airflow in mid to high-rise multi-unit residential … ricketts.pp...components in a holistic...
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Airflow in Mid to High-rise Multi-Unit Residential Buildings
LORNE RICKETTS, MASC RDH BUILDING ENGINEERING LTD. VANCOUVER, BC CO-AUTHORS: GRAHAM FINCH, MASC, P.ENG. – RDH BUILDING ENGINEERING LTD. DR. JOHN STRAUBE, PHD, P.ENG. – UNIVERSITY OF WATERLOO
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AIA Credits
National Institute of Building Sciences – Provider #G168 Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. ___________________________________________ Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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AIA Credits – Learning Objectives
Participants will: 1. Learn how to link the performance of individual building enclosure components in a holistic framework to achieve high-performance buildings.
2. Explore, through built case studies, how building envelope design determines overall energy conservation and sustainability capabilities 3. Learn innovative practices for avoiding heat loss as well as moisture and air infiltration in enclosure design for healthy new and existing buildings. 4. Understand the role of building enclosure commissioning in the design, construction, and operation and maintenance of commercial facilities.
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Outline
Introduction & Background
Testing and Measurement Program Measured Ventilation Rates (PFT testing) Cause of Ventilation Rates
Extension of Study Findings
Conclusions & Recommendations
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Introduction & Background
Most apartments/condos (multi-unit residential buildings) are
ventilated using pressurized corridor systems
Decades of research and experience indicates that this
system likely does not work very well
Still most common system
Few physical measurements
Particularly relevant now, as newer more airtight building
have less tolerance for poorly performing ventilation
systems
Less infiltration and exfiltration to supplement ventilation
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Pressurized Corridor Ventilation System
DESIGN INTENT
Provide ventilation air to all zones
Control flow of air contaminates
between zones
HOW
Provides air to corridors directly
via a vertical shaft which
pressurizes the corridor
Corridor pressurization forces air
into suites via intentional gaps
under the entrance doors
Introduction & Background
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Case Study Building
13-storey multi-unit residential
building in Vancouver, Canada with
37 residential suites
Constructed 1986
Enclosure renewal 2012
Below grade parking garage located
under the building
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: PFT Sources (7 distinct types)
Capillary absorption tube
samplers (CATS)
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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Order of magnitude variation in the ventilation rates
Significantly higher rates for upper suites than lower suites
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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Summary:
Over ventilation and under ventilation of most suites Higher ventilation rates in upper suites than lower suites 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?
Custom powered flow hood used to measure intake flow rate of the make-up air unit
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?
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?
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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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
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.
𝟒𝟒𝟒𝟒𝟒 × 𝟐𝟐𝟒𝟒𝟒 = 𝟖𝟖𝟒
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Pressure differences were
monitored with a focus on an
upper floor and a lower floor
(Floors 11 & 3)
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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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
Pres
sure
Diff
eren
ce [P
a]
Floor 02 Floor 03 Floor 04 Floor 10 Floor 11 Floor 12
Measurement with MAU OffMeasurement with MAU Recently Turned On
Corr
idor
-to-
Suite
Pre
ssur
e Di
ffere
nce
[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
Exte
rior T
empe
ratu
re [°
C]
Corr
idor
-to-
Suite
Pre
ssur
e Di
ffer
ence
[Pa]
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
Exte
rior T
empe
ratu
re [°
C]
Corr
idor
-to-
Suite
Pre
ssur
e Di
ffer
ence
[Pa]
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
Exte
rior T
empe
ratu
re [°
C]
Corr
idor
-to-
Suite
Pre
ssur
e Di
ffer
ence
[Pa]
Floor 02 Floor 03 Floor 04
Floor 10 Floor 11 Floor 12
Exterior Temperature [°C]
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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Stack effect pressures found to distribute 69% across the corridor to
suite boundary and 9% across exterior enclosure
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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Vancouver is a relatively moderate climate Should consider
other climates
Case study building is 13 storeys Should consider different
building heights
Extension of Study Findings
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Extension of Study Findings
Stack effect is more significant in taller buildings
Proportion of wind pressures remains relatively the same
Relative magnitude of mechanical pressures decreases as
height increases
0%
10%
20%
30%
40%
50%
60%
70%
Stack Effect Wind Mechanical(10 Pa)
Perc
enta
ge o
f Driv
ing
Forc
e Pr
essu
re
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
Stack effect more significant in cold climates
Wind highly variable, but typically more significant in
warm climates
0%
10%
20%
30%
40%
50%
60%
70%
Stack Effect Wind Mechanical(10 Pa)
Perc
enta
ge o
f Driv
ing
Forc
e Pr
essu
re
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
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
This is exaggerated for buildings located in more extreme
climates than Vancouver
Ventilation system can not practically overwhelm nature.
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Conclusion
Corridor pressurization does not provide intended
ventilation rates to a large number of suites Some significantly over ventilated while others significantly
under ventilated
Significant leakage along the ventilation air flow path
from the duct and the corridor (wasted ventilation) Uncontrolled airflow wastes energy and provides poor
ventilation
Stack effect and wind pressures are often similar or
greater than mechanically-induced pressures Ventilation system can not practically overwhelm nature
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Conclusions – Theory & Reality
Results could have been readily predicted by physics
i.e These problems were foreseeable
When designing ventilation systems, need to design
building as a system and account for all factors
Enclosure and compartment airtightness
Driving forces: stack effect and wind
Mechanical system
Occupants
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Recommendations for Ventilation System Design
Mid- to High-Rise Multi-Unit Residential Buildings
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
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