Ralph Muehleisen's profile - activity

What is the purpose of the change? Are you trying to simulate daylighting with clouds? Or solar generation? Then addi

Are you doing this to try to simulate opening doors and windows at night to provide natural ventilation?

If you are using EnergyPlus, the better way to do this is to use the air flow network and open windows.

Check out the AirflowNetwork_MultiZone_SmallOffice examples in the EnergyPlus examples directory that uses forced ventilation during the day and natural ventilation in the evening.

The info and links to NIST data in @mdahlhausen's answer is really good, so do make use of it even if you use the air flow network and simulate open doors/windows.

It should be. Complex electrical building loads are needed for microgrid, distribution, and transmission network design and control. NERC just made a requirement that transmission operators needed new complex dynamic load models for buildings for better reliability.

Adding to the list: 32. Electrical Storage (e.g. electric battery model)
33. Complex Electric Power calculations (ie. magnitude and phase)

As Amir suggests, DOE 2.2 doesn't have a VRF model. Modeling VRFs in eQuest was discussed in a previous question on Unmet hours in Question 294 .

So, a reviewer that is asking you to validate EnergyPlus against DOE 2.2 is quite uninformed. I would try to gracefully let the reviewer know that Equest/DOE 2.2 should not be used as a reference for validating your VRF model.

One thing you could do is use therm to model the curvature in small segements (to get the area close to right) and then do runs using standard vertical wall convection coefficients for the whole surface and the other using a convection coefficient appropriate for the largest angle. You can find convection coefficients for angled planes in the ASHRAE handbook of fundamentals in the heat transfer section.

Then you can get a bound on the U value you would have if you used software that computes true convection. If they end up being close, you might want to use the average of the two as your estimate. if they differ wildly (meaning that convection effects dominated heat transfer) then you know you probably need to go to a more complete heat transfer program like Fluent or Comsol Multiphysics. You might still use the average as a guess.

Oh, and is there a reason why the updaters from anything but the previous version are not included in the current release?

Including links in the readme to a place to download and install the required update files is helpful but why are they not included in the distribution in the first place?

The link in the readme (which I found after I had already found the files digging around the help site and posted this question) didn't seem to work right (I tried it after I had already downloaded the files). I didn't get a 404 but I couldn't download either. I had to go back to the main helpsite, go to the download directory and then look at the bottom of the download files to be able to find a link to the windows downloads that would actually download.

Is there a reason why the files to convert older energyplus files to the latest version are not included with the EnergyPlus releases? Can this be corrected?

At one time (and according to the current documentation) the files to update and IDF from older versions of EnergyPlus were not included for space reasons in the install package. That's obviously not a concern with modern internet technology. So, does anyone know why the older IDF update files haven't been incorporated into the newer releases?

With the move over to hosting the EnergyPlus downloads on github and updates to the main DOE front page, it is increasingly hard to find those files. It took me forever to find where they were hiding on http://EnergyPlus.helpserve.com

I think that making it difficult for users to make those updates from older IDF files is going to keep users away from EnergyPlus and OpenStudio. Adding these files into the standard EnergyPlus installer would be a great idea.

For the rest of the world, I did some experiments and analysis of other data to get some rough estimates. On my laptop, a small building runs in just under a minute and a larger building in closer to six minutes. A benchmarking program run with the same background processes yields a speed of 60 GFlops.

Figuring out the total number of floating point operations and then working back how many time steps, I get that a small building is, to rough order, about 1 kFlop and a larger building is about 10 kFlop.

I also got similar numbers working back from some results from ORNL where they ran 525k simulations on 130k CPU in about 68 min on Titan and knowing about the CPUs that were used (Opteron 6274s)

Now I can get some estimates of how much CPU power is required to do coupled building/transportation/grid simulations in large urban areas. Working from information about the building stock in Chicago, it takes about 10MFlop to simulate a time step of a 1 mi^2 area. The traffic system only takes about 100 kFlop per time step to simulate the same area. I haven't got estimates for a detailed grid simulation but I'm a bit scared that it will be several orders of magnitude higher computational requirements.

I need to give some rough "computational effort" numbers for looking at very detailed models for urban regions. What I need to estimate is how much CPU power is needed to model something like every building in a large urban area (New York, Chicago, LA, etc) at a very high time resolution (maybe even using the next generation energy modeling engine and going beyond EnergyPlus).

I can do some simulations of prototypical buildings and then use multipliers to get computational efforts. But, what I need to figure out is the number of floating point and integer operations needed to run a model.

Is there an output in some report in EnergyPlus or OpenStudio that gives the number of flops/IOPS? I can't find one.

Thanks,

If you are trying to represent the actual physics of infiltration, then you need to look at values of infiltration that are appropriate for your building type (see more info below). If you are using infiltration rate as a calibration parameter that you adjust so that your energy predictions match reality, then I advise you to find other parameters to adjust and go back to a more physically appropriate infiltration rate.

Infiltration is one of the parameters with the highest uncertainty for several reasons including 1) it changes in time and varies around the building, 2) there can be lots of leakage points on buildings that are not well known, 3) opening and closing of doors for people and equipment entering/leaving can sometimes dwarf actual infiltration but is often left out of the model. This is one reason why I advocate for using probabilistic modeling and actually propagating the uncertainty through the model.

Besides PNNL 18898 "Infiltration Modeling Guidelines for Commercial Building Energy Analysis " mentioned in a previous answer, there are several places to get information about infiltration in real buildings and modelling

Alex Berge of Chalmers University, did an MS thesis on the topic.

A good list of resources for measured infiltration can be found in AIVC TN 66:Building air leakage databases in energy conservation policies: analysis of selected initiatives in 4 European countries and the USA

Malcom Orme and Nurul Leksomono put together a ventilation modeling guide in AIVC Guide 5: Ventilation Modelling Data Guide.

Unfortunately, the AIVC papers/reports are not publicly available, but if you are in the right country, you can get free access.

Good Luck!

These tools are both simple in input and simplified in algorithm. Geometry is simplified to 8 walls (N, NE, E ...), one roof. Building is one zone only. Walls/windows are described by simple U values, SHGC, etc. Internal loads are defined in terms of power densities (W/m2). Ground heat transfer is ignored (ISO 13790 has a method but it's not included yet in any of our implementations or the GaTech version). Schedules are highly simplified too. I have a spreadsheet interface to generate an input file for our C++ standalone and/or MATLAB version.

I'll see what I can track down for you Neal. I know that Moncef Krarti of U. of Colorado has several papers in ASHRAE transactions and in Energy and Buildings that you can find in Google Scholar (but which won't give you access to the papers). My first introduction was in Kreider's book "Heating and Cooling of Buildings". I don't have access to it right now, but I'm sure there will be some references to the original work in there.

Sorry to disagree with you Neal but I do not believe that all those of us who think ground heat transfer are trying to avoid the calculations. I, for one, really like differential equations and would love and opportunity to apply neat methods like conformal mapping to solve the problems but with some problem types, such as high-rise buildings, the fraction of heat transfer through basements/floors is just too small to worry about.

In addition to SBEM and the OpenStudio implementation of the ISOmodel, another simple model/interface you might consider is ComCheck which is designed for use in checking compliance with prescriptive building energy code. I used to teach it to students as a great simple building envelope energy modeling tool. There are desktop and web versions.

ComCheck.

I don't think that comcheck does any real energy modeling though. As I recall (it's been a few years since I used it) it is an interface to a regression analysis of a pile of simulations done by Pacific Northwest National Lab. It may also no longer give an EUI but only the amount that the building "fails" or "passes" code by. I think the detailed reports may give the actual estimated EUI though.

SBEM is indeed a good and free implementation of the CEN/ISO 13790 methodology mentioned in the other answer. If you have no need of the rest of OpenStudio, you might take a look.

I don't know that the Georgia Tech spreadsheet has ever been officially publicly released. As @Amir Roth says, feel free to contact me for information on the OpenStudio implementation, a stand alone C++ implementation that is not yet released, or a MATLAB implementation of the the monthly ISO method.

So I guess the new working phrase for OpenStudio is going to be "there is a measure for that" :-)

Thanks for letting us now about it.

@Neal Kruis I think the time of day variation in heat load you discuss is so minimal that it never has to be a concern. The uncertainty in actual elevator usage dwarfs any possible effects on heating load. I agree that just changing the peak load should be fine. The hardest part is going to be getting justifiable data from the manufacturer to back up the reduction claim.

@Kent Benson, your link in the above address seems to be broken. Can you correct/update it?

@macumber, thanks for responding.

I am thinking of a production workflow where you do design work for a particular building, it would be great to be able to take the entire OpenStudio system + models and archive them. That way, if you have to revisit, you just extract the archive and run OpenStudio again. This lets you keep a working system intact in the archive but update the OpenStudio for new projects. Similarly, I could do the same for individual projects/papers/reports.

Ralph

@macumber, thanks for responding.

I am thinking of a production workflow where you do design work for a particular building, it would be great to be able to take the entire OpenStudio system + models and archive them. That way, if you have to revisit, you just extract the archive and run OpenStudio again. This lets you keep a working system intact in the archive but update the OpenStudio for new projects. Otherwise, you are refraining from upgrading your system to keep compatibility with old files.

In my own workflow, I'd love to keep all the files related to a single research project/report/paper together along with the full OpenStudio environment so that I can always go back and recreate my previous work without having to worry about compatibility issues.

Ralph

Dan, Thinking on this it would be incredibly great if there were a way to have an OpenStudio install be portable with all the config files housed in the install directory structure. I've seen a number of large packages do this (the largest of which is probably winpython). Has there been any thought to this? I'm sure its low on the priority list if it has, but it would still be nice to know it is being considered.

Irina,

EXTRA - New Info Just Posted 11/12/2014

Jason Glazer recently posted info on bldg-sim about the Building Technology Heritage Library. You might be able to get some info on old building construction from some of those docs

https://archive.org/details/buildingt...

I think you are going to be out of luck on this quest. We've been trying to find similar information for the past few years and have been unable to find any good studies of the kind. I've unsuccessfully tried to get funding to develop such a resource but I'll keep at it. Asking this question shows that industry really needs such a resource

For famous or historically important buildings, we have sometimes found drawings in architectural literature and magazines. When that fails, we see if the architect designed similar buildings of the same type that are described in the literature.

Besides the architectural journals and magazines, some resources we have used in the past for our projects include:

• ASHRAE Handbook (Fundamentals Chapters on Heating Load Calcs and Thermal Resistance Calcs)
• Architectural Time Saver Standards Building Materials and Systems
• Architectural Time Saver Standards Exterior Wall Design
• Mehta, Scarborough, Armpriest "Building Cosntruction, Materials, and Systems"
• Linda Brock, "Designing the Exterior Wall"
• Stein, Reynolds, Grondzik, Kwok "Mechanical and Electrical Equipment for Buildings"

Those resources help understand various wall designs. To assign an age to different wall designs we then tried to look up information about buildings of various vintages in other databases such as

• Emporis
• Commercial Building Inventory (from COMMBuildings)
• CBECS
• Buildings Energy Databook
• NEEA Commercial Building Stock Assessment
• DOE Building Performance Database (Interface makes this very difficult at present)
• NREL report "U.S. Department of Energy Commercial Reference Building Models of the National Building Stock"

Good Luck!

Joe, I absolutely agree with your comment about exfiltration needing to be made up. Pressurization can help reduce the required heating/cooling energy because you can use heat recovery to reduce the energy required to heat/cool the intake air, but if you set infiltration to zero, your system will never intake that extra air required to maintain pressurization and you will underestimate the intake air and the energy required to condition it.

Along with the high-level schematic is a fairly well informed set of default values for parameters and schedules. If you are limited in your data or just want a very quick rough answer, you can get it fairly quickly in eQuest using the defaults.

Some of these features are available in other commercial programs but I they are not yet available in as easy to use fashion in either EnergyPlus or OpenStudio.

To answer your equation about the equation, your equation is correct except the standard definition uses the same number for the base and threshold i.e. you would do HDD12 or HDD20 not HDD20/12. You sum up the difference in temperature between the base and the actual when the actual is above or below the base. You also need to use the average daily temperature. Most calculators will actually do the sum on an hourly basis and then divide by 24 to get the daily numbers.

An important question to ask is what base do you want to use? Here in the US where we do it in Fahrenheight, typical numbers for building scientists are HDD50/CDD50 and HDD65/CDD65. You can find lots of data at http://www.degreedays.net/

Your question about metric is not clear enough. What is the paper about and what are you trying to describe about the climate? Are you trying to just compare the required heating and cooling potential? Then HDD and CDD are fairly decent and well accepted.

If you want to succinctly discuss the effect on building design and overall energy including things like humidity, then I think talking about the ASHRAE climate zones is better (i.e. things like 2A, 4C, 7B, etc). These are more comprehensive, but coarse, distinctions. But, then you need to reference a paper that describes how these were determined rather than give an equation.

If you have a discussion of renewable energy in the paper, then neither describes the solar or wind potential at all and you would want another measure like average solar energy potential Wh/m²/day.

I too recommend the PNNL report as a starting point. Keep in mind that even if you use an infiltration model that uses wind speed variation to modify infiltration rates, you are very rarely using the right wind speeds. While the temperature and solar insolation might not differ much from your building to the weather station, the instantaneous wind speed and direction will often change greatly. So, the infiltration using the detailed model won't be right. I feel (only "feel", I can't prove) that you are just as accurate, for monthly and yearly calcs, to use a static infiltration rate that is only modified by the pressurization.

To clarify, I was saying the 3d to 2d conversion was more accurate than the 2d to 1d conversion. You are reducing your degrees of freedom from 3 to 2 which is a 33% reduction whereas when you do 2d to 1d it is a 50% reduction. I kind of think of it as bounding the error. In 2d to 1d I do the upper and lower limits and take the average, I should be within 50% of the right answer. Similarly, if I do that in 3D to 2D I should be within 33% of the right answer.

That said, if you can exploit symmetry in problems when you break it up (just like in 2d to 1d) you know your answer will be closer to the parallel path answer and you can take a guess closer to the high limit you get from the parallel path method.