Knitted Heating Mats

The paper deals with conceptual designs and research on flexible knitted heating mats differing in construction from textile heaters on low-elastic woven or nonwoven-foil substrates. Two variants of heating mats with elasticity from 100 to 300 % of relative elongation were designed and manufactured using knitting technology. The heating elements of the mats were parallel-connected sets of electrically conducted carbon threads and synthetic threads coated with silver. With considerable elongation in the range of 210 divided by 270 % no damage was observed to the heating elements and resistance changes during the stretching process equaled from 0.015 to 0.22 omega/% of elongation. The optimum power of the knitted heater in the range from 16 to 41 W, with high thermal efficiency for a 12 V supply voltage, was obtained thanks to proper density of the electrically conductive threads (resistors) and the appropriate structure of the knitted fabric. The surface temperature of the heater can be adjusted from 34 to 43 C-degrees, which corresponds to human thermal comfort. One of the variants of the knitted heaters was applied in the construction of the seat and backrest of an office chair.