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  1. #1
    Join Date
    Apr 2008
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    Princeton, NJ
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    581

    Is supply temperature of 41F to low?

    The supply temp inside the trunk duct about 3 feet after the coil sometimes drops as low as 41 degrees.

    So far I have seen no indication of the E-coil freezing.

    Some Background: In April 2008 a new trane XL15i 4-ton Ac was installed in my home along with a 5 ton ADP coil and a 100k btu XV95 furnace for a 2800 square foot home in central NJ.

    The system was greatly oversized for my ductwork and my ESP started at 1.2. Modifications to solve the high esp issue included adding a helper duct for the supply, increasing my return drop from 24x10 to 25x20, switching from a 1 inch restrictive filter to a 5 inch media filter, and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton. These changes appear on the surface to have solved all my problems including a high humidity issue that I had. The house is now quite comfortable and the ESP is down from 1.2 to 0.57. The reality is I probally could have gotten away with a 3 ton system but I knew nothing about proper sizing at the time.

    My current question:

    1. Since my initial refrigerent charge (410) was not adjusted are there potential issues?

    2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions

    Key1
    In the land of the blind.....the man with one eye is king....

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Since your system doesn't operate at normal conditions(probably never moved 400CFM per ton). That 20° means nothing.

    Also, since it probably wasn't moving 400CFM per ton when it was originally charged.
    I doubt its flooding the compressor. But is probably on the edge of freezing the coil.

    Is the 41° when the system first comes on, and is comfort r enabled.

    If its only that cold at start up and comfort r is enabled. I wouldn't worry about it.

    If it is at that temp the whole on cycle. Your a little too cold.
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  3. #3
    Join Date
    Apr 2008
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    Quote Originally Posted by beenthere View Post
    Since your system doesn't operate at normal conditions(probably never moved 400CFM per ton). That 20° means nothing.

    Also, since it probably wasn't moving 400CFM per ton when it was originally charged.
    I doubt its flooding the compressor. But is probably on the edge of freezing the coil.

    Is the 41° when the system first comes on, and is comfort r enabled.

    If its only that cold at start up and comfort r is enabled. I wouldn't worry about it.

    If it is at that temp the whole on cycle. Your a little too cold.
    Thanks for the quick response...

    the comfort R feature is not enabled. It seems to get cooler and cooler the longer it stays on and it bottoms out at 41F. It used to bottom out at 43F...then 42F....now 41F. I am certain it has not gone below 41F as I have a constant temperature monitor installed that saves the maximum and minimum temperature values

    I like the fact that the supply air is so cold since that compensates for my reduced air flow. I have less air going to each room but the air that goes there is cooler.

    What would be the symptoms if the compressor was being flooded?

    Also are there warning signs before the E-coil freezes? How do I know it is not freezing already?....since the coil is cased?
    Key1
    In the land of the blind.....the man with one eye is king....

  4. #4
    Join Date
    Aug 2006
    Location
    Columbus Ohio
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    1,980
    Have you ever taken superheat and subcooling readings after a 10min run time to determine if you are flooding back?

    41*F is a very low supply temp. Why again did you drop the fan speed?
    UA LU189

    10mm, because it's better than .45acp

  5. #5
    Join Date
    Apr 2008
    Location
    Princeton, NJ
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    Quote Originally Posted by zw17 View Post
    41*F is a very low supply temp. Why again did you drop the fan speed?
    To reduce in-home Humidity from more than 65% to less than 45% (it worked) and to reduce static pressure from 1.2 to 0.57...

    Key1
    In the land of the blind.....the man with one eye is king....

  6. #6
    Join Date
    Aug 2006
    Location
    Columbus Ohio
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    Quote Originally Posted by key1cc View Post
    To reduce in-home Humidity from more than 65% to less than 45% (it worked) and to reduce static pressure from 1.2 to 0.57...

    Key1
    It sounds like you need to improve your duct work and size the equipment properly.

    5tons of cooling where 3 tons was the right size will give you the 'cave cooling' effect. Cold but muggy.

    Take a proper superheat reading to determine whether you are flooding back or not.
    UA LU189

    10mm, because it's better than .45acp

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,755
    You wouldn't really get a warning sign that the compressor is getting a flood back, per say.

    Sudden noise change in the compressor may or may not be a sign. Lights dimming, may or may not be.

    Too many possibilities that can also be caused by other things.

    No way to know if the coil is starting to freeze, other then if you start to see frost/ice on the vapor line.
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  8. #8
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    Aug 2002
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    Quote Originally Posted by beenthere View Post
    No way to know if the oil is starting to freeze, .
    Oil

  9. #9
    Join Date
    Jan 2004
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    Lancaster PA
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    Quote Originally Posted by pecmsg View Post
    Coil
    ROFL...

    Fixed it. Now it says coil.
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  10. #10
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by key1cc View Post

    April 2008 a new trane XL15i 4-ton Ac
    for a 2800 square foot home in central NJ

    , and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton.


    2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions
    I would set air flow to _ 310 CFM/ton _ as a compromise and some 'protection' /margin against a freeze.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Aug 2009
    Location
    n.j.
    Posts
    30
    Quote Originally Posted by key1cc View Post
    The supply temp inside the trunk duct about 3 feet after the coil sometimes drops as low as 41 degrees.

    So far I have seen no indication of the E-coil freezing.

    Some Background: In April 2008 a new trane XL15i 4-ton Ac was installed in my home along with a 5 ton ADP coil and a 100k btu XV95 furnace for a 2800 square foot home in central NJ.

    The system was greatly oversized for my ductwork and my ESP started at 1.2. Modifications to solve the high esp issue included adding a helper duct for the supply, increasing my return drop from 24x10 to 25x20, switching from a 1 inch restrictive filter to a 5 inch media filter, and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton. These changes appear on the surface to have solved all my problems including a high humidity issue that I had. The house is now quite comfortable and the ESP is down from 1.2 to 0.57. The reality is I probally could have gotten away with a 3 ton system but I knew nothing about proper sizing at the time.

    My current question:

    1. Since my initial refrigerent charge (410) was not adjusted are there potential issues?

    2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions

    Key1
    Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.
    Last edited by beenthere; 09-12-2009 at 09:18 PM. Reason: Removed DIY suggestion

  12. #12
    Join Date
    Jan 2004
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    Quote Originally Posted by yankee fan View Post
    Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.
    Read site rules.

    We don't suggest DIY here. Since we're not a DIY site.
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  13. #13
    Join Date
    Apr 2008
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    Princeton, NJ
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    Quote Originally Posted by yankee fan View Post
    Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.
    Not sure what you are saying that I should check from the statement quoted above....It appears to have been altered by the moderator.....but I assure you that the temperature measument is acurrate. I checked the temperature monitor against a more expensive thermocouple and they match within one degree. The temperature in that supply trunk has gotten that cold and the only source of the cold is the coil during operation. Keep in mind this is only ~3 ft from the coil.

    Key1
    In the land of the blind.....the man with one eye is king....

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