REFLECTORS AND BEAM PATTERNS

The method of transferring and directing the infrared energy to the work level is an important factor in the heating design and will greatly affect the efficiency of the heating system.

Reflectors are used to direct the radiant energy from the source to the work area. The higher the efficiency of the reflector; the more radiant energy will be transferred to the work level. The reflector efficiency is influenced by the reflector material, its shape and contour.

One method of measuring the efficiency of the material is by the emissivity factor. Emissivity is defined as the ratio of the amount of energy given off by radiation from a perfect black body; and is equal to the rate that material will absorb energy. The lower the emissivity number the less the material will absorb; hence the better the reflectivity of the material.

Few materials can be considered for use as reflectors in comfort heating equipment. They must have high reflectivity of infrared energy; resist corrosion, heat, moisture; and be easily cleaned.

Aluminum is a common reflector material and must be anodized to provide suitable reflectivity and withstand the heat levels present in an infrared heater. Gold anodized aluminum is best suited as a reflector material when the combined factors of cost, workability and weight are considered.

Dirt will accumulate ON the surface and not IN the chemical composition with the gold. Within the infrared energy portion of the spectrum, clear anodized aluminum reflectors achieve 89 percent reflectivity. Gold anodized aluminum reflectors achieve 92 percent reflectivity. The most highly efficient reflector readily available is a specular gold plated material, which is rarely used due to the prohibitive cost of gold. Fostoria uses gold anodized aluminum for reflectors and end caps in their electric infrared heating equipment to provide the highest economical reflectivity and durability.

The beam pattern created by the reflector must be emphasized in the heating design. First the reflector must create a straight vertical line from the heat source to the work area. This is the pattern centerline. Secondly, the reflector will converge or concentrate the energy into a choice of wide, medium or narrow patterns. In the electric infrared comfort heat industry, reflectors are also designed for asymmetric, symmetric and offset patterns as shown below.

A specific heat pattern can easily be identified by the number of bends in the reflector in addition to the angle of the reflector.