The chain reaction of heat transfer
– by Peter Bos, 28 November 2018
When you are in the office, place your hand on the desk; or some other wooden surface. Done? Feel the temperature..? Now place your hand on something metal which is in the same room, like the metal legs of your chair… And? Does it feel colder? Very good, you just witnessed the conduction of heat.
So why exactly does the metal feel colder than the wood? Both are standing in the same room and have the same temperature. Simply put, metal leads heat away from your skin much more efficiently than wood. The metal surface feels colder because of the specific qualities of its molecules.
Heat flows from hot to cold
Temperature is the parameter that measures the kinetic energy of molecules. The higher the temperature, the more energy an object contains and the faster its molecules are moving. Hot, rapidly-moving molecules bump into cold, slow molecules, setting them in motion and conducting heat. This is the reason why heat tends to flow from hot to cold. It reflects nature’s common tendency towards equilibrium.
Wood vs metal
Back to the desk. Your body temperature is higher than the temperature of the desk, so the molecules in your hand are more energetic and move faster. By touching the metal surface, the molecules that make up your skin bump into the ones making up the desk and transfer kinetic energy to them. Wood is more porous than metal, which means its molecules are less tightly packed and conduct energy less efficiently. This is why metal has a higher heat flow or heat transfer, and subtracts heat from your body more quickly.
The big picture
Heat conduction has a major impact on HVAC design. One of the main components of the relevant engineering is calculating heat flow. This tells us what we need to know about the capacity of our cooling machine, the amount of air and the size of the boiler.
An important factor in heat flow or transmission calculations is the type of material of which a vessel is built – think of the wood/metal experiment – and the temperature difference involved. A large temperature differential would cause the flow of heat to be bigger. Once temperature is equal on both sides, the flow ceases.
The conduction of heat – through a heat exchanger, cooling coil or even pipes – is crucial in a HVAC system because it is central to the concept. Sometimes it needs to be reduced to a minimum, like through the walls of a freezing cell, and sometimes it needs to be fast, like in a heat exchanger. We build our systems based on the properties of different materials, thereby contributing to the most efficient installation possible.
Peter Bos | Sales Manager
Peter Bos has been working at Heinen & Hopman for almost 30 years. He devotes most of his attention to selling HVAC&R systems to clients like Damen Shipyards and Feadship. Additionally, Peter offers sales support to our subsidiaries abroad as well. He highly values reliability and a no-nonsense approach and stands behind what he sells.