Investigation of Free Cooling to Reduce Data Center Energy Consumption: Maxnet Limited Data Center Case Study

Abstract

Data centers electricity consumption is the fastest growing electricity consuming sector in the United States (US), with data centers electricity consumption projected to quadruple between 2010 and 2030 from an annual consumption of 125TWh to over 500TWh. In 2006, worldwide data centers electricity consumption accounted for 1% or 170.4TWh of global electricity consumption at an estimated cost of $US12.57 billion. Worldwide data centers carbon emission was 0.2% of global emission in 2007, which was twice Zealand’s emission level at that time, emission levels are expected to quadruple by 2020. These are some of the startling figures that have captured the attention of Information Technology (IT) Corporations and governments alike, resulting in an increase number of research geared at improving data center energy consumption.

The primary focus of this study is to investigate the potential of free cooling energy to reduce data center energy consumption. This is done through a case study of Maxnet Limited data center. An energy audit of the data center revealed that 4,934.8MWh of electricity or 17,765 GJ of energy was consumed between the period June 2009 to August 2010, with the cooling network consuming 26.2% of this energy. The audit also revealed several other potential cost saving opportunities.

The present cooling infrastructure does not allow for free cooling, hence cooling systems capable of providing free cooling were proposed. Semi-empirical and mathematical expressions derived from mass and energy balances, were used to create a robust simulation code to quantify the waterside and airside free cooling potential of the proposed cooling systems, based on present and projected data center cooling demand.

The study found that at higher chilled water temperatures and cooling capacities, the amount of power saved by airside and waterside free cooling increases. Based on simulated results for the data center operating at a cooling demand of 830kW and a leaving chiller evaporator water temperature of 12oC, combined airside and waterside free cooling is capable of providing 40% (2,870MWh) of the annual cooling demand, which reduces the required cooling system energy consumption by 28% (250MWh) whilst realising a cost saving of $NZD 24,550 per annum.

A financial feasibility analysis of implementing the proposed cooling system to provide free cooling was assessed using Net Present Value (NPV) and Internal Rate of Return (IRR) financial metrics. The results of these analyses not only showed free cooling as a viable option to reducing data center energy consumption, but also showed that free cooling is a financially viable solution. Apart from being financially viable, free cooling can also significantly reduce data center carbon dioxide emissions.