airflow in mid to high-rise multi-unit residential buildings
TRANSCRIPT
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
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.
AIA Credits – Learning Objectives
Participants will: 1. Understand typical ventilation practices for multi-unit residential buildings including corridor pressurization systems.
2. Understand performance issues associated with the ventilation of high-rise multi-unit residential buildings including the impacts of stack effect, wind, and airtightness. 3. Learn about how the theory of airflow relates well to what is measured in-service, but that the well understood theory is not always taken into account in design.
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
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 Particularly relevant now, as newer more airtight building
have less tolerance for poorly performing ventilation
systems
à Less infiltration and exfiltration to supplement ventilation
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
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
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
10
28
1125
48
7058
154
193
121
0
20
40
60
80
100
120
140
160
180
200
220
Suite202
Suite301
Suite302
Suite303
Suite402
Suite1003
Suite1101
Suite1102
Suite1103
Suite1203
Airflow [cfm
]
Total Airflow Into Suites from All Sources
Lower Suites Upper Suites
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 ≈ 85 cfm per suite
Waste of Energy
Indoor Air Quality Issues
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
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 3,300 cfm (1,560 L/s)
Cause of Ventilation Rates
0
2
4
6
8
10
12
14
0 50 100 150 200 250 300 350
Floo
r Num
ber
Flow Rate [cfm]
MAU Supply to Corridors
Pre-‐Retrofit (70°F) Post-‐Retrofit (43°F) Post-‐Retrofit (61°C)
Pre-‐Retrofit (21°C) Total = 1257 cfm Post-‐Retrofit (6°C) Total = 1184 cfm
Post-‐Retrofit (16°C) Total = 1229 cfm
Fire Damper noted to be closed on Floors 4, 8, & 12.
Maybe the ventilation air isn’t reaching the corridors?
à Only 40% of intake flow reaches the corridors directly
Cause of Ventilation Rates
1 L/s ≈ 2 cfm
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 335 cfm, 10%
945 cfm, 29%
1,297 cfm, 41%
627 cfm, 20%
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%
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
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
-‐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
23
32
41
50
59
68
77
Exterio
r Tem
perature [°F]
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
14 Exterio
r Tem
perature [°F]
32
50
68
86
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
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
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
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.
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
Conclusions – Theory & Reality
à Results could have been readily predicted by physics à i.e these problems were largely foreseeable
à When designing ventilation systems, need to design
building as a system and account for all factors à Enclosure and compartment airtightness
à Driving forces: stack effect and wind
à Mechanical system
à Occupants
Recommendations for Ventilation System Design
Mid- to High-Rise Multi-Unit Residential Buildings
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
