Fire Fighting System circulation

[youwon_choi]

thread404-157369
Hi Designers/ experts in Fire Fighting System

I am curious about the circulation pump head and flow rate in the design of fire hydrant system inside the tunnel.

1. The length of the tunnel is 8.5 km
2. The flow rate of the fire fighting main piping is 1200 lpm, the fire-fighting water line 150(A), Piping pressure 10kg / cm2
3. A much smaller flow rate is required for the circulation at the first and last 500m of the tunnels to avoid icing
--- Circulation pump piping length is 500m x 2

Question : How to select the circulation pump head and flow rate? (Please attach a reference code and equipment calculation)

 

[LittleInch]

Hmmmm,

Fire fighting systems tend to be laws unto themselves and you really need to check your particular code or with the AHJ.

I don't believe there is any code type calculation for this, but I would tend to pump from the warmer end to the colder end so the first one is correct, but turn the other one around. flowrate though? Equivalent to 1 metre per minute maybe? A lot depends on temperatures at either end, ambient temps etc.

Pressure drop will be all about the friction drop in your small bore return line so size it accordingly to make it between 1 to 3 bar.

You probably need to look at or think about insulation and trace heating, though as this is a fire system there are rather stringent rules about trace heating - look at this e.g.

http://www.eng-tips.com/viewthread.cfm?qid=433913

and note that the HT system would need to be approved. I would have thought it was a better solution myself.

What about the section from the pumps to the tunnel?

Not everything is about codes and standards.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dbill74]

First step is to determine a flow rate that will not freeze. This will be a function of fluid velocity, ambient temperature and insulation. I'd have to go back to college text books to find an appropriate equation.
Step two would be to convert the velocity to LPS.
Step three calculate head losses for your LPS through the piping.
I would think and hope these last two steps are fairly straight forward.

How do you plan to protect water in the individual drops and sprinkler heads from freezing? Circulating water through the main will certainly keep the mains from freezing, but what about the drops for the sprinkler heads? Back when I did some FP design, I would use a preaction/dry pipe system in areas subject to freezing such as loading docks. Is there some reason to not use a preaction system at either end of the tunnel where freezing is a concern?