How to achieve Lower Data Center PUE and Better IAQ?
It has been reported that data centers account for up to 1.5% of global electricity use and that may be as high as over 2.5% in some sophisticated regions like U.S.A. About 35% – 40% or more of energy consumption of a data center goes towards cooling IT equipment. While data center infrastructure consultants and operators have deployed many energy efficient systems/equipment to save energy, there are still about 40% of data centers are running at an average efficiency with a PUE of 1.5 – 2 (Power Usage Effectiveness, a metric that is used to determine and monitor how efficient a data center is operated). A data center with a PUE over 1.5 could not be considered as efficient.
IT and Facility management professionals are under pressure to improve the PUE. In the last decade, economizer and free cooling has been increasingly used to save energy in data center. It has caused higher IT equipment failure rate due to gaseous contamination particularly in developing Asian countries where air pollution problem is more serious, the situation is further deteriorated by fluctuation of temperature and relative humidity inside data center. The subject has been thoroughly discussed in our previous issue of newsletter – Gaseous contamination in data center.
Unlike PUE, IAQ (Indoor Air Quality) does not get reasonably adequate concerns. It does not only relate to protecting health of people working therein but also a ‘clean’ environment that protect IT equipment from damages due to gaseous contamination.
With reference to the ‘Particulate and gaseous contamination guidelines for data centers (ASHRAE 2011)’. Data centers must be kept clean to ISO 14644-1 Class 8 (ISO 2014). This level of cleanliness can generally be achieved by an appropriate filtration scheme as outlined here:
- The room air may be continuously filtered with MERV 8 filters (G4/F5, 25-30% dust spot).
- Air entering a data center may be filtered with MERV 11 (F6, 60-65% dust spot) or MERV 13 (F7, 80-90% dust spot) filters.
Gaseous contamination should be within the ISA-71.04-2013 severity level of G1-Mild that meets:
- A copper reactivity rate of less than 300 angstroms (Å) per month, and
- A silver reactivity rate of less than 200 Å per month.
Since the gas molecules are 100 – 1000 times smaller than that of ultrafine particles, even a HEPA filter, with an efficiency of 99.97% or higher @0.3µm, cannot stop it. For data centers with high gaseous contamination levels, gas-phase filtration of the inlet air and the air in the data center is highly recommended.
Prominently, both reliability and energy efficiency are two major concerns of a data center. We do not only need to improve the PUE but also make sure that airborne contaminants that affect reliability of IT equipment are eliminated.
While the data center infrastructure consultants and operators keep looking at energy efficient system/equipment to improve the PUE, such as free cooling, highly efficient UPS, hot or cold air aisle containment, and etc., air filters that links with both IAQ and energy saving are always overlooked probably due to its insignificant effect on operating cost of a data center. However, from perspective of Total Cost of Ownership (TCO), the cost of an air filter is only 20% – 25% of the TCO and the associated electricity cost constitutes 60% – 70%.
The power consumption on airside is directly proportional to the air flow rate and operating pressure as depicted in the equation below:
Q: air flow rate | P: operating pressure | c: constant | µ: system efficiency (multiple of µ of motor, fan, inverter, driving belt, etc.)
The pressure drop due to air filter is one of the elements of the system operating pressure. It is desired to have a filter with high filtration efficiency (MERV 11 to MERV 13) but a low pressure drop, in order to save energy.
Glass fiber filter media can be used for making pocket or pleated panel filter to achieve a high filtration efficiency while its pressure drop and rate of change of pressure drop across its operating life is comparatively high.
Given that data centers are operating 24 hours a day and 7 days a week, the electricity consumption due to one PA increase in the average pressure drop of a 600 mm x 600 mm air filter could be up to 10 – 12 kWh per annum.
Nanofil Mini-pleated Molecular Filter made of composite filter media comprising layers of electrostatic fiber, activated carbon net, and electro-spun nanofiber is specifically designed for use in data center to reduce harmful gases and fine particulates, and reduce energy consumption. It is revealed that ‘The composite micro-nanoﬁber ﬁlter stands out as the best performer in terms of pressure drop coupled with very high capture eﬃciency for the entire ﬁltration.’ Separation and Purification Technology 206 (2018) 26–38, W.W.-F. Leung et al.
In addition, the filter has a high anti-bacterial and anti-viral performance thanks to its specially formulated nanofiber membrane. According to the test report by SGS, it can kill greater than 99.9% of commonly found airborne bacteria such as E-coli.
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