Data centers must assure not only the integrity of the data they process and store, but the integrity of mechanical systems that drive their operations. While designers’ thoughts often turn to security technologies, climate control and uptime metrics, passive elements of the data center are essential to high-performing facilities. This article will cover several factors to consider when designing insulation systems for the pipework that circulates chilled water throughout the data center.
1. Heat and H2O
To appreciate the importance of insulation, keep in mind two obvious but omnipresent threats in the data center environment: heat and water. Managing tremendous levels of heat generated by equipment and servers is essential. Unlike domestic computers that are cooled by fans, data center servers make use of extensive liquid cooling systems that cool using principles of HVACR systems.
Then, there's the water risk to consider. Water poses a tremendous hazard to computing equipment. Data centers typically require more sophisticated sprinkler systems or alternative systems to those used in commercial buildings. Insulating the piping is essential to support the thermal performance of the system — keeping the cold water cool and managing moisture associated with vapor drive.
Data centers can require 100 to 200 times as much energy as a typical commercial building, highlighting the importance of every element that can help maintain or reduce energy consumption. This includes the insulation used on chilled water systems. Cooling systems face potential damage from heat exchanger inefficiency, dust, and moisture ingress. This can reduce the life span of installed insulation and reduce heat exchanger efficiency. It is possible to design an insulation system to account for these challenges. The process starts with selecting the correct materials to mitigate risks.
2. Ask, “What Could Go Wrong?”
Insulation for chilled water cooling systems in data centers is often designed around average ambient working conditions. It can be more cost-effective, however, to develop the system for common “worst-case” scenarios, such as power outages, high ambient temperatures, or other severe weather. Added benefits of designing for more rigorous conditions include increased system life span coupled with a reduced need for repair or retrofit work. Taking a moment to ask “what could go wrong?” at the outset can help form strategies to mitigate future problems and reduce future repair costs.
Repairing or retrofitting a chilled water insulation system can be more expensive than starting with a properly designed system intended to function through more rigorous conditions. Insulation system replacement could be three to four times the initial cost of the original installation and have add-on consequences.
Selecting insulation for chilled water systems intended to last throughout the life span of the building with minimal maintenance is possible — system elements must be thoughtfully selected, accurately designed, and properly installed. Some insulation materials can be damaged and degrade over time with repeated wear and tear. However, insulation systems using more durable, inorganic materials, like closed-cell, cellular glass insulation, can have a longer life span. Impervious to moisture and trusted in mission critical buildings for decades, cellular glass insulation has demonstrated the ability to remain effective while in place and resist deterioration.
3. Engineer for System Efficiency
Another challenge faced by chilled water systems is to maintain efficiency with limited heat transfer. Inefficient systems must work harder, stressing chillers and requiring more energy expenditure.
One way to protect function is to design an insulation system with the correct emissivity and operating conditions so the outmost edge of the insulation remains above the anticipated dew point at the expected ambient conditions. Maintaining close to the ambient temperature on the outer surface of the insulation system helps prevent moisture condensation and reduces the potential for moisture ingress.
Allowing moisture to penetrate the insulation of a chilled water system has a negative effect on thermal performance of the system. A series of studies done in 2002 and 2012 found that insulation’s thermal conductivity increases when moisture is present. A 1% increase in moisture level within insulation can increase thermal conductivity of the insulation material by 23%. Saturated insulation alters overall energy use and may require the replacement of insulating materials. ASHRAE specifies that the most economical insulation to provide lifetime performance is one with little to no permeability.
4. Solve for What You Can and Cannot See
Chilled water systems face challenges from heat and moisture because of vapor pressure drive or the imbalance in pipe and ambient air temperature. Chilled water pipes often operate in a range from minus 25° to 59°F, potentially below the ambient temperatures in regions where many data centers are located. Facilities in locations with high humidity levels may also face additional vapor pressure from moisture, even if outside temperatures are not high.
Chilled water system pipes can be home to both visible and hidden damage from moisture. Visible damage can show up as the collection of moisture on the outside of the insulation jacket as well as mold or mildew formation on the surface. In facilities with ceiling pipes, external condensation can damage floors, walls, ceiling tiles, or nearby equipment and generate a safety/slipping hazard. Condensation on the outside of pipes also allows for oxidation of galvanized support structures. This type of oxidation may prompt the onset of corrosion within heat exchangers — further restricting the system’s energy efficiency.
Moisture in the hidden areas of data centers is another risk. Moisture seeping into permeable insulation is harder to spot and can create conditions for corrosion under insulation (CUI). Forming on chilled water piping, CUI can potentially cause leaks requiring unexpected downtime and significant repair costs. Corrosion in the facility can even impact performance of server equipment. Insulation damage can increase heat transfer, meaning more energy is needed to maintain the operating temperature of the chilled water. This adds stress to chillers and increases operating cost.
5. Spec Materials With Ancillary Benefits
While thermal performance and moisture resistance are key factors contributing to the effectiveness of an insulation system, there are additional factors. Insulation jacketing is a good example. Any damage to the outer jacketing or applied moisture barriers can allow moisture to collect or seep into the system. Installing an impermeable, nonabsorbent product provides an additional level of protection by resisting moisture ingress.
Another factor to consider is combustibility. Selecting insulation that will not burn or generate noxious smoke during a fire is advantageous. Data centers — like all buildings — will always look to materials that minimize risk of fire. In addition to being impermeable and non-wicking, cellular glass insulation can contribute to a strategy that addresses fire and smoke concerns.
Compressive strength is important on chilled water applications, since many of these systems are designed with the load of the pipe and contents supported by the insulation itself. Insulation with a high compressive strength can be used on pipes that are above ground, at ground level, or recessed. It also increases the ability of the insulation system to withstand external weight. Cellular glass insulation is rigid, has a high compressive strength, and is not subject to deflection, making it well-suited for use at insulated chilled water pipe supports.
There are several design elements to consider when selecting insulating materials for data centers, including life span, control of heat gain, and moisture vapor pressure, as well as the physical location of the insulated system within the facility. Selecting nonpermeable cellular glass insulation can help facilities address these challenges while preserving system function and thermal efficiency.