Building Design and Construction Handbook - Merritt - Ventech!

WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS 14.55
FIGURE 14.15 Alarm-check valve.
time delay to serve as the retard function and they can easily be monitored as a
fire alarm device. Figure 14.15 shows a typical alarm-check valve.
14.28.2 Antifreeze Systems
Where a wet-pipe sprinkler system is installed but small unheated areas such as
truck docks or attics exist, an antifreeze system, normally a subsystem to a wetpipe
system, will be employed. In most instances, when the capacity of an antifreeze
system exceeds 40 gallons, the cost of system maintenance becomes prohibitive
and a dry-pipe system is more appropriate.
An antifreeze system consists of an antifreeze U-Loop (Figure 14.16) which
includes an indicating control valve, antifreeze solution test ports and drain connection
and a check valve or backflow preventer to restrict the migration of antifreeze
from the antifreeze side of a system to the wet-pipe side. Since the waterside
of an antifreeze U-loop is subject to freezing, the U-loop must be located in a
heated area. The operation of a sprinkler on an antifreeze system is identical to that
of a wet-pipe system; however, rather than water flowing from the sprinkler immediately,
it is first the antifreeze solution, followed by water. While it may be of
concern, the antifreeze solutions currently permitted by NFPA 13 are tested for
their ability to control fire and they do not detract from the characteristics of water
as an extinguishing medium.
Given today’s increasingly stringent environmental regulations, the installation
of backflow prevention devices are often required on antifreeze systems to prevent
antifreeze from flowing into wet-pipe sprinkler systems and endangering potable
water supplies. The presence of a backflow preventer in an antifreeze system causes
special problems with respect to excess system pressures and where a reducedpressure
backflow (RPV) preventer is used, proper maintenance of antifreeze solution
concentrations. Where backflow preventers are included in antifreeze system
design, expansion chambers must be used to absorb the excess pressures that may
build up on the antifreeze side of the system. Where RPV’s are employed, the
system owner or person in charge of antifreeze system maintenance must be aware
that the antifreeze system solution may change over time if antifreeze bleeds from
the system through the RPV’s interstitial zone.
14.28.3 Dry-Pipe Systems
In locations where it is impractical to maintain sufficient heat to prevent freezing
and the area is too large to be protected by an antifreeze system, dry-pipe systems