Showing papers in "International journal of ambient energy in 2002"
TL;DR: In this article, the optimum thickness of an insulation layer in a typical building wall is determined under steady periodic conditions using the climatic data of Riyadh using a finite-volume implicit procedure.
Abstract: SYNOPSIS The optimum thickness of an insulation layer in a typical building wall is determined under steady periodic conditions using the climatic data of Riyadh. A finite-volume implicit procedure, which has been previously validated, is used to compute the yearly heat transmission loads for various insulation thicknesses. These loads are input to an economic model, based on the present worth method, in order to minimise the total cost of insulation and energy consumption over the lifetime of the building. Cooling and heating loads are integrated separately over the year and treated with different costs in the economic analysis. The wall yearly transmission loads, yearly-averaged dynamic R-value, time lag and decrement factor are presented versus insulation thickness and compared for different wall orientations. A parametric study is performed to establish the sensitivity of the results to changes in economic parameters. The optimum insulation thickness is found to increase with the cost of electricity, ...
69 citations
TL;DR: In this paper, the use of 100% ethanol with ignition improver in a 4.4 kW single cylinder, direct injection, constant speed diesel engine was presented, which is an excellent fuel suitable for spark ignition (S.I.) engines.
Abstract: SYNOPSIS Diesel engines are preferred power plants in the transportation sector due to their higher efficiency and lower operational cost. But the major problem of diesel engines is the emission of smoke, particulate matter and oxides of nitrogen (NOx) from its exhaust. Hence stringent emission regulations and the depletion of fossil fuels have necessitated a look at alternative fuels for internal combustion (I.C.) engines. Ethanol is an excellent fuel suitable for spark ignition (S.I.) engines, but has a very low cetane number and cannot be used in compression ignition engines unless gas temperatures are high enough at the time of fuel injection [1]. Different types of systems were developed to assist auto ignition of directly injected ethanol which include glow plugs or spark plugs, low heat rejection operation, and ignition improvers. This paper presents the use of 100% ethanol with ignition improver in a 4.4 kW single cylinder, direct injection, constant speed diesel engine. Experimental results indic...
66 citations
TL;DR: In this article, the potential for CO2, emissions mitigation using three renewable energy technologies (biogas plants, improved biomass cookstoves and box type solar cookers) for domestic cooking in India has been estimated.
Abstract: SYNOPSIS The potential for CO2, emissions mitigation using three renewable energy technologies (biogas plants, improved biomass cookstoves and box type solar cookers) for domestic cooking in India has been estimated. The use of renewable energy technologies for domestic cooking has the potential for saving over 550 million tonnes of CO2, emissions annually. The costs of reducing CO2, emissions by the three options have also been estimated. Using the data available in the literature and the simple frameworks presented in this paper, results of some typical calculations are presented and discussed.
16 citations
TL;DR: In this article, the U, SHGC, and VT values for different window systems in different climatic zones of the Indian subcontinent were analyzed using WINDOW 4.1.
Abstract: SYNOPSIS The paper deals with detailed calculations of the U, SHGC, and VT values for different window systems in different climatic zones of the Indian subcontinent. Since the average summer and winter conditions in the Indian subcontinent are very different from the values used in ASHRAE and European norms, the external and internal heat transfer coefficients have been evaluated from the basic expressions. The detailed numerical results, obtained by integration of ho & hi values with the software WINDOW 4.1, show that for a single glazed window the U values for hot & dry conditions can be higher by 15% than those available in standard books. The U & SHGC value also changes with incident solar radiation and wind velocity, for which the data has been presented in this paper. Efforts are being made to transfer the generated data to the DOE program for load & energy calculations in buildings.
13 citations
TL;DR: In this paper, the experimental performance of a lab-scale ceiling type free convected Thermoelectric (TE) Air Conditioner (TEAC) was described, where the whole set-up was slightly inclined (5°) from the horizontal plane to collect the condensed water at the cold fins and to accelerate the downward airflow.
Abstract: SYNOPSIS This paper describes the experimental performance of a lab-scale ceiling type free convected Thermoelectric (TE) Air Conditioner (TEAC). The TEAC is composed of seven TE modules (Tianjin Lantian model TEC1-12708), a free convected rectangular fin heat exchanger at the cold side and a force convected skive fin heat exchanger at the hot side of the TE modules. Tests were conducted for various operating conditions using two well insulated chambers of different volume, namely 0.024 and 1 m3. The whole set-up was slightly inclined (5°) from the horizontal plane to collect the condensed water at the cold fins and to accelerate the downward airflow. It was found that the cooling performance of the system depended, as with the forced type TEAC, on the electrical power supply and the mass flow rate of hot air. Under the design conditions used here, suitable operating conditions were 3 amps and 0.027 kg.s−1, respectively. The corresponding cooling capacity was 169 W and the average chamber temperature vari...
9 citations
TL;DR: In this article, the effect of a north wall has been numerically evaluated in an even span, uneven span, modified arch, vinery, and modified IARI greenhouse, and it has been concluded that the greenhouse shape affects the room temperature and thermal load levelling significantly.
Abstract: SYNOPSIS This paper presents a comparison in the performance of greenhouses with various shapes for a composite climate (New Delhi). The shapes under study are: even span, uneven span, modified arch, vinery and modified IARI. The performance of the greenhouses has been evaluated with the help of an experimentally validated model. A parametric study has also been presented. The effect of a north wall has been numerically evaluated in an even span, uneven span and modified arch shaped greenhouse. Based on numerical computations, which were carried out for a typical day in summer and one in winter, it could be concluded that: i. greenhouse shape affects the room temperature and thermal load levelling significantly, which is higher in winter as expected; ii. The maximum room temperature (15°C and 20°C) and thermal load levelling (0.10 and 0.12) were increased due to the north wall in winter and summer conditions, respectively; iii. the fluctuations in room temperatures were reduced due to the increase in isot...
9 citations
TL;DR: In this article, the optimal operating conditions for the process of longan drying were determined for specific energy consumption and drying time, and the results were verified by comparison between the predicted results and experimental measurements.
Abstract: SYNOPSIS The objective of this work is to determine the optimal operating conditions for the process of longan drying. The evaluation criteria of the process are the specific energy consumption and the drying time. Mathematical models were developed to simulate the longan drying process. The models are verified by comparison between the predicted results and experimental measurements. Comparisons between the predicted results and the measurements showed good agreement. The models were used to evaluate the effects of the operating parameters on the specific energy consumption. The operating parameters are drying air temperature, specific airflow rate, and the fraction of recycled air. At the optimal operating conditions, the specific energy consumption was determined to be 4.2 MJ/kg-water.
8 citations
TL;DR: In this article, a pulsating-steam water pump with thermal energy was studied and its behavior characteristics were investigated. But the results of the model did not agree with the measured results and the discharge water volume directly depended on the discharge pressure setting and the total height.
Abstract: SYNOPSIS A device for lifting water with thermal energy, a pulsating-steam water pump, is studied and its behaviour characteristics are investigated. The pump system consists of an evaporator tank, a condenser tank, and a heater. The general operation, involving four stages (heating, pumping, cooling and suction), is considered and a model of each stage is also developed. The system performance parameters such as suction height, discharge water volume and efficiency are investigated. It is found that the predicted results from the model agree quite well with the measured results. The discharge water volume directly depended on the discharge pressure setting and the total height.
7 citations
TL;DR: In this article, the authors compared the results obtained from these audits, with particular attention to the effects of ventilation or air conditioning systems and climate, and found that the number of building related symptoms is, on the average, significantly smaller in the buildings audited in Singapore than in Europe.
Abstract: SYNOPSIS Indoor environment quality audits were performed in six European countries and in Singapore using the same methodology. Five to eight office buildings were audited in each country. The audits included airflow rate measurements, energy audit, indoor air quality (VOC1 CO2, dust concentrations), and questionnaires to occupants. Questions to occupants addressed their health, their comfort and well-being, as well as their perception of their environment. This paper compares the results obtained from these audits, with particular attention to the effects of ventilation or air conditioning systems and climate. The number of building related symptoms is, on the average, significantly smaller in the buildings audited in Singapore than in Europe. One of the reasons may be the non-smoking policy common in Singapore. It is also once more observed that buildings are often over-warmed in cold climates and overcooled in warm climates. Surprising, but not new, is that there are no correlations between specific a...
5 citations
TL;DR: In this paper, a 12-blade, 45° pitched-blade impulse micro turbine was used to generate electricity by operating with selected working fluids, namely, water, n-pentane, methanol and R141b.
Abstract: SYNOPSIS A 12-blade, 45° pitched-blade impulse micro turbine was used to generate electricity by operating with selected working fluids, namely, water, n-pentane, methanol and R141b. The turbine geometry was fixed during the investigation but the flow area of the working fluid was varied in order to determine its effect on performance. A number of inlet and outlet conditions were assumed and CFD numerical prediction was carried out using the FLUENT code. The simulation results allowed the percentage of un-blocked flow area to be determined for different working fluids and different inlet/outlet conditions, and the optimum working fluid and operation conditions to be found. An experimental trial was carried out using n-pentane as the working fluid at an inlet pressure of 5.14 bar(a) and an outlet pressure of 1.15 bar(a), in order to demonstrate the thermal and power characteristics of the micro turbine. CFD modelling predictions were validated by comparison with the experimental results.
4 citations
TL;DR: In this paper, a thin membrane heat pipe solar collector was designed to be a compact, efficient and low cost heat generator capable of achieving temperatures up to 250°C and suitable for generating electricity and hot water for domestic and industrial use.
Abstract: SYNOPSIS A novel thin membrane heat pipe solar collector was designed to be a compact, efficient and low cost heat generator capable of achieving temperatures up to 250°C and suitable for generating electricity and hot water for domestic and industrial use. Two variations of this, “normal” and “thermosyphon”, were indicated and their performance was investigated. The mathematical theory and simulation approach used for efficiency and solar irradiation calculation, geometry and size optimisation as well as numerical analysis were summarised. Influences of geometry, liquid fill level, inclination and working temperature on collector performance were analysed, and the thermal behaviours of the collector under given conditions, including liquid and vapour cross-sectional areas, liquid and vapour pressures, liquid, vapour and wall temperatures, mass flow rate and start-up process, were described in detail. A number of conclusions regarding the aspects above were given.
TL;DR: In this paper, the authors investigated an air turbine with self-pitch-controlled blades operating in the airflow generated by an oscillating water column taking real air flows to the turbine into account to determine turbine performance and identify the optimum blade pitch angle setting.
Abstract: SYNOPSIS This work investigated an air turbine with self-pitch-controlled blades operating in the airflow generated by an oscillating water column taking real air flows to the turbine into account in order to determine turbine performance and identify the optimum blade pitch angle setting. Experimental investigations were performed by model testing of a rotor with fixed blades under steady flow conditions. Then, the running and starting characteristics under sinusoidally oscillating flow conditions were obtained by a computer simulation using a quasi-steady analysis. As a result, the performances of the air turbine using self-pitch-controlled blades under real sea conditions were clarified, and a suitable choice of design factor has been suggested for the setting angle of the rotor.
TL;DR: In this article, the performance of photovoltaic (PV) fans was investigated for cooling load reduction by reducing heat gain through the ceiling and for improving occupants thermal comfort.
Abstract: SYNOPSIS This paper investigates the performance attic ventilation, driven by photovoltaic (PV) fans, for cooling load reduction (by reducing heat gain through the ceiling) and for improving occupants thermal comfort. The ventilation fans are driven directly by a 27 Wp photovoltaic (PV) panel i.e, no battery is used. To assess the performance, two lab-scale houses each with a volume of 2.8 m3 were built using common construction materials. One of them served as a reference. Two patterns of ventilation were examined, namely external ventilation and cross ventilation. With the first, only the attic was ventilated while with the second, the ambient air was first admitted into the room and then into the attic. In addition, both non-insulated and insulated attics and those with and without a radiant barrier were considered. Tests were performed during the summer. Experimental results showed that cross ventilation could significantly reduce the heat flux transferred through the ceiling by about 3–5 W/m2. It cou...
TL;DR: In this paper, the analysis and quantification of passive cooling concepts in conditioned and non-conditioned buildings have been performed in Indian climatic conditions, and the concepts considered are: orientation, over-hangs, surface colour, cavity walls and roof, and insulation on roof and walls.
Abstract: SYNOPSIS The analysis and quantification of Passive Cooling Concepts in conditioned and non-conditioned buildings have been performed in this paper for Indian climatic conditions. The concepts considered are: orientation, over-hangs, surface colour, cavity walls and roof, and insulation on roof and walls. In air-conditioned buildings, insulation on walls and roofs can bring down the thermal specific energy consumption from 400 kWh/m2a to 116 kWh/m2a. If the set point is raised to a slightly higher temperature, i.e. 26°C, the energy consumption reduces to 102 kWh/m2a. In non-conditioned buildings in a harsh climate such as Delhi, no passive concept is able to reduce the operative temperature to comfort level. However, white wash (surface colour) on walls and roof and an earthberm can reduce the maximum room temperature from 41.5°C to 35.6°C, a reduction of 6°C.
TL;DR: In this article, an economic comparison between the sensible and the total energy recovery for HVAC systems in the Italian climate is dealt with, both all-outdoor-air and mixed-air systems are considered.
Abstract: SYNOPSIS In this paper an economic comparison between the sensible and the total energy recovery for HVAC systems in the Italian climate is dealt with. Both all-outdoor-air and mixed-air systems are considered. During the summer period, the energy saving by the sensible device is achieved by evaporative cooling. The performance of the hybrid innovative HVAC system and the traditional one, for both the heating and cooling season, are calculated hour by hour following the Test Reference Year (TRY) profile.
TL;DR: In this article, the authors investigated the emission characteristics of a diesel engine running on natural gas using these pilot fuels as a means of initiating combustion and found that natural gas is more attractive alternative fuel for i.c engines due to its high octane number and environmental friendly nature.
Abstract: SYNOPSIS In recent years, researchers have intensified efforts in a bid to identify greener alternative fuels for internal combustion (i.c) engines. Combustion of fossil fuel is the main culprit in raising the carbon dioxide (CO2) content of the atmosphere. This contributes up to 60% of greenhouse gases whose consequence is global warming. The combustion of biofuels has fewer adverse effects and the effects are more localised than those of fossil fuels. Many energy sources (natural gas, bio-derived gas and liquids) are now being investigated as potential substitutes for the present conventional fossil fuels. Natural gas is more attractive alternative fuel for i.c engines due to its high octane number and environmental friendly nature. The pilot fuels used are diesel fuel, rapeseed methyl ester (RME) and neat rapeseed oil. This paper investigates the emission characteristics of a diesel engine running on natural gas using these pilot fuels as a means of initiating combustion. The test results show that the...
TL;DR: In this paper, a new type of thermodynamic cycle, which is accomplished by a chemical pump operating among three reservoirs at different chemical potentials, is investigated, where the influence of the irreversibility of finite-rate mass transfer is taken into account.
Abstract: SYNOPSIS A new type of thermodynamic cycle, which is accomplished by a chemical pump operating among three reservoirs at different chemical potentials, is investigated. The chemical pump may be conceived as a combined system having a chemical pump operating between two reservoirs driven by a chemical engine. The influence of the irreversibility of finite-rate mass transfer is taken into account. The fundamental optimal relations of the chemical engine and pump operating between two reservoirs are used to derive the fundamental optimal relation of the chemical pump operating among three reservoirs. Consequently, it is proved that such a combined cycle system is equivalent to the chemical pump operating among three reservoirs at different chemical potentials. Moreover, The maximum rate of energy pumping is calculated. The other optimum performance characteristics of the chemical pump are discussed in detail. The results obtained here may provide some theoretical bases for the development of chemical pumps.
TL;DR: In this article, the authors presented a simulation of the flow and heat transfer characteristics of the enthalpy wheel, which is used to exchange sensible and latent heat between the fresh air and the return exhaust air.
Abstract: SYNOPSIS Maintaining good Indoor Air Quality inside air-conditioned spaces demands more fresh air for ventilation. This in turn increases the heat load on the evaporator coil. For minimising this additional load, a heat recovery unit called an enthalpy wheel is introduced to exchange sensible and latent heat between the fresh air and the return exhaust air. This paper aims to present a simulation of the flow and heat transfer characteristics of the enthalpy wheel. A typical case of hot and humid ambient conditions is considered for analysis. As the wheel is under quasi steady state, transient flow patterns are included to predict the performance of the enthalpy wheel. The amount of energy transferred, during the counter current flows of fresh and return air, is deduced from the heat and mass transfer analysis. It has been found that the effectiveness of heat exchange is nearly 77%. This analysis would be very useful in optimising the design parameters for increasing the heat transferred by the enthalpy wheel.
TL;DR: In this article, a mathematical model of the condensation process from a vapour flowing downwards between two vertical plates of constant wall temperature is presented, and it is shown that as the distance between the plates increases the condenser heat rate decreases.
Abstract: SYNOPSIS A mathematical model of the condensation process from a vapour flowing downwards between two vertical plates of constant wall temperature is presented. With this model it is possible to calculate the condensate film thickness, condensate mass flow, vapour pressure difference, vapour mass flow and condenser heat rate. The case where all the vapour condenses is also considered. It is shown in both cases that as the distance between the plates increases the condenser heat rate decreases.
TL;DR: In this paper, a two-tray reverse absorber type cabinet dryer with a glass cover for direct entry of solar radiation from the top has been proposed for crop drying.
Abstract: SYNOPSIS Different kinds of solar dryers have been developed based on the scientific utilisation of solar energy for crop drying purposes. In this paper, a two-tray reverse absorber type cabinet dryer having a glass cover for the direct entry of solar radiation from the top has been proposed. It combines the features of a normal cabinet dryer and the reverse absorber cabinet dryer proposed by many researchers. Thermal modelling has been done to examine the effect of the glass cover on aspects related to crop drying.
TL;DR: In this paper, the effect of roof solar chimney design on indoor temperature and induced air change was investigated and five lab-scale houses with different roof configurations were designed and tested.
Abstract: SYNOPSIS This paper reports on an experimental investigation of the effect of roof solar chimney design on indoor temperature and induced air change. Five lab-scale houses with different roof configurations were designed and tested. The roof and walls were made from CPAC monier concrete boards. The ceiling was made from gypsum board. The volume of each house was about 1.5 m3. Three roofs were designed to act as a solar chimney whereas two houses with a flat gypsum ceiling served as references (one of them included 1 cm fibreglass insulation) so that no ventilation occurred. In addition, all the houses included two closed-windows located on the northern and southern sides. The three ventilated houses have a rectangular opening located below the northern window through which ambient air is admitted. Experimental results showed that the three solar chimney vented roofs could induce an airflow of 36 m3/h approximately. The corresponding air change is about 24. Indoor temperature stratification varied dependin...