IIAR Takes on Optimum Pipe Sizing Research Project

A new research project, recently implemented by the International Institute of Ammonia Refrigeration, will revisit the economic sizing methodology the industry uses to determine optimum pipe sizing.

The project, expected to be completed in the next year, will provide a computer tool that will allow end users to determine optimum pipe sizing based on input data that includes the initial cost of a piping system, energy cost, life expectancy and refrigeration system operating efficiency.

The concept of economic pipe sizing was introduced to the ammonia refrigeration industry in 1984 by Bill Richards, one of the founding members of IIAR. Richards initially established the capital cost of piping by looking at diameter and length, and provided corrective factors for piping systems with varied costs relative to a baseline value, while also making adjustments for energy costs and hours of usage.

“This project is intended as an update of Richards’ methods,” said Bruce Nelson, IIAR Research Committee Chair and President of Colmac Coil Manufacturing, Inc. “It is a balancing of the initial cost for a facility with the operating costs.”

For example, a facility could use a small pipe that is cheap to install but has a high pressure drop, so operating costs are higher, or they might go to a large pipe with low pressure drops that is more expensive to install but has lower operating costs.

“This computer tool will help facilities make the decision on how much to spend initially and what the return will be on that investment,” said Nelson.

In the years following Richards’ initial analysis, the cost of electricity for industrial customers has remained flat, but expenses for pipe, labor, fittings and insulation systems has risen dramatically.

And the sizing criterion for portions of piping systems – such as two-phase vertical risers – is not based on economics. Instead, it is dictated by the need to ensure superfi cial velocity during operation to maintain a consistent level of liquid, said Nelson.

In addition, piping in today’s industrial ammonia refrigeration systems are generally in service beyond the 15 years that Richards assumed, and his analysis did not include other key elements of capital costs such as exterior pipe preparation, valves, insulation systems and pipe support infrastructure. It also did not differentiate labor and material costs and quality assurance.

IIAR’s Nelson said the project is intended to deliver recommended pipe sizing tables in the IIAR Piping Handbook that are updated and expanded to account for these new variables.

Under the project, researchers will evaluate and document economic sizing bases for a number of industrial refrigeration piping subsystems, including vapor-only piping, suction piping, overfeed return piping and liquid-only piping, he added.

Initially, Richards assumed piping capital cost in proportion to pipe size. The new project will use current piping system cost data to test this assumption, including materials and labor. The capital cost analysis will also consider specialty piping materials that are commonly used for low temperature piping systems. Stainless steel piping, currently popular among end-users and contractors, will also be studied.

“The funding from ARF and the commitment of our industry is making these types of research projects possible,” Nelson said. “We have a very active research committee with some of the best and the brightest in the refrigeration industry. Thanks to them, we are able to identify and conduct this research, generating valuable information for our members and our industry.”