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What is the difference between assigning the demand directly at Tank vs assigning demand at downstream node in EPS

In the water distribution model of feeder main, where I have given separate inlet at the tank, what difference it makes if I assign the demand at tank or if I assign the demand at the D/S node instead of tank?

Which option shall be used in which case? 

What is the significance of having the demand allocation option at the tanks?

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  • Hello Chetan,

    Demands at tanks are used in following cases;

    1. If you are modeling a complex network where there are some junctions very close to the tanks which results in very short pipes connecting from the tank. In such cases you can club the demands for these junctions and add them to your tank. This will result in a cleaner and a more manageable network.

    2. If you want to model a fixed inflow to the tank. In WaterGEMS / WaterCAD, you can model a fixed inflow to the tank by introducing a "negative" demand. E.g. for a fixed inflow of 5 L/s you have to put the demand as -5 L/s. This will result in a fixed inflow to the tank irrespective of downstream demands. However, if your tank is having an upstream source (such as a reservoir) you have to simply enter a positive demand (like 5 L/s)

    3. If you are modeling individual household connections with underground tanks then adding demands to the tanks will prove beneficial.

    See the below article for more details on this;

    Modeling Fixed Inflow from a Marginal Source

    Another forum post had a similar discussion. See below for details;

    Forum Post - Tank's demand

    Hope this helps.


    Regards,

    Yashodhan Joshi

Reply
  • Hello Chetan,

    Demands at tanks are used in following cases;

    1. If you are modeling a complex network where there are some junctions very close to the tanks which results in very short pipes connecting from the tank. In such cases you can club the demands for these junctions and add them to your tank. This will result in a cleaner and a more manageable network.

    2. If you want to model a fixed inflow to the tank. In WaterGEMS / WaterCAD, you can model a fixed inflow to the tank by introducing a "negative" demand. E.g. for a fixed inflow of 5 L/s you have to put the demand as -5 L/s. This will result in a fixed inflow to the tank irrespective of downstream demands. However, if your tank is having an upstream source (such as a reservoir) you have to simply enter a positive demand (like 5 L/s)

    3. If you are modeling individual household connections with underground tanks then adding demands to the tanks will prove beneficial.

    See the below article for more details on this;

    Modeling Fixed Inflow from a Marginal Source

    Another forum post had a similar discussion. See below for details;

    Forum Post - Tank's demand

    Hope this helps.


    Regards,

    Yashodhan Joshi

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