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

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

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 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]


Pressure Differen

ce [P

a]

Average Suite to Corridor Pressures by Floor and ExteriorTemperature -‐ 24 Hour Moving Average

Floor 02 Floor 03 Floor 04


Exterior Temperature [°C]

-‐5

0

5

10

15

20

25

-‐10

-‐5

0

5

10

15

20

Exterio

r Tem

perature [°C]


Pressure Differen

ce [P

a]





-‐5

0

5

10

15

20

25

-‐10

-‐5

0

5

10

15

20

Exterio

r Tem

perature [°C]


Pressure Differen

ce [P

a]





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%

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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%


Percen

tage of D


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%


Percen

tage of D


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%


Percen

tage of D


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


Wind Stack Effect Mechanical (10 Pa)

à Climate

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Percen

tage of D



Wind

Stack Effect

Mechanical(10 Pa)

20m Tall Building in Toronto

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Percen

tage of D



Wind

Stack Effect

Mechanical(10 Pa)

40m Tall Building in Toronto

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Percen

tage of D



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%


Percen

tage of D



Wind

Stack Effect

Mechanical(10 Pa)


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)

Percen

tage of D


Average Proportions of Driving Force Pressure Differences -‐ Vancouver

20 m

40 m

60 m

80 m

100 m

BuildingHeight


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


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 [email protected] – 604-873-1181

Engineering

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