The server outlet temperature is an important thermal condition to the operation of an air free-cooled data center that uses fans to continuously pass the outside air through the server room to cool ...the computing devices. However, the standard server’s management and monitoring tool cannot read the server’s built-in outlet temperature sensors fast enough to catch up the fast dynamics of the server outlet thermal condition caused by the changing server workload. Moreover, many server models do not have built-in sensors that can measure the server outlet temperature. In this paper, we develop a data-assisted first-principle model that leverages available built-in sensors and server’s operating monitoring tools to achieve low-latency estimation of the server outlet temperature. Specifically, the developed model takes the inlet and processor core temperatures, server’s fan speed, and processor utilization which are measured by hardware/software sensors as inputs to predict the outlet temperature with low latencies. Our extensive evaluation based on real data traces collected from a real air free-cooled data center testbed shows that our model can accurately predict the outlet temperature with an average root mean squared error ranging from 1.21 °C to 1.46 °C under various cold supply air temperatures and processor utilization levels.
•Predict the server outlet temperature in data centers with low latencies.•Evaluate the proposed model based on data traces from a real data center testbed.•Achieve the prediction accuracy with an average RMSE from 1.21 °C to 1.46 °C.
Buildings have a major contribution to the global energy consumption. Heating, ventilating and air conditioning systems (HVAC) are responsible for most of the energy use in buildings. Thus, clean and ...sustainable alternatives such as free cooling of buildings have recently gained much attention as means to reduce the operation hours and capacity of the conventional cooling and heating systems. The free cooling could be provided by collecting the natural cold energy during night time in appropriate thermal storage form and this could be retrieved when needed. Phase change materials are exploited by a number of investigators as a storage medium in free cooling applications, as these substances possess high energy densities, and absorb and release heat at a narrow temperature range, hence, the comfort temperature can be maintained day and night. The objectives of this article are to provide a comprehensive review on recent development on free cooling technologies incorporating latent heat storage and to shit lights on the most significant parameters affecting the performance of these materials in free cooling strategy. The outcomes of this review would be helpful in providing clear insight information on potential improvements that can be applied to the storage materials. All the reviewed studies demonstrated that the night cooling strategy using PCMs has the capacity to maintain the indoor temperature well within the comfort zone whilst providing a considerable reduction in cooling loads in all considered climates.
The increasing energy consumption of data centers has become a global concern. Over 30% of the total energy use in a data center is consumed by the cooling system and it is necessary to reduce this ...consumption by efficient cooling techniques. Free cooling is an alternative method, which means utilizing natural cold source when the outdoor temperature is lower than the indoor temperature to achieve energy-saving. Thermosyphon and its integrated system have distinct advantages over other free cooling methods and have great application potential. In this paper, the states of the art are reviewed and overviews are presented for thermosyphon and its integrated system, respectively. The features of existing designs are compared and shortcomings of current studies are concluded. This paper will be helpful for researchers in this field and promote the application of this new free cooling method.
In the past two decades, data centers have significantly grown in size and number around the globe, leading to substantial energy and water stress wherever they operate. Thermal management typically ...represents half of the total energy consumption in traditional data centers. This work studies the energy and water savings that air-side free-cooling yields under diverse weather conditions. We modeled a free-cooling system and a conventional data center using MATLAB. The hourly weather data was obtained from a publicly available online repository for the Chilean territory. Using air-side free-cooling for data center thermal management is feasible in various weather conditions. Locations with colder temperatures (< 20 °C) and higher humidity (> 60%) are more favorable as they require minimal use of the chiller and/or humidifier. These conditions are present in BSk’(s) Cold Semi-arid climate with dry summer and oceanic influence, as well as Csb’ Mediterranean climate (warm summer) with oceanic influence. However, locations with drier air (< 50%) and warmer temperatures (> 20 °C), such as those found in ET(w) Tundra climate with dry winter, BWk(w) Cold Desert climate with dry winter, or BSk(s) Cold Semi-arid climate with dry summer, are less suitable for air free cooling. Even under suboptimal energy and water savings, the air-side economizer still performed considerably better than a conventional data center cooling method (using CRAH units).
•Free-cooling and conventional data centers are modeled using hourly weather data.•Air-side free-cooling economizer may save energy and water depending on the weather.•BSk’(s) and Csb’ climates show significant energy and water savings.•Negligible usage of chiller and humidifier in some weather conditions.
The concept of Green building is gaining importance in the present energy scenario and related environmental issues. Free cooling or ventilation cooling is truly a green concept since even 1
g of ...carbon is not burnt for the purpose of cooling. Also it ensures that a good indoor air quality is maintained in the building. In this paper a detailed review of work carried out by various researchers on free cooling or ventilation cooling is presented. In addition the major challenges and facts posed in the use of phase change material for free cooling system design such as thermal resistance of air and phase change materials, geometry of encapsulation are discussed in detail. Also the method of energy efficient charging and discharging, effect of phase change temperature, insulation and geographical location are also discussed in this paper. This paper also provides lists the PCM candidates used for free cooling.
•PCM based cold thermal storage is more advantageous than other techniques such as sensible and thermo-chemical storage techniques.•The heat transfer rate of the PCM can be increased by the inclusion ...of nanostructures.•Use of less corrosive material is important while developing a cold thermal storage system.•Cold thermal storage systems aid to increase the efficiency of the air-conditioning system.
This paper gives a comprehensive review on recent developments and the previous research studies on cold thermal energy storage using phase change materials (PCM). Such commercially available PCMs having the potential to be used as material for cold energy storage are categorised and listed with their melting point and latent heat of fusion. Also techniques for improving the thermo-physical properties of PCM such as heat transfer enhancement, encapsulation, inclusion of nanostructures and shape stabilization are reviewed. The effect of stability due to the corrosion of construction materials is also reported. Finally, different applications where the PCM can be employed for cold energy storage such as free cooling of building, air-conditioning, refrigerated trucks and cold packing are discussed.
In order to reduce energy consumption in buildings, a solution using phase change materials (PCMs) as thermal energy storage (TES) is presented. During summer nights, cold is stored and delivered ...during the day to reduce cooling load, whereas in winter, heat from solar air collector is stored for heating during morning and evening hours. Proposed is a stand-alone unit suitable for offices, which consists of plates filled with paraffin RT22HC. The objective of the paper is to examine the functioning of the suggested TES system on an annual basis and to explore the feasibility of using it for both, cooling and heating. First numerical model is set up, which assumes 2D geometry and evaluates thermal response, calculations are carried out in Fluent. Then validation of simulations with experimental results is established. Finally the feasibility of storage unit on an annual basis is demonstrated.
Optimal design of building envelopes/HVAC systems and free cooling strategies are today necessary to reduce energy, economic and environmental impact of telecommunication, electricity distribution, ...or electric transportations infrastructures. To this aim, designers and operators require advanced techniques and tools.
Target of this paper is to present the development of a simulation model for assessing and optimizing cooling performance of new/existing infrastructures to be designed/refurbished from the energy point of view. The model is implemented in a computer tool to assess the related potential benefits of different energy saving technologies/strategies and optimize different objective functions.
By the presented approach new design and operating criteria are developed by varying all the occurring boundary conditions (weather, temperature limitations, electricity tariffs, etc.).
To show the capability and suitability of the proposed approach, a case study concerning the equipment cooling of a railway substation is developed. The analysis is conducted for different Italian climates, obtaining remarkable energy savings. Specifically, by optimizing free cooling operation and thermal insulation the cooling energy consumption can be decreased up to 80% and 10%, respectively. By an energy refurbishment of all the Italian railway substations an annual electricity cost reduction due to equipment conditioning of about 0.5 M€ can be achieved, 47% lower.
•Distributed building infrastructures have great potential of reducing cooling energy consumption.•Dynamic simulation is a paramount tool to design enhanced energy management strategies.•Free cooling contributes to 50% reduction of energy demand for equipment cooling.•Operational energy and use of material can be reduced with optimal envelope design.•The study proposes design criteria aimed at increasing energy efficiency at the infrastructure level.
•Open-source Modelica models for chiller plants with water-side economizer were developed.•The developed model can evaluate the control performance of multiple control sequences.•Flexible capability ...of the developed chiller plants with WSE models was demonstrated.•Opportunities in improving the control performance of water-side economizer were identified.
There are several cooling mode control sequences for chiller plants with water-side economizers adopted in industry and academia, and it is widely known that this supervisory control significantly affects energy consumption; however, there is a lack of a modeling resource to allow multiple control sequences to be evaluated systematically under different settings, such as system configurations, load types, and climate locations. To fill this gap, this paper develops open-source Modelica models to simulate the control and energy performance of multiple cooling mode control sequences for chiller plants with water-side economizers. These models allow users to develop and test their advanced control sequences for chiller plants with water-side economizers for their target climates and system configurations. To demonstrate how these models can be utilized, a chiller plant with an integrated water-side economizer is simulated using two advanced cooling mode control sequences, two cooling load types, and six climates, for a total of 24 simulation cases. This study revealed that the energy saving potential varied from 8.6% to 36.8% for constant load profiles in all of the considered climates, and from 6.3% to 25.8% for variable load profiles in most of the climates. Results also showed that the developed system models are able to capture transient control details and reveal counterintuitive energy performance.
•A tap water-based free cooling (TWFC) method was proposed.•The energy efficiency of TWFC was 2.2-fold higher than cooling tower system.•The CO2 reduction rate of the TWFC was 4.4-fold greater than ...cooling tower system.•With a short payback period, the TWFC is an attractive solution for energy saving.
Buildings account for a large portion of global energy consumption and CO2 emissions. Therefore, reducing the energy demands of buildings has become a global topic for sustainable development. A central cooling system accounts for a significant part of a building’s energy consumption. This study proposes a tap water-based free cooling system that recovers heat from spaces for tap water preheating in winter. The tap water-based free cooling and cooling tower free cooling systems integrated with a water-cooled central cooling system were applied in a semiconductor manufacturing factory. Based on the whole-year operation data, the performance of the tap water-based free cooling and cooling tower free cooling systems were compared from thermodynamic, energy, environmental, and economic perspectives. The results showed that free cooling was the dominant cooling method in winter in Tianjin. Compared with the cooling tower free cooling system, the tap water-based free cooling system could provide slightly higher chilled water temperature resulting in 10% shorter operating time. The energy analysis revealed that the coefficient of performance (COP) of the tap water-based free cooling system was approximately 7.4-fold and 2.2-fold higher than that of the mechanical cooling and cooling tower free cooling systems, respectively. Using the two free cooling methods reduced electricity consumption by 6,044 MWh and reached an annual energy-saving rate of 15.1%. Furthermore, the tap water-based free cooling system saved 1.48×105 kg of natural gas for tap water preheating. Energy reductions attributed to two free cooling methods reduced CO2 emissions by 6,236 tons. The tap water-based free cooling is more environmentally friendly with a 4.4-fold greater CO2 emission reduction rate than the cooling tower free cooling method. From the economic perspective, with a short payback period (1.4 years), the tap water-based free cooling system is an attractive solution for improving the energy efficiency of central cooling systems.
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