Fenix ELSR-M - Manual (Page 5)

3. USE OF TEMPERATURE REGULATION TO PROTECT PIPES AGAINST
FREEZING
• Heating cables placed on metal or plastic pipes provide protection against the
freezing of liquids in the pipes when the surrounding temperature is lower then
0°C.
3. a) Dimensioning
The required performance of the cable per 1 m of length can be determined by a
calculation using the following formula:
For the determination of the needed performance of the cable it is necessary to multiply
the heat loss by the coefficient 1.3 and the length of the pipe.
EXAMPLE: a pipe with an inner radius of 25 mm, 13 m long, and insulated with 20 mm
Mirelon needs to be protected against freezing according to the following calculation:
) ( *
) ( * 2 2
p m
t t
d
r r
Q
−
+
= λ
π
down to a lowest surrounding temperature of -20°C (we always consider the non-
freezing temperature to be +5°C).
Pk = Q*1.3*l Pk – performance of the cable
l – length of the cable
Q – heat loss per 1 m of pipe (W/m)
l – coefficient of the heat conductivity of the insulation (W/m*K)
r – radius of the pipe (m)
d – thickness of the insulation (m)
tm – temperature of the medium (°C)
tp – temperature of the environment (°C)
Interior diameter of pipe
½˝ 15 mm
¾˝ 20 mm
1˝ 25 mm
1¼˝ 32 mm
1½˝ 40 mm
2˝ 50 mm
2½˝ 65 mm
3˝ 80 mm
4˝ 100 mm
6˝ 150 mm
8˝ 200 mm
10˝ 250 mm
SOLUTION:
The total wattage of the heating cable must be 171 W or higher. We will use 13 m of self-insulating cable
ELSR – M – M15-2-BO
) ( *
) ( * 2 2
p m
t t
d
r r
Q
−
+
= λ
π
=
1 . 10 )) 20 ( 5 ( 05 . 0 *
02 . 0
) 025 . 0 025 . 0 ( * 2 2
= − −
+ π
W/m
Pk – Q*1.3*l = 10.1*1.3*13=170.69 W