Psychrometrics Made Simple

Join CaptiveAire for a professional development hour (PDH) all about psychrometrics and the Psychrometric Chart--how it came to be, how it's used, and why it's important in HVAC design. This topic is particularly helpful for anyone who works in HVAC, especially HVAC engineers and consultants, or anyone who wants to gain a deeper understanding of the world around us. Learn more about CaptiveAire at captiveaire.com.
To receive PDH certification for this video, please visit CaptiveAire.com/library and click Request Access under the Professional Development section. Fill out the form on the pop up that appears and click Send. CaptiveAire will then add you to a professional development portal where you can access a certificate to confirm your training.
0:00 Introduction
0:37 A very brief history of the psychrometric chart
2:15 Part 1 - The Fundamentals
3:08 Dry bulb vs wet bulb temperatures
5:47 Relative humidity
9:40 Dewpoint
11:30 Moisture content
13:06 Enthalpy
15:56 Specific volume
17:22 Finding all parameters example
18:53 Part 2 - Mapping HVAC Processes
19:06 Basic directions on the chart
21:25 Evaporative cooling and the adiabatic process
22:16 The comfort zone
22:43 The cooling process
25:05 Internal heat gains and the sensible heat ratio (SHR)
27:10 The heating process
28:36 Part 3 - Sizing HVAC Equipment
29:42 Sizing Example 1 - A simple enthalpy calculation
31:52 Sizing Example 2 - Peak dry bulb vs. dehumidification conditions
35:22 Other factors influencing equipment sizing
37:55 Part 4 - Modulation, Gas Reheat, and Economizers
37:58 Modulation
40:22 Reheat
43:13 Economizers
46:20 Conclusion

[@BaronVonSTFU]

You all need to figure out KZbin's algorithm because this video was buried. I watched many many videos of professors describing the psychrometric chart. They were good and they made sense. But this video has great production value and you obviously put a lot of time into it. I appreciate it. More people need to see it.

[@CAPTIVEAIRE]

We're starting to get a little traction but it always helps if you share and spread the word! Thanks for the kind words :)

[@unicornofthought]

@@CAPTIVEAIRE This video was top noch! I'm not in the industry, but it was great to get a better understanding of how the equipment in a space functions :)

[@michaelszczys8316]

If it were renamed ' Woke Psychrometric Chart "' everybody would see it

[@ccantieny88]

Went over psychrometrics for two weeks in thermo 2. Didn't garner anywhere near the amount of useful info as I did in this 50 mins. Thank you guys!

[@ananthakrishnan2206]

We need more videos like this .. appreciate more videos especially on HVAC equipment selection using real scenarios

[@azizkhalili1249]

I don't think I have ever learned more from a video. Remarkable job.

[@jeffreyrex8232]

Hands down this video explaining physcrometrics is by far the best I’ve seen. Another Johnson Controls tech here, well until a few months back. I now find myself in a different part of the world where humidity control is a very big deal. This video has helped me brush up on the theory a great deal. Thank you CaptiveAir 👍🏻

[@antonkorolev8059]

This is one of the best HVAC videos I have ever seen. I work at Johnson Controls and I recommend this to everyone!! Thank you so much!

[@CAPTIVEAIRE]

Wow, thanks! We need more people like you to keep sharing these, haha

[@AtousaParish]

I really appreciated this video and found it extremely helpful! However, I noticed a significant ERROR regarding wind towers (wind catchers). While the video mentions that they were made by the Egyptians, it's important to clarify that wind catchers, also known as "Badgirs," actually originated in Iran and have been a traditional architectural element in Persian architecture for centuries. They are also found in other Middle Eastern countries, including Egypt, but their invention is credited to Iran. I am surprised that a great video like this made this huge mistake! I hope this can be corrected for accuracy. Thank you for the great content!

[@vonpilcher3900]

Love it! Very informative. Thank you for producing this video.

[@mikebracket8570]

I have been using the psych chart for years, but this webinar showed me some new things.

[@taylorwong6183]

Best video for psychrometric chart ever!

[@dadknockd5507]

This channel really has to be brought to everyone’s attention. I start school in May and just trying to get a brief explanation of the things I’ll see and this video is absolutely so informative. I appreciate videos/channels like this because they help people like me who do have a tougher time learning new things. At first I looked up that chart and almost fainted this video gives me all confidence going into the course. P.S the editing on this video and everything on your channel is beyond exceptional. Thank you!!!

[@HighresROBERT]

There has never been a more useful video for a more obscure topic. I can't believe something like this exists. Unbelievably useful.

[@CAPTIVEAIRE]

Thank you, I'm glad it's useful. - German

[@Erasedbrain]

This is pure gold ❤

[@DilaonDGC]

This video is amazing! I've stopped the video several times to dive deep...Thank you for sharing.

[@Uptown212HVAC]

This was excellent in addition to Psycrometrics Without Tears book. As an installer/tech, it opened my eyes to the processes I work with and makes me far better at my work.

[@fuzzbucket00]

I have been studying psychometrics for the ARE and this is some of the best content I have come across. I love your videos and the way you explain these topics. Thank you so much! ❤

[@TheFuzy11]

I’m not even half way through this video but I had to stop to comment because I’m learning so much, thank you from a random in 🇬🇧

[@metilarancio7609]

Thank you for such a clear-headed outline of psychometric charts! This video is the best resource I've run across yet

[@MTauhaA]

Great explanation of the different psychrometric phenomenon and use of climate design data. My suggestion would be also mention bypass factor as it seems that was the only core concept missing without getting too complicated with designs dealing with fresh air. Bypass factor affects evaporator coil size for a given flow rate. 1-BF= (Tair,in-Tair,out)/(Tair,in-Tcoil,dew point). it also helps in relating psychrometric phenomenon with refrigeration cycle. high ventilation applications typically have small BF.

[@kurtburrell]

Wow! These videos are amazing! I've been an engineer for nearly a decade now, and these are by far the best videos I've ever found in this industry. Please keep up the great work! I'll be forwarding these videos to my team for sure. Thank you so much for all of the work and production value you put into these videos. Did I mention this video was incredible 😄

[@waleedsn1085]

This is the masterclass.

[@andrewlnguyen]

Agree. Best hvac video I have seen.

[@VA-gu1jq]

One of best videos I’ve found on the subject, and I’m only half way through!

[@david4804]

Amazing video! The visuals you created make the explanations much easier to understand. Also, Bill presents the information so clearly. Printed off a chart for myself and found it very easy to understand + follow along with the video. Thank you!

[@angus7898]

it is a fantastic video, solved 10+ questions I have for 6-7 years of being a mechanical engineer. Thanks!

[@gregisaaclicayan6342]

This video is criminally underrated. The amount of production quality is top notch. I enjoyed and learned throughout the video. Thank you!

[@CAPTIVEAIRE]

Much appreciated!

[@tuaigets77]

One of the best videos on Psychrometrics. Good job 👍🏼.

[@Astroneer90-ur2tv]

I work for a hyperscale data center provider. I always share these videos with our internal clients (construction, electrical, sales, etc) because they are based. Great job my goodman!

[@CAPTIVEAIRE]

That's great to hear! What do you do on your day-to-day, and do you like it?

[@Astroneer90-ur2tv]

@@CAPTIVEAIRE Mechanical Engineer. Went from Consulting side to Client side. My day-to-day is reviewing designs, working with EORs, many meetings, and also getting to create new standards for our designs. I LOVE this job.

[@philipoakley5498]

Excellent. I particularly liked the inclusion of the discussion about saturation and how it happens. Additional points of interest: Could also mention that the relative humidity (RH) *is* the ratio of the current water content relative to the saturation water content up and down the 'dry' air line (i.e. that it's got that differentiator called 'bulb', not 'air' to the temperature). The fact that the RH lines look curved doesn't stop it being 'linear' when viewed as tick marks up/down the 'dry' air line (calling it 'dry' air can be confusing when you have 100% RH saturated dry air !) The water content of air (and by implications fabrics and sponge fills) shown in the Box Store example can also be extended to aircraft like the 747 which gains extra weight when left idle for a long time and looses weight (better flying) after the internal air conditioning reduces the RH and removes the excess water. I also missed the distinction between the constant wet bulb lines and the enthalpy lines, which IIUC, are not quite the same!

[@a.msalah1864]

Thank you so much

[@redzel9710]

GREAT VIDEO

[@user-ms3pm4gy9s]

Perfect. As a mechanical engineer, I really enjoyed it.

[@avincastelino3920]

This taught me a lot. Thank you.

[@CAPTIVEAIRE]

Glad it helped. Thanks for watching!

[@Studentofhvac]

This is a fantastic study on the psychrometric chart.

[@olegluzanov6012]

Great video, thank you

[@user-nz3tt1vy6h]

amazing. Thank you very much!

[@petarbabic9409]

Great video! I am currently learning thermodynamics and was puzzled by humid air, but thanks to this video i get it now.

[@shannonhill3356]

I bought a 9th edition Cengage textbook for myself to help become a better tech. It sat for three months and I finally cracked it. First handful of pages I grabbed opened up to the Psychrometric chart and I was immediately horrified, anxiety riddled, and super excited. I spent 45 minutes trying to figure out how to read it - then realized I didn’t know what enthalpy, moisture grains, or even what WB TRULY measured just how to read a differential. This video has made me a better tech in 45 minutes, able to confidently begin actually understanding my psychrometers, as well as be able to accurately use the paychrometric chart. I’ve been doing service going in four years, and these are the questions that even the old blood can’t really go into as they don’t see it as necessary in residential. Well, news flash - residential isn’t where I plan to retire 💪🏼

[@CAPTIVEAIRE]

I'm glad you got something out of the video! And I've experienced the same in many fields, it's common to only "know what you need to know." But others like you and myself like to learn the why, and I find it helpful in many ways. Thanks for the comment, German Tabor (filmmaker).

[@UMEryen]

Much Needed video for Psychrometry Thanks a lot

[@suheladesilva2933]

This is seriously a brilliant video, it cleared a lot of my doubts. Thanks a lot for the time and effort you put into this.

[@CAPTIVEAIRE]

That's the goal, thanks for sharing!

[@ilayarajdurairaj9211]

Amazing information anyone can understand from A to Z, thank you so much for Educating us. We wish you and you team to achieve all the greatest success.❤❤❤❤

[@scottieb6442]

100% Going to just send them your videos when my interns get too annoying!

[@mikehouver4499]

Excellent video. I've suggested it to all our young mechanical engineers. The only issue I have is that "condensate" is a noun and "condense" is a verb. Minor issue for sure but I cant unhear it.

[@rubensz0671]

Beautiful video. Thank you guys.

[@imadffgun6976]

Thank you 🤗 for this

[@jeremyangel8877]

Great Video, one of the best and I have watched a ton over the years. I agree with the last comment. I watch videos like this all of the time and I only discovered this about a week ago.

[@majdalbasher759]

That's the most awesome video i have ever seen

[@NikolayBychkovRus]

Thank you for the video. It is brilliant!

[@praveenkarunanithi936]

exceptional video... great info on HVAC design

[@abhyankaratharv]

Thank you so much!

[@harshptl1]

thank you so much. this is best explained video ever nake on ph diagram. it helps me a lot

[@thecurious6721]

Thanks for the great video 🙏👍

[@SharlsRS]

Spectacular material. Two things that I think worth mention. The chart gives the enthalpy value at saturation, so correction factor is needed. And the charts are plotted for a specific pressure. Please correct me if Im wrong. I know that maybe you didnt mention that for simplicity in the explanation. Thank you for a great video!

[@CAPTIVEAIRE]

Thanks for your feedback SharlsRS. Yes, sometimes we leave some stuff out purposely, sometimes it slips through, yours are very good points nonetheless.

[@thatguywecalldana]

Awesome video!!!

[@mariamoine4327]

INCREDIBLE video. thank you

[@CAPTIVEAIRE]

Glad you enjoyed it!

[@abwbakrismail2957]

amazing work! wish if had knew this vid back when i am in uni, beside that i never know tony soprano the gangsta is also a gangistavta HVAC

[@MrRavikiranElijahNRI]

Great videos.✍🏻

[@abdullahshereiqi]

Great vedio indeed 👍

[@sabitrzazade9144]

Best video ever! Bravo

[@ganjaplaystaion]

Great, great and great!

[@qumartanweer6589]

Very helpful

[@nishanthmurthy3467]

such a beautiful explanation ! thanks a 12,000 BTU/H. not sure why this doesnt pop up when you search psychrometrics.

[@CAPTIVEAIRE]

You're welcome a ton!

[@michaelobrien9092]

Condensate is a noun. Condense is a verb. Water vapor doesn't "condensate", it "condenses" (verb). The resulting liquid is called condensate (noun).

[@CAPTIVEAIRE]

You're correct, we'll get it right next time!

[@Intygra]

"Condensate" could also be used in a verb form.

[@Softdattel]

Very good.

[@muthyamnavakanth1035]

It is great video I ever seen in my carrier, could you explain more about the reheat Kw calculation. Thanks.

[@Adrian-yz7oe]

How could we affect and control vapor pressure inside a closed space (like in a walk in fridge)?

[@MattHarris3]

Agree with all the comments here, what a great video for what can be a pretty dry subject. Will be sharing! Any chance of an SI version? 😉

[@CAPTIVEAIRE]

Good suggestion, we will try adding SI equivalents for future videos.

[@abdelwahidsaeed7030]

Thanks sir From sudan sent my regards

[@VinOng-er6ks]

In the calculation of sensible and latent heat, aren't the temperatures supposed to be absolute?

[@rajinchaulagai5478]

what if the temperature is more that we cannot fit in psychrometric chart like. wet bulb temperature is more than 37 degree then how can we put the temperature..

[@aaronb483]

Is this something that is important to home HVAC or for industrial, like using chillers?

[@seek3n]

I thought sensible heat is also (convection and conduction energy) and latent is (radiation energy). Shpuldnt kitchen have higher sensible heat? Pls correct me if im wrong

[@vietbui1600]

Many Thanks for explanation. However it should be slower progress for easy understanding. I often stopped video in order to think clearly what you are talking.

[@CAPTIVEAIRE]

Thank you for your feedback!

[@tarikamer3703]

I have a couple questions. Great video BTW! 1. does reheat defeat the purpose of supplying colder air to achieve the setpoint? 2. Although during sensible heating the humidity ratio stays the same, the RH% decreases. Would that create a feeling of increased dryness since the body loses moisture more easily?

[@CAPTIVEAIRE]

Great questions. We have a video on load calculations that may be helpful to give more context to this here kzbin.info/www/bejne/Zoqmqn1nl7Zmp9E 1. Yes in a way. The thing is, we generally want a discharge temperature when cooling no lower than 55°F (there are exceptions). This is for comfort purposes, as colder air would feel too cold to the people in the building. So typically equipment is sized based on 55°F and the corresponding airflow CFM to ensure that in peak conditions this still provides enough sensible cooling. However, although sensible loads may be met, 55°F dry bulb also means roughly a 55°F leaving air dew point, and sometimes this isn't enough latent cooling to dehumidify the space to offset latent loads, so we may have to continue cooling the air to say a 48°F as this removes more moisture from the air. But now that discharge may be too cold to be comfortable. It also may mean that, depending on space loads and the sensible heat ratio of the space, we can't really achieve the window of space conditions we want to target. This is where reheat comes in, allowing us to "decouple" in a way how we handle the latent and sensible loads. We can cool the air however low we need to in order to offset latent loads, then reheat to the perfect temperature to ensure the discharge temperature is perfectly matched to the sensible loads. One example of where we may not care too much if we just discharge 48°F air is a kitchen, where the staff may not mind a cooler discharge since they're exposed to so much heat from within the kitchen. We don't have to use reheat, it's just an option that in certain cases allows for more comfort and tighter control over space and discharge conditions. 2. RH% of the leaving air would decrease as you say. But ultimately what we're concerned with is this discharge mixing with the air in the space, and the final mix having the correct temperature and humidity.

[@tarikamer3703]

thank you for the explanation!@@CAPTIVEAIRE

[@yasithsandaruwan514]

❤

[@dalvindersinghmanku8243]

Sit as service maintenance provider in New Delhi for last 2 year....but not a single HVAC teacher doesn't teach like you studied...s..can I convert another language....

[@user-zh7yb3kk8q]

👌🏻👌🏻

[@sidharthm3805]

👍🏻👍🏻👍🏻

[@brianskellenger9344]

👏

[@angelamarodelgado7016]

👏👍

[@tealkerberus748]

We know the Americans took up driving on the opposite side of the road just to be different to the English, and they called their currency the dollar just to be different to the English, and they amended their constitution to let every prospective school shooter buy a whole lot of guns just in case the English invaded and tried to burn down their capital again, but does anyone know why they're still using the old English Imperial units of measurement? Is that just to be different to the English too, because the English found out how much better metric is for doing science and shifted to using metric units of measurement like everyone else? Are the English really that scary? C'mon people. Minds out of the stone age. Use metric.

[@brentlackey8316]

How can the bottle condense? It already solid. The water from the air condenses on the bottle. Water int he bottle gets warmer and some of it evaporates. No mercy for new hires no mercy for fancy professionals.

[@0913593504]

Great Video