Equipment List

  1. 7 HOBO Data loggers with external temperature sensors (6 foot cord)
  2. Raytek Infrared Thermometer
  3. Drill and drill bits
  4. Plastic drinking straws (about 8" long - 1/4" diameter)
  5. Masking tape and duct tape
  6. Cotton batting
  7. Measuring tape
  8. Permanent marker
  9. Utility knife
  10. Wood for 12 hour woodstove firing (not pictured)

Data Logger Placement

We placed 5 data logger temperature sensors on and at various depths inside the interior north wall of the building. All these were located about 4 feet from the wood stove, our main heat source. The sensors were placed at the following depth levels:

  • Interior Surface
  • 1" depth
  • 2" depth
  • 3" depth
  • 4" depth

An additional data logger was placed on the surface of the north wall. The location was directly opposite interior hobos.

Rationale and Process

We chose the north wall of the structure for the hobo placement for two reasons: (a) The north wall does not get solar radiation and (b) it is in close proximity to the wood burning stove - the main heat source. We placed the data logger temperature sensors at various depths in the wall to track the heat movement through the wall.

The following is a step-by-step outline of our data gathering process.

  1. Baseline
    The cob building was left unheated for an extended period so the temperature of the walls, indoor and outdoor temperatures were close to equal.

  2. Launching data loggers
    We launched the data loggers to collect temperature readings from the temperature sensors every 10 minutes.

  3. Preparing the sensors
    To achieve rigidity and to reduce air infiltration, we split the plastic straws lengthwise with the utility knife, inserted the temperature sensors and cotton batting, and taped the straw closed. The tip of the temperature sensor aligned with the tip of the straw. This increased rigidity allowed for easier temperature sensor placement, and the batting provided insulation to reduce air infiltration.

  4. Installing the indoor sensors
    We then drilled holes in the cob wall and inserted the straws/temperature sensors to the correct depths. The holes were drilled to have as small diameter as possible to reduce air infiltration.

  5. Reducing air infiltration
    To further reduce air infiltration, we inserted additional cotton batting around the base of the straw and taped the straw and batting in place using duct tape.

  6. Installing outdoor sensor
    The outdoor surface temperature sensor was taped in place under a patch of cotton batting.

  7. Heating period
    After waiting for a short period to establish a base line, we started the fire in the woodstove. The fire was kept burning for 12 hours, and then allowed to die out. We ensured that the space was not reheated before retrieving the data loggers (one of us stayed overnight, and we put up signs for the following day).

  8. 54 hour data collection period
    The data loggers were kept in place and collected data for a total of 54 hours.

  9. Collecting data
    After the test period, we transferred the data collected by the data loggers to a PC using the HOBO Boxcar software.

  10. Charts
    We used Microsoft Excel (spreadsheet software) to create charts to help us with the interpretation of the data.


home | abstract | intro | hypothesis | methods | data
analysis | conclusions | appendix | acknowledgments

Cob Comfort - a study of heat transfer through cob walls
Kathy Bevers | Per Kielland-Lund | Arch 591 Fall 2003 | GTF: Sara Goenner