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[EnergyPlus_Support] Re: Thermal Chimney modelling method
Hi,
As far as I can tell, it seems to be possible to reach agreement between a model using the object thermalchimney and a model using airflownetwork. I see you try to combine 2 natural ventilation effects, so did I in my first set of question.
So my advice to you is first to isolate both of them and get them work properly one by one.
You can for instance do the thermalchimney object only in your zone to see what enhance flow rate you get. Then, try to do it with airflow network. To get this to work, you need to be careful about the size and location of your openings since you want the model to generate one way flow through them, i.e. avoid large vertical shapes...
You need also another opening (small windows or vent) in the adjacent zone that you want to cool down so that the thermal chimney will draw from this. So try to get this mass flow distribution first with similar airflow rates and temperature as for the thermal chimney algorithm. It works.
Then combining with your cross ventilation strategy should be a matter of detailed parameters in your model.
I did lots of iteration but I got mine to work that way. The physics behind seems to work.
Good luck!
Aymeric
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Wonjun" <lesthesia@...> wrote:
>
> I can't understand the compatibility between Thermal Chimney and Airflow Network. So I should make all these things clear by your help.
>
>
> I tried to model a building applied cross ventilation boosted by Thermal chimney. So there are openable windows attached on interanl walls to facilitate wind flow.
> I thought this can be done by using 2 objects as I stated above(Thermal chimney and airflow network.).
> But if it's not possible as you said, how I can model this idea in E+? I know one thing that I should use Airflow Network because of cross ventilation.
> The problem is the boosted flow rate by absorbing of solar radiation which is the key of this idea, but I don't know how to solve this.
> And I don't know how can I can take into consideration the "Width of the Absorver Wall" in the "Zone Thermal Chimney."
>
> Need your help.
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Lixing Gu <gu@> wrote:
> >
> > The AirlfowNetwork model does not support thermal chimney right now. The combined capability is listed in a wish list.
> >
> >
> >
> > Lixing
> >
> >
> >
> > From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Fernando Sa
> > Sent: Friday, March 19, 2010 7:26 PM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > Subject: Re: [EnergyPlus_Support] Re: Thermal Chimney modelling method
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > I'm working with Thermal Chimney in Brazil, but i'm not working with zone:thermalchimney because this object is incompatible with airflownetwork, and is limited to model studied for Ong (2003) with vertical chimney, i prefer to work with airflownetwork only.
> >
> > --- Gio 18/3/10, Kwang Ho Lee <kwhlee@> ha scritto:
> >
> >
> > Da: Kwang Ho Lee <kwhlee@>
> > Oggetto: Re: [EnergyPlus_Support] Re: Thermal Chimney modelling method
> > A: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > Data: Giovedì 18 marzo 2010, 14:14
> >
> >
> >
> > You do not need to specify Zone:Infiltration object to use
> > Zone:ThermalChimney object. If you use Zone:Infiltration object, the
> > total infiltration airflow through the zone is the sum of the airflow
> > from Zone:Infiltration and the enhanced natural ventilation from
> > Zone:Thermal Chimney.
> >
> > As I mentioned below, I don't have anough experience with AirflowNetwork,
> > but I am pretty sure that the discharge airflow through the upper opening
> > in the thermal chimney model does NOT automatically interact with upper
> > window specified AirflowNetWork object unless you manually connect them.
> > The discharge air "temperature" through the chimney upper opening is only
> > used "internally" inside the thermal chimney algorithm. So it does not
> > directly affect other heat balances in EPlus. Only the enhanced natural
> > ventilation rate affects the heat balances.
> >
> > Kwang
> >
> > > A last observation I made explains why the airflownetwork method is not
> > > working properly:
> > > Actually, the suction effect of the chimney is linked, even defined by the
> > > discharge air outlet description (as it is the case in the algorithm for
> > > ThermalChimney object). In fact in the airflownetwork calculation, this
> > > discharge opening does not behave as a one way flow opening. Because it
> > > uses LVO theoretical background most of the air mass exchange occurs at
> > > the opening and a very little fraction is actually sucked from the lower
> > > part. From there, all the massflow equilibrium at the different openings
> > > or cracks of this system cannot represent the situation.
> > >
> > > Do you see a solution in this? I am using Eplus V3 which has only LVO
> > > models capabilities. I know in V4 there is a new large horizontal opening
> > > model that might be able not to have this behavior right?
> > >
> > > Best Regards
> > > Aymeric
> > >
> > > --- In EnergyPlus_Support@ yahoogroups. com, "aymericnovel"
> > > <aymericnovel@ ...> wrote:
> > >>
> > >> Dear Kwang,
> > >>
> > >> Thank you very much for this explanation. Actually, it works quite well
> > >> with the ThermalChimney object. Correct me if I'm wrong but it requires
> > >> to have a ZoneInfiltration object in the zone to be cooled down (it is
> > >> not written in the manual...)
> > >> Therefore, it is impossible to use this in addition to AirflowNetwork
> > >> objects since they automatically desactivate ZoneInfiltration object...
> > >>
> > >> So I guess unless I find a way to represent well the chimney algorithm
> > >> with Airflow Network object I cannot try to compare windows natural
> > >> ventilation against windows+chimney natural ventilation.
> > >>
> > >> I had another issue: There are holes in other parts of the building and
> > >> it seemed to mess with the airflow calculation of the zone I was
> > >> studying. So, the mass balance of the network is set at the building
> > >> level right? Because I had weird airflow through my ceiling although it
> > >> does not connect with outside. Isn't it some numerical balancing the
> > >> software uses to reach building's global balance?
> > >>
> > >> Thanks a million!
> > >> Aymeric
> > >>
> > >> --- In EnergyPlus_Support@ yahoogroups. com, "Kwang Ho Lee" <kwhlee@>
> > >> wrote:
> > >> >
> > >> > Dear Aymeric,
> > >> >
> > >> > A little mis-explanation in my previous email. The solar radiation
> > >> does
> > >> > peak at noon (of course!), but the natural ventilation caused by the
> > >> > thermal chimney does not necessarily peaks at noon due to the sotrage
> > >> > effect of constructions including chimney absorption wall.
> > >> >
> > >> > Going back to your question below, EPlus Zone:ThermalChimney object
> > >> > assumes that all the natural ventilation airflows induced by the
> > >> chimney
> > >> > are replaced by the "infiltration" . After EPlus calculates the
> > >> enhanced
> > >> > ventilation airflow due to the chimney, the office space (in your
> > >> case)
> > >> > would act like it is having the Zone:Infiltration object. So, the
> > >> window
> > >> > opening won't have big impact on the chimney airflow.
> > >> >
> > >> > Again, I don't have enough experience with AirflowNetwork object, but
> > >> I
> > >> > believe that it doesn't automatically calculate all the key algorithm
> > >> > needed to predict the thermal chimney performance such as thermal
> > >> > gradient and enhanced air volume, etc. (You need to doublechek the
> > >> > documentations. Maybe I am wrong)
> > >> >
> > >> > Regards,
> > >> >
> > >> > Kwang
> > >> >
> > >> > > yes it means chimney temperature.
> > >> > > And indeed, in my model, when the office zone that is adjacent to
> > >> the
> > >> > > chimney does not have opened windows, the natural ventilation
> > >> flowing from
> > >> > > the office to outside via the chimney does peak around noon.
> > >> > >
> > >> > > But to be realistic, I wanted to open office's windows (20% of their
> > >> area)
> > >> > > so that I can quantify the natural ventilation flow rate increase if
> > >> I use
> > >> > > the chimney to boost it, i.e I try to compare a single sided
> > >> ventilation
> > >> > > (just the window is opened) with a cross ventilation assisted by the
> > >> solar
> > >> > > chimney (window opened and solar chimney opened).
> > >> > >
> > >> > > In the second case, it does increase the ventilation rate but
> > >> temperature
> > >> > > decrease in the office is not as much as this Pr would expect + when
> > >> > > windows are opened airflow rate peaks at night because in the
> > >> airflow
> > >> > > network calculation it seems that windows keep a dominant role with
> > >> their
> > >> > > large vertical opening gravitational flow.
> > >> > >
> > >> > > I know all of this is a bit confused, I hope it is clear enough...
> > >> > >
> > >> > > I will try with the thermalchimney object. Do I have to remove the
> > >> airflow
> > >> > > network object from the chimney zone to use the thermalchimney
> > >> object?
> > >> > >
> > >> > > Thanks, great help!
> > >> > > Aymeric
> > >> > >
> > >> > > --- In EnergyPlus_Support@ yahoogroups. com, "Kwang Ho Lee" <kwhlee@>
> > >> > > wrote:
> > >> > >>
> > >> > >> Dear Aymeric,
> > >> > >>
> > >> > >> Based on my experience, the natural venilation caused by the
> > >> thermal
> > >> > >> chimney does not always peak at noon. I observed many cases peaking
> > >> in
> > >> > >> the afternoon (1 ~ 3pm) when the solar radiation ramps up.
> > >> > >>
> > >> > >> In "forced ventilation is proportional to room temperature" , the
> > >> room
> > >> > >> temperature means the thermal chimney zone temp, not the office
> > >> space,
> > >> > >> right?
> > >> > >>
> > >> > >> Regards,
> > >> > >>
> > >> > >> Kwang
> > >> > >>
> > >> > >>
> > >> > >> > Hi Pedro,
> > >> > >> >
> > >> > >> > Thanks a lot for your help. do you think the airflow network
> > >> object is
> > >> > >> > better or not as good as using Thermalchimney object?
> > >> > >> >
> > >> > >> > Another thing, below is the comment of a university professor:
> > >> > >> > "in the case of solar chimney, air flow increases with solar
> > >> radiation
> > >> > >> and
> > >> > >> > temperature of the plate in the chimney. In such case, air flow
> > >> > >> velocities
> > >> > >> > increase to maximum value at noon and decreases again in the
> > >> > >> afternoon.
> > >> > >> > This means that forced ventilation is proportional to room
> > >> temperature
> > >> > >> > which increases to maximum at noon. For that, I strongly believe
> > >> that
> > >> > >> > there is some difference between the chimney we are using and
> > >> that
> > >> > >> used by
> > >> > >> > the simulation software"
> > >> > >> >
> > >> > >> > I believe the guy is mistaking between the fact that the airflow
> > >> is
> > >> > >> > proportional to chinmney temperature and proportional to the
> > >> > >> temperature
> > >> > >> > difference between chimney and outside... What do you think?
> > >> > >> >
> > >> > >> > Thanks again!
> > >> > >> > Aymeric
> > >> > >> >
> > >> > >> > --- In EnergyPlus_Support@ yahoogroups. com, Pedro Peixeiro
> > >> > >> > <pedro_peixeiro@ > wrote:
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Hello.
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> My experience, I modelled a DSF using an independent zone for
> > >> the
> > >> > >> >> middle cavity. It is important to model the natural ventilation
> > >> using
> > >> > >> >> the AirFlow network objects to take advantage of a better
> > >> simulation
> > >> > >> of
> > >> > >> >> the effects of pressure difference between inlet/outlet due to
> > >> wind
> > >> > >> >> effect and temperature rise. Even so, it is very hard to
> > >> simulate
> > >> > >> >> natural ventilation in these types of building elements,
> > >> specially
> > >> > >> the
> > >> > >> >> air flow. My results
> > >> > >> >> were not entirely accurate, and I am still to do some more
> > >> trials on
> > >> > >> >> E+.
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> One thing you can do to improve your results is 1. create
> > >> independent
> > >> > >> >> zones for the inlet and outlet of the chimney so to introduce
> > >> the
> > >> > >> right
> > >> > >> >> pressure coefficients of each one of these (experimentaly
> > >> observed);
> > >> > >> 2.
> > >> > >> >> change the wind
> > >> > >> >> pressure coefficients of the outdoor surface side of the chimney
> > >> so
> > >> > >> to
> > >> > >> >> aproximate your air flow results to the experimental
> > >> > >> >> data, and thus obtain a better funcionality. Unfortunately, #2
> > >> might
> > >> > >> be
> > >> > >> >> a
> > >> > >> >> bit laborous trial and error attempt. As far as the temperature
> > >> > >> gradient
> > >> > >> >> is concerned, you can divide your chimney into several vertical
> > >> > >> zones,
> > >> > >> >> or use the Room Air Models to try to find a good aproximation
> > >> (note
> > >> > >> that
> > >> > >> >> the larger the gap depth and width is, the less accurate will be
> > >> the
> > >> > >> air
> > >> > >> >> flow transition between vertical zones).
> > >> > >> >>
> > >> > >> >> Pedro.
> > >> > >> >>
> > >> > >> >> To: EnergyPlus_Support@ yahoogroups. com
> > >> > >> >> From: aymericnovel@
> > >> > >> >> Date: Tue, 16 Mar 2010 10:26:57 +0000
> > >> > >> >> Subject: [EnergyPlus_ Support] Thermal Chimney modelling method
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Dear all,
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> I am struggeling to know whether or not I did simulate properly
> > >> a
> > >> > >> solar
> > >> > >> >> chimney. It is in Jerusalem climate.
> > >> > >> >>
> > >> > >> >> I first modelled a zone adjacent to the office I want to cool
> > >> down. I
> > >> > >> >> positionned a low opening on the partition wall separating the
> > >> two
> > >> > >> >> zones. This wall is of course composed by a structural part,
> > >> here
> > >> > >> >> concrete, 2.5cm polyurethan board insulation and a black
> > >> selective
> > >> > >> metal
> > >> > >> >> plate. The outer wall of the chimney is a glazed wall with an
> > >> upper
> > >> > >> >> opening.
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Although it seems to work logically, it doesn't match
> > >> experimental
> > >> > >> >> results. Basically it seems it doesn't enhance enough the
> > >> natural
> > >> > >> >> ventilation. ..
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Using this method, I certainly don't take into account the
> > >> > >> temperature
> > >> > >> >> gradient within the thermal chimney, right? Is it more reliable
> > >> to
> > >> > >> use
> > >> > >> >> the object Zone:ThermalChimney ?
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Plus, an additional problem I can't explain is that I get some
> > >> > >> massflow
> > >> > >> >> through ceilings although I do not activate infiltration
> > >> > >> calculations. ..
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> If anyone has experience modelling thermal chimney, I would be
> > >> happy
> > >> > >> to
> > >> > >> >> know more about that!
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> Thanks a million
> > >> > >> >>
> > >> > >> >> Aymeric
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >>
> > >> > >> >> ____________ _________ _________ _________ _________ _________ _
> > >> > >> >> Hotmail: Trusted email with Microsoft's powerful SPAM
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> > >> > >>
> > >> > >
> > >> > >
> > >> > >
> > >> >
> > >>
> > >
> > >
> > >
> >
>
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