Relative Humidity: This describes the water vapour in the air, as opposed to the maximum amount that the air could hold, at a given temperature and pressure. The relative humidity is shown as a percentage.
Absolute Humidity: This describes the amount of water vapour in the air, regardless of temperature. This is shown as grams of water per kilogram of air.
Dew Point: This is the temperature at which airborne water vapour will condense to form liquid drops, as dew or condensation. This happens when the absolute humidity reaches a relative humidity of 100%, and so the dew point will vary depending on the temperature and air pressure.
Mollier Diagram: A Mollier Diagram is a chart showing the relationship between air temperature, moisture content, and enthalpy. It is an essential tool for an air-conditioning engineer, and is used to help determine which systems will be most suitable in any given situation.
Enthalpy of Vaporisation: Also known as heat of evaporation, this is the energy (enthalpy) needed to covert a liquid into a vapour.
Adiabatic Humidification: This is a method of humidification whereby the energy needed to covert a liquid (water) to vapour is drawn from the surrounding air in the form of heat. This has a cooling effect on the air.
Isothermal Humidification: This is the humidification method whereby the energy needed to convert water to vapour is provided by an external energy source. The water is converted into steam before being propelled into the air. The temperature of the surrounding air remains constant.
German Degrees: This is a system measuring the levels of calcium carbonate and other minerals found in drinking water.
Conductivity: The conductivity of water is expressed in microsiemens, and is directly related to the quantity of conductive ions carried by salts and other matter dissolved in the water. Pure water, therefore, does not conduct electricity. Drinking water has a conductivity of around 600-1000 microsiemens per centimetre.
Reverse Osmosis Water: Also known as RO water or permeate water, this is water that has been filtered through a semi-permeable membrane by reverse osmosis. The water is free from bacteria and viruses, and virtually all minerals. It is used, for example, in car washes as it dries without streaking. The RO water used in humidification processes has, on average, a conductivity of 10-20 microsiemens.
Demi Water: Also known as demineralised water, this is water from which all minerals and salts have been removed. It has a conductivity of 0,05 microsiemens.
Legionella: This is a family of very commonly occurring bacteria. If inhaled, the bacteria can cause legionellosis, or Legionnaire’s disease, a very serious pneumonia-like lung infection with serious side effects such as memory and concentration loss. For those with reduced immunity, Legionnaire’s disease is very often fatal.