ASHRAE Journal - November 2020 - 15

TECHNICAL FEATURE

and cooling and heating zone setpoints are
assumed to be 75°F (23.9°C).
Five different cases are presented in
Table 1, using 8,760 hourly data obtained
from eQuest. Parameters included are time,
outdoor air temperatures (OAT), outdoor air
dew-point temperature (OA DP) and zone sensible loads. Negative numbers indicate heating
loads. Latent loads are calculated based on the
number of people in each zone (200 Btu/h per
person, or 59 W per person).

West (Zone 4) Area = 2,147 ft2 N# People = 11
Design Airflow = 5,000 cfm Minimum Airflow = 1,000 cfm*

North (Zone 5) Area = 2,147 ft2 N# People = 11
Design Airflow = 4,000 cfm Minimum Airflow = 800 cfm*

Typical Single-Duct VAV System

Core (Zone 3)
Area = 16,410 ft2, N# People = 82
Design Airflow = 8,000 cfm
Minimum Airflow = 1,600 cfm*

South (Zone 1) Area = 2,147 ft2 N# People = 11

East (Zone 2) Area = 2,147 ft2 N# People = 11
Design Airflow = 5,000 cfm Minimum Airflow = 1,000 cfm*

FIGURE 1 Floor plan for the example 25,000 ft2 (2323 m2) office building.

Design Airflow = 5,000 cfm Minimum Airflow = 1,000 cfm*
The VAV system typically consists of a single
AHU fan to supply conditioned air (with ade- *Minimum Airflow is 20% of Maximum Design Airflow
quate fresh air) to multiple zones through a
single-duct air distribution system. Let us
The five zones are served by single-duct VAV boxes
examine the previous office building example. The
and a single AHU, called AHU1. Table 3 shows the
zone airflow rates and reheat requirements† for the
system-level results,‡ which include system airflow
same five cases are shown in Table 2. These are calcurates, ventilation requirements calculated based on the
lated based on two supply air temperature (SAT) reset ASHRAE Standard 62.2-2016 multizone Ventilation Rate
strategies: Table 2a shows keeping SAT constant at 55°F Procedure,2 actual outdoor airflow rate (OA), outdoor air
fraction (OAF), mixing air temperature (MAT), supply
(12.7°C) and varying the SAT as a function of outdoor
air temperature (SAT), total cooling load, sensible coolair temperature (OAT). In the latter strategy (shown
ing load, system heating load and total reheat use.
in Table 2b), the SAT is 65°F (18.3°C) if the OAT is less
Case 3 is illustrated in Figure 2. In Table 3a, when the
than 50°F (10°C); the SAT is 55°F (12.7°C) if the OAT is
OAT is 58°F (14.4°C) (the dew-point temperature is
greater than 65°F (18.3°C). Otherwise, the SAT varies
55°F [12.8°C]), the economizer is "on," and the outdoor
linearly with the OAT.
TABLE 1 Sensible cooling and heating loads obtained from the building energy simulation software eQuest for an example office building in Cincinnati.
CASE

CONDITIONS (°F)

TIME

SENSIBLE LOADS (BTU/H)

Month

Day

Hour

OAT

OA DP

South (Zone 1

East (Zone 2)

Core (Zone 3)

West (Zone 4)

North (Zone 5)

1

1

3

11

38

27

25,342.7

16,454.5

79,975.0

-3,180.1

-1,103.3

2

3

21

10

41

27

11,173.0

29,825.0

82,544.8

-494.8

2,572.2

3

4

12

10

58

55

14,284.8

14,438.4

101,311.0

14,200.7

14,437.0

4

10

22

10

67

52

40,114.9

45,255.8

102,882.0

18,205.1

18,750.2

5

5

21

16

82

53

41,040.8

35,878.4

133,838.0

63,516.0

35,829.4

†The

airflow rate and reheat are calculated based on the sensible heat equation: a multiplication of mass flow rate, specific heat, and
temperature difference. For the airflow rate calculations, the temperature difference is equal to the supply air temperature (SAT) minus
zone air temperature. If the calculated airflow rate is below the minimum limit, it will be kept at the minimum value, and if the zone
temperature drops below the heating temperature setpoint, reheat will be activated. The amount of reheat is calculated using the same
sensible heat equation.

‡The system airflow rate is calculated as the sum of zone airflow rates. The return air humidity ratio is calculated based on the latent heat
equation: a multiplication of latent heat of water evaporation, mass flow rate and humidity ratio change. The initial supply humidity ratio is
assumed. The following iteration process is then applied: the mixing air conditions are calculated using energy and mass equations for
two streams of return and outdoor air. Ventilation is calculated based on the ASHRAE Standard 62.1-2016 multizone Ventilation Rate
Procedure. The dual-temperature economizer control algorithm is used. The cooling load is calculated as a multiplication of mass flow
rate and the mixing and supply air enthalpy difference.
N OVEM BER 2020

ashrae.org

ASHRAE JOURNAL

15


https://www.ashrae.org/

ASHRAE Journal - November 2020

Table of Contents for the Digital Edition of ASHRAE Journal - November 2020

Contents
ASHRAE Journal - November 2020 - Intro
ASHRAE Journal - November 2020 - Cover1
ASHRAE Journal - November 2020 - Cover2
ASHRAE Journal - November 2020 - 1
ASHRAE Journal - November 2020 - Contents
ASHRAE Journal - November 2020 - 3
ASHRAE Journal - November 2020 - 4
ASHRAE Journal - November 2020 - 5
ASHRAE Journal - November 2020 - 6
ASHRAE Journal - November 2020 - 7
ASHRAE Journal - November 2020 - 8
ASHRAE Journal - November 2020 - 9
ASHRAE Journal - November 2020 - 10
ASHRAE Journal - November 2020 - 11
ASHRAE Journal - November 2020 - 12
ASHRAE Journal - November 2020 - 13
ASHRAE Journal - November 2020 - 14
ASHRAE Journal - November 2020 - 15
ASHRAE Journal - November 2020 - 16
ASHRAE Journal - November 2020 - 17
ASHRAE Journal - November 2020 - 18
ASHRAE Journal - November 2020 - 19
ASHRAE Journal - November 2020 - 20
ASHRAE Journal - November 2020 - 21
ASHRAE Journal - November 2020 - 22
ASHRAE Journal - November 2020 - 23
ASHRAE Journal - November 2020 - 24
ASHRAE Journal - November 2020 - 25
ASHRAE Journal - November 2020 - 26
ASHRAE Journal - November 2020 - 27
ASHRAE Journal - November 2020 - 28
ASHRAE Journal - November 2020 - 29
ASHRAE Journal - November 2020 - 30
ASHRAE Journal - November 2020 - 31
ASHRAE Journal - November 2020 - 32
ASHRAE Journal - November 2020 - 33
ASHRAE Journal - November 2020 - 34
ASHRAE Journal - November 2020 - 35
ASHRAE Journal - November 2020 - 36
ASHRAE Journal - November 2020 - 37
ASHRAE Journal - November 2020 - 38
ASHRAE Journal - November 2020 - 39
ASHRAE Journal - November 2020 - 40
ASHRAE Journal - November 2020 - 41
ASHRAE Journal - November 2020 - 42
ASHRAE Journal - November 2020 - 43
ASHRAE Journal - November 2020 - 44
ASHRAE Journal - November 2020 - 45
ASHRAE Journal - November 2020 - 46
ASHRAE Journal - November 2020 - 47
ASHRAE Journal - November 2020 - 48
ASHRAE Journal - November 2020 - 49
ASHRAE Journal - November 2020 - 50
ASHRAE Journal - November 2020 - 51
ASHRAE Journal - November 2020 - 52
ASHRAE Journal - November 2020 - 53
ASHRAE Journal - November 2020 - 54
ASHRAE Journal - November 2020 - 55
ASHRAE Journal - November 2020 - 56
ASHRAE Journal - November 2020 - 57
ASHRAE Journal - November 2020 - 58
ASHRAE Journal - November 2020 - 59
ASHRAE Journal - November 2020 - 60
ASHRAE Journal - November 2020 - 61
ASHRAE Journal - November 2020 - 62
ASHRAE Journal - November 2020 - 63
ASHRAE Journal - November 2020 - 64
ASHRAE Journal - November 2020 - 65
ASHRAE Journal - November 2020 - 66
ASHRAE Journal - November 2020 - 67
ASHRAE Journal - November 2020 - 68
ASHRAE Journal - November 2020 - 69
ASHRAE Journal - November 2020 - 70
ASHRAE Journal - November 2020 - 71
ASHRAE Journal - November 2020 - 72
ASHRAE Journal - November 2020 - 73
ASHRAE Journal - November 2020 - 74
ASHRAE Journal - November 2020 - 75
ASHRAE Journal - November 2020 - 76
ASHRAE Journal - November 2020 - 77
ASHRAE Journal - November 2020 - 78
ASHRAE Journal - November 2020 - 79
ASHRAE Journal - November 2020 - 80
ASHRAE Journal - November 2020 - Cover3
ASHRAE Journal - November 2020 - Cover4
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FYONLJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2024november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2024november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_BDMHLG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WJDGRY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ATMAHK
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