Fire flow analysis

I guess RSP means how to run the model with two hydrant at the same time, i.e. the automated fire flow to check two hydrant opened at the same time for two hours.

Unfortunately the automated fire scenario is design to check only one hydrant, and I guess you should do it manually at one hydrant and automated for the second one; unless somebody else has other way.

I wish if WaterGEMS/WaterCAD has capability to run automated fire scenario at two locations.  

As I explained, the fire flow analysis does not tell you how much water comes out of one hydrant or two hydrants or ten hydrants. It tells you how much water can be delivered to that node at the required residual.  

The actual flow that you get out may be limited by the number of hydrants that you have. If you look at the kinds of equations that the fire flow analysis uses, there is no input for number of hydrants. It just determines how much water is available. That number may be reduced if there are not enough hydrants.

That's all you can really do because the real fire flow will be determined by the laying length of hose, how many hoses and hose streams,the size of the hoses, what size pump is on the fire truck, what nozzles the fire fighters will be using, etc. and the engineer has no knowledge of that at the time he is doing design.

As I explained, the fire flow analysis does not tell you how much water comes out of one hydrant or two hydrants or ten hydrants. It tells you how much water can be delivered to that node at the required residual.  

The actual flow that you get out may be limited by the number of hydrants that you have. If you look at the kinds of equations that the fire flow analysis uses, there is no input for number of hydrants. It just determines how much water is available. That number may be reduced if there are not enough hydrants.

That's all you can really do because the real fire flow will be determined by the laying length of hose, how many hoses and hose streams,the size of the hoses, what size pump is on the fire truck, what nozzles the fire fighters will be using, etc. and the engineer has no knowledge of that at the time he is doing design.

Yes, as mentioned by Mohammed, i need to run a fire flow analysis for total 64 lps but with 2 fire hydrants running in parallel with 32 lps. this is as per the NFPA -14 guidelines.  

Is there any option in Water gems to perform this option.

You folks aren't listening. The WaterGEMS fire flow analysis is a two hydrants analysis and it is a one hydrant analysis and it is a three hydrant analysis... What WaterGEMS does is calculate the amount of water that can be delivered to a node in the system at the specified residual pressure (usually 20 psi in the US). After that, it is up to you to check that you have enough hydrants to get the water out of the node.

In your case, it sounds as if they only allow you to take credit for 500 gpm for each hydrant so that you need to have two hydrants within a reasonable distance of the node.

This is a somewhat conservative number but it is pretty accurate.

Can you send me the exact wording from NFPA-14 that you are referring to? Send it to tom.walski@bentley.com.

Tom,

One question I have regarding the fire flow analysis to make sure I understand it correctly.  Example: If I run the analysis and the results indicate that hydrant H-1 can deliver a flow of 2500 gpm.  

Am I understanding this correctly that it doesn't actually mean that H-1 can deliver 2500 but that junction/node in the system can bring that much water to the area.  If there isn't enough hydrants in that area to flow 2500 gpm then you will be limited to the flow that your hydrants can deliver?

Is there a way other than field conducted flow tests to determine how much flow you can actually deliver?

More clarification;

I understand your point clearly Dr.Tom, but what I wanted to say that I know in Middle East there are some municipalities want to run fire flow analysis for two fire event at the same time in different locations (let's say one in the east and the other in the west at the same time) and they ask for the report and analysis proof that and Auxiliary output while two fire event simultaneously.  

As I understand that fire flow results and browser  show the available fire flow assuming  one hydrant (one fire flow event); is that correct?

for example if the fire flow results shows the available fire flow for J1 (as example) 500 gpm and it is located at east of the city, and the fire flow available for J2 is 300 gpm which located at west of the city, that means that I can get 500 gpm in case fire event at east within certain radiuc but that with no fire at other location; and vise versa for the J2.

Regards........Mohamad.

There are a couple of things going on here.

First, you don't want to run a fire flow analysis for an exhaustive combination of all pairs of nodes. Let's say you have 20,000 node model. Running every pair would results in 400,000,000 runs which would take a long, long time to run and you'd probably run out of memory along the way. So that's not feasible.

Second, when you are talking about multiple fires (not multiple hydrants for the same fire), the fires are generally far enough apart that distribution capacity is not the issue. The limitation is  usually source/storage. Do you have enough water in storage to make it through 2 hours? In this case, I would just set up a few EPS scenarios with two fires running at the needed fire flow and watch how the pumps and tanks behave.

Third, it makes a difference if the fires are in the same pressure zone or different zones. If they are in different zones, there may be very little interaction between fhe fires if each zone has its own storage.