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Re: [EnergyPlus_Support] infiltration

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] infiltration
From: Chris Jones <cj@xxxxxxxxx>
Date: Wed, 11 Dec 2002 20:14:42 -0500
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In ASHRAE 90.1-1989, the energy cost budget called for a value of 0.038 
cfm/sq.ft of exterior wall area when the fans are off, see ASHRAE 90.1-1989 
13.7.3.2 except for MURBS, hotels and motels which are to assume 
infiltration at all times.

That value likely has little bearing on what really happens which is why 
references to infiltration are not included in ASHRAE 
90.1-1999.  multi-residential buildings have a big problem with 
infiltration.  The typical HVAC system in older buildings is some fresh air 
dumped into the corridors with the assumption that bathroom and kitchen 
fans will  drag the air through  the carpet filter under the entrance 
door.  Due to poor fitting windows, etc. the costs due to infiltration 
(below the neutral plane and exfiltration about it) are tremendous.

If you are trying to simulate true effects of infiltration, you will need 
to get ahold of some papers dealing with measurements in existing buildings.



>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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Chris Jones, P. Eng.
14 Oneida Avenue
Toronto, ON M5J 2E3
Tel. 416 203-7465
Fax. 416 203-8249




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References:
- Re: [EnergyPlus_Support] infiltration
  - From: HSIEH Chun-Ming
- Re: [EnergyPlus_Support] infiltration
  - From: Michael J. Witte

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