ASHRAE Journal - June 2019 - 4

COMMENTARY
1791 Tullie Circle NE
Atlanta, GA 30329-2305
Phone: 404-636-8400
Fax: 404-321-5478 | www.ashrae.org
DIRECTOR OF ASHRAE PUBLICATIONS & EDUCATION
Mark S. Owen
EDITORIAL
Editor
Jay Scott
jayscott@ashrae.org
Managing Editor
Sarah Foster
sfoster@ashrae.org
Associate Editor
Rebecca Matyasovski
rmatyasovski@ashrae.org
Associate Editor
Jeri Alger
jalger@ashrae.org
Associate Editor
Mary Kate McGowan
mmcgowan@ashrae.org
Associate Editor
Courtney Payne
cpayne@ashrae.org
Assistant Editor
Tani Palefski
tpalefski@ashrae.org
Contributing Editor, Europe & Middle East
W. Stephen Comstock
PUBLISHING SERVICES
Publishing Services Manager
David Soltis
Production
Jayne Jackson
ADVERTISING
Associate Publisher,
ASHRAE Media Advertising
Greg Martin
gmartin@ashrae.org
Advertising Production Coordinator
Vanessa Johnson
vjohnson@ashrae.org
ASHRAE OFFICERS
President
Sheila J. Hayter, P.E.
President-Elect
Darryl K. Boyce, P.Eng.
Treasurer
Charles E. Gulledge III, P.E.
Vice Presidents
Julia A. Keen, Ph.D., P.E.
Malcolm Dennis Knight, P.E.
Farooq Mehboob, P.E.
Michael Schwedler, P.E.
Secretary & Executive Vice President
Jeff H. Littleton
POLICY GROUP
2018 - 19 Chair
Publications Committee
José Correa, P.E.
Washington Office
washdc@ashrae.org

4

ASHRAE JOURNAL

Jay Scott

Studying Unidirectional Airflow
Unidirectional airflow (often referred
to as "laminar" airflow) is used in
cleanrooms, hospital operating rooms,
laboratories, and elsewhere where a
high level of cleanliness is desired.
Perfectly unidirectional flows are
rare in HVAC applications, according to a technical feature this month.
Obstructions such as occupants, furniture, and equipment along with the
upward buoyant plumes from heat
sources can disrupt the directionality
of these airflows and form recirculation zones. Such turbulent flows promote mixing and entrainment of the
surrounding air, which can compromise the sterility of a space.
THE AUTHOR SYSTEMATICALLY
analyzed the behavior of unidirectional airflow with what he calls a
rather simple setup of a test chamber.
The CFD study evaluated the impact of
supply air velocity on the overall airflow patterns, temperature and velocity distribution under isothermal and
non-isothermal conditions. Also, the
entrainment of the surrounding air
was evaluated by studying the acceleration in the centerline velocity of the
supply air jet under these conditions.
Under isothermal conditions when
the cooling capacity of the supply air is
much higher than the sensible cooling
load in the space, such as in cleanrooms with high air change rates, the
supply airflow rate (discharge velocity)
has little impact on the directionality
of the laminar flow.

When the flow rate or the cooling
capacity of the supply air is much
lower than the sensible cooling load,
the discharge air cannot sustain the
downward unidirectional motion due
to upward resistance of the buoyant
plume from the heat sources. However,
such airflow patterns can form a protective layer of hot air surrounding the
heat sources and help create nearly
isothermal conditions in the space, the
author states,
WHEN THE COOLING CAPACITY
of the supply air exceeds about three
times the cooling load, the air jet can
sustain the downward unidirectional
motion. However, non-isothermal
conditions surrounding the supply
diffuser, created by significant lighting load near the ceiling or thermal
stratification in the space, can cause
entrainment and acceleration of the
supply air jet.
This study found that with ceilingmounted laminar diffusers the local
thermal gradients can significantly
affect the directionality of laminar flow
and entrainment from the surrounding air. The room layout can affect the
airflow patterns and temperature distribution in the space, which in turn
affects the performance of unidirectional flows. In-depth CFD analysis can
predict airflow patterns, temperature
distribution, and potential entrainment from the surrounding air, the
author concludes.
Enjoy the issue.

Mission Statement: ASHRAE Journal reviews current HVAC&R technology of broad interest through publication of application-oriented articles. ASHRAE Journal's editorial content ranges from back-to-basics features
to reviews of emerging technologies, covering the entire spectrum of professional interest from design and
construction practices to commissioning and the service life of HVAC&R environmental systems.
ashrae.org

J U N E 2 0 19


http://www.ashrae.org https://www.ashrae.org/

ASHRAE Journal - June 2019

Table of Contents for the Digital Edition of ASHRAE Journal - June 2019

Contents
ASHRAE Journal - June 2019 - Intro
ASHRAE Journal - June 2019 - Cover1
ASHRAE Journal - June 2019 - Cover2
ASHRAE Journal - June 2019 - 1
ASHRAE Journal - June 2019 - Contents
ASHRAE Journal - June 2019 - 3
ASHRAE Journal - June 2019 - 4
ASHRAE Journal - June 2019 - 5
ASHRAE Journal - June 2019 - 6
ASHRAE Journal - June 2019 - 7
ASHRAE Journal - June 2019 - 8
ASHRAE Journal - June 2019 - 9
ASHRAE Journal - June 2019 - 10
ASHRAE Journal - June 2019 - 11
ASHRAE Journal - June 2019 - 12
ASHRAE Journal - June 2019 - 13
ASHRAE Journal - June 2019 - 14
ASHRAE Journal - June 2019 - 15
ASHRAE Journal - June 2019 - 16
ASHRAE Journal - June 2019 - 17
ASHRAE Journal - June 2019 - 18
ASHRAE Journal - June 2019 - 19
ASHRAE Journal - June 2019 - 20
ASHRAE Journal - June 2019 - 21
ASHRAE Journal - June 2019 - 22
ASHRAE Journal - June 2019 - 23
ASHRAE Journal - June 2019 - 24
ASHRAE Journal - June 2019 - 25
ASHRAE Journal - June 2019 - 26
ASHRAE Journal - June 2019 - 27
ASHRAE Journal - June 2019 - 28
ASHRAE Journal - June 2019 - 29
ASHRAE Journal - June 2019 - 30
ASHRAE Journal - June 2019 - 31
ASHRAE Journal - June 2019 - 32
ASHRAE Journal - June 2019 - 33
ASHRAE Journal - June 2019 - 34
ASHRAE Journal - June 2019 - 35
ASHRAE Journal - June 2019 - 36
ASHRAE Journal - June 2019 - 37
ASHRAE Journal - June 2019 - 38
ASHRAE Journal - June 2019 - 39
ASHRAE Journal - June 2019 - 40
ASHRAE Journal - June 2019 - 41
ASHRAE Journal - June 2019 - 42
ASHRAE Journal - June 2019 - 43
ASHRAE Journal - June 2019 - 44
ASHRAE Journal - June 2019 - 45
ASHRAE Journal - June 2019 - 46
ASHRAE Journal - June 2019 - 47
ASHRAE Journal - June 2019 - 48
ASHRAE Journal - June 2019 - 49
ASHRAE Journal - June 2019 - 50
ASHRAE Journal - June 2019 - 51
ASHRAE Journal - June 2019 - 52
ASHRAE Journal - June 2019 - 53
ASHRAE Journal - June 2019 - 54
ASHRAE Journal - June 2019 - 55
ASHRAE Journal - June 2019 - 56
ASHRAE Journal - June 2019 - 57
ASHRAE Journal - June 2019 - 58
ASHRAE Journal - June 2019 - 59
ASHRAE Journal - June 2019 - 60
ASHRAE Journal - June 2019 - 61
ASHRAE Journal - June 2019 - 62
ASHRAE Journal - June 2019 - 63
ASHRAE Journal - June 2019 - 64
ASHRAE Journal - June 2019 - 65
ASHRAE Journal - June 2019 - 66
ASHRAE Journal - June 2019 - 67
ASHRAE Journal - June 2019 - 68
ASHRAE Journal - June 2019 - 69
ASHRAE Journal - June 2019 - 70
ASHRAE Journal - June 2019 - 71
ASHRAE Journal - June 2019 - 72
ASHRAE Journal - June 2019 - 73
ASHRAE Journal - June 2019 - 74
ASHRAE Journal - June 2019 - 75
ASHRAE Journal - June 2019 - 76
ASHRAE Journal - June 2019 - 77
ASHRAE Journal - June 2019 - 78
ASHRAE Journal - June 2019 - 79
ASHRAE Journal - June 2019 - 80
ASHRAE Journal - June 2019 - Cover3
ASHRAE Journal - June 2019 - Cover4
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PDRKLS
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