wet to anti freeze

[cdafd]

A business wants to change from a wet system to anti freeze.

as ahj I understand the system requirements

BUT does the system have to be recalculated??? becuase of the anti freeze use??

 

[TravisMack]

If the system is >40 gallon capacity, then it must be calculated using DW not HW. So, in my opinion, YES. It must be re-calculated.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[cdafd]

And not being an engineer what could that impact??

Size of pipe not correct to support the pressure needed???


Other????

 

[b1ueshift]

It could possibly mean that the pipes are too small for the available water supply. Some modification may be required if this is the case.

I worked with a designer once who took pride in getting his sprinkler systems as close to the water supply curve as he possibly could to minimise the cost. Hopefully he didn't design this one.

 

[LCREP]

Also if they do not have a RPZ backflow devise, they will most likely need one with antifreeze if connected to a public water supply. A RPZ can suck up 5-15 psi, and make the hydraulics go from OK to now you need a fire pump depending on the original safety cushion on the design. Also NFPA may limit the % of antifreeze solution and type as well as requiring premix solutions, check out NFPA.org to be sure.



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Fire Sprinklers Save Firefighters’ Lives Too!

 

[skdesigner]

cda: to expand on Travis' post, NFPA 13 2010 22.4.4.5.1 states "For antifreeze systems greater than 40 gal in size, the friction loss shall aslo be calculated using the darcy-weisbach equation shown in 22.4.2.1.3 using a moody diagram, sigma factors that are representative of aged pipe, and adjusted k factors for fluid properties. The discharge from individual sprinklers shall be based on the adjusted k factors for fluid properties and shall be based on the following formula (look it up, don't feel like typing it out).

Basically, the equation is going to allow for the viscosity of the antifreeze based on your lowest expected temperature - if it gets real cold there, the liquid is going to be very thick, and not have the same hydraulic properties as water, so you're going to (possibly) see the pressure demand skyrocket.

Long story short, yeah they're going to have to re-calc, but make sure they calc right. The moody diagram is easy to flub if you're not looking real close at it.

 

[TravisMack]

As stated above, I have done systems right around the time of the requirement for DW calcs where there was a 80 psi greater demand using DW calcs instead of HW. When you factor the viscosity / density of Glycerine at -10°F, it doesn't move very well and had a much higher system demand.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[nitrosup]

Would anyone know if adding an expansion chamber to the new anti-freeze system is required or simply recommended?

 

[skdesigner]

You have to be able to relieve the system pressure somehow. A wet system would use a pressure relief valve, which, at a pre-set pressure, dumps water until the system pressure has decreased to below the relief valve setting. In an antifreeze system, where concentration determines the effectiveness, dumping solution and allowing more water to flow in is going to dilute the solution, rendering it ineffective. An expansion chamber has a bladder containing compressed gas. As the system pressure increases, the solution will expand into the chamber, push on the bladder and compress the gas contained therein. As the pressure decreases in the system, the compressed gas will push back on the solution, and force it back into the piping.

This is somewhat of a moot point if you're installing systems where the design temperature is less than NFPA's TIA allows for pre-mixed solutions.

 

[cdafd]

Thought expansion chamber was based on how you pipe it

Do not have the book

But not required when you do a loop, because the check has a hole in the flapper

 

[skdesigner]

expansion chamber is used if the system has an RP that the pressure will build up against.