Various applications to different ground floor situations are
considered in BS EN ISO 13370. The following is an example for a
solid concrete slab in direct contact with the ground. The data
used is from the previous page.
Floor section
Perimeter = 18 m (exposed)
Floor area = 20 m^2
for 90 mm insulation = 0.03 W/mK
Characteristic floor dimension = B^1
B^1 = Floor area...(1/2 exp. perimeter)
B^1 =20...9 = 2.222 m
Formula to calculate total equivalent floor thickness for
uninsulated and insulated all over floor:
dt =w+(Rsi+Rf+Rso)
where:dt = total equivalent floor thickness (m)
w = wall thickness (m)
= thermal conductivity of soil (W/mK) [see page 471]
Rsi= internal surface resistance (m^2 K/W) [see page 469]
Rf = insulation resistance (0.09...0.03 = 3 m^2 K/W)
Rso= external surface resistance (m^2 K/W) [see page 469]Uninsulated:dt= 0.3+1.5 (0.148+ (^0) +0.04) = 0.582 m
Insulated: dt= 0.3+1.5 (0.148+ (^3) +0.04) = 5.082 m
Formulae to calculate U-values ~
Uninsulated or poorly insulated floor,dt<B^1 :
U=(2)...[(pB^1 )+dt]¾ln [(pB^1 ...dt)+1]
Well insulated floor,dt >† B^1 :
U=...[(0.457¾B^1 )+dt]
where: U = thermal transmittance coefficient (W/m^2 /K)
= thermal conductivity of soil (W/mK)
B^1 = characteristic floor dimension (m)
dt = total equivalent floor thickness (m)
ln = natural logarithm
Uninsulated floor ~
U=(2¾1.5)...[(3.142¾2.222)+0.582]¾ln [(3.142¾2.222)...0.582+1]
U = 0.397¾ln 12.996 = 1.02 W/m^2 K
Insulated floor ~
U = 1.5...[(0.457¾2.222)+5.082] = 1.5...6.097 = 0.246 W/m^2 K
Compares with the tabulated figure of 0.250 W/m^2 Konthe
previous page.
Thermal Insulation, Calculating U-Values---1