48 UV-PRC001-EN
Electric Heat Coil Selection
The heating capacity of the electric
fin-tube coil depends solely on the
kW rating of the coil. For selection,
refer to Table P16 or the TOPPS se-
lection program. This table lists
the kW rating of each coil and the
MBh equivalent. Determine the
smallest electric coil that will meet
room heating capacity require-
ments.
Example:
Given:
Total heating requirement = 86.5 MBh
Outside design conditions = 0 F
Inside design conditions = 70 F
Outside air = 33%
Classroom air conditioner previously
selected = Size 125
Electric classroom air conditioners
provide safe, functional and eco-
nomical operation, utilizing a new
concept of electric heat coil de-
sign. The Trane electric coil is built
by placing electric heating ele-
ments inside a specially designed
extended surface fin-tube bundle.
This design results in a consider-
Selection Procedure
Electric Heat Coils/Steam Coils
able reduction in fin and element
surface temperatures. Also, the
Trane coil has more even temper-
ature distribution across the ele-
ment. Since coil life expectancy is
dependent upon watt density
(watts per inch of element), tem-
perature at which the coil is oper-
ating and air distribution over the
coil, the unique Trane coil design
helps maximize coil life.
Steam Coil Selection
The capacity of steam heating coils
is determined by the entering (mix-
ture) air temperature to the coil
and the pressure of saturated
steam to the coil. Select the coil
with a capacity equal to or greater
than the total heating require-
ments. Steam pressures of less
than 5 psi may adversely affect coil
performance.
Example:
Given:
Total heating requirement = 110.5 MBh
Outside design conditions = 20 F
Inside design conditions = 70 F
Outside air = 27%
Saturated steam pressure = 5 lbs
Classroom air conditioner previously
selected = Size 125
Entering air temp to coil = 70 - [.27 x
(70-20)] = 56.5 F
The K2 coil at these conditions has a
capacity of 111.0 MBh. Therefore, a K2
coil meets the room heating require-
ments.
The air temperature rise = 80 F.
Leaving air temperature = 45.7 + 95 =
125.7 F
Outside design conditions = 20 F.
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