Radiant Heating Explained: Methods of Heat Transfer
A radiant heating system is not just about supplying heat to a room. A good system is made to make the people in the room experience true thermal comfort, which is achieved when the rate at which the body produces heat and the rate at which it’s released remain the same. There are four major factors that affect the heat transfer to and from the body: evaporation, convection, conduction and radiation.
Evaporation of moisture from our body surface consumes about a quarter of our bodies’ total heat output. The rate of evaporation decreases when the air is damp; that is the reason people tend to feel uncomfortable when the weather is humid.
Convection is a heat loss process during which heat transfers from the body unto the surrounding air. Once the air has been warmed by the body temperature, it rises and gets replaced with cooler air. Air temperature and wind speed have a direct effect on the convection rate. The colder the air, the higher the heat loss rate is. The same rule applies to the wind: convection is higher when the colder air is blowing at higher speeds.
Conduction takes place when there is a direct contact between a body and a colder surface. An example of conduction would be touching a cold wheel in a car during winter. In this case, the wheel will become warmer due to the influx of heat from the body.
Radiation is the most significant mode of bodily heat transfer, responsible for 50% of the body’s heat loss. The body always radiates heat whenever it’s surrounded by colder objects. The surrounding objects absorb the heat, which in turn raises their temperature.
The body is naturally equipped to manage these 4 modes of heat transfer and adjust to them accordingly as the need arises. Whenever outside temperatures are hot, the body will raise its own temperature, thus making the outside temperature cooler and enabling the heat loss processes to continue. By maintaining an average room temperature at the required level, a radiant heating system is able to maintain the heat transfer processes at equilibrium and as a result provide a great deal of comfort.