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[EnergyPlus_Support] Re: Residential Multifamily Infiltration & Ventilation
I was completely wrong, I have taken a look again to ASHRAE fundamentals and it's true that is not so easy to determine the neutral pressure level and thus the "height difference".
ASHRAE: The neutral pressure level (NPL) is that location or locations in the building envelope where there is no pressure difference. Internal partitions, stairwells, elevator shafts, utility ducts, chimneys, vents, operable windows, and mechanical supply and exhaust systems complicate the analysis of NPL location. An opening with a large area relative to the total building leakage causes the NPL to shift toward the location of the opening. In particular, chimneys and openings at or above roof height raise the NPL in small buildings. Exhaust systems increase the height of the NPL; outdoor air supply systems lower it.
A guess for the "height difference" as Lixing says could be the distance from the midpoint of the building height to the mid point of the opening area.
Natural ventilation is the flow of outdoor air due to wind and
thermal pressures through intentional openings in the building
such as windows, doors, vents..
I think the best way to evaluate ventilation and infiltration is using the airflownetwork, we should learn how to use it. There is also a program called "contam" which gets similar results to "energy+" and it can help to understand how energy+ works in that issue.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aleagerman22" <agerman@...> wrote:
>
> Hello and thank you for the response. I have played around with changing the height difference and have found, for my model at least, which doesn't have a significant window open area available for natural ventilation, the results are not too sensitive to changes in the height. If using the ZoneVentilation:DesignFlowRate object you have to somehow estimate a design flow rate, which I don't understand how to do when talking about natural ventilation. Do you have any guidance?
> Thanks again,
> Alea
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Lixing Gu <gu@> wrote:
> >
> > Alea:
> >
> > It is not easy to figure out the values of "height difference". This
> > object is mainly for people to use if the height difference could be
> > esitmated. A half of buildign heaight is a good guess. If you can not
> > determine the value, it is better to use the
> > ZoneVentilation:DesignFlowRate object.
> >
> > Hope this helps.
> >
> > Lixing
> >
> > Quoting adcamtor <adcamtor@>:
> >
> > >
> > >
> > > Hi Alea,
> > >
> > > I am at the same stage, I have calculated the ventilation with the
> > > WindandStackOpenArea objects and the results seem to be accetable.
> > > But, I am not sure if I have done it correctly estimating the
> > > "height difference", I have used one half height of each opening
> > > area, in my case, small ventilation openings (no doors, no windows).
> > >
> > > Regarding the "height difference", I have read in the ASHRAE
> > > fundamentals the next paragraph:
> > >
> > > Estimation of "height difference to neutral pressure level" is
> > > difficult for naturally ventilated buildings. If one window or door
> > > represents a large fraction (approximately 90%) of the total opening
> > > area in the envelope, then the NPL is at the mid-height of that
> > > aperture, and height difference to NPL equals one-half the height
> > > of the aperture. For this condition, flow through the opening is
> > > bidirectional (i.e., air from the warmer side flows through the top
> > > of the opening, and air from the colder side flows through the
> > > bottom).
> > >
> > > I cannot help you too much, I hope someone more expert helps us.
> > >
> > > Adrian.
> > >
> > >
> > >
> > >
> > >
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aleagerman22"
> > > <agerman@> wrote:
> > >>
> > >> Hello,
> > >> I am new to Energy+ and am modeling two new construction
> > >> multi-family buildings. One is 3 stories with exterior entrances
> > >> and the other is 10 stories with interior hallways. I am struglling
> > >> with how best to model natural ventilation and infiltration, both
> > >> due to exhaust fan operation and envelope leakage based on a
> > >> measured/expected SLA. My zoning is fairly simple with a single
> > >> zone per apartment unit. This is new construction so the assumption
> > >> is that envelope sealing is decent and there is not significant
> > >> connection between the individual units.
> > >>
> > >> The AirflowNetwork module appears to be a very powerful tool but
> > >> perhaps too complex for what I'm trying to do. Also, there are many
> > >> modeling inputs, like Wind Pressure Coefficients, that I don't have
> > >> and would have to use defaults or those measured by others which
> > >> may reduce accuracy. Thoughts? The other alternative appears to be
> > >> through ZoneVentilation & ZoneInfiltration. However, if I enter my
> > >> exhaust fans and envelope leakage separately, total infiltration
> > >> will be a summation of the natural infiltration and mechanical
> > >> ventilation and will be overestimated according to ASHRAE.
> > >> Regarding natural ventilation the
> > >> ZoneVentilation:WindandStackOpenArea appears to be a good option;
> > >> however, the E+ documentation advises against it because the
> > >> "height difference" is particularly difficult to estimate. Is the
> > >> ZoneVentilation:DesignFlowRate to the best way to go?
> > >>
> > >> I would greatly appreciate any advice or guidance from anyone who
> > >> has experience with this. Thank you in advance.
> > >>
> > >> Alea
> > >>
> > >
> > >
> > >
> > > ------------------------------------
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> >
> >
> > ----------------------------------------------------------------
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> >
>
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