Part 1 Case Study: Economic Justification for Replacing Ice-Laden Refrigerant Pipe Thermal Insulation

Gordon H. Hart

June 1, 2015

Introduction

In 2011, following a severe hail storm, the owner of a large food-processing plant discovered that the thermal insulation systems on his roof-top ammonia refrigeration pipes had been badly damaged. A subsequent inspection conducted soon after the storm by the building owner revealed that the pipe insulation was ice laden and/or soaked with water after its 15 years of continuous service. To remedy the situation, the owner hired an insulation contractor to replace the ice-laden and wet insulation over the course of several years, as his budget and schedule would allow, using a different insulation system design. After the owner made the decision to replace the old insulation system with new materials, an energy analysis was conducted to determine the cost effectiveness of that replacement based on the value of energy saved and the cost of replacement. The decision to replace the original insulation system with a new one of a different design was made solely by the facility owner. The author had no role in that decision or recommendation. It should also be noted that the type of replacement insulation used, polyolefin, is no longer commercially available.

Description of the Refrigerant Pipes and Original
Thermal Insulation

The damaged pipe insulation was located on the roofs of 2 food-processing buildings, located adjacent to each another in central South Carolina. The affected ammonia pipes included suction lines with a design operating temperature as low as -25°F, hot gas lines with a design operating temperature of 60°F, and others with design operating temperatures that fell between these 2 extremes. Pipe sizes varied from as small as ¾-inch nominal pipe size (NPS) to as large as 12-inches NPS. In total, there were 4,756 lineal feet of pipe requiring insulation system replacement servicing 39 roof-top evaporators on the 2 buildings.

The original pipe insulation system consisted of extruded polystyrene (XPS) foam covered with an All Service Jacket (ASJ) vapor retarder plus vapor retarder mastic in the fittings. This type of ASJ is a laminate of white Kraft paper (on the outer surface), glass fiber scrim reinforcement, and thin aluminum foil with a thickness of 0.00035 inches. The ASJ was sealed using ASJ tape, a tape made of the same materials as ASJ and with a pressure-sensitive adhesive inner surface. Note that the use of ASJ on outdoor refrigeration pipes is not recommended by the current International Institute of Ammonia Refrigeration (IIAR) Ammonia Refrigeration Piping Handbook, Chapter 7.1 The straight pipes were then covered with 0.016-inch-thick aluminum protective jacketing with fittings covered with 0.020-inch-thick polyvinyl chloride (PVC) molded fittings as the protective jacketing. Note that the use of PVC jackets on outdoor applications is also not recommended by the Ammonia Refrigeration Piping Handbook, which recommends the use of 0.030-inch-thick, rather than 0.020-inch-thick, PVC.2 Pipe supports, on the mostly horizontal pipes, were insulated with the same type of insulation, ASJ vapor retarder, and protective jacketing. Figure 1 shows an array of several of the affected insulated roof-top refrigeration pipes.

Condition of the Original Refrigerant Pipe Insulation

The damaging hail storm occurred in the spring of 2011. Prior to that, the facility owner had noticed that some of the PVC fitting covers had been damaged before the storm. Following the storm and upon inspection of the pipe insulation, the facility owner noted that even though some of the metal jacketing had holes punched in it by the storm, and these holes had gone through the ASJ vapor retarder jacketing, the ASJ had been damaged–apparently by moisture–in other locations that were not hail damaged. Observing the insulation to be ice laden or very wet in most locations inspected, the facility owner decided that all the original pipe insulation materials needed to be replaced. Note that the author had no role in that decision, in the selection of the new insulation system design, or in the selection of the contractor.

The insulation system replacement started in late 2012. About a year later, I had the opportunity to inspect some of the original pipe insulation system that was being removed and replaced with a new insulation system. The inspection occurred during the late fall of 2013 on a day when the absolute humidity was low and the bare pipes, which were charged, would not experience much surface condensation while bare. The original pipe insulation was heavily ice laden. Due to this condition, the insulation contractor’s insulators were observed using hammers and chisels to chip the insulation away from the pipe until it was bare and cleaned of most ice and insulation. In this laborious process, the insulator team worked on several lineal feet at a time so as not to leave a large length of the pipe exposed to the ambient humidity for more than half an hour. (See Figures 2—4 on pages 16 and 17.)

This observation showed that the original insulation was ice laden. The ice extended from the pipe surface to the insulation outer surface. The ASJ, after visual and physical inspection, was very wet, but not frozen.

As mentioned earlier, some of the PVC jacketing on insulated fittings had been damaged by the hail storm. This is illustrated by the photograph in Figure 5.

The XPS polystyrene insulation, with a water vapor permeance of 1.5 perm-inch and a water absorption of 1.0% by volume, cannot by itself prevent vapor migration from the ambient to the pipe, and its subsequent absorption by the insulation.3 This insulation requires a high-performance, continuously sealed vapor retarder. The ASJ vapor retarder on the straight pipes, combined with the vapor retarder mastic on the fittings, clearly did not perform sufficiently, resulting in a total pipe insulation system failure due to water-vapor intrusion and absorption by the insulation. Perhaps this explains why the Ammonia Refrigeration Piping Handbook recommends against the use of an ASJ vapor retarder on straight pipe and PVC-fitting covers that are exposed to the weather. 4 What the facility owner acknowledged is that after 15 years, the insulation system became saturated with ice, water, or both, and it needed to be replaced to perform effectively. Furthermore, the facility owner concluded that replacement by the same insulation system design (i.e., including insulation, ASJ vapor retarder, mastic, PVC fitting covers, and jacket) would likely result in a recurrence of this moisture failure. Consequently, he selected a new insulation system design using different materials and decided to spend a considerable about of money to have this insulation system replacement performed.

Description of the Replacement Pipe Insulation and Replacement Process

Following the removal of the original pipe insulation, the insulators installed new replacement insulation of the same thickness as the original. The replacement material selected by the facility owner was polyolefin insulation, sometimes also referred to as polyethylene insulation. The material installed meets or exceeds the performance requirements of ASTM specification C1427.5 Per the ASTM specification, this insulation material has a water vapor permeability less than or equal to 0.05 perm-inch and a water absorption by submersion performance of less than 0.2% by volume. The insulation manufacturer’s product data sheet gave even lower values, of 0.048 perm-inch and 0.05% by volume, respectively. It was noted earlier that the insulation manufacturer no longer manufactures and sells this product (it has not been commercially available as of October 2014). The vapor retarder installed is a 4 mil-thick polyvinylidene chloride (PVDC) film that meets or exceeds the requirements of ASTM specification C1136, Type XIII.6 It has a permeance less than or equal to 0.1 perm and, as a homogeneous material free of paper (i.e., it is not a paper-containing laminate), can be sealed tightly with matching PVDC tape that has a pressure-sensitive adhesive. The new 0.016-inch-thick aluminum jacketing meets or exceeds the requirements of ASTM specification C1729 Type I Class A.7

During installation, the insulators secured the insulation on the pipe with strapping tape. When installing the outermost layer of the 2-layer insulation system, the insulators applied a sealant to the butt and lap joints to prevent moisture intrusion beneath the outer layer, should water vapor bypass the vapor retarder film. While the use of the sealant may not have been necessary, since the sealed PVDC film vapor retarder should suffice in excluding water vapor intrusion, the sealant use was a design decision made by the facility owner, not by the author. Thus, this replacement insulation system has a double vapor retarder, the first being the 4-mil PVDC film (with a permeance less than or equal to 0.01 perm), and the second one being the outer inch of polyolefin insulation (with a permeance less than or equal to 0.05 perm). This constitutes a redundant vapor retarder system. While perhaps not necessary, redundancy can be valuable under certain circumstances, such as following a future damaging hail storm.

Cost of the Pipe Insulation Replacement

The facility owner received a price from the insulation contractor to remove the original insulation system and replace it with the new insulation system described for about $550,000, including the material and labor to remove and discard the old insulation, and material and labor to install the new insulation, as well as contractor overhead. As of the fall of 2013, when I observed the insulation system replacement, much of this work had already been completed, with the remainder scheduled to be completed by early 2015.

So, the question remains, was this insulation system replacement worth the money? Stay tuned for the second and concluding part of this case study in the July issue of Insulation Outlook, where the energy savings from the pipe insulation system replacement will be addressed.

References:

  1. International Institute of Ammonia Refrigeration, 2014. Ammonia Refrigeration Piping Handbook, Chapter 7, “Insulation for Refrigeration Systems.”
  2. Ibid.
  3. ASTM International, “Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation,” ASTM C578, ASTM International, West Conshohocken, PA (2014).
  4. International Institute of Ammonia Refrigeration, 2014. Ammonia Refrigeration Piping Handbook, Chapter 7, “Insulation for Refrigeration Systems.”
  5. ASTM International, “Standard Specification for Extruded Preformed Flexible Cellular Polyolefin Thermal Insulation in Sheet and Tubular Form,” ASTM C1427, ASTM International, West Conshohocken, PA (2013).
  6. ASTM International, “Standard Specification for Flexible, Low Permeance Vapor Retarders for Thermal Insulation,” ASTM C1136, ASTM International, West Conshockhen, PA (2012).
  7. ASTM International, “Standard Specification for Aluminum Jacketing for Insulation,” ASTM C1729, ASTM International, West Conshohocken, PA (2014).