Overview of environmental humidity. Variable percentage of water vapor in the air (better known as relative humidity) is a fundamental parameter for evaluating the environmental healthiness and liveability. This value together with the environmental temperature are two parameters to be controlled and, as far as possible, adjusted to enjoy good health in the home. Temperature control is a widespread practice (who does not have heating or air conditioning systems at home?) However, knowing also humidity value is essential in order to optimize environmental comfort where we live, as this parameter influences on the perceived temperature a lot. We will show you the generic characteristics of environmental humidity and some of its peculiarities.
Relative humidity: definition
The term Relative Humidity indicates the percentage ratio of water vapor into an air mass to the maximum amount (i.e. saturation) at the same conditions of temperature and pressure. A 100% Relative Humidity value does not mean that the air mass is totally composed of water or steam, but that it holds water vapor in the maximum quantity which can be contained under these conditions, without condensing. The amount of water vapor contained in an air mass decreases with decreasing temperature, nearing to zero at -40° (this value coincides in Celsius and Fahrenheit scales).
Saturation and condensation humidity: dew point
The maximum amount of water vapor per air volume depends on the temperature; Saturation Humidity indicates the maximum quantity of water vapor at a given temperature (balance between molecules that evaporate and molecules that condense). In real conditions, saturation depends also on the evaporating water properties (phase, solutes and their charge, shape of the evaporating surface). The condition of "dew point" corresponds to the 100% of relative humidity. Above the "dew point" the air is over-saturated, and the water vapor condenses, dispersing small water drops into the air.
Effects of humidity on living beings and, in particular, on humans
Humidity rate over 70-75% causes problems both in the event of heat, making heat feel excessively sultry, and in the event of cold, creating the conditions for cold damp. Even in the opposite case, when humidity is lower than 20-25%, there are health risks. In dry air conditions, following problems may occur: dry out of throat and airways, inflammation, discomfort in breathing and difficulty in producing saliva. Therefore, humidity rate should always be between the range of 40-45% and 60-65%, depending on environmental temperature. Human body (like other living beings) is able to counteract, through defense mechanisms, any humidity conditions even if not optimal (e.g. by sweating). We shall avoid creating conditions which activate these mechanisms, to live in a healthy and comfortable environment.