Condensation Control on Chilled Water Systems: Getting Cold Insulation Right

If you have read our article on corrosion under insulation (CUI), you will know that moisture is the great enemy of any insulated system. On hot pipework, the challenge is keeping external moisture out. On cold systems — chilled water, refrigeration lines, and cold process piping — the problem is fundamentally different. Here, the moisture is already in the air around the pipe, and the laws of physics are actively driving it towards the cold surface. When the pipe surface temperature drops below the dew point of the surrounding air, water vapour condenses into liquid. In Ireland, where relative humidity sits between 75% and 90% for most of the year, this happens rapidly and relentlessly on any cold surface that is not properly insulated.

Why Condensation on Cold Systems Matters

Condensation on chilled water pipework is not merely an aesthetic nuisance. Left unchecked, it creates a cascade of problems that can be costly, disruptive, and in some cases dangerous:

• Water damage to building fabric — dripping pipes saturate ceiling tiles, stain plasterwork, and damage finishes. In plant rooms above occupied spaces, this is a persistent headache.
• Equipment and electronics damage — critical in data centres, where a single drip from a condensing pipe can destroy servers or network switches worth tens of thousands of euro.
• Slip hazards — water pooling on plant room floors creates an immediate safety risk.
• Mould and biological growth — persistent dampness promotes mould on insulation, ceiling tiles, and surrounding surfaces, compromising air quality in healthcare and pharmaceutical environments.
• Corrosion of pipework and steelwork — just as with CUI on hot systems, persistent moisture corrodes pipes, supports, and surrounding structural steel.
• Electrical safety — water ingress into cable trays or junction boxes can cause short circuits, earth faults, and fire hazards.

In data centres, where chilled water pipework runs close to IT equipment, condensation control is a fundamental design requirement. The same applies in pharmaceutical clean rooms, hospitals, and food production facilities.

The Dew Point: Understanding the Physics

The dew point is the temperature at which air becomes saturated and water vapour condenses into liquid. It depends on air temperature and relative humidity. At 20°C and 60% RH — a controlled indoor environment — the dew point is approximately 12°C. Any surface at or below 12°C will attract condensation. Chilled water systems typically operate between 6°C and 12°C, so the supply pipework is always below the dew point.

In Ireland, real-world conditions are often worse than textbook figures. Plant rooms, risers, and service corridors frequently see 70–80% RH or higher. At 20°C and 80% RH, the dew point rises to approximately 16.4°C — meaning even pipework at 15°C or 16°C will condense. The margin between chilled water temperature and dew point is razor-thin, and in many Irish buildings there is no margin at all.

The primary purpose of cold insulation is therefore not to prevent heat gain (though that matters for efficiency) but to keep the outer surface of the insulation above the dew point, preventing condensation from forming.

Key Principles of Cold Insulation

Cold insulation operates under different rules to hot insulation. On a hot system, the vapour drive is outward — from the hot pipe towards cooler ambient air. On a cold system, it reverses: warm, humid air drives inward towards the cold pipe surface. This reversal changes everything about how the insulation must be designed, specified, and installed.

The vapour barrier is more important than the insulation itself

On a hot system, a small gap means localised heat loss — annoying, but not catastrophic. On a cold system, a breach in the vapour barrier allows warm, humid air to migrate through the insulation towards the cold pipe. As it cools, it reaches dew point and condenses within the insulation — not on the outer surface where you can see it, but inside the material itself. The insulation becomes waterlogged from the inside out, losing its thermal performance and creating exactly the conditions it was meant to prevent.

Closed-cell materials with built-in vapour resistance

Closed-cell elastomeric foams — Armaflex, Kaiflex — are the most common choice for chilled water because each cell is sealed, giving the material intrinsic resistance to moisture vapour transmission. Unlike mineral wool, which relies entirely on an external vapour barrier, closed-cell materials provide a secondary line of defence even if the outer surface is compromised.

All joints sealed with proprietary vapour-barrier adhesive

Every joint must be sealed using the manufacturer's recommended vapour-barrier contact adhesive — not general-purpose tape, not duct tape, not silicone. The adhesive creates a continuous, chemically bonded vapour seal. Self-adhesive tapes can be used over glued joints as secondary protection, but are not a substitute. This is where many installations fail — the material may be excellent, but if joints are not properly glued, moisture finds its way in.

Continuity — no gaps, no exposed pipe, no thermal bridges

Every millimetre of cold pipe surface must be covered. A single exposed section — even a 20mm gap — will condense immediately, and moisture will wick along the pipe beneath the insulation, undermining sections that appear properly insulated. Valves, flanges, strainers, sensors, and all fittings must be insulated.

Pipe supports and hangers need insulated inserts

A bare metal support in contact with a cold pipe acts as a thermal bridge, creating a localised cold spot where condensation forms. Purpose-made insulated inserts (such as Armacell Armafix) must be used to thermally isolate the pipe from its support. Without these, condensation forms at every support point, dripping water and corroding both pipe and steelwork.

Materials for Cold Insulation

Choosing the right insulation material for a chilled water system depends on the operating temperature, pipe size, environment, and criticality of the application. The main options are:

Elastomeric foam (Armaflex, Kaiflex)

Closed-cell elastomeric rubber foam is the most widely used material for chilled water insulation. It has a built-in vapour barrier due to its closed-cell structure, is flexible and easy to work with, has low thermal conductivity (typically 0.033–0.038 W/mK at 0°C), and is available in pre-formed tubes or sheet form. Joints are sealed with proprietary contact adhesive to maintain vapour barrier continuity. Armaflex (manufactured by Armacell) and Kaiflex (manufactured by Kaimann) are the two most commonly specified brands in Ireland and the UK. For most chilled water applications in the 6–12°C range, elastomeric foam in the correct thickness is the standard solution.

Cellular glass (Foamglas)

Foamglas is a rigid, inorganic insulation made from recycled glass with absolutely zero moisture absorption. This makes it the material of choice for the most critical cold applications: sub-zero systems, cryogenic pipework, and situations where long-term vapour barrier integrity is paramount. It is more expensive and requires skilled installation, but for applications where failure is not an option — critical pharmaceutical lines or high-value data centre infrastructure — it provides the highest level of assurance.

Phenolic foam with separate vapour barrier wrap

Phenolic foam (such as Kingspan Kooltherm) offers excellent thermal performance with one of the lowest thermal conductivities available (typically around 0.021 W/mK). On larger pipe diameters where elastomeric foam becomes impractical, phenolic sections with an aluminium foil vapour barrier can be a practical solution. However, the vapour barrier is external rather than integral — any damage to the foil facing compromises the system, so meticulous sealing of all joints and laps is essential.

Mineral wool with vapour barrier foil

Mineral wool with an aluminium foil vapour barrier is the traditional approach, widely used on hot systems. On cold systems, however, it is the most failure-prone option. Mineral wool is open-fibred and absorbs moisture readily — it relies entirely on the integrity of the external foil. Maintaining a continuous vapour seal across all joints, fittings, and support points is extremely difficult in practice. While it can work if installed to an exceptionally high standard, the industry has largely moved towards closed-cell materials for chilled water because the risk of failure is significantly lower.

Common Failure Points

Understanding where cold insulation systems typically fail helps both specifiers and maintenance teams focus their attention on the areas that matter most:

• Unsealed or poorly sealed joints — the most common failure. Joints taped but not glued, or glued without correct tack time, allow vapour migration and internal condensation.
• Damage not repaired after maintenance — insulation removed for valve or sensor access is frequently not reinstated properly. Exposed pipe starts condensing immediately and undermines adjacent insulation.
• Missing insulation at valves, flanges, and fittings — the most difficult areas to insulate, often left exposed. Every uninsulated fitting is a condensation source and moisture entry point.
• Inadequate insulation thickness — if too thin, the outer surface stays below dew point and condensation forms on the insulation exterior. Thickness must account for worst-case humidity, not average conditions.
• Uninsulated pipe supports — thermal bridges that cause localised condensation, dripping, and corrosion at every support point.
• Unsealed terminations — where insulation ends at equipment, walls, or floor penetrations, the termination must be sealed to prevent vapour ingress.

Getting It Right: Guidance for Specifiers and Contractors

Cold insulation is a specialist discipline requiring different materials, techniques, and a rigorous attention to detail. Here is what good practice looks like:

For specifiers and consulting engineers

• Calculate insulation thickness for worst-case conditions — in Ireland, design for 25°C ambient and 80% relative humidity as a minimum for indoor plant rooms. For outdoor applications, consider 90% RH.
• Specify the vapour barrier requirement explicitly — material, adhesive, sealing method at joints, and treatment at terminations and penetrations. Do not assume the contractor will get this right without clear specification.
• Specify insulated pipe supports — include them on the drawings. If they are not specified, they will not be installed.
• Require insulation of all valves and fittings — specify removable insulation jackets for items needing regular maintenance access.
• Require photographic evidence — insist on documentation of vapour barrier sealing before jacketing is applied. Once cladding is on, you cannot verify the quality beneath.

For insulation contractors

• Follow manufacturer's installation guides — Armacell and Kaimann both publish detailed instructions. Adhesive application, open time, and joint treatment are specified for good reason.
• Glue every joint — no exceptions. Apply contact adhesive to both surfaces, allow correct tack time, press firmly, then seal with self-adhesive tape as secondary protection.
• Insulate continuously — do not leave gaps at supports or fittings to "come back to later." Those gaps start condensing immediately.
• Protect finished insulation — elastomeric foam is easily damaged by follow-on trades. Damaged sections must be fully repaired with proper adhesive, not patched with tape.
• Document your work — photograph before concealment by cladding or ceiling tiles. Good contractors take pride in their work.

The Cost of Getting It Wrong

The consequences of poor cold insulation are not always immediately visible, but they are always expensive. Waterlogged insulation must be completely stripped and replaced — it cannot be dried out. Corroded pipe supports need replacing, often requiring scaffolding and system shutdowns. In data centres, a single condensation event can cause equipment losses that dwarf the cost of the insulation system many times over.

Conversely, a properly designed and installed cold insulation system will perform reliably for 25 years or more with minimal maintenance. The additional cost of doing the job properly at installation is a fraction of the cost of remediation. Cold insulation is not an area where shortcuts are recoverable — invest in the right materials, the right details, and the right people.