The effect of greenhouse vegetation coverage and area on the performance of an earth-to-air heat exchanger for heating and cooling modes

The underground temperature at a depth of about 3–4 m is almost constant all the year round. In summer, the underground temperature is lower than the ambient temperature, but in winter it is vice versa. This potentiality is considered for greenhouse cooling and heating by using an earth-to-air heat exchanger (EAHE). This paper considers the effects of two parameters as independent variables including the area of greenhouse and the percentage of vegetation coverage inside the greenhouse on the performance of an EAHE system during both cooling and heating modes. The inside temperature, the thermal energy exchange and the coefficient of performance (COP) of the system were considered as dependent variables. The results showed that both greenhouse area and the percentage of vegetation coverage inside the greenhouse had significant effects on the performance of the EAHE system during both cooling and heating modes. However, the COP of the EAHE system was higher in the cooling mode (4.32) than during the heating mode (1.01). The percentage of vegetation coverage negatively affected the performance of the EAHE system in the cooling mode. However, the performance of the EAHE system improved with the increase in the percentage of vegetation coverage during the heating mode.     

Experimental investigation of solar-powered desiccant cooling system by using composite desiccant “CaCl<Subscript>2</Subscript>/jute”

A solar-powered composite desiccant cooling system has been experimentally investigated. It consists of evacuated tube solar water heater, composite desiccant bed heat exchanger (CDBHE), direct evaporative cooling unit and cooling tower. The composite desiccant material has been synthesized by using iron mesh and jute layer impregnated with calcium chloride solution, and this composite desiccant is placed in shell- and tube-type heat exchanger to make CDBHE. In this desiccant cooling system, the evacuated tube solar water heater is used to produce required hot water for regeneration of composite desiccant material. A cooling tower is used to produce cooling water which is pumped into CDBHE during dehumidification process to remove heat of adsorption. Direct evaporative cooling unit is used to cool the outlet process air of CDBHE. It has been found that the average dehumidification rate increases by 54.1 % when using circulating cooling water. The COP_th of desiccant cooling system has been found to be 0.46 with a cooling capacity of 353.8 W.     

Experimental analysis of thermal performance of evacuated tube and flat-plate solar air collectors at different air flow rates

The thermal performances of an evacuated tube collector (ETC) and flat-plate solar air collector (FPC) are experimentally investigated at different air flow rates. To investigate the performance of the ETC and FPC, experimental set-ups were fabricated. Air was used as a working fluid and tested at the same climatic conditions. The ETC had 15 evacuated tubes with a surface area of 1.66 m². The experimental set-up consisted of a header with a hollow pipe (square pipe) in the centre through which the air flowed. The flat-plate collector had a surface area of 1.35 m². The FPC had a black painted absorber sheet which divides the collector into two sections. The air flowed through the upper and the lower sections parallel to the collector to minimize the overall heat loss. The temperature of the outlet air depends on several factors along with the airflow rate and the intensity of the solar radiation. It was found that during the day at high flow rates, the efficiency of the ETC varies from 0.12 to 0.5, and for the flat plate it was from 0.29 to 0.68. The maximum temperature of the air was 56.7°C for the ETC and 25.7°C for the FPC.     

The performance of solar powered desiccant dehumidifier in India: an experimental investigation

The regeneration and adsorption of desiccant wheel for producing the dry air was experimentally investigated. The air needed for regeneration was heated in an evacuated tube solar collector with surface area 4.44 m². The desiccant wheel is regenerated at the temperature in the range of 43.9–72.6°C. The regeneration and adsorption performances are affected by the regeneration temperature, wheel rotation, air flow rate (process and regeneration) and ambient conditions. By comparing the adsorption and regeneration performance at different air flow rate and constant rph, it was found that maximum adsorption and regeneration rates are obtained at air flow rate of 210.789 kg/h. Regeneration temperature directly affects the effectiveness of the desiccant wheel. Maximum desiccant wheel effectiveness of regeneration sector and adsorption sector is obtained at air flow rate of 105.394 kg/h. The regeneration performance of desiccant wheel with evacuated tube solar air collector is suitable for the Indian climate.     

Regional climate sensitivity of wetland environments in Rwanda: the need for a location-specific approach

Wetlands are sustaining large communities of people in Rwanda where 10 % of its land surface consists of many local wetlands. Sustainable future management of these numerous wetlands requires a reliable inventory of their location and a dynamic quantitative characterization that allows assessment of their climate change sensitivity. The aim of this study was to assess the importance of climatic factors for determining wetland location at different regional scales. Wetland locations were analyzed and statistically modeled using their location factors with logistic regression. Wetland location probability was determined using topographic (elevation, slope), hydrological (contributing area) and climatic (temperature and rainfall) location factors. A wetland location probability map was made that demonstrated a calibration accuracy of 87.9 % correct at national level compared to an existing inventory, displaying even better fits at subnational level (reaching up to 98 % correct). A validation accuracy of 86.2 % was obtained using an independently collected dataset. A sensitivity analysis was applied to the threshold values used as cutoff value between wetland/non-wetland, demonstrating a robust performance. The developed models were used in a sensitivity scenario analysis to assess future wetland location probability to changes in temperature and rainfall. In particular, wetlands in the central regions of Rwanda demonstrate a high sensitivity to changes in temperature (1 % increase causes a net probable wetland area decline by 12.4 %) and rainfall (+1 % causes a net increase by 1.6 %). This potentially significant impact on wetland number and location probability indicates that climate-sensitive future planning of wetland use is required in Rwanda.     

Recycling and Reusing Heat Energy During the Production of Powdery Phospholipid

The temperature is 56.5°C when acetone gas is rectified during the production of powdery phospholipid. If heat exchanger is added, heat energy that is reclaimed can be used by other heaters. On the basis of exchange hot water (51°C) 4m³ every minute, a factory with the productivity of powdery phospholipid being 10 ton a day can save 533.2 ton standard coal which is equivalent to 746.48 ton common coal. If this technique of saving energy and reducing emission could be widely used in correlative industries of all over the country, economic benefits will be prominent.     

Mapping of bioclimatic comfort for potential planning using GIS in Aydin

People are relaxed (satisfied or well-off) in what is described as comfortable climatic conditions. In such conditions, a person’s energy balance is not disturbed because of stresses from extreme heat or cold. Bioclimatic structure has been well researched and should be a consideration in the planning process for arranging comfortable spaces. It represents the understanding that energy balance is one of the basic elements of a sustainable landscape design. The goals of this study have been to create ideal places for human thermal comfort and to advance objectives focused on the importance of sustainable and ecological landscape planning and design work, along with their accompanying economic benefits. In this study, which focuses on the climate of the Province of Aydin, the most suitable areas for bioclimatic comfort have been identified. The climate values for the Aydin Province have been taken from a total of 22 meteorological stations. Stations at altitudes ranging from 11 to 871 m were used to note the climate changes that occurred. The average temperature, relative humidity, and wind speed from each station, including data collected using Geographic Information System (GIS) software, were transferred. GIS maps were then created from the imported data, and areas of optimal comfort around the city of Aydin were determined. The results show the range that is suitable for a bioclimatic comfort zone in Aydin. The bioclimatic comfort range was determined to be roughly 17 °C for Aydin, and the city of Aydin demonstrated a comfort range between 14 and 19 °C. As a result, the city of Aydin was shown to be a suitable area for bioclimatic comfort.     

Simulation and analysis of a combined cycle heat and power plant process

The regulations of process efficiency and stricter environmental policies require analysis of large-scale thermal energy systems to produce highly efficient, cost effective and low environmental impact energy. For analysis, it is beneficial to simulate an energy system. In this paper, simulation models are developed for the analysis of a combined cycle heat and power plant located in Göteborg, Sweden. With the help of simulation models, characteristics between district heating (DH) water temperature and key parameters such as overall district heat duty, electrical power and electrical efficiency has been developed. The characteristics are useful to estimate and maximize the key parameters during varying DH water temperature. According to a comparison between the full-load simulation models of 2006 and 2013 for the selected power plant, a loss of 2 MW is noticed for gas turbine and a loss of 2.18 MW of heat flow occurs for heat recovery steam generator in the year 2013. The feasibility analysis of modifying the connection between DH economizer and main DH line provides good performance indicators in a winter scenario. The conclusions in this paper are good references to plan and improve the performance of existing large-scale thermal power plants.     

Characterizing heat stress on livestock using the temperature humidity index (THI)—prospects for a warmer Caribbean

There is an urgent need to mitigate climate change-induced heat stress in livestock and poultry in the Caribbean, given the deleterious effects it has on food and nutrition security. The temperature humidity index (THI) was used to assess the potential for heat stress on four types of livestock and poultry (broiler and layer chickens, pigs and ruminants) for three different agro-ecological locations in Jamaica. The THI was formulated specifically to each livestock type and was examined for 2001–2012 for seasonal and annual patterns of variability. Differences in THI were observed between summer (July to September) and winter (December to February) with some moderation due to agro-ecological location. Our results suggest that animals in ambient field conditions in Jamaica may already be experiencing considerable periods of heat stress even during the relatively cooler northern hemisphere winter months. Future patterns of heat stress relative to a 1961–1990 baseline were derived from a regional climate model when mean global surface air temperature is 1.5, 2.0 and 2.5 °C above pre-industrial levels. At 1.5 °C, marked increases were noted in THI and almost persistent year-round heat stress is projected for Caribbean livestock. Conditions will be exacerbated at the higher global warming states. Possible response strategies such as cooling technologies are discussed.     

Contrasting impacts of climate change across seasons: effects on flatfish cohorts

The Senegal sole, Solea senegalensis, is a species of flatfish that has several distinct cohorts of 0-group juveniles which use estuarine nurseries in summer and winter. The early cohort is more abundant and grows faster than the late cohort that stays in the nurseries during winter; however, climate warming may have an impact on the dynamics of this species’ juveniles. This study aimed to compare mortality, metabolic response and growth of S. senegalensis juveniles at different temperatures, reflecting present-day temperature (winter—12 °C; summer—24 °C) and future temperature (plus 3 °C) conditions, in estuarine nurseries in the southern European population. Mortality was low at 12 °C, being only 10 %, increasing to 30 % at 15 °C, 40 % at 24 °C and at 27 °C it hit 70 %. Metabolic rate increased steadily with increasing temperatures, yet it increased steeply from 24 to 27 °C. Thermal sensitivity was high for the temperature interval between 24 and 27 °C. Growth was very slow at 12 °C, at a rate of 0.03 mm day^?1, increasing to 0.22 mm day^?1 at 15 °C, and to 0.60 mm day^?1, at 24 °C. However, at 27 °C growth rapidly declined to 0.12 mm day^?1. Warming will be beneficial for the late cohort, resulting in a major increase in growth. However, the early cohort will not benefit from warming, due to high mortality and arrested growth, which clearly indicates that this species is under severe thermal stress at 27 °C. Thus, here we show, for the first time, that climate change may induce contrasting seasonal impacts on fish bio-ecology and physiology, namely in species with several cohorts over the course of the year. Phenotypic and/or genotypic plasticity may limit the impacts of climate change.     

Climate change impacts on a pine stand in Central Siberia

The objective of this paper is to analyse the impacts of climate change on a pine forest stand in Central Siberia (Zotino) to assess benefits and risks for such forests in the future. We use the regional statistical climate model STARS to develop a set of climate change scenarios assuming a temperature increase by mid-century of 1, 2, 3 and 4 K. The process-based forest growth model 4C is applied to a 200-year-old pine forest to analyse impacts on carbon and water balance as well as the risk of fire under these climate change scenarios. The climate scenarios indicate precipitation increases mainly during winter and decreases during summer with increasing temperature trend. They cause rising forest productivity up to about 20 % in spite of increasing respiration losses. At the same time, the water-use efficiency increases slightly from 2.0 g C l^?1 H₂O under current climate to 2.1 g C l^?1 H₂O under 4 K scenario indicating that higher water losses from increasing evapotranspiration do not appear to lead to water limitations for the productivity at this site. The simulated actual evaporation increases by up to 32 %, but the climatic water balance decreases by up to 20 % with increasing temperature trend. In contrast, the risk of fire indicated by the Nesterov index clearly increases. Our analysis confirms increasing productivity of the boreal pine stand but also highlights increasing drought stress and risks from abiotic disturbances which could cancel out productivity gains.     

The design of cyclonic pre-heaters in suspension cement kilns

Cement manufacturing consumes two main types of energy: fuel and electricity. On average, energy costs represent 40% of the total production costs per ton of cement. The challenge is to reduce the consumption of energy to about 3000 MJ/ton clinker without the consumption of massive additional amounts of electricity, which is normally associated with additional fuel-saving measures. This can only be achieved by implementing sound thermal energy optimization measures. Energy-efficient suspension cement kilns are now widely applied and use a cascade of cyclonic pre-heaters of moist particulate feedstock, with heat transfer from hot kiln exhaust gas to particles being a function of heat transfer coefficient, temperature difference and gas–solid contact mode and time. The gas–solid contact mode and time depend on particle movement in cyclones, which has previously been studied by positron emission particle tracking. Heat transfer is governed by Nusselt–Reynolds equations, with gas velocity and properties being a function of the temperature profile along the cascade of cyclones. A stepwise approach of the design thus combines changing hydrodynamics and heat transfer along the successive cyclones, with the overall thermal balance of the cascade as control. This approach leads to major design recommendations, as developed in the present paper.     

Energy and exergy analysis of solar hybrid adsorption refrigeration system

In this paper, performance of a solar hybrid adsorption refrigeration (AR) system is investigated experimentally. Such a system was built and tested under the conditions at National Institute of Technology Calicut, Kerala, India. The hybrid system has been designed for heating 50 l of water from 25 to 90°C as well as cooling 10 l of water from 25 to 10°C. The experimental results demonstrate that the refrigerator has a cooling capacity of 47–78 W with a cycle coefficient of performance (COP) of 0.19 and maximum possible COP of 0.45. In exergy analysis of the system, the irreversibility and exergetic efficiency of each component of the system have been calculated. The exergy analysis reveals that the main source of irreversibility is the adsorbent bed of the AR system, emphasising that the input heat energy is not utilised efficiently due to material constraints. The exergetic efficiencies of condenser, expansion device, evaporator and adsorbent bed are found as 42.3%, 79.8%, 54.7% and 11%, respectively.     

Thermal performance of a central annular cavity vessel with fins of a box-type solar cooker

Solar cooker is an alternate device used for reducing the problems of energy supply for cooking needs, especially in rural households. Though solar cookers have been commercialised in rural and other domestic areas, further research is still required to enhance the efficiency of the solar cooker. Previous studies have helped to ascertain that the central annular cylindrical hole in the cooking vessel reduces the length of the heat-transfer path and provides higher heat-transfer rate to the water kept in the vessel. Convective heat transfer can be further increased by providing additional surface area in the cylindrical hole. This study proposes a new cooking vessel with central annular cavity and fins attachment that will help in increasing the heat-transfer rate to the cooking vessel. Experiments are conducted with three types of vessels, i.e. conventional cooking vessel, cooking vessel with central annular cavity and cooking vessel with rectangular fins in the central annular cavity. For the annular cavity with fins vessel, a peak temperature of 98°C is observed. The maximum temperature difference of 30°C has been observed between annular cavity vessel with fins and conventional vessel. As the height of the lug is also expected to play an important role, experiments are conducted to determine the effect of lug height on the heat transfer to the cooking vessel. This study indicates that a lug height of 9 mm is optimum for maximum heat transfer to the cooking vessel.     

Evaluation of an air-to-air heat exchanger

A room-size, residential air-to-air heat exchanger was tested for effectiveness of heat recovery. The experiments were conducted in a small (16.6 m³), wood frame building, the Test Chamber, on the roof of a laboratory building. The Test Chamber is a controlled and instrumented structure for which we have the ability to predict within 1% the heat loss rate over a 6-h nighttime period. With the heat exchanger installed and operating in the Test Chamber, the heat recovery efficiency was determined by comparing the actual heat loss to that expected due to the mechanically induced ventilation. The heat exchanger recovered almost 50% of the heat contained in the outgoing air flow. Additional experiments quantified effects of fan power consumption and heat conduction through the case of the device. By considering these effects, we determined that the heat exchanger itself works at an efficiency less than the manufacturer's claim. Conducting the experiments in a real building has provided insights and evaluations not possible in an indoor laboratory.     

Exposure of atoll population to coastal erosion and flooding: a South Tarawa assessment, Kiribati

Atoll countries are particularly vulnerable to coastal hazards in the context of global change, which justifies the interest in population exposure assessments. This paper contributes to addressing this need by assessing the current exposure of the population of two areas of the South Tarawa Urban District (Tarawa Atoll, Republic of Kiribati) to coastal erosion and flooding. The assessment is based on data relating to island morphology (digital terrain models and shoreline change), land use (building extension and coastal works) and environmental changes reconstructed for the 1969–2008 period. The results highlight rapid changes in land use and significant differences in current population exposure to coastal erosion and flooding between and within study sites. Between 1969 and 2007–2008, the built area located less than 20 m from the reference shoreline has increased by a factor of 4.2 at Bairiki and by a factor of 32.2 at Eita–Bangantebure, enhancing population exposure given that land elevation is low (12.6 and 77.4 % <2 m at Bairiki and Eita–Bangantebure, respectively). Nevertheless, in Bairiki, 87.5 % of the built area is currently not exposed to coastal erosion (>20 m from the coastline) and flooding (>1.5 m). Building exposure is higher at Eita–Bangantebure, where 71.3 % of the built area is currently not exposed (using the same criteria), but 17.1 % shows medium to very high levels of exposure, due to very low land elevation (22.3 % of the land area <1.5 m) and shoreline recession. The Eita–Bangantebure case study exemplifies the maladaptive trajectories of change that have been reported in other atoll countries.     

Spatio-temporal analysis of climatic variables in the western part of Bangladesh

Monitoring and detecting trends of climatic variables like rainfall and temperature are essential for agricultural developments in the context of climate change. The present study has detected trends in annual and cropping seasonal rainfall and temperature data for the period of 1961–2011 using Mann–Kendall (MK) test, Spearman’s rho (SR) test and modified Mann–Kendall test that has been applied to the significant lag-1 serial correlated time series data, and slope has been estimated using Sen’s Slope estimator for twelve meteorological stations located in the western part of Bangladesh covering about 41 % of the country. Almost 71 % trends explored by MK test in annual rainfall are statistically insignificant, and SR test also complies it. The spatial distribution of rainfall trend shows insignificant positive trends in major part of the area. Significant positive trends both by MK test and by SR test at 95 % confidence levels are observed at rates of 8.56, 11.15 and 13.66 mm/year at Dinajpur, Rangpur and Khepupara stations, respectively, and the Kharif season rainfall of these stations also shows significant increasing trends except Dinajpur. On the other hand, significant decreasing trends in annual rainfall are found at Bhola (?11.67 mm/year) and Rajshahi (?5.951 mm/year) stations and decreasing trends in rainfall dominated the Pre-Kharif season over the area. But, 83.33 % of the stations show rising trends in annual mean temperature with significant positive trends (as observed by both MK test and SR test) at Rangpur, Bogra, Faridpur, Jessore and Bhola stations where the rate of changes vary from 0.013 °C/year at Faridpur to 0.08 °C/year at Bhola. Most of the trends in Rabi and Pre-Kharif seasons of mean temperatures are not statistically significant. However, all stations except Barisal show significant rising trends in temperature in Kharif season. To cope with this changing pattern of rainfall and temperature, effective adaptation strategies should be taken to keep up the agricultural production that is related to livelihood of the most people and to ensure the country’s food security.     

Dynamic simulation of a decentralized polygeneration plant providing SNG,steam and power

The behaviour of a decentralized polygeneration plant providing synthetic natural gas (SNG), steam and electrical power is simulated in three scenarios in this study. The plant size is based on an assumed capacity of decentralized polygeneration plants processing 1070 m³ h^?1 (STP) of syngas. 396 m³ h^?1 (STP) of raw SNG, 0.4 t h^?1 of steam at 5 bar and 670 kW of electrical power can be generated by the plant at the reference scenario. Methanation reactor and steam generator are modelled in detail. Further results indicate that such a polygeneration plant can provide positive and negative operation reserves for the electricity network to the extent of 100% of the reference power output, while the amount of generated steam varies by less than 40%. At the same time, the generated SNG quality keeps constant. Lower variations in the amount of generated steam are applicable when reducing the operation reserve capacity.     

Increasing concentrations of aerosols offset the benefits of climate warming on rice yields during 1980–2008 in Jiangsu Province, China

The impacts of climate change on crop yield have increasingly been of concern. In this study, we investigated the impacts of trends in sunshine duration (S) and maximum temperature (T _max) on rice yields in Jiangsu Province at both the provincial and county level during the period from 1980 to 2008. The results showed that although S and T _max both were positively correlated with rice yields, the combined impacts of the decreasing trend of S (0.37 h/decade) and the increasing trend of T _max (0.34 °C/decade) in August caused a reduction of 0.16 t ha^?1 in rice yields (approximately 1.8 %) in Jiangsu Province, and the trend of S had played a dominant role in the yield losses. Further analyses suggest that the increasing concentration of aerosols from rapid economic development in Jiangsu Province has caused a significant solar dimming at least since 1960, making mitigations and adaptation measurements on regional haze impact imperative. Our study provides a prototype for detecting negative feedback on agricultural production caused by intensified anthropogenic activities that aim only to create rapid economic development.     

Performance analysis of a new sustainable evaporative cooling pad made from coconut coir

This paper reports a performance analysis for a new sustainable engineering application to beneficially reuse an abundant agricultural waste, coconut coir (Cocos nucifera), in evaporative cooling pads. Two small coconut coir pads of different configurations were fabricated and tested using a laboratory‐scale experimental arrangement. The air supply velocity was controlled and varied between 1.88 and 2.79 m s^?1. Heat and mass transfer coefficients, evaporative cooling efficiency and pressure drop across the two types of coconut coir pad were analysed and compared with those of a commercial rigid media paper pad. Results show that the cooling efficiency of the manufactured coconut coir evaporative cooling pad was fairly good (about 50%) and close to that of the commercial paper pad (about 47%). The average pressure drop across the two coconut coir pads was 1.5 and 5.1 Pa respectively. Correlations for heat and mass transfer coefficients expressed using Nusselt and Sherwood numbers are also reported. In addition, the cooling potential of the coconut coir pads was analysed using the average climatic conditions of the central region in Thailand throughout the year. The analysis showed that the air temperature leaving the coconut coir pad varied from 23 to 28°C. Commercial development appears feasible given the coconut coir pad's good performance, lower cost and its availability throughout the country.