# Am I missing something?



## california kid (Jul 17, 2011)

I am new to the world of fire sprinkler design and find myself at a quandry. Im working on a design that requires 31.04 gpm @ 25.949psi with a safty margin of 16.044psi. These calcs were run with a 1" pvc run from the meter to the riser. All of the house's around here that i have looked at (some on the same block, similar in size, and with flat ceilings) have 1 1/4" to 2" runs to the riser. I have triple checked my information but cant shake the feelin im missing something....could this just be a case of bigger is better?


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## cda (Jul 18, 2011)

Do you happen to have a flow test with static and residual??

and what is it

Or just pressure Gage and what is it???

Do you have the hydraulic calculations to back up the design????


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## TimNY (Jul 18, 2011)

Two things I find most overlooked:

1.  The elevation of the house as compared to the hydrant where the flow test is done (just 'cause there's 50psi at the bottom of the hill doesn't mean you get 50psi at the top of the hill)

2.  Failing to account for all of the elbows, tees, valves, RPZ, flow switch etc.  I routinely see calcs where they have 2 elbows from 1st to 2nd floor.  When I get there they have a dozen.

If you are close on 1" do not paint yourself into a corner when they have to install additional elbows to get around beams, columns etc.


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## california kid (Jul 18, 2011)

According to the water company there is 50psi at the supply. My calculations back up my design with all things considered PLsup,PLsvc,PLm,PLd,and PLe leaving me a healthy cushion. I guess my question is...should i be taking into consideration future demand to the system such as landscaping or future additions?


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## Builder Bob (Jul 18, 2011)

What is the cost associated with a 1 inch tap vs. a 1 1/4" or 2 inch tap?   I beleive you may find the answer when talking to the water purveyor or for impact fees.


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## cda (Jul 18, 2011)

California

Do you design fire sprinkler systems for a living??

Is this a cvpc system or pex plumbing system??

I think I would confirm with own ideas pressure available

If you truly do have  a 16 psi safety not much more you can do for future problems


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## california kid (Jul 18, 2011)

My design is a residential  stand-alone systems piped in cpvc. Mabe I'm over thinking it. I thought mabe there was an unwritten rule or consideration for oversizing the service pipe even though flows and preasure did not dictate it.


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## cda (Jul 18, 2011)

Sound like you are good to go if the hydraulic calcs support the design

And flow test show you have the water, which once again would like to see in person

So how long have you been designing systems???


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## TimNY (Jul 18, 2011)

california kid said:
			
		

> According to the water company there is 50psi at the supply. My calculations back up my design with all things considered PLsup,PLsvc,PLm,PLd,and PLe leaving me a healthy cushion. I guess my question is...should i be taking into consideration future demand to the system such as landscaping or future additions?


What does the water authority guarantee as the minimum level of service?  Did they provide you with a historic low for the area?


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## AegisFPE (Jul 18, 2011)

The systems with larger pipe sizes may have been serving both the domestic demand as well as the sprinkler supply.  If you have two taps, and one is dedicated to sprinkler service, your calc may be appropriate.  But, if you have a single tap that tee's inside the house (and there is no valve to shut-off the domestic side during a fire event, then you may need to increase your flow to account for domestic water usage in addition to sprinkler operation - this can drive a larger pipe size.


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## california kid (Jul 18, 2011)

I have been working on sprinkler designs for less than a year. I use a program from MEP CAD for the calculations. Our area does not require that we design to historic lows but i understand that some do. ....Kid


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## california kid (Jul 18, 2011)

Aegis, the sprinklers and domestic have a common supply pipe, i have added 5gpm to the flow to compensate. Is there any consideration for landscape demand? I can find nothing in the code for this.


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