You are allowed to use refill as shown by NFPA 25 adding a section on
refill valves last cycle. I'm not aware of any standard telling you
HOW to apply it. Go with what Todd said.
Roland
On May 22, 2008, at 7:20 AM, Todd Williams - FPDC wrote:
Geoff,
Let me see if I have this right. The hose demand is 500 gpm and the
sprinkler demand is 600 gpm for a total demand of 1100 gpm combined.
The duration is 90 minutes, so the total water demand is 99000
gallons. Your flow test shows only 600 gpm at 29 psi, therefore a
tank, and presumedly pump, is required. In this situation, would the
hose demand be taken before of after the proposed tank? It sounds
like it might be taken before the tank. Therefore, you need to make
the 600 gpm sprinkler demand off of the tank. The available tank
capacity would need to be 600 x 90 or 54,000 gallons. The actual
tank would be around 60,000 gallons. What you want to do is try to
decrease the size of the tank by deducting the fill rate. Your
assumption is that 100 gpm at 29 psi would be available after the
hose streams to fill the tank. Somehow I don't think that you can
automatically assume that because you cannot predict what the actual
fill rate would be, based on a flow test alone. I think that factors
such as pipe size, supply vs tank elevation, etc need to be
considered. Also, If you have 20 ft of head in the tank, then you
have a 8.7 psi fighting the 29 psi, which could decrease the
potential flow. Personally, I don't like to include refill rate in
sizing the tank, because it is not predictable. Besides, you are
only potentially dealing with a 50,000 gallon tank vs. a 60,000
gallon tank. How much of a savings would there really be?
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