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  1. #40
    Join Date
    Dec 2012
    Location
    columbus, OH
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    1,864
    "Water Vapor or Vapor Emissions: Acts according to the physical laws of gasses or chemical equilibrium. Water travels from one area to another whenever a difference of vapor pressure exists. In a controlled climate (HVAC), the temperature in the room is 70 to 80 F and the relative humidity is 30% to 50%. Therefore, the air above the slab can and wants to hold more moisture, and satisfies itself by pulling moisture from the slab 24 hours a day, 7 days a week, 365 days a year until equilibrium exists which rarely if ever happens. The amount of water air absorbs is affected by temperature - the cooler the air, the less water absorbed while the warmer the air the more water absorbed. Water vapor is capable of penetrating where water in a liquid form cannot. By comparing the vapor pressure in differing environments, one can estimate the movement of vapor pressure through concrete. However, in reality, vapor emissions levels are complex due to variations in temperature, humidity, permeability, and flow path through the concrete. For these reasons, vapor emissions cannot be accurately calculated but may be measured. Anhydrous Calcium Chloride testing has shown that moisture may travel through a concrete slab more readily as vapor than as a liquid. Water vapor is a mixture of air and water." Floorexperts.com

  2. #41
    Join Date
    Jun 2002
    Location
    Dacula, GA
    Posts
    12,014
    What I would like to know is who will be next to offer a training video by them for a critique here on HVAC-TALK on a deep subject like the "use psychometric air charts"? LOL Thank you very much
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."
    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them."
    Barry Goldwater

  3. #42
    Join Date
    Dec 2003
    Posts
    2,266
    Quote Originally Posted by teddy bear View Post
    When a surface temperature of the floor material is 1^F below the dew point of the air, condensation forms on the surface. By raising the temperature of the material above the dew point of the air, the condensation stops and the moisture evaporates.
    Or if you lower the dew point of the air 1^F below the surface temperature, the moisture evaporates.
    Occupants in a gym humidify the space, raising the air dew point. Raising the air temperature warms the temperature of the floor. Warming the air does not raise the dew point of the air. Temperature of the floor and the dew point of the air determines wet or dry floor.
    Trying to keep it simple.
    Regards TB
    I think there was more going on than the floor being lower than the dp. I have played bb in this gym for 20 years and cant remember this happening before. I think it was just a rainy humid night and as the ambient temperature dropped water started separating from the saturated air. Kinda like dew making the ground wet at night in the summer. Anyhow, the floor dried out within 5 minutes of turning on the heater.

    Adam, I did not mean to give you a hard time at all about this and I dont think anyone else did either. Thanks for posting your video which led to this discussion.

  4. #43
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    1,980
    New concrete is a chemical reaction and is exothermic (gives out heat), this internal heat can vapourise some of the internal moisture (giving greater vapour pressure) Depending upon air flow within the building the newly moisture laden air "high dew point" can hit cold supply air (lower temp than air that has passed the concrete) , causing rain which hits the floor as droplets. The reason that large new buildings need to be reduced in temp slowly.
    So in theory if the concrete mass has had time to warm to a highish temp and has plenty of free moisture, then when AC is suddenly turned on, a similar effect could be achieved. How ever this would not last as long, because as the moisture evaporates from the concrete, part of the heat required will come from the concrete itself, reducing the temp of the concrete, reducing the energy for further vaporization, hence droping the dew point.

  5. #44
    Join Date
    Aug 2011
    Location
    Myrtle Beach SC
    Posts
    94
    Quote Originally Posted by bigtime View Post
    Adam, I did not mean to give you a hard time at all about this and I dont think anyone else did either. Thanks for posting your video which led to this discussion.
    I don't mind. I only lost it when my grade was down graded and my instructors were called failures. I knew the video would receive critical view points and arguments would ensue. That's partly why I posted it. I am only 8 months into my study of air. Surprised I am even using the correct terminology.

    Thanks for the engage conversation.

    Cheers friend.

  6. #45
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,063
    Quote Originally Posted by bigtime View Post
    I think there was more going on than the floor being lower than the dp. I have played bb in this gym for 20 years and cant remember this happening before. I think it was just a rainy humid night and as the ambient temperature dropped water started separating from the saturated air. Kinda like dew making the ground wet at night in the summer. Anyhow, the floor dried out within 5 minutes of turning on the heater.

    Adam, I did not mean to give you a hard time at all about this and I dont think anyone else did either. Thanks for posting your video which led to this discussion.
    Lets expand on the effect of outside air. A small amount of outside air is constantly infiltrating any structure. The dew point of the inside air is the same dew point as the outside air plus or minus the moisture added/removed by activities inside the space. With occupants exercizing in the space, 1 lb. or more of moisture per hour per occupant is being added to the space. If the inside dew is one degree above the floor temperature, condensate forms on the surface of the sealed floor. Heating raises the floor surface temp and probably increased building air change. The outdoor dew point outside will be lower the outside temp even if it is raining outside. Heating does not add or remove the moisture in the inside air. It makes sense to me. Raise the floor temp or lower the dew point of the inside air eliminates the condensate on the floor.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #46
    Join Date
    Aug 2011
    Location
    Myrtle Beach SC
    Posts
    94
    Updated situation, similar to the room I was dealing with.

    I was on the beach, just hanging out with my girl. The temperature dropped 10* to 15* when the wind shifted and blew cold air up to the beach.(Happens a lot this time of year) Anyway, fog instantly appeared and soaked everything. This lasted for about 10-20 min. about 1/4 mile of the beach was foggy. the wind changed direction and the fog blew out to sea where it quickly diapered and the wet beach Items(towel , chairs,etc.) dried really fast. You could watch it and feel it.

    Why was everything on the beach wet?
    Why did every thing dry so fast?

    "I did not take any readings but it was warm 75* and the water was cold,maybe 63* the sand was vary warm.

  8. #47
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,063
    Quote Originally Posted by Adamscarpentry View Post
    Updated situation, similar to the room I was dealing with.

    I was on the beach, just hanging out with my girl. The temperature dropped 10* to 15* when the wind shifted and blew cold air up to the beach.(Happens a lot this time of year) Anyway, fog instantly appeared and soaked everything. This lasted for about 10-20 min. about 1/4 mile of the beach was foggy. the wind changed direction and the fog blew out to sea where it quickly diapered and the wet beach Items(towel , chairs,etc.) dried really fast. You could watch it and feel it.

    Why was everything on the beach wet?
    Why did every thing dry so fast?

    "I did not take any readings but it was warm 75* and the water was cold,maybe 63* the sand was vary warm.
    That was a slow warm front/cold front movement. The temperatures of the materials that got wet were below the dew point of of the warm front. The differences in temperature was extreme and the movement was slow. As the warm air is cooled below it's dew point, small fog droplets form. Clouds and fog on your glasses are all similar to this.
    When these conditions last for long periods, your home needs a dehumidifier to avoid getting damp and growing mold.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #48
    Join Date
    Jun 2009
    Location
    South Carolina
    Posts
    403
    Classroom looks the same as when i was in it. I graduated the residential program in 2009 and completed the half semester course of commercial the fall 2009.

    Wish i kept my notes for residential. Every now and then i am like i know we went over that but i cannot remember. But i did keep most of my paperwork and notes for commercial and it is great info to look back on. Good luck with the program and Mr. Britt and Mr. Watkins are great guys.
    are you taking night or day classes. by your presentation i would say day but just curious

  10. #49
    Join Date
    Jul 2005
    Posts
    5,153
    Quote Originally Posted by teddy bear View Post
    That was a slow warm front/cold front movement. The temperatures of the materials that got wet were below the dew point of of the warm front. The differences in temperature was extreme and the movement was slow. As the warm air is cooled below it's dew point, small fog droplets form. Clouds and fog on your glasses are all similar to this.
    When these conditions last for long periods, your home needs a dehumidifier to avoid getting damp and growing mold.
    Regards TB
    I agree, if there's fog inside the house, then a dehumidifier would be a good thing to have.

    Here's a picture the OP might enjoy.

    Name:  ht_fog_clouds_4_jef_120210_wblog.jpg
Views: 129
Size:  30.9 KB

  11. #50
    Join Date
    Aug 2011
    Location
    Myrtle Beach SC
    Posts
    94
    Quote Originally Posted by klee7013 View Post
    Classroom looks the same as when i was in it. I graduated the residential program in 2009 and completed the half semester course of commercial the fall 2009.

    Wish i kept my notes for residential. Every now and then i am like i know we went over that but i cannot remember. But i did keep most of my paperwork and notes for commercial and it is great info to look back on. Good luck with the program and Mr. Britt and Mr. Watkins are great guys.
    are you taking night or day classes. by your presentation i would say day but just curious
    Day class.
    I have great notes and 250 hours of recorded lecture. I would share them with a fellow Britt kid.
    Are you still working in the area?
    I am going to take the commercial class this summer.

  12. #51
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,864
    Quote Originally Posted by Adamscarpentry View Post
    Day class.
    I have great notes and 250 hours of recorded lecture. I would share them with a fellow Britt kid.
    Are you still working in the area?
    I am going to take the commercial class this summer.
    So after your schooling and input from this webpage do you feel you were right or wrong? I hold opinions on this website high if undisputed. None the less great presentation.

  13. #52
    Join Date
    Aug 2011
    Location
    Myrtle Beach SC
    Posts
    94
    Quote Originally Posted by Core_d View Post
    So after your schooling and input from this webpage do you feel you were right or wrong? I hold opinions on this website high if undisputed. None the less great presentation.
    Space
    56* air @ 52% R.H

    Supply air
    120* air @ 100% humidity (My understanding is that air in the duct id 90%-100%)

    I don't know enough about psychometrics to say right or wrong. What I do know is what happened.

    In the presentation I was trying to lead the class along, to challenge me with it. I felt I left it wide open for dispute and was hoping someone in the class would catch it.(Not seen in the video are about 12 questions that got vary close.) The air was not condescending on the floor. (At the end of the presentation I pointed that out) It was accumulating on the floor. While the group dispersed for the 3.5 hours the super and I took a closer look at the units. The supply ducts were soaked and the evap. coils were ice. As the heat strips came on it sent hot humid air in to the cold humid space and made what I think was a thin fog that accumulated on the floor.

    Using the psychrometric chart I was able to convince the crowd and get them off are backs for 3.5 hours. I know when they came back it had worked. Everyone was happy.

    Sitting on the beach the other afternoon and experiencing the same thing, I think I was right.

    I think most people don't make it to the end of the video where I point out the accumulation part.

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