Re: [EnergyPlus_Support] Re: Zone Temperature Peaks too Early

How are you dealing with the linear thermal bridges? In a normal building these are neglected but in a passive house they are usually considered. I would think that most bridges would conduct rapidly since by definition they are weaknesses in the thermal envelope.

Also in doe2 I remember some cautions in how radiation was modeled for very low solar angles. Could this be a factor?

Feel like sharing your model so we can dig?

On 8/05/2013 9:00 PM, "Joe Huang" <YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Well, at least you got a little bit of rise with one of the following (the 0.3 W/m2-K convection coefficient) :-) I was thinking primarily of reducing the convection coefficient in steps, maybe by halves, but 0.3 W/m2-K equates to R-19 (IP units), which seems like a lot to me. Does this building have a slab-on-grade, and if so, how are you modeling that? Can't think of anything else because from your description the building is largely empty.

Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 5/8/2013 12:13 AM, jeffreylauck wrote:

OK, here's a summary of what I've tried and the results:

Changed ZoneCapacitanceMultiplier from 1 to 2 ==> No change in peak time

Set convection coefficient for AllInteriorWalls to 7.7 W/m2-K ==> No change in peak time

Set convection coefficient for AllInteriorSurfaces to 7.7 W/m2-K ==> No change in peak time

Set convection coefficient for AllInteriorWalls to 1 W/m2-K ==> No change in peak time

Set convection coefficient for AllInteriorSurfaces to 0.3 W/m2-K ==> Peaks shifted to a later time for several of the days but it's not consistent

I'm beginning to think it's something other than convection. Any thoughts?

Thanks,

Jeff

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Joe Huang <YJHuang@...> wrote:
>
> From the sounds of it, i.e., hourly profiles are similar but just shifted forward, my
> guess is that the amount of thermal capacitance is okay, but that the coupling to the air,
> i.e., convection coefficients, are the source of the problem.
>
> Joe
>
> Joe Huang
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 108D
> Moraga CA 94556
> yjhuang@...
> www.whiteboxtechnologies.com
> (o) (925)388-0265
> (c) (510)928-2683
> "building energy simulations at your fingertips"
>
>
> On 5/7/2013 3:39 PM, Griffith, Brent wrote:
> >
> > An easy thing to try is to increase the sensible thermal capacitance of the zone's air
> > using the ZoneCapacitanceMultiplier:ResearchSpecial object.
> >
> > *From:*EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
> > *On Behalf Of *jeffreylauck
> > *Sent:* Tuesday, May 07, 2013 4:02 PM
> > *To:* EnergyPlus_Support@xxxxxxxxxxxxxxx
> > *Subject:* [EnergyPlus_Support] Re: Zone Temperature Peaks too Early
> >
> > Jean,
> >
> > Thanks for your response. I suppose it's possible that internal surfaces are slowing
> > convection heat transfer in the actual house, but there's not a lot of furniture in the
> > space. A small couch, a chair, and a table are about it.
> >
> > The only way I can think of to test this theory is to increase the roughness of the
> > internal surfaces in the zone. Do you have any other suggestions?
> >
> > Thanks,
> >
> > Jeff
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx <mailto:EnergyPlus_Support%40yahoogroups.com>,
> > "Jean marais" <jeannieboef@ <mailto:jeannieboef@>> wrote:
> > >
> > > Could it be that the actual convection from surfaces is different or more or less than
> > those modelled thereby transfering heat from surfaces to air faster or slower. Are there
> > more internal surfaces like furniture which could contribute the these effects?
> > >
> > > Jean
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, "jeffreylauck" <JeffLau ck@> wrote:
> > > >
> > > > Hello All,
> > > >
> > > > First off, thanks for a great community. I've learned a lot from searching through
> > the message archives over the past few months.
> > > >
> > > > I have a model of a Passive House that I am trying to validate using measured data
> > from the actual house. I've created an hourly schedule file for the lights, electric
> > equipment, window usage, blind usage, and hot water consumption based on sub-hourly data
> > collected at the site. I'm using a custom weather file from the roof-top weather station
> > that monitors dry bulb temp, relative humidity, wind speed and direction, and global
> > horizontal solar radiation. The diffuse radiation component was estimated using the Erbs
> > model prior to importing the data into the weather utility. Currently I'm only looking
> > at the summer of 2012.
> > > >
> > > > The problem I'm having is that the peak temperatures in the model occur 2-4 hours
> > before the measured data (2-3 hours in July and September, 3-4 hours in August). Here's
> > what I've determined so far:
> > > >
> > > > 1. It's not due to a time shift in the data. I've verified that all data is GMT-8
> > and that no Daylight Savings flags are included in the IDF.
> > > > 2. It's not due to a lack of thermal mass. I added a bunch of internal mass as a
> > test and the peaks were reduced but occurred at the same time as previous models. Also,
> > I'm using CondFD with 9 nodes and a 1-minute timestep.
> > > > 3. I don't think it's due to my custom weather file, as I get a similar results
> > using TMY data.
> > > >
> > > > Does anyone have any suggestions on where to look next? Any ideas would be greatly
> > appreciated.
> > > >
> > > > Thanks,
> > > >
> > > > Jeff
> > > >
> > >
> >
> >
>