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ABSTRACT
A novel lumped parameter approach is introduced to predict data center exergy destruction due to airflow mixing, resulting in a speedup of several orders of magnitude compared to detailed computational fluid dynamics (CFD) simulations. Both lumped parameter and detailed CFD methods agree within 8.5% for 11 test cases on an example data center. A significant time-saving design strategy is also introduced using two detailed CFD simulations to predict bulk flow parameters, and then applying lumped parameter analysis on flow-independent design parameters. The strategy shows agreement within 0.39% when computer room air conditioner (CRAC) supply temperature is varied from 12–20°C.
Nomenclature
| A | = | area, m2 |
| CFM | = | cubic feet per minute, ft3/min |
| cp | = | mass-based heat capacity, J/kg K |
| Dh | = | hydraulic diameter, m |
| err | = | error, dimensionless |
| f | = | Darcy friction factor, dimensionless |
| fB | = | flow bypass factor, dimensionless |
| F | = | open area fraction, dimensionless |
| g | = | gravitational acceleration, m/s2 |
| h | = | specific enthalpy, J/kg |
| K | = | minor loss factor, dimensionless |
| L | = | length, m |
| = | mass flow rate, kg/s | |
| N | = | quantity |
| p | = | pressure, Pa |
| P | = | perimeter, m |
| Q | = | flow rate, m3/s |
| = | heat flow, W | |
| R | = | flow resistance, Pa-s2/m6 |
| = | mass-based ideal gas constant, J/kg K | |
| = | thermal resistance, K/W | |
| s | = | specific entropy, J/kg K |
| S | = | entropy, J/K |
| SHI | = | supply heat index, dimensionless |
| V | = | speed, m/s |
| = | mechanical work, W | |
| z | = | elevation, m |
| α | = | thermal diffusivity, m2/s |
| Δp | = | pressure drop, Pa |
| = | pressure gain, Pa | |
| ε | = | turbulent dissipation, J/kg s |
| ρ | = | mass density, kg/m3 |
| ψ | = | specific exergy, J/kg |
| = | exergy destruction, W | |
| = | nondimensionalized exergy destruction, dimensionless | |
| Subscripts | = | |
| c | = | cold aisle |
| ch | = | cold aisle to hot aisle through row of racks |
| cr | = | cold aisle to return plenum |
| DC | = | data center |
| e | = | exit |
| eq | = | equivalent |
| f | = | fan |
| gen | = | generation |
| h | = | hot aisle |
| hc | = | hot aisle to cold aisle (recirculation) |
| hr | = | hot aisle to return plenum |
| i | = | inlet |
| j | = | rack designation |
| k | = | server designation |
| l | = | row designation |
| mix | = | airflow mixing |
| n | = | nonserver equipment on rack |
| nre | = | nonrack equipment |
| r | = | return plenum |
| rack | = | rack |
| row | = | row-based |
| s | = | supply plenum |
| sc | = | supply plenum to cold aisle |
| sh | = | supply plenum to hot aisle |
| S | = | surface |
| sv | = | server |
| t | = | turbulent |
| th | = | thermal |
| x, y, z | = | coordinate direction-based |
| 0 | = | reference condition |
Nomenclature
| A | = | area, m2 |
| CFM | = | cubic feet per minute, ft3/min |
| cp | = | mass-based heat capacity, J/kg K |
| Dh | = | hydraulic diameter, m |
| err | = | error, dimensionless |
| f | = | Darcy friction factor, dimensionless |
| fB | = | flow bypass factor, dimensionless |
| F | = | open area fraction, dimensionless |
| g | = | gravitational acceleration, m/s2 |
| h | = | specific enthalpy, J/kg |
| K | = | minor loss factor, dimensionless |
| L | = | length, m |
| = | mass flow rate, kg/s | |
| N | = | quantity |
| p | = | pressure, Pa |
| P | = | perimeter, m |
| Q | = | flow rate, m3/s |
| = | heat flow, W | |
| R | = | flow resistance, Pa-s2/m6 |
| = | mass-based ideal gas constant, J/kg K | |
| = | thermal resistance, K/W | |
| s | = | specific entropy, J/kg K |
| S | = | entropy, J/K |
| SHI | = | supply heat index, dimensionless |
| V | = | speed, m/s |
| = | mechanical work, W | |
| z | = | elevation, m |
| α | = | thermal diffusivity, m2/s |
| Δp | = | pressure drop, Pa |
| = | pressure gain, Pa | |
| ε | = | turbulent dissipation, J/kg s |
| ρ | = | mass density, kg/m3 |
| ψ | = | specific exergy, J/kg |
| = | exergy destruction, W | |
| = | nondimensionalized exergy destruction, dimensionless | |
| Subscripts | = | |
| c | = | cold aisle |
| ch | = | cold aisle to hot aisle through row of racks |
| cr | = | cold aisle to return plenum |
| DC | = | data center |
| e | = | exit |
| eq | = | equivalent |
| f | = | fan |
| gen | = | generation |
| h | = | hot aisle |
| hc | = | hot aisle to cold aisle (recirculation) |
| hr | = | hot aisle to return plenum |
| i | = | inlet |
| j | = | rack designation |
| k | = | server designation |
| l | = | row designation |
| mix | = | airflow mixing |
| n | = | nonserver equipment on rack |
| nre | = | nonrack equipment |
| r | = | return plenum |
| rack | = | rack |
| row | = | row-based |
| s | = | supply plenum |
| sc | = | supply plenum to cold aisle |
| sh | = | supply plenum to hot aisle |
| S | = | surface |
| sv | = | server |
| t | = | turbulent |
| th | = | thermal |
| x, y, z | = | coordinate direction-based |
| 0 | = | reference condition |