Hello my first post,
I'm wondering if there is anyone about who could advise on the calculations involved in determining flow networks for natural ventilation. I'm studying a distance learning masters in sustainable design and there is something for this assignment I'm just not getting.
I've been through
A Guide to Energy Efficient Ventilation, Martin W Liddament – AVIC
Air Infiltration Calculation Techniques - An Applications Guide, Martin W. Liddament – AVIC
2009 ASHRAE® Handbook Fundamentals
Ventilation for Acceptable Indoor Air Quality, ASHRAEE standard 62.1
And several other presentations, book and publications.
and in part of this I found a couple of Discussions here that have helped but not fully covered what I need.
If anyone can help I'll go into more detail but the basic layout is below. Obviously I don't want to solution calculated for me as that would be cheating but just people to bounce off would be nice.
Tags:
Pascals for stack has been discussed to death here
Wind is pretty easy to find & if need be I would recommend googleing Bernoulli's principle on wind
Unfortunately just looking at the diagram without some context it is hard to know what you need help with
https://www.linkedin.com/groups/6942179/6942179-6030115404729307139 'm not sure this is what your exactly looking for Daniel but it should direct you to the right area.
I asked this question to Colin Genge really one of best minds regarding this in the business. Anyone can theorize but measuring is why most of us are here. If your going to measure one thing against another do it the same way every time. This escapes some in our industry...Anyway take the time to read what he wrote on set-up and join his group. Best of luck and share what you come up with.
Daniel,
I'm assuming you're trying to predict the airflows through the different openings W1, ... ? It is very unclear from the drawing. You're probably aware, but solving the problem requires calculating the pressure differentials at each opening, as they vary with height and temperature difference. The airflow is then simplified as an orifice flow, typically with flow and pressure coefficients that characterize the size and shape of the opening. Wind is trickier, but is generally treated similarly. I know the relevant equations are in the Liddament books, but can't remember specifically where.
So I wanted to start with a basic who can help then go into more detail later.
But yes find the air flows through the openings and area of the openings.
I've approached it now as airflow/m^2 of opening then used air rates per person (EN 13770:2004) to specify a target rate for winter and summer and size the openings from that.
This hasn't been the most precise and consistent course and assignment I've ever carried out.
My tutor got back to me and while areas don't quite feel right a little to much assumptions and things not quite adding up in the examples I'm slowly moving on.
We have a certain amount of freedom to manipulate the design so to simplify things I've closed off L1 as suggested by the tutor.
The thing that got me was having calculated the stack pressure based on the lowest opening and then added the wind how do I determine the flow networks.
The examples have the flow rates calculated end to end so combining the pressures W3 and L2 for the air flow right through the building. Treating each floor as individual zones.
Now the assignment is only meant to represent very early calculation estimates so I guess this is ok, personally I'd then move to use CFD software after the heavily simplified systems for better predictions.
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