nbec 2014 - airflow in mid to high-rise multi-unit residential buildings
TRANSCRIPT
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Airflow in Mid to High-rise Multi-Unit Residential Buildings
LORNE RICKETTS, MASC
RDH BUILDING ENGINEERING LTD. VANCOUVER, BC
CO-AUTHOR: DR. JOHN STRAUBE, PHD, P.ENG.
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Outline
à Introduction & Background
à Testing and Measurement Program à Measured Ventilation Rates (PFT testing) à Cause of Ventilation Rates
à Extension of Study Findings
à Conclusions & Recommendations
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Introduction & Background
à Most apartments/condos (multi-unit residential buildings) are
ventilated using pressurized corridor systems
à Decades of research and experience indicates that this
system likely does not work very well
à Still most common system
à Few physical measurements
à Particularly relevant now, as newer more airtight building
have less tolerance for poorly performing ventilation
systems
à Less infiltration and exfiltration to supplement ventilation
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Pressurized Corridor Ventilation System
à DESIGN INTENT
à Provide ventilation air to all zones
à Control flow of air contaminates
between zones
à HOW
à Provides air to corridors directly
via a vertical shaft which
pressurizes the corridor
à Corridor pressurization forces air
into suites via intentional gaps
under the entrance doors
Introduction & Background
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Case Study Building
à 13-storey multi-unit residential
building in Vancouver, Canada with
37 residential suites
à Constructed 1986
à Enclosure renewal 2012
à Below grade parking garage located
under the building
à Ventilated using pressurized
corridor system by a single make-
up air unit (MAU) on the roof
Introduction & Background
Overall, is typical of high-rise multi-unit residential buildings
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Perfluorocarbon (PFT) Testing
Two component system: à PFT Sources (7 distinct types)
à Capillary absorption tube
samplers (CATS)
à Sources release distinct PFT tracer gasses in different
zones and use CATS to sample
the concentrations
Measured Ventilation Rates
Sources
CATS
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à Order of magnitude variation in the ventilation rates
à Significantly higher rates for upper suites than lower suites
à Most suites under-ventilated or over-ventilated
Measured Ventilation Rates
ASHRAE 62.1-‐2010 ≈ 40 L/s per suite
Waste of Energy
Indoor Air Quality Issues
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PMCP Released in MAU
Measured Ventilation Rates
PDCB Released in Parking Garage
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à Carbon dioxide concentration were monitored as an
indicator of indoor air quality (IAQ)
à Significantly higher concentration in the lower suites
Measured Ventilation Rates
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à Summary: à Over ventilation and under ventilation of most suites à Higher ventilation rates in upper suites than lower suites à Better indoor air quality in upper suites than lower suites
Why is this happening?
Measured Ventilation Rates
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Maybe the MAU isn’t working correctly?
à Custom powered flow hood used to measure intake flow rate of the make-up air unit
à MAU airflow approximately the same as design flow rate of 1,560 L/s (3,300 cfm)
Cause of Ventilation Rates
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Maybe the ventilation air isn’t reaching the corridors?
à Only 40% of intake flow reaches the corridors directly
Cause of Ventilation Rates
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150
Floo
r Num
ber
Flow Rate [L/s]
MAU Supply to Corridors
Pre-‐Retrofit (21°C) Post-‐Retrofit (6°C) Post-‐Retrofit (16°C)
Pre-‐Retrofit (21°C) Total = 593 L/s Post-‐Retrofit (6°C) Total = 559 L/s
Post-‐Retrofit (16°C) Total = 580 L/s
Fire Damper noted to be closed on Floors 4, 8, & 12.
1 L/s ≈ 2 cfm
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Maybe the air isn’t reaching the suites from the corridors?
à Airtightness tested corridors and found significant flow paths other than to
the suites through the suite entrance doors. Only 20% to the suites
Cause of Ventilation Rates
1 L/s ≈ 2 cfm
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à Theoretically, only 8% of intended ventilation actually
goes where it is supposed to! Waste of ventilation air,
and the energy needed to move and condition it.
Cause of Ventilation Rates
à If only 40% of the flow rate reaches the corridors
And, only 20% of that air reaches the suites…
Leakage of air along ventilation flow path is a major issue.
𝟒𝟎%×𝟐𝟎%=𝟖%
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à Pressure differences were
monitored with a focus on an
upper floor and a lower floor
(Floors 11 & 3)
à Assessed relationship between
exterior temperature (stack
effect) and wind events using a
weather station on the roof
Maybe pressure differences are an important factor?
Cause of Ventilation Rates
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à Mechanical ventilation system creates pressure of 5 to 10 Pa
Cause of Ventilation Rates
-‐20
-‐15
-‐10
-‐5
0
5
10
15
20
Feb 8 6:00 Feb 8 8:00 Feb 8 10:00 Feb 8 12:00 Feb 8 14:00 Feb 8 16:00 Feb 8 18:00
Pressure Differen
ce [P
a]
Average Corridor to Suite Pressure by Floor when MAU Off
Floor 02 Floor 03 Floor 04 Floor 10 Floor 11 Floor 12
Measurement with MAU OffMeasurement with MAU Recently Turned On
Corridor-‐to-‐Suite
Pressure Diffe
rence [Pa] ≈10 Pa
≈5 Pa
Corridor-to-Suite Pressure Difference
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-‐5
0
5
10
15
20
25
-‐10
-‐5
0
5
10
15
20
Exterio
r Tem
perature [°C]
Corridor-‐to-‐Suite
Pressure Differen
ce [P
a]
Average Suite to Corridor Pressures by Floor and ExteriorTemperature -‐ 24 Hour Moving Average
Floor 02 Floor 03 Floor 04
Floor 10 Floor 11 Floor 12
Exterior Temperature [°C]
-‐5
0
5
10
15
20
25
-‐10
-‐5
0
5
10
15
20
Exterio
r Tem
perature [°C]
Corridor-‐to-‐Suite
Pressure Differen
ce [P
a]
Average Suite to Corridor Pressures by Floor and ExteriorTemperature -‐ 24 Hour Moving Average
Floor 02 Floor 03 Floor 04
Floor 10 Floor 11 Floor 12
Exterior Temperature [°C]
-‐5
0
5
10
15
20
25
-‐10
-‐5
0
5
10
15
20
Exterio
r Tem
perature [°C]
Corridor-‐to-‐Suite
Pressure Differen
ce [P
a]
Average Suite to Corridor Pressures by Floor and ExteriorTemperature -‐ 24 Hour Moving Average
Floor 02 Floor 03 Floor 04
Floor 10 Floor 11 Floor 12
Exterior Temperature [°C]
à Pressures created by stack effect found to be of similar
magnitude (10 to 15 Pa) as mechanical pressures
Cause of Ventilation Rates
Corridor-to-Suite Pressure Difference
10 – 15 Pa
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à Stack effect pressures found to distribute 69% across the corridor to
suite boundary and 9% across exterior enclosure
à Stack effect pressure acts primarily in the same location as mechanical
pressures intended to provide ventilation and control contaminate flow
Cause of Ventilation Rates
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à Vancouver is a relatively moderate climate à Should consider
other climates
à Case study building is 13 storeys à Should consider different
building heights
Extension of Study Findings
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 40 m Tall Building in Miami
Wind
Stack Effect
Mechanical(10 Pa)
40m Tall Building in Miami
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 40 m Tall Building in Vancouver
Wind
Stack Effect
Mechanical(10 Pa)
40m Tall Building in Vancouver 40m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 40 m Tall Building in Toronto
Wind
Stack Effect
Mechanical(10 Pa)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 40 m Tall Building in Fairbanks
Wind
Stack Effect
Mechanical(10 Pa)
40m Tall Building in Fairbanks
Extension of Study Findings
Wind Stack Effect Mechanical (10 Pa)
à Climate
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 20 m Tall Building in Toronto
Wind
Stack Effect
Mechanical(10 Pa)
20m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 40 m Tall Building in Toronto
Wind
Stack Effect
Mechanical(10 Pa)
40m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 60 m Tall Building in Toronto
Wind
Stack Effect
Mechanical(10 Pa)
60m Tall Building in Toronto 80m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percen
tage of D
riving Force Pressure
Daily Average Distribution of Pressure Difference due to DrivingForces for a 80 m Tall Building in Toronto
Wind
Stack Effect
Mechanical(10 Pa)
Extension of Study Findings
Wind Stack Effect Mechanical (10 Pa)
à Building Height
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Extension of Study Findings
à Stack effect is more significant in taller buildings
à Proportion of wind pressures remains relatively the same
à Relative magnitude of mechanical pressures decreases as
height increases
0%
10%
20%
30%
40%
50%
60%
70%
Stack Effect Wind Mechanical(10 Pa)
Percen
tage of D
riving Force Pressure
Average Proportions of Driving Force Pressure Differences -‐ Vancouver
20 m
40 m
60 m
80 m
100 m
BuildingHeight
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Extension of Study Findings
à Stack effect more significant in cold climates
à Wind highly variable, but typically more significant in
warm climates
0%
10%
20%
30%
40%
50%
60%
70%
Stack Effect Wind Mechanical(10 Pa)
Percen
tage of D
riving Force Pressure
Average Proportions of Driving Force Pressure Differnces -‐ 40m Tall Building
Miami
Houston
Los Angeles
New York
Vancouver
Toronto
Calgary
Fairbanks
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Comparison of Driving Forces
à Since all of the pressure differences created by the driving forces
(stack effect, wind, & mechanical systems) are of similar
magnitude, it is possible that any one could dominate
à This is exaggerated for buildings located in more extreme
climates than Vancouver
Ventilation system can not practically overwhelm nature.
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Conclusion
à Corridor pressurization does not provide intended
ventilation rates to a large number of suites à Some significantly over ventilated while others significantly
under ventilated
à Significant leakage along the ventilation air flow path
from the duct and the corridor (wasted ventilation) à Uncontrolled airflow wastes energy and provides poor
ventilation
à Stack effect and wind pressures are often similar or
greater than mechanically-induced pressures à Ventilation system can not practically overwhelm nature
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Recommendations for Ventilation System Design
à Ventilation air should be directly supplied to suites to
limit the potential of loss along the flow path and of the
system being overwhelmed by stack effect and wind
à The exterior enclosure should be airtight, and suites
and vertical shafts should be compartmentalized
(airtight) to limit the impact of wind and stack effect on
ventilation