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  1. #1
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    Jul 2012
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    Trane TAM7 Dip Switches

    Trane's older 4TEE air handler had 4 dip switches to set the cooling and heating CFM/ton airflow setting independently. The newer TAM7 only has two dip switches to control "CFM/ton." For instance with the 4 ton model, if cooling is set to 370 cfm/ton, heating is automatically 420 cfm/ton, and if cooling is 390 cfm/ton heating is 440 cfm/ton, etc. Can anyone explain why Trane would do this or how it is beneficial (besides simplifying setup)? This seems like a limitation as a home's ductwork may be able to support 1560 cfm for a 4 ton heat pump system (390 cfm/ton), but the resultant heating cfm would be 1760 cfm which may be pushing the limits in terms of air velocity and static pressure. The heating cfm in this case is indeed the airflow for heat pump mode, not electric heat, as described in the TAM7 sequence of operation.Name:  tranedpsw.jpg
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  2. #2
    Join Date
    Dec 2005
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    Cincinnati, Oh
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    450 CFM for heating with a heat pump would be standard.
    350-400 cfm would be standard for AC.

    Lower CFM = more dehumidification.
    No Dehumidification can happen in heat pump mode. Thus, a higher cfm is better.


    Trane would tell you that it's a contractors job to have correct ductwork attached to the system for the best efficiency, and it's not tranes responsibility to tailor their systems to a crappy duct system.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #3
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    Jul 2012
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    Quote Originally Posted by hvacvegas View Post
    450 CFM for heating with a heat pump would be standard.
    350-400 cfm would be standard for AC.

    Lower CFM = more dehumidification.
    No Dehumidification can happen in heat pump mode. Thus, a higher cfm is better.


    Trane would tell you that it's a contractors job to have correct ductwork attached to the system for the best efficiency, and it's not tranes responsibility to tailor their systems to a crappy duct system.
    Thanks for the response. It is hard to dispute that point of view, although I do wonder why Trane would introduce a new air handler that gives less control over the airflow settings for heating/cooling modes. Here is why I ask this question in the first place:

    A Manual J performed on the house showed that 3.7 tons (1601 cfm to be exact) was required to maintain our usual summer indoor temperature (72) at design conditions. To get close to this, presumably the installers would set the system to 390 cfm/ton providing ~1560 cfm. Whether the ductwork I have will adequately handle the higher airflow in heating mode, I don't know -- but I will bring this up with the dealer. Ducts leaving the box above where the air handler will sit are sized as follows: 8x8, 14x8 transitioning to 16x8 (due to space constraint), and 12x8. I found an online duct sizing resource which seems to suggest that these sizes could handle the airflow required for heating mode (~1760 cfm), but it would be at the maximum recommended velocity (~900 fpm).

    Current heat pump has a leak, and it's probably a matter of a couple weeks until it starts to freeze up again -- time will tell. This has bought me some time to do a bit of research on various systems, and I'm pretty settled on a 4 ton XL16i with the TAM7 air handler, as my dealer recommends. I don't want to be splitting hairs or getting into details that I don't need to worry about, but I'm a pretty technical person and like to learn about this kind of stuff. Thanks for any additional thoughts.

  4. #4
    Join Date
    Dec 2005
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    Cincinnati, Oh
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    Your getting into some super technical stuff.

    You'll get a 4 ton unit, it'll move roughly 1600 cfm. If the duct is sized for 1600 cfm, the increase in 160 cfm isn't going to be that noticable. Especially reletive to the size of the system.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  5. #5
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    The heating CFM dip switches on the older air handler only affected the blower speed for the electric heat.
    The blower would run at the same speed for cooling or heating with the heat pump.

    The TAM7 doesn't have a setting for the electric heat CFM because it is automatically determined by the number of heating elements operating in the heat package. The control board in the heat package communicates with the control board for the air handler.

    I haven't tried it, or confirmed it with anyone, but I think you can get it to only use the cooling CFM by switching S1-3 on, so the AFC board doesn't know there is a heat pump installed.
    I'm not sure if this would mess with the operation of the aux heat, or generate error codes in the heating mode though.
    If more government is the answer, then it's a really stupid question.

  6. #6
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    Jul 2012
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    Quote Originally Posted by mark beiser View Post
    The heating CFM dip switches on the older air handler only affected the blower speed for the electric heat.
    The blower would run at the same speed for cooling or heating with the heat pump.

    The TAM7 doesn't have a setting for the electric heat CFM because it is automatically determined by the number of heating elements operating in the heat package. The control board in the heat package communicates with the control board for the air handler.

    I haven't tried it, or confirmed it with anyone, but I think you can get it to only use the cooling CFM by switching S1-3 on, so the AFC board doesn't know there is a heat pump installed.
    I'm not sure if this would mess with the operation of the aux heat, or generate error codes in the heating mode though.
    Thanks Mark -- I appreciate your responses to the questions I've had re: Trane systems in this thread and my previous one. I don't doubt your first-hand experience with these systems, but below is a caption from the 4TEE installation guide I found showing dip switches for heating, cooling, and auxiliary heat airflow settings -- unless "auxiliary heat speeds" does not pertain to the airflow setting.
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  7. #7
    Join Date
    Aug 2004
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    North Richland Hills, Texas
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    Quote Originally Posted by rdh126 View Post
    Thanks Mark -- I appreciate your responses to the questions I've had re: Trane systems in this thread and my previous one. I don't doubt at all doubt your first-hand experience with these systems, but below is a caption from the 4TEE installation guide I found showing dip switches for heating, cooling, and auxiliary heat airflow settings -- unless "auxiliary heat speeds" does not pertain to the airflow setting.
    On that switch block, switches 1 and 2 are to set the outdoor unit size, switches 3 and 4 are to set the CFM/ton. The choices for CFM/ton are 350, 400, and 450. The airflow is the same in cooling and heat pump heating.

    The TAM7 air handler has significantly more control options for fine tuning the airflow for the application than the 4TEE air handlers did.
    If more government is the answer, then it's a really stupid question.

  8. #8
    Join Date
    Jul 2012
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    20
    Quote Originally Posted by mark beiser View Post
    On that switch block, switches 1 and 2 are to set the outdoor unit size, switches 3 and 4 are to set the CFM/ton. The choices for CFM/ton are 350, 400, and 450. The airflow is the same in cooling and heat pump heating.

    The TAM7 air handler has significantly more control options for fine tuning the airflow for the application than the 4TEE air handlers did.
    Thanks for explaining this, Mark. I'm confident in the dealer I chose to do the work, so I'm sure they will set up the air handler to provide the airflow needed and suitable for my ductwork. Following the installation, the dealer also plans to come back and balance the system.

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