What is the effect of a low-e coating on the inner surface of a window glass on the \((a)\) heat loss in winter and (b) heat gain in summer through the window?

Low-emissivity (low-e) coating is a thin metallic layer applied to the surface of a window glass to reduce the amount of radiant heat transfer through the glass. It is designed to minimize the amount of infrared rays that pass through the glass while allowing visible light to transmit through.

In winter, low-e coating on the inner surface of a window glass helps to minimize heat loss from inside the room to the outside environment. It does so by reflecting the radiant heat back into the room. Let's break down its effect on heat loss in winter: Step 1: Radiant heat (infrared rays) from inside the room strikes the low-e coated surface of the window glass. Step 2: The low-e coating reflects a majority of the radiant heat back into the room, thus reducing the amount of heat that would otherwise escape through the glass to the outside environment. Step 3: As a result, the room remains warmer, lesser energy is required to maintain the desired indoor temperature, and heat loss through the window is reduced.

In summer, the low-e coating on the inner surface of a window glass helps to reduce the unwanted heat gain from the outside environment. It does so by reflecting the incident solar radiation back outside. Let's break down its effect on heat gain in summer: Step 1: Solar radiation, composed of visible light, ultraviolet, and infrared rays, strikes the outer surface of the window glass. Step 2: The window glass absorbs a portion of the solar radiation, while some of it passes directly through the glass. The low-insulated glass covered with low-e coating inner surface performs better in reduction of heat gain during summers. Step 3: The low-e coating on the inner surface of the glass reflects a significant amount of the incident solar radiation (especially infrared rays), thus reducing the amount of heat that enters the room. Step 4: As a result, the room remains cooler, air conditioning requirements are reduced, and unwanted heat gain through the window is minimized. In summary, a low-e coating on the inner surface of a window glass effectively reduces (a) heat loss in winter and (b) heat gain in summer, resulting in energy-efficient windows and significant energy savings.