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Mismatching coils

Can someone please explain in detail what happens / what may happen if a condenser coil is larger than an evaporator coil and vice versa ?

Comments

  • Techman
    Techman Member Posts: 2,144
    Coils

    Does this mis-matched coil sizing have anything to do with the SEER rating of the two coils?
  • don_9
    don_9 Member Posts: 395
    dx coil matching

    If the condenser coil is match larger then the evaporator coil you would have more latent capacity and less sensible capacity.That is if the airflow across the evaporator coil is the same.

    Depending on how much bigger your condenser and what type of metering device choose you may get flooding on startup as well during run cycle.

    let me just say i knew of a guy in texas that often match five ton condenser to three ton evaporator coil.he did this to control the humidity bc in the area he lived in the humidity was the bigger issue.

    Matching evaporator and condensing units are to achieve desire cooling performace.

    Alway remember that the evaporator capacity always decreases as the suction temperature increases.And the condensensing unit capacity increases when the suction temperature increases.

    Look into the Manual S residential equipment selection book offer by ACCA.that will help shine some light on the subject.
  • meplumber
    meplumber Member Posts: 678
    Similar in reverse.

    Up here in Maine, we frequently put a larger evap coil on a smaller condenser. On the coast, most of my customers are on the immediate coast, we have little to no cooling load. What we do is basically drop the interior humidity to a comfortable level and simply keep the indoor temp below 74 deg with Outside Design Temp at 84 deg.



    For instance, a 4 ton evap coil on a 3 ton condenser causes longer run times. Thereby increasing the air contact time with the coil. As long as the airflow is set for the smaller condenser then you are ok. So you would set the fan in the 4 ton evap to flow at a 3 ton equivalent CFM.
  • RDSTEAM
    RDSTEAM Member Posts: 134
    you have

    this backwards. you upsize your evaporator to allow for more latent (humidity) heat removal. this can also be done by slowing down your fan speed as well.
  • RDSTEAM
    RDSTEAM Member Posts: 134
    you have

    this backwards. you upsize your evaporator to allow for more latent (humidity) heat removal. this can also be done by slowing down your fan speed as well.
  • don_9
    don_9 Member Posts: 395
    Not really

    The name of the game when it comes to removing the latent capacity is keeping the coil temps below dew point.

    Yes more tonnage can be extracted from a condensing unit when it match with a larger evaporator coil.However the tonnage increase is accompanied by an increase in suction temperature and a corresponding decrease in latent capacity.

    So a bigger coil much bigger then the condenser is going to increase the suction temperature which increases the surface temperature of the coil, which cause the latent capacity of the coil to decrease.
  • Techman
    Techman Member Posts: 2,144
    edited June 2012
    which way to go

    I think having a 3t load,3t ducting, a 3t cond unit and a 4t evap set on 3t fan speed is correct for hi humid areas.Having a larger evap pulls out more moisture based on size,but there is a slight loss of the dehumidification effect by the larger evap pulling out more heat and raising the evap temp a little.Any PROPERLY SIZED  evap coil size is based on two BTU factors,latent and sensible. Upon first starting up ,the pulldown load is Kinda Sorta (3t) , 28-31,000 BTU removes moisture and the rest drops the sensible just a little. Then HOURS later when the house has  "stabilized" the opposite BTU ratio has occured.Even though the evap temp is a little higher I think it will not be noticed at stabilized conditions.And in the O.P. how does the structures actual BTU load figure into the larger/smaller evap/cond coil picture?
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