# Using Appropriate Diagrams And References, The Three Main Mechanisms Of Heat Transfer Relevant For Building Services Engineering

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Describe using appropriate diagrams and references, the three main mechanisms of heat transfer relevant to Building Services Engineering. (P1.1)

Heat transfer occurs between 2 zones/masses with a difference in temperature, the direction of transfer taking place from the warmer one to the cooler one, until thermal equilibrium is achieved. There are 3 main mechanism of heat transfer relevant to Building Services Engineering: Conduction Convection Radiation

Conduction represents the passage of heat from molecule to molecule across a body or between 2 separate bodies in contact (for example hot water in pipes).
The rate of heat transfer is expressed by thermal conductivity, k, and represents the ability of a material to conduct heat.

To calculate conduction across a slab of material we use Fourier’s law:

Q=(k A 〖(T〗_1-T_2))/d

Where
Q = heat flux, thermal energy (W) k = thermal conductivity (W/m K)
A = surface (m2)
T1 – T2 = the temperature difference (K) d = thickness (m)

In Building Services Engineering, one of the many applications of conduction can be found in the operation of a boiler.
As seen in the following diagram, when in function the flame from the gas burner heats up the metal pipe through radiation (step 1). The metal atoms gain energy, vibrate faster and transmit the heat through conduction to the water molecules that come in direct contact with the pipe (step