assumptions about indoor environments mark lawton p.eng patrick roppel m.a.sc
TRANSCRIPT
Assumptions about Indoor Environments
Mark Lawton P.Eng
Patrick 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
pe
ratu
re (o
C)
20
30
40
50
60
70
80
90
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
Vap
ou
r P
ress
ure
(P
a)
Outdoor VP
Measured 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
64
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
Va
po
ur
Pre
ss
ure
(P
a)
Calculated VP (0.15 ACH) Measured VP
Monthly Avg - Calculated (0.15 ACH) Monthly Avg- Measured
Monthly 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
0
200
400
600
800
1000
1200
1400
1600
1800
2000
3/9/0612:28
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CO
2 (P
PM
)
0
5
10
15
20
25
Tem
per
atu
re (
oC
)
CO2
Temperature
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
1000
1200
1400
1600
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2000
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3/21/0612:28
CO
2 (P
PM
)
0
10
20
30
40
50
60
RH
(%
)
CO2
RH
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
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Vap
ou
r P
ress
ure
(P
a)
Airport Exterior Vapour Pressure
Measured Interior Vapour Pressure
Calculated 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
50
55
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95
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
50
55
60
65
70
75
80
85
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