Question

On a cold windy day, a window will feel colder than on an equally cold day with no wind. This is true even if no air leaks in near the window. Why?

Short answer

On windy days, the heat transfer through the windows takes place through conduction. The convection process removes the warmer air just outside the windows, and it feels cooler. On a day with no wind, no heat transfer occurs through the windows, and it remains warmer.

Step-by-step solution

Understanding the heat loss through the windows

The windows lose heat energy by the convection process. Heat is transferred through the frame of the windows by the process of conduction. The radiation and air leakage also contribute to the loss of heat energy through the windows.

Explanation for why the windows feel colder on windy days as compared to a cold day with no wind 

The air temperature outside the window will increase due to the conduction process through the windows, and the heat will be transferred to the air.

On windy days, the convection process will remove the air just outside the window whose temperature is more. Due to this, the heat is transferred by the conduction process through the window.

However, there is no wind on cold days; so no warmer air removal takes place just outside the window. This is true even if no air infiltration takes place as there is no air leakage from the windows. So, no heat transfer by the process of conduction occurs through the windows.

That is why the windows feel colder on a windy day than on a cold day with no wind.