NBEC 2014 - Airflow in Mid to High-rise Multi-Unit Residential Buildings

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.

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  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

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

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
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

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
ASHRAE
62.1-‐2010

≈
40
L/s
per
suite

Waste
of

Energy

Indoor
Air

Quality

Issues

PMCP
Released
in
MAU

PDCB
Released
in
Parking
Garage

à  Carbon dioxide concentration were monitored as an
indicator of indoor air quality (IAQ)
à  Significantly higher concentration in the lower suites

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?

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

Maybe the ventilation air isn’t reaching the corridors?
à  Only 40% of intake flow reaches the corridors directly
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150
Floor
Number
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

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
1
L/s
≈
2
cfm

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.
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?

à  Mechanical ventilation system creates pressure of 5 to 10 Pa
-‐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
Difference
[Pa]
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
Off
Measurement with
MAU
Recently
Turned
On
Corridor-‐to-‐Suite
Pressure
Diﬀerence
[Pa]

≈10 Pa
≈5 Pa
Corridor-to-Suite Pressure Difference

-‐5
0
5
10
15
20
25
-‐10
-‐5
0
5
10
15
20
Exterior
Temperature
[°C]
Pressure
Difference
[Pa]
Average
Suite
to
Corridor
Pressures
by
Floor
and
Exterior
Temperature
-‐ 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
Exterior
Temperature
[°C]
Pressure
Difference
[Pa]
Average
Suite
to
Corridor
Pressures
by
Floor
and
Exterior
Temperature
-‐ 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
Exterior
Temperature
[°C]
Pressure
Difference
[Pa]
Average
Suite
to
Corridor
Pressures
by
Floor
and
Exterior
Temperature
-‐ 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
Corridor-to-Suite Pressure Difference
10 – 15 Pa

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

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

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

40
m
Tall
Building
in

Miami
40m Tall Building in Miami
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

40
m
Tall
Building
in
Vancouver
40m Tall Building in Vancouver40m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

40
m
Tall
Building
in
Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

40
m
Tall
Building
in
Fairbanks
40m Tall Building in Fairbanks
Wind Stack Effect Mechanical
(10 Pa)
à  Climate

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

20
m
Tall
Building
in
Toronto
20m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

40
m
Tall
Building
in
Toronto
40m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

60
m
Tall
Building
in
Toronto
60m Tall Building in Toronto80m Tall Building in Toronto
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Percentage
of
Driving
Force
Pressure
Daily
Average
Distribution
of
Pressure
Difference
due
to

Driving
Forces
for
a

80
m
Tall
Building
in
Toronto
Wind Stack Effect Mechanical
(10 Pa)
à  Building Height

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)
Percentage
of
Driving
Force
Pressure
Average
Proportions
of
Driving
Force
Pressure
Differences
-‐ Vancouver
20
m
40
m
60
m
80
m
100
m
Building
Height

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)
Percentage
of
Driving
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

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

à  rdh.com
Questions
LORNE RICKETTS, MASC, EIT
LRICKETTS@RDH.COM – 604-873-1181

NBEC 2014 - Airflow in Mid to High-rise Multi-Unit Residential Buildings

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