Humidity Basics

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Bryan covers some humidity basics, including the difference between relative humidity and total moisture content (in pounds or grains).

First of all, air has weight and takes up space. At sea level, the air pressure is 14.7 PSI due to the atmosphere, which consists of nitrogen, oxygen, carbon dioxide, argon, some more trace elements, and water vapor. The amount of water vapor in the atmosphere is variable based on different environmental conditions, and it depends a lot on temperature.

Relative humidity refers to the amount of humidity there currently is compared to how much humidity the air could possibly hold (100% RH or saturation). The point of 100% RH or saturation is also known as the dew point temperature. Once the air reaches saturation or the dew point temperature, it can no longer hold any more moisture. We keep evaporator coils cold so that the air reaches the dew point and has to drop some moisture as it cools; that moisture then drains out as liquid water.

It's also worth noting that water vapor is lighter than air and travels up in the atmosphere; from there, it hits the dew point and forms a cloud.

Warmer air can hold more moisture before saturation is reached. Air can hold less moisture on a cold day, so you could be at 100% RH and still have less total moisture in the air than on a hot day. You can think about tea or coffee: high amounts of sugar won't dissolve in cold tea or coffee, but more will dissolve when you heat the tea or coffee.

Humidity is a huge driver of comfort or indoor air quality. Higher humidity levels make it harder for us to dissipate heat through sweat; our bodies aren't able to dissipate heat via evaporation as easily. The target relative humidity range from a comfort standpoint is typically between 30 and 60%. From an IAQ standpoint, it's typically good to stay between 40 and 50%. Moisture buildup due to conversation in homes with high relative humidity can lead to microbial growth and present a health hazard.

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God Bless this guy! . Love !!! -- His sound quality alone exceeds most. I'm convinced this guy does his homework on everything in life. This was so relevant and helpful to anyone wanting to learn about humidity.

bwrinn

Helping engineers and technicians! Wonderful video thank you.

janeturner

Just about one of the best, time sensitive explanations of this topics, both dealing with the physics, the human aspect, and the technological for HVAC. TY.

HaikuAutomation

This guy deserves a medal! So simple and straightforward, thank you good sir!

OG.eL_niNo

I’m an graduate from GTCC’s accredited HVACR program and this is great stuff!! Keep it up man. It really helps when I need a quick refresher on a subject and you hit every key detail.

chriszr

This channel is going like a rocket.... all the way up

buildingstatux

Man, you're amazing! Great lesson on the basics of moisture in the air. Thank you!!

acreguy

Excellent video, thank you for sharing your knowledge.

DanO

I’m old but now I get it thanks to your excellent explanation. Thank you👍

King-Arthur-The-First

thank you very much . You are easy to understand and so helpful !

felipegonzales

Excellent explanation and video production. Thank you!

LinearGiraffe

An excellent video with a clear and concise explanation, thanks.

HARRi_UK

Excellent explanation. Thanks a bunch 🙏🏾

chelseaFC

I’m from Thailand thank you for this lesson.

daowara

Hi. I found your channel whilst looking for an explanation as to why my thermostat says it is 71 in my home, but the humidity is 80%, and I do not feel all that cool. Normally, at 73 F I start to feel a little chilled unless I am doing some sort of physical labour. Here is the situation. Maybe you can advise me what is happening?

I lease an approximately 905 sq ft home that was built in 1926. The owners had an all electric HVAC system installed August '23. My heating bill last Winter was outrageous, and a friend told me that was because my furnace is electric. I had always had gas before this, and my bill was never remotely that high---close to $300 before I dropped the temp to 59 F and kept it there 24/7. Even after dropping the temp to 59 and feeling quite cold in here, my heating bill only dropped to about $240. I was so chagrined.

Then, the hot and humid weather began (I live in the south). I feel hot in the house even though the HVAC is set to 71 and reads a temp of 71. I have little table top thermostats in each room of the house. No two areas have them same temp, but all areas have pretty high humidity---talking about 77%-80% as of May 2nd. At 71 I expect to feel uncomfortably cold, yet I feel hot and oily from the humidity. All windows and doors are kept closed. I am nervous to see what my upcoming electric bill will be. How can the temp in the living room, for example, read 71 yet the humidity read 80% ? The HVAC thermostat is in the living room. It seems to me that if the temp is really 71, the the humidity should not read 80%, and I should. not feel uncomfortably warm and oily from the humidity.

I am worried because the temps here will soar into triple digits soon. We managed to squeak by in April without any triple digit days, but I think that is because most days were either overcast with rain in the forecast, or a high pressure system had moved in and dropped the outdoor temperature to a very comfortable temp in the lower to mid 60s. That is already changing. We are already getting temps in the mid to high 80s before the heat index is factored in. It is about to turn really hot soon.

I would like to figure out what is going on and if there is anything to do to fix this problem. Thank you!!

lzdmlky