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7FIN-PRC004-EN
Selection
Procedure
Hydronic/Steam Wall Fin
Selection
Hot Water Systems
The capacity rating of wall fin in a hot
water heating system depends on the
difference between average water
temperature and entering air
temperature, and on the velocity at
which water is circulated through the
tube. The effect of water velocity on the
capacity rating is appreciable (see Chart
S-1) and should be taken into account
when selecting wall fin. Following are
example selections for hot water
systems.
Hot Water Systems
Example 1
Assume a two-pipe system is being used
with 180°F average water temperature,
20°F temperature drop and 65°F entering
air temperature. Assume a calculated
heat loss of 20,000 Btu, for which one
row of 1
1
/4” steel element in a Type 12S
enclosure is desired.
From Chart S-1, reading from 20,000 Btu
(under 20°F temperature drop) across to
a 1
1
/4” steel element and down, indicates
a water velocity of approximately .45 ft/
sec. The water velocity correction factor
corresponding to .45 ft/sec is .920. The
radiation is selected so that it would
deliver
20,000 Btu (calculated heat loss)
0.920 (velocity correction factor)
or 21,739 Btu if the water velocity were 3
ft/sec. It will then deliver the required
20,000 Btu at the actual water velocity of
.45 ft/sec.
From Table PD-8, the output of 1
1
/4”
steel, Series 52 element in a Type 12S
enclosure is (looking under 180°F
average water, 65°F entering air) 1060
Btu/lineal foot at 3 ft/sec water velocity.
Wall fin required:
21,739 Btu = 20.5 lineal feet.
1060 Btu/ft
Length Selection — Loop Systems
Example 2
If the unit in Example 1 above was part
of a 100,000 Btu loop with a 20°F drop
(across the entire loop) the water
velocity through the loop would be 2.20
ft/sec and the water velocity correction
factor for all units on this loop would be
approximately .987. For the unit being
considered, the radiation would be
selected to deliver 20,300
20,000
( .987 )
Btu at 3 ft/sec water velocity.
Steam Systems — Selecting Wall Fin
Lengths
The capacity rating of wall fin in a steam
heating system depends upon the
difference between the steam
temperature and the entering air
temperature. For any steam system, to
establish the lineal feet of wall fin
required: divide the heat loss by the
capacity rating per foot at the steam
system and entering air conditions.
Ratings for 1 psi steam and 65°F
entering air can be found on Tables
PD-1 through PD-21. Ratings for other
steam and air conditions can be
obtained by multiplying the 1 psi —
65°F capacity ratings by the proper
steam correction factor from Table S-2.
Example 1
Assume a steam system with 1 psi
steam and 65°F entering air conditions.
Also assume a 15,000 Btu heat loss for
which a 1” copper-aluminum element 40
fins/foot in a Type 10S enclosure is
desired.
Wall fin required:
15,000 Btu = 13.9 lineal feet.
1080 Btu/ft
Example 2
Assume a steam system with 20 psi
steam and 55°F entering air conditions.
Also assume a 25,000 Btu heat loss for
which 2 rows of 1
1
/4” steel, Series 40
element on 9
1
/2” centers will be used
without a cover. The capacity rating per
lineal foot from Table PD-3 at 1 psi steam
and 65°F entering air is 2120 Btu/ft.
Multiplying this capacity rating by 1.52
(steam correction factor from Table S-2)
gives a rating of 3222 Btu/ft with 20 psi
steam and 55°F entering air.
Wall fin required:
25,000 Btu
3222 Btu/ft
= 8 lineal feet, 2 rows high.