May 27, 2019 by Lance MacNevin
By its very nature, the engineering profession is based on the constant search for new and better ways of accomplishing a task. However, there is also a well-known human tendency to do things the way we have always done them.
Engineers who design and specify chiller systems find themselves squarely in the centre of these two worlds. Chiller system engineers may be well-versed on the latest advances in chiller and cooling tower technology but may be unaware of the other options for customers when it comes to another critical element of the system – the piping. A tendency to specify steel or copper by rote is understandable, as those are the piping systems used in chiller systems for generations. But there is another option.
Thermoplastic polypropylene (PP) pipe, along with its variants poly¬propylene-random (PP-R) and polypropylene raised crystallization temperature (PP-RCT), are often viewed as “new” or perhaps even as a novelty. However, PP has been used for projects around the world for nearly 40 years and in a range of mechanical, plumbing, and industrial applications in North America for roughly a dozen years. It is engineered to offer unique benefits for mechanical applications (see compliance and resources below).
CHILLER APPLICATIONS FOR PP
PP pipe is hydrophobic and chemically inert making it suited for use in chiller systems. PP material resists any form of change to the material wall, such as scaling or corrosion, which means a consistent flow rate throughout its long life. In addition, chillers operate at temperatures well within the range suitable for PP pipe.
In a chiller system, PP pipe can be used to transport heated water, chilled water, or condensate. Depending on the wall thickness of the pipe (expressed in SDR, or standard dimension ratio, which is a ratio of the wall thickness to the overall diameter of the pipe), many PP piping systems can handle fluids at 100 psi up to 180F, as well as extremely low operating temperatures.
Typically, PP piping includes a fibreglass reinforcement layer that significantly reduces thermal expansion and contraction, keeping it comparable to metal piping traditionally used in these systems. This is also true for low-temp chiller applications where the temperature differential from start-up to operating conditions can be significant.
Chillers are tough and durable pieces of equipment, as is PP pipe with an anticipated lifespan of 50 years or more. Light weight in comparison to other options, PP lends itself well to “real-world” chiller installations.
In addition, as chiller systems become more complex in an era of changing refrigerant regulations and increasing efficiency standards, PP pipe can be used to transport a secondary coolant or refrigerant such as glycol or brine.
Even an excellent chiller system design relies on a contractor’s installation team to see it through. Increased productivity and ease of installation are two benefits of PP pipe.
Joined using heat fusion, the PP pipe can be used almost immediately and the connection process does not introduce any foreign materials into the system. When properly executed, heat fusion joints create a bond as strong as the pipe itself, with no leak paths.
PP offers stable, predictable pricing and has no value to thieves. In addition, PP materials are 100 per cent recyclable.
Although there is a learning curve to working with PP, pipefitters and those already familiar with heat fusion are usually able to run with it very quickly. A factory training typically prepares even the most inexperienced crews to perform heat fusion, which can lead to significant labour savings.
PP pipe’s light weight and versatile orientations available using the fusion process simplify fabrication of custom spools either on the jobsite or remotely. Some manufacturers of PP systems offer design and fabrication services and have BIM files available for their products.
Labour savings of fabrication can be significant. In most cases, the vast majority of fixtures and spools can be fabricated offsite and shipped directly to the jobsite. Thanks to the pipe’s light weight, the fabricated assemblies arrive ready to hang.
KNOW YOUR OPTIONS
Engineers who design and specify chiller systems are responsible for one of the largest investments a building owner or manager will make. Chillers and their components have experienced a host of innovations and advancements in the past several years. Your customers will be well-served to know all their options when it comes to piping, which is an integral part of the chiller system. <>
Lance MacNevin, P.E., is director of engineering for PPI’s Building & Construction Division, focusing on pressure piping materials for plumbing and mechanical systems. He serves on committees within ASPE, ASTM, AWWA, CSA, IAPMO, IGSHPA, NSF, RPA and other industry organizations.
COMPLIANCE AND RESOURCES
Most PP pressure pipe currently available in North America is compliant with the International Plumbing Code; International Mechanical Code; Uniform Plumbing Code; Uniform Mechanical Code; and Uniform Solar, Hydronic, and Geothermal Code for physical properties and temperature and pressure ratings
Check with the manufacturer of the pipe or contact the Plastics Pipe Institute (PPI) before specifying a particular brand. PPI is a trade association representing all segments of the plastics piping industry. The association and its members work together for education, standards development, code updates, and other initiatives to advance the adoption of plastic piping systems.
In late 2017, PPI’s Building & Construction Division formed the Polypropylene Pressure Pipe Steering Committee to reflect the rapid growth and continuing acceptance of PP pressure pipe in the North American market.
PPI offers resources to engineers interested in specifying plastic pipe. The webpage https://plasticpipe.org/building-construction/bcd-pp.html contains technical information, links to product standards, advantages and applications, plus links to member firms that produce PP systems.
In addition, the PPI Plastic Pressure Pipe Design Calculator is a free, online tool that performs calculations for pressure and head loss, thermal expansion and contraction, surge pressures, and pipe weight and volume for plastic piping materials. It is relevant to plumbing, water service, hydronic heating and cooling, snow and ice melting, fire protection and geothermal applications. It can be accessed at www.plasticpipecalculator.com.
PPI’s Hydrostatic Stress Board (HSB) is developing policies for listing long-term pressure ratings of polypropylene pressure pipes, similar to its listing programs for materials such as PVC, CPVC, HDPE, and PEX.