We have a client request to run a surge model to check impact of electrical pump startup on the fire network.
The operation of this network is different from standard. The jockey pumps are selected for a flow of 60m3/hr at a head of 35m, while the main fire pumps are selected to run for a flow of 4000m3/hr at a head of 110 meters.
The system is designed so that jockey pumps can cater for smaller demands which require less residual head of 25meters only . In case of increased demands due to fire, the fire pumps will start to run to satisfy a residual pressure of 7 bars at the most remote point, which will require a head of 110meters at the pumping station main pumps.
I need to run a surge model to analyze the impact of fire pumps startup on the system, while jockey pumps are already running. How can I make a different demand pattern, that will be considered in the transient conditions, as follows:
- First 100 seconds, system demand is 60m3/hr only and requries a haed at pump of 35 meters. After 100 seconds, I need to introduce a demand change from 60 to 4000m3/hr, that will require main pump startup. Therefore I introduced a pump startup scenario starting from 100 seconds reaching duty point in 10 seconds that is after 110 seconds from the beginning of the run.
I built the model using the following patterns:
Jockey pump water demands pattern (the 60m3/hr):
:
Main water demands pattern (the 4000m3/hr):
Main Pumps transient Pattern 9 (showing startup after 100 seconds, that is when the 4000m3/hr comes):
As per the results, I am getting that the main pumps will start to run at the required flow after 100 seconds, as required, but the flow will go to zero again, eventhough the 4000m3/hr demand is still there (refer to pattern) which is my main question!!
Above graph is time series at main discharge header. after 110 seconds, the flow goest back to zero while as per the demand pattern the demand is 4060m3/hr?!
I am afraid that the issue occurs when the demand starts immediately, while the pump takes time to satisfy it, which leads to network inbalance..I am sure there is a better way to create this required demand variation coinciding with pumps startup.
Help Please...
Hello,
Regarding the demand patterns, you have entered a hydraulic pattern to adjust the demands. However, this pattern is not used by HAMMER. It is only used for the initial conditions, particularly for EPS runs. When you compute the initial conditions. That is typical of an EPS analysis. However, that pattern is not used by HAMMER's transient solver. Instead, it will use the demands calculated in the initial conditions, which is likely still the 60 m^3/hr demands used initially.
The way you would need to model this will depend on how the system is expected to work. If the demand increases before the pumps turn on, the simplest way to model this would be to simply start with an initial demand of 4000 m^3/hr and then set up the pump operating rule to turn the pumps on at the appropriate time.
However, if the demands gradually increase as the pump is starting up, you will need to set up your model a little differently. HAMMER comes with an element called Periodic Head-Flow. This is used when you need to control the flow or head in the system. You can find some additional in formation on this element in the Help documentation. It basically allow you to define how the flow or head changes with time.
So what you would is replace the fire flow demand node with the Periodic Head-Flow element. Open the properties for the element and set Transient Parameter to "Flow". Click the ellipsis (...) button in the Flow Pattern field to open the table. Enter the flow expected at this node. The pump set up as it currently is, with an operating rule that turns it on. When you compute the model, this should allow for the an increase of demand as the pump turns on.
Note that the Period Head-Flow elements only allows from one pipe connection. In other words, it needs to be at the end of the system. If there are nodes and demands downstream of the fire flow node, you could leave the current set up as is, then add a pipe at a tee with the Period Head-Flow element attached to it. Make the pipe a large diameter with a smooth friction factor, so that addition losses are not introduced. This type of setup will allow you to model demands downstream of the fire flow node. Of course, if the fire flow node is at the end of the system as it is currently modeled, you can simply replace the node with a Periodic Head-Flow element.
If further assistance is needed, it would be good to have a copy of the model. 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
Regards,
Scott Kampa
Bentley Technical Support
Answer Verified By: Scott Kampa
Thank you sooo much Scott..I will try the tool and upload the model if I need further assistance..