Establishing Primary Airflow in WBCS Systemstorontoashrae.com/resources/Documents/ASHRAE Chilled...
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Establishing Primary Airflow in WBCS
Systems
Establishing Primary Airflow in WBCS
Systems
Chilled Beam Design Principles
How is capacity measured?
•Tested & reported as an assembly
•Is not simply a sum of component capacity
•ASHRAE Standard 200
How is capacity certified?
AHRI Standard 1240/1241 certification program
More information:
3
Chilled Beam Design Principles
Agenda
• WBCS Concept
• Occupant Comfort
• Establishing Primary Airflow Rate
• Energy Impact
• Demand Control Ventilation
• WBCS Concept
• Occupant Comfort
• Establishing Primary Airflow Rate
• Energy Impact
• Demand Control Ventilation
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Focusing on what our customers care about
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o Comfort vs. Capacity
o System Design vs. Product Features
VS.
Water Borne Climate System Concept
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Transportation Costs
7 2015-12-15 Company Presentation
Air
10” duct
Capacity 9900 Btuh
(20 ft/s Δt 14°F)
Water
3/4” pipe
Capacity 9900 Btuh
(110 ft/m Δt 7°F)
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Treated fresh air
Cooling CoilNozzles
Inducedwarm room air
Supply air
Operates through induction
How a chilled beam works
WBCS Basics
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Comfort Modules & Chilled Beams
1-Way 2-Way 4-Way
1-W
ay
1-W
ay
Chilled Beams and Occupant Comfort
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Heating/Cooling Capacity & Air Distribution
• A chilled beam is a combination energy source
and air distribution system so the selection is
doubly important.
• The space air distribution is equally important
to capacity in determining the comfort level.
Poor air distribution will result in poor comfort
no matter how much capacity is available.
• A chilled beam is a combination energy source
and air distribution system so the selection is
doubly important.
• The space air distribution is equally important
to capacity in determining the comfort level.
Poor air distribution will result in poor comfort
no matter how much capacity is available.
Chilled Beam – Energy source + air diffuser
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Controllable by
chilled beam
Metabolic rate x
Clothing insulation x
Air temperature �
Radiant temperature x
Air speed �
Air direction / throw �
Humidity x
User adjustability �
ASHRAE Standard 55 Comfort Considerations
Air Distribution
Mixed SystemsMixed Systems
• All the air in the space is
mixed to same the same
temperature
• Overhead mixed air
systems use Coanda
effect
• Most beams are based
on mixed air approach
(overhead)
• All the air in the space is
mixed to same the same
temperature
• Overhead mixed air
systems use Coanda
effect
• Most beams are based
on mixed air approach
(overhead)
Displacement SystemsDisplacement Systems
• Air is introduced at floor
level at very low velocities
• Space is deliberately
stratified
• Only the occupant zone is
conditioned
• Air is introduced at floor
level at very low velocities
• Space is deliberately
stratified
• Only the occupant zone is
conditioned
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Coanda effect
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Thanks to the negative pressure, the air follows the ceiling instead of falling straight down when it leaves the module
When the air reaches the occupied zone, it has attained a temperature and speed that reduces the risk of draft
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Induction and Coanda Effect
Creating Coanda Effect
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Diffuser nozzle design
• Beams have built in “Diffuser” technology
• Beam selection and placement to ensure comfort is
an important as when selecting diffusers
• “One big beam in a space may meet cooling load but
may not deliver the comfort that two smaller beams
would deliver”
Airflow Pattern
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• Beams can offer wide range of airflow patterns to
suit space
202015-12-15 Indoor Climate Systems - Water based or Air?
2-way discharge strategy • Uses only small area of the ceiling• Air volume distributed into narrow region
4-way discharge strategy• Maximizes use of available ceiling area• Air volume distributed diffusely, more slowly• Flexible discharge patterns / field adjustable
Beam Selection For Comfort
WBCS Primary Airflow Analysis
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loads and Primary Airflow
Compare Office Vs. School
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Cooling Load Summary
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Sensible Load Latent Load Total Load SHR
Btu/h Btu/h-ft² Btu/h Btu/h-ft² Btu/h Btu/h-ft²
Classroom 24756 24.8 7795 7.8 32551 32.6 0.76
Office 23116 23.1 2573 2.6 25688 25.7 0.9
Cooling Load Calculations
• Loads same regardless of HVAC system
• Fancoil, WSHP, GSHP and VRF need zone latent and sensible loads separate from outdoor air load
• WBCS need zone sensible load separate from zone latent load and outdoor air latent and sensible load
• Loads same regardless of HVAC system
• Fancoil, WSHP, GSHP and VRF need zone latent and sensible loads separate from outdoor air load
• WBCS need zone sensible load separate from zone latent load and outdoor air latent and sensible load
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WBCS Primary Airflow Design
• The primary airflow rate must be the larger of;
• The air flow rate to meet the ventilation rate required
to deliver acceptable indoor air quality.
• The airflow rate to provide latent cooling in the zone.
• The airflow rate required to assist in meeting the zone
sensible cooling rate.
• The primary airflow rate must be the larger of;
• The air flow rate to meet the ventilation rate required
to deliver acceptable indoor air quality.
• The airflow rate to provide latent cooling in the zone.
• The airflow rate required to assist in meeting the zone
sensible cooling rate.
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Ventilation Rate
• Office
• Ventilation rate = 10 x 5 cfm
+ 0.06 x 1000 ft² = 110 cfm
• = 0.11 cfm/ft²
• Classroom
• Ventilation rate = 30 x 10 cfm
+ 0.12 x 1000 ft² = 423 cfm
• = 0.42 cfm/ft²
• Office
• Ventilation rate = 10 x 5 cfm
+ 0.06 x 1000 ft² = 110 cfm
• = 0.11 cfm/ft²
• Classroom
• Ventilation rate = 30 x 10 cfm
+ 0.12 x 1000 ft² = 423 cfm
• = 0.42 cfm/ft²
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Latent Rate
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75 °F DB
50% RH
64.6 gr/lb HR
Qp = Platent/(0.68 x (Wr - Wprimary air))
Sensible Rate
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75 °F DB
50% RH
64.6 gr/lb HR
Qp = Psensible /(1.085 x ((Tr – Tp) + IR x (Tr – Ta))
Primary Airflow Summary
• Can’t go below ventilation rate
• Latent load usually dominates
• Offices 0.4 to 0.6 cfm/ft², 53 °F off coil
• Classroom 0.6 to 0.8 cfm/ft², 49 °F off coil (reheat required)
• Can’t go below ventilation rate
• Latent load usually dominates
• Offices 0.4 to 0.6 cfm/ft², 53 °F off coil
• Classroom 0.6 to 0.8 cfm/ft², 49 °F off coil (reheat required)
Ventilation Rate Latent Rate Sensible Rate
Btu/h cfm/ft² Btu/h cfm/ft² Btu/h cfm/ft²
Classroom 423 0.43 740 0.75 761 0.76
Office 110 0.11 461 0.46 333 0.33
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Primary Airflow
Primary Airflow Summary
• The zone sensible cooling load should be between 20 to 40 Btu/h·ft².
• The primary airflow will be most likely set by the zone latent load. A good range is 0.4 to 0.6 cfm/ft².
• A good office system has 1/3 of the load met by the primary air and 2/3 of the load met by the chilled beam coil.
• Assume an induction ratio between 2.5 to 3.5. Start with 3.
• The zone sensible cooling load should be between 20 to 40 Btu/h·ft².
• The primary airflow will be most likely set by the zone latent load. A good range is 0.4 to 0.6 cfm/ft².
• A good office system has 1/3 of the load met by the primary air and 2/3 of the load met by the chilled beam coil.
• Assume an induction ratio between 2.5 to 3.5. Start with 3.
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Primary Airflow Summary
• The chilled water supply temperature should
be 2-3 °F above space dew point. 57 °F is a
common supply water temperature.
• The chilled water temperature range will be 4
to 6 °F. Consider putting the primary air
system in series with the chilled beams.
• The chilled water supply temperature should
be 2-3 °F above space dew point. 57 °F is a
common supply water temperature.
• The chilled water temperature range will be 4
to 6 °F. Consider putting the primary air
system in series with the chilled beams.
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WBCS Energy Considerations
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Design vs. Annual Energy Usage
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Fans
25%
Chiller
56%
Pumps
14%
Tower
5%
Design Day
Fans
44%
Chiller
32%
Pumps
21%
Tower
3%
Annual
Annual Cooling Load Profile
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0
50
100
150
200
250
300
350
400
450
500
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Ho
urs
Percent Cooling Load
Standard DOAS Unit
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Primary Airflow vs. Delta Humidity Ratio
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• All points of curve deliver same amount latent cooling to space
Platent = 0.68*Qp* (Wr – Wprimary air )
0
10
20
30
40
50
60
70
80
90
100
3.8 6.1 8.3 10.5 12.6 14.6 16.5
Pri
ma
ry A
irfl
ow
(cf
m)
Delta Humidity Ratio (gr/lb)
Cooling Capacity of Primary Airflow
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0
10
20
30
40
50
60
70
80
90
100
2062 1352 1043 864 753 678 625
Pri
ma
ry A
irfl
ow
(cf
m)
Primary Air Sensible Capacity (Btu/h)
• Primary cooling capacity drops off as airflow is reduced
• Shifts load to beam
Primary Airflow vs. Induction Ratio
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0
10
20
30
40
50
60
70
80
90
100
1.1 2.8 4.4 5.9 7.4 8.9 10.2
Pri
am
ry A
irfl
ow
(cf
m)
Induction Ratio
• Higher beam load requires higher induction rate
• APD and noise become issue
DOAS Energy Model Design Parameters
Off Coil DB SA DB SA HR Delta HR SA Airflow
F F gr/lb gr/lb cfm
55 56 62.6 3.8 100
54 55 60.3 6.1 62
53 54 58.1 8.3 46
52 53 55.9 10.5 36
51 52 53.8 12.6 30
50 51 51.8 14.6 26
49 50 49.9 16.5 23
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Annual Energy Usage Std DOAS Unit
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0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
100 62 46 36 30 26 23
An
nu
al E
ne
rgy
Usa
ge
(kW
h)
Primary Airflow (cfm)Rotor BIN Watts kWh SA Fan BIN Watts kWh
Chiller Plant BIN Watts kWh HW Plant BIN Watts kWh
RA Fan BIN Watts kWh
Energy Analysis Summary
• Fan work is dominant
• Generally shifting sensible load to beams from primary
is more efficient
• Practical limitation on induction ratio (5) and primary
air temperature (53 °)
• Reheat increases operating cost – only do it if you
have to (schools)
• Fan work is dominant
• Generally shifting sensible load to beams from primary
is more efficient
• Practical limitation on induction ratio (5) and primary
air temperature (53 °)
• Reheat increases operating cost – only do it if you
have to (schools)
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Demand Control Ventilation
Demand Control Ventilation
• Classrooms occupied 35%
• Offices occupied 22-38%
• ASHRAE Std 90.1
• 500 ft²
• 25 people per 1000 ft²
• greater than 3000 cfm
• ASHRAE Std 62
• Minimum airflow ≥ building load
component (Ra x Az)
• Classrooms occupied 35%
• Offices occupied 22-38%
• ASHRAE Std 90.1
• 500 ft²
• 25 people per 1000 ft²
• greater than 3000 cfm
• ASHRAE Std 62
• Minimum airflow ≥ building load
component (Ra x Az)
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Demand Control Ventilation
• Vary Primary airflow based on
• Occupancy
• Temperature
• CO2
• VOC
• Vary Primary airflow based on
• Occupancy
• Temperature
• CO2
• VOC
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06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
Time
Air Volume l/s
150
200
250
Saving
CAV
DCV
100
Impact of Reduced Primary Airflow on Induction
0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Chilled Beam Discharge(CFM)
Primary Airflow Demand(CFM)
Induced
Primary
Chilled Beam with
Integral Damper
Discharge,
chilled beam
with upstream
VAV damper
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Demand Control VentilationDemand Control Ventilation
Dampers
ZONEDOAS
Demand Control Ventilation Summary
• DCV increases chilled beam turndown from 3 to 1 to
10 to 1
• Improves occupant comfort
• Spaces are rarely at design occupancy
• DCV allows significant fan power savings
• DCV control can be based on
• Occupancy sensor (single occupant office)
• CO2 or VOC (modulating for multi occupant
spaces)
• DCV increases chilled beam turndown from 3 to 1 to
10 to 1
• Improves occupant comfort
• Spaces are rarely at design occupancy
• DCV allows significant fan power savings
• DCV control can be based on
• Occupancy sensor (single occupant office)
• CO2 or VOC (modulating for multi occupant
spaces)
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THANK YOU FOR YOUR TIME