Operating and Start-up Load & Operating and Start-up Current Calculation for Heat Tracing System

1.    Operating and Start-up Load & Operating and Start-up Current Calculation for Heat Tracing System

 

Operating Load Calculation: -

Lo = TL X Om ---------------------------------------------------------- (1)

Where

Lo = Operating Load

TL = Total Heating Cable Length

Om = Output of Heating Cable at Maintain Temperature

TL = (L X SR + V X A + F x A + S X A + I X A +M) 

Where

TL = Total Heating Cable Length

L = Pipe Length

SR = Heating Cable Runs

A = Allowance Heating Cable

V = Valve

F = Flange

S = Support

I = Instrument

M = Power and End Termination Margin

Output of Heating Cable: - We are already decision in the previous articles that how we calculated output of series heating cable and output of self-regulating heating cable.

Start-up Load Calculation: -

Ls = TL X Oa ---------------------------------------------------------- (2)

Where

Ls = Start-up Load

TL = Total Heating Cable Length

Oa = Output of Heating cable at Minimum Ambient Temperature

Unit of Load:-

Load = m X W/m

Load = W

OR

Load = W/1000 = kW

Operating Current Calculation: -

Io = Lo / Vs

Where

Io = Operating Current

Lo = Operating Load

Vs = Supply Voltage

Operating Load will be calculated as per above formula / equation (1).

Supply Voltage will be given by customer.

Start-up Current Calculation: -

Is = Ls / Vs

Where

Is = Start-up Current

Ls = Start-up Load

Vs = Supply Voltage

Start-up Load will be calculated as per above formula / equation (2).

Supply Voltage will be given by customer.

Unit of Current:-

Current = W / V

Current = A

Output of Self-Regulating Heating Cable

Output of Self-Regulating Heating Cable

Output of Self-Regulating Heating Cable = (c + (m X Tm)) X Vo / Vs)

Where

c = Output of Heating Cable at 0◦C.

Vo = Voltage of Measuring Output.

Vs = Supply Voltage.

Tm = Maintain Temperature.

m = Output difference of per ◦C

 

m = (Os – Om) / (Ts – Tmm)

Where

Os = Output of Heating Cable Declared by Manufacturer’s at Standard Temperature.

Om = Output of Heating Cable Declared by Manufacturer’s at Maximum Maintain Temperature.

Ts = Manufacturer’s Declared output at Standard Temperature.

Tmm = Manufacturer’s Declared Maximum Maintain Temperature of Hating Cable

 

 

c = (Os – (Ts X m))

Where

Os = Output of Heating Cable Declared by Manufacturer’s at Standard Temperature.

Ts = Manufacturer’s Declared output at Standard Temperature

m = Output difference of per ◦C

Example:-

A Manufacturer denoted the 5 W/ft @ 10◦C at 230 V. i.e.

5 W/ft = Output of Heating Cable per Feet

10◦C = Standard Temperature for 5 W/Ft Output.

230 V = Supply Voltage.

If 1 W/ft @ 150◦C at 230 V then Value of

m = (5 - 1) / (10 - 150)

   = 4 / (-140)

  = -0.0285

c = 5 – (10 X (-0.0285))

   = 5.28 W/ft @ 0◦C

If we calculate output at 30◦C for 230 V:-

 O = (5.28 + ((-0.0285) X 30)) X (230/230)

O = 5.28 + (-0.855) X 1

O = 4.425 W/ft

Output of Series Heating Cable (Type-1)

How can be the output calculations for the series heating cable are done: 

Firstly we have some input:

V = Supply Voltage (V)

HL = Heat Loss (W/m)

TL = Total heating Cable Length (m)

𝛼 = Temperature Coefficient (1/◦C)

∆T = Temperature difference b/w maintain temperature and 20◦C

Now we find Ideal resistance (𝑅𝑖):- 

𝑅𝑖 = 𝑉2 / (𝐻𝐿 × 𝑇𝐿2) / (1 + 𝛼∆𝑇)

 Find out Unit 

𝑅𝑖 = 𝑉2/ ((𝑊/𝑚) × 𝑚2) / (1 + (1/◦ C) ×◦ C)

  

Unit of 𝑅𝑖 = (𝑂ℎ𝑚/𝑚) 

Now we will be select cable of less resistance from ideal resistance.

Now we will be calculating resistance on the maintain temperature (𝑅𝑚):-

𝑅𝑚 = 𝑅𝑐 × (1 + α∆𝑇) 

𝑅𝑐 =  𝑆𝑒𝑙𝑒𝑐𝑡𝑒𝑑 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝐶𝑎𝑏𝑙𝑒 (𝑂ℎ𝑚/𝑚) 

α =  Temperature Coefficient (1/◦ C)  

∆𝑇 =  Temperature difference b/w maintain temperature and 20 ◦ C  

Unit of 𝑅𝑚 = 𝑂ℎ𝑚/𝑚

 Note:-  α value change as per heating cable resistance.

Now we will be calculating Output of heating cable:- 

𝑂𝑢𝑡𝑝𝑢𝑡 = 𝑉2 / 𝑅𝑚 / 𝑇𝐿2

 Find out Unit

𝑂𝑢𝑡𝑝𝑢𝑡 = 𝑉2 / (𝑂ℎ𝑚/𝑚) / 𝑚2

 

Unit of 𝑂𝑢𝑡𝑝𝑢𝑡 = 𝑊/𝑚

 

 

Design Calculations For The Heating Element

Designing a Tape Element

 

Here is how the design calculations for the heating element are done:

1.  To calculate the tape size and length required for a specific heating element in heater, operating at a maximum temperature of °C, the total resistance of the element at operating temperature (Rt) will be:

R_t = V² / W

Where:

·         V = Voltage (Volts)

·         W = Power (Watts)

2.  Using specific heating element alloy wire, find the Temperature Resistance Factor at °C operating temperature as F thus the total resistance of the element at 20°C (R) will be:

R_t = R_t / F

Where:

·         R_t = Element Resistance at Operating Temperature (ohms)

·         F = Temperature-Resistance Factor

3.  Knowing the dimensions of the heater, the length of the tape that may be wound round it may be estimated. Thus, the resistance required per metre of tape will be:

A = R / L

Where:

·         A = Resistance per meter (ohms/m)

·         R = Element Resistance at 20°C (ohms)

·         L = Total Element Length (m)

4.  Find a heating element tape of standard size of b mm x t mm having a standard resistance per metre of stock size which is near to A ohms/m.

Where:

·         b = Tape width (mm)

·         t = Tape thickness (mm)

5.  To verify the actual tape length (L)

L = R / A

Where:

·         L = Total Element Length (m)

·         R = Element Resistance at 20°C (ohms)

·         A = Resistance per meter (ohms/m)

A change in tape length may mean altering the pitch of the tape to achieve the total resistance value required.

6.  To verify the surface area loading (S):

S = W / 20 x (b + t) x L

Where:

·         W = Power (Watts)

·         b = Tape width (mm)

·         t = Tape thickness (mm)

·         L = Total Element Length (m)

 

Reference: www.heating-element-alloy.com/heating_element_design_factors.html