THE EFFECT OF PRESET STORAGE TANK TEMPERATURE ON THE STAGNATION OF A FORCED CIRCULATION TYPE SOLAR WATER HEATING SYSTEM

This study focuses on the modelling and simulation of an existing active forced circulation solar water heating system in the College of Science and Technology under the Royal University of Bhutan. The installed prototype solar system consists of five flat-panel collectors connected in parallel, with a gross surface area of 10 m2, and a 500-litre water storage tank with a built-in heat exchanger to preheat the water in the student mess. The TRNSYS (Transient System Simulation Software) program is used to model and simulate an identical replica of the installed system. The simulation model is validated by comparing the simulation results with actual measurements. The effects of hot tank temperature and stagnation are simulated. When the temperature of the hot tank reaches a preset value of 60 °C, the circulation pump is turned off, causing the temperature of the solar collector to increase exponentially to stagnation. However, by increasing the hot tank set temperature to 80 ˚C, the stagnation time could be extended by two hours, during which the system can generate 25.425 kWh of thermal energy, while 60 ˚C provides only 18.45 kWh. The overall efficiency of the system increased from 27.13% to 37.88%.