ASHRAE Journal - August 2021 - 47

TECHNICAL FEATURE
passes through chilled water coils
and is cooled to approximately 15°C
(59°F). A CRAH unit has a maximum
cooling capacity of 230 kW. The fans
in a CRAH unit have a supply air of
770 m3/min (24,721 cfm).
Figure 3 shows the analysis models
of the HAC and CAC, the air containment
methods of the test IT room.
The cool air is recirculated back to the
racks through perforated tiles in the
raised fl oor plenum. The air movers
pressurize the plenum with cool air.
The HAC has ducted (contained) air
return with cooling units, and the
CAC uses a room (fl ooded) air return
air distribution system. The downfl ow
CRAH units were applied for the raised fl oor, and three
EC fans were installed in each CRAH unit (Figure 2c).
The supply air temperature of the CRAH unit was 15°C
(59°F).
Hot-Aisle
Containment
B. Cold-Aisle Containment with Flooded Air Return
Cold-Aisle Containment
FIGURE 3 Air containment model. (a) Hot-aisle containment and (b) cold-aisle containment.
A. Hot-Aisle Containment with Ducted Air Return
RA (Return Air)
Duct of
Hot-Aisle
Containment
RA Chamber
CRAH Units
RA (Return Air) Grilles of
Cold-Aisle Containment
CRAH Units
In the HAC, return air (RA) ducts were installed at the
top so that the return air could return to the CRAH units.
The ducts of the containment area installed at each hot
aisle were connected again to the RA chamber. No leakage
in the ducts was assumed, and it was also assumed
that the containment area had no leakage except for the
gap under the air containment area's entrance door and
the cable cutouts at the rack.
The most essential element in evaluating the thermal
performance of a cooling system in a data center is the
distribution of the inlet air temperature of the rack
servers. If it is too low, it causes waste of energy. If it
is too high, the heat of the server cannot be effectively
removed.7 ASHRAE's Thermal Guideline for Data Processing
Environments book8 has been widely used as the IT environment
classes of data centers and proposes proper
server inlet air temperatures. The adequacy of the
results of this study was determined by applying these
temperature ranges .
The CFD result in the medium-power density rack
server zone was that the HAC and CAC have very similar
inlet air temperature distribution of rack servers.
Both air containment systems would be well-controlled
without any trouble. But inlet air temperature distribution
of rack servers in the high-density rack server zone
was very different from within the HAC and CAC. This
is because insuffi cient cool air is supplied into the cold
aisles (rack servers) with CAC than with HAC.
Figure 4a shows the mean inlet air temperatures distribution
of rack servers for the HAC. All of the rack servers
operated within the recommended temperature range
of ASHRAE, resulting in a very good IT environment .
However, a proper airfl ow rate was not supplied to the
fi rst and tenth rack servers compared to other rack
servers, which resulted in relatively high inlet air temperatures
for the rack servers. This happens due to high
air velocity and corresponding high velocity pressure
in these areas in the raised fl oor near the CRAH units.
Nevertheless, the maximum inlet air temperature was
20.6°C (69.1°F) (mean 16.5°C [61.7°F]), which was very
proper.
In the case of the CAC shown in Figure 4b, it was found
that all of the rack servers also satisfi ed the recommenced
temperature range. However, 5% of them (fi ve
rack servers) exceeded 26°C (79°F), and they were the
A-type high-density rack servers. Among them, one
server exhibited a maximum inlet air temperature of
27.0°C (80.6°F) (mean 18.5°C [65.3°F]), which was 6.4°C
(11.5°F) higher compared to the HAC.
The hot aisle in the HAC is only affected by leakage
from the cable cutouts at each rack, and the exhaust air
from IT equipment is directly captured and returned to
CRAH units via ducts, whereas the hot aisle in the CAC is
affected by cable cutouts at the rack. Some hot air from
racks is recirculated to the cold aisle because the return
air path from the hot aisle back to the CRAH via the
A U G U S T 2 0 2 1 ashrae.org ASHRAE JOURNAL
47
http://www.ashrae.org

ASHRAE Journal - August 2021

Table of Contents for the Digital Edition of ASHRAE Journal - August 2021

Contents
ASHRAE Journal - August 2021 - Intro
ASHRAE Journal - August 2021 - Cover1
ASHRAE Journal - August 2021 - Cover2
ASHRAE Journal - August 2021 - 1
ASHRAE Journal - August 2021 - Contents
ASHRAE Journal - August 2021 - 3
ASHRAE Journal - August 2021 - 4
ASHRAE Journal - August 2021 - 5
ASHRAE Journal - August 2021 - 6
ASHRAE Journal - August 2021 - 7
ASHRAE Journal - August 2021 - 8
ASHRAE Journal - August 2021 - 9
ASHRAE Journal - August 2021 - 10
ASHRAE Journal - August 2021 - 11
ASHRAE Journal - August 2021 - 12
ASHRAE Journal - August 2021 - 13
ASHRAE Journal - August 2021 - 14
ASHRAE Journal - August 2021 - 15
ASHRAE Journal - August 2021 - 16
ASHRAE Journal - August 2021 - 17
ASHRAE Journal - August 2021 - 18
ASHRAE Journal - August 2021 - 19
ASHRAE Journal - August 2021 - 20
ASHRAE Journal - August 2021 - 21
ASHRAE Journal - August 2021 - 22
ASHRAE Journal - August 2021 - 23
ASHRAE Journal - August 2021 - 24
ASHRAE Journal - August 2021 - 25
ASHRAE Journal - August 2021 - 26
ASHRAE Journal - August 2021 - 27
ASHRAE Journal - August 2021 - 28
ASHRAE Journal - August 2021 - 29
ASHRAE Journal - August 2021 - 30
ASHRAE Journal - August 2021 - 31
ASHRAE Journal - August 2021 - 32
ASHRAE Journal - August 2021 - 33
ASHRAE Journal - August 2021 - 34
ASHRAE Journal - August 2021 - 35
ASHRAE Journal - August 2021 - 36
ASHRAE Journal - August 2021 - 37
ASHRAE Journal - August 2021 - 38
ASHRAE Journal - August 2021 - 39
ASHRAE Journal - August 2021 - 40
ASHRAE Journal - August 2021 - 41
ASHRAE Journal - August 2021 - 42
ASHRAE Journal - August 2021 - 43
ASHRAE Journal - August 2021 - 44
ASHRAE Journal - August 2021 - 45
ASHRAE Journal - August 2021 - 46
ASHRAE Journal - August 2021 - 47
ASHRAE Journal - August 2021 - 48
ASHRAE Journal - August 2021 - 49
ASHRAE Journal - August 2021 - 50
ASHRAE Journal - August 2021 - 51
ASHRAE Journal - August 2021 - 52
ASHRAE Journal - August 2021 - 53
ASHRAE Journal - August 2021 - 54
ASHRAE Journal - August 2021 - 55
ASHRAE Journal - August 2021 - 56
ASHRAE Journal - August 2021 - 57
ASHRAE Journal - August 2021 - 58
ASHRAE Journal - August 2021 - 59
ASHRAE Journal - August 2021 - 60
ASHRAE Journal - August 2021 - 61
ASHRAE Journal - August 2021 - 62
ASHRAE Journal - August 2021 - 63
ASHRAE Journal - August 2021 - 64
ASHRAE Journal - August 2021 - 65
ASHRAE Journal - August 2021 - 66
ASHRAE Journal - August 2021 - 67
ASHRAE Journal - August 2021 - 68
ASHRAE Journal - August 2021 - 69
ASHRAE Journal - August 2021 - 70
ASHRAE Journal - August 2021 - 71
ASHRAE Journal - August 2021 - 72
ASHRAE Journal - August 2021 - 73
ASHRAE Journal - August 2021 - 74
ASHRAE Journal - August 2021 - 75
ASHRAE Journal - August 2021 - 76
ASHRAE Journal - August 2021 - 77
ASHRAE Journal - August 2021 - 78
ASHRAE Journal - August 2021 - 79
ASHRAE Journal - August 2021 - 80
ASHRAE Journal - August 2021 - Cover3
ASHRAE Journal - August 2021 - Cover4
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2021november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2021november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XCODFR
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QSLFGO
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ILKVNM
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2021
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OPDJKD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VJKSRY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SDHUTC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JPPKRR
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SDLTTH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_CKLLES
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SLDOX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_HJETUK
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OLUHGE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2020october
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2020october_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ZERDGH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QVMNEO
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RTPOKE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_BBATRE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_STUBMW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TPEMPE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JNMKDS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FBTTPA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WQMMNE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TVBRYN
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_showguide2020
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_KTUZMA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ABEDGD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201910
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201909
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019septmeber_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019september
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201908
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201907
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201906
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201905
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201904
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019april
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201903
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019march
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201902
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201901
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_showguide2019
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018december
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018october
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2018
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201810
https://www.nxtbook.com/nxtbooks/ashrae/ashraeinsights_201806
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201805
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201804
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201803
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201712
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201711
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201710
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201709
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201705
https://www.nxtbook.com/nxtbooks/ashrae/ashrae_meetinginsert_201610
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acrexindia
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer
https://www.nxtbook.com/nxtbooks/amca/2014summer2
https://www.nxtbook.com/nxtbooks/amca/2014summer
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acma_2014summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201311
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201309
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acmasupp_2013fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201305
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201303
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2013winter
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201211
https://www.nxtbook.com/nxtbooks/ashrae/achr_expo_mexico2012
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201209
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v3
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v2
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201205
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201203
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012winter
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201111_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201109_v2
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2011summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201105
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201103
https://www.nxtbookmedia.com