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  1. #1
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    Aug 2009
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    Trane Tracer high low limit question

    I have a question about the heating high limit and cooling low limit setpoints in Trane's tracer summit software. I read that the heating and cooling high and low limit setpoints 'CAP' the operating heating and cooling setpoints. Does this mean they override/have priority and become the operating setpoints? To be perfectly honest our controls person isn't the most self motivated one. We technicians experience some of our systems heating competing against the cooling, back and forth. It seems to me that the high and low limit for heating and cooling should be the same as the desired heating and cooling setpoint when you don't wish the person occupying the space to have control of the room temp. Any knowledgeable input is appreciated.

  2. #2
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    May 2004
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    Not knowing exactly what controllers you have this is an example of a typical VAV. If the high setpoint limit is set to 74 and the thumb wheel is set to 85 the active cool setpoint will be 76 and and active heat setpoint will be 74. If the low limit is set to 70 and the thumb wheel is set to 55 the active heat setpoint will be 68 and the active cool setpoint will be 70. There are some offset settings will effect the active setpoints as well. As you can see there still will be some adjustment available. The correct way to prevent the occupant from changing the setpoint is to disable the thumb wheel. There should be local setpoints in the system as well which are only active when the thumb wheel is disabled.

  3. #3
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    The thumbwheel is disabled. the setpoints are set at 74 cooling and 71 for heating. My question is should the heating high limit be not be higher than the heating setpoint and the cooling low limit not be lower than the cooling setpoint? We don't want the people with access to the stats to be able to adjust the temps.

  4. #4
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    The setpoint limits are not in effect if The thumb wheel is disabled. Disabled means they can play with the setpoint until their fingers fall off and nothing will happen and your setpoints will be used.

  5. #5
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    Thanks i know that. Let me explain a little better about what were working with here, It's in a large public education environment. The thumbwheels are disabled. So the units cycle based on the setpoints in Tracer. This being the situation my question is should a high limit heating setpoint and a low limit cooling setpoint be saved/used in Tracer? Personally I do not see why since we want to operate at the cooling and heating setpoints of 74 cooling and 71 heating which are the operating setpoints. But our controls person is assigning a high heating limit and low cooling limit setpoint. It seems that the high and low limits would have priority over the actual setpoints and become the operating ranges.

  6. #6
    Join Date
    Aug 2009
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    Prattville, Alabama
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    I believe the limits will be capable of having an effect with both the thumbwheel setpoint (with the thumbwheel enabled) and the Summit-programmed setpoint (with the thumbwheel disabled). It will limit either, so that the resulting active setpoint will not be "outside" the limits.
    But that effect will only occur when the setpoint is attempted to be set outside the limits.

    There are actually 4 limits: cooling high limit, cooling low limit, heating high limit, and heating low limit. Rather than thinking "high heating limit" and "low cooling limit", think of "high limits" and "low limits". Ensure both high limits are above both your programmed setpoints, and both low limits are below both your programmed setpoints. That way your programmed setpoint will not be affected by those limits. And I think there has to be some value, or number, assigned to the limits.

  7. #7
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    Thanks

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