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Dew point definition full#

But which is which and going where and what is this and what do we do with it?īefore we begin parsing this out, the answer to your question is YES. Notice that there are temperatures, absolute humidity and relative humidity in there. They are not strictly accurate charts, but are only being used diagramatically. Don't worry about the actual numbers in the following charts. Let's leave those to the engineers and HVAC specialists. For the sake of clarity and because conservators don't really need to use them, I have not drawn in the enthalpy or volume lines. The psychrometric chart is a really intimidating looking graph with a ton of lines going in 6 different directions. This helps explain how, if the only thing you can control is temperature, you can lower it to increase humidity, or increase it to lower humidity. If you look at the above example, you can see that in an imaginary space that holds 5g of water per cubic metre of air, the relative humidity will vary depending on the temperature even though the amount of water in the space has not changed. Numbers calculated using Michell instruments calculator Relative humidity is that amount of water expressed as a percentage of the total amount of water that can be "held" by air at that same particular temperature and pressure.Įxample in an imaginary space Absolute humidity in g/m3.Or similar measurements using feet and pounds. Or grams of water per cubic metre of air. So it can be in grams of water per kilograms of dry air. It is expressed as weight of water per weight or volume of air.It's actually more about vapour pressure equilibrium, but let's not overcomplicate for now and use the word "hold". Assuming constant atmospheric pressure, absolute humidity is the actual amount of water (in weight) that can be "held" by air at a particular temperature.You will find much better, more scientific definitions in physics sites, but the following are supposed to be straightforward and clear. Relative humidityīefore going a bit more into dew point, it's important we understand two concepts clearly.

If you look closely, you will notice that the dew point line is basically the same as the temperature but a few degrees below it. There is no artificial humidifying or dehumidifying or heating or cooling.

This is a space without any HVAC control.

In other words, it is not something you want if you want to keep your things dry.

If your dew point is well below the dry air temperature, your RH is low.

If your dew point temperature is close to your dry air temperature, your RH is high.

This means that the dew point is the temperature at which dew will begin forming in your space.

Dew point is the temperature at which Relative Humidity (RH) in your space is at 100% so that the moisture will start condensing out of the air.

It represents the absolute moisture content of the air.

What does it tell us? I have found several explanations of dew point, so I will attempt to sum it up here as clearly as possible: The dew point line, and this line can be a bit trickier to interpret. What is the dew point, in simple terms? When you look at your environmental monitoring charts, you are used to seeing the temperature and relative humidity lines.

What can the psychrometric chart do for you?.

Dew point definition full#

The psychrometric chart again in full colour.