# Space Habitat Data Centers--For Future Computing
## 2 Background  
[PERSON] et al. [1] examine the power consumption in modern data centres. The discussion recognizes that the operation of data centres poses significant impact as regards increasing carbon dioxide emissions. In addition, data centre facilities comprise active and redundant powering and cooling systems. The power and cooling systems are recognized to consume a significant amount of power. The global power consumption of data centres increased by 19.7% over a five-year period spanning 2007 to 2012. The paper presents analysis of the power usage effectiveness of data centres for the period 2009-2016. The role of the data centre location in influencing the PUE is also examined. The presented results show that the lowest PUEs are obtained for data centres sited in Nordic countries (average PUE of 1.71) and northern/central Europe (average PUE of 1.72). The discussion by [PERSON] et al. [1] aims to determine the best practices that can be used to enhance data centre energy efficiency, i.e., ensure a low PUE figure is obtained and also reduce their carbon dioxide emissions. This is aimed at ensuring the environment friendliness of data centres to be deployed in the future. The focus of the discussion by [PERSON] et al. [1] is twofold. The first is determining the measures that can reduce the degrading effect of data centres on the environment. This is because they have identified other measures such as the use of energy from alternative and sustainable sources in future data centre operation. The second is determining best practices that can provide useful information for data centre operators enabling them to improve data centre facility energy efficiency. A similar perspective but with focus on analysing the PUE trends is also examined by [PERSON] et al. [2]. Though the use of free cooling is recognized as suitable, its use here is limited to the terrestrial environment. However, the use of free cooling with relation to data centres applies to other domains such as the underwater environment. The suitability of the underwater environment has received research consideration in several studies by [PERSON] [13], [PERSON] et al. [14] and [PERSON] et al. [15]. The need to reduce the water footprint is considered by [PERSON] et al. [3]. Water usage effectiveness (WUE) is recognized as a metric that is important to data centre operation. The challenge being addressed in [PERSON] et al. [3] is the optimization of water usage and power consumption for a data centre coupled with a micro-grid system. The discussion presents a scheduling mechanism aiming to reduce the costs and fees associated with energy payment and water usage. The joint optimization i.e., reducing water and electricity costs is the novelty of the contribution in [PERSON] et al. [3]. This is done with the aim of determining the combination of water and electricity usage that results in the most profitable operation of the data centre facility. The analysis of results in [PERSON] et al. [3] recognizes that the ideal WUE figure is zero. However, a figure of WUE is assumed to be infeasible. This is because the focus of the analysis by [PERSON] et al. [3] is the optimization of terrestrial data centre systems. A condition that can make the WUE ideally zero is the use of a cooling system that is not reliant on Earth's water resources. However, the conduct of research to determine the existence and feasibility of cooling systems with a zero WUE was not considered in [PERSON] et al. [3]. Instead, the focus is on determining the optimal water and power usage for a given data centre with different computing workload sizes. [PERSON] et al. [11] recognize the potential and role of free cooling technologies in enhancing data centre power usage effectiveness. Different free cooling technology strategies such as direct fresh air, rotating wheel heat exchanger, heat pipe back rack and water driven free cooling system are recognized.