Browsing by Author "Daraghmeh, Hafiz M."

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A review of current status of free cooling in datacenters
(2017-03-05)
Daraghmeh, Hafiz M.
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
In this study, an overview of current status of the free cooling technologies applicable for datacenters had been discussed, including airside economizers, waterside economizers, and heat pipe technology. By introducing the free cooling technologies, the compressor loading of refrigeration systern,can be partially or completely relieved. Utilization of airside or waterside free cooling relies strongly on the ambient conditions, yet either airside free cooling or waterside free cooling may be integrated with other systems such as absorption, solar system, adsorption, geothermal, evaporative cooling, and the like to extend its performance. On the other hand, thermosiphon heat exchangers and pulsating heat pipes feature unique characteristics to transfer heat at small temperature difference are quite promising for datacenter free cooling. (C) 2016 Elsevier Ltd. All rights reserved.
Energy-saving potential of separated two-phase thermosiphon loops for data center cooling
(2020-07-01)
Sulaiman, Mohammed W.
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Daraghmeh, Hafiz M.
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
This study aims to experimentally examine the energy-saving potential by using R-134a filled separated two-phase thermosiphon loop (STPTL) for data center applications. A parametric study had been made to compare the energy consumption of two data center racks. Two fin-and-tube heat exchangers were attached to one of the racks to form two individual thermosiphon loops. The experiments were carried out subject to different operating conditions, including three ambient temperatures (20 degrees C, 23 degrees C, and 27 degrees C) and filling ratios ranging from 30 to 90% in association with heating loads ranging between 1.5 kW and 6 kW. Parametric influences regarding concentrated heat loading or uniform heat loading are studied. It was found that an appreciable energy-savings can be obtained at high filling ratios and a maximum of 49% energy-saving with the assistance of thermosiphon is observed. Accordingly, the rising of system pressure will result in noticeable savings. Relative to the uniform heat loading of the data rack, the thermosiphon shows even more energy-saving potential in concentrated heat loading. This phenomenon is more pronounced at a lower ambient temperature like 20 degrees C. On the other hand, there is no appreciable energy-saving for the thermosiphon between concentrated and uniform heating loads when the ambient temperature is high (27 degrees C). Furthermore, the influence of airflow rate was also investigated under various ambient temperatures with a 90% filling ratio and a heating load of 6 kW. The results revealed that the lower airflow rate in the thermosiphon yields comparatively better energy-saving than the higher flow rate. The study on the influence of using two STPTLs indicated that 15-23% energy-saving can be achieved at a 90% filling ratio and 6 kW heating load for all the studied ambient conditions if compared with testing each loop separately. Lower thermal resistance is seen at the higher filling ratios, ambient temperatures, and heating loads.
Investigation of Separated Two-Phase Thermosiphon Loop for Relieving the Air-Conditioning Loading in Datacenter
(2019-01-01)
Daraghmeh, Hafiz M.
;
Sulaiman, Mohammed W.
;
Yang, Kai-Shing
;
Wang, Chi-Chuan
;
機械工程學系
This study investigates the feasibility of using R-134a filled separated two-phase thermosiphon loop (STPTL) as a free cooling technique in datacenters. Two data center racks one of them is attached with fin and tube thermosiphon were cooled by CRAC unit (computer room air conditioning unit) individually. Thermosiphon can help to partially eliminate the compressor loading of the CRAC; thus, energy saving potential of thermosiphon loop was investigated. The condenser is a water-cooled design and perfluoroalkoxy pipes were used as adiabatic riser/downcomer for easier installation and mobile capability. Tests were conducted with filling ratio ranging from 0 to 90%. The test results indicate that the energy saving increases with the rise of filling ratio and an optimum energy savings of 38.7% can be achieved at filling ratios of 70%, a further increase of filling ratio leads to a reduction in energy saving. At a low filling ratio like 10%, the evaporator starves for refrigerant and a very uneven air temperature distribution occurring at the exit of data rack. The uneven temperature distribution is relieved considerably when the evaporator is fully flooded. It is also found that the energy saving is in line with the rise of system pressure. Overfilling of the evaporator may lead to a decline of system pressure. A lower thermal resistance occurs at high filling ratios and higher ambient temperature.