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[EnergyPlus_Support] Re: Zone Temperature Peaks too Early
Joe,
Thanks for the suggestion. The building is in Portland, OR. I'll try using SLAB and see if that does anything.
Jeff
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Joe Huang <YJHuang@...> wrote:
>
> Achk!! So you're modeling the slab with no soil underneath and the ground temperature set
> at a constant 18C ? That's not very realistic. Where is the building
> located? I've never used the SLAB preprocessor, so take what I say following with a
> grain of salt, but you should model the slab with at least a foot or two of underlying
> soil in order to get its thermal capacitance in play with the building, and then use SLAB
> to get realistic ground temperatures at the appropriate interface between the modeled slab
> and the ground further down. For what I read, SLAB requires you in input the average
> monthly air temperature of the space above. For a passive building, that's difficult to
> determine, so you should start with the average daily air temperature and then iterate if
> necessary. Hopefully, this change will make an appreciable change in the resultant space
> temperature profile.
>
> 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 5/8/2013 1:42 PM, jeffreylauck wrote:
> >
> > OK, there's a lot of questions to answer so I'll try to be brief.
> >
> > The slab is modeled with three layers: 6.75" of perlite in contact with the ground, 4"
> > EPS insulation, and 4" concrete slab. Total R-value (IP) should be about 35. Ground
> > temps are currently set to the default of 18C year round. Surface emissivity of the
> > concrete is set to 0.9.
> >
> > The exterior wall has 4" of polyiso insulation under the siding, so I don't think
> > thermal bridging is significant. Also, like Joe, I would expect thermal bridging to
> > cause the peaks to be earlier if it was a significant source of gain.
> >
> > Infiltration is modeled using the ZoneInfiltration:DesignFlowRate object and is set to
> > 0.0105 ACH (with coefficients 1,0,0,0). This is based on a blower door test of the
> > actual house, which showed 0.21 ACH at 50 Pa. The 0.21 was then divided by 20 (based on
> > a paper by Max Sherman) to estimate the natural infiltration rate. I'm also using the
> > simplified models for zone mixing and zone ventilation. I realize AirflowNetwork would
> > be a better way to model this stuff, but I don't have any experience with it and I'm not
> > sure I have the time to figure it out.
> >
> > The actual house also has a heat recovery ventilator, which has exhaust ducts in some
> > rooms and supply ducts in others. I've modeled this using an air loop with a heat
> > exchanger, outdoor air system, a dummy cooling coil that is always off, and a fan that
> > is always on.
> >
> > The solar radiation question brings up a good point. Due to the limitation of one
> > shading surface per window, I have the operable windows modeled with only an exterior
> > screen and fixed windows modeled with only an interior blind. In reality, the operable
> > windows have both an interior blind and an exterior screen. I wouldn't think that the
> > interior blind would make THAT much of a difference, but is it possible?
> >
> > I'll try to get some charts posted of the measured vs. modeled temperatures. And, again,
> > thank you all for your help.
> >
> > Jeff
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx <mailto:EnergyPlus_Support%40yahoogroups.com>,
> > Joe Huang <YJHuang@> wrote:
> > >
> > > There might be a slight mix-up about the original model mentioned by Jeff. Since that
> > > model was done in EnergyPlus, I don't think any supposed problems of DOE-2
> > > in handling solar radiation at low angles would apply. Having said that, this is the
> > > first I've heard of DOE-2 having such a problem, so could you (Jason) inform me about it
> > > (preferably offline since it doesn't have anything to do with EnergyPlus...)?
> > >
> > > The difficulty I have with exploring thermal bridging is that wouldn't it tend to quicken
> > > even more the time of the peak?
> > >
> > > Having exhausted the other proposed remedies, I would like to get back to the modeling of
> > > the slab foundation.
> > >
> > > 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 5/8/2013 3:00 AM, Jason Quinn wrote:
> > > >
> > > > 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@
> > > > <mailto:YJHuang@>> 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@ <mailto:yjhuang@>
> > > > www.whiteboxtechnologies.com <http://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 <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> <mailto:EnergyPlus_Support%40yahoogroups.com>, Joe Huang <YJHuang@>
> > > >> <mailto: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 <http://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:%2AEnergyPlus_Support%40yahoogroups.com>
> > > >> <mailto:%2AEnergyPlus_Support%40yahoogroups.com>
> > > >> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> <mailto:EnergyPlus_Support%40yahoogroups.com>]
> > > >> > > *On Behalf Of *jeffreylauck
> > > >> > > *Sent:* Tuesday, May 07, 2013 4:02 PM
> > > >> > > *To:* EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> > > *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>
> > > >> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> <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>
> > > >> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > >> > > <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
> > > >> > > > >
> > > >> > > >
> > > >> > >
> > > >> > >
> > > >> >
> > > >>
> > > >
> > >
> >
> >
>
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