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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Best breakdown on this subject that I've seen. Thank you.
Good job! 👍
Tho it can b tough following these vids r gospel
Love this!
Good knowledge
Great video
Will dew point limit supply air temperature leaving an evaporator?
#RH
Thank you
Thanks a lot. It was really helpful
Thank you❤️
Thank you, this was awesome.
✅
I did enjoy myself thank you.
Nice and clear, now I understand.
It is wrong to say that air "holds" more moisture when it is warmer. Air does not hold water vapor. Air is a mixture of gases, including water vapor, not a sponge. RH is a measure of how much energy is available to evaporate water relative to the amount of energy it takes to saturate the air with water vapor. Saturation is the point at which the number of water molecules leaving a liquid water source (evaporating) equals the number of water molecules (in the form of vapor) returning to the liquid water state (condensing). Higher temperature is higher energy, hence more evaporation. 30% RH means the energy available for evaporation is 30% of that required for saturation. Further, the "dew pont" is the temperature at which condensation occurs. To prevent condensation, the temperature must kept higher than the dew point. Window surfaces colder than the inside ambient air will condense the water vapor in your home when they are below the dew point. When the inside relative humidity is higher, the dew point gets closer to the ambient temperature so the window surfaces have to be less colder than the inside air to form condensation. When the relative humidity is 100%, the dew point equals the ambient temperature so any drop in temperature will cause condensation. In your house, condensation would recuce the amount of water in the air and thus lower the ambient humidity if there was no more water being added to the air and condensation will stop, but then the job of your humidifier is to keep adding water so condensation continues, potentially causing damage to window frames and inside walls and ceilings.
So more TOTAL humidity in the same given temperature can impair people from releasing heat from the body? So do people living in very high TOTAL humidity climates be prone to get overheated and heat stroke compared to lower total humidity with same temperature? Maybe it is easier to run in low humidity climates because of that
how is water vapour lighter than air?
Too much information but less details. Is there a video to learn all what he said in details?
My ac handler is inside the closet. The door is close. The door is solid has no hole. I found a pin hole after the handler in the insulation. I put a tape on it and now I have grow on the insulation. A friend suggested to change the in dilation and make it better i sulfate. What you digest?
I'm wondering what your thoughts about running a standalone (plug-in) dehumidifier in your home in. This has been recommended on several sites but I'm wondering the true value of it. I certainly understand that relative humidity over 50% starts to get uncomfortable and that lower humidity is good and can allow you to even raise your temperature setpoint. However, the waste heat from the compressor is being dropped directly into my home (albeit the basement). this introduces an additional (and considerable sensible load) to the home. I haven't measures the flowrate or the temperature gain but it is normal fan speed over a 3" by 15" opening (0.3 ft^2) and the temp out is in the high 80's.
Bryan Orr – you are one talented teacher! I had zero interest in HVAC but now I think it's the most fascinating subject there is.
Huh
Interesting! 👍👍