What I am saying is that if the zone moisture content (e.g., humidity ratio, relative humidity, etc at constant temperature) changes, the latent capacity delivered to (or removed from) the zone will be different than the latent load added to the zone. If the infiltration latent load is equal to the ideal load air system latent capacity, the zone moisture content should not change. Do not compare latent capacity and latent load unless the zone moisture content is constant, otherwise you will be including the latent capacity needed to change the zone moisture content.
On 6/17/2011 9:29 AM, yangxiaoshan@xxxxxxxx wrote:
Hey, Richard
Thanks a lot. I am not quite understand your idea. Since The Idea Load Air System component does not control zone humidity levels (just control zone air temperature). The zone humidity level varies with the outdoor conditions via infiltration. For "Idea Load Air System",the constant air temperature and humidity of the air supplied for cooling the zone are 13 degree Celsius and 9 g/kg. According the ASHRAE sizing method (used by E+), total Cooling is the rate at which total energy (sensible and latent) is removed from the mixed outside and return air stream in order to bring the mixed air stream to the specified temperature and humidity ratio of the supply air stream. For this case, the only source of latent heat gain is by infiltration, and the infiltration latent heat gain should be equal to total latent cooling load. But it isn't......
Xiaoshan
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad <RRaustad@...> wrote:
>
> Are you reporting the zone relative humidity? If the zone moisture level
> is dropping, this would explain the difference. You need to keep the
> zone conditions constant for this to work.
>
> On 6/17/2011 8:56 AM, yangxiaoshan@... wrote:
> >
> > Hi,
> > Thanks for your reply. I had set the infiltration rate to 0 or other
> > values. If ACH is 0, there is no latent cooling load and total cooling
> > load equals to total sensible cooling load. That makes sense. But once
> > the ACH is not 0, the infiltration heat gain is always less than
> > latent cooling load. I do not know what else items could be also
> > included in the latent cooling load component.
> >
> > Best,
> > Xiaoshan
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, YuanLu Li <yli006@>
> > wrote:
> > >
> > >
> > > Try changing the infiltration air change per hour to zero and to 2
> > to compare.
> > >
> > > There may be other compoent included in the total cooling load.
> > >
> > > Dr. Li
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > From: yangxiaoshan@
> > > Date: Fri, 17 Jun 2011 06:37:59 +0800
> > > Subject: [EnergyPlus_Support] A question about Latent Cooling Load in E+
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Dear Colleagues,
> > >
> > >
> > > I got a question about latent cooling load in EnergyPlus. The
> > simulation settings are: a single zone with constant cooling setpoint
> > (26â"f through the day), no internal heat gain, 1 air changes per hour
> > and "Idea Load Air System" automatically used for HVAC configuration.
> > Theoratically, due to there is no internal heat gain in this case, the
> > follow correlation should be valid: "Total cooling load - Total
> > sensible cooling load = Latent cooling load = Infiltration latent heat
> > gain". But the simulation results shown that the infiltration latent
> > heat gain is always less than the latent cooling load (Total cooling
> > load - Total sensible cooling load), 2% for this case (8-9% less was
> > found in other simulation case). I cannot understand why the
> > infiltration heat gain is not equal to the calculated latent cooling
> > load. Really headache! Look forward to discussing with you, thanks
> > very much.
> > >
> > > Best regards,
> > > Xiaoshan
> > >
> >
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
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