Cabinet cooling is the next, higher
level of the thermal management
challenge. There are two traditional
cabinet cooling approaches:
horizontal and vertical. The
standard cabinet volume (W2’x D4’x
H7’) tends to stay unchanged because
of industrial floor tile standard (2’x4’).
Due to constantly increasing power
consumption per cabinet, both
approaches require more and more air
for cooling.
HORIZONTAL
In the
horizontal approach, modules in the
cabinet are stacked horizontally
(“pizza pans”), and cooling air
moves from one side of the rack
(cold isle) to another (hot isle).
Air may be supplied centrally
(plenum with one or more fan trays,
or by one cabinet fan with turning
vanes), or with multiple fans
per blade. In that approach
thermal gradient through the module
is minimal, but the air pressure
available per module is limited by
multiple losses in the supply air
ducts. Hot/Cold isles ramifications
of that approach makes cooling even
more difficult due to hot isle’s air
propagation into the cold isle area.
VERTICAL
In the vertically integrated cabinet
modules, blades are arranged
vertically (“book shelf”) with one
or more fans (or fan trays), moving
the air from the bottom with the exhaust at the cabinet’s
top. In this case the exhaust from
one level of cabinet’s modules
(cage) preheats the inlet to the
next cage, etc. The result is the top (usually the 3d)
cage in the rack gets the most heat
and is most difficult to cool.
Existing data centers (designed to
ASHRAE guidelines) cannot cope with
the increasing air flow requirements
for two reasons:
- Insufficient data center floor
space for extra Computer Room A/C (CRAC) units (already
taken by the computer and peripheral
equipment);
- Unprecedented difficulties to
“spread” under floor cold air
between computer cabinets because of
the limited floor plenum height.
Adding CRAC units is
associated with extra cost
and increased facility
energy consumption – higher
TCO (Total Cost of
Ownership) for the computer
equipment. To resolve floor
plenum limitations very
often requires raising floor
tiles from 12 or 18” to 24”,
or even 36”.
When facility ceiling height
allows raising the floor,
cost adds to the TCO.
However, more often it’s not
possible due to construction
code violation (ceiling fire
sprinklers should be at the
given minimal height from
the top of computer
cabinets).
Being stuck between the
given facility size and the
necessity to meet new
cabinets power requirements
causes the following issue
for mentioned two types of
the data center cooling:
- Horizontally
air cooled layouts: need to
address hot/cold isles’
crossovers related hot
spots. That requires
additional (higher density)
spot cooling equipment with
the corresponding TCO
increase. Because of the
under floor air pressure
limitations, top modules do
not have enough cold air
compared to the lower ones.
To mitigate that problem,
the
computer air supplying fan
has to run faster,
causing increased energy
consumption and noise.
- Vertically air cooled layouts (blade servers and supercomputers)
require much more powerful,
expensive,
energy consuming and noisier
fans to meet “energy balance
end met”. Top (hotter) cage
cooling challenge requires
special (internal to
cabinet) internal air flow
balancing, associated with
the increased system
impedance and additional
pressure requirements to the
cabinet’s central fan.
The pressure drop through the cabinet could exceed 7”WG and the fan’s power could be > 5 KW.
PLMC Cabinets/Rack
cooling alleviates
these problems as follows:
1. Introducing more
efficient cooling at blade
(module) level reduces air
cooling inefficiency related
air flow consumption. (Read
more about blade cooling.)
2. Due to minimal parasitic
power consumption, PLMC
provides the highest COP
efficiency compared to any
other available liquid
cooled systems (Pumped
Liquid Single Phase, Vapor
Compression Refrigeration,
etc.)
Pumped
Liquid Single Phase
Vapor
Compression
Refrigeration
Pumped
Liquid Two Phase
Parasitic
Power
2760W
2133W
340W
COP
air/water cooled
control
2.3
3
19/71
Condensation/Dew
Point
N/A
Difficult
N/A
Ambient Air
Sink
Easy
Difficult
Easy
Variable
Load/No Load
Easy
Difficult
Inherent
Reliability
50K hrs
(pump)
12K-20K hrs
(compressor)
50K hrs
(pump)
Cost
Intermediate
Highest
Lowest
Cold
Plate/Evaporator U
Lowest
Highest
Highest
Required
Area
Highest
Lowest
Lowest
3. The isothermal nature of
the PLMC cabinet’s cooling
adaptive control
(variable/no load operation)
is addressed naturally
without adding additional
PID controls
4. Combines high heat
removal of two phase systems
with the reliability of
liquid pumping.
5. Uses well known cost
effective components and
materials from the HVAC
industry in a novel
configuration.
6. Modular, scalable and hot
swappable.
- Insufficient data center floor
space for extra Computer Room A/C (CRAC) units (already
taken by the computer and peripheral
equipment); 
