Radiation is a form of energy related to frequencies. The earth is surrounded by the electromagnetic spectrum, or EM spectrum, which emits all types of radiation. The EM spectrum, as seen in figure 1, contains gamma rays – lightening; x-rays – airport scanners; ultraviolet light – warms our skin; visible light – rainbows; infrared light – night vision googles; and the self-explanatory microwaves and radio waves.
Radiation has been with Planet Earth since the day it was formed. It is the sole source of energy for everything on the planet: “Almost all of the energy available at Earth’s surface comes from the sun”. The most commonly known source of radiation is solar; and radiation equals heat energy. Heat energy “…has no mass and travels at the speed of light” and “…moves from [the] source through a material or vacuum…”
- Conduction: heat moves from a warm object to a cooler one.
For example: warm hands vs. cold hands – the cold hands absorb the heat from the warm hands. This is a transfer of heat.
- Convection: heat moves with a substance.
For example: a convection oven, the most common type, heats the air and transfers the heated air to the object in the oven.
The sun has delivered a continuous source of energy for 4.5 billion years, and it is estimated that our solar neighbour will continue its life-giving support, in one form or another, for an additional 5 billion years.
Our sun has a surface temperature of over 5000°C. The radiation created moves through the vacuum of space at the speed of light and enters our atmosphere. Although there is no heat associated with solar radiation, we are fully capable of utilizing its heat energy.
Characteristics of radiation:
- does not heat air
- travels in a straight line at the speed of light (299,792 kilometers per second)
- can be reflected
- can NOT be deflected
- absorbs in cooler objects and creates heat by molecular motion
Radiation heating is not delivered by air. The Mean Radiant Temperature, or MRT, is a measurement of all the surface temperatures in a room. The rate at which radiation travels into the room is what delivers the comfort services. If you stand outside on a bitterly cold day, and face the sun, you will feel heat. This is exactly the same process.
Hot air normally rises; convection heating delivers a 10 to 15°C temperature increase near our ceiling. The heat is useless up there. Radiation creates an inverted temperature stratification which means the warmest temperatures remain closer to the floor.
North America favours the finite energies of fossil fuels rather than use the sustainable energy offered through solar radiation. Solar radiation travels at the speed of light through 150,000,000 kilometers of -273°C space and delivers 5042 kilowatts per meter (or 444 Btu per square foot) to the Earth. Air temperature does not restrict the travel of radiation.
One of the oldest forms of heating our homes is radiation. The Romans used radiant heat in 60 AD. Our 21st-century technology are capable of capturing, storing, and using solar radiation.
The greatest restriction of seasonal radiation is the hours of daily sun, not temperature. Face the sun on a -40°C day, and you will feel heat!