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Plumbing News
Plumbing Study Shows
Higher Flow Velocities and Right-Sizing Design Strategies Key to
Building Water Quality.
A new study from the Plastic Pipe and Fittings Association,
conducted by researchers at Drexel University suggests higher flow
velocities and smaller diameter plumbing results in better building
water quality.
The Premise Plumbing Flow Rates, Linear Velocity, and Nitrification
study, sponsored by the Plastic Pipe and Fittings Association, is a
crucial first step toward the ultimate goal: obtaining clear,
realistic and holistic scientific results to support the safe and
appropriate right-sizing of North American water distribution
systems and improving plumbing design in model plumbing codes.
The Drexel research team investigated key proxies for water safety
and biological activity in plumbing systems, including the impact of
flow velocity on biofilm activity and the oxidation of ammonia, also
known as nitrification, as well as the potential emission of
pathogens from pipes. Tests were conducted on multiple materials.
Pipes made of copper, PEX, and CPVC, were flushed five days a week
or once a week and the discharged water analyzed.
Critically, researchers utilized a pre-existing, aged-in-place,
single-pass plumbing system rig supplied with municipal chloramine-treated
water. Prior studies have not typically examined the impact of
velocity on biological water quality in real building systems, as
they were often conducted in non-plumbing systems, with new pipes,
or with synthetic recirculating water, and did not represent a real
plumbing system.
Key Study Findings:
Higher flow velocity generally leads to better water quality,
with higher residual disinfectant levels, less degradation of
ammonia, lower turbidity (cloudiness) levels, and lower adenosine
triphosphate (ATP) levels, which indicates the presence and quantity
of microorganisms. This suggests that higher flow rates can help
scour the biofilm, potentially alter the morphology (the form,
structure, and outward appearance) of the biofilm and reduce
microbial activity and nitrification.
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The most significant benefits for biofilm
control are found in smaller diameter pipes (3/8") with
high flow velocity.
Frequent flushing is crucial for maintaining water quality.
Pipes flushed only once a week tended to reach a similar
state of disinfectant loss and nitrification progression,
regardless of pipe material, diameter, or velocity. This
highlights the importance of regular water use or flushing
to prevent water quality degradation due to stagnation.
Deciding on the ideal plumbing system design involves
weighing multiple factors, including cost, durability, and
water quality considerations.
• Although copper pipes provided some level
of microbial inhibition for ammonia, the report cautions
that copper might selectively favor the growth of
opportunistic pathogens such as Legionella.
• In low-use conditions, cloudiness and
opaqueness (known as turbidity) were substantially higher in
copper pipes compared to PEX and CPVC.
"The study clearly demonstrates that flow velocity in
plumbing systems is a critical factor in maintaining water
quality and provides significant evidence for pipe
selection," said Mike Cudahy, Codes and Standards Specialist
of The Plastic Pipe and Fittings Association. "We hope it
will serve as an aspirational starting point for future
scientific studies by other researchers to focus tests on
realistic water sources and plumbing scenarios.”
Further work is needed to understand the generality of the
results from this study, explore additional factors such as
water temperature, and to develop evidence-based guidelines
for building plumbing system design and operation.
About the Plastic Pipe and Fittings Association
Established in 1978, the Plastic Pipe and Fittings
Association (PPFA) is a trade organization that represents
manufacturers and suppliers of plastic piping systems. PPFA
works collaboratively with federal, state, and local
regulatory bodies to help develop and implement effective
standards and regulations. Learn more at
https://www.ppfahome.org.
About Drexel University
Drexel University is a comprehensive global research
university ranked among the top 100 in the nation. With over
21,000 students, Drexel is one of Philadelphia's largest
private universities and a major driver of economic
development in the region. Drexel is characterized by its
focus on innovation, real-world application of knowledge,
and commitment to community engagement. |
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