combined irrigation and firefighting network

Charbel · Nov 11, 2016

Dear,

I am working in designing a control system for a combined irrigation fire fighting network.
Flow switches has to be added to all fire hydrants. Flow switches are being monitored by remote telemetry units, remote telemetry units are connected in daisy chain to a fail-safe PLC. Fail safe PLC will be able to controlling and monitoring the irrigation pumps and monitoring the fire pumps.

During irrigation schedule, when any of the flow switch opens, then this is an indication of the opening fire hydrant, in this case, the following occurs:
1- fire pumps will sense a high drop in pressure in the network and they automatically start.
2- since fire hydrant flow switch is opened, then this is a fire event, irrigation controller will close al the solenoid irrigation valves and the irrigation pumps will stop through the fail safe PLC.
3- in this case, fire pumps will be serving the opened fire hydrant(s).

please advise if this system has been implemented, and if you see any drawback and how I can improve this system if possible.

your comments are highly appreciated.

thank you,

Charbel

Saffa · Nov 11, 2016

Seems complex. I do fire pumps in utility water pump stations and we generally start them based on a flow rate leaving the pump station, and / or the "normal duty" pumps being at full speed. I'll test my parameter set on several hydrants across the water network to make sure there are no weird situations which might stop it from working as expected. Sometimes there are hydraulic issues like undersized pipes or closed valves that prevent my fire conditions from being met.

Yes, if there's a mains break then you spill more water but that's a small risk compared to not being able to put out a fire.

My concern about using flow switches on hydrants is you now have a lot of devices to test for operation on a regular basis, depending on how many hydrants you have.

It's also an incredibly expensive option. You'd be better off with redundant flowmeters and pressure sensors at your pump station in my opinion, and use those to determine fire flow conditions.

questions:

How do you plan on turning the fire pumps off once a fire condition has been detected?
What communications system are you using for the RTUs? How are they powered?
What sort of flow rates are being designed for the irrigation, and what's your fire service requirement for flow from a hydrant? Is this a residential area or is this firefighting service for an oil refinery?

Depending on the scale, it would almost be cheaper and more reliable to run separate fire fighting and irrigation pipework and keep the systems separate. Never practical for municipal systems but if this is for a big commercial complex it may well be. HDPE pipe is cheap these days.

mhulbert · Nov 12, 2016

Is there a way you can just get the output of your irrigation controller (sprinkler timer?) into the PLC? Then setup your program so if the timer has a zone valve open, it is expecting a certain amount of flow. If the flow is much higher than expected, close all your irrigation valves and start your big pumps. Seems much simpler than rtu at every hydrant. You could also have a sequence to shutdown sprinklers and see if flow returns to zero, which would tell you that the fire hydrants are closed, but that you have a broken pipe on your irrigation system. Some of the smarter sprinkler timers have this exact feature to check for broken sprinkler lines...

Charbel · Nov 14, 2016

Saffa said:
Seems complex. I do fire pumps in utility water pump stations and we generally start them based on a flow rate leaving the pump station, and / or the "normal duty" pumps being at full speed. I'll test my parameter set on several hydrants across the water network to make sure there are no weird situations which might stop it from working as expected. Sometimes there are hydraulic issues like undersized pipes or closed valves that prevent my fire conditions from being met.

Yes, if there's a mains break then you spill more water but that's a small risk compared to not being able to put out a fire.

My concern about using flow switches on hydrants is you now have a lot of devices to test for operation on a regular basis, depending on how many hydrants you have.

It's also an incredibly expensive option. You'd be better off with redundant flowmeters and pressure sensors at your pump station in my opinion, and use those to determine fire flow conditions.

questions:

How do you plan on turning the fire pumps off once a fire condition has been detected?
What communications system are you using for the RTUs? How are they powered?
What sort of flow rates are being designed for the irrigation, and what's your fire service requirement for flow from a hydrant? Is this a residential area or is this firefighting service for an oil refinery?

Depending on the scale, it would almost be cheaper and more reliable to run separate fire fighting and irrigation pipework and keep the systems separate. Never practical for municipal systems but if this is for a big commercial complex it may well be. HDPE pipe is cheap these days.

Dear safa,
you mean turning on the fire pumps once a fire condition has been detected?, if that is what you mean, fire pumps are turned on by pressure drop, flow switches on the fire pumps will be used to turn off the irrigation pumps through the irrigation controller (which is giving them a prerequisite for starting)
RTU are using safety based communication, and they are designed to be fail safe RTU's, they are powered by UPS
fire hydrant requirement is 63lps.
Flow irrigation requirement starts from 7 lps to 38 lps depending on the area to be served.
Residential area is used.

it is a big scale network so that they are using both irrigation and firefighting in one combined network.

thank you!!

combined irrigation and firefighting network

Charbel

Member

Saffa

Member

mhulbert

Member

Charbel

Member

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