Free cooling is now widely regarded as one of the best strategies to reduce chiller energy consumption. Free cooling saves data center operators a lot of money and energy, as well as enhances the overall Power Usage Effectiveness (PUE) rating of a facility. However, the air-to-water heat exchangers that are a necessary feature of a free cooling system are susceptible to corrosion.
Corrosion is defined as a metal’s reaction to its surroundings. It’s a progressive process that can damage the functionality of a single component or even an entire system over time. Even though corrosion happens everywhere, in theory, specific environmental circumstances might hasten the erosion process significantly.
Corrosion is caused by chemical or electrochemical contaminants in the air, as well as contact between two metals. Air to water heat exchangers can be damaged to the point that they become distorted and airflow blockages diminish a system’s overall operational efficacy. Any material construction damage is frequently irreparable and necessitates costly repairs or replacement.
Types Of Corrosion
Oxygen and acid corrosion are frequent in air conditioning systems put outside. When a metal reacts with oxygen to generate oxides, this is known as oxygen corrosion. The ensuing natural oxide layer protects the inside of copper and aluminum, thus oxidation can even be regarded as advantageous in some cases, but this is the exception rather than the rule. Acid corrosion, on the other hand, is significantly more aggressive than oxygen corrosion processes.
Any emissions, such as nitrogen and sulfur oxides, as well as ammonia, chlorides, and carbon monoxide, combined with copper and aluminum to generate acids that can induce microscopic indentations, can dramaticallyaccelerate the corrosion rate in areas with high industrial pollution. This is known as pitting, and it can cause serious damage in as little as a few months. Locations with substantial industry, high traffic density, or those directlyadjacent to agricultural land provide the highest risk of accelerated corrosive erosion.
Galvanic corrosion can occur when more than one metal is employed in an air conditioning component. When two dissimilar metals come into electrical contact underwater, something happens. Ions of a less noble metal begin to flow towards a more noble metal in the presence of an electrolyte such as saltwater. With the slow disintegration of the substance, the less noble metal gives up electrons and is oxidized. Copper and aluminum components, as well as metal combinations in saltwater-contaminated environments, are particularly vulnerable.
Aluminum microchannel heat exchangers coupled with copper tubes can be severely corroded by galvanic corrosion. Partial pressure losses or even refrigerant leakage might result from the fine microchannels being fractured and blocked. Other factors, such as the use of low-grade metals, increase the danger of corrosion, while surface fractures and holes can allow more water to accumulate, speeding up decomposition. In general, a warm, humid climate with frequent temperature swings raises the danger of corrosion.
Corrosion is also a concern with the water used in water-cooled systems. Precision air conditioners with integrated direct evaporation (DX) refrigeration circuits or chilled water (CW) indoor units connected to a central chiller via air to water heat exchangers are the two main water-cooled systems types utilized in data centers.
Both require an oxygen-tight water circuit that is free of foreign particles and sedimenting chemicals. Corrosion damage can happen in a few years in closed circuits like those found in chilled and cooling water systems. This is an issue since flaked-off corrosion particles can block pumps, filters, and capillaries, in addition to causing pipe damage and leaks.
PH, water hardness, and conductivity are all elements that contribute to the corrosiveness of flowing water. The amount of alkaline earth metal ions in water determines its hardness. Carbonate hardness, also known as transient hardness, exists on one hand, while permanent hardness exists on the other. When non-permanent hydrogen carbonates dissolve in water when a circuit is filled, they produce precipitates and carbon dioxide, resulting in carbonates in the warm regions of the circuit and efficiency losses.
The quality of the water in the circuit is important since it affects the direct risk of corrosion damage. A higher danger of corrosion might be predicted if the water contains a lot of oxygen, but this is reduced in closed systems. However, in this type of circuit, there are several different forms of corrosion that might develop.
Although oxygen decomposes over time in closed systems, residual oxygen content can normallybe expected. When oxygen, water, and metal come into contact, the metal oxidizes or corrodes. Acid corrosion occurs when metals are attacked by acid due to a low pH value, resulting in a breakdown process. Without oxygen, the process can proceed more quickly and in a more acidic environment. Bacterial corrosion, in which bacteria take electrons from the metal and oxidize it, is also a concern. The bacteria’s waste product is sulfur oxide, which gives out a strong stink in the environment.
How To Prevent Corrosion?
Data Center Design and Operation Requirements
Photo Credit: datacenterfrontier.com
Maintenance, infrastructure, and equipment upgrades occur on a regular basis. However, if not handled with care, these seemingly routine actions could result in the introduction of airborne pollutants.
Even data centers in places where air quality is not an issue may struggle to maintain a safe environment for sensitive electronic equipment due to the rising use of air-side economizers for free cooling. Any air utilized for these purposes should be purified before being introduced into the data center.
To eliminate airborne contaminants and meet warranty requirements for new IT and datacom equipment. Datacenter owners and operators must take the following action:
Measure the corrosion rates both within and outside the data center.
Seal all doors, windows, and wall penetrations in the data center.
If the data center envelope is built to be positively pressurized, install room pressure monitors.
Measure airflow at the supply and exhaust air grills, and at each computer room air-conditioning (CRAC) unit.
Develop a temperature and humidity profile.
Datacenter managers must monitor and mitigate both gaseous and particle contamination in their facilities in order to ensure hardware reliability. ASHRAE has established standards that outline allowable contamination levels in collaboration with many of the world’s leading computer system vendors.
ISA Standard 71.04-2013, presents a simple quantitative approach for determining airborne corrosivity in a data center environment. The “reactivity monitoring” method entails using copper and silver sensors that have been exposed to the environment for a length of time in order to evaluate corrosion layer thickness and chemistry. The evaluation includes silver reactivity monitoring, which provides a detailed accounting of the types of corrosive chemical species present in the data center.
For electrical and electronic systems, ISA 71.04 identifies four levels of environmental severity, providing a gauge of the environment’s corrosion potential. The higher the total copper and silver reactivity rates, the higher the overall categorization.
When it comes to air quality monitoring for data center applications, there are numerous solutions to consider. Monitoring of outdoor and ambient air at various locations inside and outside the data center is required for the proper assessment of environmental conditions in the data center. Furthermore, room size and layout should be considered when determining the right placement and kind of CCCs, which can aid in determining compliance with air-quality criteria, as well as real-time atmospheric corrosion monitors (ACM). Data from the ACMs can aid in the statistically reliable assessment of corrosion rates and corrosion control measures in the environment. Either monitoring method can offer the information needed to troubleshoot and minimize contamination issues within the data center.
CCCs are often used for an initial survey of ambient air quality and the data center environment, and they can also be utilized to give historical data on an ongoing basis. This is especially significant when equipment warranties stipulate that an ISA Class G1 environment be established and maintained. Seasonality is a significant issue, and outdoor air should be evaluated at various periods throughout the year.
Real-time monitoring is also possible but should be restricted to the data center. ACMs placed in a number of areas can help establish if contamination is widespread or limited to a specific area when corrosion concerns have been discovered. After establishing a baseline, some of the monitors could be repositioned around the issue area to assess the efficacy of pollution control techniques. Once the data center environment is under control and meets the manufacturer’s warranty requirements, the optimum permanent ACM locations for specific applications can be determined.
Corrosion monitoring can be utilized to identify pollutant types such as active sulfur, sulfur oxides, and inorganic chloride with high confidence. These conclusions can be confirmed using independent sources of environmental data to confirm the corrosion monitoring results.
AKCP Wireless Air Quality Sensor
AKCP Air Quality Monitoring System detects levels of hazardous gases such as SO2, H2S, and CO in the data center. These gases are known to be hazardous to the data center equipment.
Wireless Tunnel Air Quality Sensor
AKCP features air quality sensors that can detect PM0.5, PM1.0, PM2.5, PM4, and PM1 particles. The PM1.0 to PM10 mass concentration of particles, as well as particle number concentration in the PM0.5 to PM10 range, can be measured using the Wireless Air Quality Sensor. This sensor can detect the following dangerous airborne particles:
Acetone (eg. paints and glues)
Toluene (eg. furniture)
Ethanol (eg. perfume, cleaning fluids)
Hydrogen Sulfide (eg. decaying food)
Benzene (eg. Cigarette smoke)
AKCP Wireless Temperature And Humidity
This wireless sensor maintains required ambient conditions, log and graph data over time, and receive real-time alerts when user-defined sensor criteria are exceeded. When in range, use as a data logger with data buffered and synchronized to the gateway.
AKCP Wireless Temperature and Humidity
Wireless Sensor Features:
4x AA Battery powered, with 10-year life*
4x AA Batteries with 10 years guaranteed battery life*
5VDC or 12VDC powered
IP66 rated waterproof enclosure
LED indicators for power, status, and RSSI
Optional DIN rail or pipe mounting accessories
Optional cable up to 15ft for sensor placement
When it comes to data center operations, even minor downtime can cost a lot of money. Understanding the various protection measures for outside air-exposed heat exchangers, as well as the operations that take place in a chilled and cooling water circuit, provides the foundation for a proactive maintenance approach.
Case Study: AKCP Monitors The Lubbock 911 Call Centers
AKCP, the world's oldest and largest supplier of networked wired and wireless sensor solutions, has supplied a monitoring system for the Lubbock, Texas, 9-1-1 call centers.
The Lubbock Emergency Communication District is responsible for providing 24/7 call availability too all 9-1-1 call centers in the county. The data center, located at the Lubbock emergency communication district, receives all 9-1-1 calls. These are distributed to one of 9 public safety answering points throughout the county. The data center also serves as the connection for SMS to 9-1-1 services.