposed giving the expressions of these currents as a function of their reference values, which are determined from both the data provided by the manufacturer and the different temperature values. This study indicated how the parameters of the proposed model were determined. Predicted current–voltage curves were compared with the De Soto one-diode model and experimental data from a building integrated photovoltaic facility at the National Institute of Standards and Technology (NIST) for two different cell technologies (single crystalline, polycrystalline). The maximum power calculated by the proposed model was calculated to compare the single-diode of the Soto model to the two cell type at the four conditions of generation rate. The proposed simple and easy model shows a better agreement with the NIST data than the De Soto one.

This paper proposes an optimization algorithm for coordinating charging/discharging activities of plug-in hybrid electric vehicles (PHEVs) within the electricity market environment. PHEV Fleets are considered as a promising solution to provide vehicle-to-grid (V2G) services. The interactions between PHEVs and the power grid will bring many challenges to the current power market. In this paper, V2G is taken into account in the ancillary service market for providing frequency regulation service. Large-scale PHEV fleet integration will cause load volatility and destabilize the grid if it is implemented without proper control. This paper proposes an optimal strategy to maximize the V2G profits while minimizing the charging costs. The optimal strategy is based on the price forecast for both residential electricity and market regulation. Because of the stochastic nature of electricity price, the proposed optimal problem is solved using stochastic dynamic programming to obtain an optimal solution with the price uncertainties taken into account. Constraints related to vehicle use as well as technical limitations are also considered. Numerical results show the effectiveness of the proposed optimal control strategy and the additional costs arising from discharging batteries for ancillary service can be partially or completely compensated by V2G profits.

For the first time, a high performance cobalt oxide catalyst for hydrogen generation has been developed in a cost-effective way. The novel cobalt oxide catalyst was prepared by microwave-assisted thermal oxidation of cobalt metal. Microwave heating produced cobalt oxide from cobalt metal powder within 10 min through oxidation and consolidation simultaneously. An as-synthesized cobalt oxide catalyst (a centimeter-sized chip) has revealed high activity for the catalytic hydrolysis of sodium borohydride (${\mathrm{NaBH}}_4$) showing a maximum hydrogen evolution rate of $\mathrm{6,000}\mathrm{mL}/\min \text{-}\mathrm{g}$ from an aqueous solution containing 20 wt% of ${\mathrm{NaBH}}_4+5\mathrm{wt}\%$ of sodium hydroxide (NaOH) under room temperature. Furthermore, a powder sample of cobalt oxide showed a maximum hydrogen evolution rate of $\mathrm{13,412}\mathrm{mL}/\min \text{-}\mathrm{g}$ under the same conditions as above. The hydrogen evolution rates were affected by temperature and concentrations of ${\mathrm{NaBH}}_4$ and NaOH as well as the amount of the cobalt oxide catalyst. Based on X-ray photoelectron spectroscopy and X-ray diffraction studies, the structural transformations of the catalyst were observed after catalytic hydrolysis of ${\mathrm{NaBH}}_4$.

In this work, the failure mode of the lead acid battery under 17.5% depth of discharge was predicted. Both the developed lead acid absorbent glass ma (AGM) battery for microhybrid applications and the standard flooded battery were tested. The end of discharge voltage and the charging factor were presented for each type of battery. The analysis of the negative plates after cycling was carried out for the two types of batteries. The test results revealed that they significantly depend on the battery technology. The standard flooded battery fails from the second unit of the test, whereas the AGM performs 16 units. For the standard flooded, a stratification of lead sulfate is observed and causes the end of the battery life. However, the sulfate is homogeneous according to the plate’s area for the AGM battery.

This study investigated the feasibility of a combined cycle comprising a topping ${\mathrm{SCO}}_2$ cycle and a bottoming ${\mathrm{TCO}}_2$ cycle (${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle). A simple ${\mathrm{SCO}}_2$ cycle and a recompression ${\mathrm{SCO}}_2$ cycle were considered as the topping configurations. Thermodynamic analyses and comparison were performed to evaluate the effects of key thermodynamic parameters on the behavior of combined ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycles. In addition, a parameter optimization was achieved by means of a genetic algorithm to reach the maximum overall thermal efficiency. The results show that the thermal efficiency of the simple ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle increased with an increase in ${\mathrm{SCO}}_2$ turbine expansion ratio and compressor inlet temperature. However, for the recompression ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle the thermal efficiency increased and then decreased as the ${\mathrm{SCO}}_2$ turbine expansion ratio increased. Both the modified ${\mathrm{SCO}}_2$ cycles with a bottoming ${\mathrm{TCO}}_2$ cycle had higher performance, with thermal efficiency increase of 10.12 and 19.34% for combined recompression and simple configurations, respectively, in comparison to their original values. Furthermore, the values of exergy efficiency were 60.72 and 64.79% for the simple ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle and recompression ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle, respectively. The simple ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle and recompression ${\mathrm{SCO}}_2\text{-}{\mathrm{TCO}}_2$ cycle had a power ratio of 16.21 and 11.26%, respectively.

A conceptual gas turbine–powered cogeneration system is proposed where a reverse Brayton refrigeration cycle is employed for compressor inlet air cooling that can reduce the inlet air temperature close to 0° C or lower, which cannot be achieved through evaporative and absorption inlet cooling techniques, respectively. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) are both investigated for the system under various operating conditions. The results indicated that both energetic and exergetic efficiencies of the cogeneration cycle are considerably varied with the change in the extraction pressure ratio, extracted mass rate, turbine inlet temperature, and process heat pressure, and least affected by the ambient relative humidity. Exergy analysis of the proposed cogeneration shows that maximum exergy is destroyed during the combustion and steam generation process, which represents more than 87% of the total exergy destruction in the overall cogeneration cycle. Comparison of the cogeneration and noncogeneration cycle shows that the first-law and second-law efficiencies of the cogeneration cycle are 64 and 40% higher than the efficiencies of the noncogeneration cycle for a given extraction pressure ratio. Further, it is shown that the gas-turbine cycle coupled with the reverse Brayton refrigeration cycle for inlet air cooling provides higher energy efficiency than the gas turbines coupled with other commonly used inlet air-cooling systems. The results provide information about the research and development priorities in the future for gas-turbine performance enhancement.

The permanent magnet synchronous generator (PMSG)–based small wind turbines (SWT) are studied in recent years because of their high reliability, high efficiency and low cost. To achieve maximum power point tracking (MPPT) without mechanical sensors and improve efficiency, a novel MPPT control method is proposed in this paper. Without measurement of the shaft speed, the conventional MPPT control strategy based on the $\omega –P$ curve does not work. However, it is possible to impose the relationship between the RMS of generator output voltage ($U$) and the output power ($P$) on the optimum operating points. The innovations focus on obtaining the $U–P$ curve by relating the RMS of $U$ to the shaft speed $\omega$ and designing the controller by using the control strategy based on the $U–P$ curve. After building the whole model of the PMSG–based SWT, the RMS of $U$ is calculated theoretically from the $\omega$, and the $U-P$ curve is obtained. The generator speed controller is designed by using the control strategy based on the $U-P$ curve. The efficiency of the proposed MPPT control method is verified.

This study investigates the effect of concentrated turbulence in the spark plug zone on engine performance and combustion parameters in a hydrogen engine. The swirling flow in the cylinder was directed to the spark plug zone by a turbulator-shaped piston head during the compression stroke. The engine was operated under lean mixture and wide-open throttle (WOT) conditions at different engine speeds. Depending on the engine speed, it was found that the concentrated turbulence around the spark plug zone enhances the engine performance between 4.3 and 7.8%. The combustion duration and the cyclic variation in the engine were also reduced with the concentrated turbulence in the spark plug zone. The reduction in combustion duration was higher in the first combustion period [0–10% mass fraction burned (mfb)] than that in the other two combustion periods (10–90% and 90–100 mfb). While the indicated mean effective pressure (imep) increased, the coefficient of variations of imep was markedly decreased thanks to the concentrated turbulence around the spark plug zone.

A kinetic characterization of the ${\mathrm{CO}}_2$ gasification of chars from Chinese low-rank lignite coal is performed by isothermal thermogravimetry. The isothermal condition is 1,073 K, and the ${\mathrm{CO}}_2$ concentration range is 10–90%. Alkali and alkali earth catalysts were used to promote the gasification reactivity. The gasification rate of the char was increased with the carbon dioxide (${\mathrm{CO}}_2$) concentration. The gasification rate increment was reduced at a higher concentration, which inhibited the ${\mathrm{CO}}_2$ gasification rate. The best ${\mathrm{CO}}_2$ ratio for gasification was 70%. The gasification rate of the char with ${\mathrm{CO}}_2$ is fast and proceeded in the following order: sodium carbonate $({\mathrm{Na}}_2{\mathrm{CO}}_3)>\mathrm{potassium}$ carbonate $({\mathrm{K}}_2{\mathrm{CO}}_3)>\mathrm{calcium}$ carbonate $({\mathrm{CaCO}}_3)>\mathrm{dolomite}$. In this study, the following gas–solid reaction models are compared: the shrinking core model, the volumetric reaction model, the modified volumetric reaction model (MVRM), and the random pore model. The correlation coefficient values of the MVRM were the highest of all the models at all concentrations.

The biomass yield and mesophilic anaerobic digestion performance of Pennisetum hybrid that were collected at different harvest periods and cutting frequencies were investigated. Results indicated that chemical composition, biomass yield, and specific methane yield of Pennisetum hybrid were significantly influenced by harvest period and cutting frequency. The contents of total solids, volatile solids, carbon, cellulose, lignin and starch increased with a prolonged harvest period, whereas the nitrogen and crude protein content decreased. Specific methane yields decreased considerably from 280 to $119\mathrm{mL}/\mathrm{g}$ VS with a prolonged harvest period, whereas the biomass yield per hectare increased. A maximum dry matter yield of $41.63\mathrm{t}/\mathrm{ha}$ was achieved when the Pennisetum hybrid was harvested in October. When the cutting frequencies increased from twice to three times per year, the specific methane yields increased as the biomass yield decreased. Because of the reverse trend of anaerobic digestion performance and biomass yield with different harvest periods and cutting frequencies, the methane yield per hectare increased with prolonged harvest period and decreased cutting frequency. A maximum area-specific methane yield of $\mathrm{4,466}{\mathrm{m}}^3$ was obtained; the corresponding energy production per hectare was approximately 169.71 Gj. Methane yield from the Pennisetum hybrid in southern China suggested that this grass could be an alternative feedstock for biogas production.

The aim of this study is to investigate the use of computational fluid dynamics (CFD) in evaluating the thermal performance of a parallel/counterparallel flow heat exchanger used as part of a fluid warmer to treat hypothermia. The developed CFD model was validated in a parametric study using previously collected experimental data. The effects of heat exchanger length and inlet mass flow rate were considered. To more accurately represent the thermodynamic average temperature profile, the current CFD analysis evaluated outlet temperatures in terms of mean bulk temperature as opposed to the centerpoint temperature probe used in the experimental study. Despite this difference, the CFD results were found to agree well with the experimental values. As such, the CFD simulations are not only applicable to future design considerations but elicit further understanding of the thermal and hydrodynamic characteristics within the heat exchanger. Using the validated CFD model, thermal hydraulic entrance lengths and pressure drop within the semiannular geometry of the heat exchanger were investigated. CFD results of the semiannulus were compared to calculated values for a true concentric annulus. It was shown that the entrance length of a concentric annulus is generally longer than the semiannulus under laminar flow, and the difference is more prominent for increasing Reynolds number. Under both laminar and turbulent flow, the studied semiannulus of the hot water region demonstrated a greater pressure drop than a true concentric annulus with similar dimensions and flow conditions. The thermal and hydrodynamic properties revealed in this CFD analysis can be used to improve future design considerations, which may lead to improved hypothermia treatment protocols.

In this study, a transport gasifier–based integrated gasification combined cycle (IGCC) with 90% ${\mathrm{CO}}_2$ capture rate was analyzed to predict possible net power output and net efficiency distributions in the system under uncertainties. Moreover, the influence of each parameter on the total model output uncertainty was quantified and displayed using Pareto charts. Uncertainties in parameters of the gasifier, Selexol-${\mathrm{CO}}_2$ capture process, hydrogen-fueled gas turbine, compressors, steam turbines, and pumps were considered and quantitatively represented in uniform, triangle, or normal distributions. Monte Carlo simulation was adopted to propagate the parameters through process modeling. Results showed that the predicted median net plant efficiency of the system was 37.71% with a standard deviation of 0.41%. The unconverted carbon rate in the gasifier and the gas turbine combustor temperature (gtCMBT) exhibited the greatest effect on predicting uncertainties in efficiency and power output, respectively. Thus, future work should focus on reducing these parameter uncertainties. Comparisons are conducted between the transport gasifer–based system and the dry-feed entrained flow gasifier–based system with similar configuration. The results indicate that, even in the worst case scenario, IGCC with the oxygen-blown gasifier has a similar net efficiency to IGCC with the dry-feed entrained flow gasifier.

Since wind fluctuates with strong variation even within a short-term period, it is quite difficult to describe the characteristics of wind or to estimate the power output that will be injected into the grid. In particular, short-term wind speed forecasting, an essential support for regulatory actions and short-term load dispatching planning during the operation of wind farms, is currently regarded as one of the most difficult problems to solve. This paper contributes to multistep forecasting for short-term wind speed by developing a three-stage hybrid approach named MECE; it is a combination of the ensemble empirical model decomposition (EEMD) method, cuckoo search (CS) algorithm, and extreme learning machine (ELM) method. As the first stage of the hybrid MECE approach, a signal filtering based on a decomposition and reconstruction strategy is adopted and copied by the EEMD method, and a denoised series can be obtained. Then, the CS-optimized ELM is designed as a novel learning method to construct a single layer feed-forward neural network (SLFN); the input weights and biases are determined by the CS algorithm instead of the random initialization within the original ELM. Next, a training and forecasting stage is taken; three different strategies are adopted for multistep forecasting. The chosen data sets are half-hour wind speed observations, including 16 samples, and the simulation indicates that the proposed MECE approach performs much better than the traditional ones when addressing short-term wind speed forecasting problems.

One kind of renewable and clean fuel is n-butanol, called the second-generation biofuel. Recently, it has attracted more and more interests from energy researchers and many oil companies. Almost all related research focus on the effects of the addition of n-butanol on engine performance, combustion and emission characteristics. However, there are no previous works which can fully explain the puzzle of ${\mathrm{NO}}_{\mathrm{X}}$ emission increases. Because flame temperature has a great effect on ${\mathrm{NO}}_{\mathrm{X}}$ formation, the effects of n-butanol ratio in n-butanol-diesel fuel blends on flame temperature under open-air environment have been analyzed. The results show that as the n-butanol ratio increased in the blends, flame temperature of different layers, relative mean value of the flame temperature, the number and corresponding area of high temperature points, relative fuel consumption rate and constant pressure adiabatic flame temperature all increased. This is primarily attributable to higher oxygen content and the lower viscosity of n-butanol compared with diesel fuel.

A closed-loop system based on a detailed flat-plate collector model and a water storage tank operating in a fully mixed regime has been considered. The system operates in Timisoara, Romania, under a southeastern European temperate continental climate. Four empirical strategies for flow-rate control have been compared with an optimal control strategy, used as an ideal reference. Days for all seasons and all cloudiness classes have been considered. Also, days with more-stable or less-stable radiative regimes have been used. Under the specific climatic conditions, the most appropriate empirical control strategy uses the momentary values of solar irradiance as input data. It provides good results during all seasons, independent of the class of relative sunshine and the stability of the radiative regime. An empirical strategy based on the constant-mass flow rate has been also identified as a good alternative. This strategy might be easier to implement since it involves a single-speed pump. The recommended lag in the input data time-series is less than 10 min for all empirical strategies.

To comply with the stringent Euro VI emission standards, two techniques have been proposed for natural gas engines, namely, lean-burn combustion with oxidation catalyst (OC) and stoichiometric combustion with three-way catalyst (TWC). In this paper, comparisons are drawn between the two techniques in terms of carbon monoxide (CO), nitrogen oxides (${\mathrm{NO}}_x$), and methane (${\mathrm{CH}}_4$) emissions and fuel economy. The results indicated that the postcatalyst CO emissions of lean-burn combustion with OC are lower, whereas the postcatalyst ${\mathrm{NO}}_x$ and ${\mathrm{CH}}_4$ emissions are higher than those of stoichiometric combustion with TWC. This can be explained by the combined effects of lower engine-out CO emissions and higher engine-out ${\mathrm{NO}}_x$ and ${\mathrm{CH}}_4$ emissions as well as lower overall conversion efficiency for all emissions with the adoption of lean-burn combustion with OC. Thus, it can be concluded that although the fuel economy of stoichiometric combustion with TWC is inferior to lean-burn combustion with OC, it is still considered a more preferred technique when aiming at achieving Euro VI emission standards for its distinctive advantages in emission performance. However, it is also pointed out that further optimization of the calibration of air-to-fuel ratio is necessary for the stoichiometric operation.

Three-dimensional numerical simulations were carried out to study fuel-staged low-NOx burners (LNB). The effect of the number of staged guns (four and six) and quarl style (Venturi and boss) on the performance of the LNBs was investigated. The flow field, flame temperature, OH radical field, and NO emission were analyzed. The turbulence, radiation, and chemical reactions were simulated with the standard $k\text{-}\epsilon$ model, discrete ordinate (DO) model, and probability density function mixture fraction model, respectively, using a commercial computational fluid dynamics code. The numerical model was validated with experimental measurements at different excess air conditions. The agreement of the calculated and measured NO emission is remarkable; therefore, the present model is considered reliable. The results indicate that the number of staged guns has little effect on the NO emission; the boss quarl increases mean air velocity, changes staged gas flow direction, and reduces peak flame temperature and peak OH mole fraction. The boss quarl reduces more than 60% of the NO emission compared with the Venturi quarl.

An ethylene/air inverse diffusion flame burner was assumed to generate a stable flame, and soot samples were captured at different locations around the outer edge along the height of the flame. The soot samples were then analyzed with transmission electron microscopy (TEM), gas chromatography-mass spectrometry (GC-MS), and other detection means, and a photoacoustic analyzer was introduced to detect the mass concentration of soot nanoparticles after inception based on their optical features. The results showed that the plot of soot concentration had the same tendency as the gas temperature’s, which increased first and then declined with the increase in flame height, but these two curves had two different turning points. As to the measurements of TEM, the morphology of soot particles exhibited diverse shapes and structures at different flame heights. Alkanes, cycloalkanes, olefins, benzene, anthracene, pyrene, and aromatic compounds were determined as the main components of soot by the detection of GC-MS. The soot formation process in the ethylene flame can be speculated to be ethylene pyrolysis, soot growth, and oxidation, as well as particulate coagulation.

The aim of this work was to propose a novel system combines both solar chimney and thermo siphon solar tower systems. To this end, theoretical study to the proposed system was conducted. In this new system, the solar tower was installed at the exit of the solar chimney. The results of the theoretical study showed that, the new system generates more power compared with the conventional system. It was found that the maximum power extracted from the new system was about two times that obtained from the conventional system at the same height, for the specified range studied in this work. In addition, it was found that the new system has higher overall efficiency and generates higher speeds of air at the chimney inlet. This increase in both maximum power and air speed at the chimney inlet from the new system is enhanced with the rise in solar irradiance, radius of collector, and ratio of solar tower height to solar chimney height. Moreover, the results indicated that there is a certain ratio between solar tower length and width at which the maximum extracted mechanical power reached a maximum value for the specified parameters of solar irradiance, collector radius, height of chimney, and height of solar tower.

This paper presents start-up and a shut-down control strategies for modular multilevel converter (MMC) based multiterminal high-voltage direct-current (HVDC) systems (MMC-MTDC). An AC system charging method with voltage slop control and a DC line charging method with sequentially unblock control are firstly discussed. Based on the above two charging methods and considering the strength of the connected AC systems, a start-up control scheme suitable for MMC-MTDC systems is described. The scheduled shut-down control strategy is divided into three stages: in energy feedback stage, four methods including increasing modulation index, adjusting transformer tap, introducing third harmonic voltage injection and inserting redundant submodules (SMs) are presented; and the second stage is energy dissipation stage, in which the SM capacitor voltage is discharged to its lower limit; The SM capacitors are fully discharged by SM internal resistor in the third stage. Finally, a simulation model of five-terminal MMC-HVDC is realized in PSCAD/EMTDC. The results show that the system can be start-up smoothly as well as be shut-down rapidly and reliably, which verifies the feasibility of the proposed control strategies.

The technique of heat transfer enhancement of a nonfin cross-flow heat exchanger by a modified air angle of attack is investigated experimentally in this study. Six air angles of attack (i.e., 0°, 30°, 60°, 90°, 120°, and 150°) with the same perimeter are examined to determine their relationships to the overall heat transfer coefficient and the pressure drop; the heat exchanger performance are also tested. In the experiment, hot water (at a temperature of 75°C) with a constant flow rate and air at ambient conditions with various velocities (ranging from 2 to $7\mathrm{m}/\mathrm{s}$) flows through the heat exchanger. The results indicate that the modified air angle of attack technique can enhance the overall heat transfer coefficient; however, the pressure drop is also increased.

Combined heat and power (CHP) generates electricity and heat from the same fuel source and can provide these services at higher equivalent conversion efficiency relative to grid-purchased electricity and stand-alone steam production. Previous work has focused on the economic factors and optimal operation strategy that influence the decision to install a single CHP unit. The approach discussed in this paper is to assess the economic potential for CHP in an electricity-market equilibrium framework, accounting for the impact that CHP adoption at scale will have on electricity prices—incremental installations of CHP reduce the demand for grid-provided electricity in some locations, thus reducing wholesale prices in that location. A statistical model of electricity supply and pricing is utilized to estimate locational electricity supply curves that reflect the impact of transmission congestion on locational price formation and location-specific elasticities of supply. The zonal electricity pricing model is coupled with the model of CHP adoption and utilization in commercial buildings for two locations in the PJM power grid. Under a range of operational assumptions and fuel prices, returns to incremental CHP deployment decrease rapidly in both locations for the first 100 MW of building-integrated CHP deployed, although CHP becomes an uneconomical decision only at much higher deployment levels. Although the elasticity of supply is an important determinant of economic potential for CHP, the authors find that in most cases, operating CHP units to follow building thermal demand (versus electrical demand, which would offset peak electricity-demand periods) yields higher returns over a broader range of CHP deployment levels.

This paper presents a new approach to estimate wind speed and install a wind power turbine (WPT) in a power system. The entire installation procedure includes selecting appropriate buses and verifying the power system after installing the WPT. Two reliability indices, the power index in crisis time (PICT) and the endurance index of crisis hours (EICH), were developed and used for determining the reliability level of target buses for WPT installation. The stability and reliability of the hybrid power system formed was verified by determining the reference frequency and voltage. The results described in this paper can be applied to other small power systems using distributed generation, such as hydroelectric power generation.

The present research evaluates the thermal effectiveness of a reflective surface at the outdoor surface of a concrete roof. The objective of the reflective surface is to reduce the heat gain by reflecting most of the solar radiation in the daytime and emitting a large amount of radiation. A testing room was constructed and equipped with thermocouples, heat flux sensors, and a data acquisition module. The outdoor space is a real weather condition, whereas the indoor environment is controlled. A numerical method is employed to study the effect of the solar reflectivity of the roof and the operating month, and heat gain for all the case studies is determined. The numerical results are validated with the experimental results, which were conducted during August, and the roof with concrete and white color surfaces are tested. The results show a significant heat gain reduction when the solar reflectivity of the roof is increased, and the net heat gain through the roof can be reduced by 50%. However, the results indicate that the effectiveness of the solar radiation reflector is nearly independent of the operating month.