MartinAir
Industrial
- Jan 21, 2004
- 3
Hi all. I'm new here, nice to be here. I can start with stating that I'm not a student. 
At my job I do adjustments of ventilation systems, all done with different types of flow meters. Now I thought I could do this theoretically in some way.
Overview
I have a question on how to theoretically calculate settings on valves/diffusers in a ventilation system (air).
I have made a simple example overview of the situation in the picture below. I know what the output from the diffusers SHOULD be (that's QP in liter/sec), I know the size of the pipes (stated in the picture).
When you adjust a valve/diffuser in a ventilation system, you normally change the k-factor to get the correct flow, a little bit of trial 'n error, you lower the k-factor to get a lower flow (vice versa for the opposit of course) and see if it's close to QP (What flow you want to have there). The formula looks like this:
Q is the flow in liter/sec, and I know what I want here (it should say QP, but it doesn't matter). K is the k-factor for the diffuser, a diffuser has many different k-factors. At last we have DeltaP which is the differential pressure.
Problem
Calculate what k-factor the diffusers should have to get the correct flow (QP). We know QP(Q), we want the K. So I guess we need the DeltaP? Maybe the k-factor isnt enough, maybe I need to know the effective area on the diffuser?
I guess the total flowrate of the fan would also be good to know.
Thoughts
I have read some fluid mechanics, but I don't know how to put all pieces together. I have some theory on how to calculate it though:
1. Get velocity (dividing volumetric flow rate by cross-sectional area)
2. Calculate the pressure loss per some unit length
3. Calculate the total length (with bends etc)
4. Calculate the total pressure loss.
----
The problem with my example is that the pipes get smaller from the MP (MainPipe), I guess the bernoulli's equation would be used here.
Last thoughts
If it's something more you need to know about this example, just assume some values. Thank You.
Example
At my job I do adjustments of ventilation systems, all done with different types of flow meters. Now I thought I could do this theoretically in some way.Overview
I have a question on how to theoretically calculate settings on valves/diffusers in a ventilation system (air).
I have made a simple example overview of the situation in the picture below. I know what the output from the diffusers SHOULD be (that's QP in liter/sec), I know the size of the pipes (stated in the picture).
When you adjust a valve/diffuser in a ventilation system, you normally change the k-factor to get the correct flow, a little bit of trial 'n error, you lower the k-factor to get a lower flow (vice versa for the opposit of course) and see if it's close to QP (What flow you want to have there). The formula looks like this:
Q is the flow in liter/sec, and I know what I want here (it should say QP, but it doesn't matter). K is the k-factor for the diffuser, a diffuser has many different k-factors. At last we have DeltaP which is the differential pressure.
Problem
Calculate what k-factor the diffusers should have to get the correct flow (QP). We know QP(Q), we want the K. So I guess we need the DeltaP? Maybe the k-factor isnt enough, maybe I need to know the effective area on the diffuser?
I guess the total flowrate of the fan would also be good to know.
Thoughts
I have read some fluid mechanics, but I don't know how to put all pieces together. I have some theory on how to calculate it though:
1. Get velocity (dividing volumetric flow rate by cross-sectional area)
2. Calculate the pressure loss per some unit length
3. Calculate the total length (with bends etc)
4. Calculate the total pressure loss.
----
The problem with my example is that the pipes get smaller from the MP (MainPipe), I guess the bernoulli's equation would be used here.
Last thoughts
If it's something more you need to know about this example, just assume some values. Thank You.
Example
