Articles » About humidity

How to measure the humidity level

26/08/2011

The humidity value can be measured with special instruments called hygrometers or, more technically, psychrometers that give us the percentage of water vapor in the air referred to it's saturation point. When the instrument reads 100% Relative Humidity, i.e. 100% R.H., the air is saturated. When the humidity level is 50% R.H. means that the quantity of water vapor in the air is 50% of the total capacity at that temperature and pressure.
To evaluate the relative humidity of the air at different temperatures there is a diagram, well-known to all heat technicians, called the psychrometric diagram or Mollier's diagram.
Generally, the percentage of humidity present is higher in cooler environments such as cellars or underground or basement rooms. For example, if the outdoor temperature in summer is 28 °C (82.4 °F)and the humidity 70% R.H., a cellar could have a temperature of 22 °C (71,6 °F). In this case the relative humidity would be 100% R.H and water condensation should be observed, seeing that the air has reached it's saturation point at that temperature. The opposite happens in heated rooms. For example on a rainy winter day the outdoor temperature could be 2 °C (35,6 °F) and the humidity 90% R.H.: the same air in a flat heated at 20 °C (68 °F)the relative humidity would be about 28% R.H.! There are rooms where, independently of other conditions, the relative humidity tends to be high: for example those rooms where sports activities are carried on, in locker rooms with showers, in swimming pools, in hairdressing salons, in restaurants, in kitchens, in dance halls, in ironing rooms, laundries, etc.

How to measure the humidity level How to measure the humidity level