Avoiding Condensation on Systems that Operate at Below-Ambient Temperatures
Mechanical insulation on any type of operating system requires continual supervision and maintenance to perform properly. Unfortunately, insulation is often overlooked or taken for granted, despite the fact that insulation offers the simplest, most economical opportunity to save energy costsif it is maintained. Insulation on systems that operate at below-ambient temperatures is prone to condensation (i.e., moisture), and the issues associated with moisture require regular inspection and maintenance. Even isolated damaged insulation on a system that operates at below-ambient temperatures (i.e., cold water, chilled water, refrigeration, and duct work), if left unrepaired, can cause a failure of the total system, resulting in costly repairs and downtime to the system. An understanding of condensation will help prevent future problems.
Proper System Design
The first step in minimizing maintenance on an insulation system is proper design. One aspect of proper design is to consider the availability of maintenance on site. If it is known
that little or no maintenance is going to be available, a more durable insulation system should be specified. Some insulation systems are much easier to repair if they are damaged by mechanical abuse, and should be given a high priority if in-house maintenance is limited. Various insulation materials will respond differently to the same set of conditions. For example, at higher temperatures, even short-term spikes consider defrost cycles on refrigeration linescan cause certain insulations to fail (melt). Systems that cycle from hot to cold will experience more stress on the butt joints, and insulation with a low modulus (low force to expand and contract) will exhibit less joint separation. With constant mechanical abuse, a brittle material will break. After compression, many materials will not recover their thickness. Even though warnings can be posted not to
walk on the insulation or lean ladders against it, if this type of mechanical abuse is possible, the insulation system and the protective jacketing specified should be designed to withstand this type of abuse. If the insulation specified requires a vapor barrier or jacket, it has to be as strong and damage resistant as the insulation. In fact, it is more
critical that the vapor barrier and/or jacket can withstand the mechanical abuse in order to protect the insulation inside. To reduce the effects of isolated damage to the insulation, vapor dams that limit the spread of moisture in the system should be specified in the design.
The second step to proper maintenance of a cold system is regular inspection. Usually this involves a visual inspection looking for insulation or jacketing that is wet, has ice buildup, indications of mold growth, or mechanical damage. The use of infrared meters to detect surface temperature variations or moisture meters is generally uncommon. In many situations, visual inspection is difficult because the insulation is hidden behind walls, ceilings, or is jacketed. In these situations, one needs to look for signs of moisture such as stained ceiling tiles, etc. It may be necessary to remove the insulation in a small section to properly inspect it. If vapor dams (water stops) are used, it will be possible to limit the repair to a damaged section. When it comes to insulation system failures, there are basically 2 general types of failures that can occur on a system that operates at below-ambient temperatures. It is important to understand why the system failed in order to perform proper maintenance.
Condensation Formation on the Surface of the Insulation
Condensation will occur if the operating conditions (including environmental conditions) exceed the design conditions. Condensation may not be able to be completely eliminated on a below-ambient system 100% of the time, especially in an outdoor system or an indoor system that is exposed to unconditioned air periodically. At some point in time,
the relative humidity will exceed the design conditions. This is referred to as casual condensation, which usually does not cause a major problem since it occurs for a relatively short period of time and dissipates quickly. The type of insulation and jacket specified can minimize the effects of casual condensation. If the insulation selected is a closed cell material, the issue of casual condensation is minimized, since the insulation is inherently resistant to moisture absorption, even without a jacket. If a jacket or moisture vapor retarder is required for the insulation, a jacket should be used that provides a 0.02 perm-inch rating (as per ASHRAE 2013 Handbook of Fundamentals, Chapter 23), is more puncture resistant, and is completely adhered to the insulation.
There are several options to remedy the problem of casual condensation: add another layer of insulation; install a drip pan to catch the condensation; provide for additional
air movement (i.e., a fan) during high humidity conditions; and determine if the insulation or jacket emissivity could be an issue. The aforementioned remedies may be able to mitigate any issues resulting from casual condensation.
Condensation Formation Between the Insulation and
When moisture is found between the insulation and the pipe, generally the only remedy is replacement, unless the failure is detected very early. This scenario is frequently the result of an open seam (butt joint, longitudinal seam, or termination point) or damage to the jacket (seams are most susceptible to damage). This type of damage often occurs at fitting locations (i.e., tees, elbows, valves, etc.); damage at these locations is the worst case scenario as it is hardest to detect and most difficult to remedy. It is especially difficult to detect if the insulation has been lagged, jacketed, or covered in any way.
Once the moisture penetrates the insulation, it reduces the thermal conductivity of the insulation, which results in condensation being formed under less severe conditions and
before long, the insulation is waterlogged. Most insulation systems are designed to prevent moisture penetration and thus, they also prevent moisture from leaving the insulation if it becomes wet. In most cases, this type of failure will require the removal of insulation unless it is detected very early.
Preventing Damage on Below-Ambient Systems
It is important to commit to ongoing inspection of insulation for damage or open seams that will result in condensation formation (i.e., moisture or ice). These must be immediately assessed and repaired in a timely manner before further damage is done. Moisture tends to travel to the lowest point and will accumulate there, drip by drip, which will result in a major problem. The damaged seam is often not in the same location as the buildup of moisture, and the insulation is usually behind a sealed wall and is not easily inspected. Any sign of moisture (water-stained walls or ceiling tile), or mold growth, is probably an indication of insulation failure resulting in moisture formation. One note of caution, mold remediation is not a job for amateurs. Mold is susceptible to becoming airborne and spreading rapidly if the remediation is not done properly. If the insulation is jacketed, any damage to the jacket or jacket seams must be investigated further to determine if there is any damage to the insulation (moisture intrusion).
The aforementioned steps—proper design and periodic inspection—are essential to minimizing damage on below-ambient systems. By understanding the 2 types of failures that can occur on systems that operate at below-ambient temperatures, you can better understand remedies that can be used to mitigate the problems. Ongoing inspection and timely repair of any damage are key to maintaining the performance and safety of the operating system. If the insulation system is properly designed, maintenance and repair an be kept to a minimum.