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KNOWLEDGE COLLECTION Effects of passive ventilation in subslab or crawlspaces to reduce the impact of contaminated vapour on indoor air Environmental project no. 1348 2010
Henrik Husum Nielsen, NIRAS Nanna Muchitsch, NIRAS, now DMR Anders G. Christensen, NIRAS
Follow-up group Ole Kiilerich, The Danish Environmental Protection Agency Susanne Pedersen, Region Zealand Lotte Tombak, Region Zealand Henrik Jannerup, Region Zealand Peder Johansen, The Capital Region Marianna Engberg Pedersen, The Capital Region
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Outline
– Background and objective
– Systems and principles
– Data collection
– Systems in Denmark with passive ventilation under houses
– 38 selected cases with focus on: – Pollution situation
– Construction details
– Preliminary investigations and design basis
– System specifications
– Operation and monitoring
– Achieved effect by passive ventilation
– Economy
– Conclusion and recommendations
3
Background and objective (1 of 2)
Background
– During the last 10 years, passive ventilation has been used as a remediation method to reduce unacceptable transport of contaminated vapours to the indoor air in residential buildings.
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Background and objective (2 of 2)
Objective
– The overall objective of the project is to be able to present a status for the method and its application in Denmark during the period 1999-2009.
– The deployment of the technique, use, effect, and economy is presented, and recommendations for the further activities using the method are outlined.
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Ventilation drain in capillary-breaking layer connected to a wind-powered cowl on roof with air intake (under existing and new floor)
Ventilation drain in capillary-breaking layer connected to goose necks or similar (primarily under new floor)
Ventilation drain in capillary-breaking layer connected to a wind-powered cowl on roof without air intake (under existing and new floor)
Ventilation of existing crawl space
Systems and principles (1 of 2)
System types Wind-powered cowl
GVS
Capillary-breaking layer Concrete floor
Pollution
Groundwater level
Wind-powered cowl
GVS
Capillary-breaking layer Concrete
floor
Pollution
Groundwater level
GVS
Capillary-breaking layer Concrete floor
Pollution
Groundwater level
GVS
Capillary-breaking layer
Concrete floor
Pollution
Groundwater level
Wind-powered cowl
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Systems and principles (2 of 2)
Principle Spreading of pollution to indoor air by advection and diffusion
Pollution
Groundwater level
Csoil gas Psoil gas
Cindoor climate DIFFUSION
Pindoor climate ADVECTION
DIFFUSION Csoil gas > Cindoor climate
ADVECTION Psoil gas > Pindoor climate
Remediation by reduction of advection (reduction of pressure gradient) and diffusion (reduction of diffusive gradient by lowering concentration under the floor)
Air intake
Wind-operated cowl
Pollution
Groundwater level
Capillary-breaking layer
Vent pipe
Csoil gas Psoil gas
Cindoor climate DIFFUSION, reduced
Pindoor climate ADVECTION, reduced (reduced pressure gradient)
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Data collection
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Empirical data collection
Quantitative data – gross list
125 systems
Qualitative data –
site specific from
38 systems
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Systems in Denmark with passive ventilation under buildings (1 of 2)
Gross list 125 systems
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74%
5%
2% 19%
VENTILATION OF: Capillary-breaking layer
Crawl space
No data
Other
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Systems in Denmark with passive ventilation under buildings (2 of 2)
Gross list 125 systems
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0
20
40
60
80
100
27
97
1
Num
ber
of
syste
ms
New building
Existingbuilding
Partially
0
20
40
60
8075
44
5 1
Nu
mb
er
of
syste
ms
New floor
Existing floor
New and existingfloor
No data
10
38 selected cases
38 cases primarily selected
– in order to analyze the variation in the existing systems.
– when on basis of the gross list it is assessed (consultant/contractor) that the case presents a good data basis.
– when the passive ventilation has had the intended effect, but also cases with no effect.
– in order that all consultants and contractors are represented.
Must be careful not to conclude anything statistically, but directions / trends are apparent.
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38 selected cases with focus on (1 of 14)
Pollution situation
SOURCE
Dry-cleaner
21
Metal factory
3
Other
2
CONTAMINANT
Landfill gas
4
Hydrocarbons
8
Chlorinated solvents
26
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before 1920 11
1920-1970111970-2000
5
after 2000 5
no data6
Contruction year
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38 selected cases with focus on (2 of 14)
Construction details
Characteristics
– Buildings before 1970 – ground deck directly on ground
– Buildings after 1970 – capillary-breaking layer
– Buildings before 1960 – can be with crawl space
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38 selected cases with focus on (3 of 14)
Preliminary investigations and design basis
Allways
Pollution investigation and risk assessment
(soil gas and indoor climate measurements. Soil samples in case of new building)
Often
Examination of construction details on-site.
Infrequent
Design related investigations. In certain cases ventilation tests in capillary-breaking layers. Investigation of sinks and pathways.
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38 selected cases with focus on (4 of 14)
System specifications. Choice of materials
Capillary-breaking layer:
Coarse gravel, pebbles, leca and gravel in layer thickness 80-400 mm
Ventilation pipes under ground:
PE or PVC ø50-110 mm (drain and pipes)
Coarse gravel 32-64 mm Pebbles 16-32 mm Leca 8-22 mm
Course Region Syddanmark, AAB, Grontmij | Carl Bro
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38 selected cases with focus on (5 of 14)
System specifications. Choice of materials
Difusion reducing membrane (used on approx. ¼ of the 38 selected cases):
R.A.C. membrane
Generally no investigations of the tightness of the membrane performed after
installation.
Tightness examined in 2 cases with PID-gauge of type ppbRAE and by
thermography and blower door.
ppbRAE: Some leakages in corners
Termografi: Many leakages at clamping rails and in corners NORDROCS 19. September 2012
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38 selected cases with focus on (6 of 14)
System specifications. Choice of materials
Piping above ground: Wind operated cowl:
ø70-80 mm galvanized pipes SupaVent 10’
Source Region Syddanmark, Rambøll
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38 selected cases with focus on (7 of 14)
Operation and monitoring
Indoor air measurements performed:
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Yes 26
No 12
- Landfill gas (4)
- Oil Pullution (6)
- Not established as indoor climate protection (1)
- System established in existing dry-cleaning establishment (1)
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38 selected cases with focus on (8 of 14)
Operation and monitoring Monitoring of airflow and air sampling of discharge air
(system with wind-operated cowl):
– In connection with measurements of airflow, point measurements and continuous
measurements over several weeks have been performed.
– Performing point measurements gives an ”up-to-the-minute account” of the airflow under the actual wind conditions.
– Continuous measurements allow the possibility of obtaining a picture of the average airflow, including periods with reduced airflow, corresponding to periods with weak wind action.
Airflow
Datalogger box
air velocity Air sample
Source Region Syddanmark, LIDL, Grontmij | Carl Bro
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38 selected cases with focus on (9 of 14)
Operation and monitoring
Monitoring of airflow and air sampling of discharge air
(system with goose necks or similar):
– Airflow not measured
– Air sample often taken out from goosenecks or similar
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38 selected cases with focus on (10 of 14)
Operation and monitoring
Monitoring of concentrations in the air in capillary-breaking layer:
(established on approx. 1/3 of the 38 selected cases)
Ex. ø6 mm copper pipes installed under floor and let up along the wall and fitted with a ball valve in a monitoring box.
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38 selected cases with focus on (11 of 14)
Operation and monitoring
Monitoring frequency
(typically 2 monitoring campaigns)
(each year or several times per year)
(each 2 year or less)
Monitoring period
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38 selected cases with focus on (12 of 14)
Operation and monitoring
Supplementary investigations
Supplementary investigations at sites with inadequate effect have included:
– Monitoring of groundwater level in surficial aquifers
– Mapping of pollution in the unsaturated zone with Gore-Sorber
– Identification of pathways using a VOC sensing instrument
– Identification of pathways using tracer gas measurements
– Identification of pathways by thermographi and blower door
– Air flow measurements and measurements of wind velocity
– Tracer test for control of ventilation in capillary-breaking layer
– Atmosphere, wind, and barometer (weather conditions)
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38 selected cases with focus on (13 of 14)
Achieved effect of passive ventilation under buildings
Effective: Concentrations in the indoor air reduced to a level below the indoor air criteria
Partly effective: Concentrations in the indoor air reduced, but not below the indoor air criteria
ex. other pathways
Not effective: Concentrations in the indoor air not reduced to a level below the indoor air criteria
Uncertain: ? Effect difficult to assess
ex. excavation of pollution in connection with establishment, active ventilation in combination with passive ventilation, natural degradation of oil
15
?
10
9
4
SITE SPECIFIC FORMS
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38 selected cases with focus on (14 of 14)
Economy € excl. VAT
CONSTRUCTION COSTS
No data
15
>130.000
3
65.000- 130.000
6
15.000- 65.000
10
<15.000 4
ANNUAL OPERATION AND MONITORING COSTS
2.500-5.500 15
5.500-8.000 4
>8.000 3
No data 15
<2.500 1
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Conclusion and recommendations for further activities (1 of 4)
Conclusion
– Despite the simple principle, it is difficult to achieve the effect desired
(only approximately 40% reaches the goal – under indoor air criteria)
– The varying success could be related to a limited design basis
– Often, the systems are solely based on risk assessments made in the investigation phase
– Insufficient focus on the documentation of the ”tightness” of the selected method.
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Conclusion and recommendations for further activities (2 of 4)
Conclusion
– In the monitoring phase, the function of the systems is documented by
– In the monitoring phase, a series of supplementary investigations were carried out where the established passive ventilation under buildings did not have the desired effect.
Pollution
Groundwater level
Wind-powered
cowl
Soil gas measurements under floor
Measurements of airflow (point and continuous)
: systems with goosenecks or similar
Contaminants in discharge air
Indoor climate measurements ( oil pollution)
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Conclusion and recommendations for further activities (3 of 4)
Recommendations for further activities It is assessed that the certainty of effect can be substantially increased by future
investments in improved design/basis before construction of the systems.
It is recommended
– That a conceptual model for evaluation and understanding of possible pathways are always made.
– Based on the conceptual model, it is possible to carry out supplementary investigations. Investigations which were earlier performed in the operation and monitoring phase, ex. tracer gas measurements and thermography, and new types ex. radon measurements for clarification of i.a. attenuation factor above floor constructions.
– By mapping the pathways, it is investigated whether passive ventilation should be selected in combination with other methods of remediation or be left out of consideration.
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Conclusion and recommendations for further activities (4 of 4)
Recommendations for further activities
It is recommended that a catalogue of methods be assembled.
The catalogue should contain instructions and descriptions of practical tools that can be used in the dimensioning, design, and control of systems with passive ventilation.
The catalogue will be linked to the conceptual model in connection with the identification of pathways.
Catalogue of Methods
Conceptual model
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