Radiant heating

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Heat transfer mechanisms include:

• Radiation.
• Convection.
• Conduction.
• Phase change.

All bodies which are hotter than 0°K emit thermal radiation. They also absorb thermal radiation emitted by their surroundings. The difference in the total amount of radiation emitted and absorbed by a body at any given moment may result in a net heat transfer which will produce a change in the temperature of that body.

Solar radiation may be considered to include the ultra violet, visible and near or short wave infra-red radiation. However, most 'terrestrial' radiation, emitted by bodies at normal temperatures on earth, is far or long wave infra-red radiation.

Radiant heat transmits in straight lines, only warming surfaces that are ‘visible’ to the source. However, these surfaces in turn re-radiate heat and warm air adjacent to them by convection. This allows heat from a radiant source to distribute through a space. Because it is directly heating, rather than heating the air (as in convective heating), it can be more efficient, particularly in large spaces, in spaces with poor insulation or in unenclosed or semi-enclosed spaces.

Radiant heating systems tend either to be low-temperature systems spread over large surface areas, or high temperature localised systems.

Radiant heating systems include:

• Underfloor heating systems.
• Wall heating systems.
• Radiant ceiling panels.
• Integrated service modules.
• Gas fired heated tubes.
• Gas powered ceramic burners.
• Local electric heaters.
• Open fires.

Some radiant heating systems also heat by convection, for example hot water radiators, often found in domestic buildings, radiate heat directly to their surroundings, but also draw air through heated elements resulting in convective heating.

Water-based systems such as underfloor heating can be used to provide cooling as well as heating. Radiant heating systems can incorporate renewable energy sources such as solar thermal panels, solar photovoltaics, ground source heat pumps, air source heat pumps and so on. They may also be used in combination with thermal mass and night-time purging.

Compared to other forms of heating, radiant heating (depending on the system used) can be:

• More healthy, separating heating from ventilation, and so reducing problems associated with dust, pollen and other pollutants.
• More durable.
• More comfortable, giving a more even temperature distribution.
• More instantaneous.
• Space saving and unobtrusive.
• Quieter.
• Less expensive to run in certain situations. Low temperature systems in particular can run at a lower overall temperature than conventional heating systems whilst still achieving comfortable conditions.
• Easier to maintain.
• More directed.

Radiant heating also has less impact on air moisture content than other heating methods.

However, depending on the system adopted:

• High temperature electric radiant heaters can be expensive to run.
• It can impose restrictions on floor and wall coverings.
• It can be expensive to install.
• It can be less effective at cooling, and there can be condensation issues.
• There can be poor familiarity amongst designers and installers.
• It can be difficult to retrofit.
• It can be difficult to repair.

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[edit] Related articles on Designing Buildings Wiki

• Air handling unit.
• Approved documents.
• Building services.
• Building services engineer.
• Building regulations.
• Co-heating test.
• Cold stress.
• Cooling.
• Corrosion in heating and cooling systems.
• Fan coil unit.
• Heating.
• Heat pump.
• Heat recovery.
• Heat stress.
• Heat transfer.
• HVAC.
• Radiation.
• Thermal comfort.
• Underfloor heating.