Industry Research Leads to New Insight on Optimum Pipe Sizing

After extensive research and analysis, IIAR’s Ammonia Refrigeration Foundation has released new information on the economics of piping selection and on the proper selection of ammonia wet suction risers, which can help end users prevent oversizing of piping and using more energy than is necessary.

The research and analysis projects resulted in new information that has been incorporated in the new IIAR Piping Handbook, as well as in three new software tools available with the purchase of the new handbook.

The results of two ARF-funded research projects have been used to improve the information found in the newly published IIAR Piping Handbook, said Bruce Nelson, president of Colmac Coil.

“The first study, ‘Development of Void Fraction Correlation for Ammonia Twophase Flow in Risers’, conducted by Dr. John Thome, used pressure-drop data collected during an ASHRAE-ARF co-funded research project (RP-1327) conducted at the Danish Technological Institute – DTI,” Nelson said. “This research project provided a new method for proper and accurate sizing of ammonia wet suction risers based on measured data.”

Nelson said the second study, “Optimum Pipe Sizing” conducted by Robert Sterling, president of Sterling Andrews Engineering PLCC, examined, corrected and expanded the work on economic pipe sizing developed by Bill Richards for the original Piping Handbook.

“Chapter 1 in the IIAR Piping Handbook now reflects work done over many years by many people,” said Gordon Struder, director of advanced engineering for EVAPCO and chairman of IIAR’s piping committee.

Multiple studies and ongoing analysis lead to the findings. Struder said the work started as a research project funded by ASHRAE sponsored by the TC 10.03 refrigerant piping group. As part of that study, the Danish Technological Institute conducted testing and acquired data on a two-inch and four-inch wet vertical suction riser section. “The research project started more than seven years ago. IIAR continued the research with funding from the Ammonia Refrigeration Foundation,” Struder explained.

ARF continued the study and used the information for the suction-riser sizing method developed by Thome.

Struder said this is the first time the IIAR Piping Handbook has covered two-phase ammonia upward flow in refrigerant piping. “From my perspective, this has really consolidated the industry knowledge that was out there and provides a very reliable method to calculate pressure drop regarding a wet vertical riser pipe. This has never been available before in the piping handbook,” he said.

As part of the project, IIAR developed equations and created software that users can access to predict the appropriate pipe sizes for their system design, Struder said.

The second ARF-funded study on “Optimum Pipe Sizing”, done by Sterling, also made an important contribution to the new Piping Handbook, not only in the form of the equations and explanations contained in Chapter 1, but also in the form of a new easy-touse software program, Nelson said.

“The selection software was part of the end goal of the study, so that methods developed in the research could be applied quickly and easily by an informed user,” Sterling said. “It is fairly simple, requiring a number of inputs like line type (suction, liquid, hot gas, etc.), energy rates, labor rates and insulation thicknesses, and, using industry data, calculates the optimum pipe size based on cost of ownership for a user-defined system life.”

Sterling explained that using a computer to look at different options can quickly give a design team a lot more insight – from an overall standpoint — on how sizing impacts what they’re doing for a particular system. The software allows the designer to measure the cost of ownership, rather than just looking at pressure drop or velocity.

Sterling added that the study was important because the original method and sizes were developed at a time when it was impractical to do a detailed analysis of energy costs, material costs, and labor rates, utilization of the system, and system design life as they impact the cost of owning a particular section of pipe.

“It is obvious in hindsight, but nevertheless one of the important findings was that for a given peak load, for the same size and length of pipe in two different installations, cost of ownership can vary widely. The best pipe size isn’t always straight forward,” Sterling said.

“The energy impact when choosing a particular pipe section can vary widely with what you’re doing with that pipe. A certain pipe designed for a certain peak load may be used a little or a lot, may be harder or easier to transport or install, etc.,” he said.

Design benchmarks, rules of thumb and project costs can vary widely from firm to firm, and there is really no benchmark as to how to design a piping system, Sterling said.

The outputs are based on a 100-foot section of piping, Sterling explained. “It is up to the user/system designer to take that information, which is actually only a piece of the puzzle, and incorporate it into an overall project strategy that considers many other factors. The software can’t design a system, it can only give a single piece of information, which according to the inputs is the present value of owning a particular section of piping,” he said. In order to ensure that documentation of various scenarios is possible, it also includes a feature that prints a table of software inputs and outputs for any particular ‘run.’”

“I can’t speak for the Research Committee, but in my opinion, having a stake you can put in the ground and compare different options based on a range of factors that give a hard number as to what it may cost for an owner to buy this particular piping section and own it for the life of the system is important. There is always value in identifying things like energy penalties that are hidden when just looking at first cost and using an industry-available tool to flush out the information,” Sterling said. “Even if the particular costs are not 100% accurate, comparing them among various designs can give an idea of what the best choice is, and that’s important in my view.”