Sohif Mat

Simulation Analysis of the Four Configurations of Solar Desiccant Cooling System Using Evaporative Cooling in Tropical Weather in Malaysia

A high demand for air conditioning systems exists in hot and humid regions because of the warm climate during the year. The high energy consumption of conventional air conditioning system is the reason for our investigation of the solar desiccant cooling system as an energy-efficient cooling system. Four model configurations were considered to determine the best configuration of a solar desiccant cooling system: one-stage ventilation, one-stage recirculation, two-stage ventilation, and two-stage recirculation. These models were stimulated for 8,760 hr of operation under hot and humid weather in Malaysia. Several parameters (i.e., coefficient of performance or COP, room temperature and humidity ratio, and the solar fraction of each system) were evaluated by detecting the temperature and humidity ratio of the different points of each configuration by TRNSYS simulation. The latent and sensible loads of the test room were 0.875 kW and 2.625 kW, respectively. By investigating the simulation results of the four systems, the ventilation modes were found to be higher than the recirculation modes in the one- and two-stage solar desiccant cooling systems. The isothermal dehumidification COP of the two-stage ventilation was higher than that of the two-stage recirculation. Hence, the two-stage ventilation mode desiccant cooling system in a hot and humid area has higher efficiency than the other configurations.

Heat Transfer Enhancement for PCM Thermal Energy Storage in Triplex Tube Heat Exchanger

Thermal energy storage is critical for reducing the discrepancy between energy supply and energy demand, as well as for improving the efficiency of solar thermal energy systems. Among the different types of thermal energy storage, phase-change materials (PCM) thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. This study experimentally investigates the using of a triplex tube heat exchanger (TTHX) with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air-conditioning system. Four longitudinal fins were welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the thermal storage. The energy storage efficiency of the TTHX was determined. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The PCM melting time is reduced to 86% by increasing of the inlet heat transfer fluid. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%, meaning that 28.2% of the heat actually was lost.

A thermal comfort investigation of a facility department of a hospital in hot-humid climate: Correlation between objective and subjective measurements

A field study on assessing thermal comfort has been performed on one of the large-scale hospitals in Malaysia, a country where the climate is classified as hot-humid. The main objective of this study was to examine the comfort criteria by American Society of Heating, Air conditioning & Refrigeration Engineers, US (ASHRAE) standards in hot-humid regions and also to find the correlation between predicted mean vote (PMV) according to Fanger’s theory and thermal sensation vote (TSV) according to occupant votes. Therefore, both objective and subjective data was collected in this hospital, and this study’s results have confirmed that the preferred temperature is not necessarily in compliance with a neutral temperature, and people in hot-humid areas would prefer cooler environment to neutral temperature. In addition, by analyzing linear regression, a strong correlation between PMV and TSV was found while R2 = 0.950, and also the neutral temperature point in this field study was around +0.75 on the seven-point ASHRAE thermal sensation scale.

The Prediction of Drying Uniformity in Tray Dryer System using CFD Simulation

Tray dryer is the most extensively used because of its simple and economic design. In a tray dryer, more products can be loaded as the trays are arranged at different levels. The product is spread out on trays at an acceptable thickness. The drawback of this dryer is non-uniformity in the desired moisture content of end product due to poor air flow distribution in the drying chamber. Computational fluid dynamics (CFD) is used extensively because of its capability to solve equations for the conservation of mass, momentum, and energy using numerical methods to predict the temperature, velocity, and pressure profiles. This research is to predict drying uniformity of new design of the commercial tray dryer for agricultural product. The temperature and velocity profile, streamline and velocity on each tray was analysed to study the uniformity of the drying. The 3D simulation is done to represent the actual model. Generally the temperatures are considered uniform for all trays. However the average air velocity at several trays which is at tray number 1,7,8 and 15 are much higher than others tray. The rest of the trays are look more uniform. The average air velocity above the tray is about 0.38 m/s.

Performance Study of a Photovoltaic Thermal System With an Oscillatory Flow Design

In this study, integrated photovoltaic thermal roofing system has been successfully built and tested to improve the photovoltaic efficiency as well as providing domestic hot water supply. The major components of the solar photovoltaic thermal (PV/T) collector in this study comprise of amorphous silicon solar cells arranged in series that were adhered to the roofing structure. Unified structure of copper tube absorbers with oscillatory flow configuration was attached to the back plate which was insulated with glass wool from the surrounding. The entire PV/T collector has been mounted on a manual two degree solar tracker that can be adjusted toward the exposure of maximum solar irradiation. The effect of altering parameters such as water mass flow rate and irradiance on the collectors efficiencies has been carried out. The combined efficiency including photovoltaic and thermal efficiencies varies from 70.53% to 81.5% in the PV/T system with the oscillatory flow configuration. The present study has shown better results in terms of PV/T efficiency in comparison with the prior corresponding experiments.

Design and Modeling of One Refrigeration Ton Solar Assisted Adsorption Air Conditioning System

The modeling of the performance of a one refrigeration ton (RT) solar assisted adsorp-tion air-conditioning refrigeration system using activated carbon fiber/ethanol as theadsorbent/adsorbate pair has been undertaken in this study. The effects of hot water,cooling water, chilled water inlet temperatures, and hot water and chilled water flowrates were taken into consideration in the optimization of the system and in the design ofthe condenser, evaporator, and hot water storage tank. The study includes analysis of theweather data and its effect on both the adsorption system and the cooling load. This isthen followed by estimation of the cooling capacity and coefficient of performance (COP)of the adsorption system as a function of the input parameters. The results of the modelwill be compared to experimental data in a next step. [DOI: 10.1115/1.4027964]Keywords: solar energy, adsorption air conditioning, activated carbon fiber/ethanol,cooling load

The reliability of Predicted Mean Vote model predictions in an air-conditioned mosque during daily prayer times in Malaysia

A field study was conducted to investigate the relationship between the estimated Predicted Mean Vote (PMV) for comfort and the actual measured climate data and occupant comfort sensations recorded in an air-conditioned mosque building in Malaysia. The study was conducted between November 2012 and April 2013 during the five daily periods of prayer. PMV was calculated using the Fanger equations while the Actual Mean Vote (AMV) was gathered from the survey data of 330 randomly selected worshippers. The results show that the thermal responses from worshippers during the five daily prayer periods largely recorded in the neutral zone. PMV model calculations underestimated the temperatures at which people could be comfortable (25.9°C) in the mosque when compared to the AMV of respondents at 30.4°C. The difference of 4.6 K between PMV and AMV indicates that ASHRAE Standard-55 is considerable and obviously has serious energy implications for this organization if temperatures were to be kept at the PMV-required temperatures. It was concluded that worshippers in this air-conditioned mosque located in the hot and humid climate of Malaysia found the indoor thermal conditions to be thermally acceptable at the temperatures they experienced.

The CFD Simulation of Tray Dryer Design for Kenaf Core Drying

Tray dryer is the most extensively use for kenaf core drying because of its simple and economic design. The product is spread out on trays at an acceptable thickness so that the product can be dried uniformly. Most tray dryers use hot air stream where water is vaporized from the product and removed by air stream. In a tray dryer, more products can be loaded as the trays are arranged at different levels. The drawback of this dryer is non-uniformity in the desired moisture content of end product. The key to the successful operation of the tray dryer is uniform airflow distribution over the trays. Therefore, the good design of the drying chamber configuration in a tray dryer is necessary to obtain optimum performance. This research is to design the uniform airflow distribution throughout the drying chamber using CFD simulation for kenaf core drying. Several configurations of drying chamber and trays position was designed and simulated to determine the tray dryer which can produce better airflow distribution. It was found that the design B gives a more uniform airflow distribution compared to others design. The good design of kenaf core dryer should be able to produce uniform drying at high drying capacity and shorter drying time.

Case study of wind-induced natural ventilation tower in hot and humid climatic conditions

This paper investigates the performance of a wind-induced natural ventilation tower through an empirical analysis in hot and humid climatic conditions. There are mainly two methods for inducing natural ventilation; namely stack ventilation and wind-induced ventilation. Due to the relatively lower difference between the indoor and outdoor temperature in hot and humid conditions, stack ventilation method alone is rendered insufficient to create desirable air flow between outdoor and indoor building environment to achieve comfort and indoor air quality for the building occupant. Hence, wind-induced ventilation method can be used to achieve the desired air flow rates and improve the indoor air quality for the building. This study revealed that at external wind speed of 0.1m/s, the aerodynamic inverted airfoil roof geometry on the wind-induced natural ventilation tower is able to generate extraction air flow rate of 10,000m3/h with average of 57 ACH to provide comfort and indoor air quality to the internal building environment in hot and humid climatic conditions.

Thermal Performance Enhancement of Triplex Tube Latent Thermal Storage Using Fins-Nano-Phase Change Material Technique

ABSTRACT Latent heat thermal energy storage (LHTES) systems using a phase change material (PCM) can reduce the heat-transfer rates during charging/discharging processes because of their inherently low thermal conductivity. In this study, heat-transfer enhancement using various configurations of longitudinal fins employing both a PCM and a nano-PCM in a large triplex-tube heat exchanger (TTHX) was numerically investigated via the Fluent 15 software. The results showed that the thermal conductivity of the pure PCM (0.2 W/m K) can be observably enhanced by dispersing 10% alumina (Al2O3) to 25%. Therefore, the melting time is reduced to 12%, 11%, and 17% for the internal, internal-external, and external fins, respectively, compared with the case of the PCM without nanoparticle. It is concluded that the model of external fins-nano-PCM embedded in a large TTHX is the most efficient model for achieving complete PCM melting in a short time (188 min), where improving the thermal performance to 14% and 11% compared with the TTHX with internal and internal-external fins-nano-PCM, respectively. The simulation results are validated and agree well with experimental results for the PCM and nano-PCM.