FTI 2022 WFN 0049
Abstract
The “Intrinsic Dew Point Heating” project has developed a flexible textile heating system for drying masonry that does not require sensors or controls.
Problem
The self-regulating textile dew point heating system is designed to heat only when the temperature on the wall falls below the dew point. The textile heating system does not require any electronic controls for this purpose. The heating conductor is the water that condenses in the textile heating structure when the temperature falls below the dew point. The conductivity of the condensation water is adjusted using an electrolytic textile finish.
Solution
The technical basis of the textile heating surface is an interdigital structure that is subjected to alternating voltage. Moisture separation on the surface changes the resistance between the voltage-applied threads of the woven interdigital structure (Figure 1).
Fig. 1: Schematic representation of textile dew point heating = self-regulating heating for drying and preventing structural Damage
Only a low voltage in the form of an alternating voltage needs to be applied to the interdigital structure woven from corrosion-resistant yarns (Bekinox steel fiber yarn, stainless steel wires). The voltage-supplying electrodes, through which higher currents flow, are made of current-carrying CuAg strands. They must be protected from moisture to prevent corrosion. Figure 2 shows a heating fabric in which the voltage supply is implemented on one side of the fabric.
Fig. 2: Heating fabric - woven
The project developed a test setup to simulate wall moisture caused by temperatures falling below the dew point. In this setup, an aluminum plate is cooled by two Peltier elements so that moisture forms on the aluminum plate when the temperature falls below the dew point. The heat generated on the other side of the Peltier elements is dissipated by a CPU cooler.
This provides a functional simulator for wall moisture, which was used to test the heating fabrics developed in the project. During the tests, the measured values were recorded visually with a camera. This allows all measured values to be recorded and evaluated on a PC. Figure 3 shows the final test setup.
Fig. 3: Test setup simulation of wall moisture
The simulator has been used to conduct tests with various electrolytic and hydrophilic heating fabrics.
The surface heating power can be determined as a function of time from the measured currents. Diagram 1 shows an example of the heating and control behavior of a dew point heater equipped with NaCl. The heater was switched on after 25 minutes of moisture exposure at a temperature of 9 °C on the aluminum sheet.
Diagram 1: Surface heating power of the dew point heater
Initially, a high surface heating output of almost 400 W/m² is observed, which drops to approx. 40 W/m² within a few seconds.
The necessary NaCl electrolyte content to achieve the desired heating power can be determined from the simulation calculations and the measured values. Diagram 2 shows the surface heating power as a function of the saline concentration at a distance of 5 mm between the interdigital electrodes.
Diagram 2: Area coverage depending on NaCl application in milligrams per square meter
The necessary electrolyte content of NaCl is approx. 25–45 mg/m² at a distance of 5 mm between the heating electrodes in order to achieve a heating output of 100–200 W/m².
Results and Application
The “Intrinsic Dew Point Heating” project demonstrated that woven interdigital structures can be used to create self-regulating textile dew point heating systems that do not require additional electronic controls and can be operated at low voltages. This provides a cost-effective way of preventing damage to building structures and mold growth caused by condensation.
Contact
Dr. Andreas Neudeck
E-Mail:
The project underlying these results was funded by the Free State of Thuringia under number 2022 WFN 0049 and co-financed by the European Union under the European Regional Development Fund (ERDF).
