การเพิ่มสมรรถนะของการทำความเย็นแบบระเหย โดยชุดทำน้ำเย็นแบบโฟโตโวลตาอิกส์

Abstract

Nowadays, the direct evaporative cooling (DEC) system is well known and widely used due to its low energy consumption and high environmental friendliness. However, the application of evaporative cooling is more suitable for low relative humidity areas due to that the minimum outlet air temperature of the DEC that could be reduced is equal to the ambient wet bulb temperature. Therefore, the cooling performance of the system will be reduced in tropical areas including Thailand. Decreasing inlet feed water temperature and controlling water - air mass ratio are efficient methods to increase the performance of DEC, which is the aim of this study. The first objective of this research is to study the parameters that effect on evaporative cooling performance. The second one is to develop a mathematical model for predicting evaporative cooling performance. The last one is to study the suitable size of photovoltaics modules for the evaporative with water chiller. This research has 3 main parts, simulation, experimental and economics analysis. For the simulation part, the mathematical model was used to predict the outlet air temperature of evaporative cooling system with different inlet feed water temperatures (same as and different to wet bulb air temperature) and different values of water - air mass ratio. For experimenting part, the evaporative cooling system with chiller were tested. The experiments were conducted with specified conditions and the data were used to verify the results from the developed mathematical model. For analyzing economic part, a greenhouse size 6 10 3.5 m3 with an evaporative cooling system and photovoltaic water chiller was simulated by mathematical model with Chiang Mai's climate in Thailand. The operating condition is that a greenhouse could maintain temperatures below 25oC throughout the year. Then, the number of photovoltaics panels (425 W) was analyzed to estimate number of solar panels, which optimal economic cost-effective with the payback period and internal rate of return method. The simulation results showed that decreasing the feed water temperature could be enhance the performance of evaporative cooling systems. Moreover, the water -air mass ratio controlling able to reduce the air temperature, which divided into 3 cases as follows 1.) When the feed water temperature is higher than the wet bulb air temperature. lower the mass ratio was electively to improve the performance of system. 2.) On the other hand, when the inlet water temperature was lower than the inlet wet bulb temperature. In this case higher MR gave higher performance of system. 3.) When the feed water is equal to wet bulb air temperature, the water - air mass ratio did not give the effect on the outlet air temperature and the outlet air temperature was nearly constant when MR was increased. The simulation results showed that decreasing the feed water temperature could be enhance the performance of evaporative cooling systems. Moreover, the water - air mass ratio controlling able to reduce the air temperature, which divided into 3 cases as follows 1.) When the feed water temperature is higher than the wet bulb air temperature. lower the mass ratio was effectively to improve the performance of system. 2.) On the other hand, when the inlet water temperature was lower than the inlet wet bulb temperature. In this case higher MR gave higher performance of system. 3.) When the feed water is equal to wet bulb air temperature, the water - air mass ratio did not give the effect on the outlet air temperature and the outlet air temperature was nearly constant when MR was increased. For mathematic model, when the operating conditions were defined, the outlet air temperature of evaporative cooling system could be pointed out immediately. When comparing the outlet air temperature between experiment and mathematic model, both results agreed very well with 0.53% and 6.78% average error for the feed water temperature was equal to and higher than wet bulb air temperature, respectively. In the economics analysis for a greenhouse with evaporative cooling systems and photovoltaics water chiller. It could be seen that a greenhouse could be maintain inside temperatures below 25o C throughout the year with using 15o C of feed water temperature and the water-air mass ratio of 0.45 and the optimal economical number of photovoltaics panel is 55 panels with the internal rate of return of 22.05 and the payback period is 4.01 and 5.01 years for the normal and discounted payback period, respectively.