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  1. #1
    Friend of mine has a 5 Ton Evap. with a 3.5 ton condenser.The house is 2800 sq. Ft. with two T-stats driving two dampers. One damper is for the upstairs and the other is for the downstairs. there's not a problem with heating the house in the winter months, but in the summer on days above 90 F the condenser runs all the time he can't get the temp below 80 F. The way this unit works is if the temp is warmer upstairs the damper will close for the downstairs so you will not have any condition air flow to the downstairs until the temp of the upstairs is lower. Then the downstairs damper will open and the upstairs will close its damper so basically means only one damper can be open at a time which bring me to my question is that why they have a 3.5 ton condenser because of lack of air flow across the coil? so they under sized the condenser with refrigerant less volumn? IF I would put a 5 ton condenser in would the evap freeze up because of choked supply? The furnace has a 20" return Need help Thanks

  2. #2
    Join Date
    Nov 2001
    Posts
    1,874
    First answere to your last question,,,Yes

    Having a 5 ton indoor coil supplied by a 3.5 ton condenser.
    The indoor coil is being starved for refrigerant.

    During the cooling season it's only working at half capacity. They need a load calc. done to determine what the actual load is, and then see if the ductwork is capable of providing that amount of air.

    Then have the proper size equipment installed, to match the load and ductwork.

    Life long Steerler fan,

    [Edited by Toolpusher on 01-25-2006 at 10:03 PM]
    If you try to fail, and succeed.
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  3. #3
    Join Date
    Oct 2003
    Location
    Florida's space coast
    Posts
    2,538
    Sounds like a really sucky zoning system.

    As far as the sizing goes you would have to do a heat load on the home.

    A 5 ton air handler with a 3 1/2 ton condenser is not that uncommon.

    Check ARI ratings to see if you have a matched system.

    If its a match and the evaporator has a TXV you should be ok but if its a fixed metering device it must be sized to match the condenser.

    Hope this helps.
    We've been doing so much,for so long,with so little, that now we can do almost anything, with nothing at all.

  4. #4
    Join Date
    Nov 2000
    Location
    Eastern PA
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    There is technically no such thing as a 5 ton evap or any specific capacity evap for that matter. Capacity is only determined by the condensing unit or heat pump capacity.
    Government is a disease...
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    Ecclesiastes 10:2 NIV


  5. #5
    Join Date
    Nov 2001
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    Then why do the Mfg's make so many coils to match their own condensers ?

    With your statement they would only need 1 coil for all units.

    Did I mis-read something again ?
    If you try to fail, and succeed.
    Which have you done ?



  6. #6
    Join Date
    Nov 2000
    Location
    Eastern PA
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    Originally posted by Toolpusher
    Then why do the Mfg's make so many coils to match their own condensers ?

    With your statement they would only need 1 coil for all units.

    Did I mis-read something again ?
    I didn't state that the coils don't need to be different sizes depending on capacity and efficiency of the outdoor unit, just that the coil itself does not dictate capacity.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #7
    Join Date
    Nov 2001
    Posts
    1,874
    just that the coil itself does not dictate capacity. [/B][/QUOTE]


    I'd agree with that,
    But it read different from this side of the screen. Sorry.
    If you try to fail, and succeed.
    Which have you done ?



  8. #8
    Join Date
    Jan 2006
    Location
    McQueeney, Texas
    Posts
    4,033
    A bit of a trick answer. The total capacity comes from the OD unit, however the ability to regulate that capacity can be done with the evaporator in relation to sens terms.
    In my opinion a 5 ton evaporator should not be used with a 3.5 ton outdoor unit due to the fine tuning envolved and exact and consistant operating conditions.
    The upstairs/downstairs dampining should be 80%/20% in my opinion for the best adjustable cfm per duct capacity usage.
    I had only one system similar to this and I had to re- meter the indoor coil and reduce the blower speed to get the system to dry out the damp cave like atomosphere in the home. This was with a Trane system and their 5 ton coils as some of you know are humongous.
    Getting with a contractor that deals with that system and can give you figures would help. Maybe they have design differences with their equipment.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,768
    That could be a matched system, depending on the seer rating of the OD unit.

    The system may have been designed for an 80° indoor temp.

    What drive blower does it have.

    Check your air flow.

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    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Nov 2000
    Location
    Eastern PA
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    Everyone is basically correct here. It is the manufacturing decision to put numbers in the nomenclature of the coils that messes us up in the field.

    Some manufacturers use different nomenclature for their model numbers even though, aside from the metering, the coils are identical. For example; a coil rated with a 3 ton 10 SEER system may have a 36 in the model nomenclature while that same identical coil may have a 24 in the nomenclature when matched to a two ton 13 SEER system. Of course you could use the one with the 36 in the model on the 2 ton 13 SEER system, but then it would appear that you have used a 3 ton coil with a 2 ton system.

    I would really like to see indoor coil model nomenclature go to alphabetical designation. That way you just match up an "A" "B" "C" etc. coil with whatever outdoor unit you are using and no one gets all bent out of shape over thinking the coil is the wrong size.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  11. #11
    Join Date
    Jan 2006
    Posts
    25
    I just had Trane system installed with RXC061S3HPC0 coil and 2TTR3036A condenser. Does it sound like a matched system or I'll have problems with it in a summer?

  12. #12
    Join Date
    Jan 2006
    Posts
    21
    In a normal residential heat cool split system there are four components to consider. The air handler, condensing unit, evaporator coil and metering device. The components used must be compatible with each other, but you have to take a couple of factors into account. The total BTUH capacity and the SEER rating. Considering airflow only, the air handlers manufactured are designed to move a set amount of air in the cooling and heating modes based on a set factor per ton of cooling and heating capacities. The condensing unit BTUH should be sized to match the CFM capacity of the air-handling device. Considering BTUH In residential heating and cooling, the condensing unit should match the evaporator coil and metering device. However, the calculation must take into account the SEER rating of the equipment used. Looking at various SEER ratings for the same BTUH condensing units, there are different volumes of refrigerant for each of the different SEER ratings being moved through the system. This volume of refrigerant must be taken into account in sizing the evaporator coil and metering device. As the SEER rating increases on the condensing unit being used, so does the volume of refrigerant being circulated through the system. In order to properly accommodate this increase in volume of refrigerant, the metering device would need to be sized to supply an additional volume of refrigerant to the evaporator coil. The evaporator coil then would need to have a psychical internal area large enough to hold this increase in volume of refrigerant. We then must consider not just the BTUH rating of the condensing unit, but also the SEER rating of the equipment, in determining the proper size metering device and evaporator coil. At this point we must assume that the type of refrigerant being used is the same for each component as designed by the manufacturer. Normally the manufactures rate condensing units in BTUH or in laymen terms tonnage and in SEER or EER rating, but the Evaporator coils and metering devices are normally rated in tonnage only. This factor means that it would not be unusual to find a condensing units rated BTUH to be different from the rated BTUH of the metering device and evaporator to get the operating SEER of the system to match the manufactures SEER rating of the condensing unit. In addition, you can easily find examples of exceeding the manufactures SEER rating on a condensing unit, by modifying the type and size of the metering device and evaporator coil. Keep in mind the duct system design also plays an important part in determining the performance of the equipment used, but I have chosen to focus on the equipment only in this reply.
    Ignorance is the lack of knowledge, Stupid is the lack of ability to gain knowledge.

  13. #13
    Join Date
    Jan 2006
    Posts
    25
    I need word of advice. On the new Trane install I got 5 ton RXC061S3HPC0 coil and 3 ton 2TTR3036A condenser. I just realized that this system largely mismatched. Should I request a contractor to match the system capacity or this configuration will be just fine?

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