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  1. #53
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579


    The air with the highest humidity (nearly at 100% RH) is the supply air right off the leaving side of the evaporator.

    Do you know why? I'll give you a shot at it before I give you the answer.


  2. #54

    OK NORM

    Looks like I don't have a patent on taking words out of context, but I don't remember taking them out of context and putting them into a whole new context as you seem to do at will. I did not say that we shouldn't take it at the outdoor unit just that we do because it is convenient the discussion at the time of my comment was about coils not linesets or total system superheat thank you,

    The air on the leavung side of the coil is as close as it ever will be to its dewpoint as it goes through the system therefore it is the highest rh at that point.

  3. #55
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579


    eddy, your posts are not always clear. You are correct on the reason why the leaving air is near 100% RH.


  4. #56

    Wink I think Norm is right

    I think Norm Chris is right on
    I think fatt boy,is maybe?? too sucssesfull he is forgeting the FACT'S,but i do see what he is "trying' to say
    Fatt's is right BUT Norm is righter!!! that is what i like about HVAC & R,their is no such thing as being a littel bit pregnant,also Fatt's money isnt EVERYTHING,but i like to see someone live with out it!!!Norm Chris is right 100%

  5. #57
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,088
    I just realize that when the conditioned air reaches its area, it has already been de-humidified at the unit ( to whatever point that it can at that time and return air humidity level ). The air coming out of my supply register is producing only sensible effects of heat removal.
    Heat removal, both sensible and latent, is accomplished at the evaporator coil, nowhere else. Heat is reduced in a room by first extracting the warmer air (return) and replacing it with cooler air (supply), but the removed air must have its heat removed before being returned to the room to accomplish cooling of that room.

    You might be able to reduce the temperature of a room by injecting it with cold air, but with little or no return air, the overall conditioning effect will be diminished.

    I would place more emphasis on the heat removal capacity of the refrigeration circuit coupled with the proper exchange of supply and return air per room sized to design condition heat loads over how cold the air emerging from the supply register might be.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #58
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Shophound

    Heat removal, both sensible and latent, is accomplished at the evaporator coil, nowhere else. 'end quote'

    So, the air entering the room ( from the supply register )at a temperature of 55 'f' 90+% humidity, is not? exchanging heat with the warmer room air. It is just pushing the warmer air back to the return ????. Is that what yur saying? I consider the cooler air blown into the room as a heat exchange between the warmer air and the cooler air, with the relsultant air ( at some temp in between ) being then drawn into the return air system. This heat exchange, also produces a reduced humidity level in the room as the cooler air absorbs heat from the warmer air. And therefore, the return air will be at a lower humidity level as well.

  7. #59
    Join Date
    Dec 2004
    Posts
    200
    IS THERE A BETTER WAY TO CHARGE A SYSTEM OTHER THAN SUPERHEAT OR SUBCOOLING<<<<<<NOOOOOOOOOOOO>>>>>>>THAN YOU SHOULD NOT TEACH A STUDENT TO DO IT ANY OTHER WAY

  8. #60
    Join Date
    Dec 2003
    Location
    Nevada
    Posts
    1,815

    Re: Shophound

    Originally posted by bornriding
    Heat removal, both sensible and latent, is accomplished at the evaporator coil, nowhere else. 'end quote'

    So, the air entering the room ( from the supply register )at a temperature of 55 'f' 90+% humidity, is not? exchanging heat with the warmer room air. It is just pushing the warmer air back to the return ????. Is that what yur saying? I consider the cooler air blown into the room as a heat exchange between the warmer air and the cooler air, with the relsultant air ( at some temp in between ) being then drawn into the return air system. This heat exchange, also produces a reduced humidity level in the room as the cooler air absorbs heat from the warmer air. And therefore, the return air will be at a lower humidity level as well.

    The SA and space air does not exchange humidity unless you have dew in surfaces in the room. Humidity is removed by lowering the dew point.
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  9. #61
    Join Date
    Dec 2004
    Location
    Louisiana
    Posts
    4
    By no means am I trying to tell you guys how to do a/c work as I am a tin knocker. But learning as much as I can in the service part. Tell me if I am wrong, inorder for a unit to be most eff. It must be sized properly in order to remove the heat from the structure. It must not only change the temp of the air in the room but change the temp of the walls and furniture in the room. Remove air temp to fast is not efficient as the unit will cycle on and off to much because the heat has been removed from the air and reached the t-stat causing it to cycle off with leather furniture still giving off the same heat that has not been removed. If a system was sized right we would not need t-stats on the wall they would be placed in the return next to the unit and be auto. Why is there a chart for charging a system by the manufactor on a 12 seer if it doesn't mean anything? With a 10 year warranty I think it does mean something. I except all comments as I said I am a tin knocker and from reading some of these post going to school may be a bad idea.

  10. #62
    Join Date
    Sep 2004
    Posts
    3,157
    How much good do those sight glasses do when using a blended refrigerant

  11. #63
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,088

    Re: Shophound

    Originally posted by bornriding
    Heat removal, both sensible and latent, is accomplished at the evaporator coil, nowhere else. 'end quote'

    So, the air entering the room ( from the supply register )at a temperature of 55 'f' 90+% humidity, is not? exchanging heat with the warmer room air. It is just pushing the warmer air back to the return ????. Is that what yur saying? I consider the cooler air blown into the room as a heat exchange between the warmer air and the cooler air, with the relsultant air ( at some temp in between ) being then drawn into the return air system. This heat exchange, also produces a reduced humidity level in the room as the cooler air absorbs heat from the warmer air. And therefore, the return air will be at a lower humidity level as well.
    The air removed from the room by the return air ductwork or path is passed over the evaporator coil, where it gives up both latent and sensible heat. From that point it becomes supply air, cooled and dehumidified, and is returned to the room to replace the air removed by the return air path.

    The cooling and dehumidification of air is accomplished at the evaporator coil. The undesirable levels of heat in the room was transferred to the evap coil. Air was returned to the room at a lower temperature. This was a result of the air removed from the room having given up its heat to the refrigeration circuit.

    In essence you are replacing warmer air with cooler air. But the warmer air must be removed first, have its unwanted heat removed, then returned to the space as conditioned air.

    Yes, you can cool a room by placing flat plate evaporators on the walls, and the room will lose heat to the colder plates, without an exchange of air in the room. You can also cool a room by placing a huge chunk of ice in the room, so the heat within the room flows into the ice, thereby leaving the room colder. This also would require no air exchange.

    But we are speaking about forced air refrigeration, not static air cooling. For this you must remove/return or recirculate the air to be cooled to accomplish the desired temperature level.

    The air leaving the evaporator coil is at the highest cooled and conditioned state. As it leaves the supply register and mixes with the air in the room, the warmer air in the room will move toward the cooler air and attempt to equalize with the supply air temperature. The warmer air will lose some heat in this fashion, but the first cause of the supply air being colder to begin with is due to the evaporator having already extracted heat from the room from the return air.

    So, yes, you could say that the supply air is accomplishing a measure of direct cooling of the room air by merely flowing into the room, just as sticking a hose flowing out cold water into a tank of hot water will cause the tank of heated (let's say it is continually heated by a burner) water to cool.
    However, to maintain the cooler temperature of the tank against the constant addition of heat from the burner, the water hose must remain in the tank, emitting the same colder water. Eventually the tank would overflow unless some measure of recirculation was established that would remove a portion of water, pass it over a cooling medium, then return it to the tank at a cooler temperature.

    Same goes for a room. If you just kept pumping cold air into a room without providing an escape or return air path, it would "overflow" with air and reduce the volume of air entering the room due to back pressure (if the room was fairly airtight). A reduction of volume would reduce the amount of cold air entering the room, which would in turn reduce the amount of cooling available.
    So, it's recirculated.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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