Thermolec Application &Technical Notes - Manual (Page 15)

THREE EASY STEPS
STEP 2 - (continued)
OPEN COIL vs TUBULAR elements
THERMOLEC manufactures both open coil and tubular duct heaters.
It is widely acknowledged that tubular elements find practical application under certain circumstances
(service conditions include possible contact by personnel, presence of dust or particles in the air flows or
atmospheric conditions).
But, where heating filtered air is the sole function, the open coil heater is superior for many reasons:
• Longer life
• More kilowatts per square foot
• Less stratification by equal
distribution of the elements
• Lower wire surface temperature
• Less maintenance
• Greater serviceability
• Better heat distribution across
heater face
• Less pressure drop
• Lighter weight
• Low shipping costs
• Less sensitivity to moisture
• More flexibility of size
and capacity
• Cost effective
• Smaller size
• Large electrical clearance
Ther
mol
ec
Tub
ula
r E
lem
en
t D
uc
t
He
at
er
Therm
olec O
pen
Coil
Duct
Hea
ter
0 300 600 900 1200
.25
.20
.15
.10
.05 Pressure drop (inches of water)
Air Velocity (FPM)
0 100 200 300 400 500 600 700 800 900
14
13
12
11
10
9
8
7
6
5
4
3
2
1
KW / sq. foot / stage
Air Velocity (FPM)
Op
en
Co
il
He
at
er
Tu
bu
lar
Ele
m
en
t H
ea
te
r
FPM
Pressure Drop for Tubes
Minimum Air Velocity for tubes