WETCORR in buildings
Material deterioration is caused by biological and chemical reactions where moisture plays an important role. The reactions increase with increasing humidity, and for most materials a critical humidity level can be defined. Above this level the deterioration is usually substantial. The time period when the material is exposed to conditions above this critical level is defined as the Time of Critical Humidity (TOCH).
The understanding of the deterioration processes is best known for metals and wood, but the humidity impact has also been observed for other building materials like stone, rendering and concrete.
Consequently there is a great need for mapping the humidity conditions in the micro-environment; on the surfaces and inside various building materials. The WetCorr instrument is designd to cover these two conditions by using a WetCorr sensor for surface moisture and a WetCorr InWood sensor for moisture in wood constructions.
The instrument is module-designed with the following parts:
1 System Controller (SC)
1 - 16 Sensor Adapters (SA)
1 - 64 Sensors WetCorr and InWood
The System Controller (SC):
- Is the control unit for communication between the SA and SC. SC is also the centre for external communication to a PC directly or through a modem
- Gives power to the sensors and SA
- Represents the sampling and storing unit for all measured data
The Sensor Adapter (SA):
- Controls and records signals from four sensors
- Measures temperature and current as an average over a selected sampling period
- Converts temperature and current measurements to digital signals
- Is designed for outdoor condition.
- Is rain proof and can operate between - 28 to + 85 °C.
All sensors are delivered with a 2 meter long shielded cable for connection to the Sensor Adapter.
A WetCorr sensor consists of one temperature sensor (Pt-1000) and one sensor for measuring the surface wetness through recording the current flow continuously. The limit current for wet surface iwet is defined. The whole WetCorr sensor is mounted on a thin aluminium oxide backing with a total size of 30 x 23 mm.
The InWood sensor consists of one Pt-1000 temperature sensor mounted inside an aluminium tube and two stainless steel screws as electrodes. Except for the tip of the screw the rest is insulated for current flow. A calibration curve relating the current flow to moisture content in the wood is elaborated. Only one InWood sensor should be applied to the same SA to prevent stray current problems.
Typical data to obtain is:
- Current and temperature versus time
- Percentage of time for current above iwet
- Percentage of time below freezing
- Minimum and maximum values
Measurements on wood constructions
Through the EU-project WOOD-ASSESS substantial evaluation of the WetCorr system has been carried out. To illustrate the information obtained by WetCorr and the InWood sensors a test was performed on one spruce and one pine panel.
The panels were exposed at an angle of 45° to the ground facing South. The InWood sensors were applied to the backside of the panel rain protected. The WetCorr sensor was applied on the panel side facing the rain.
The results showed that the WetCorr sensor responded quickly on the rain events 1st and 2nd day of July. The current past the WetCorr limit of 15 nA for rain was reached quickly and after the rain had stopped the sensor also dried out again quickly.
The result for the moisture content in the panels was different. After two days with rain it took 1.5 day before the moisture level was below the moisture content with risk for rotting.