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ABSTRACT
Hybrid cooling solutions, which consist of the installation of heat exchangers near IT equipment, aim to eliminate hot spots in data centers containing high-density computer cabinets. In addition, cold aisle containment is often used to reduce hot air recirculation to improve energy efficiency. However, the viability and efficiency of each hybrid cooling strategy with or without containment depend on the IT load and equipment arrangement, and no formal procedure exists for selecting the most efficient strategy for a given application. Therefore, this study provides a computational approach for ranking the performance of different cooling strategies based on their capacity and cooling efficiency. The results of analyses indicate that applying containment is beneficial in (1) lowering the maximum temperature of the air entering the racks as airflow rates are increased, and (2) increasing the uniformity of rack inlet temperatures. However, applying containment also requires additional mechanical work by the computer room air handler (CRAH) fan, which may raise the data center power usage effectiveness (PUE). Application of the computational approach discussed here highlights the use of hybrid cooling to lower PUE by reducing the CRAH fan power.
Nomenclature
| Latin letters | = | |
| cp | = | specific heat capacity at constant pressure, J/kg K |
| COP | = | coefficient of performance, dimensionless |
| g | = | gravitational acceleration, m/s2 |
| HP | = | pump head, m |
| = | mass flow rate, kg/s | |
| P | = | power, W |
| T | = | temperature, K |
| = | rack heat load, W | |
| = | heat removal from chiller, W | |
| = | hybrid cooler heat removal, W | |
| Vin | = | CRAH inlet air velocity, m/s |
| = | volume flow rate, m3/s | |
| a | = | nonuniformity value, dimensionless |
| μ | = | dynamic viscosity, kg/m.s |
| ρ | = | density, kg/m3 |
| η | = | efficiency, dimensionless |
| = | exergy destruction, W | |
| Subscripts | = | |
| a | = | air |
| ai | = | air inlet |
| ao | = | air outlet |
| avg | = | averaged value |
| ch | = | chilled water |
| CFD | = | computational fluid dynamics |
| FN | = | flow network |
| IT | = | IT equipment |
| HC | = | hybrid cooler property |
| max | = | maximum |
Nomenclature
| Latin letters | = | |
| cp | = | specific heat capacity at constant pressure, J/kg K |
| COP | = | coefficient of performance, dimensionless |
| g | = | gravitational acceleration, m/s2 |
| HP | = | pump head, m |
| = | mass flow rate, kg/s | |
| P | = | power, W |
| T | = | temperature, K |
| = | rack heat load, W | |
| = | heat removal from chiller, W | |
| = | hybrid cooler heat removal, W | |
| Vin | = | CRAH inlet air velocity, m/s |
| = | volume flow rate, m3/s | |
| a | = | nonuniformity value, dimensionless |
| μ | = | dynamic viscosity, kg/m.s |
| ρ | = | density, kg/m3 |
| η | = | efficiency, dimensionless |
| = | exergy destruction, W | |
| Subscripts | = | |
| a | = | air |
| ai | = | air inlet |
| ao | = | air outlet |
| avg | = | averaged value |
| ch | = | chilled water |
| CFD | = | computational fluid dynamics |
| FN | = | flow network |
| IT | = | IT equipment |
| HC | = | hybrid cooler property |
| max | = | maximum |
Acknowledgments
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