Far infrared radiation and space heating.

Infrared spectrum is generally divided into two distinct regions; near infrared with wavelengths shorter than about 4μm and far infrared with wavelengths greater than about 4μm. In this paper, thermal properties of infrared radiation and effectiveness of far infrared radiation for space heating are investigeted.The thermal properties of infrared radiation are as follows:1) For human skin and clothing fabrics, the reflection of radiation is low in the wavelength region over 2μm while the radiation emitted by a radiant space heater exists almost in this region.2) For the skin, the transmission of near infrared radiation is higher than that of far infrared radiation.3) The thermal sensation for each wavelength is not different in the wavelength region over 2μm.It is generally accepted that space heaters emitting far infrared radiation make comfortable environment. But the investigation of infrared radiation properties shows that far infrared radiation itself is not specially effective for space heating. On the other hand, far infrared radiant heaters make comfortable environment because they are low temperature radiant heaters which make uniform and moderate radiant environment without any excessive wind that makes human body feel uncomfortable.