[esp-r] Re: VAV and Positive Air Pressure Control

[Jon Hand]

A recent question (below)...

If the "VAV control function" is the one in the ideal zone controls
it does not assume any relationship with an air flow network and
no air flow network is required when using this ideal zone control. 
The zone controller has a number of parameters (source temperature,
throttling range etc.) but there is no parameter which describes
the specific characteristics of a return path.

There is an exemplar model which demonstrates the use of this
zone control and you might want to look at that model.

If the "VAV control function" is for an air flow network control
there isn't one labeled as "VAV".  You could join several flow
components and controls to approximate the actions of
a VAV.  In a flow network you are able to describe connections
to other zones and to the outside e.g. the return path. And
if you want the return air to be some fixed percentage of
the incoming air that is going to take a rather clever flow
control (there is no example of this).

The question is not quite clear how the 90CMH is represented
in the model.  If a flow network is being used please re-submit
the question and include a sketch of the flow network.

-Jon Hand

-----Original Message-----
From: esp-r-bounces at lists.strath.ac.uk on behalf of Lewis Yook
Sent: Wed 3/5/2008 6:08 AM
To: ESP-r User Forum
Subject: [esp-r] VAV and Positive Air Pressure Control
 
Dear All.

This question is about VAV in control function.
Let me assume one zone to which 100 CMH air volume is supplied for heating. And the 90 CMH air volume is returned through diffuser in the same zone. 
The surplus 10 CMH air supply volume plays the role of the source of positive net pressure that prevents the air infiltration from the adjacent zones.

In this case, how should i set the the max air volume flow rate in control law? 
1) Real volume 100 CMH? or net volume 10 CMH?

2) How can I describe the supply and return separately in VAV control law?

And, I have done above simulation with the setting of  the supply air volume as net volume 10 CMH.

I found some strange results which seem to be fluctuating.
In other words, in some nodes, the flow direction changes in every time step from positive to negative and from negative to positive.
I tried to adjust the time step. However, the flow direction fluctuates between positive and negative value regardless of the time step.

3) Do you think this kind of pattern can be obtained in VAV control?

I appreciate for your interests and ideas.


Lewis Yook
Team Manager,
Integrated Simulation Team.
Design and Simulation for Sustainability (DASS) consultants Ltd.

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