air movement: ed arens, hui zhang its role in · ccaliforniaalifornia airair resourcesresources...
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CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015 CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air movement:
its role in
conditioning building
interiors efficiently
Ed Arens, Hui Zhang
Center for the Built Environment
Funded by:
California Air Resources Board
Armstrong World Industries
CBE
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Presentation outline
Building environment and human comfort
• Cooling of the indoor environment
• The energy problem with existing approaches
• The comfort problem with existing approaches
Energy-efficient cooling: the role of air movement
• Human response
• Practical issues of how to implement air movement indoors
Air movement and air quality, perceived and real
Barriers for fan adoption in practice
Future opportunities for air movement in buildings
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air movement related to thermal comfort and energy
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
4 environmental factors affect thermal comfort
Air temperature
Surrounding surface temperature
Humidity
Air speed
Design has always focused on the first three (use of
operative temperature and the psychrometric chart)
Air speed has largely been seen as a problem to be
avoided (draft) in conditioned spaces
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
ASHRAE Standard 55 comfort zones
In practice there is often a narrow zone year-round:
~ 71 – 75°F
Winter and summer
zones
Zones satisfy 80% of
people
Require still air
Setpoint ranges in
US are narrower —
winter temperatures
year-round;
buildings are
overcooled in
summer
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Actual temperatures lower than setpoints (BASE data: 95 office buildings, 1994 – 1998)
71ºF 75ºF
50 57 64 72 79 86 93
(ºF)
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
0
10
20
30
40
50
60
70
80
60 65 70 75 80 85 90
HV
AC
en
erg
y sa
vin
gs [
%]
Heating / Cooling setpoint [°F]
MiamiPhoenixSan-FranciscoFresnoBaltimoreChicagoDuluth
The cost of maintaining range of indoor conditions
Hoyt, T., E. Arens, and H. Zhang. 2014. Extending air temperature setpoints: Simulated energy savings and design considerations for new and retrofit buildings. Building and Environment. doi: 10.1016/j.buildenv.2014.09.010 https://escholarship.org/uc/item/13s1q2xc
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air movement: building occupants often want more
Want Less:
Want More: 52%
No Change: 45%
Air Movement Preference, ASHRAE Sensation -0.7 to 1.5 (n = 3230)
Zhang, H., E. Arens, S. Abbaszadeh, C. Huizenga, G. Brager, G. Paliaga, and L. Zagreus, 2007. Air movement preferences observed in office buildings. International Journal of Biometeorology, 51, 349–360
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air movement acceptability, and preferences
Want Less: 7%No Change:
Want More: 84%
Acceptable Air Movement
71%
Unacceptable Air
Movement
Air Movement Acceptability and Air Movement
Preference
ibid
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Example of what is possible:
a zero net energy building in Phoenix Arizona, 82ºF
(28ºC)
But is it OK for its white-collar occupants?
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Thermal satisfaction ranking 91% in the CBE database
Mean Scores - Thermal Comfort
LEED (n=31) compared to CBE database (n=257)
-3
0
3
0% 25% 50% 75% 100%
Percentile Rank
Me
an S
atis
facti
on S
core
leed median: 0.42
db median: -0.13
mixed mode median: 0.62
LEED (n=31), mixed mode (n=5) compared to CBE database (n=257)
DPR
DPR mean: 0.97
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Windows (aka ‘natural ventilation’) and fans
Operable windows
Operable windows and fans
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Standard 55 comfort zone for naturally ventilated
buildings
Empirical adaptive comfort model (adopted 2004)
Limited to buildings with operable windows
Local conditioning of environment– air movement cooling
13 degree F range!
Causes not fully
known; occupants’
personal control of
air movement seems
to be a major factor
de Dear, Richard; & Brager, G. S.(1998). Developing an adaptive model of thermal comfort and preference. ASHRAE Transaction, 104
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Elevated air movement ASHRAE standard
(2013,4)
Arens E., S. Turner, H. Zhang, G. Paliaga, 2009, “A Standard for Elevated Air Speed in Neutral and Warm Environments,”
ASHRAE Journal, May 51 (25), 8 – 18
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Implementing air movement within a space
Overhead fans are most general source
Design guidance lacking
Objective of CARB study: determine cooling effectiveness under several conditions at 82.5°F
• With and without desks
• Fan fixed and oscillating
• Low and medium fan speed levels
• Varying distance from the fan
Added tests to cover hotter and more humid environmental conditions
Image from Armstrong World Industries
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Study 1: test of fixed and oscillating fan 82.5°F
Oscillating fan, front positions
Oscillating fan, side positions
Summer clothing with short-sleeve shirts; 0.5clo Office tasks
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Test condition—comfort and energy
ASHRAE Standard 55
82.5°F 50% RH
82.5
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air flow configurations
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Whole-body thermal comfort
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Velocity profiles for “oscillating” configuration
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Results of the first study
Both the fixed and oscillating fans provided comfort at the
test condition
However the oscillating mode was not statistically
different from the base case without a fan
The chosen oscillation frequency was too low, causing
discomfort in the ~15 second period that air movement
was absent. The recurrence interval should be
shortened.
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Study 2 and 3: Ceiling and floor fan comfort
studies in warm and humid environments
Study 3:
Horizontal airflow
Floor fan
Control
Six environmental conditions
Study 2:
Vertical airflow
Ceiling fan
No control
Six environmental conditions
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Test conditions
86°F 80%
79°F 60%
79°F 60% 86°F 60%
82.5°F 60%
82.5°F 80%
82.5°F 50%
ASHRAE Standard 55
Studies 2,3 Study 1
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Thermal comfort with ceiling fan
Vertical air movement maintains thermal comfort
E ffe c tiv e te m p e ra tu re (° F )
Th
erm
al
co
mfo
rt
7 8 8 0 8 2 8 4 8 6 8 8 9 0 9 2
-3
-2
-1
0
1
2
3
n o f a n
0 .3 m /s
0 .7 m /s
0 .8 5 m /s
1 .2 m /s
1 .6 m /s
1 .8 m /s
v e r y
c o m fo r ta b le
v e r y
u n c o m fo r ta b le
69F
60
%
69F
80
%
82F
60
%
82F
80
%
86F
60
%
86F
80
%
79
79
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Perceived air quality with ceiling fan
Air movement maintains perceived air quality
E ffe c tiv e te m p e ra tu re (° F )
Pe
rce
ive
d a
ir q
ua
lity
7 8 8 0 8 2 8 4 8 6 8 8 9 0 9 2
-3
-2
-1
0
1
2
3
n o f a n
0 .3 m /s
0 .7 m /s
0 .8 5 m /s
1 .2 m /s
1 .6 m /s
1 .8 m /s
v e r y
a c c e p ta b le
v e r y
u n a c c e p ta b le
69F
60
%
69F
80
%
82F
60
%
82F
80
%
86F
60
%
86F
80
%
79
79
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Preferred air speed for comfort
• With vertical air flow, subjects’ preferred air speed can
exceed ASHRAE 55 limit (existing no-control limit is 0.8
m/s)
• Air speed chosen by subjects with horizontal air flow
vary but can also exceed the ASHRAE 55 with-control
limit of 1.2 m/s)
E ffe c tiv e te m p e ra tu re (° F )
Air
sp
ee
d (
m/s
)
7 8 8 0 8 2 8 4 8 6 8 8 9 0 9 2
0 .0
0 .4
0 .8
1 .2
1 .6
2 .0
A S H R A E 5 5 lim it
C e ilin g fa n - v e r tic a l a ir f lo w
69F
60
%
69F
80
%
82F
60
%
82F
80
%
86F
60
%
86F
80
%
E ffe c tiv e te m p e ra tu re (° F )
Air
sp
ee
d (
m/s
)
7 8 8 0 8 2 8 4 8 6 8 8 9 0 9 2
0 .0
0 .4
0 .8
1 .2
1 .6
2 .0
A S H R A E 5 5 lim it
F lo o r fa n - h o r iz o n a l a ir f lo w
69F
60
%
69F
80
%
82F
60
%
82F
80
%
86F
60
%
86F
80
%
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
E ffe c tiv e te m p e ra tu re (° F )
Po
we
r (W
)
7 8 8 0 8 2 8 4 8 6 8 8 9 0 9 2
0
2
4
6
8
1 0
1 2u s e r-c o n tro l
c e il in g fa n
69F
60
%
69F
80
%
82F
60
%
82F
80
%
86F
60
%
86F
80
%
Measured power consumption of fans
5 W
Power consumption of both ceiling and floor fans is very
low. Fan power per occupant was around 3W at 79º F, 5W
at 82.4º F, and around 10W at 86º F.
3 W
Floor fan
Ceiling fan
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Study 4 – air movement cooling in sport facilities
Objectives
Study air movement
cooling at higher than
sedentary activity levels
(met rates)
Approach
Physiological tests
Comfort surveys
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Test conditions
ASHRAE Standard 55
base condition (68F, 50%, no fan)
68, 72, 75, 78°F, 50%
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Study design
Metabolic level: 2, 4, 6 met
Subjects: 10 males, 10 females
20 minute rides for each met level
Ceiling fan controller
Survey
Heart rate monitor
T, RH sensor
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Fans provided comfort at high temperatures
68°F 68°F 72°F 75°F 78°F
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Summary of related work: near-body air movement within
a heated/cooled chair (lab study at 84°F 50% RH)
Fan
Comfortable rate (%) 91 19 Control unit
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
2. Cesar Chavez Student Union : Summer and
winter
Building
No mechanical cooling
Objective
Provide occupant thermal comfort
Approach
Installed wireless temperature sensors in
each of 18 workstations
Survey finished
• Without PCSs (Sept. 25 2013, base case)
• With PCSs (Oct. 2013 – Feb. 2014)
About 1300 survey responses received
Funding
CIEE through SPEED program
CBE chair
PCS chair
USB fan
Field study of chair in a campus building
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Acceptability rates with and without chairs (summer)
Indoor air temperature (°F) Without PCS, acceptability rate is about 50 – 75%
With PCS, acceptability rate is about 75 – 90%
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
+
+ +
+ + + +
+ + + + +
+
+
Summary of air movement studies in the literature
Zhang, H., E. Arens, Y. Zhai 2015, “Review of the corrective power of personal comfort systems in non-
neutral ambient environments” Building and Environment, April
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Occupant satisfaction rates under air movement cooling
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Air movement and perceived air quality
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Study of air movement cooling
2 tests/day
2 people/test
28ºC (82.4F), 50%RH
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Impact of airspeed on perceived air quality
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Thermal comfort versus acceptability of perceived air
quality
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Investigating body plume effects
Without a collar With a collar
Collar can deflect the plume effectively
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Creating body odor; isolating body plume
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Scent intensity: collar versus airspeed disruption
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Intr
od
uct
ion
O
bje
ctiv
es &
Stu
dy
Des
ign
M
eth
od
olo
gy
Res
ult
s C
on
clu
sio
ns
Human convective boundary layer and its
impact on personal exposure
Body plume affects inhaled air quality Boundary layer air is 1 – 2°F higher than the ambient air tempearture
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Interaction of the human CBL with the downward ventilation flow from above
Intr
od
uct
ion
O
bje
ctiv
es &
Stu
dy
Des
ign
M
eth
od
olo
gy
Res
ult
s C
on
clu
sio
ns
The CBL in ventilated environment - Study by Dusan Licina
Interaction of the human CBL with the ventilation flow from front
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Normalized concentration of cough released from 3 m distance from the manikin – Influence of the CBL, the direction and magnitude of invading airflow
0.0
0.2
0.4
0.6
0.8
1.0
1.2
No
rmal
ized
con
centr
atio
n
CBL
Assisting 0.175 m/s
Assisting 0.3 m/s
Assisting 0.425 m/s
Opposing 0.175 m/s
Opposing 0.3 m/s
Opposing 0.425 m/s
Trans. Front 0.175 m/s
Trans. Front 0.3 m/s
Trans. Front 0.425 m/s
Trans. Back 0.175 m/s
Trans. Back 0.3 m/s
Trans. Back 0.425 m/s
Trans. Side 0.175 m/s
Trans. Side 0.3 m/s
Trans. Side 0.425 m/s
Intr
od
uct
ion
O
bje
ctiv
es &
Stu
dy
Des
ign
M
eth
od
olo
gy
Res
ult
s C
on
clu
sio
ns
Personal exposure in ventilated environment
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Radiant cooling + acoustical panels + fans
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Problem: heat transfer is blocked by suspended
panels
60% Radiant heat exchange 40% Convective heat exchange
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Goals and method
Goals
Investigate the impacts
of acoustical ceiling
panels on radiant slab
systems
Study the ability of
ceiling integrated fan to
increase the ceiling
convection coefficient
Method
CFD model of a portion
of office equipped with
radiant ceiling
16 configurations
User
Computer
Inlet
Outlet
Radiant Ceiling
Funded by CBE and CARB in collaboration with Armstrong
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Configurations tested
Baseline with no fan and no panels
Five different levels of acoustical panel coverage (26%, 35%, 43%, 56%, 68%)
Two fan configurations (fan blowing up or down). Air speed at the blade level equal to 98.4 fpm
P1: 26%
P3: 43%
P4: 56%
P5: 68%
Fan (exposed)
P2: 35%
P2: 35%
P3: 43%
Acoustic ceiling panels configuration
UP
DOWN
Exposed
Exposed
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Panels coverage
No fan
Fan down
Fan up
0% (baseline) 100% ND ND
26% 96% 144% 144%
35% 91% 139% 153%
43% 88% 139% 154%
56% 88% 139% 151%
68% 89% 132% 152%
Results
Fan down
Fan up
Velocity [fpm]
128 64 0
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Overcoming barriers to fan use; future prospects
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Contributions to ceiling fan design and evaluation
Objective
Work with industry to produce a
standard ceiling fan performance
index
Guidance for designers about fan
placement and the effects of
workstation furniture
Test facilities
CBE environmental chamber
Thermal manikin
Funding
CEC/PIER Changing the Rules project,
CBE
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Quantifying airflow interaction with furniture
No furniture With partition With table
0R 0.5R 1R 2R
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Airspeed distributions with furniture
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Focusing fans within the workstation
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Progress in the industry and future prospects
Appearance—major progress in the fan industry
Power efficiency improved with DC motors
Intelligent controls for comfort and energy
effectiveness—links with internet building automation
We believe the momentum is underway for cooling with
air movement
An elevated air speed should be the base condition
before compressor cooling is initiated—this requires a
fundamental change to the practice of the last 50 years,
but is not beyond reach
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Creating architectural acceptance
CALIFORNIA AIR RESOURCES BOARD MARCH 24, 2015
Thank you!