Book - School of Science and Technology

Steady state and dynamic response 65methods. For such dynamic calculations, knowledge of other properties of the elementsmaking up that structure are required, in addition to the U value. The more important ofthese are:Admittance (Y value). This is a measure of the ability of a surface to smooth outtemperture variations in a space and represents the rate of energy entry into a structurerather than that of passage through it. The units are W/m 2 K.Decrement factor (f ). This represents the ability of a structural element to moderate themagnitude of a temperature change or swing at one face before this penetrates to theother. It is largely a function of the thickness of the element and is dimensionless.Surface factor (F ). This relates the admission and absorbtion of energy to the thermalcapacity of a structural element. It is dimensionless.For values of these factors and further details of these more probing calculations,reference should be made to the Guide Section A3.As mentioned earlier there is considerable international debate on the preferredmethods for these load calculations and Guide Section A5 offers guidance on steady stateand dynamic calculation techniques. In practice for most buildings hand calculationsshould use the simple steady state method. For computer based calculations the simpledynamic model is also usually appropriate. Guide Section A5 provides an in-depthanalysis of the background to these techniques with worked examples where furtheramplification can be obtained.