Hello,
I'm modeling a community water system in WaterCAD CONNECT Edition 3 (10.03.01.08). The system has a pump connected to a reservoir on one side, an elevated tank on the other end, and all the piping in between. When the tank reaches a preset low level, it calls for the pump to turn on, and when full, calls for the pump to turn off.
The fire flow analysis I'm performing is steady-state. What is the most appropriate way to model the available fire flows - with the pump on or off?
Modeling with the pump off provides a conservative available fire flow, but modeling with the pump on provides a better picture of what could be available. Is there solid guidance on this subject?
My system has the potential such that a 60 minute fire at 2,500 gpm could be completely within the tank's operating range and not trigger a pump run cycle.
Thanks!
Aaron
There are no rigid guidelines for this. I once wrote a paper complaining about this uncertainty. It's left to engineering judgement. In most cases, the design engineer assumes (reasonably) that the operators would turn on whatever pumps are needed during the fire.
This is reasonable in most cases although there are exceptions. For example, during the wildfires out west, power lines are being shut down during the fires or after an earthquake, power may be out for a while. You generally don't design for these cases.
Answer Verified By: Aaron Van Proyem
Thanks for the response, Tom. I had a feeling it was a judgement call, but wanted the assurance that I wasn't missing something. The area near my model is not prone to fires, wild or otherwise, and in fact the fire department hasn't had to use a hydrant to fight a fire in about 20 years.
Hopefully, they exercise the hydrants and valves at least annually.
Just to close the loop on this thread - I have added a note about this in the article How does the Automated Fire Flow analysis work?
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.