RADIANT principles apply to equip ment with radiant source temperatures
ranging from 300 to 5000°F. Radiant equipment with source
temperatures in this range is categorized into three groups as
• Low intensity
• Medium intensity
• High intensity
Radiant equipment with source temperatures from below room temperature
to 300°F is classified as panel
heating and cooling equipment.
Low-intensity source temperatures range from 300 to 1200°F.
A typical low-intensity heater is mounted on the ceiling and may
be constructed of a 4 in. steel tube 20 to 30 ft long. A gas burner
inserted into the end of the tube raises the tube temperature,
and because most units are equipped with a reflector, the radiant
energy emitted is directed down to the conditioned space.
Medium-intensity source temperatures range from 1200 to 1800°F.
Typical sources include porous matrix gas-fired infrared units
or metal sheathed electric units.
High-intensity radiant source temperatures range from 1800 to
5000°F. A typical high-intensity unit is an electrical reflector
lamp with a resistor temperature of 4050°F.
Low-, medium-, and high-intensity infrared heaters are frequently
applied in aircraft hangars, factories, warehouses, foundries,
greenhouses, and gymnasiums. They are applied to open areas including
loading docks, racetrack stands, under marquees, outdoor restaurants,
and around swimming pools. Infrared heaters are also used for
snow and ice melting
When infrared is used, the environment is characterized by
1. A directional radiant field created by the infrared heaters
2. A radiant field consisting of reradiation and reflection from
the walls and/or enclosing surfaces
3. Ambient air temperatures often lower than those found with
convective systems The combined action of these factors determines
and the thermal acceptability of the environment.
Infrared heating units are effective for spot heating. However,
due to efficient performance, they are also used for total heating
of large areas and entire buildings. Radiant heaters transfer
energy directly to solid objects. Little energy is lost during
transmission because air is a poor absorber of radiant heat.
As infrared energy warms floors and objects, they in turn release
heat to the air by convection. Reradiation to surrounding objects
also contributes to comfort in the area. An energy-saving advantage
is that radiant heat can be turned off when it is not needed;
when it is turned on again, it is effective in minutes.
Human comfort is determined by the average of mean radiant and
dry-bulb temperatures. With radiant heating, the dry-bulb temperature
may be kept lower for a given comfort level than with other forms
of heating. As a result, the heat lost to ventilating air and
via conduction through the shell of the structure is proportionally
smaller, as is energy consumption. Infiltration loss, which is
a function of temperature, is also reduced.
Due to the unique split of radiant and convective components
in radiant heating and cooling, air movement and stratification
in the conditioned space is minimal. This reduces the infiltration
and transmission heat losses.
INFRARED ENERGY GENERATORS
Modern gas-fired infrared heaters burn gas to heat a specific
radiating surface. The surface is heated by direct flame contact
or with combustion gases.
.The wavelength span over which radiation from a heated surface
is distributed can be controlled by design. The specific radiating
surface of a properly designed unit directs radiation toward the
load. Heaters are available in the following types
Indirect infrared radiation units are internally fired and have
the radiating surface between the hot gases and the load. Combustion
takes place within the radiating elements, which operate with
surface temperatures up to 1200°F. The elements may be tubes
or panels with metal or ceramic components. Indirect infrared
radiation units are usually vented and may require eductors.
Radiant Floor Heating