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96-14E November 1996
Manitoba Water Use Efficiency Program
Preventing Frozen Water Pipes
Many cold climate communities struggle each winter to prevent water
supply pipes from freezing. Northern communities have explored various
prevention techniques and technologies. This Information Bulletin
suggests a number of techniques that may help to prevent pipes from
freezing and reduce water waste.
Design Factors
A community should consider several factors when exploring ways to
prevent pipes from freezing. These include pipe design, pipe depth,
expected water and ground temperatures, and accessibility of pipes in
winter for thawing and repairing.
Depth
The depth at which to bury the piping is a major consideration
during installation of a community's water supply system. System
designers must ensure all factors, including the type of soil and its
insulating properties, are considered prior to installation. Areas of
permafrost will have unique considerations.
Insulate Pipes
Insulating pipes will reduce the amount of heat lost from the
water. The service connection should be insulated right into the
heated portion of the house or house trailer; otherwise freezing can
still occur. Although expensive, factory insulated pipes reduce
on-site labour and ensure that no breaks occur in the insulation
during installation.
Continuous Circulation
Some water supply systems involve laying various configurations of
pipe which allow continuous water flow. A commonly used layout
consists of a single pipe that loops back to its origin. The water
flows through the pipe, including through the service connections to
each house. Unused water continues to move through the pipe, and is
returned to the water plant. To ensure the water being distributed
remains above freezing, a boiler is often used to heat the water to
about 4_C.
Double Piping
In the past, some communities have installed a double pipe
configuration, but it has been an expensive option, both in terms of
installation and maintenance. Two pipes are laid beside one another.
The larger is the supply pipe; the smaller returns water to the origin
for heating and recirculation.
Both the single and double pipe configurations avoid water waste.
However, heating the water uses considerable energy.
Bleeding
Bleeding means the controlled wasting of water through orifices to
maintain water flow in the main lines, service lines, and sewers to
prevent freezing of the pipes. Originally, communities installed
carefully sized orifices in the dead end of single line supply
systems. The water then flowed continuously through this hole, usually
to the sewer pipe. This resulted in water being wasted throughout the
year. Although it may seem like an inexpensive option, it results in
the ongoing costs of treatment of large volumes of water that flow
directly into the sewer system. These large volumes of water can
dilute wastewater to a point where treatment is ineffective. This
method can also result in cross-contamination between potable water
and wastewater.
To reduce water wasted from bleeders, two options to regulate
bleeders have been developed:
Timers
The first, "Timers", turn bleeders on and off
automatically. Timers are set to clear water from the pipe before the
water reaches ice-forming temperatures. If the electricity is
interrupted, or the timer is turned off, the bleeder should remain
open. Timers should be set to the worst case scenario (assume coldest
possible temperatures) unless the timers can be adjusted from above
ground. In addition, if the timers can be adjusted from above ground,
the bleeders can be closed during the summer. The capital cost is
relatively low, but the system still wastes large volumes of water.
Temperature Sensors
The second, "Temperature Sensors", waste the least amount
of water of all bleeder methods, but is also the most expensive and
difficult to install and maintain. Sensors are installed in the
coldest sections of the supply pipes. Therefore, locations must be
examined, and trials must be performed to verify the most appropriate
positioning of sensors. When the sensor reads below a preset
temperature (usually just above freezing), the sensor triggers the
opening of the bleeder. The bleeder closes when the sensor reads above
another preset temperature. If electricity is interrupted, the system
automatically allows a continuous water flow, which will last until
the electricity is reinstated.
Note:
In many Northern homes, a tap is left running during cold months to
prevent pipes from freezing. This practice wastes water. Therefore,
orifice plates can be installed on a special tap, and a lesser
amount of water (less than 0.5 gpm) can be wasted from within the
home. A shut-off valve can be installed to conserve water during
warmer months.
Heat Tracing
Another technology that can help prevent water pipes from freezing
is heat tracing. A long element heats the pipe and water to prevent
freezing; and can also be used to thaw frozen pipes. There are three
methods of heat tracing:
Glycol Heat Tracing System
Glycol heat-tracing systems transfer heat by using a series of
pipes in a closed loop circulation system. The system consists of
boilers to supply heat, a heat exchanger from a main heat reservoir,
circulating pump(s), an expansion tank, specialty valves, and
controls. The output heat exchanger is the heat trace tubing that runs
in a loop next to the pipe requiring heat. While the total system
efficiency of a boiler-fired glycol heat-tracing loop is greater than
that for electric resistance heat tapes, their maintenance
requirements (including heated space for the boilers, pumps, etc.) are
often considered their main disadvantage. Cross contamination is a
risk. In addition, because of the increased pump capacity
requirements, installation costs, and loop leaking potential, glycol
heat-tracing along a length greater than 600 to 900 metres is rare.
Heat Tape
The second heat tracing method requires placement of a heat tape (a
wire imbedded in a rubber type compound) alongside the supply pipe. If
some sections of pipe are especially susceptible to freezing, the heat
tape may be applied to only those areas of the pipe. There are several
disadvantages of this method including: the system will not function
if power is interrupted, thermostat malfunctions can result in
overheating or under-heating in the system; or wires inside the tape
can short circuit or break without detection, allowing the water to
freeze. For safety and fire-prevention reasons, ground fault
interrupters should be used with all heat tape installations.
Ordinarily, the heat tape does not last as long as the pipe. The
vulnerable areas may have to be excavated more frequently to replace
the tape. This is expensive and inconvenient. Even with surface
monitoring, the pipes would still have to be excavated on an emergency
basis.
Please note: Every fall, carefully inspect any heat tape before
using. As with any electrical cord, connections or insulation can
erode creating a potential hazard.
In-Line Heat Tracing
The third method of heat tracing is called "In-Line Heat
Tracing". Several communities in northern Manitoba have used this
method; one northern community has successfully used this method for
the last ten years. A 5/8 inch copper pipe (refrigerant copper pipe)
is placed in the water supply pipe. Inside the pipe is an electrical
heat tape which can run to a maximum of 180 metres (600 feet). If the
tape fails, it can be replaced without digging up the entire length of
affected pipe. Access to the heat tape is through the connection point
between the water supply line and the copper pipe. If the electricity
is interrupted, the heat tape can thaw any ice that forms. The copper
pipe is flexible, so it does not break when frost heaves occur. The
Canadian Standards Association has recently approved heat tape without
the copper pipe container for use inside water supply pipes This
should result in an approximate 50% decrease in cost for the in-line
system.
Water Heating
Some communities heat water in boilers to about 4 degrees C before
distribution through the supply system. This method is used in
conjunction with other systems, especially when challenging freezing
problems occur. This system works well in some areas, but the energy
and maintenance costs can be considerable.
Pump-back Reservoir Systems
Reservoir systems consist of a tank with a pump attached. The tank
and pump are located inside the house and are connected between the
municipality's pipe supplying the water and the house's supply pipe.
The tank gradually fills; if the household does not use the water, it
is pumped back into the municipal supply pipe. The system uses
household heat to increase the water temperature so the water will not
freeze when pumped back into the supply pipe. This system wastes no
water, but each unit is quite expensive.
However, the householder must maintain the unit. If the householder
unplugs the pump, or there is a power failure, the tank will drain,
and water will flow to the drain at a preset rate. The result is a
continuous bleeder for the duration of the power interruption. One way
to ensure that the units are maintained and are not unplugged is to
install water meters, and to charge for water use by the unit.
There are industrial versions of this technology, which may be more
effective in saving water overall. Because of the cost, industry has
only installed them if there was a serious commitment to water
conservation.
Utilidor
An expensive but effective way to solve all these challenges is for
the community to build a utilidor. This heated tunnel can house all
utilities (electrical, gas and water), thereby making them easily
accessible for installation and maintenance. If sufficient in size, it
can also be used as a pedestrian passageway between buildings.
Conclusion
All of these freezing prevention strategies have strong and weak
points. They will reduce the incidence of frozen pipes during our cold
winters. However, all methods described may still leave supply pipes
susceptible to freezing. Therefore, provisions should ALWAYS be made
so that a frozen pipe can be thawed as easily and economically as
possible. A cost/benefit analysis may be useful to help determine
which technique or set of techniques will provide the most favourable
investment for a particular community.
The occurrence of frozen water supply pipes can be reduced
substantially while also reducing water and energy waste. Improving
efficiency of water use can decrease costs of water and wastewater
handling, and assist in protecting the environment.
Inquiries on Manitoba's Water Use Efficiency Program may be
directed to the Water Use Efficiency Coordinator at:
Pollution Prevention Branch
Manitoba Environment
123 Main Street
Suite 160
Winnipeg MB R3C 1A5
Telephone: (204) 945-8980
Toll Free: 1-800-282-8069, ext. 8980
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