Hey thanks for watching this is a quick video introducing you to the concept of humidity and specifically we're gon na, be focusing on relative humidity. We're going to talk about a few other things around that this is not an advanced psychometrics course. This is an introduction to humidity for technicians or people who are looking to get into the trade who really don't understand its significance. So first off air has weight and takes up space.

I know it seems like air is nothing. You know this stuff around me. It's clear, you can't see it, but it does have weight and it does take up space, and it's actually pretty significant. It makes up.

Minutes makes you what makes up our atmosphere, and so at sea level, which is pretty close to here in Central Florida, where I am at sea level. We have fourteen point seven pounds per square inch of pressure, pushing down on us on all sides because of the atmosphere and that's above us and that atmosphere. The air around us is made up of a few different kind of key components and the primary things that make up air are nitrogen oxygen, carbon dioxide, argon, a bunch of other trace gases and water vapor, and the amount of water vapor is actually pretty variable. It changes quite a bit and it changes with a few different factors and there's pretty deep science into this water is a really really crazy thing.

It's got a lot of really unique properties, and so I don't intend to give you an entire physics and chemistry course here, but it's something that I would encourage you to look into more there's a lot of really interesting facts about water, but but water does change Its levels in the atmosphere - and it depends a lot on temperature just to be clear when we say relative humidity. What are we saying? We're saying the humidity relative to the amount of humidity there could be and that term of could be is the maximum. That's what we call saturation so a hundred percent relative humidity is also called saturation, is also called the dew point temperature, and that is the point at which the air is no longer gon na hold any more moisture. In fact, if there is any moisture - and it hits dew point - that moisture is going to start coming out, so a cloud is an example.

You know you have that water vapor that rises up water vapor is actually lighter than air. A lot of people think they don't get that because they think all it feels muggy out here, but actually water vapor is lighter than air, and so water vapor travels up into the atmosphere and eventually it hits. Dew point actually makes these clouds these formations and so that's what that's, what clouds are and then eventually you get enough build-up and then they'll actually start to rain that that's we experience that all the time if you go outside and you see dew on the lawn You've experienced dew point if you see some droplets of water on a glass of water, you've experienced dew point if you've ever woken up in the morning and looked at your windows and on the outside, there were some water on the outside of the glass. That's because the air hit dew point and another way of saying dew point is a hundred percent relative humidity.

That means that the air cannot hold any more moisture and in reality it's actually not even that the air, because air doesn't really hold moisture. It's just moisture is a constituent part of the air. That's a that's a little bit more advanced there, but the the basic idea that you need to know - and the most important thing is that relative humidity is very. But the amount of moisture that the air can hold is contingent on a few factors.

But the biggest one being temperature, so the hotter that air is the more total amount of moisture it can hold. So you have a cold day. The air can hold less moisture, so you could be at a hundred percent relative humidity on a cold day or with a cold airmass and have less moisture in the air than you have on a hot day, and my favorite example of this is a glass of Tea or a glass of coffee, if you take cold coffee, cold tea, you try to stir sugar in it. You'll notice that the sugar does not dissipate, it isn't absorbed into the fluid.

Now you heat up that same cup of coffee to that same cup of tea and now all of a sudden, the sugar starts to disappear because the hotter coffee, the hotter tea, can hold more sugar. So the air, when it is warmer when it is hotter, when it is higher temperature, can hold more moisture, and so we often will kind of equates things we'll say it's hot and humid outside. But it depends on what we mean by humid. We could mean the total amount of moisture that it has or we could mean the relative humidity.

So you could have a time where it's say I don't know 40 degrees outside and you could have very high relative humidity. So you could have 80 % relative humidities, but now you take that same air and if you were to put it in a jar or something and heat it up, and that relative humidity would keep dropping. As long as there was no exchange of moisture in or out of it, because relative humidity is relative to the amount of moisture it can hold and warmer air can hold more moisture colder air can hold less moisture. So there's two different things.

You have to look at total moisture content, which we generally measure in or be measured in grains and then also relative humidity. There's a lot of different things that you need to know about humidity from a practical standpoint. One is: is that humidity is a huge driver and comfort and indoor air quality when relative humidities are higher. It affects our body's ability to eject heat via evaporation, which is sweat, but you don't have to be soaked in sweat to be evaporating a little bit.

Our body gives off in a small amount of moisture and it and it exchanges with the our atmosphere and it causes us to be cooled. And so, when we have higher relative humidities, we do feel sticky and muggy. And that's because our body isn't able to reject heat and when a body's not able to reject heat via evaporation, we don't feel right. This is why, from a comfort standpoint, relative humidity is between 30 and 60 percent.

Relative humidities are really what you look for in humid climates. You want to try to keep it right around 50 percent relative humidity and in drier climates you'd like to try to keep it yeah. 35. 40 percent relative humidity.

If you can that's for human comfort, the lower the relative humidity, the colder, we tend to feel because the lower the relative humidity, the more our body, gives up heat via evaporation, and so that's that's a big factor, especially when it's hot outside. That's why people? You know where I am in Orlando tend to feel very hot, even when you know at a temperature like 90 degrees, whereas in Phoenix Arizona where it's very dry, it might be over a hundred and not feel even quite as hot as it does here, because the Relative humidity is so low there that your body is able to reject heat through evaporation more easily. So that's a big factor, indoor air quality, also when you're in that sort of center range between 40 and 50 percent relative humidity, where you like to be then a lot of the conditions that people have with either on the dry side, their mucus, membranes drying out And feeling uncomfortable or on the wet side, different, bacterias and fungus and things can grow in the air and can cause more problems. You also tend to get more moisture build-up due to condensation on walls and around vents and things that can cause unhealthy conditions, and so controlling relative humidity is really really important in the HVAC industry.

There's a lot of different strategies that we use to do that, but most of our dehumidification with an air conditioning, happens on the evaporator coil. So this is a removal of moisture on the evaporator coil, because that evaporator coil gets cold and it it's what we call dewpoint and we mentioned that. But that's the temperature at which the air hits 100 percent relative humidity and starts to give up its moisture. So that's why the air comes in contact with that evaporator coil drops the air temperature and now, all of a sudden, that moisture is sort of squeezed out of the air onto that of a protocol and it drains outside and that's how we de humidify, the air Using air conditioning, but we kind of are behind the eight ball because simultaneously, as we squeeze some of that moisture out of the air, we're also cooling it, and so we're also reducing the amount of moisture that that air can hold.

So as air goes through the duct system, as an air conditioner, when it's cooling, the relative humidity of that air, is actually quite high until that air hits the space mixes with the other air. And now the relative humidity drops back down again. So relative humidity is always relative to temperature. Hotter air can hold more relative humidity cooler.

Air can hold less relative humidity. Hopefully that's a good starting point for you. There we'll catch you in the next video.