Analysis of methods for assessing the energy efficiency of data centers using the power usage effectiveness method

The article deals with the analysis of methods for assessing the energy efficiency of data centers according to the Power Usage Effectiveness method. The demand for data centers which consumes a large amount of electricity is growing with the growth of digitalization and the accumulation of big data in the network. The energy consumption of the cooling system for the machine room accounts for a significant part of the operating costs of the building. Free cooling in a refrigeration system reduces energy consumption much more than operating systems with a vapor-compression cycle. In 2006 according to The Green Grid, the assessment method of Power Usage Effectiveness has become an international standard for measuring energy efficiency and is widely used in the design and operation of data centers. In this regard, the operation principles of free-cooling chillers are considered. The calculation example of the system payback in free-cooling is also given.

Influence of ambient temperature on the efficiency of underground spot cooling system

In mine air conditioning systems, the vapour compression refrigeration cycle seems to be currently the most widespread method of artificial cooling. In literature some other methods for cooling a mine are also presented, like using free-cooling in refrigeration systems. Mine workings in Jiu Valley are using the primary and secondary ventilation system for cooling the underground. Today the activities are focused mainly on mine closure as a part of transition to the low carbon economy, and this situation brings new challenges regarding the mine ventilation system, which was designed to meet the needs of a full-scale operation. As a result, locally ambient temperatures can rise, and spot cooling systems can be used, in order to cool the air. Such a system has been considered and calculations have been made to evaluate its thermal efficiency at different ambient temperatures.

Research Progress on the Phase Change Materials for Cold Thermal Energy Storage

Thermal energy storage based on phase change materials (PCMs) can improve the efficiency of energy utilization by eliminating the mismatch between energy supply and demand. It has become a hot research topic in recent years, especially for cold thermal energy storage (CTES), such as free cooling of buildings, food transportation, electronic cooling, telecommunications cooling, etc. This paper summarizes the latest research progress of the PCMs-based CTES. Firstly, the classification of PCMs for low temperature storage is introduced; the thermal physical properties (e.g., phase change temperature (PCT) and latent heat) of suitable PCM candidates (−97 to 30 °C) for CTES are summarized as well. Secondly, the techniques proposed to enhance the thermal properties of PCMs are presented, including the addition of nanomaterials, the microencapsulation and the shape stabilization. Finally, several representative applications (−97 to 65 °C) of PCMs in different CTES systems are discussed. The present review provides a comprehensive summary, systematical analysis, and comparison for the PCMs-based CTES systems, which can be helpful for the future development in this field.

Laboratory tests of a prototypical user-centric radiant cooling solution

Radiant cooling systems are being increasingly promoted because of their energy efficient operation as well as their potential to improve occupants’ thermal comfort due to a draft-free cooling process. This paper focuses on a specific radiant cooling approach, which was introduced in previous contributions. This approach involves the positioning of relatively small-sized vertical radiant panels in the close proximity to occupants. Furthermore, the panels incorporate drainage systems or collection elements to accommodate, if needed, water vapour condensation. Consequently, the surface temperature of the radiant panels does not need to stay above the dew point temperature. We present the outcome of a preliminary experimental investigation of such a personal radiant cooling system. In this context, prototypical radiant panels were installed in a laboratory and multiple experiments were conducted. The uniformity level of the panels’ surface temperature distribution was documented. Moreover, near-panel air flow velocities were measured at several positions. Likewise, the formation of condensed water on panels was observed for different panel surface temperatures, room temperatures, and room humidity levels. The results of the preliminary laboratory investigation do not point to any risk of draft or turbulence discomfort.

Inorganic PCMs applications in passive cooling of buildings - A review

Buildings consume around 40% of total world energy and are responsible for 30-35% greenhouse gas emissions globally. Latent heat thermal energy storage is one of the most promising techniques being investigated currently to reduce the thermal load of buildings. Different types of phase change materials (PCMs) i.e. organic, inorganic and eutectics with different thermophysical properties have been investigated for passive cooling of buildings showing great potential for saving energy. Due to their higher thermal conductivity and high heat storage capacity per unit volume, inorganic phase change materials take advantage over organic ones. They can be used as stand-alone heat storage systems for free cooling, embedded in building walls, windows, roofs and ceilings etc. Studies have shown that there are some drawbacks of inorganic PCMs as well like corrosion of container material, phase separation and supercooling which require solutions.

Long range correlations and slow time scales in a boundary driven granular model

We consider a velocity field with linear viscous interactions defined on a one dimensional lattice. Brownian baths with different parameters can be coupled to the boundary sites and to the bulk sites, determining different kinds of non-equilibrium steady states or free-cooling dynamics. Analytical results for spatial and temporal correlations are provided by analytical diagonalisation of the system’s equations in the infinite size limit. We demonstrate that spatial correlations are scale-free and time-scales become exceedingly long when the system is driven only at the boundaries. On the contrary, in the case a bath is coupled to the bulk sites too, an exponential correlation decay is found with a finite characteristic length. This is also true in the free cooling regime, but in this case the correlation length grows diffusively in time. We discuss the crucial role of boundary driving for long-range correlations and slow time-scales, proposing an analogy between this simplified dynamical model and dense vibro-fluidized granular materials. Several generalizations and connections with the statistical physics of active matter are also suggested.