IBPSA-USA Research Committee: Automated 2D Heat Transfer with Grasshopper (1 LU)

The predominant tool for 2D heat transfer analysis is THERM which has a toilsome interface for drafting and post-processing façade details. The proposed interoperable algorithmic modeling (IAM) workflow utilizes the friendly drafting environment in Rhino as inputs to a Grasshopper (GH) file that utilizes open source Ladybug Tools to set up, simulate and post-process unique customizable heat transfer results. The GH file is interoperable with THERM and InDesign to generate and automate the generation of a consistent thermal analysis report. This workflow cuts down on production time, generates consistent outputs, and advocates interoperability in a user-friendly environment.

The IAM Workflow was used effectively for a hospital located in Minneapolis, MN. Many contributors were all brought to the table to evaluate the performance of an existing curtainwall. The extreme climate in conjunction with humidified zones is the perfect breeding ground for condensation. This fourteen year old hospital presented moisture reports within the first few years of occupancy. The specification of condensation resistance factor (CRF) was incorrect and also not a guarantee of no condensation as the present day two dimensional finite element thermal analysis reinforced. The hospital is replacing the punched window and curtainwall assemblies with the priority of eliminating condensation reports; this process involved the architect, owner, operator, contractor and simulation analyst collaboration to develop informed simulations to provide confidence that the new assemblies would eliminate the perpetual winter condensation issue.

Real time evaluation of framing options, material selection, and design detailing on weekly calls with the entire team created an environment of understanding and trust across the team. A valuable exchange of information occurred to better inform the two-dimensional heat transfer modeling of the fenestration details to ensure the design solution would deliver on reduced condensation reports and informed operational strategies on the design day conditions. Six weeks of collaboration and analysis with the team decided on a solution everyone stood behind. Façade replacement began during the winter when Minneapolis did experience actual design day conditions. This presented the modeler with the task of verifying that the ‘field measurements the client took at the existing condition and in-progress replacement assemblies matched the predicted temperature from the model. The delta between the actual and simulated surface temperatures was deemed acceptable as the restraints of the simulation software were explained. The accuracy of the surface temperatures gave further credibility to the simulation process as a predictive indicator of condensation risk probability and mitigation.