# Re: [EnergyPlus_Support] infiltration

```1.  As Najad stated, for pressurized commercial buildings,
infiltration is often assumed to be zero when the HVAC fans are in
operation.  (Although there is some debate about whether it is truly
zero under these conditions.)  But this still leaves the question of
what value applies when the HVAC system is shut off (perhaps on
nights and weekends) and for other types of spaces which are not
pressurized.  This depends on many factors including the tightness of
construction, stack effects, etc., and you will need to consult HVAC
handbooks for guidance on this.  The key thing to remember is that
your design value must be consistent with the specific temperature
difference and windspeed values that are the basis for the set of
A,B,C,D coefficients that you are using.

2.  When ventilation is active, the flow is calculated using the same
form of equation as infiltration.

Mike

On 10 Dec 2002, at 22:08, HSIEH Chun-Ming wrote:

> Here we discussed the A, B, C and D values of infiltration/ventilation
> equation.
>
> 1. But, do you have any idea about how to set the Design Volume.
> It might depend on the how much area of window is opened and the wind
> speed outside, right? I am not sure. Do we have any simple way to
> calculate the value of Design Volume? It's hard for me to imagine that
> how much the value should be?
>
> 2. The design volume of Ventilation with windows opened should be much
> higher than that of infilation , right? by the way, except the Delta
> T, the calculation in infiltration and ventilation are the same,
> right?
>
> Thank you very much.
>
> Chunming
>
>
> Michael J. Witte wrote:
>
> > The question of typical values for these coefficients is subject to
> > debate.  Ideally, one should do a detailed analysis of the
> > infiltration situation and then determine a custom set of
> > coefficients using methods such as those laid out in Chapter 26 of
> > the ASHRAE Handbook of Fundamentals.  The EnergyPlus defaults are
> > 1,0,0,0 which gives a constant volume flow of infiltration under all
> > conditions.
> >
> > BLAST used the following values as defaults:  0.606, 0.0202,
> > 0.000598, 0.  These coefficients produce a value of 1.0 at 0C deltaT
> > and 3.35 m/s (7.5 mph) windspeed, which corresponds to a typical
> > summer condition.  At a winter condition of 40C deltaT and 6 m/s
> > (13.4 mph) windspeed, these coefficients would increase the
> > infiltration rate by a factor of 2.75.
> >
> > In DOE-2, the air change method defaults are (adjusted to SI units)
> > 0, 0, 0.224 (windspeed), 0.  With these coefficients, the summer
> > conditions above would give a factor of 0.75, and the winter
> > conditions would give 1.34.  A windspeed of 4.47 m/s (10 mph) gives
> > a factor of 1.0.
> >
> > The source of the BLAST defaults is noted in the BLAST documentation
> > as:
> >
> > "Empirical equation and the coefficient default were determined from
> > ASHRAE journal articles and other data on the effects of outdoor
> > weather conditions."
> >
> > The source of the DOE-2 defaults is based on examining the
> > infiltration relationships decsribed in the ASHRAE Handbook of
> > Fundamentals.
> >
> > Mike
> >
> >
> > On 19 Nov 2002, at 16:48, nuno lourenço wrote:
> >
> > >
> > >
> > >
> > >
> > > In the input-output reference manual (pag 161) you give some
> > > values for the parameter A-Constant term coefficient,
> > > B-Temperature Term coefficient, C-Velocity Term Coefficient,
> > > D-Velocity Squared Term Coefficient. How do you obtained this
> > > values? I found my error in the cooling and heating loads. My
> > > values for this Parameter were "quite" different and I obtained
> > > very high loads.But if I put "our" values the loads are quite
> > > similar to those I am expecting.
> > >
> > > Best regards,
> > >
> > > Nuno Lourenço
> > >
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