Energy and $ savings of insulation vs. no insulation?

Question

I need to insulate about 920' of piping but before I do I need to find the energy and cost savings of having insulation on the pipes vs. not putting insulation on them. Any formula or calculation available for these I can use?

Answer 1

Well, i'm supposing you are trying to insulate a vapor system or a hot air system for an ac device. Well, what you have to do is that you need to calculate the loss of energy coming from the pipes with and without the insulation. This is kind of a lot of work to do, so i would recommend you try to find a program to do this.

But if it helps, you have to calculate the energy loss due to convection, radiation and conduction through your pipes.

For conduction, the equation would be

q = kA(t1-t2)

where k is the conduction constant of the material of the pipe. A is the surface area of the pipe and t1 is the inner temperature of the pipe and t2 is the outer temperature of the pipe.

Now for convection there is this equation.

q = hA(t1-t2)

where h is the convection coefficient of air outside the pipe and the convection coefficient of the vapor or gas inside the pipe.

for radiation, the equation would be:

q = h(t1-t2)

where

h = dF(t1^4-t2^4)/(t1-t2)

where d is the emissivity of the material of the pipe, F is the interchange factor between two surfaces, t1 is the temperature of one surface and t2 is the temperature of the other surface.

You have to calculate all this things at the same time, so you need to make a thermic balance of all the heat sources and solve it for the temperature outside and inside the pipes and then iterate them in order to get a good value of heat loss.

After you do this with the pipe alone, you have to do the same with the insulation, changing the proper constants.

As you may see, this is a lot of work, so it would be good you get a program that does all of that for you or contract someone who specializes on thermic analysis.

Well, after you get the total heat loss difference, then you have to evaluate it according to the energy you are getting from your fuel. Let's say you are using gas to heat the vapor or the air. Then you have to make a chemical balance of it burning, like this:

CH3 + O2 = H2O + CO2

and then get the change of enthalpy you get from that reaction.

That change of enthalpy you have to multiply it by a burner efficiency in order to get a better approach of the energy you are getting out of your fuel.

Then with the heat difference you calculated at the beginning, you have to divide it into the change of enthalpy you get from your fuel, like this

mass = heat loss difference / enthalpy

then with the mass of fuel you are saving, just multiply it by it's price and then you will get how much money you are saving.

Hope this helps.