A methodology to assess suitability of a site for small scale wet and dry CSP systems

This study presents a methodology to assess suitability of a site for small scale concentrated solar power (CSP) systems for its energy conversion efficiency and make‐up water requirement. Energy conversion efficiency of CSPs relies not only on the level of direct solar radiation but also on the performance of the cooling system. Regions with high solar potential have to deal with heat rejection at elevated temperatures which causes reduced energy conversion efficiencies due to high condenser temperatures. It is desirable to utilize wet cooling systems as they can achieve temperatures lower than the dry bulb temperature by evaporative cooling. On the other hand, such regions usually lack water resources which deteriorate the sustainable nature of CSP applications. This study combines various available models for both solar resource estimation and cooling systems' performance considering (i) the influence of ambient temperatures, and (ii) the influence of humidity levels. These models are integrated together to analyze the use of dry or wet cooling systems in terms of overall energy output and water consumption at a selected site in northern Cyprus. The model inputs consist of only annual hourly surface weather data and the location of the site of interest. The results show that dry cooling unit at northern Cyprus is capable of saving water about 18.7 ton/MWh while it produces 27% less energy compared to the wet cooling alternative for the representative annual weather data. Copyright © 2015 John Wiley & Sons, Ltd.     

The thermal efficiency improvement of a steam Rankine cycle by innovative design of a hybrid cooling tower and a solar chimney concept

In the present work, a dry cooling tower and a solar chimney design are recombined in order to increase the thermal efficiency of a steam Rankine cycle. The rejected heat from the condenser into the dry cooling tower supplemented by the solar radiation gained through its transparent cover are the sources of wind energy generation that is captured by a wind turbine which is located at the beginning of the chimney. In this research a case study for a 250 MW steam power plant of Shahid Rajaee in Iran has been performed. A CFD finite volume code is developed to find the generated wind velocity at the turbine entrance for a 250 m dry cooling tower base diameter and a chimney height of 200 m. Calculations have been iterated for different ambient temperatures and solar irradiances, representing temperature gradient within day length. A range of 360 kW to 3 MW power is obtained for the change in the chimney diameter from 10 to 50 m. The results show a maximum of 0.37 percent increase in the thermal efficiency of a 250 MW fossil fuel power plant unit; which proves this design to be a significant improvement in efficiency of thermal power plants, by capturing the heat that is dissipated from dry cooling towers.     

Study on a silica gel–water adsorption chiller integrated with a closed wet cooling tower

A silica gel–water adsorption chiller integrated with a closed wet cooling tower is proposed. This adsorption chiller consists of two vacuum chambers, each with one adsorber, one condenser and one evaporator. Vacuum valves were not adopted in this chiller in order to enhance the reliability. A novel heat recovery process was carried out after a mass recovery-like process to improve the coefficient of performance (COP). Integration of the closed wet cooling tower into the chiller could ensure the cleanliness of cooling water circulating in the chiller and also promote the convenient setup of the chiller. A transient one-dimensional mathematical model was adopted to study this adsorption chiller. The simulated results showed that the cooling power and COP were 10.76 kW and 0.51 respectively when the hot water inlet temperature, the chilled water inlet temperature, the air inlet wet bulb temperature and dry bulb temperature were 85, 15, 28 and 30 °C respectively.     

The role of integrated landscape design in energy conservation in detached dwellings in the Arabian Gulf region

This paper presents an overview of the landscape design considerations, rationale for the selection of specific hard and soft landscape elements and initial observations of their influence in controlling the microclimate in detached residential buildings in the Arabian Gulf region. This experiment is part of a wider research programme in the field of passive solar cooling strategies at the King Faisal University, sponsored by the Joint United States-Saudi Arabian Programme for Cooperation in the field of Solar Energy (SOLERAS). The objective is to identify the comfort enhancement potential of a carefully planned and executed integrated landscape design in a full-scale prototype passive solar cooling test house. Conventional concrete-block load-bearing construction with external insulation and heavy internal thermal mass was used. Fanger Predicted Mean Vote, as a function of dry bulb temperature, wet bulb temperature, air velocity and mean radiant temperature, was calculated and recorded continuously. These values have been averaged to evaluate hourly comfort conditions in various zones of the test house. Outdoor solar radiation and heat transferred through walls, openings and roof were similarly recorded before landscape layout and during the initial growth process of the plant material. The full potential of an integrated landscape design towards comfort enhancement can only be assessed after several years of continuous monitoring during the growth period of the plant material. Initial observations, nevertheless, tend to confirm results obtained by other researchers in their studies of the effects of specific individual landscape elements.     

Thermodynamic assessment of gas removal systems for single-flash geothermal power plants

Geothermal fluids contain non-condensable gases (NCGs) at various amounts. NCGs flow to a conventional geothermal power plant (GPP) with steam phase and should be withdrawn from the condenser by a gas removal system to prevent increase in condenser pressure and consequently decrease in power generation. Therefore, to remove NCGs from the system is critical especially at high NCG fractions. In this study, the net power output and specific steam consumption of a single-flash GPP is evaluated depending on the separator pressure, NCG fraction and wet bulb temperature of the environment, and three different conventional gas removal options which are two-stage steam jet ejector system, two-stage hybrid system and two-stage compressor system. A simulation code is written in EES to model the plant for each option. The model uses the data of Kizildere Geothermal Power Plant (KGPP) – Turkey, which is a single-flash plant with extremely high NCG fraction, to allow a comparison between the results of the modelling and the operational data of an actual single-flash GPP. Under given conditions, thermodynamic analysis resulted that NCG fraction is the most significant factor on GPP performance and the compressor system is the most efficient and robust option where the influence of the NCG fraction is limited.     

Modelling of a solar-operated absorption air conditioner system with refrigerant storage

A detailed dynamic model of a solar air conditioning system is reported. The model, including the solar collector and cooling tower, is described in terms of design parameters. Ambient wet and dry bulb temperatures and solar radiation are the required inputs. System temperatures, energy flows and coefficient of performance can be predicted. Careful attention is given to the evaporator model and the control of refrigerant flow. Typical performance results are discussed. Finally several recommendations for future investigations are made.     

Solar enhanced natural draft dry cooling tower for geothermal power applications

This paper presents a new concept of hybrid cooling, named solar enhanced natural draft dry cooling tower (SENDDCT), in which solar collectors are added to traditional natural draft dry cooling towers to increase their performance. The purpose of using solar energy in this new cooling system is to increase the suction through the tower so that more air flow is achieved through the compact heat exchangers that cool condensers of a geothermal power plant. For the same size of the cooling tower, more air flow across the heat exchangers means more heat can be rejected by the system. The governing equations for the SENDDCT are similar to those of a conventional natural draft dry cooling tower except that solar heating is added after the heat exchanger bundles. Performance comparisons show that SENDDCT has substantial advantages over conventional natural draft dry cooling towers for geothermal power plants as well as standalone solar chimney power plants.     

Thermal Performance Investigation of Mechanical Draft Cooling Tower Using Psychrometric Gun Technique

This paper presents an experimental work that studies the performance of a counterflow cooling tower with expanded wire mesh packing. Due to complicated configuration of the expanded wire mesh packing surface, it is not possible to measure the temperature of the air in the intermediate section of the cooling tower, but only that of the exit air and water temperature. In the experimental study a new concept of psychrometric gun technique is used to measure dry/wet bulb temperature of air at intermediate points of tower packing. First, the paper elaborates on the effect of atmospheric conditions, water mass flow rate and inlet temperature on the variation of the thermodynamics properties of moist air inside the cooling tower and thermal performance characteristics. Second, exergy analysis is applied to study the cooling tower potential of performance using the psychrometric gun technique. An analytical model was compared with experimental data.     

Investigation of solar pond surface zone temperature assumptions

This paper presents the results of tests concerning two assumptions about the surface zone of a solar pond. The first assumption is that the surface zone temperature of the solar pond is equal to the air dry bulb temperature, and the second one is that it is equal to the air wet bulb temperature. The surface zone temperature and the storage zone temperature are predicted by using a lumped-parameter model. The experimental results of the surface zone conform well with theoretical values. The results indicate that the air dry bulb temperature is more accurate in winter-time but that the errors generated by both assumptions are almost equal in the summer-time.     

Performance and cost of wet and dry cooling systems for pulverized coal power plants with and without carbon capture and storage

Thermoelectric power plants require significant quantities of water, primarily for the purpose of cooling. Water also is becoming critically important for low-carbon power generation. To reduce greenhouse gas emissions from pulverized coal (PC) power plants, post-combustion carbon capture and storage (CCS) systems are receiving considerable attention. However, current CO₂ capture systems require a significant amount of cooling. This paper evaluates and quantifies the plant-level performance and cost of different cooling technologies for PC power plants with and without CO₂ capture. Included are recirculating systems with wet cooling towers and air-cooled condensers (ACCs) for dry cooling. We examine a range of key factors affecting cooling system performance, cost and plant water use, including the plant steam cycle design, coal type, carbon capture system design, and local ambient conditions. Options for reducing power plant water consumption also are presented.     

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2·5% dry bulb temperatures, 2·5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system. © 1998 John Wiley & Sons, Ltd.     

Simple predictive tool to estimate relative humidity using wet bulb depression and dry bulb temperature

In this work, a simple predictive tool is presented to estimate relative humidity as a function of wet bulb depression and dry bulb temperature. The predictive tool is simple, straightforward, and can be readily implemented in any standard spreadsheet program leading to accurate, smooth, and non-oscillatory datapoints. The prime application of the method is as a quick-and-easy evaluation tool in conceptual development and scoping studies where the estimation of the relative humidity, as a function of wet bulb depression and temperature, is being considered. Results from the proposed correlation are successfully compared to available data in the literature for a wide range of wet bulb depression and dry bulb temperatures. This gives us the confidence to offer our findings for engineering applications where a rough and ready programmable estimate is sought.     

Parametric analysis of a solar energy based multigeneration plant with SOFC for hydrogen generation

Renewable energy-based hydrogen production plants can offer potential solutions to both ensuring sustainability in energy generation systems and designing environmentally friendly systems. In this combined work, a novel solar energy supported plant is proposed that can generate hydrogen, electricity, heating, cooling and hot water. With the suggested integrated plant, the potential of solar energy usage is increased for energy generation systems. The modeled integrated system generally consists of the solar power cycle, solid oxide fuel cell plant, gas turbine process, supercritical power plant, organic Rankine cycle, cooling cycle, hydrogen production and liquefaction plant, and hot water production sub-system. To conduct a comprehensive thermodynamic performance analysis of the suggested plant, the combined plant is modeled according to thermodynamic equilibrium equations. A performance assessment is also conducted to evaluate the impact of several plant indicators on performance characteristics of integrated system and its sub-parts. Hydrogen production rate in the suggested plant according to the performance analysis performed is realized as 0.0642 kg/s. While maximum exergy destruction rate is seen in the solar power plant with 8279 kW, the cooling plant has the lowest exergy destruction rate as 1098 kW. Also, the highest power generation is obtained from gas turbine cycle with 7053 kW. In addition, energetic and exergetic efficiencies of solar power based combined cycle are found as 56.48% and 54.06%, respectively.     

单元式露点蒸发冷却装置的实验研究

本研究设计了一台由干、湿通道相结合的单元式露点蒸发冷却装置,通过实验研究了蒸发冷却装置在空气经过一级冷却的模式1和经过二级冷却的模式2两种运行模式下,不同空气入口参数时的换热效果。实验结果表明,空气的入口温度越高,换热效果越好;低湿度时空气的进出口温差比高湿度时大,但其湿球效率和露点效率反而较低,这说明2种效率并不适用于不同湿度间的冷却效果对比;模式2运行时的换热效果比模式1好。与已有研究成果对比表明,该单元式露点蒸发冷却装置的湿球效率和露点效率分别可以达到120%和88%,为露点蒸发冷却装置的优化设计提供理论依据和优化方向。     

A new scheme for cooling tower water conservation in arid-zone countries

Cooling towers (CTs) that are used for heat rejection in water-cooled (WC) systems consume a large quantity of water, which is generally not available naturally. CTs are selected when the maximal cooling load is desired and under the worst design conditions. Typically, CTs operate under partial-load conditions and/or favorable weather conditions. Moreover, for most of the summer season, the dry bulb temperature (DBT) of the incoming ambient air is significantly greater than the incoming hot water temperature, and the air undergoes sensible cooling. Currently, the control scheme that is commonly used in most CTs maintains a constant exiting water temperature for different cooling loads and a different ambient wet bulb temperature (WBT) by regulating the air circulation through the CT. The air circulation is reduced with the help of a variable frequency drive (VFD), which results in a significant reduction in the fan power of the CT. This paper presents an assessment of CT performance with a VFD application using a computer simulation program and illustrates a proposed scheme for maximal water savings. These theoretical results demonstrated that reducing the air flow by applying a VFD in a CT can achieve at least a 25% reduction in water consumption.     

Performance enhancement of gas turbines by inlet air‐cooling in hot and humid climates

In this paper, a model to study the effect of inlet air‐cooling on gas turbines power and efficiency is developed for two different cooling techniques, direct mechanical refrigeration and an evaporative water spray cooler. Energy analysis is used to present the performance improvement in terms of power gain ratio and thermal efficiency change factors. Relationships are derived for an open gas turbine cycle with irreversible compression and expansion processes coupled to air‐cooling systems. The obtained results show that the power and efficiency improvements are functions of the ambient conditions and the gas turbine pressure ratio. The performance improvement is calculated for, ambient temperatures from 30 to 50°C, the whole range of humidity ratio (10–100%) and pressure ratio from 8 to 12. For direct mechanical refrigeration air‐cooling, the power improvement is associated with appreciable drop in the thermal efficiency. The maximum power gain can be obtained if the air temperature is reduced to its lowest limit that is the refrigerant evaporation temperature plus the evaporator design temperature difference. Water spray cooling process is sensitive to the ambient relative humidity and is suitable for dry air conditions. The power gain and efficiency enhancement are limited by the wet bulb temperature. The performance of spray evaporative cooler is presented in a dimensionless working graph. The daily performance of the cooling methods is examined for an ABB‐11D5 gas turbine operating under the hot humid conditions of Jeddah, Saudi Arabia. The results indicate that the direct mechanical refrigeration increased the daily power output by 6.77% versus 2.57% for the spray air‐cooling. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance simulation of solar-boosted ocean thermal energy conversion plant

Ocean thermal energy conversion (OTEC) is a power generation method that utilizes small temperature difference between the warm surface water and cold deep water of the ocean. This paper describes the performance simulation results of an OTEC plant that utilizes not only ocean thermal energy but also solar thermal energy as a heat source. This power generation system was termed SOTEC (solar-boosted ocean thermal energy conversion). In SOTEC, the temperature of warm sea water was boosted by using a typical low-cost solar thermal collector. In order to estimate the potential thermal efficiency and required effective area of a solar collector for a 100-kWe SOTEC plant, first-order modeling and simulation were carried out under the ambient conditions at Kumejima Island in southern part of Japan. The results show that the proposed SOTEC plant can potentially enhance the annual mean net thermal efficiency up to a value that is approximately 1.5 times higher than that of the conventional OTEC plant if a single-glazed flat-plate solar collector of 5000-m² effective area is installed to boost the temperature of warm sea water by 20 K.     

Evaluation of cooling technologies of concentrated solar power plants and their combination with desalination in the mediterranean area

Different alternatives for the effective integration of desalination technologies in the cooling of concentrating solar power (CSP) plants in the Mediterranean area are discussed and evaluated. Two cases are considered where a low temperature multi-effect distillation (LT-MED) plant is integrated into a CSP plant replacing the condenser of the power cycle. In one case, a LT-MED plant is fed by steam at the outlet of the turbine expanded to 70 °C. In the other case a LT-MED is fed by the steam obtained from a thermal vapour compressor (TVC) which uses the exhaust steam of the CSP plant (at 37 °C, 0.063 bar) together with some from the high pressure turbine extraction (17 bar). The two cases are compared with that of a reverse osmosis (RO) unit powered by the electricity produced by the CSP plant. In this case, two different wet cooling technologies, once-through and evaporative water cooling, and a dry air cooling are considered for the CSP plant. Thermodynamic simulations are presented for all cases, together with an economic analysis.     

Energetic and exergetic assessments of a novel solar power tower based multigeneration system with hydrogen production and liquefaction

In this article, a thermodynamic investigation of solar power tower assisted multigeneration system with hydrogen production and liquefaction is presented for more environmentally-benign multigenerational outputs. The proposed multigeneration system is consisted of mainly eight sub-systems, such as a solar power tower, a high temperature solid oxide steam electrolyzer, a steam Rankine cycle with two turbines, a hydrogen generation and liquefaction cycle, a quadruple effect absorption cooling process, a drying process, a membrane distillation unit and a domestic hot water tank to supply hydrogen, electrical power, heating, cooling, dry products, fresh and hot water generation for a community. The energetic and exergetic efficiencies for the performance of the present multigeneration system are found as 65.17% and 62.35%, respectively. Also, numerous operating conditions and parameters of the systems and their effects on the respective energy and exergy efficiencies are investigated, evaluated and discussed in this study. A parametric study is carried out to analyze the impact of various system design indicators on the sub-systems, exergy destruction rates and exergetic efficiencies and COPs. In addition, the impacts of varying the ambient temperature and solar radiation intensity on the irreversibility and exergetic performance for the present multigeneration system and its components are investigated and evaluated comparatively. According to the modeling results, the solar irradiation intensity is found to be the most influential parameter among other conditions and factors on system performance.     

Development and thermodynamic assessment of a novel solar and biomass energy based integrated plant for liquid hydrogen production

In this paper, a combined power plant based on the dish collector and biomass gasifier has been designed to produce liquefied hydrogen and beneficial outputs. The proposed solar and biomass energy based combined power system consists of seven different subplants, such as solar power process, biomass gasification plant, gas turbine cycle, hydrogen generation and liquefaction system, Kalina cycle, organic Rankine cycle, and single-effect absorption plant with ejector. The main useful outputs from the combined plant include power, liquid hydrogen, heating-cooling, and hot water. To evaluate the efficiency of integrated solar energy plant, energetic and exergetic effectiveness of both the whole plant and the sub-plants are performed. For this solar and biomass gasification based combined plant, the generation rates for useful outputs covering the total electricity, cooling, heating and hydrogen, and hot water are obtained as nearly 3.9 MW, 6584 kW, 4206 kW, and 0.087 kg/s in the base design situations. The energy and exergy performances of the whole system are calculated as 51.93% and 47.14%. Also, the functional exergy of the whole system is calculated as 9.18% for the base working parameters. In addition to calculating thermodynamic efficiencies, a parametric plant is conducted to examine the impacts of reference temperature, solar radiation intensity, gasifier temperature, combustion temperature, compression ratio of Brayton cycle, inlet temperature of separator 2, organic Rankine cycle turbine and pump input temperature, and gas turbine input temperature on the combined plant performance.