When relative humidity is less than 40%, the risk of disease is increased. What are the correct amounts of relative humidity for a correct environment?įor a pleasant working environment, it is important to make sure relative humidity does not fall below 40%. One can now appoint the density as 1,20 kg/m 3 and there will be about 7,3 g of water per kg of air. Example: at a temperature of 20 ☌, the relative humidity is measured 50%. Naturally, this can all be controlled by a Mollier diagram. When air is heated, but not moisturized, relative humidity will decrease, whereas the number of grams of H 2O per kilogram remains the same.Īnother example: how much water vanishes from a smokestack which emits 80,000 Nm 3/hour of water-saturized air (100% RH) that has a temperature of 75 ☌? (answer = 31,394 litres/hour – or a reversed waterfall). Principally, when air is warmer, it can contain more fluids. When it is raining, relative humidity draws near 100% and when it is a cold day, relative humidity is very low. This data is based on estimates, because relative humidity cannot be measured accurately in outside air. Humans feel their best at a relative humidity of 40% or above. There appears to be a direct relation between relative humidity and phsychological wellfare of humans. For example, in winter at an outside temperature of -10 ☌ and a relative humidity of 30%, one wishes to create a satisfactory indoor climate (such as 20 ☌ and a minimal relative humidity of 40%). In practise, one should adopt a worst-case scenario. How much moist must be added to this air? must be added.Īccording to this method, one can determine how much moist a moisturizer must spray. Imagine: there is a building in which % of the air is recycled and is refreshed by outside air. Which equals for the space mentioned above:Īt an adopted weight of one cubic metre of air of kg/m 3, needs to be added to the air within the room to achieve the above-mentioned relative humidity. Required amount of H 2O (gram) per kg air to reach the desired Setpoint relative humidity inside closed space: With the following fields you can calculate the (new) relative humidity is the outside air is heated in a closed space (room, office, factory hall e.g.).:Ĭalculated relative humidity inside closed space: Separation and Concentration Purification Request.Plant Inspection & Process Optimalisation.Finally, a historical perspective is given with anecdotes about some of the early work in this field. Several useful applications of the simple conversion are presented, in particular the computation of the cumulus cloud-base level (or lifting condensation level) as z LCL > (20 + t/5)(100 – RH), where z LCL is in meters when t is in degrees Celcius and RH in percent. This article examines the mathematical basis and accuracy of this and other relationships between the dewpoint and relative humidity. However, there is a very simple rule of thumb that can be very useful for approximating the conversion for moist air (RH > 50%), which does not appear to be widely known by the meteorological community: t d decreases by about 1☌ for every 5% decrease in RH (starting at t d= t, the dry bulb temperature, when RH = 100%). The exact conversion from RH to t d, as well as highly accurate approximations, are too complex to be done easily without the help of a calculator or computer. The relative humidity (RH) and the dewpoint temperature ( t d) are two widely used indicators of the amount of moisture in air.
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