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Why is there no residual pressure despite have fire flow needs exceeded?

dculeton
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When I run the fire flow analysis it returns values for "Flow (Total Available)(gpm)" which are higher than "Flow (Total Needed)(gpm)". Logically, if there is excess flow there should be residual pressure. The results of my automated fire flow analysis that has an upper limit available flow of 2000 gpm requires 505 gpm (500 fire flow + 5 base demand) show that an available flow of 1931 gpm will produce 71.7 psi of residual pressure. However, another junction has an available flow of 2005 gpm and 0 residual pressure.

What might be causing this discrepancy?

Thanks,

David

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    Hello David,

    It may depend some on the setup of your fire flow alternative and other results in your flow flow report. For instance, the residual pressure at the node isn't the only pressure result that needs to be satisfied. The pressures for all nodes in the same pressure zone must also satisfy the lower limit zone pressure assigned to the fire flow alternative.

    So what may be happening is in the first case, the zone lower limit is being met at some other node in the same pressure zone, which is keeping the fire flow from reaching the upper limit. For the second case, the zone pressures are higher so the upper limit of the fire flow is being reached.

    The following TechNote may be useful for interpreting the results: communities.bentley.com/.../2614.understanding-automated-fire-flow-results-tn.aspx

    If that doesn't help, we will need to see the model files. There are two options for sharing your model files on BE Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

    communities.bentley.com/.../bentleysecurefilesupload.aspx

    If you upload the model files to Sharefile, please post a message here so we know they are available.

    Regards,

    Scott Kampa

    Bentley Technical Support

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  • 0 Offline

    Hello David,

    It may depend some on the setup of your fire flow alternative and other results in your flow flow report. For instance, the residual pressure at the node isn't the only pressure result that needs to be satisfied. The pressures for all nodes in the same pressure zone must also satisfy the lower limit zone pressure assigned to the fire flow alternative.

    So what may be happening is in the first case, the zone lower limit is being met at some other node in the same pressure zone, which is keeping the fire flow from reaching the upper limit. For the second case, the zone pressures are higher so the upper limit of the fire flow is being reached.

    The following TechNote may be useful for interpreting the results: communities.bentley.com/.../2614.understanding-automated-fire-flow-results-tn.aspx

    If that doesn't help, we will need to see the model files. There are two options for sharing your model files on BE Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

    communities.bentley.com/.../bentleysecurefilesupload.aspx

    If you upload the model files to Sharefile, please post a message here so we know they are available.

    Regards,

    Scott Kampa

    Bentley Technical Support

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