Ask a Modeler: Are There Any Aspects of Buildings That Current Simulation Tools Do Not or Cannot Address?


Are there any aspects of buildings that current simulation tools do not or cannot address?
-Testing the Limits

Dear Testing,

The short answers are yes and yes, which is why whole building simulation engines and modeling tools are continually evolving. When developers consider adding a new functionality, they perform a balancing act of the impact of a building characteristic or element on consumption, equipment sizing, comfort, and safety against the cost and complexity of implementing, modeling, and simulating that building characteristic or element. In many cases a single whole building simulation tool does not need to solve the entire problem. As brought up in last month’s “Ask a Modeler” thermal bridging analysis is typically performed as a pre-process to produce inputs needed for 1D heat transfer in whole building energy simulation engines. Yes, it would be nice if these became tightly integrated into a seamless user workflow in more simulation tools to provide more transparent representation of thermal bridging inputs; but it is possible today for an energy modeler to link these tools together to make the connection. Ground modeling in EnergyPlus, which used to be handled as a pre-process and is now directly available with Kiva integrated into EnergyPlus1, is an example of improved integration.

So far, I have mentioned phenomena that can be simulated but have low priority to implement in whole building energy modeling tools. More pressing are the high priority issues for which we still lack effective simulation methodologies. Consider how building simulation tools might deal with Covid-19 transmission. Every business would like to know how modifications to mechanical systems and other factors of operation (such as social distancing, staggered schedules, temperature checks, remote working) will affect the likelihood of Covid-19 transmission. They want to know this within a well-defined uncertainty distribution and beyond this, how these changes will impact the sales in retail settings, or employee effectiveness in an office or manufacturing setting. This would be challenging with a well-known virus but is almost impossible for a novel virus for which epidemiological data is unavailable.

Building simulation tools offer promise to tie together aspects of Covid transmission such as airflow, mechanical systems, occupant schedules, and individual risk factors. However, we cannot just strap existing simulation tools together to answer this; yes, CFD and existing contaminant simulation capabilities would be very helpful, but we need a better understanding of the virus, and details around occupant interactions and behavior to confidently determine risk of transmission within the building. If our analyses are going to be used to make decisions on building operation, HVAC controls, or equipment changes as buildings more fully reopen, we need to be very confident that any measures we recommend have a positive or negligible negative impact on occupant health. 

So, what do we need to enable simulation of transmission well enough to produce actionable insights? Time, experimental transmission lab data from interdisciplinary research across medical and building science organizations, and an epidemiological feedback loop before and after implementation to monitor and improve the input data, the model, and the simulations. Initial solutions will be strapped together using multiple tools to solve the immediate need. Research to develop models to represent transmission are already producing results, such as the “COVID-19 Airborne Transmission Estimator2 developed by Jose Jimenez at the University of Colorado-Boulder. This is just one of many transmission models that have or will be developed that whole building energy modelers can leverage. While Jose Jimenez’s model works from high level inputs, I expect some transmission models will make use of more detailed inputs such as the position of HVAC elements, interior partitions, and occupants. The more detailed models will likely build on top of existing CFD analysis capability as well as discrete event simulation tools such as AnyLogic, which has already been used for modeling occupants, assets, and procedures in healthcare facilities.3

So yes and yes, there are aspects of buildings that current whole building simulation tools do not address because they are low priority, and others that we cannot address yet, but are working hard to do so in the future. The answer is to tie together multiple tools into streamlined workflows, and to continue research in the areas we don’t yet understand well so that we can provide better solutions in the future. Also, remember that you can be a part of setting priorities for developing and implementing new features. Most building simulation tool developers are eager to hear from you how you use their products and what they can do to better meet your needs.


David Goldwasser, LEED AP, Board of Directors IBPSA-USA 
Software Developer and Researcher, National Renewable Energy Laboratory - Buildings and Thermal Sciences Center




Do you have anything to add or your own answer to contribute? Please share your thoughts by emailing; you are an expert too! Do you have your own question for the expert? Submit your question to be considered for a future column. Note that questions requiring an immediate response should be submitted to the community of experts at If you are interested in replying to a question as a featured expert or have any other feedback about Ask a Modeler please email

See past columns in our "Ask a Modeler" archive.