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 |