The dew point is a better representative of the amount of moisture in the air. This is why we don’t feel “sticky” in an office building with 50% RH. For example, 50% RH at a warm temperature has more water vapor than 50% RH at a colder temperature. Warm air temperature holds more moisture than cold temperature. The important point to remember is that RH is relative to the temperature of the air at that moment. Now, MEMs-type (micro-electro-mechanical systems) relative humidity sensor ICs can accurately measure the RH level using the principles of an electrical signal change from a moisture absorbing film or structure.
Through the dry bulb temperature and the delta of the wet and dry bulb temperature (depression), the relative humidity can be determined. A rudimentary way to calculate it is by using a psychrometer to measure the dry and wet bulb temperature. Relative humidity (RH) is the ratio between the amount of water vapor (moisture) in the air at a given temperature to the maximum amount of water vapor the air can hold at that temperature. Before we look at the relationship between relative humidity and dew point, let’s look at the basics of each. The accuracy of the relative humidity sensor (RH sensor) will determine the accuracy of the calculated dew point. Instead, relative humidity sensors are used to calculate the dew point in most of these devices.
High-precision dew point meters are expensive, bulky and typically not used in the household, such as home weather stations. Our body cools us down through evaporation of perspiration and moist air will inhibit that. When we express how comfortable or uncomfortable we feel, we are really referring to the dew point.
So, why is the relative humidity practically the same in both instances? And what makes us tend to say “It feels hotter than it is out there?” In a typical office building, for example, where I am sitting at the moment of writing this, the relative humidity is measuring 50.15% RH with an ambient temperature of 73.54☏ (23.08☌), which is quite comfortable. On hot summer days, we tend to hear people say, “It’s so humid” or “It’s sticky out there.” To the surprise of most people who check the relative humidity level, they find it to be relatively low, for instance, 52% RH.
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