Computer Room Air Conditioning Units Research Articles

Airflow uniformity and energy consumption investigation on data centers enhanced by jet fans

Active adjustment of the airflow organization in data centers (DC) has been increasingly applied due to its superior adjustment performance. But for now, the main focus is on the airflow distribution optimization in the horizontal direction, while few research has been conducted to investigate the additional energy consumption of active method. This paper introduced the jet-induced ventilation into under-floor air distribution (UFAD), then the coupling air supply system (CASS) was established. Taking the CASS data center as an example, this paper focuses on the impact of the active adjustment method on both airflow organization and energy consumption of the DC, and analyzes the energy consumption of the system while meeting the security operations of the thermal environment. The results showed that the incorporation of jet-induced ventilation effectively improved the airflow distribution uniformity, while the active adjustment of the airflow organization in the DC has little effect on the overall energy consumption. On the premise of meeting the demand of thermal environment, the energy consumption of the CRAC (Computer room air conditioning) units in the CASS is reduced and the change of the overall energy consumption is small, while the total energy consumption increased with the increase of airflow uniformity.

Experimentally Validated Computational Fluid Dynamics Model for Data Center With Active Tiles

Abstract This paper presents an experimentally validated room-level computational fluid dynamics (CFD) model for raised-floor data center configurations employing active tiles. Active tiles are perforated floor tiles with integrated fans, which increase the local volume flow rate by redistributing the cold air supplied by the computer room air conditioning (CRAC) unit to the under-floor plenum. The numerical model of the data center room consists of one cold aisle with 12 racks arranged on both sides and three CRAC units sited around the periphery of the room. The commercial CFD software package futurefacilities6sigmadcx is used to develop the model for three configurations: (a) an aisle populated with ten (i.e., all) passive tiles; (b) a single active tile and nine passive tiles in the cold aisle; and (c) an aisle populated with all active tiles. The predictions from the CFD model are found to be in good agreement with the experimental data, with an average discrepancy between the measured and computed values for total flow rate and rack inlet temperature less than 4% and 1.7 °C, respectively. The validated models were then used to simulate steady-state and transient scenarios following cooling failure. This physics-based and experimentally validated room-level model can be used for temperature and flow distributions prediction and identifying optimal number and locations of active tiles for hot spot mitigation in data centers.

Effect of CRAC units layout on thermal management of data center

Comprehensive numerical studies of thermal management of data centers were presented by several investigators for different geometric and operating conditions of data centers. In the present work, a technical note regarding the effect of the computer room air conditioning (CRAC) units layout arrangements is presented. Two arrangements of CRAC units layouts are investigated; namely locating CRACs units in line with the racks row and locating the CRACs units perpendicular to the rack row. Temperature distributions, air flow characteristics particularly air recirculation and bypass and thermal management in data centers are evaluated in terms of the measureable overall performance parameters: supply/return heat indices (SHI/RHI) and return temperature indices (RTI). The results showed that locating CRAC units perpendicular to the racks row has the following effects: (i) enhances the uniformity of the air flow from the perforated tiles along the rack row, (ii) reduces the hot air recirculation at the ends racks of the row and the cold air bypass at the middle rack of the row and (iii) enhances the data center performance parameters RTI, SHI and RHI.

Experimental investigation on hygrothermal behaviour and the surface condensation risk of a data centre

Condensation under the floor slabs of office rooms adjoining data centres is a serious concern because thermal comfort and information and communications technology equipment are both sensitive to high humidity levels. Surface condensation risk depends mainly on the surface energy balance and moisture content of ambient air. This paper describes an evaluation method for assessing condensation risk of indoor environment conditions and the effect of remedial measures and presents a strategy to solve the condensation risk problems using experimental measurements and numerical simulations. The condensation risks due to air temperature and humidity were calculated for two zones between information and communications technology server rooms and office areas. We analysed the structural insulation performance and space cooling conditions, supply air temperature of the information and communications technology server rooms. The change in indoor temperature of non-information and communications technology spaces was predicted to find the cause of the condensation state. The results show that application of floor slab insulation and high supply air temperature by the computer room air-conditioning unit can substantially increase the lowest temperature of the interior surfaces and the temperature factor and reduce indoor relative humidity, thus preventing surface condensation in the non-information and communications technology spaces adjacent to the information and communications technology server rooms.

CFD investigations of data centers’ thermal performance for different configurations of CRACs units and aisles separation

The thermal performance of data centers is numerically studied for different configurations of computer room air conditioning (CRAC) units and physical separations of cold and hot aisles. Temperature distribution, air flow characteristics and thermal management of data centers racks array are predicted and evaluated for the different arrangements. Measureable performance indices: supply/return heat index (SHI/RHI), return temperature index (RTI) and return cooling index (RCI) are used to measure the thermal management effectiveness of data center racks. The results showed that: (i) hot air recirculation, cold air bypass and the measurable performance indices of the racks strongly depend on the racks location in the racks array, (ii) the CRACs units layout affects the thermal managements of the racks array especially the sides and middle racks in the array, and (iii) using cold aisle containments enhances the thermal performance of the data center.

Numerical investigation and parametric study for thermal and energy management enhancements in data centers' buildings

A CFD numerical investigation of air flow and temperature distribution in data centers is presented for different operating and geometric conditions. Numerical experiments were conducted to parametrically study the effects of perforated tiles opening ratio, data center power density and locations of Computer Room Air Conditioning (CRAC) on the data center performance. Temperature distribution especially hot spot points, air flow characteristics particularly air recirculation and bypass and thermal management in data centers are evaluated in terms of the measureable overall performance parameters: supply/return heat indices (SHI/RHI), return temperature indices (RTI) and return cooling indices (RCI). Techniques of using cold aisle containments for enhancing the cooling effectiveness of data centers are investigated and evaluated. The results showed that (i) increasing the perforation ratio of perforated tails decreases the recirculation and bypass of air flow around the rack, (ii) increasing data centers' power density and supplied air flow rates increases the air bypass and air re-circulation, (iii) changing the spacing between the CRAC units and cold aisle slightly changes of air recirculation and bypass around the racks, and (iv) using appropriate cold aisle containment improves the performance of cooling of data centers, especially at high power density.

Reduced Order Thermal Modeling of Data Centers via Distributed Sensor Data

In this paper, an effective and computationally efficient proper orthogonal decomposition (POD) based reduced order modeling approach is presented, which utilizes selected sets of observed thermal sensor data inside the data centers to help predict the data center temperature field as a function of the air flow rates of computer room air conditioning (CRAC) units. The approach is demonstrated through application to an operational data center of 102.2 m2 (1100 square feet) with a hot and cold aisle arrangement of racks cooled by one CRAC unit. While the thermal data throughout the facility can be collected in about 30 min using a 3D temperature mapping tool, the POD method is able to generate temperature field throughout the data center in less than 2 s on a high end desktop personal computer (PC). Comparing the obtained POD temperature fields with the experimentally measured data for two different values of CRAC flow rates shows that the method can predict the temperature field with the average error of 0.68 °C or 3.2%. The maximum local error is around 8 °C, but the total number of points where the local error is larger than 1 °C, is only ∼6% of the total domain points.

Investigation of air management and energy performance in a data center in Finland: Case study

This is the first research paper on data center from Finland. The objectives of this study are to evaluate air management and energy performance of cooling system and investigate the possibilities of energy saving and reuse in the data center. Field measurements, particularly for long term's IT and facility powers, were conducted. Different performance metrics for the cooling system and power consumption were examined and analysed. Key problem areas and energy saving opportunities were identified. The electrical end use breakdown was estimated. Results show that IT equipment intake conditions were within the recommended or allowable ranges from ASHRAE. The Power Usage Effectiveness (PUE) value for a typical year was about 1.33. Noticeable recirculation of hot air was not observed, but extreme bypass air was found. The air change rate was set much bigger than the recommended ASHRAE's value. There was no heat recovery system. The air management and heat recovery issues therefore need to be addressed. Fan speeds (Computer Room Air-Conditioning Unit) should be reduced and the ventilation rate should be minimized. Further, a simulated heat recovery system was presented demonstrating that the data center could potentially provide yearly space and hot water heating for 30,916 m 2 non-domestic building.

Numerical Modeling of Perforated Tile Flow Distribution in a Raised-Floor Data Center

This paper is centered on quantifying the effect of computer room and computer room air conditioning (CRAC) unit modeling on the perforated tile flow distribution in a representative raised-floor data center. Also, this study quantifies the effect of plenum pipes and perforated tile porosity on the operating points of the CRAC blowers, total CRAC air flow rate, and its distribution. It is concluded that modeling the computer room, the CRAC units, and/or the plenum pipes could make an average change of up to 17% in the tile flow rates with a maximum of up to 135% for the facility with 56% open tiles while the average and maximum changes for the facility with 25% open tiles are 6% and 60%, respectively.

Data Centers Revisited: Assessment of the Energy Impact of Retrofits and Technology Trends in a High-Density Computing Facility

As information and communications technology matures, the nature of the infrastructure that supports it evolves and specializes. While the telephone infrastructure had been built as a network with central offices acting as hubs, the information and communications technology maintains a similar structure, but instead, has hubs of specialized Internet data centers which house the routers and servers. This paper updates one of the first studies to document the electricity consumption and power distribution within an Internet data center. For this study, electricity billing data, metering data, and facility floor space allocation data were used to calculate computer room, total computer room, and building power densities for July 2002. The results of this 2002 study indicate that although the data center had expanded its operations by roughly 33% from the previous year and increased the electricity demand associated with the computer equipment by 55%, the total computer room power density (which includes cooling and auxiliary equipment) remained the same as the previous year at 355 W/m2. The facility’s efforts to improve energy efficiency offset the energy demand from an increased, electrically active, computer room area. The energy-efficiency measures included better optimization of power distribution units, power management modules, computer room air-conditioning units, alterations to operating conditions, facilitywide reductions in lighting, and improved facility controls. A key recommendation is to expand this research to address the need to develop metrics to capture the energy efficiency of the data network throughput.