冷凍系統一般的方式是使用定頻式壓縮機,藉由壓縮機的運轉與關閉或者是加裝額外的加熱裝置來控制溫度,但是這種方法會造成電源的浪費以及壓縮機較容易損壞,所以運用變頻控制的技術可以有效解決這些問題並且能夠達到更精確的溫度控制。 低溫冷凍通常使用的方法是以壓縮機系統為主,壓縮機系統在一般環境中有著能源效率比比值較高而且製冷能力大的優點,但是因為使用的是冷媒蒸發溫度越低時,冷凍裝置的效率則會明顯的降低,所以在接近超低溫範圍時(-40℃以下),都會搭配其他的裝置來達到低溫的目的,一般使用的方法是二級式冷凍或者二元式冷凍。 本研究為設計一個新式的模糊控制變頻式二級式冷凍系統,採用的方法為壓縮機循環系統加上熱電致冷器,其目的為”壓縮機隨著輸入熱量不同而轉速也不同”之方式來節省能源,並且也使用二級式冷凍的方式使得熱電致冷器的熱面溫度下降,讓熱面與冷面之溫差大幅減小,使其冷面能夠有足夠的致冷力讓冷凍液水溫可以二次降溫降到所需之目標輸出溫度-40℃。 由模擬結果顯示,設計之二級冷凍系統在65瓦、30瓦與10瓦的負載下,其壓縮機之轉速不一樣,所消耗之功率也隨著負載降低而降低,並且輸出之冷凍液溫穩定保持在-40℃,達到研究之目的。
In general, the refrigeration system controls the temperature by turning on or turning off the fixed-frequency compressor, or installing the heating device, but these methods waste too much electricity. The main method of controlling low temperature is using compressor system. Compressor system has a high energy efficiency and large refrigeration capacity in the general environment. However, when the evaporation temperature is lower, the efficiency of refrigeration device will decrease significantly. Therefore, we try to work this compressor system with other devices under the range of ultra-low temperature (-40 ℃ below) to maintain the low temperature. In this study, we design a cascade system which is controlled by fuzzy, and operate the compressor system with Thermoelectric Cooler. We try to economize energy by" inputting different heat energy to change the speed of compressor." On the other hand, we also cool down the surface of the Thermoelectric Cooler by using of the cascade, and reducing the difference temperature of the hot and cold surface substantially. Therefore, it is cold enough to achieve the target output temperature, -40 ℃, in second times. According to the simulation results, the speeds of the compressor are different with operating the cascade refrigeration system at 65 watts, 30 watts and 10 watts respectively, and the power consumption is also reduced with lower load. Finally, the water temperature remains at -40 ℃ stably with our investigation.