Calculating Heat Transfer Requirements for Steel Wall

In summary, the conversation is about calculating the necessary watts or Kw needed to heat up a space, using given measurements and temperatures. There is a discussion about the material used and its effect on heat transfer, as well as the importance of considering convection in the calculations. The conversation ends with the realization that the initial calculation for the necessary heat output may have been incorrect and a new calculation is needed. There is also a question about the relationship between watts, Kw, and Btu/Hr and their effect on temperature output in a heater.
  • #1
math111
43
0
I am getting crazy values so I need help.

I want to find out how many watts or even Kw I need to heat up a space.
Here are the givens:
Sizes: Width:1.1176m, Length:1.6764m, Height:1.8288m
Temp-outside: -9.44C
Temp-inside:12.78C
Material: Steel[thinckness(.00635m), thermal K=43]

I just want to calculate 1 face(Front--?widthxheight) of the wall because that will help me on the other faces

I did Q=(k*Area*Temp Difference)/thk
Q=(43*2.04*22.22)/.00635
Q=306950.5watts or 307kW.


Does this mean I will need at the minimum at 307kW heater just based on one wall and that mean it will be even greater by alot!That seems too high or is this correct and I am not giving the proper information to solve the problem at hand??

Steel has a very high K so it might make sense. I am concerned about why making the mat'l thinnner would need more watts to make a higher temperature difference ?
 
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  • #2
You need to include the natural convection heat transfer coefficients on the inside and outside of the walls. These are much more significant than the conduction term you used.
 
  • #3
Well, that's not really that high considering your problem. You've got a big, 6mm thin steel box that's -10 Celsius on the outside and 12 Celsius inside. There's not that much thermal mass and steel is a fairly good conductor of heat. If you thickened up the walls with an insulator, you would severely decrease the loss of heat. However, in any case, I do agree with edgepflow that convection (natural and even forced if there's wind) is a major source of heat loss, so reducing that is a primary concern.
 
  • #4
math111;3425638 Steel has a very high K so it might make sense. I am concerned about why making the mat'l thinnner would need more watts to make a higher temperature difference ?[/QUOTE said:
You have to imagine it with heat resistivity. The thicker the wall/plate is the higher resistivity is and less heat will pass trough.
 
  • #5
math111 said:
Steel has a very high K so it might make sense. I am concerned about why making the mat'l thinnner would need more watts to make a higher temperature difference ?

You have to imagine it with heat resistivity. The thicker the wall/plate is the higher resistivity is and less heat will pass trough.
 
  • #6
Post #2 is right. The basic mistake in your calculations is assuming the temperature of the inside and outside face of the METAL. are at 12.78C and -9.44C. The correct assumption is that the inside and outside AIR temperatures are 12.78C and -9.44C.

300kW can't possibly be right. Find out what is the heat output of your home heating system. Unless you live in a very large house, it will be way smaller than that, to heat the entire house not just a box smaller than one room.

You can made the heat input as small as you like by insulating the box. If you covered it in some polystyrene sheet, or even plywood, you would probably need more like 30W of heating, not 300 kW.
 
  • #7
AlephZero said:
Post #2 is right. The basic mistake in your calculations is assuming the temperature of the inside and outside face of the METAL. are at 12.78C and -9.44C. The correct assumption is that the inside and outside AIR temperatures are 12.78C and -9.44C.

300kW can't possibly be right. Find out what is the heat output of your home heating system. Unless you live in a very large house, it will be way smaller than that, to heat the entire house not just a box smaller than one room.

You can made the heat input as small as you like by insulating the box. If you covered it in some polystyrene sheet, or even plywood, you would probably need more like 30W of heating, not 300 kW.

I red-did the problem and got around the 500-600 watts range. So I think I did something right. I am learnig this stuff at a snails pace but don't mind.
 
  • #8
Right now I trying to figure out how to connect power with temperature.

1. Does Watts, Kw, Btu/Hr have any relation to temperature of let's say a heater??

EXAMPLE:if I have a 1kw heater compared to a 2kw heater what is the difference in temperature it will output?

I know the 2KW will output more heat but at a higher temp? or is that not true and just outputs more heat of the same temperature as the 1kw heater.
 

Related to Calculating Heat Transfer Requirements for Steel Wall

1. How do I calculate the heat transfer requirements for a steel wall?

To calculate the heat transfer requirements for a steel wall, you will need to first determine the wall's surface area and its thermal conductivity. Then, you can use the formula Q = U x A x ΔT, where Q is the heat transfer rate, U is the overall heat transfer coefficient, A is the surface area, and ΔT is the temperature difference between the two sides of the wall.

2. What is the overall heat transfer coefficient for a steel wall?

The overall heat transfer coefficient for a steel wall depends on various factors such as the material properties, surface conditions, and geometry of the wall. It can be calculated by considering the individual heat transfer coefficients for conduction, convection, and radiation, and combining them using the appropriate equations.

3. How does the thickness of a steel wall affect the heat transfer requirements?

The thickness of a steel wall has a significant impact on the heat transfer requirements. A thicker wall will have a larger surface area and a higher thermal resistance, making it more difficult for heat to transfer through it. This means that a thicker steel wall will require a higher heat transfer rate to maintain a desired temperature difference.

4. Can I use the same heat transfer requirements for all types of steel walls?

No, the heat transfer requirements for steel walls can vary depending on the type of steel used, its thickness, and other factors. It is important to consider the specific properties of the steel wall in question when calculating the heat transfer requirements.

5. How can I reduce the heat transfer requirements for a steel wall?

There are several ways to reduce the heat transfer requirements for a steel wall. One option is to improve the insulation of the wall by adding materials with lower thermal conductivity. Another option is to increase the thickness of the wall, which will decrease the heat transfer rate. Additionally, reducing the temperature difference between the two sides of the wall can also lower the heat transfer requirements.

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