[esp-r] Re: solar chimney and understand flow patterns

[Jon Hand]

The positive and negative sign on the flow provides information on the direction of the
flow - if you defined a connection from node A to node B then a positive flow is flow
along the same direction as the connection was defined.  I tend to define connections
to the outside via the outside node to the inside node so that flows entering the zone
are positive and flows leaving the room are negative.

The ventilation and infiltration reporting of energy is, essentially the energy transfer
implied by the movement of mass between the inside and outside (infiltration) or
between two zones (ventilation) taking into account the temperature difference and
the mass flow rate.  cool air entering a room alters the zone energy balance and
can be a negative flux.  If you graph or list out the individual components of the zone
energy balance on a timestep basis then a pattern might be observed.

Flow into a zone shows up in the ventilation and infiltration reporting.
Flow out of a room is noticed in the 'other' zone.

Flow in a solar chimney might, in fact reverse under certain conditions. Buoyancy might be
a weak driving force in comparison to pressure elsewhere.

One hint - you can turn on trace of the network flow solution and that will dump out
all of the flows and pressures at each timestep and sometimes it is easier to detect
patterns of flow in that form than looking at the individual flow rates via the results
analysis module.

-Jon Hand
________________________________________
From: Ehsan Baharvand [ebaharvand at yahoo.com]
Sent: 04 April 2011 15:06
To: Jon Hand
Cc: esp-r at lists.strath.ac.uk
Subject: Re: [esp-r] Re: solar chimney

Hi,

Thank you for your mail Jon.

One question to see if I'm interpreting things in a correct manner:
 When looking to volume flow rate and selecting a infiltration connection via Volume Flow Rate of AirFlow Result File the flow rate becomes sometimes negative! What does Negative result mean actually? Does it mean that the air is towards outdoors or from outdoors?

Jon's question:
Well, I checked the results by choosing the timstep itegration turned OFF. The results stayed the same. I looked to the energy balance per thermal zone, and the results weren't so strange at all. Especially when looking to the ratio of chimney's main stream and what comes in as infiltration air rate. It is 1/10 of the chimney's main stream with dT of 5 - 8 Kelvin depending on the height of the chimney!

What attracted my attention was the infiltration rate direction per thermal zone! When looking more in detail - for a particular problem -  the ambient infiltration in the upper level of the chimney becomes negative. This means that the upper level air of the chimney goes simply to outside before it reaches the outlet of the system?!
On the other side, the zones in the lower level have positive infiltration rates when looking to these connections.

Thanking you in advance.

Kind Regards,
Ehsan

________________________________
From: Jon Hand <jon at esru.strath.ac.uk>
To: Ehsan Baharvand <ebaharvand at yahoo.com>; Achim.geissler <achim.geissler at intergga.ch>; "esp-r at lists.strath.ac.uk" <esp-r at lists.strath.ac.uk>
Sent: Sun, April 3, 2011 10:57:56 PM
Subject: RE: [esp-r] Re: solar chimney


In an earlier email the simulation parameters were stated.  What caught my attention
was the 60 timesteps per hour with timestep integration turn ON.  This will write out
information once per hour.  I suggest that you save the information at each timestep
so that the actual flows and flux at each timestep is available for inspection.

-Jon Hand
________________________________________

. . .
b) how long is your pre-simulation period, how long is your simulation period and what does "temperature does not change" mean? "Not at all" or "not as much as expected"?
Pre-simulation = 12 days
Simulation period = 1 day (24h)
Time-step = 60
Integration per hour = yes
. . .
Kind regards,
Ehsan
________________________________