ASHRAE Journal - March 2021 - 44

ENGINEER'S NOTEBOOK
COLUMN

Nathan Ho

Low System Pressure Case Study

Troubleshooting Campus
Chilled Water Systems
BY NATHAN HO, P.E., MEMBER ASHRAE

On one of the hottest days on record for Southern California, with temperatures
reaching 105°F (40.6°C), a medical institution in the region experienced a sudden loss
of cooling at one of its campus research facilities, and the author's team was called to
investigate. This column presents a case study in troubleshooting and solving a chilled
water (CHW) distribution issue related to low system pressure.
Background
The facility in question is a four-story mixed-use
medical research facility with one of the four stories
located underground. A year earlier, the facility underwent a major renovation with new roofing, HVAC equipment, controls, lighting systems and interior finishes.
In that project our team upgraded the cooling system,
replacing rooftop air-handling units (AHUs) that used
direct-expansion refrigerant coils with two new AHUs
using chilled water coils; these were served by a new
chilled water riser with connection to the campus'
chilled water utility distribution piping (recently added
under a separate project by another design-build team).
Start-up and commissioning were completed during the
summer, and for a year the building's CHW system proceeded to function as designed. Then came the mysterious cooling failure.

First 24 Hours-Investigation
Late morning on what was already a hot day, the
facility owner's project manager received a call from
users in a research suite on the underground level,
44

ASHRAE JOURNAL

ashrae.org

MARCH 2021

stating that room temperatures were substantially
warmer than setpoint. Sensing that the day would
become significantly hotter, and knowing that the
AHU serving the space is a 100% outdoor air unit, the
project manager proactively called in our designbuild team to investigate.
Upon arriving, we first checked the overheated areas
and confirmed that the supply air temperature at the
diffusers serving these spaces was indeed too warm to
cool the space. We quickly determined that the elevated
supply air temperature was not due to a failed duct
heating hot water control valve; the associated heating
coils serving these zones were cool to the touch, and
the measured supply air temperature was similar to
the supply air temperature found at the corresponding
rooftop AHU. (See the observations on the next page for
AHU-1's supply air temperature.)
Moving further upstream in the HVAC system, we
proceeded to the roof to check global system performance. Figure 1 shows the CHW system layout, with " CC "
Nathan Ho, P.E., is an associate principal and engineering group leader with P2S Inc., in Irvine,
Calif. He is the chair of ASHRAE SPC 110.



http://ashrae.org

ASHRAE Journal - March 2021

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

Contents
ASHRAE Journal - March 2021 - Intro
ASHRAE Journal - March 2021 - Cover1
ASHRAE Journal - March 2021 - Cover2
ASHRAE Journal - March 2021 - 1
ASHRAE Journal - March 2021 - Contents
ASHRAE Journal - March 2021 - 3
ASHRAE Journal - March 2021 - 4
ASHRAE Journal - March 2021 - 5
ASHRAE Journal - March 2021 - 6
ASHRAE Journal - March 2021 - 7
ASHRAE Journal - March 2021 - 8
ASHRAE Journal - March 2021 - 9
ASHRAE Journal - March 2021 - 10
ASHRAE Journal - March 2021 - 11
ASHRAE Journal - March 2021 - 12
ASHRAE Journal - March 2021 - 13
ASHRAE Journal - March 2021 - 14
ASHRAE Journal - March 2021 - 15
ASHRAE Journal - March 2021 - 16
ASHRAE Journal - March 2021 - 17
ASHRAE Journal - March 2021 - 18
ASHRAE Journal - March 2021 - 19
ASHRAE Journal - March 2021 - 20
ASHRAE Journal - March 2021 - 21
ASHRAE Journal - March 2021 - 22
ASHRAE Journal - March 2021 - 23
ASHRAE Journal - March 2021 - 24
ASHRAE Journal - March 2021 - 25
ASHRAE Journal - March 2021 - 26
ASHRAE Journal - March 2021 - 27
ASHRAE Journal - March 2021 - 28
ASHRAE Journal - March 2021 - 29
ASHRAE Journal - March 2021 - 30
ASHRAE Journal - March 2021 - 31
ASHRAE Journal - March 2021 - 32
ASHRAE Journal - March 2021 - 33
ASHRAE Journal - March 2021 - 34
ASHRAE Journal - March 2021 - 35
ASHRAE Journal - March 2021 - 36
ASHRAE Journal - March 2021 - 37
ASHRAE Journal - March 2021 - 38
ASHRAE Journal - March 2021 - 39
ASHRAE Journal - March 2021 - 40
ASHRAE Journal - March 2021 - 41
ASHRAE Journal - March 2021 - 42
ASHRAE Journal - March 2021 - 43
ASHRAE Journal - March 2021 - 44
ASHRAE Journal - March 2021 - 45
ASHRAE Journal - March 2021 - 46
ASHRAE Journal - March 2021 - 47
ASHRAE Journal - March 2021 - 48
ASHRAE Journal - March 2021 - 49
ASHRAE Journal - March 2021 - 50
ASHRAE Journal - March 2021 - 51
ASHRAE Journal - March 2021 - 52
ASHRAE Journal - March 2021 - 53
ASHRAE Journal - March 2021 - 54
ASHRAE Journal - March 2021 - 55
ASHRAE Journal - March 2021 - 56
ASHRAE Journal - March 2021 - 57
ASHRAE Journal - March 2021 - 58
ASHRAE Journal - March 2021 - 59
ASHRAE Journal - March 2021 - 60
ASHRAE Journal - March 2021 - 61
ASHRAE Journal - March 2021 - 62
ASHRAE Journal - March 2021 - 63
ASHRAE Journal - March 2021 - 64
ASHRAE Journal - March 2021 - 65
ASHRAE Journal - March 2021 - 66
ASHRAE Journal - March 2021 - 67
ASHRAE Journal - March 2021 - 68
ASHRAE Journal - March 2021 - 69
ASHRAE Journal - March 2021 - 70
ASHRAE Journal - March 2021 - 71
ASHRAE Journal - March 2021 - 72
ASHRAE Journal - March 2021 - 73
ASHRAE Journal - March 2021 - 74
ASHRAE Journal - March 2021 - 75
ASHRAE Journal - March 2021 - 76
ASHRAE Journal - March 2021 - 77
ASHRAE Journal - March 2021 - 78
ASHRAE Journal - March 2021 - 79
ASHRAE Journal - March 2021 - 80
ASHRAE Journal - March 2021 - 81
ASHRAE Journal - March 2021 - 82
ASHRAE Journal - March 2021 - 83
ASHRAE Journal - March 2021 - 84
ASHRAE Journal - March 2021 - 85
ASHRAE Journal - March 2021 - 86
ASHRAE Journal - March 2021 - 87
ASHRAE Journal - March 2021 - 88
ASHRAE Journal - March 2021 - 89
ASHRAE Journal - March 2021 - 90
ASHRAE Journal - March 2021 - 91
ASHRAE Journal - March 2021 - 92
ASHRAE Journal - March 2021 - 93
ASHRAE Journal - March 2021 - 94
ASHRAE Journal - March 2021 - 95
ASHRAE Journal - March 2021 - 96
ASHRAE Journal - March 2021 - 97
ASHRAE Journal - March 2021 - 98
ASHRAE Journal - March 2021 - 99
ASHRAE Journal - March 2021 - 100
ASHRAE Journal - March 2021 - 101
ASHRAE Journal - March 2021 - 102
ASHRAE Journal - March 2021 - 103
ASHRAE Journal - March 2021 - 104
ASHRAE Journal - March 2021 - Cover3
ASHRAE Journal - March 2021 - Cover4
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VHQRAW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XGMDXI
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_YELQLJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QJLWMC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_MCDEBX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WNYSQY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XATVOD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FJSHSS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_CCBZDS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XDEFVG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2023november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2023november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VHGNBL
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WPKBNJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_UUVCDE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RTGDEW
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2023
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LKRFXS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_AZSOFG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ERCDBH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QWDFRV
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JHGVDF
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OPUYHG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SREIBM
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LRTGLK
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OKRFGH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2022november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2022november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TZSERA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LVRUIX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RPTVYZ
https://www.nxtbook.com/nxtbooks/ashrae/mini_pub_catalog
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XIYTGD
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2022
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RFGDOB
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PABXNU
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_REMKLS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PICVBT
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_AOYTVW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JQOPLS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_IOYTBC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SGAJJF
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_IGHYER
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