Is My Calculation for Pressure Loss in German Pipework Accurate?

In summary, the speaker is seeking help with determining the correct pipe size for a district heating system using a new type of German pipework. They are used to calculating pressure loss in copper pipework, but the new pipework has different values. They need a flow rate of 2.38 l/s over an equivalent pipe length of 250m for a 200kW biomass wood pellet boiler. They are unsure if their assumptions are correct and are looking for helpful direction.
  • #1
vespak
7
0
My sincere apologies if this is not the right place however I will pose the problem: Being a humble plumber rather than a physicist I am used to calculating pressure loss in copper pipework for hot water heating systems by determining the required flow rate kW/h / specific heat x delta T. Looking on my resistance chart measured in m/head and by selecting a pipe size that is suitable for the index circuit multiplying the total equivalent length by the resistance figure given in the chart (which I have always assumed to be in kPa/m) to give me the m/head calculation to select the right size pump. Sorry I know that's all very basic. I now have to deal with a new type of German pipework that has completely different values in the pressure loss chart and I just want to know if I am making the right assumptions. I need a pipe size that will give me a flow rate of 2.38 l/s over an equivalent pipe length of 250m (district heating main flow/return for a 200kW biomass wood pellet boiler. The value line I am looking at for 76mm carbon steel pipe reads as follows:
Q(w) (kg/h) v (m/s) DeltaP (Pa/m)
200000 8598.5 0.59 42

I have made the following assumptions:
Q=energy and so given the value v 0.59 m/s equals a transfer rate of 20kW x 0.59m/s
My 2.38 l/s x 3600 = 8568 l/h which is the same as kg/h and is the nearest equivalent I can find on the chart.
v is just above the acceptable level for the slowest movement of heating water even though it is a closed pressurized system
DeltaP in Pa/m is converted to kPa/m to give me the total resistance to calculate my pump size: 250m*0.042=10.5 m/head
If this is all completely wrong or just in the wrong place please feel free to express your opinions to that effect however I would be grateful for some helpful direction.
Many thanks
 
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  • #2
This is totally unfamiliar - but unless someone with specific knowledge can step in, I'll give it a go.
flow rate in kW/h / specific heat x delta T makes sense - that would be the volume of water required to transfer that amount of heat energy per second.

However - I baulk at
'given the value v 0.59 m/s equals a transfer rate of 20kW x 0.59m/s' (I think you meant 200kW)

I'm not clear on what transfer rate means in this context - you have a power multiplied by a speed - that is energy-per-second multiplied by metres-per-second. That doesn't give a result that means anything to me physically. But if it were divided instead of multiplied, you would have energy-per-meter - that is the total energy in a length of pipe . That sounds like a useful thing to know? (roughly 339 kilowatt-seconds per meter)

Am I helping or hindering? :smile:
 

1. How do you calculate pressure loss?

The formula for pressure loss is generally calculated using the Bernoulli's equation, which takes into account factors such as fluid density, velocity, and elevation. Other common methods include using a pressure drop chart or using specific equations for different types of flow.

2. What factors affect pressure loss?

Pressure loss can be affected by several factors, including the type of fluid being transported, the size and length of the pipe, the flow rate, and any obstructions in the system. Changes in elevation and fluid viscosity can also impact pressure loss.

3. How does pipe diameter affect pressure loss?

The larger the pipe diameter, the lower the pressure loss will be. This is because a larger pipe allows for a higher flow rate and therefore a lower velocity, reducing the friction and thus the pressure loss. In contrast, a smaller pipe diameter will result in a higher pressure loss due to the increased friction.

4. What is the difference between pressure drop and pressure loss?

Pressure drop refers to the decrease in pressure along the length of a pipe or system, while pressure loss refers to the overall decrease in pressure from the start to the end of the system. Pressure loss takes into account all factors that contribute to a decrease in pressure, such as friction, elevation changes, and obstructions.

5. How can pressure loss be minimized?

There are several ways to minimize pressure loss, including using a larger pipe diameter, reducing the length of the pipe, and smoothing out any sharp bends or obstructions in the system. Maintaining a consistent flow rate and reducing elevation changes can also help minimize pressure loss.

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