![]() The higher the skin temperature, the higher the back and edge loss. What affects efficiency now is the back and edge loss, which is directly impacted by the surface temperature, or skin temperature, of the radiant piping. We’ve already concluded that the room’s heating intensity is the same since the load is dictated by the room construction, not the floor. This total energy includes not only the energy provided to the room but also energy lost to miscellaneous sources, called back and edge losses (the area below and to the side of our radiant panel). We need to identify efficiency - the ratio of useable energy to total energy provided. So, what happens to our design if we change tubing options? To better understand this change, we need to dive into the mechanics of what’s happening between the fluid inside the tubing and the floor. We still need an 80☏ floor surface temperature, but we can now achieve the require heating intensity with a smaller ∆T (a lower supply fluid temperature) between the 80☏ floor surface and the tubing, assuming the rest of the floor construction remains the same. Since we changed the floor covering to tile, the overall material resistance went down, increasing the overall conductivity value of the floor. Even though the design conditions are the same, the construction is not. If we change our floor covering in our example room from carpet to tile, the required energy is still the same - 25 Btuh/square foot - and the surface temperature still needs to be 80☏. Or, rather, the higher the material resistance, the greater the ∆T needs to be to transfer the same amount of energy through the material. Having a more restrictive floor covering or construction mandates more energy. ![]() The greater the temperature change (delta T, or ∆T), the greater the energy movement through a given material. Remember, heat moves to cold in a very predictable manner. Our calculations show the room will not meet our design heat load if the floor surface temperature is below 80☏. To help illustrate the mechanics of heat transfer, let’s walk through the following example: A typical 20 x 20 foot room has a heating intensity of 25 Btuh/square foot and a desired room temperature of 70☏. ![]() With radiant heat, the key phrase to remember is that heat moves from hot to cold.Īll three methods - teamwork, if you like sports analogies - go into making a radiant floor system work. The hotter lamp keeps the fresh fries hot. A good example of this is a heat lamp hanging over a basket of fries at the local drive-through. Radiant transfer is when a warmer object emits energy to a colder object via energy waves. In a radiant system, conduction takes place anywhere the radiant tubing is in contact with a flooring material, or subfloor - or in some cases, with the help of a heat transfer plate. ![]() The pole, being more conductive, allows the heat to leave your hand quickly, causing you to feel colder. Think about your hand on that steel pole mentioned earlier. The warmer object will impart heat energy to the cooler object via the area of contact. Many of you know this, but I’ve got to state it anyway: Water is several times more conductive than air and many times more capable of moving energy than air.Ĭonductive transfer is when two objects of different temperature come in contact. Water moves heat energy from the boiler out to the radiant zone. In a hydronic system, the air is replaced with water and the fan is replaced with a circulator. Convective systems rely on a medium - generally air - to be moved from one location to another by some mechanical means, usually a fan.
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