How To Calculate Heat Loss?

Conduction is the transfer of heat or electricity through a substance by direct contact. The heat transfer rate is dependent upon how much resistance exists between objects of differing temperatures. (That's insulation) A good example of conduction is placing a spoon in a glass of hot coffee. The metal spoon warms up because it touched the hot molecules. The coffee solution actually had heat loss.

Now not all objects are good conductors of heat. Metal is a good conductor, so it heats up fast in hot coffee. Glass is a poor conductor. The outside of the glass is cooler than the metal spoon, even though they are both touching hot coffee.

Whether a substance acts as a thermal conductor or insulator depends on the thermal resistive properties of the matter. Thermal resistance (R) is a measure of an object's ability to decrease heat transfer by way of conduction through a given thickness of the substance. Mathematically, R is: Calculating Heat Loss from Industrial Systems to determine heat tracing where L is the insulation thickness in inches, k is thermal conductivity, (BTU)(in)/(ft2)(oF)(hr) As the thickness (L) changes, it affects the R value, or thermal resistance of an insulation. K values are constants that are specific to the physical properties of a given material. They measure thermal conductivity. Here is the Conduction Formula

When \(a \ne 0\), there are two solutions to \(ax^2 + bx + c = 0\) and they are $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$ $$ R = {L \over k}$$

Convection is the transfer of heat through fluids (gases or liquids) from a warmer spot to a cooler spot. Place an ice cube in hot coffee and the molecules on top become cooler and dense therefore moving to the bottom.

If you heated the bottom of the coffee mug the opposite would happen. The more dense liquid on bottom would expand becoming lighter and would move to the top. This movement of heat is called convection.

Radiation is the transition of energy (heat) from one body in the form of waves or particles.

Sounds simple but radiation can come in different forms and energy strengths, here are some examples of radiation:

• •  ultraviolet light from the sun
• •  heat from a camp fire
• •  light from a candle
• •  x-rays from an x-ray device
• •  alpha particles emitted from radioactive decay of uranium
• •  cooking waves from a microwave oven
• •  electromagnetic radiation from your mobile phone

Electricity is normally sold by kilowatt hours, but the equations above are BTU/hr. Just convert BTU to watts, where 1 watt equals 3.412142 BTU and multiply times (L).  The answer will be in W/hr.

$$ Q = {k(A)(ΔT)(1.1) \over (L)(3.412142)} $$

Conductive heat transfer can be expressed with:

q = (k / s) A dT  

   = U A dT                               (1)

where

q = heat transfer (W, J/s, Btu/hr)

k = Thermal Conductivity of material (W/m K or W/m Cº, Btu/(hr Fº ft²/ft))

s = material thickness (m, ft)

A = heat transfer area (m², ft²)

U = k / s

  =  Coefficient of Heat Transfer (W/(m²K), Btu/(ft² h Fº)

    = temperature gradient - difference - over the material (Fº)