Transcript Selecting Outdoor, Return and Relief Dampers for VAV

Field Experience
Controlling a Dedicated
Outdoor Air System
(DOAS)
ASHRAE Denver Symp #2
June 26, 2005
Stanley A. Mumma, Ph.D., P.E., Prof.
Jae-Weon Jeong, Ph.D., Instructor
Department of Architectural Engineering
Penn State University, @ Univ. Park, PA
http://doas-radiant.psu.edu
Presentation outline
 DOAS and Test Site Defined
 Controlled Devices, Instrumentation, and
Control
 The Why & How of Continual
Performance Monitoring
 Measured Air Diffusion Performance
Index (ADPI) of System:
f (Effective Draft Temperature)
 Measured Thermal Comfort, PPD
 Conclusions
2
DOAS Defined for this
presentation
100% OA
No Recirc.
DOAS Unit
W/ Energy
Recovery
Parallel
Sensible
Cooling System
Cool/Dry
Supply, CV
High
Induction
Diffuser
Building
With
Sensible
and Latent
cooling
decoupled
3
Parallel Terminal Systems
DOAS air
Induction Nozzle
Sen Cooling Coil
Radiant Cooling Panels
Room air
Chilled Beams
Fan Coil Units
Air Handling Units
Unitary ACs
4
Building Site
5
An Inside
View
6
Another inside view
7
FM1
T7
DOAS Schematic
8
90
.0 196
28
60%
80
80%
.0168
24
40%
EW full Speed
.0 1112
6
.084
12
60
wet
20%
EW Off
.0 56
08
50
dry
40
.0 028
4
EW Modulate
40
50
60
70
80
90
100
D R Y B U LB T EM P E R A T U R E (F )
120
Humidity ratio (grains/lb)
W
B
et
l
ub
)
(F 7 0
HUM D
I T
I Y RA T O
I (Lbv /Lba )
.0 2140
0
Continual Performance
Monitoring—the Need
 Dr. J Woods reports that 5-10% of entire
non industrial building stock has
building related illnesses.
 And 10-25% of the Stock has
sick building syndrome.
 These are facilities that began their life
with no known problems, then
degraded.
 Also, DOE reports that monitoring
could save 0.45 Quads/yr of energy.
10
Categories of performance
degradation
 Insufficient diagnostic and alarm
tools for early warning of
degradation.
 Management’s lack of awareness of
the economic consequences.
 Management’s Indifference.
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Avoiding Potential Degradation
in a DOAS-Radiant System
 Compromised SA quantity: equipment
problems, dirt, etc: FM 1 used to detect.
 Compromised building pressurization,
(infiltration): FM 5 used to detect.
 Compromised supply air temperature:
detect EW using T6-7-10, or CC T8.
 Condensation: Cond sensor to detect.
Note: sensors color coded with next slide
12
FM1
T7
DOAS Schematic
13
ADPI achieved w/ the DOAS system
 For the test facility, the air flow rate was
about 0.3 cfm/ft2, or about 30% of a
VAV (at design). Some have expressed
concern about satisfactory air motion.
 Experiments were performed in the
winter, when convective action was not
supplemented by the overhead cooling
panels (no panel cooling).
 Even in the winter the space has a
cooling load—so no convective impact
from heating.
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ADPI Defined
 An indication of the %of the locations in
a space with a velocity of 70 fpm or less
and an EDT between -3F and +2F.
Effective Draft Temperature (EDT):
q=(TL-TR)-0.07*(VL-30)
Where
q, EDT, °F
TL, local mean air stream DBT, °F
TR, average room DBT, °F
VL, local mean air stream velocity, fpm
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Figure 4, Effective Draft Temperature, q
ADPI=(34/35)*100=97%, or 97% of the observations were between -3<q2 F
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q=- 3
33
q=0
q=2
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31
30
29
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Local Mean Air Velocity, ft/min
The mean velocity at
the 35 stations
ranged from 12 to 30
fpm (all below 70
fpm). The EDT for 34
of the 35 locations
ranged from
-3<q, EDT  +2.
Therefore the
ADPI was
[34/35]*100=97%
35
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25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
-5
-4
-3
-2
-1
0
1
2
3
T-Tc (F), [local - ambient air temperature]
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ADPI conclusion
 DOAS can deliver exceptionally high
ADPI’s; a very favorable finding!
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Thermal Comfort

Thermal comfort is a function of the following
variables that influence metabolic heat transfer:
1.
2.
3.
4.
5.
6.

Dry-bulb temperature (DBT),
Relative humidity,
Mean radiant temperature,
Air movement,
Metabolism, and
Clothing worn by the occupants.
Comfort, then, is almost completely a function of
the space air distribution, provided there is
sufficient heating or cooling to meet the thermal
and humidity control requirements. (i.e. ADPI
important).
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Measuring Thermal Comfort:
Thermal Comfort Meter
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Thermal Comfort Test Results
 -0.01<PMV<+0.07
Where, PMV subjective scale:
+3 hot
+2 warm
+1 slightly warm
0 neutral
-1 slightly cool
-2 cool
-3 cold
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Predicted Percent Dissatisfied
(PPD)
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
85
75
65
55
45
35
25
15
5
-2.5
PPD
(Predicted % Dissastified)
Thermal Comfort Index
PMV
(Predicted Mean Vote)
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Predicted Percent Dissatisfied
(PPD) test results
 The PPD for the tests:
5.1%<PPD<5.4%
 That means almost 95% of the
occupants were satisfied.
 ASHRAE’s accepted thermal comfort
design guidelines permits PPD to be as
high as 20%. Satisfying nearly 95% of
the occupants is certainly far superior to
the ASHRAE target of 80% satisfied .
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Conclusions
 Dedicated outdoor air systems (DOAS), when
properly designed and controlled, are capable
of delivering very stable and comfortable
environments (PPD = 5%).
 The authors have experienced no difficulties
making the system and controls perform as
designed/desired.
 Perhaps the keys to success are:
– the proper control of the enthalpy wheel, and
– the control of the cooling equipment to
assure that the space latent loads are
completely handled by the ventilation air.
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Conclusions
 It has been demonstrated that good air
motion is achieved (ADPI of 97%) with
ventilation air flow alone (typically around
20-30% of that required for thermal control),
 It is not necessary to deliver large quantities
of primary air to provide thermal comfort.
 As a result, there can be significant air
movement energy savings when a CRCP
hydronic parallel system is used to meet the
balance of the space sensible load not met
with the ventilation air.
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Conclusions
 Finally, because of the ability of the DOAS
to decouple the space latent control from
the sensible control, space relative humidity
levels are maintained at the desired design
level.
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Inherent problems with VAV
Systems
Poor air distribution.
Poor humidity control.
Poor acoustical properties.
Poor use of plenum and mechanical shaft space.
Serious control problems, particularly with
tracking return fan systems.
 Poor energy transport medium, air.
 Poor resistance to the threat of biological and
chemical terrorism, and
 Poor and unpredictable ventilation performance.





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VAV problems solved with
DOAS/Radiant








Poor air distribution.
Poor humidity control.
Poor acoustical properties.
Poor use of plenum and mechanical shaft
space.
Serious control problems, particularly with
tracking return fan systems.
Poor energy transport medium, air.
Poor resistance to the threat of biological and
chemical terrorism, and
Poor and unpredictable ventilation
performance.
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Consequences of system
degradation—Ref: Dr. Jim Woods
 20% of US workers experiencing health
related symptoms
 Another 20% of US workers are
experiencing hampered performance
 50% of US workers have lost confidence
in management’s ability to deal with
the situation.
 A major economic investment is needed
to mitigate each problem and recover
workers “goodwill”.
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Computing Occupancy From
Measured DCO2 Data
 Steady state vs transient computations.
 Why count people in light of ASHRAE
Std. 62.1-2004?
– Floor component.
– Occupant component.
– Causes space CO2 concentration to change
with occupancy.
– DCV made more difficult.
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Computing Occupancy From
Measured DCO2 Data
 Transient equation in difference form:
Pep=(V*(N-N1)/Dt + SA*(N-Ci))/(G*1,000,000)
where
Pep = number of occupants
V = the space air volume, ft3
N = the space CO2 concentration at the present time
step, ppm
N1= the space CO2 concentration one time step back, ppm
Dt = the time step, min.
SA = the supply airflow rate, scfm
Ci = the CO2 concentration in the supply air, ppm
G = the CO2 generation rate per person, scfm
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Computing Occupancy From
Measured DCO2 Data
 How well does it work?
– As long as the temperatures remain nearly
steady, the accuracy is remarkably good
(within 2 people for a 40 person space).
– But when the OA temperature drops, error
is introduced in the CO2 measurements.
 When the SA flow is large (many
people), the counts can be off by many
people. For the test site, by about +5
people.
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Measuring Thermal Comfort
 A thermal comfort meter can measure the
influence the six variables.
 The instrument uses a heated ellipsoidal
transducer designed to simulate the thermal
pattern of a human being. It contains a surface
temperature sensor, and a surface-heating
element whose power is adjusted
automatically by the thermal comfort meter to
bring the surface to a temperature similar to
that of a thermally comfortable human.
 The rate of heat production needed to attain
this temperature is used as a measure of the
environmental conditions.
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