ASHRAE Journal - June 2020 - 55
COLUMN DIGITAL LABORATORY
(Table 1) portion of the total heat flow. In addition, even
in a system where air speeds are higher, not every single
surface in that space will see those high air speeds, and
the radiant heat transfer effect may still be important.
Doesn't the solar load stay at the perimeter? This is a
regularly used assumption that isn't valid even if shading is used. The way solar load enters the space is a complicated process given the prevalence of double- and triple-pane windows and low emissivity (low-e) coatings.
Shading devices further complicate this process. In very
simple terms, a solar load that is incident on a window
is split into three components: the reflected portion,
the transmitted portion and the absorbed portion. Only
the transmitted and absorbed portions of the solar load
affect the heat balance in the space, while the absorbed
portion has a strong effect on the surface temperature of
the glass.
The transmitted load is the critical one because it
affects all the surfaces in an indoor environment (to
varying degrees) through absorption and reflection.
Even if an interior shade is used, unless it's 100% reflective, the solar load transmitted through a window heats
up the shade, which in turn reradiates that heat back
into the space. Even though a high performance window and shading system can do a great job reducing the
transmitted solar load (by reflecting it back outdoors) it
does not eliminate it nor does it "lock" it at the window.
What about thermal comfort? In addition to indirectly heating the air in an indoor space, thermal radiation directly affects comfort via three thermal comfort
metrics outlined in ASHRAE Standard 55-2017, Thermal
Environmental Conditions for Human Occupancy. One of those
is the predicted mean vote (PMV) index (Section §5.3.2),
which is a measure of whole body comfort for a representative occupant. This index is directly tied to thermal
radiation through the mean radiant temperature in the
space. The mean radiant temperature is a measure of
the thermal radiation heat transfer from all the surfaces
in an indoor space to the human body. It is essentially
an aggregate temperature that a human body "sees" as
a result of the radiant heat transfer in the space from
internal and external (solar) sources.
The second comfort index affected by thermal radiation is the radiant asymmetry in the space (Standard
55-2017, Section §5.3.4.2), which is a measure of how the
difference in surface temperatures in the indoor environment affects thermal comfort. Finally, the vertical air
TABLE 1 Radiant heat transfer fraction for various indoor heat sources.
HEAT
SOURCE
RADIANT
FRACTION (%)
NOTES
2017 ASHRAE HANDBOOKFUNDAMENTALS, CH. 18
Occupant
27 to 60
Seated, Very Light Work
Table 1
38 to 58
Moderately Active Office
Work
35 to 49
Moderate Dancing
Lighting
Equipment
55 to 60
Linear Pendant LED
61 to 73
Recessed Fluorescent
Luminaire with Lens
Table 3
15 to 18
Recessed LED Downlight
10
Desktop
Table 8A
25
Laptop
Table 8B
40
Monitor
Table 8D
30
Printer
Table 9
temperature difference in the space (Standard 55-2017,
Section §5.3.4.3) is affected by thermal radiation heat
transfer from a warm ceiling to a cold floor and vice
versa, attenuating this quantity in practice.
We will explore the comparative effects of thermal
radiation in air-based HVAC systems by exploring CFD
results from two office building projects: one with an
underfloor system and one with an overhead mixing
system. A summary of the design parameters for both
examples is shown in Table 2. We will focus on a simple
comparison of the CFD results with and without a thermal radiation model for both of these projects. The total
thermal loads (heat sources) will be kept identical in
both cases. When the thermal radiation model is active,
the thermal loads will be split according to a recommended radiant fraction taken from the 2017 ASHRAE
Handbook-Fundamentals.
Office Building with Underfloor System
This example is a CFD simulation of a 5,000 ft2
(465 m2) section of office from a five-story office
building (290,000 ft2 [26 942 m2] total size) project
in Delaware. A snapshot of the CFD model is shown
in Figure 1, while the design details and CFD modeling parameters are shown in Table 2. The CFD model
includes the occupied space, the underfloor plenum,
the ceiling plenum and the ceiling and floor concrete
slabs. The various pieces of the model are interfaced
to allow heat transfer between them based on the heat
gain in the office. The model also includes the effects of
heat gain/loss from adjacent floors (above and below) by
J U N E 2020
ashrae.org
ASHRAE JOURNAL
55
https://www.ashrae.org/
ASHRAE Journal - June 2020
Table of Contents for the Digital Edition of ASHRAE Journal - June 2020
Contents
ASHRAE Journal - June 2020 - Intro
ASHRAE Journal - June 2020 - Cover1
ASHRAE Journal - June 2020 - Cover2
ASHRAE Journal - June 2020 - 1
ASHRAE Journal - June 2020 - Contents
ASHRAE Journal - June 2020 - 3
ASHRAE Journal - June 2020 - 4
ASHRAE Journal - June 2020 - 5
ASHRAE Journal - June 2020 - 6
ASHRAE Journal - June 2020 - 7
ASHRAE Journal - June 2020 - 8
ASHRAE Journal - June 2020 - 9
ASHRAE Journal - June 2020 - 10
ASHRAE Journal - June 2020 - 11
ASHRAE Journal - June 2020 - 12
ASHRAE Journal - June 2020 - 13
ASHRAE Journal - June 2020 - 14
ASHRAE Journal - June 2020 - 15
ASHRAE Journal - June 2020 - 16
ASHRAE Journal - June 2020 - 17
ASHRAE Journal - June 2020 - 18
ASHRAE Journal - June 2020 - 19
ASHRAE Journal - June 2020 - 20
ASHRAE Journal - June 2020 - 21
ASHRAE Journal - June 2020 - 22
ASHRAE Journal - June 2020 - 23
ASHRAE Journal - June 2020 - 24
ASHRAE Journal - June 2020 - 25
ASHRAE Journal - June 2020 - 26
ASHRAE Journal - June 2020 - 27
ASHRAE Journal - June 2020 - 28
ASHRAE Journal - June 2020 - 29
ASHRAE Journal - June 2020 - 30
ASHRAE Journal - June 2020 - 31
ASHRAE Journal - June 2020 - 32
ASHRAE Journal - June 2020 - 33
ASHRAE Journal - June 2020 - 34
ASHRAE Journal - June 2020 - 35
ASHRAE Journal - June 2020 - 36
ASHRAE Journal - June 2020 - 37
ASHRAE Journal - June 2020 - 38
ASHRAE Journal - June 2020 - 39
ASHRAE Journal - June 2020 - 40
ASHRAE Journal - June 2020 - 41
ASHRAE Journal - June 2020 - 42
ASHRAE Journal - June 2020 - 43
ASHRAE Journal - June 2020 - 44
ASHRAE Journal - June 2020 - 45
ASHRAE Journal - June 2020 - 46
ASHRAE Journal - June 2020 - 47
ASHRAE Journal - June 2020 - 48
ASHRAE Journal - June 2020 - 49
ASHRAE Journal - June 2020 - 50
ASHRAE Journal - June 2020 - 51
ASHRAE Journal - June 2020 - 52
ASHRAE Journal - June 2020 - 53
ASHRAE Journal - June 2020 - 54
ASHRAE Journal - June 2020 - 55
ASHRAE Journal - June 2020 - 56
ASHRAE Journal - June 2020 - 57
ASHRAE Journal - June 2020 - 58
ASHRAE Journal - June 2020 - 59
ASHRAE Journal - June 2020 - 60
ASHRAE Journal - June 2020 - 61
ASHRAE Journal - June 2020 - 62
ASHRAE Journal - June 2020 - 63
ASHRAE Journal - June 2020 - 64
ASHRAE Journal - June 2020 - 65
ASHRAE Journal - June 2020 - 66
ASHRAE Journal - June 2020 - 67
ASHRAE Journal - June 2020 - 68
ASHRAE Journal - June 2020 - 69
ASHRAE Journal - June 2020 - 70
ASHRAE Journal - June 2020 - 71
ASHRAE Journal - June 2020 - 72
ASHRAE Journal - June 2020 - 73
ASHRAE Journal - June 2020 - 74
ASHRAE Journal - June 2020 - 75
ASHRAE Journal - June 2020 - 76
ASHRAE Journal - June 2020 - 77
ASHRAE Journal - June 2020 - 78
ASHRAE Journal - June 2020 - 79
ASHRAE Journal - June 2020 - 80
ASHRAE Journal - June 2020 - 81
ASHRAE Journal - June 2020 - 82
ASHRAE Journal - June 2020 - 83
ASHRAE Journal - June 2020 - 84
ASHRAE Journal - June 2020 - 85
ASHRAE Journal - June 2020 - 86
ASHRAE Journal - June 2020 - 87
ASHRAE Journal - June 2020 - 88
ASHRAE Journal - June 2020 - Cover3
ASHRAE Journal - June 2020 - Cover4
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