Clearing the air in the data centre
Wed 30 Mar 2016
We are all routinely using web-based services, either directly and/or through our personal and business activities. Data centre demand is increasing each year and is projected to increase for the foreseeable future.
Data centre buildings have different needs to other large buildings that are used principally by people. We need to focus on the requirements of the data handling and storage equipment, and the best means of ensuring reliable performance with minimal running costs. Clean air at the correct temperature and humidity improves reliability and reduces running costs.
Energy consumption Power Usage Effectiveness (PUE) is the measure widely used to benchmark energy efficiency in data centre sites. The ratio of IT energy use is compared to other services using energy on the site. Historically a PUE of 2 was common but as system design has improved this has moved towards a PUE of 1.2.
A large part of the energy consumption is taken up with air management in these facilities. Moving the air, cleaning the air and cooling the air. A reduction in non-IT energy use from 100% of IT down to 20% of IT is principally the benefit of a more efficient air plant.
The hidden cost of airborne contaminants
Data centre servers generate significant amounts of heat, and so require a constant draught of cool air. Warmed air must be re-cooled for recirculation or extracted and replaced by external cooler air in a process known as free cooling. This, if available, offers the opportunity to minimise air plant running costs, because large amounts of energy would be otherwise consumed by the chiller compressors needed to cool re-circulated air. However, it is only possible to use free cooling with outside air if it is clean and free from airborne contaminants.
Effective air filtration of supply air into the data centre is necessary to clean the air but careful selection is required to ensure as much of the harmful particle and gas contaminants are removed as possible. Current guidance advises that F7 class particle filters to standard EN779:2012 are required (F7 is equivalent to MERV13). The dust particle concentration should not exceed Class 8 of ISO 14644-1 (1999). To minimise the air system fan motor energy consumption it is recommended that Eurovent A+ Energy rated filters, as defined by 4/21 2014, are used.
For harmful gaseous contaminants such as NOx, SOx, and H2S molecular gas, filters using activated carbon are recommended, as they will have the required high level of filtration efficiency.
Apart from main air supply system filtration, it is possible to use standalone recirculation air purifier units that can capture contaminants in local areas that are not adequately serviced by a main air system. These units can be fitted with the appropriate combination of particle and molecular gas filtration. Free-standing recirculation units are low energy, as they have no ducting attached.
Health and safety
High levels of humidity over 60% should be avoided where possible because deposited dust from air and corrosive gases will react with metal surfaces to a greater extent causing increased problems. In general, the benefit of clean air is underestimated in maintaining the working efficiency of data centre servers, air moving plant efficiency, and the working efficiency of people working inside these centres.
Peter Dyment is technical manager at Camfil Ltd. His principal areas of activity are: waste, printing, heavy industry, public and commercial buildings, particulate and molecular/gas phase air filtration, upgrading existing air systems and standalone air purification systems.
This article first appeared in Data Centre Management, Spring 2016