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A hybrid evaporative pre-cooled air-conditioning system has been proposed for operation in humid tropical climatic conditions. The indirect evaporative heat exchanger (IEHX) works in tandem with a conventional air handling unit (AHU). The IEHX operates as an evaporative-enhanced heat recovery device to treat the ambient intake air. An experimental study has been carried out to systematically investigate the performance of a lab-scale IEHX when combined with a chiller under steady-state conditions. In addition, a mathematical model is judiciously developed for both the IEHX and cooling coil. Key results have indicated that the IEHX is capable of pre-cooling and pre-dehumidifying the ambient intake air. In addition, the pre-cooling process facilitates the supply of a higher chilled water supply temperature to meet cooling needs particularly at higher outdoor air fractions. Finally, the hybrid evaporative pre-cooled air-conditioning system is evaluated in terms of its energy consumption performance based on a design day weather condition.

A hybrid air treatment cooling system (HATCS) has been proposed to simultaneously promote energy efficiency and improve indoor air quality (IAQ). The HATCS involves a plug-and-play air treatment system. It comprises an energy-efficient oxygen production process, an ozone-based oxidation treatment unit, and an air scrubbing device. Experimental studies have been carried out to investigate the air-purification performance and the energy consumption performance. To address the issue of outdoor air pollution, the proposed HATCS has demonstrated its capability to reduce the supply of ambient polluted air and maintain an acceptable IAQ. Experimental data have demonstrated the feasibility of employing a higher chilled water supply temperature through the cooling coil due to the reduced outdoor air intake. In addition, case studies have been carried out to investigate the energy consumption performance of the proposed HATCS in a typical office building under tropical climates. Simulation results have indicated that a lower outdoor air flow rate leads to a significant reduction on total electricity consumption for cooling. For the selected cases, it is estimated that the total annual electricity consumption saving is up to 59.3 kWh/m2 by employing the air treatment system.

Concrete is the most undisputable material being used in infrastructure development throughout the world. Natural sand is a prime material used for the preparation of concrete. Nowadays river erosion and other environmental issues have led to the scarcity of river sand. The reduction in the sources of natural sand and in the cost of concrete production has resulted in the increased need to find new alternative materials to replace river sand, so that excess river erosion is prevented and high strength concrete is obtained at lower cost. The aim of the study is to minimizes the cost and achieve sustainable development of concrete pavement. Cement, sand and aggregate are basic needs but the new alternative materials that is used foundry sand which is generated by metal casting industry and in the tiles industry, about 15%-30% production goes as waste, these are partially replaced by river sand. The fine aggregate has been replaced by used foundry sand accordingly in the range of 10%, 20%, 30%, 40% & 50% by weight and also same for tiles dust for M-20 grade concrete. Concrete mixtures are produced to make (6 in × 6 in × 6 in) cube for compressive strength test at 7, 14, 28 days and (4 in × 4 in × 20 in) beam for flexural strength test at 28 days curing period, tested and compared in terms of compressive and flexural strength with the conventional concrete. Maximum compressive and flexural strength are found for 20% replacement of used foundry sand (FA2) and for 10% replacement of tiles dust (TA1) with respect to the conventional concrete (A0). By using alternative materials, the strength of concrete was increased significantly and for showing cost effectiveness a concrete pavement from Talaimari MOR to Kalpona Cinema Hall was designed for 4500 commercial vehicles per day. The pavement thickness required for conventional concrete is 28 cm whereas the pavement thickness required for concrete FA2and TA1are 22 cm and 24 cm respectively. Since the thickness of pavement slab is reduced, the cost of pavement construction is reduced almost 22% and 15% for concrete FA2and concrete TA1respectively.

Desiccant-based dehumidification has gained significant attention in recent years to develop the energy efficient hybrid air-conditioning systems particularly for the tropical climate. Thus far, complex and tedious theoretical models have been developed to analyze the heat and mass transfer phenomena involved in liquid desiccant dehumidification processes. In the present study, a simple theoretical model has been presented to quantify the heat and mass transfer rates of the water-cooled liquid desiccant dehumidification and cooling processes for air-conditioning applications. Seven coupled ordinary differential equations have been developed to describe the complex heat and mass transfer processes. As far as the solution approach and practical application are concerned, the governing equations are solved simultaneously using the numerically stable 4th order Runge-Kutta scheme while preserving its accuracy to 6% in construct to full-scale model simulation. The developed model is rationally modified to study the performance of adiabatic dehumidifiers. The dehumidification and cooling performances of the adiabatic and water-cooled dehumidifiers are analyzed over a wide range of operating conditions. Finally, the energy performance enhancement potentials of the hybrid liquid desiccant air-conditioning system have been demonstrated. By analyzing the dehumidification and cooling performance, an energy saving of up to 25% can be achieved using the hybrid air-conditioning systems.

The paper describes the development of a hybrid solution that improves air dehumidification. It comprises the integration of a composite desiccant and a nano-woven membrane for air dehumidification. The solution compliments any building HVAC project where the removing moisture from the air via an energy-efficient means is a concern. Longer sustainable performance of the desiccant is achieved as the non-regenerative membrane assists in partial air dehumidification. Accordingly, the hybrid system requires a lower regenerating temperature while producing air of very low humidity. In sum, the proposed hybrid solution involves the composite desiccant and membrane to work hand-in-hand in order to achieve enhanced moisture removal efficiency and improved energy efficiency by up to 40% compared to the best grade commercial silica-gel desiccant.

Vacuum-based membrane dehumidification (VMD) unit is an energy-efficient alternative to the conventional mechanical vapor compression air-conditioning technology. Since the latent component of the cooling load can be independently handled by the VMD unit, the energy cost for cooling is substantially reduced. In this work, we investigate the dehumidification potential of a hollow membrane for VMD application. The hollow membrane offers higher dehumidification density and is more compact when compared to the flat-sheet types, thereby leading to a smaller air-handling unit (AHU) requirement. The developed hollow membrane is constructed from a polyetherimide (PEI) substrate and coated with PVA/LiCl active layers. Its apparent water vapor permeance and selectivity are 3395 gas permeation units (GPU) and 4240, respectively. During the lab-scale experimental study of a 3 m2 hollow membrane with varying air flowrates spanning 3 to 36 m3/h, it is observed that the attainable percentage of moisture removal of the membrane module is up to 86%, and the maximum dehumidification COP is 1.9. In contrast to a flat-sheet membrane module with a similar effective membrane area, the hollow membrane module is just half the size but displays the same dehumidification performance.

The experiment was conducted during Rabi season of 2015-2016 and 2016-2017 at the Regional Agricultural Research station, BARI, Ishurdi, Pabna, Bangladesh, to determine the water requirements of wheat on raised bed and the effect of different deficit irrigation on yield, water use efficiency and applied water productivity under raised bed wheat. This study consisted of following irrigation treatments: T1 = Irrigations up to 100% field capacity (FC) at crown root initiation (CRI), botting and grain filling stages (flat bed), T2 = Irrigations up to 100% FC at CRI, botting and grain filling stages on raised bed, T3 = Irrigations up to 80% FC at CRI, botting and grain filling stages on raised bed and T4 = Irrigations up to 60% FC at CRI, botting and grain filling stages on raised bed and laid out in a randomize complete block design with three replications. The result showed that significant effect of irrigation treatments were observed on plant height, spike per m2 and grain yield. Highest grain yield (4.66 t/ha) was obtained from treatment, irrigations up to 100% FC at CRI, botting and grain filling stages on raised bed, followed by irrigation up to 100% FC at same stages on flat bed. At raised bed wheat cultivation saving 14.30% water with increasing 15.66% grain yield than flat bed. Besides, comparing deficit irrigation (20% and 40% of full irrigation) and full irrigation condition on raised bed seeding system water use could be reduced about 4.18% to 5.57%, while scarifying 18.20% to 32.33% grain yield, where reduced 14.17% to 27.54% water use efficiency. Maximum applied water productivity 1.81 kg m−3 was observed in raised bed full irrigation condition. The rate of daily evaporation started to increase as the temperature started to rise and humidity started to decrease during the crop growing period. The results will be helpful for taking policy decision regarding efficient irrigation and water management under prevailing water scarce situation.

The design of air conditioning mechanical ventilation (ACMV) system affects the building energy performance and the indoor pollutant removal process. The present study aims to reduce energy consumption on ACMV systems by employing a renewable air treatment system (ATS). The ATS is able to purify the recirculated air through the ozone-based oxidation process and air scrubbing devices. The air purification performance of primary equipment in the ATS has been studied in order to demonstrate the capability to remove indoor air pollutants. Due to the air purification process, the ATS allows a reduced supply of outdoor-air translating to a lower cooling load. In addition, the reduced outdoor-air fraction results in an improved chiller efficiency. Therefore, the ATS is capable of achieving marked energy savings because of the reduced cooling load for conditioning outdoor airflow. The proposed ATS is particular adept during a period when Singapore faces periodic bad haze situations. Activating the ATS while decreasing the outdoor-air fraction can be an attractive solution. Based on Singapore climatic condition, an energy consumption analysis has been carried out to estimate the energy saving potential of the proposed ATS with varying outdoor-air intake. The “plug-and-play” ATS can be easily integrated into any new or existing ACMV systems to realize immediate improvement in indoor air quality and building energy efficiency.

The paper describes the development of a hybrid solution that improves air dehumidification. It comprises the integration of a composite desiccant and a nano-woven membrane for air dehumidifcation. The solution compliments any building HVAC project where the removing moisture from the air via an energy-efficient means is a concern. Longer sustainable performance of the desiccant is achieved as the non-regenerative membrane assists in partial air dehumidification. Accordingly, the hybrid system requires a lower regenerating temperature while producing air of very low humidity. In sum, the proposed hybrid solution involves the composite desiccant and membrane to work hand-in-hand in order to achieve enhanced moisture removal efficiency and improved energy efficiency by up to 40% compared to the best grade commercial silica-gel desiccant.

The present study introduces an air treatment system (ATS) for improving indoor air quality and reducing the energy consumption of air-conditioning system. The ATS has been proposed to combine three sub-systems, namely, (i) energy-efficient oxygen production sub-system, (ii) ozone-based oxidation treatment sub-system, and (iii) air scrubbing sub-system. Experimental setups have been designed and constructed to study the performance of primary equipment in the ATS. The proposed air-purification process is able to reduce the concentration of indoor air pollutants such as volatile organic compound. The experimental results have demonstrated that the proposed ATS enables a lower outdoor air intake rate resulting in a reduced cooling load. Considering the energy consumption of primary equipment of the ATS operating in tropical climates, the total energy consumption can be reduced from 52.18 W/m 2 to 41.26W/m 2 by regulating the outdoor air intake rate from 10 L/s per person to 4 L/s per person.

The latent heat energy storage performance of Tetradecane is measured experimentally. A simple theoretical model is developed by incorporating an effective thermal conductivity that accounts for the effects of the natural convection current of liquid Tetradecane. The simulation results showed good agreement with the experimental data with the maximum discrepancy of about 5.4%. The effects of the coolant inlet temperatures and flow rates on the local solidification rate of Tetradecane are studied. The theoretical model can be used conveniently for the design of the latent heat energy storage systems, especially for air conditioning applications.

A simple theoretical model has been developed on the coupled heat and mass transfer processes involved in the internally cooled liquid desiccant dehumidification and cooling processes for air-conditioning applications. Governing seven coupled differential equations are solved simultaneously with appropriate boundary conditions using the 4th order Runge-Kutta scheme. The calculation speed is improved remarkably (computational time is less than 6 minutes). The simulation results showed good agreement with the published data with the maximum discrepancy of about 6%. The validated model is used to investigate the performance of dehumidification and cooling of air under different operating conditions. Simulation results show that the internally cooled liquid desiccant dehumidification and cooling processes can dehumidify the air effectively. However, additional sensible cooling of the air is required to maintain comfort condition for air-conditioning applications.

Vacuum-based membrane dehumidification (VMD) has attracted much research interest due to its potential in increasing energy efficiency for air conditioning systems. However, there is a lack of reports on practical VMD systems and their performance efficiency. In this work, VMD was systematically studied via both theoretical and experimental analyses. Thermodynamics analysis was carried out to evaluate the energy efficiency of a VMD with varying feed air temperature, humidity, and membrane selectivity. It is shown that coefficient of performance ( COP ) of 2–3 is achievable in a VMD system under the least efficient operation of isentropic compression. A compact VMD prototype with an effective membrane area of 2.45 m 2 was developed based on a thin film composite membrane. Apparent membrane permeance and selectivity as high as 11,900 GPU and 1780, were respectively attained. The thermodynamic analysis is validated with experimental results. Energy efficiency of the membrane's dehumidification process increases with higher temperature and humidity. Vacuum pump's efficiency markedly affects the overall VMD system. A survey of commercial vacuum pumps was subsequently conducted and the practical limit of the current vacuum pump technology was observed. A COP value close to the thermodynamic limit is obtainable with a few selected vacuum pumps which possess pumping speeds that are higher than 2000 m 3 /h.

The present study attempts to reduce the supply of outdoor air in conditioning building spaces for energy saving while improving the indoor air quality. A hybrid air treatment system incorporating a cooling system is introduced for tropical climates. The air treatment system (ATS) comprises an ozone-based oxidation process and an air scrubbing device. The air purification process has been experimentally investigated. Experimental results demonstrated the feasibility of the proposed ATS to provide improved indoor air quality. A validated mathematical model has been employed to study the air cooling and dehumidification process through the cooling coil. The reduced outdoor air intake facilitates a higher chilled water supply temperature resulting in an improved chiller performance and reduction of cooling load. The energy consumption performance of the proposed hybrid ATS air-conditioning system has been evaluated for an office building experiencing tropical climatic conditions. The cooling load on a design day has demonstrated that the reduction of outdoor air intake enabled marked energy savings potential in terms of the cooling demand. By analysing the building performance based on tropical climatic data, an annual energy consumption saving of up to 64.6 kW h/m2 can be achieved via the hybrid ATS air-conditioning system.

An air treatment system incorporating an air-purification unit has been proposed to reduce the energy consumption of air-conditioning system and improve indoor air quality. This system employs a lower outdoor-air fraction to realize the acceptable indoor air quality and thermal comfort resulting in marked energy savings due to the reduced cooling load for the outdoor air. The performance of the primary equipment of the air treatment system has been individually investigated. Experimental systems have been constructed to study the air-purification process and to evaluate the chiller’s performance. Experimental results have demonstrated that the proposed air-purification unit is able to remove indoor air pollutants such as volatile organic compound. A computational model has concurrently been developed to determine the performance of the air handling cooling coil which is impacted by the outdoor-air fraction and the chilled water temperature. A higher chilled water supply temperature is adopted by reducing the outdoor-air fraction without compromising the supply air cooling capacity. Having a reduced outdoor air cooling load and a better chiller’s energy efficiency operating with higher chilled water temperatures, the achievable energy savings of the air-conditioning system has been demonstrated to be up to 36% under a tropical hot and humid climate.

PEM fuel cells are considered to be viable alternatives to Internal Combustion Engines (ICEs) in automotive applications due to their many advantages. However, one of the challenges is the need to remove considerable heat at relatively low temperatures (i.e. ∼60–80 °C). Nanofluids may offer a promising solution to help reduce the size of thermal management part of PEM fuel cell systems. This paper describes a simulation model developed to theoretically study the effect of using of nanofluids as coolants on the size of the heat exchanger (HE) and the pumping power in PEM fuel cell cooling systems. Considering a 2.4 kW PEM fuel cell, 50/50 water-ethylene glycol based nanofluids with concentration of 0.05–2 vol% have been investigated. By using 0.05 vol% concentration, ∼21% reduction of frontal area of the HE is obtained compared with that using the base fluid at constant coolant mass flow rate. By increasing nanoparticle concentration from 0.05 to 2 vol%, a further reduction of only ∼4% of the frontal area of HE can be obtained. No significant difference was found in pumping power when using nanofluids compared that using the base fluid. Using standard models there is negligible differences in the thermal performance using a variety of nanofluids.

The present article aims to determine a minimum parametric representation for evaluating the thermal performance of a counter-flow regenerative IEHX (indirect evaporative heat exchanger). Three dimensionless groups have been identified in order to develop a performance correlation based on non-dimensional forms of the governing equations. Numerical simulations were carried out to determine the empirical constants of the correlation by fitting the simulated dimensionless outlet temperature as a function of each dimensionless group. Simulations have been conducted by changing the value of each dimensionless group while keeping a constant value for other parameters. The simulated dimensionless outlet temperature was varied from 0.20 to 0.73. A prototype of a counter-flow regenerative IEHX was designed and experimentally studied. The correlation was validated by comparing the calculated results with experimental findings as well as published experimental data acquired from literature. The developed correlation is able to predict the performance of the counter-flow regenerative IEHX within a discrepancy of 12%. We further demonstrated that the correlation could be a practical approach to predict the performance and optimize the configuration of the IEHX.

Productivity of rice is adversely affected by salinity and water logging stresses in coastal zones, and affected areas are progressively expanding as consequences of climate change and overexploitation of natural resources to meet the needs of increasing populations. Several varieties were developed and commercialized in this region in recent years, including some salt and stagnant flood (SF, medium deep, 25–50 cm water depth) tolerant varieties. However, suitability of these varieties based on adaptation to local conditions across the region and farmers’ preferences have not been sufficiently evaluated. Genotype by environment analysis leads to identification of varieties with stable performance, or suitability to specific regions. Two frequently used statistical analyses are additive main effects and multiplicative interaction (AMMI); and the genotype main effects and genotype × environment interaction effects (GGE). These models were used in this study to identify stable rice varieties for the wet and dry seasons in South Bangladesh. Experiments were conducted at six sites over four years (2010–2013) in coastal Bangladesh, using eight and five varieties for wet and dry season, respectively. The trials were laid in a randomized complete block design (RCBD) with three replications. Genotypic contribution was much higher than the environmental effect on grain yield in the wet season, while the environmental contribution was much higher than genotypic effect during the dry season. SF stress affected yield of wet season rice; but in the dry season, salinity stress had major effect on grain yield. The variety BRRI dhan54 was identified as the most suitable genotype with wider adaptability in the region during the wet season, followed by BRRI dhan40 and BRRI dhan53, while BRRI dhan47 was the most stable variety followed by BRRI dhan61 and BINA dhan8 for the dry season across all sites. However, when these varieties were evaluated based on farmers’ preferences in participatory varietal selection, BRRI dhan53; a short duration variety with medium slender grains was the most preferred, followed by BRRI dhan54 and BRRI dhan40 for wet season, and in the dry season BRRI dhan47 was the most popular variety followed by BRRI dhan61, which agreed with ranking based on yield. Modern varieties were far superior over traditional varieties based on grain yield and farmers’ preferences, and should be targeted for large-scale seed production and dissemination.

A compact desiccant-evaporative HMX (heat and mass exchanger) has been proposed by combining the benefits of the regenerative indirect evaporative cooling and the liquid desiccant dehumidification. In this design, the compact HMX was able to cool and dehumidify the product air simultaneously in a single unit. A computational model has been developed and validated using experimental data. The model displayed good agreement with the experimental findings with maximum discrepancy of 8%. The heat and mass transfer behavior was theoretically investigated to illustrate the detailed air treatment performance of the HMX. Simulations were performed to study the effect of several key parameters on the HMX's performance. Due to the effect of pre-cooling and pre-dehumidification, the working air showed improved cooling potential in the working channel. Consequently, the temperature of the product air could be reduced below the dew-point temperature of intake air. Simulation results showed that the outlet temperature of the product air was affected by the working-to-intake air flow rate ratio and the dimensionless channel length, while the outlet humidity ratio of the product air was influenced by the length of the liquid desiccant film and the dimensionless channel length.

A hybrid system, that combines an indirect evaporative heat exchanger (IEHX) and a vapor compression system, is introduced for humid tropical climate application. The chief purpose of the IEHX is to pre-cool the incoming air for vapor compression system. In the IEHX unit, the outdoor humid air in the product channel may potentially condense when heat is exchanged with the room exhaust air. A computational model has been developed to theoretically investigate the performance of an IEHX with condensation from the product air by employing the room exhaust air as the working air. We validated the model by comparing its temperature distribution and predicted heat flux against experimental data acquired from literature sources. The numerical model showed good agreement with the experimental findings with maximum average discrepancy of 9.7%. The validated model was employed to investigate the performance of two types of IEHX in terms of the air treatment process, temperature and humidity distribution, cooling effectiveness, cooling capacity, and energy consumption. Simulation results have indicated that the IEHX unit is able to fulfill 47% of the cooling load for the outdoor humid air while incurring a small amount of fan power. Consequently, the hybrid system is able to realize significant energy savings.

This paper explores the potential and challenges of using nanofluids in cooling systems for Proton Exchange Membrane Fuel Cells (PEMFCs) in automotive applications. PEMFCs have clearly emerged as a promising alternative to existing conventional internal combustion engines (ICEs) in vehicles, mainly due to their relatively high electrical energy conversion efficiency (around 55% based on the high heating value of hydrogen), and zero emissions in operation. Despite their relatively low heat generation and low operating temperature (~65 °C), PEMFCs require a relatively large radiator in their cooling systems, which is unfavourable in automotive applications. Nanofluids have attracted great interest as coolants due to their superior heat transfer properties. This paper thus reviews the using of nanoparticles with a suitable base fluid as a coolant in PEMFCs. It is found that a nanofluid coolant in a PEMFC can reduce the size of the radiator needed to dissipate its thermal load (by up to 10% relative to standard heat transfer fluids), eliminate the need for a deionizing filter, and lower the freezing point of the base fluid.

The performance of an air-conditioning unit with evaporately-cooled condenser coil is studied experimentally and numerically. An experimental setup is fabricated by retrofitting a commercially available air-conditioning unit and installing comprehensive measuring sensors and controllers. Experimental result shows that the COP (Coefficient of Performance) of the evaporately-cooled air-conditioning unit increases by about 28% compared to the conventional air cooled air-conditioning unit. To analyze the heat and mass transfer processes involved in the evaporately-cooled condenser, a detailed theoretical model has been developed based on the fluid flow characteristics of the falling film and the thermodynamic aspect of the evaporation process. Simulated results agree well with experimental data. The numerical model provides new insights into the intrinsic links between operating variables and heat transfer characteristics of water film in evaluating the performance of evaporatively-cooled condenser system. Two heat transfer coefficients, namely, wall to bulk and bulk to interface are introduced and computed from the simulation results under different operating conditions. Finally, the overall heat transfer coefficient for the water film is computed and presented as a function of dimensionless variables which can conveniently be employed by engineers to design and analyze high performance evaporatively-cooled heat exchangers.

The increase in energy demand has caused considerable attention to be directed toward sustainable energy resources. The importance of electricity generation through solar energy has been intensively highlighted globally, but Malaysia has yet to exert efforts to develop this energy resource. This study explores the social acceptance and level of human interest in solar energy. In addition, this work identifies the difficulties in the consumption of solar energy and the expectations for solar energy development in Malaysia. Survey results show that 80 % of the respondents are highly interested in solar energy. However, the majority of the respondents have reported that some hindrances, such as expensive solar panels and lack of correct information about solar energy utilization, make fuel-generated electricity a preferable choice. Meanwhile, almost 80 % of the respondents believe that government incentives could best enhance solar energy usage nationwide. To implement new solar energy policies successfully in Malaysia, the government should support the establishment of solar power plants, as well as provide complete information and funding for independent research. Furthermore, more than 70 % of respondents perceive the government to be the main organization that should lead the development of this energy sector. Therefore, this research provides some useful references for policy makers to continue promoting the use of solar energy in Malaysia.