[EnergyPlus_Support] RE: Re: Merging zones having FCUs (Merging FCUs)

Furthermore, the fan efficiency default of 0.7 is some crazy "typical" value that has wormed it way into the world of simulation. e+ considers this field for the total effeciency of the fan system. It should be the product of

And I have NEVER seen a total efficiency of 0.7. As efficiencies scale with size, my experience values are 0.54 for a 20000m3/h AHU supply fan and 0.21 for a 30m3/h bathroom exhaust fan.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, <energyplus_support@xxxxxxxxxxxxxxx> wrote:

Hi, thanks for all contributors for their responses.
I tried to find the equivalent Delta P like this:
Eqv. Delta P= 1000 * (Total Power [W] / Total AirFlow Rate [L/s]) * Fan Total Efficiency
where:
Total Power = Sum. of the merged FCUs powers.
Total Flow = Sum. of the merged FCUs flows.
Fan Total Efficiency = left at default value of 0.7
The results gave all the equivalent powers larger by a factor of 1.25 from the actual ones, for example: 1500[W] instead of 1200, 375 instead of 300, 1125 instead of 900, and so on. I can't find where this factor came from and got itself incorporated!

So, do you know where I can find this factor and set it to 1? or should I try to include an inverse factor of 1/1.25=0.8 in my eqv. delta P calculations?

Thank you.
--
Hisham

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jeannieboef@..." <jeannieboef@...> wrote:
>
> Or work backwards... Total real FCU Rated powers = Total Rated FCU
> Volume Flow * Pressure Equivalent / (flow weighted average efficiency)
>
> ...just not sure if the efficiency should be flow or power weighted.
>
> Mit freundlichen GrÃ¼ÃŸen- Sent from my iPhone (excuse the brevity)
>
> i. A.
> Jean Marais
> b.i.g. bechtold
> Tel. +49 30 6706662-23
>
> On 18.09.2013, at 17:32, Richard Raustad <RRaustad@...> wrote:
>
> > Obviously there is a flaw in the DB approach. Try averaging the fan
> > pressure rise instead.
> >
> > Fan:ConstantVolume,
> > 75.0, !- Pressure Rise {Pa}
> >
> > On 9/18/2013 6:38 AM, hisham.rashrash wrote:
> > > Hi,
> > > For one case, I tried to merge actual zones into larger thermal
> > zones. Now, I have to model FCUs, using TemplateHVAC:Zone:FanCoil
> > objects, in such a way that I put one FCU in each zone that must
> > represent 4, 5 or even 11 real FCUs for example. I used the
> > following approach:
> > > 1. I used the formula from DesignBuilder website (http://www.designbuilder.co.uk/programhelp/fans.htm
> > ) to find Fan Delta Pressure:
> > > Delta P = 1000 * SFP * Fan total efficiency (SFP: Specific Fan
> > Power [W/(L/s)]
> > > I calculated each real FCU's Fan Delta P and added them up to find
> > the equivalent FCU's fan Delta P.
> > > For example:
> > > I have 4 FCU's one for each of 4 guest rooms that I merged into
> > one large room for simplification, the actual HVAC schedules give
> > the following:
> > >
> > > FCU No. Power [kW] Air Flow [L/s]
> > > ==================================================
> > > 1 0.3 160
> > > 2 0.3 145
> > > 3 0.3 145
> > > 4 0.3 145
> > >
> > >
> > > Eqv. Delta P= 1000*(300[W]/160[L/s]+3*300[W]/145[L/s])*0.7=5657.33
> > [Pa]
> > >
> > >
> > > 2. I found the equivalent FCU's airflow rate by adding the real
> > FCUs' flow rates:
> > > Eqv. Flow Rate=160+3*145=595[L/s]
> > >
> > >
> > > I used the above values in the HVACTemplate:Zone:FanCoil object
> > for the corresponding zone. The results were that the equivalent
> > FCU's power calculated is 5 times larger (about 6[kW]) than actual
> > component-FCUs' power when added up:
> > > >From table above: 0.3[kW/FCU]*4[FCUs]=1.2[kW]<6[kW]
> > >
> > >
> > > Please advise.
> > >
> > >
> > > Thank you very much.
> > >
> > >
> > > Regards,
> > > Hisham
> > >
> > >
> > >
> > >
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