Jeff,
You've mentioned that the modeled temperatures peak several hours too early, but how do the temperature profiles compare over the course of a day?
If the profiles are exaggerated, i.e., more swing than the measured data, then the amount of thermal mass in the model is probably too low.
If the profiles are similar, but just shifted forward, I would then second Jean's comment that perhaps the thermal mass is too tightly coupled to the indoor air, in which case you could play around with the air surface convection coefficient to see if you can get a better match. Please bear in mind that the convection coefficients are largely from measurements done on plate heat exchangers that have been repurposed to building energy simulations.
If this does work, I'd like to know your results, because (war story follows...) more than twenty years ago I had occasion to compare simulated to measured temperatures of a naturally conditioned house in California and found the former to be much more spiky. I had attributed the discrepancy to DOE-2's supposed poor handling of thermal mass, but maybe it was just a matter of using wrong inside air film coefficients.
Another thought to bear in mind is that in EnergyPlus, the solar radiation is the amount up to the time stamp, rather than from -1/2 to +1/2 of the time stamp.
Are you feeding the same into your custom weather file ?
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 5/7/2013 1:51 PM, Jean marais 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, "jeffreylauck" <JeffLauck@...> 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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