Modeling of a hazelnut dryer assisted heat pump by using artificial neural networks

The artificial neural network (ANN) approach is generic technique for mapping non-linear relationships between inputs and outputs without knowing the details of these relationships. In this paper, an application of the ANN has been presented for a PID controlled heat pump dryer. In PID controlled heat pump dryer, air velocity changed according to the temperature value which is set in process control device. Heat pump dryer was tested drying of hazelnut at 40 °C, 45 °C and 50 °C drying air temperatures. By training the experiment results with ANN, drying air velocities, moisture content of hazelnuts and total drying time were predicted for 42 °C, 44 °C, 46 °C and 48 °C drying air temperatures.     

Design and experimental testing of the performance of an outdoor LiBr/H2O solar thermal absorption cooling system with a cold store

A domestic-scale prototype experimental solar cooling system has been developed based on a LiBr/H₂O absorption system and tested during the 2007 summer and autumn months in Cardiff University, UK. The system consisted of a 12 m² vacuum tube solar collector, a 4.5 kW LiBr/H₂O absorption chiller, a 1000 l cold storage tank and a 6 kW fan coil. The system performance, as well as the performances of the individual components in the system, were evaluated based on the physical measurements of the daily solar radiation, ambient temperature, inlet and outlet fluid temperatures, mass flow rates and electrical consumption by component. The average coefficient of thermal performance (COP) of the system was 0.58, based on the thermal cooling power output per unit of available thermal solar energy from the 12 m² Thermomax DF100 vacuum tube collector on a hot sunny day with average peak insolation of 800 W/m² (between 11 and 13.30 h) and ambient temperature of 24 °C. The system produced an electrical COP of 3.6. Experimental results prove the feasibility of the new concept of cold store at this scale, with chilled water temperatures as low as 7.4 °C, demonstrating its potential use in cooling domestic scale buildings.     

The optimization of tank-volume-to-collector-area ratio for a thermosyphon solar water heater

Through the use of the TRNSYS simulation program, the performance of a domestic solar water heating system operating with natural circulation (thermosyphon) and a daily hot water load has been analysed. The effect of tank height on the annual solar fraction of the system has been investigated for different hot water load temperatures and storage tank volumes. Optimum values (values which maximize the annual solar fraction of the system) for storage tank height and volume are calculated for operating temperatures ranging from 50 to 80°C. The response of the system to the ratio of the storage tank volume to the collector area is investigated. The dependence of the solar fraction on tank height was observed to be more notable in the case of large tank volumes and high load temperatures. The results indicate the existence of an optimum value for the tank volume at a given tank height and a high load temperature. At lower temperatures, the solar fraction rises rapidly with tank volume to a nearly constant level. An optimum value of the storage-tank-volume-to-collector-area ratio was also observed at high load temperatures.     

Experimental analysis of solar thermal storage in a water tank with open side inlets

This paper investigates thermal mixing caused by the inflow from one or two round, horizontal, buoyant jets in a water storage tank, which is part of a thermal solar installation. A set of experiments was carried out in a rectangular tank with a capacity of 0.3 m³, with one or two constant temperature inflows. As a result, two correlations based on temperature measurements have been developed. One of the correlations predicts the size of a zone of homogenous temperature, referred to herein as the mixing zone, which develops when a single hot inflow impinges on the opposite wall of the tank. The other identifies the degree of mixing resulting from the interaction between a hot inflow and a cold inflow located below the hot one. The correlations are combined with energy balances to predict the amount of hot water available in a tank with open side inlets and the corresponding temperatures of the outflows. Outdoor measurements were also performed in a solar installation, in which a commercial water storage tank with a 1.5 m³ capacity, heated by a solar collector array with a useful surface area of 42.2 m², drives a LiBr-H₂O absorption chiller. Comparison of the predicted and measured outflow temperatures under a variety of weather conditions shows a maximum difference of 3 °C.     

A new version of a solar water heating system coupled with a solar water pump

This research target was to improve the thermal efficiency of a solar water heating system (SWHS) coupled with a built-in solar water pump. The designed system consists of 1.58-m² flat plate solar collectors, an overhead tank placed at the top level, the larger water storage tank without a heat exchanger at the lower level, and a one-way valve for water circulation control. The discharge heads of 1 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 10–18 kPa. It was found that water circulation within the SWHS ranged between 15 and 65 l/d depending upon solar intensity and discharge head. Moreover, the max water temperature in the storage tank is around 59 °C. The max daily pump efficiency is about 0.0017%. The SWHS could have max daily thermal efficiency of about 21%. It is concluded that the thermal efficiency was successfully improved, except for the pump one. The new SWHS with 1 m discharge head or lower is suitable for residential use. It adds less weight to a building roof and saves electrical energy for a circulation pump. It has lower cost compared to a domestic SWHS.     

Experimental studies of a new solar water heater system using a solar water pump

The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 7–14 kPa. It was found that water circulation within the SWHS ranged between 12 and 59 l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one.     

Numerical study on thermal energy storage performance of phase change material under non-steady-state inlet boundary

Due to the solar radiation intensity variation over time, the outlet temperature or mass flow rate of heat transfer fluid (HTF) presents non-steady-state characteristics for solar collector. So, in the phase change thermal energy storage (PCTES) unit which is connected to solar collector, the phase change process occurs under the non-steady-state inlet boundary condition. In present paper, regarding the non-steady-state boundary, based on enthalpy method, a two dimensional physical and mathematical model for a shell-and-tube PCTES unit was established and the simulation code was self-developed. The effects of the non-steady-state inlet condition of HTF on the thermal performance of the PCTES unit were numerically analyzed. The results show that when the average HTF inlet temperature in an hour is fixed at a constant value, the melting time (time required for PCM completely melting) decreases with the increase of initial inlet temperature. When the initial inlet temperature increases from 30 °C to 90 °C, the melting time will decrease from 42.75 min to 20.58 min. However, the total TES capacity in an hour reduces from 338.9 kJ/kg to 211.5 kJ/kg. When the average inlet mass flow rate in an hour is fixed at a constant value, with the initial HTF inlet mass flow rate increasing, the melting time of PCM decreases. The initial inlet mass flow rate increasing from 2.0 × 10⁻⁴ kg/s to 8.0 × 10⁻⁴ kg/s will lead to the melting time decreasing from 37.42 min to 23.75 min and the TES capacity of PCM increasing from 265.8 kJ/kg to 273.8 kJ/kg. Under all the studied cases, the heat flux on the tube surface increases at first, until it reaches a maximum then it decreases over time. And the larger the initial inlet temperature or mass flow rate, the earlier the maximum value appearance and the larger the maximum value.     

Modelling of solar energy potential in Nigeria using an artificial neural network model

In this study, an artificial neural network (ANN) based model for prediction of solar energy potential in Nigeria (lat. 4–14°N, log. 2–15°E) was developed. Standard multilayered, feed-forward, back-propagation neural networks with different architecture were designed using neural toolbox for MATLAB. Geographical and meteorological data of 195 cities in Nigeria for period of 10 years (1983–1993) from the NASA geo-satellite database were used for the training and testing the network. Meteorological and geographical data (latitude, longitude, altitude, month, mean sunshine duration, mean temperature, and relative humidity) were used as inputs to the network, while the solar radiation intensity was used as the output of the network. The results show that the correlation coefficients between the ANN predictions and actual mean monthly global solar radiation intensities for training and testing datasets were higher than 90%, thus suggesting a high reliability of the model for evaluation of solar radiation in locations where solar radiation data are not available. The predicted solar radiation values from the model were given in form of monthly maps. The monthly mean solar radiation potential in northern and southern regions ranged from 7.01–5.62 to 5.43–3.54 kW h/m² day, respectively. A graphical user interface (GUI) was developed for the application of the model. The model can be used easily for estimation of solar radiation for preliminary design of solar applications.     

Lithium chloride - Expanded graphite composite sorbent for solar powered ice maker

Consolidated composite material made from expanded graphite (EG) powder impregnated with LiCl salt is proposed for use in solar powered adsorption ice makers. Laboratory experiments were done to test the adsorption and desorption performance of the sorbent under different temperature conditions suitable for solar energy utilization. More than 75% of the reaction between LiCl and ammonia was completed after 30 min of synthesis at evaporation temperatures of −10 and −5 °C and adsorption temperature between 25 and 35 °C. Under the same period, it was possible to obtain 80% conversion in the desorption phase, when the generation temperatures ranged between 75 and 80 °C, and the condensation temperature varied from 25 to 35 °C. The highest average specific cooling power during the synthesis phase was 117 W per kg of the block. The calculated theoretical coefficient of performance (COP) under different cycle conditions was nearly constant at 0.47. Moreover, the new composite sorbent showed higher Specific Cooling Capacity (SCC), compared to activated carbon (AC)/methanol pair. Experiments done with blocks with different proportion of EG, showed that the proportion of EG influence the cooling capacity per unit mass of salt and had almost no influence on the cooling capacity per unit mass of the block. Moreover, the reaction enthalpy (ΔH) and entropy (ΔS) were calculated from experimental data obtained experimentally, and confirmed previous reported values.     

Thermal design of a solar hydrogen plant with a copper-chlorine cycle and molten salt energy storage

In this paper, the operating temperature ranges of various solar thermal energy technologies are analyzed, with respect to their compatibility with solar hydrogen production via thermochemical cycles. It is found that the maximum temperature of 530 °C required by the oxygen production step in the Cu-Cl cycle can be supplied by current solar thermal technologies. The heat requirements are examined for the Cu-Cl cycle and it is found that the heat source must be sufficiently high and above the maximum temperature requirement of the Cu-Cl cycle, in order to match the heat requirements of the cycle. The quantity of molten salt and solar plant dimensions for capturing and storing solar heat for an industrial hydrogen production scale are also estimated for 24 h operation per day. The flow characteristics and heat losses of molten salt transport in pipelines are studied while considering the influences of pipeline diameter, heat load and weather conditions. The heat loss from a solar salt storage tank is also calculated based on various tank diameters and heights. The intermediate product of molten salt produced in the oxygen production step gives the Cu-Cl cycle a significant advantage of linkage with current high temperature solar thermal technologies. This allows flexibility for integration of the Cu-Cl cycle and solar thermal plant. Using a thermal network analysis of the Cu-Cl cycle, the layout options for the integration of a Cu-Cl cycle with various solar thermal technologies are presented and discussed in this paper.     

Optimized solar-powered liquid desiccant system to supply building fresh water and cooling needs

This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80 m² with the objective of producing 15 l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration temperature increases with decreased heat sink temperature with values of 50.5 °C and 52 °C corresponding to sink temperatures of 19 °C and 16 °C.     

Annual variations of temperature in a sample of UK dwellings

The internal temperatures of 25 households in Northern Ireland were measured in each house at four locations: the bedrooms, living rooms, halls and kitchens, and analysed on seasonal, monthly and daily bases. In 80% of the homes the winter average daily temperature was between 15 °C and 20 °C and in summer between 20 °C and 23 °C, therefore maintaining a reasonably comfortable temperature throughout the year. In 14% of the homes, the daily average temperature was above 21 °C throughout the year, suggesting a higher household temperature than required for comfort, thus exhibiting wasteful energy behaviour. Three percent of the homes did not use their heating adequately and the winter average temperature was below 15 °C. For the majority of households, the highest indoor temperature was in August and the lowest in February. In general the peak temperatures of households occur in the evening after 8:00 pm. The peak bedroom temperatures occur between 10:00 pm and midnight and in the morning after 8:00 am. The peak living room temperature is generally in the evening while it is occupied. Correlations between the temperature difference between indoor and outdoor temperatures with outdoor temperature have been developed for each house and the four locations. The relationship between the fluctuations of average daily temperature with annual average temperature has been established.     

Performance of a non-metallic unglazed solar water heater with integrated storage system

The performance of a new design of non-metallic unglazed solar water heater integrated with a storage system has been studied. In this system, the collector and storage were installed in one unit. All parts of the system have been fabricated from fiberglass reinforced polyester (GFRP) using a special resin composition that provides good thermal conductivity and absorptivity. The storage tank has a capacity of 329 l. The design of the storage system was sandwich construction, with the core material made out of polyurethane foam, which combines stiffness and lightness of structure with very good thermal insulation. The width and length of the absorber plat were 1.4 and 1.8 m, respectively. The performance of the system has been investigated by two methods. In the first method, the storage tank was filled up with water the night before the test. The tank was then drained during the night, refilled and made ready for the next day’s test. The tests were repeated under varied environmental conditions for several days. The maximum water temperature in the storage tank of 63 °C has been achieved for a clear day operation at an average solar radiation level of 700 W m⁻² and ambient temperature of 30 °C. The decrease of water temperature with and without the thermal diode is 10 and 20 °C, respectively. In the second method, the testing was of the same way, but in this case without draw-off or draining of the hot water from the storage tank. All data readings were recorded from sunrise to sunset over the same period. The temperature was recorded for several days and ranges of 60–63 °C were obtained in the storage tank. A system efficiency of 45% was achieved at an average solar radiation level of 635 W m⁻² and ambient temperature of 31 °C.     

A numerical investigation of a diffusion-absorption refrigeration cycle based on R124-DMAC mixture for solar cooling

Research on new working fluid for uses in absorption systems has been continued. The feasibility of a solar driven DAR using the mixture R124/DMAC as working fluid is investigated by numerical simulation. The cycle is simulated for two cooling medium temperatures, 27 °C and 35 °C, and four driving heat temperatures in the range [90 °C–180 °C]. The performance characteristics of this system is analyzed parametrically by computer simulation for a design cooling capacity of 1 kW. The results show that the system performance and the lowest (minimum) evaporation temperature reached are largely dependent upon the absorber efficiency and the driving temperature. It is shown that for solar applications this fluid mixture has a higher COP and may constitute an alternative to the conventional ammonia–water system.     

Theoretical and experimental investigation on the application of solar water heater coupled with air humidifier for regeneration of liquid desiccant

Theoretical and experimental investigation on the application of flat plate solar water heater coupled with air humidifier for regeneration of liquid desiccant has been presented in this work. The heated water from the storage tank of the solar heating system is circulated in a finned tube air heater. Hot air from the air heater is blown through a packing of a honeycomb type for the purpose of regeneration of calcium chloride (CaCl₂) solution. An experimental system has been designed and installed for this purpose. The system comprises a solar water heater with a storage tank connected to an air/water heat exchanger. Hot air from the heat exchanger is blown to the air humidifier, which functions in this study as a regenerator. Calcium chloride solution is applied as the working desiccant in this study. Solution concentration is determined at the end of regeneration process and the mass of evaporated water is evaluated. It is observed that the heating temperature varies, at day time, in a range of about 5 °C. This limited variation in hot water temperature demonstrates the importance of the storage tank to attain a nearly steady state operation of the system. Experimental results show that solution with 30% concentration can be regenerated up to 50% using solar energy. In the theoretical part of this study, a multiple-layer artificial neural network (ANN) model has been applied to study the performance of a solar liquid-desiccant dehumidification/regeneration system when calcium chloride solution is applied as the working desiccant. The experimental results of the present study are used to construct and test the ANN model. Then the model has been utilized to describe and analyze the effect of the inlet conditions of air on the regeneration process. Good agreement between the outputs from the ANN model and the corresponding results from the experimental data has been found. The proposed model can work well as a predictive tool to complement the experiments.     

Effects of auxiliary heater on annual performance of thermosyphon solar water heater simulated under variable operating conditions

A thermosyphon solar water heating system with electric auxiliary heater was simulated using the TRNSYS simulation program. Location of the auxiliary heater, inside the storage tank or connected in series between the system and the user, was studied using the TMY meteorological data for Los Angeles, California. Simulations were performed for two different water load temperatures (60 and 80°C) and for two types of daily hot water volumes (250 and 150 l). Four types of daily hot water consumption profiles were used in the present study, namely; the widely used Rand profile, continuous, evening and morning profiles. Also, the simulation is extended to cover the effects of thermal and optical properties of the flatplate collector and the volume of the storage tank. The results show that if water is drawn on a schedule corresponding to the Rand draw profile, the system operates with higher efficiency when the auxiliary heater is located in the storage tank than when the auxiliary heater is outside the storage tank. When operated with each of the other three draw schedules, however, better performance is achieved by locating the auxiliary heater outside the tank. The increase in solar fraction depends on the load profile and volume, temperature setting, as well as the quality of the collector and the storage tank volume. When the values of the parameters F_R(τα)_n and F_RU_L are changed from 0.8 and 16 kJ/h m²°C to 0.6 and 30 kJ/h m²°C, the solar fraction decreases by approximately 40–50%.     

Performance prediction of a direct expansion solar assisted heat pump using artificial neural networks

This paper presents the suitability of artificial neural network (ANN) to predict the performance of a direct expansion solar assisted heat pump (DXSAHP). The experiments were performed under the meteorological conditions of Calicut city (latitude of 11.15 °N, longitude of 75.49 °E) in India. The performance parameters such as power consumption, heating capacity, energy performance ratio and compressor discharge temperature of a DXSAHP obtained from the experimentation at different solar intensities and ambient temperatures are used as training data for the network. The back propagation learning algorithm with three different variants (such as, Lavenberg–Marguardt (LM), scaled conjugate gradient (SCG) and Pola-Ribiere conjugate gradient (CGP)) and logistic sigmoid transfer function were used in the network. The results showed that LM with 10 neurons in the hidden layer is the most suitable algorithm with maximum correlation coefficients (R²) of 0.999, minimum root mean square (RMS) value and low coefficient of variance (COV). The reported results conformed that the use of ANN for performance prediction of DXSAHP is acceptable.     

Highly conductive composites made of phase change materials and graphite for thermal storage

Conventional phase change materials (PCMs) are already well known for their high thermal capacity and constant working temperature for thermal storage applications. Nevertheless, their low thermal conductivity (around 1 W m⁻¹ K⁻¹) leads to low and decreasing heat storage and discharge powers. Up to now, this major drawback has drastically inhibited their possible applications in industrial or domestic fields. The use of graphite to enhance the thermal conductivity of those materials has been already proposed in the case of paraffin but the corresponding applications are restricted to low-melting temperatures (below 150 °C). For many applications, especially for solar concentrated technologies, this temperature range is too low. In the present paper, new composites made of salts or eutectics and graphite flakes, in a melting temperature range of 200-300 °C are presented in terms of stability, storage capacity and thermal conductivity. The application of those materials to thermal storage is illustrated through simulated results according to different possible designs. The synergy between the storage composite properties and the interfacial area available for heat transfer with the working fluid is presented and discussed.     

Galactitol hexa stearate and galactitol hexa palmitate as novel solid-liquid phase change materials for thermal energy storage

Galactitol has a melting point of 187.41 °C and a fusion enthalpy of 401.76 J g⁻¹. Its melting temperature is not suitable for many thermal energy storage applications although it has good latent heat storage capacity compared to the several traditional phase change materials (PCMs). The galactitol also has high supercooling degree as about 72 °C. These unfavorable properties limit the usage potential of galactitol in thermal energy storage applications. However, the phase change temperature and supercooling degree of galactitol can be reduced to a reasonable value and therefore its feasibility for energy storage systems can be increased. For this aim, in this study, galactitol hexa stearate (GHS) and galactitol hexa palmitate (GHP) were prepared as novel solid-liquid PCM by means of esterification reaction of the galactitol with palmitic acid and stearic acid. The GHP and GHS esters were characterized chemically using FT-IR and ¹H NMR techniques. By using DSC analysis method, the melting temperature and latent heat value of the PCMs were determined as 31.78 °C and 201.66 J g⁻¹ for GHP ester and 47.79 °C and 251.05 J g⁻¹ for GHS ester. Thermal cycling test showed that the prepared PCMs had good thermal reliability after thermal 1000 melting-freezing cycles. Thermogravimetric analysis (TGA) results revealed that the PCMs have good thermal stability over their working temperatures. In addition, thermal conductivity of the prepared PCMs was increased as about 26.3% for GHP and 53.3% for GHS by addition of 5 wt.% expanded graphite. Based on all results it can be concluded that the prepared GHP and GHS esters can be considered as promising solid-liquid PCMs for many energy storage applications such as solar energy storage, indoor temperature controlling in buildings, production of smart textile and insulation clothing due to their good energy storage properties.     

Thermal coupling of a high temperature PEM fuel cell with a complex hydride tank

Sodium alanate doped with cerium catalyst has been proven to have fast kinetics for hydrogen ab- and de-sorption as well as a high gravimetric storage density around 5 wt%. The kinetics of hydrogen sorption can be improved by preparing the alanate as nanocrystalline material. However, the second decomposition step, i.e. the decomposition of the hexahydride to sodium hydride and aluminium which refers to 1.8 wt% hydrogen is supposed to happen above 110 °C. The discharge of the material is thus limited by the level of heat supplied to the hydride storage tank. Therefore, we evaluated the possibilities of a thermal coupling of a high temperature PEM fuel cell operating at 160–200 °C. The starting temperatures and temperature hold-times before starting fuel cell operation, the heat transfer characteristics of the hydride storage tanks, system temperature, fuel cell electrical power (including efficiency) as well as alanate kinetics were varied by system modelling with gPROMS^®. The kinetics of the hydride decomposition was found to have a major influence on the performance of the system. A cumulative output of 0.8 kWh was reached in a test run.