I am working on a distribution system that has very low demand (average day ~ 40 gpm and max hour ~ 230 gpm) compared to its necessary fire flow which is 2200 gpm for 2 hours. As we have it set-up right now, there is one pump that operates at 400 gpm, 60 ft head and another that is designed for 1900 gpm, 60 ft head (for fire flow). Each are in a booster station so discharge is through the same pipe.
I am having trouble with an EPS fire flow scenario I created in which when fire flow kicks in and Pump 1 (small pump) is the only one on, because of such a large fire flow it operates at 800 gpm, 0 ft head. It operates like this until the tower water level drops enough for Pump 2 to come on, then it operates under normal conditions. Below is a time series screenshot of the data.
During hours 9.45-9.6 I receive the notifications "Pump Booster station 1 exceeds the maximum operating point specified for the pump curve" and "Pump Booster station 1 cannot deliver flow or head" for each time instance. Keep in mind this fire flow is located far from a tower site whereas fires that are located near a tower site, we have no problems with. My assumption is that because it is located far from a tower site, the booster station is doing a majority of the work and therefore has to pump at greater rates. My question for you is, does this error stem from our control settings, incompatible pump curves, is it something that wouldn't happen in the field and it's just a model error, or are we always gonna have problems because of the location of the fire?
If you need more information just let me know.
Thanks,
Kyle
Kyle,
What is happening here is an artifact of modeling the fire flow as a known demand. This forces a known flow even when it may be impossible.
In reality, what would happen is that the flow delivered to the fire would be less than 2200 gpm until the big pump kicks on.
The exact flow during that short time depends on whether the fire is being fought directly through the hose or through a pumper truck. You can't be sure unless you know the characteristics of the hoses and pumps which is almost impossible t oknow.
For the time steps before the big pump kicks on, you can place a lower demand on the fire flow (something that would result in a residual pressure of around 20 psi). You can get an approximation of this value from a WaterGEMS fire flow analysis.
Tom
Answer Verified By: Kyle Blommer
Tom,
Thank you for the information!
Here is a related article in our wiki: User Notification "Pump cannot deliver flow or head" ?
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.