In our day, energy and the efficient use of energy are among the most important factors, and the main purpose of use of preinsulated pipes is to keep heat loss at the lowest possible level and obtain the highest efficiency from energy. The calculation method given below can be used for calculating the heat loss theoretically.
First of all, the average fluid temperature is calculated:
Tm (˚C) : Average temperature of the fluid
Tg (˚C) : Temperature at the direction of flow
Td (˚C) : Temperature at the direction of return
Tt (˚C) : Outdoor air temperature
In order to calculate the total thermal conductivity resistance of the preinsulated pipe system, firstly the resistances of each layer of the system must be calculated respectively.
Carrier Pipe Thermal Conductivity Resistance:
Rtbi (m.°C / W) : Thermal conductivity resistance of the carrier pipe
Din (m) : Inner diameter of the carrier pipe
Dout (m) : Outer diameter of the carrier pipe
λtb(W / m.°C) : Carrier pipe thermal conductivity coefficient (Table 1)
Type of the Service Pipe 
Thermal Conductivity Coefficient (W/m.˚C) 
Black Steel 
76 
Stainless Steel 
16 
PPR 
0,15 
Copper 
400 
CTP 
0,31 
Polyethylene 
0,43 
Table 1: Thermal Conductivity Coefficient by Types of Carrier Pipe
Polyurethane Insulation Thermal Conductivity Resistance:
Rpur= ln(DkbinDout)2× π× λpur
Rpur(m.°C / W) : PUR insulation thermal conductivity resistance
Dkbin(m): Inner diameter of the casing pipe
λpur(W / m.°C): PUR insulation thermal conductivity coefficient (0.026 W / m.°C can be taken)
Thermal Conductivity Resistance of the HDPE Casing Pipe:
Rkb(m.°C / W) : Thermal conductivity resistance of the casing pipe
Dkbout(m): Outer diameter of the casing pipe
Dkbin(m): Outer diameter of the casing pipe
λkb(W / m.°C): Thermal conductivity resistance of the casing pipe
Outdoor Thermal Conductivity Resistance:
Rt(m.°C / W) : Thermal conductivity resistance of earth
Z(m) : Filling height of earth
λt(W / m.°C): Thermal conductivity coefficient of earth (Table 2)
Type 
Density (kg/m3) 
Volumetric Humidity Rate % 
Thermal Conductivity Coefficient (W/m.˚C) 
Sand 
1500 
4 
1,04 
1800 
14 
1,7 

Clay Soil 
1500 
23 
1,5 
2000 
28 
2,6 
Table 2: Thermal Conductivity Coefficient of Earth
Rtdout(m.°C / W): Outer convection resistance of the casing pipe
hair(W / m².°C): Air convection coefficient
Thermal Conductivity Resistance between Flow  Return Pipes
Rtbin(m.°C / W): Thermal conductivity resistance between flow  return pipes
C (m) : Distance between the axes of flow  return pipes
After calculating all resistance factors, the total thermal conductivity resistance value of the preinsulated pipe system can be calculated through the formulas below:
U (W/m.˚C) : Total thermal conductivity coefficient
Total heat loss per metre in preinsulated pipes:
Q=U× To
Q (W / m) : Total heat loss per metre
The formula below can be used to calculate the fluid temperature at the end of the line according to all calculations:
L (m) : Length of line
m (kg/sec) : Water flowrate
Cp(J / kg.°C) : Fluid specific heat [Table 3]
Tson(°C) : Fluid final temperature
Temperature (˚C) 
Density (kg/m^{3}) 
Specific Heat (Kj/kg ˚C) 
0 
1000 
4210 
5 
1000 
4204 
10 
1000 
4193 
20 
998 
4183 
30 
996,02 
4179 
40 
992,06 
4179 
50 
988,14 
4182 
60 
983,28 
4185 
70 
977,52 
4191 
80 
971,82 
4198 
90 
965,25 
4208 
100 
957,85 
4219 
Table 3: Physical Specifications of Water