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Thread: The use psychrometric air charts
03-02-2013, 04:49 PM #1
The use psychrometric air charts
I am a student at HGTC and we had to give a presentation for class on the most important thing we learned.
This is my video presentation.
03-02-2013, 05:15 PM #2
Excellently done for a class of people who somewhat already understand relative humidity. Speaking strictly from a presentation standpoint, there are a few things you could have done to make that very well done presentation even better.
Provide for a few "dramatic pauses" where your audience has time to think about what you have stated. Especially where you give calculations. Provide time for those in the audience who may not be following your calculationst to ask you to give them a way to better understand how you are getting to a calculated conclusion. Involve the audience a bit more.
Be certain to give a brief definition of technical terms that may not be completely understood by all in the audience. Just because we understand the terminology we are using does not mean that all of those we are talking to do.
You have a great capacity for memorizing data which allows you to be comfortable speaking without the constant use of notes. I would suggest joining a local Toastmaster's Club to hone the skills you already have. Toastmasters is a great way to try out new speaches on others while also working with a peer group that can evaluate your speaking in positive ways. Besides, the meetings are just fun.
All in all, a good training speech.Government is a disease......masquerading as its own cure…Ecclesiastes 10:2 NIV
03-02-2013, 07:49 PM #3
The lesson was all wrong, but the presentation was very good. I'm not good at sugar coating, so that being said, I apologize for my brevity. Just understand that my comment is meant as constructive criticism. My impression is that you need further study on this subject.
Last edited by hvacrmedic; 03-02-2013 at 08:11 PM.
03-02-2013, 10:42 PM #4
Hmmm, I have to admit that I was not really paying attention to the data. I was listening more from a speaker's point of view and not really paying attention to content. I'll have to relisten to understand what is wrong with the lesson. As I was doing other things while listening to the speaking structure, it sounded convincing enough.....
Hvacrmedic, could you please comment on what was wrong with the lesson itself?Government is a disease......masquerading as its own cure…Ecclesiastes 10:2 NIV
03-02-2013, 10:57 PM #5
03-02-2013, 11:34 PM #6Government is a disease......masquerading as its own cure…Ecclesiastes 10:2 NIV
03-03-2013, 12:35 AM #7
03-03-2013, 12:55 AM #8
I'm just not understanding exactly what it is you are objecting to specifically. Can you let us know what exactly is wrong with the lesson and what would be the correct lesson learned? If the speaker is incorrect about why and how the moisture was being transferred from one medium to another and then how it was removed, can you tell us what really must have been going on?Government is a disease......masquerading as its own cure…Ecclesiastes 10:2 NIV
03-03-2013, 01:26 AM #9
56° air at 50% RH is very dry air comparatively. It has a humidity ratio of 33.75 grains per lb (da). Raising that air to a temperature of 70°, without adding or removing moisture, or IOW still at 33.75 grains, would reduce the RH to 30.56%. The dew point would remain unchanged at 37.64°, well below floor temperature, which even with evaporative cooling could be no lower than about 47° (wb temp).
So if condensation is forming on the floor, then moisture is being added to the air from some other source until its dew point is above the floor temperature. Well, if the moisture was being added to the air from the concrete floor, then it wouldn't be that same moisture collecting on the floor's surface. IOW, water cannot be evaporating and collecting simultaneously from/on the same surface. Thus the moisture had to be from infiltration and/or reevaporation from the evaporator coils. When you switch from cooling to heating mode with a short delay between modes, the moisture on the coil reevaporates, and will temporarily raise the humidity ratio and dew point in the space. This in itself could account for condensation on the floor's surface. Infiltration of wetter air could equally account for it.
03-03-2013, 08:58 AM #10
I am not going to argue about this. It's easy to be critical and have all the answers when your not the tech on site. I will ,however, give you some more information.
The original presentation was 1:18 I had to condense it down to :15. So some details that did not move towards the point, were cut out to make room.
The concrete was unsealed. So there was a considerable amount of moisture in it,and I think we were only drying the very top of it. Allowing the moisture continue to permeate through the concrete.
The idea the super had was to dry the floor and have it condense in the evaporator and exit threw the condensate line. So why did that not happen? Because the duct work became saturated on the supply side. I.E. re-evaporating.
"Raising that air to a temperature of 70°" Remember we are heating only the air in the beginning. The air coming out of a 20KW bank is 120-140*F At that temperature with 2700CFM in a 1200SF space the "air's" dew point would change and cause it to "rain" in the space and accumulate (Not condensate) on the floor. "That part I did clarify at the end of the presentation." I left it open until the end to see who would catch it.
Now. Before you go all crazy and tell me where I am wrong in all this. The point of the presentation and the purpose of the lesson was to show the importance of psychometrics and the use of charts. I was able to plot a heading on the chart and prove what I was saying would work. Satisfying the customer.
It worked. All the nonsensical arguing in the world, coupled with a litany of recorded information about the conditions of the space. Will never convince the critic. What I was experiencing in the space and what I did to solve it. Worked. So I used it in my presentation. I went over "ALL" the data with both of my instructors and they agreed.
03-03-2013, 09:55 AM #11
Thank you for sharing I enjoyed it.
03-03-2013, 12:37 PM #12
Needless to say the sensible heating of the air in and of itself did not cause the fog. It just doesn't work that way. If OTOH the very dry supply air was impacting the floor, picking up moisture from the floor and leaving with a high RH while remaining higher than average room temp, then yes, a fog could result as that air further mixed and cooled to room temp. A portion(s) of the floor would have been acting as a humidifier pad. In this case the level of condensation across the floor would not have been uniform while the heat was running, since part of the floor would necessarily be giving up moisture in this process rather than accumulating it. A similar mechanism is at work in the heat pipe. This is also the possibility that Robo was alluding to in his earlier post, but apparently couldn't pin down. I didn't go into it because you seemed to indicate that the entire floor surface was being wetted by the fog while the heat was running. At shut down, yes, the warmed portion of the floor would cool due to conduction of heat to the underlying layers of concrete, and could also accumulate condensation after the fact. You will have basically redistributed the moisture from the interior of the concrete to its surface. Now if it was literally raining from the ceiling due to condensation there, then that would be yet another scenario.
Regardless of the mechanism at work in that particular case, and I agree it was a good problem to base a lesson on. ?But the supposed purpose of the video was according to your own words a lesson in the practical use of the pscyhrometric chart. On that account, when I assume the role of a student, I can't say that I learned anything at all about the psychrometric chart from watching that video, except maybe what a psychrometric chart looks like. The definitions of the terms provided were for the most part incorrect, and the behavior of air under changing conditions was incorrectly described. It was a case of a correct solution based on faulty premises, and for that reason I have to say it fell short of its mark. Your presentation skills were however above average, and I commend you for that.
Last edited by hvacrmedic; 03-03-2013 at 01:07 PM.
03-03-2013, 01:15 PM #13
Enjoying this conversation. Medics posts often need to be re read several times before I fully comprehend- But alsways very informing .
I personally was trying to grasp the statements that the air expands In the video.