AIT Partnership Group Ltd White Paper: Free Cooling and the Efficiency of your Data Centre Using free cooling methods to increase environmental sustainability and reduce operational cost.
Contents 1. Summary... 3 2. Traditional Data Centre Cooling Methods... 4 3. Fresh Air Free Cooling... 6 4 Factors to Consider for Fresh Air Free Cooling... 7 Humidity... 7 Dust, Smoke and Air Borne Pollutants... 7 5. Adiabatic/Evaporative Cooling... 8 6. Maximising the Efficiency of your Data Centre... 9 References... 10 2
1. Summary Free cooling systems can, in most cases, offer the operator large savings on their annual operational costs over more traditional air-conditioning methods. The term free cooling refers to using external ambient air and/or water in order to cool your data centre. Cost is reduced and environmental sustainability increased due to far less power being used to cool the air through an air-conditioning unit. A water side free cooling unit is slightly different in that your data centre must be sealed, much like a traditional air conditioned data centre. This prevents outside contaminants being brought into the data centre with the hot air exhausted being cooled through coils surrounded by chilled water. In many cases using a combination of these systems will allow year round use, dependent on your location. The overwhelming majority of data centres rely on air-based cooling provided by airconditioning to keep IT equipment in the server racks below the industry standard ASHRAE (American Society of Heating, Refrigerating and Air-conditioning Engineers) guideline temperature limit of 27⁰ C. In order to achieve this air temperature is closely monitored and controlled within the data centre. IT equipment running too hot will reduce its lifetime and cause early failure, while over cooling the data centre wastes energy and increases costs. The UK s climate, for the vast majority of the year, lends itself perfectly to free cooling methods. With ASHRAE standards stating that IT equipment should be cooled to between 18⁰ C and 27⁰ C, the UK s yearly average temperature of 9.7⁰ C (www.weatherbase.com) provides suitable ambient temperatures almost all year round. The only time when a traditional air-conditioning system may have to be used is if external ambient temperatures are above 27⁰ C during the summer months, which remains relatively rare, or depending on external pollutants. Even then water side free cooling methods can remain very efficient up to 32⁰ C with adiabatic cooling installed. 3
Fig 1: Example of Water Side Free Cooling There are several other factors to consider when weighing whether to use air conditioned cooling systems over the equivalent free cooling methods. Humidity and air borne contaminants such as dust and smoke all play an important part in weighing up which option to install into your data centre. The choice of traditional approaches vs fresh air (or water side) free cooling is always a trade-off between energy saving and data centre reliability. 2. Traditional Data Centre Cooling Methods Traditional cooling methods mainly use air-conditioning units to cool the air within a data centre to within official guidelines. As with free cooling methods, there are pros and cons surrounding air conditioned units which should be considered when deciding which is best for you. Where air-conditioning is used, hot air exhausted from your data centre is cooled by the computer room air conditioning (CRAC) unit in a continuous refrigeration cycle. Pros of this method include the re-cycling of the same air limiting the introduction of contaminants from the outside environment which can harm the computer equipment. Humidity creates another problem area in data centres, with levels of 80% and above also likely to affect equipment therefore reducing the lifetime of your centre. Air-conditioning reduces humidity levels to a suitable percentage as cool air cannot hold as much moisture as warm air. Thus in certain climates and at certain times of the year, a traditional cooling facility will be more effective than an equivalent free cooling system. 4
In coastal areas the salt content of the air presents a typical scenario that forces traditional air conditioning solutions to be used. Ross Carver, Project Manager at AIT Partnership Group states salty sea air in coastal locations also causes reliability issues with connectors and IT equipment. In some areas it makes sense to seal the room and use air-conditioning to avoid costly downtime. Air-conditioning recycles the air contained within the data centre whereas free cooling methods will draw in large amounts of fresh (salty/damp) air which can attack your equipment and quickly cause reliability problems. Fig 2: Example of Traditional Air Conditioning System With air-conditioned cooling systems however comes a higher operational cost due to the compressive stages of refrigeration, consuming considerably more energy. This must be considered when selecting which option to take, creating a balance between the cost of energy consumed and the possible cost of downtime caused by external causes. Each of the factors mentioned above are vital in deciding which cooling method is preferable for you. In many cases a combination of both can be fitted to ensure year round efficiency and a balance between operational costs and PUE (Power Usage Effectiveness). The PUE, a ratio of power used by the IT equipment vs total data centre power, is a metric commonly used for assessing efficiency with an average rating of 2-2.5 and more efficient data centres between 1.2-1.8. Add to this environmental factors and potential ROI (Return on Investment) you can begin to decide which cooling solution makes sense for your particular situation. 5
3. Fresh Air Free Cooling Despite the name, fresh air free cooling isn t actually a completely free alternative to cooling your data centre. As discussed previously in this whitepaper, operational costs can be greatly reduced with free cooling methods, but only if your data centre requirements and your location are suitable. In its simplest form, a fresh air free cooling system will use a fan to draw in external ambient air into the data centre. The air is passed through filters to remove as many contaminants as possible and can then be directed through the data centre. The hot air created by the equipment rises and is extracted back out. Fig 3: Example of Fresh Air Free Cooling The use of fans means energy is required to run them efficiently. The amount of energy however is greatly reduced compared to running an air-conditioning unit. AIT Partnership Group has an innovation suite in its Reading office, cooled by external fresh air, where it tests data centre infrastructure management (DCIM) solutions. Ross Carver adds so far we haven t had any issues with fresh air free cooling and the temperature range has remained within ASHRAE guidelines. This is testament to free air cooling methods demonstrating the reliability and savings that can be made, as long as your data system requirements are suitable. 6
4 Factors to Consider for Fresh Air Free Cooling There are several important factors to take into consideration when choosing whether fresh air free cooling is right for you. Humidity The level of water carried by air will vary throughout the seasons as weather conditions change. When related to sustaining your data centre both air that is too humid and air that is too dry can have negative outcomes. Humid air may lead to corrosion of equipment meaning installing new equipment or changing parts more often. On the other hand air that is too dry is associated with static build up discharging, in turn damaging equipment and increasing downtime and therefore expense. For this reason a combination of cooling methods is often necessary, as air conditioning systems commonly have built in humidity controls. In this way external conditions do not dictate reliability and uptime when outside the norms for free air cooling. Dust, Smoke and Airborne Pollutants When a data centre is adapted from a closed architecture to an open equivalent, pollutants carried by external ambient air become an issue. With fresh air free cooling using external air, ways to reduce such pollutants from entering the data centre are of key importance. Dust and other larger airborne pollutants can build up over time on equipment reducing its life span. Smoke is harder to control with finer filtering systems required. If smoke was to enter your data centre it can trigger fire prevention equipment thus stopping operations and increasing expensive downtime. It is also worth noting that no matter how advanced your filtering system, a percentage of contaminants will always make it into your data centre. With these potential problem areas the location of your data centre is of paramount importance when choosing which cooling system if right for you. Filtering equipment is another cost to take into account and will need regular cleaning/replacing if in a polluted or coastal area. This in turn increases the maintenance overhead and can work out more expensive in the long run than a conventional air conditioned cooling system. If your data centre for example is within the confines of a city, free air cooling is most likely to cause more problems than equivalent methods. A higher location in less built up areas will result in far lower pollution levels and in turn allow free air cooling to run efficiently. 7
5. Adiabatic/Evaporative Cooling An adiabatic system can be fitted to both fresh air free cooling and water side free cooling methods and used to further cool air or humidify air slightly if too dry. A fine spray of water is used to cool the air (fresh air free cooling) or to cool the coil (water side free cooling). Adiabatic cooling allows a wide range of temperatures to be covered, retaining the efficiency of your data centre without the need for air conditioning. An example of where this has been successful comes from Tony Pompa, Data Centre Manager at Bedford Borough Council who gets an additional 5⁰ C of cooling via adiabatic methods. So long as humidity is not too high evaporative cooling can provide inlet air temperatures of 22⁰ C when outside air is 30⁰ C. Beyond 80% relative humidity or above 27⁰ C we fall back onto conventional airconditioning, but we rarely use it. Energy costs are considerably lower enabling us to get a payback on the project in less than 4 years. This demonstrates how the relatively low average temperature of the UK can provide ideal conditions for free cooling systems almost year round providing your location is suitable. Also, having a backup air conditioning unit installed ensures if conditions do change, reliability of your data centre is retained avoiding costly downtime. Fig 4: Example of Evaporative Cooling 8
6. Maximising the Efficiency of your Data Centre Whilst the cooling systems mentioned have the potential to greatly reduce operational cost while retaining efficiency, careful evaluation of your data centre is critical when deciding which system(s) to install. Before deciding which system is right for you, a survey of your locations environment will allow you to determine whether free air cooling methods are suitable for your needs. As mentioned above pollutants in built up areas and salt levels in coastal regions can result in premature damage to your equipment leading to higher costs and reduced efficiency. In these cases air conditioning units or water side free cooling will be the most efficient, providing the lowest overall operational costs. Another factor to consider is your reputation for reliable service. The inability to provide customers with computing or storage resources due to downtime caused by insufficient cooling systems would quickly harm your reputation. Air conditioning systems on the other hand, create a largely sealed environment within your data centre, so external pollutants from the intake of fresh air are no longer an issue. This will of course lead to increased operational cost due to higher energy consumption. Dependent on your location, this will still be the cheapest and most reliable system with your equipment being protected from impurities and excursions in humidity. In many cases a combination of both a free cooling and air conditioning systems can be used to ensure your data centre is covered for all eventualities. As mentioned above by Tony Pompa, air conditioning units can be installed and used when external conditions are not suitable for free cooling. This reduces any downtime as the air conditioning system can replace the free cooling arrangement instantly as and when it needs to. Dependant on your location and requirements, you may be able to install solely a free air cooling system, like AIT Partnership Group has it its Reading office. This will result in savings on operational cost and an increased efficiency, although careful monitoring of the external conditions is critical. In conclusion it is clear that the development of different free cooling systems can offer data centre owners great savings and efficiency. By careful surveying and monitoring of your surroundings you will be able to discover which method is right for your data centre, whether it be free air cooling, water side free cooling, air conditioning or a combination to cover all eventualities. 9
References AIT Opens Data Centre Innovation Suite http://aitpowersurge.co.uk/ait-opens-data-centre-innovation-suite/ ASHRAE Guidelines https://www.ashrae.org/standards-research--technology/standards--guidelines Ambient Air Cooling http://www.datacenterjournal.com/facilities/ambient-air-cooling/ Economizer Fundamentals: Smart Approaches to Energy-Efficient Free Cooling for Data Centres http://www.emersonnetworkpower.com/documents/enus/brands/liebert/documents/white%20papers/computer-cooling_24641-04-10.pdf Energy Efficient Free Cooling for Data Centers http://www.datacenterknowledge.com/archives/2011/12/13/energy-efficient-free-cooling-for-datacenters/ Using Free Cooling in the Data Center http://searchdatacenter.techtarget.com/podcast/using-free-cooling-in-the-data-center Weatherbase http://www.weatherbase.com/weather/state.php3?c=gb&countryname=united-kingdom 1 Southern Court South Street Reading RG1 4QS 0845 293 2970 All rights reserved. The AIT Logo and name is a registered trademark of the AIT Partnership Group Ltd. All other company or product names may be trademarks or registered trademarks of their respective owners. Whilst every effort has been made to ensure accuracy, neither the author nor AIT takes responsibility for the information given herein. www.ait-pg.co.uk 10