How Radiant Heating Differs From Other Heating

Radiant heating generally refers to heat-delivery systems that rely on electromagnetic waves to warm surfaces. The sun's energy that hits the earth is electromagnetic energy, including visible waves we know as sunlight. Sunlight is radiant energy that transforms into heat energy when it contacts a physical surface, like the absorber plate in a solar thermal collector. The heat is conducted through the metal of the absorber to a heat-transfer fluid, which then is pumped to where it is needed or will be stored for later use.

Radiant heating systems

Radiant heating systems rely on electromagnetic waves that we cannot see, but we can feel them as warmth. Imagine a flat panel that is like the absorber plate in a solar thermal collector. If we circulate a hot fluid through our flat panel and if the panel is warmer than the surrounding air, then the panel will emit radiation in the form of electromagnetic waves into the surrounding space. When this radiation hits a solid object, the object will get warm. When the object gets warm it will, in turn, warm the air that surrounds it. In other words, radiant heating systems heat things rather than directly heating air. By contrast, traditional forced-air heating systems and traditional hydronic heating systems heat air, and the warm air heats things it comes into contact with through convection and conduction.

The point of the above descriptions is to clearly show how fundamentally different radiant heating systems are from conventional heating systems. Conventional systems have to fill the conditioned space with hot air to achieve the desired temperature, while radiant heating systems heat the objects in the space.

Components of radiant heating systems

Any heating system comprises two main components: the heat source and the heat-delivery system. Most radiant heating systems rely on a boiler to heat a liquid that is then piped to some type of heat-transfer device, like baseboard radiators or radiant floor, wall or ceiling panels. Resistance electric heating could also be used where heating cables are embedded in floors, walls or ceilings, in which case the heat source and delivery system are the same heating cables. Baseboard radiators and most old-fashioned radiators actually work on the principle of convection, whereby the radiators heat air that is then circulated throughout the room by convection.

Operating temperature of radiant heating systems

The operating temperature of the radiant heating system and the heat load of the room being heated determine the size of the radiator needed. The warmer the operating temperature, the smaller the radiator need be to deliver a determined amount of heat. Conversely, the lower the temperature of the heating system, the larger the radiator needs to be to deliver an equal amount of heat. Modern radiant floor heating systems can operate at much lower temperatures than traditional hydronic heating systems — typically around 100°F (38°C) — because the radiators are very large, in this case the whole floor of the building. This is the critical point when relating to solar heating because solar heating systems typically operate at relatively low temperatures. It is common to see solar storage tanks operate within the 100°F to 150°F range (38°C to 66°C), while traditional baseboard heating systems typically operate at 180°F (82°C).

How Radiant Heating Differs From Other Heating copyright 2011