Originally Posted by wnabcptrNH
Newer dry systems dont always set off just because there is a loss of pressure actually. Most new systems have smoke detectors interconnected into them, so when the system gets a loss of air pressure it waits for the smoke detector to go off prior to releasing the water.
There are three kinds of dry pipe systems; standard, single interlocked and double interlocked dry pipe (correct term is preaction) systems.
A standard dry pipe system is a sprinkler system employing automatic sprinklers that are attached to a piping system containing air or nitrogen under pressure, the release of which (as from the opening of a sprinkler) permits the water pressure to open a valve known as a dry pipe valve, and the water then flows into the piping system and out the opened sprinklers.
Preaction Sprinkler System is a sprinkler system employing automatic sprinklers that are attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same areas as the sprinklers. Actuation of the detection system and sprinklers in the case of double-interlocked systems opens a valve that permits water to flow into the sprinkler piping system and to be discharged from any sprinklers that are open.
With a standard dry pipe system air pressure is used to keep a differential valves, called a dry pipe valve, closed. When the sprinkler operates compressed air escapes the overhead piping, air pressure drops (depending on the water pressure the normal air pressure might be 30 or 40 psi) and when it reaches maybe 10, 15 or 20 psi the valve opens allowing water to enter the pipe eventually reaching the open sprinkler and water will discharge. A standard dry pipe system is not connected to any type of electrical operating circuit... it's operation is all mechanical.
On a single interlocked system you have a dry pipe system but connected to it is an alarm system with smoke detectors. When smoke is detected the valve opens allowing water to flood into the overhead pipe system but no water will flow until the sprinkler head operates. The biggest benefit to these systems is it allows water to get to the open sprinkler faster.
Where water damage is a major factor, such as computer rooms (yes, we install sprinklers in many computer rooms.... IBM has them in theirs) or high value storage areas, we use a double interlocked dry (or preaction to use the correct term) system. A double interlocked preaction system the overhead pipe is charged with supervisory air so if a pipe breaks, or a sprinkler head operates or is broken, air will escape, an alarm will sound but no water will flow until the smoke detectors operate at which time a solenoid valve operates opening the valve allowing water to flood the system. With a double interlocked system if the smoke detection system operates an alarm will sound but water will not flood the overhead pipe system until the supervisory air (usually just a few pounds) escapes.
For a double interlocked system to work it takes heat fusing the sprinkler and a signal from a smoke detector to operate.
Why not use double interlocked preaction systems everywhere? Costs. They are expensive and I could easily see a standard dry system for a 30,000 sq. ft. building costing $1.25/sq ft with a double interlocked system taking it to $2.00 or more. Of course if you have high value contents, say $5 million in computers, you might want to spend the extra $20,000.
In an anti-freeze system we usually use a USP grade propylene glycol solution whenever the system is connected to a potable water supply. Propylene glycol is the main ingredient of jelly beans... NFPA #13 Table 184.108.40.206 Antifreeze Solutions to Be Used if Potable Water Is Connected to Sprinklers requires a 30% propylene glycol solution where the lowest temperatures does not drop below 9 deg. F, 40% where the lowest temperature does not drop below -6 deg F and 50% where the lowest temperature does not drop below -25 deg. F. A 60% solution (60% anti-freeze to 40% water) will protect from freezing to -60 deg. F.
I hate anti-freeze systems and always try to talk my customers out of them. If an anti-freeze system freezes most likely it is due to lack of maintenance. If the system never froze up before, if it is 5 or 10 years old, I would most likely blame the cause on lack of required maintenance.
From NFPA #25 "Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems" 2002 Edition Section 5.3.4* "Antifreeze Systems. The freezing point of solutions in antifreeze shall be tested annually
by measuring the specific gravity with a hydrometer or refractometer and adjusting the solutions if necessary." Was annual testing done? I am willing to bet it wasn't.
For anti-freeze systems it isn't just testing the mixture it is much, much more involved than that. In my opinion the only way to insure against disaster is to dry the anti-freeze completely to the point of removing the sprinkler heads, draining the solution into a barrel. Mix the barrel contents, check the freeze point and if it isn't low enough you add anti-freeze until the freeze temperature is where you want it. When this is done pump the anti-freeze back into the overhead pipe and you're good for one more year.
Here's the problem; A small anti-freeze system might cost $1,000 while a small dry pipe system might cost $3,000. You are bidding the job so you bid it the least expensive way but the owner is getting the shaft because while he may pay $2,000 less initially he will easily have $1,000 to $2,000 added to his maintenance bill every year which goes on f-o-r-e-v-e-r
. I avoid anti-freeze like the plague and usually, after a straight talk sit down with the owner, I can talk them into the more expensive dry system.
I try to give the customer a system I would want in a building I own knowing what I know. Usually it works.
Not all states are equal. In some states (such as mine) an owner is required to contract with a licensed sprinkler company who must employ a certified and licensed technician for annual testing of his fire sprinkler system. In most states our industry is heavily regulated (for good reason) and the inspection job is done right or it's our butt.... lots of damage gets done with a freezing anti-freeze system and the first thing the fire marshal will do is go over the written reports detailing exactly what was done in the last inspection. I don't ever want to be in a position where I have to explain to the state fire marshal why a system we inspected 3 months ago froze up causing $200k in damage.
Usually inspections on anti-freeze systems are done a month or two before cold weather. We generally try to get them done in September and October but if you are in New Hampshire you might want to think August and September. It can get cold in October in some areas.
But there is good news on the anti-freeze front. For anyone using NFPA 13-2010 (this is hot off the press):
NFPA 13, 2010 version, TIA 10-01, effective date 8/25/10
1. Add a new section 7.6.1 as follows:
7.6.1 Dwelling Units. Antifreeze shall not be permitted to be used within the dwelling unit portions of sprinkler systems.
2. Renumber the remainder of the section accordingly.
It's about time but it doesn't help much with systems installed years ago.
Now about the freezing.
An anti-freeze system should never freeze if it is properly maintained on an annual basis.
For a wet pipe system to freeze up without knowing the particulars of the project it is hard to find who to blame. I've seen some condo's on Lake Erie severely damaged when snowbird tenants depart for Florida shutting off the domestic water, blowing out the domestic lines and shutting off heat to save money. They forget the overhead sprinkler is full of water and will freeze. Whose fault is this?
FYI it is illegal in most states to shut off a fire sprinkler system for any reason. Even for non-payment of a bill they may shut off the domestic water but not sprinkler.
Then there is the problem of freezing pipe where it shouldn't happen. Hard to tell who is at fault here.
I design sprinkler systems (bet you guessed already) and while I know that well enough I am hardly qualified to determine insulation requirements. This isn't my area and I don't go there. What I do, whenever there is a question, is contact the licensed building professional (that is usually the architect) and put the monkey on his back. It is his building, his design, his building envelope and he should be able to tell me what areas are subject to freezing because he should know. If pipes are in the attic and need to be insulated to prevent freezing, he (as the building professional) should be able to instruct me how to do it so disaster doesn't happen. I always do this in writing so if something happens down the road the blame goes where it belongs.
Who is to blame for the problem originally written about? I don't know but if I had to guess it would most likely be the owner (homeowners association) for lack of maintenance.
As far as permits go in some areas, such as mine, you can't breath without a permit while in others it is like Dodge City. From what I have read Dodge City is in New Hampshire.