silicone spoon ceramic mug
Simply put, all ventilation chimney, known as the natural ventilation; all ventilation exhaust fan, is called mechanical ventilation. Affected by the external environment of natural ventilation, winter and summer, day and night is not the same, such as the truth is. But the natural ventilation also has its advantages, there is no power consumption, maintenance is simple. Mechanical ventilation is relatively stable, not influenced by the external environment, but it is the larger power consumption, maintenance complex.
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