Finding The Balance Between Performance and Cost

Subscribe to our Blog here. In the mechanical industry, we often strive to find the right balance between economical (i.e., cost savings) engineering and optimal performance. Often times, this leaves engineers, building owners, specifiers and contractors struggling to pick between saving money and maximizing performance as they aim to do what is best for their customers while simultaneously providing a robust system with reliable longevity. Coupled with this challenge are the ever-present and ever-evolving building code requirements that are constantly adapting to accommodate new technology, legislation, energy saving standards, green building requirements, LEED accreditations, etc. This leaves many designers hard-pressed to figure out where to cut costs, and it can frequently lead to “value-engineering” (choosing the lowest-cost system available for the job). 

In terms of mechanical systems, value-engineering can be a costly mistake when done improperly.   For example, if system designers specify insufficient insulation, or neglect to specify insulation at all, the long-term costs can start to add up from day one.

Unfortunately, value-engineering often arises from the common misconception that two materials are interchangeable. A perfect example of this misconception is using uninsulated Polypropylene-Random (PP-R) in place of insulated pipes. PP-R is a robust plastic alternative to metal piping. It is a very appealing product because it is not only non-corrosive, but it is also a better insulator than a bare metal pipe. At smaller diameters, the insulating value of PP-R is sufficient enough that, insome applicationsthat operate at ambient conditions, insulation may not even be necessary. However, in mechanical applications where the liquids in the pipes are above or below ambient temperatures, the game changes. In such instances, the insulating value of PP-R by itself is insufficient to ensure ideal performance in terms of energy savings, system optimization, and even code compliance.

For example, the table below compares the heat loss of bare steel pipes to PVC, PP-R and insulated PVC and steel pipes in a system that operates at 140°F. 

The results clearly show that the PVC and PP-R are inherently better insulators than bare steel, demonstrating 25% and 35% (respectively) better thermal efficiency.  However, when compared to the 85% increase in thermal efficiency that insulation provides, the insulating value of standalone PVC or PP-R appear comparably less-efficient for this application. While PP-R is certainly a better insulator than bare-steel pipes, it is dramatically less robust than an actual insulation.  Additionally, in order to meet ASHRAE Energy Standard 90.1, any pipe (metal or plastic) carrying fluids above or below ambient temperature needs additional insulation. In terms of PP-R, it also does not have the high-temperature performance required for steam temperatures, and for these reasons, it is not recommended for steam piping.1” pipe | 140°F process temp | 70°F ambient Temp
Calculated using North American Insulation Manufacturers Association’s (NAIMA) 3E Plus software

Bear in mind that this disparity in thermal performance doesn’t just apply to above-ambient applications. PP-R piping without an insulating jacket has often been used in chilled water applications, under the assumption that the insulating value of the plastic will be sufficient to maintain process temperatures and prevent condensation. Unfortunately, as shown below, this is not always the case.

At design conditions of 50°F process water temperature, 75°F ambient air temperature, and 50% relative humidity (which are fairly ideal mechanical room conditions), condensation will form on 2” iron and copper pipes as well as PP-R pipes*. In these circumstances, the only thing that will prevent condensation is a sealed insulation system with a vapor retarder that greatly reduces moisture drive. For this reason, ASHRAE 90.1 calls for 1” of pipe insulation on any 2” pipe that is operating at the conditions listed above.

*Calculated using NAIMA’s 3E Plus software

System performance is not the only thing that suffers in an uninsulated, value-engineered system. The energy lost due to sub-par performance can add up quickly in terms of dollars. Below is a table that shows, in dollars, the significant savings that insulation can offer on both steel pipe and PP-R.

Without and with 2” insulation (Micro-Lok HP) per ASHRAE 90.1 2013 for 2” pipe
170oF hot water process temp | 75oF  ambient air 

Calculated using North American Insulation Manufacturers Association’s (NAIMA) 3E Plus software

Given that this circumstance is referencing dollars saved perfootper year, savings on a fairly normal sized system could easily climb into the thousands of dollars over the course of one year.

As we all navigate the battle between minimizing cost and maximizing performance, it is critical to ensure that we understand what exactly the material specifications mean in terms of how it will perform in the application and what that means for your customer’s return on investment (ROI). If you have questions about whether your system requires insulation, contact us, and we’ll be happy to put you in touch with a specifications expert who can help you determine what your system needs.