Assumptions about Indoor Environments

Mark Lawton P.EngPatrick Roppel M.A.Sc.

Wall Section

Latex paint R-8 batt DensGlass SA Membrane R-8 Semi-Rigid FG Air Space Stucco

Ventilation

Operable windowsRange hoodBathroom fans on timer (principal

exhaust) Corridor pressurization system serving most suites

Issues

Very High indoor RH Winter moisture collection in DensGlass Mold growth on interior surfacesCondensation damage on window sills

Impact of Wall Construction

• There must be sufficient insulation outboard of an impermeable layer to control the time that the temperature of the sheathing is below the dewpoint of the interior air.

• VBBL allows the ratio of insulation outboard/insulation inboard of impermeable surface to be 0.2

• Lstiburek suggests ratio for Marine climate without VB is 0.3

• Ratio 0.7 for R8 is 0.5 for R12 and

Obvious Questions

Why is humidity so high? Extraordinary sources? Inadequate use of ventilation systems? Insufficient capacity of ventilation systems?

Is control by ventilation practical? Capacity Operating time Supply air source

How would a vapour barrier affect performance

Monitored Interior Conditions

0

5

10

15

20

25

30

Jan Apr Jun Sep Dec

Tem

pera

ture

(o C)

20

30

40

50

60

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100

RH

(%)

TemperatureMonthly Avg. TemperatureRHMonthly Avg. RH

Comparison of Outdoor and Indoor Vapour Pressure

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Jan Apr Jun Sep Dec

Vapo

ur P

ress

ure

(Pa)

Outdoor VPMeasured VP

Little difference in

summer

Larger difference in

coldest months

Capacity of principal exhausts

Bedrooms 2 3

No. Measured 9 5

VBBL Capacity Req’t (cfm) 45 60

% Complying 44% 20%

Measured / Req’t Ratio 0.95 0.73

No. on for 8 Hrs 2 0

Corridor Supply Air

Measure flow to corridors generally matched the VBBL required capacity of suites on the corridor

Some suites not served by indoor corridor

Most doors weather-stripped

Indoor Vapour Pressure

Depends on: Moisture sources

Typically in range of 2 kg/day per person Rate of air change

In tight building can average as low as 0.15 to 0.25 ACH

For a given set of indoor and outdoor vapour pressures conditions, there can be a range of solutions

Indoor Humidity

50

52

54

56

58

60

62

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66

68

70

1-Nov 21-Nov 11-Dec 31-Dec 20-Jan 9-Feb 29-Feb 20-Mar

RH (%

)

Measured RH Calculated RH (0.45 ACH) Calculated RH (0.15 ACH)

ASHRAE Design Comfort Limit

Indoor Humidity

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1-Nov 21-Nov 11-Dec 31-Dec 20-Jan 9-Feb 29-Feb 20-Mar

Vapo

ur P

ress

ure

(Pa)

Calculated VP (0.15 ACH) Measured VPMonthly Avg - Calculated (0.15 ACH) Monthly Avg- MeasuredMonthly Avg. - Calculated (0.45 ACH)

Winter 2004 – Suite 611•7 kg/day moisture generation•Limited use of bathroom fan (noisy)•Undercut blocked•Room heat turned down & door closed•Top floor

CO2 Measurements

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2000

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CO2 (

PPM

)

0

5

10

15

20

25

Tem

pera

ture

(o C)

CO2Temperature

fan running continuously

Suite 205•Fan with window open at 480 PPM•Peak with fan at 1200 PPM•Range of 680 to 1800 PPM without fan•Operating temperature routine constant

0

200

400

600

800

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CO

2 (P

PM)

0

10

20

30

40

50

60

RH

(%)

CO2RH

fan running continuously

Impact of Ventilation

Suite 205•Range of 36 to 47% RH with fan•Range of 42 to 56% RH without fan•Fan flow measured at 37 cfm

0

200

400

600

800

1000

1200

1400

3/9/0612:28

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Vapo

ur P

ress

ure

(Pa)

Airport Exterior Vapour PressureMeasured Interior Vapour PressureCalculated Interior Vapour Pressure

fan running continuously

Impact of Ventilation

Suite 205•4 kg/day moisture generation•Overall trend is consistent•Difference by peak ventilation •Difference by peak moisture

Impact of Ventilation

0

500

1000

1500

2000

2500

3000

3500

4000

4500

3/9/06 12:28 3/10/06 0:28 3/10/06 12:28 3/11/06 0:28 3/11/06 12:28 3/12/06 0:28 3/12/06 12:28

CO

2 (PP

M)

0

10

20

30

40

50

60

RH

(%)

CO2RH

fan running continuously

Suite 311•Data limited•Peak at 4000 without fan•Peak at 2500 with fan•Fan flow measure at 44 cfm

Impact of Ventilation

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55

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100

0 100 200 300 400 500 600 700

RH

(%)

0.15 ACH0.45 ACH0.75 ACHMeasured Interior Conditions

1-D Hygrothermal Model (WUFI)

•RH at exterior sheathing (inside)•0.3 ACH improvement results in RH maintained below 90%•0.6 ACH improvement results in RH maintained below 85%

Impact of Vapour Resistance

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55

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90

95

0 100 200 300 400 500 600 700

RH

(%)

Latex Paint

Vapour Retarding Paint

6 mil Polyethylene

1-D Hygrothermal Model (WUFI)

•Retarding paint (35 ng/m2 Pa s)•Decreases wetting potential from interior•Allows drying to interior

Impact of Winter Indoor Operating Temperature

Number of Hours that Exterior Sheathing is below Interior Air

Dewpoint Existing Operation Minimum Temperature

of 19oC

Sensor Location Suite

Number of hours

below dewpoint

Percentage of total hours

Number of hours

below dewpoint

Percentage of total hours

2nd Floor, below 3rd floor balcony-wall interface 211 & 311 47 1.1% 4 0.1%

3rd Floor, below window 311 229 5.2% 11 0.3%

6th Floor, southeast corner 611 410 9.4% 242 5.5%

5th Floor, below 6th floor balcony-wall interface 611 & 511 512 11.7% 324 7.4%

6th Floor, below window 611 62 1.4% 39 0.9%

Inadequate ventilation leads to unsatisfactory conditions for both humidity and other contaminants.

Ventilation that meets the requirements of a principal exhaust fan in the code for noise, capacity, and duration is likely sufficient for most units if it is on, and exhausted air is replaced with fresh air.

Must keep the occupant’s comfort in mind or risk them overriding controls.

For high humidity indoor environments, vapour resistance at the interior surface is recommended to control the wetting potential from the interior air.

Conclusions