Big Ladder Software


KivaTM is a free and open source ground heat transfer calculation tool written in C++. Specifically, Kiva is used to calculate heat loss and gain on a timestep basis from building foundations. The goal is to create a tool that can integrate multi-dimensional heat transfer into standard building energy simulation engines.


  • Two- and Three-dimensional heat transfer calculations
  • Flexible description of foundation structural and insulation elements (including thermal bridges)
  • Models slabs, crawlspaces, and basements
  • Validated against IEA BESTEST for ground-coupled slabs
  • Generates ground temperatures for use in whole-building energy simulation tools
  • Control over numerical and meshing inputs, though knowledge of numerical analysis is not required


Kiva was created for Neal Kruis’s Ph.D. dissertation, “Development and Application of a Numerical Framework for Building Foundation Heat Transfer Calculations”. Previous to this work, very few software tools could simulate foundation heat transfer accurately within a reasonable amount of time. This work explored many of the time consuming calculations used in brute force calculation procedures. For some foundations, brute force approaches could require weeks to solve even on supercomputers designed for problems of this size.

Kiva was designed to provide a framework for testing different numerical approaches to calculating foundation heat transfer. The goal was to identify methods that reduce overall computation time without sacrificing simulation accuracy. After improvements to the numerical scheme, initialization methods, and by using a two-dimensional approximation, Kiva was able to solve the same problems within five seconds on a personal laptop.

Kiva is undergoing continuous development to transform it from a research tool to a tool that engineers and architects can use in the context of whole-buidling energy simulations. Kiva is now integrated into EnergyPlus, with more integrations in the works.