Thermosyphon Foundations in Warm Permafrost

Transcription

1 Thermosyphon Foundations in Warm Permafrost Igor Holubec, Ph.D., P.Eng. I. Holubec Consulting Inc. March 13 & 14, 2008

2 Project Definition Sponsor - Government of Northwest Territories, Public Works and Services Thermosyphon Foundations on permafrost Climate change affecting foundations Climate design criteria Case histories Impact of design, construction and monitoring Findings & recommendations

3 Foundations in permafrost uniqueness Permafrost is a frozen ground depending on climate Buildings have a warm base Need to keep ground below building cold Life span challenge because of climate warming

4 Air & ground temperature changes in Inuvik 4 Mean annual air & ground temperatures, deg C Mean Annual Ground Temperature Mean Annual Air Temperature Warming rate ~ 1 C/decade 10 Year moving average

5 Pile foundation BUILDING PILES AIR SPACE PERMAFROST

6 Pile foundations failures

7 Reasons for research Project host concerned with performance of several buildings in Inuvik, NT, that have thermosyphon foundations What are the causes? Is this design valid? Vulnerability of thermosyphon foundations to climate warming?

8 Research Approach Looked at 10 case histories to identify issues and causes of problems and good performance Different ground and ground temperatures Design of thermosyphon system Design of underlying base and of services beneath building base Construction method and timing

9 Study approach Discuss climate warming with Environment Canada climatologists Visit 4 case histories in Inuvik, NT Obtain performance comments from owners of buildings Obtain detailed information from thermosyphon system designer and installer Collect and evaluate site ground, air and ground temperature data Input published information and own experience

10 Thermosyphon foundation, Ross River School, YU

11 Evaporator piping installation

12 Climate Factors Climate design information (air temperature) available is not directly applicable for design Climate Normals are averages of 30 years of past data and do not represent present warmer air temperatures Present air temperature warming models are underpredicting of what is being measured Climatologists are recognizing this and are starting to consider air temperature trend analysis

13 Observations 1. Thermosyphon foundations were designed to maintain frozen ground in steady climate and they have been accomplishing this 2. Their design includes a factor of safety but this may not be sufficient for climate warming in the warmer permafrost areas 3. Effectiveness can be increased by changing several components (insulation, cooling pipe spacing, radiator size etc) 4. Long-term back up is available by adding mechanical cooling using refrigeration compressor

14 Observations -Problems 1. Inadequate understanding and appreciation of design and construction of base for thermosyphon foundations and construction scheduling. 2. Inadequate operation monitoring 3. Individual proprietary thermal analysis software that is difficult to compare and check by others 4. Thermal design has not adequately incorporated climate warming for the life of the buildings

15 Recommendations 1. Establish design air temperature and climate warming criteria 2. Prepare guidelines for geotechnical investigations and collection of design information 3. Conduct a calibration and parametric thermal analysis study of thermosyphon foundation design at typical sites to better understand design and robustness of this design. 4. Identify codes and standards that apply to thermosyphon piping; it is a pressure vessel.

16 Recommendations - Continued 5. Prepare design and construction guidelines for thermosyphon foundations. 6. Prepare guidelines for the instrumentation and monitoring for buildings with thermosyphon foundations. 7. Prepare baseline documentation of at key existing thermosyphon foundation for detailed monitoring and future studies. Potential sites: Aurora College, Inuvik, NT, Health Centre, Pangnirtung, NU, Air Terminal, Kuujjuaq, QC and School, Ross River, YU.

17 Thank You, Questions for Clarification Early thaw will ruin their ride