Domain expertise is having the knowledge of the physical system we want to model. The model is an abstraction of the physical system and the simulation program executes calculations on the model to predict or explain the system’s behavior.
15 mins read
Written by Kian Wee Chen
Published on May 13th 2025
Current Modeling and Simulation Practice in Architecture Design
Architects are experts in building designs and building aesthetics. They use 3D models of varying abstractions throughout their design process to visualize their designs. This range from highly abstract 3D models in the early design stages for exploring design concepts to highly realistic models for presentation and communication to stakeholders in the detailed design stages. They use rendering programs (basically lighting simulations) with the 3D models to produce photorealistic drawings for presentation and prediction of the building design and aesthetics. Conventionally, this is how models and simulation programs are primarily used in architectural design.
With raising concerns of climate change, it is becoming common that architects model for Building Performance Simulation (BPS) even during the early design stages. BPS is a general term that encompasses all performance simulations related to building design. Daylighting and Heating Ventilation & Air-Conditioning (HVAC) related simulations are the two most commonly used by architects for predicting operational energy consumption. The general attitude towards BPS modeling is that since architects are already building 3D models for visualization, they should have the skill to effectively model for BPSs or more ideally the 3D model built by them can be readily converted for BPS with minimal modification. However, the 3D model abstraction for rendering programs differs significantly from the abstraction necessary for BPSs. Even within BPSs, daylighting, HVAC and structural simulations require significantly different modeling abstractions. As a result, most of the time architects have to remodel their designs for each different simulation based on their limited domain knowledge, making this a labor intensive and time consuming process.
The most common solution to this issue is by developing BPS plugins for 3D Computer-Aided Design (CAD) or Building Information Modeling (BIM) programs that is commonly used by architects. This enable architects to rapidly remodel their design within a familiar interface. If certain modeling rules are followed, in theory the BPS plugin can automatically retrieves and inputs the model into the simulation program. Or if the plugin is in a BIM program, in theory the BIM data is information rich, there should be minimal remodeling as the plugin should have sufficient information to readily convert the BIM data to a simulation model. This solution main drawback is it is program specific, it only benefits the users of a specific modeling program. I have discuss this issue in my other blog post on open workflows. However, this solution still do not address a more fundamental difficulty when architects utilize BPSs in their design, the lack of domain expertise when modeling for different BPSs. This is what I am interested to talk about in this article.
What is the Challenge of using BPS in Architecture Design?
The core difficulty of using BPS is architects lack domain expertise on the performances that are being simulated. This results in two issues, the inability to
- Prepare the model for input to the simulation and
- Judge the validity of the simulation results.
I will use a specific example to further elaborate on these issues. In modeling for OpenStudio Application, an open-source whole building energy simulation program, architects have to decide on the HVAC thermal zones. Thermal zones are not the same as architectural programming spaces. They are areas that share similar thermal condition requirements and thermal environment controls. In a real building, this is usually translated as the area that is sharing the same thermostat. That thermostat is providing thermal control by allowing users to define the air temperature setpoint and providing feedback to the HVAC by monitoring the actual air temperature. Thermal zones are not necessarily defined by solid objects like walls. In OpenStudio, thermal zones are defined by a closed volume geometry with no boundary surface thickness. The thermal properties are then defined in a construction object and referenced by the boundary surface that is using that construction. The construction object can be just air. Overlapping boundary surfaces of adjacent thermal zones have to be modeled in a particular way for the simulation to acccurately calculate the heat transfers. Due to the lack of HVAC knowledge, architects often confuse thermal zones with architectural spaces and model them incorrectly. As energy modeling has less tolerance for error, modeling practices acceptable for architectural visualization will not work for energy simulation. As a result, error arises and simulations are halted. I have only pointed out one issue concerning geometry modeling, not to mention the other HVAC parameters that are required for the simulation. Although, specifying HVAC parameters can often be solved with the use of HVAC templates once the geometries are properly modeled.
The second issue arises after a successful simulation run. Architects are not able to judge the validity of the results. Is the Energy Use Intensity (EUI), cooling and heating load profiles reasonable for this building type of this scale? This could be partially solved by running simulation on a typical building (PNNL provides a collection of typical buildings for multiple building types in various climates) before running the simulation on your design. Using a typical building as reference, architects might be able to have a better ball park on their results. However, it is still difficult to effectively utilize the simulations results to inform design decision. For example, if the results are not reasonable, “What has gone wrong in the model and how do I fix it?” If the results are reasonable, “What are the design variables I can change to improve the results?” It is difficult to make sense and use the result for design without the necessary domain knowledge. This example specifically illustrates the challenge when running whole building energy simulation with OpenStudio, but generally these issues apply to other BPSs too.
How should Architects use BPS in Design?
Some might ask “What do you mean architects lack architecture engineering knowledge? Shouldn’t they learn sufficient engineering knowledge from school and practice?” From my own experience being an architecture HVAC researcher and lecturer, architects I have spoken to generally lack the necessary engineering knowledge to effectively use BPS in design. It is only reasonable, in a design team there are already professional HVAC and structural engineers who are in charge of those aspects in a building design. So should architects use BPS in their design process? My answer to this question is still YES, but only when the building performances are significantly affected by the architectural design. One obvious example is daylighting as its performance is so closely linked to building orientation and window designs. If that is the case, architects will need to improve their architecture engineering knowledge. How much should an architect know then? They do not need to know as much as the engineers who are officially in charge of those engineering aspects. My view is they just need to know enough to effectively use BPS in their design process. Architects can then meaningfully consider high performance building systems when doing architectural design and facilitate an integrative design process when working with the engineers in the team.
This gives us a framework to reconsider our current architecture engineering education. I shall call it the BPS-based design oriented framework. By first defining the performance metrics useful for supporting architecture design decisions, we can then decide what are the appropriate BPSs to run to acquire those metrics during design process, and lastly learn the required engineering knowledge to meaningfully run the BPS and interpret the performance metrics for design. In my opinion, current engineering education in architecture are too detached from the design process. The knowledge is taught in isolation with no clear indication of how these knowledge can be directly applied in the architectural design process. Often times, students are overloaded with multiple architecture engineering domain knowledge (HVAC, structure, daylighting etc.) with no clear method of applying them in design. As a result, they lost interest and walk away with limited understanding on the subject.
Using a concrete example, daylighting in architectural design, we will first introduce the unit of Lux (lx) for measuring illumination. Lux measures the amount of illumination (light) falling on a horizontal plane. An acceptable value for doing office work is within range of 300-500 lx. We then continue to define an appropriate performance metric called Useful Daylight Illuminance (UDI) that could be useful for early design stages. UDI is defined as percentage of annual daytime hours that a given point in a space is within a specified illumination range, typically between 100-2000lx. The lower lux threshold can be adjusted based on the project, for example it can be adjusted to be 500 lx to ensure the space is sufficiently bright for office work. The upper lux threshold is based on the higher probability of glare when illuminance is above 2000 lx. We can then define the performance goal of 100% of floor space achieving 50% UDI.
Once the performance metric is clear, we can move on to learn about the simulation program and their underlying methods to calculate the performance metric. For example, an open-source program, OpenStudio Application is able to calculate UDI. We can elaborate on the underlying calculation method and practice how to model for OpenStudio Application. The key to this approach is it needs to focus on design oriented hands-on exercise. It is very important to explicitly state when to utlize this BPS, at which design stage and what are the design information required for the simulation modeling. Architects will learn the appropriate performance metric, how to model for the BPS, interpret the simulation result, and when to apply it in their design process. With this approach, architects can optimize their design throughout the process, but most importantly the BPS results will facilitate integrative design discussion with other engineering consultants.
Conclusion
I gave a brief description of the current BPS modeling practice in architectural design process and pointed out the main issue is the lack of domain expertise. This causes two issues; 1) the inability to appropriately model for BPS and 2) judge the validity of the simulation result. I suggest that the key to solving this issue is through improving the architecture engineering education by introducing a BPS-based design oriented curriculum. This will replace the current architecture engineering education that overloads architects with engineering knowledge with no clear method of application in design. It is a targetted approach that explicitly define the performance metric to attain, introduce the BPS program, how to model for it, and when in the design process to use the program. I hope such an approach will significantly improve engineering literacy among architects and allow them to make well-informed building performance related design decision in their projects. Architects have a major role in designing the built environment. They need to be equipped with effective architecture engineering knowledge so that they can be in a better position to facilitate and push for decarbonization of our built environment. I hope this post provides you some insights on the issue. What are your thoughts? Let’s continue the conversation in the comments!