DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF A PASSIVE SOLAR WATER HEATER

DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF A PASSIVE SOLAR WATER HEATER

ABSTRACT

A thermosyphon solar water heating system which captures and utilises the abundant solar energy to provide domestic hot water was designed, simulated, constructed and tested. The system was designed to supply a daily hot water capacity of 0.1m3 at a minimum temperature of 70oC for domestic use. The design approach was in three parts; firstly, since solar radiation and weather data which are driving function for solar systems design vary randomly with time, the monthly average daily solar radiation and weather data obtained from the typical meteorological year (TMY) solar data of Zaria were used to determine the design month as the month (August) with the least monthly average daily solar energy ratio. Solar radiation and weather data of the design month were used to design the system. Secondly, the design month solar radiations and weather data were used as input into the design equations coded using MATLAB programming language to determine the system characteristic and components sizes. A parametric study was also carried out to study the effects and sensitivity of varying some design parameters such as number of glass covers, collector tube centre to centre distance W, absorber plate thickness collector tube internal diameter and collector tilt angle on the design objective function (the heat removal factor ). Thirdly, based on the values of the system characteristics and components sizes obtained from the design calculations and the parametric study, a model for the performance simulation of the system was formulated using the Transient System Simulation (TRNSYS) software. This model was used to predict the annual hourly performance of the system for recommended average day of the months using the TMY solar radiation and weather data of Zaria as input function. The system was then constructed based on the component sizes adopted for the simulation owing to the satisfactory performance of the system as revealed from the simulated results. To validate the simulated system performance, system performance tests were conducted for 3 days and the results were compared with the simulated results. The root mean square error (RMSE) and the Nash-Sutcliffe Coefficient of Efficiency (NSE) statistical tools were used to analyse the experimental and simulated results in order to validate the predictive power of the software. The results of this research led to the conclusion that a thermosyphon solar system with collector area of 2.24 m2 operated under the weather condition of Zaria, would be capable of supplying a daily domestic water of 0.1m3 at temperature ranging from 59oC for the worst month (August) to 81oC for the best month (April).The computed NashSutcliffe Coefficient of Efficiency (NSE) values of 0.663, 0.956 and 0.885 and the low RMSE values of 8.09oC, 3.65oC and 5.31oC between the modeled tank inlet temperature and the observed tank inlet temperature for the three days tests conducted indicated that the model formulated using TRNSYS software was valid and closely agreed, capable of predicting the performance of the system with a 66.3 %, 95.6% and 88.5 % degree of accuracy for the 3 days that the experiments were conducted respectively.

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