Kiva^TM: a numerical framework for improving foundation heat transfer calculations

Abstract

Kiva^TM was developed to evaluate the energy performance of building foundation designs. This free, open-source tool can be integrated into existing annual building energy simulation software tools. This article describes the verification of Kiva's six numerical solution methods against the International Energy Agency Building Energy Simulation Test and Diagnostic Method test cases for slab-on-grade heat conduction. Comparisons of accuracy, computation time and stability between the numerical solution methods revealed their advantages and disadvantages. While each solution method satisfactorily approximates slab heat loss, many methods exhibited stability issues or required substantially longer computation time. The method least affected by these two challenges was the alternating-direction implicit (ADI) method. Kiva features four approaches of initializing the soil temperatures for an annual simulation. A new accelerated initialization approach is shown to reduce the required years of pre-simulation. The combination of the ADI method and accelerated initialization reduces the total computation time by 95% relative to the traditional implicit solutions.

Keywords:

• building foundation
• heat transfer
• numerical analysis
• computational performance

Acknowledgements

The authors would also like to thank Peter Ellis, President of Big Ladder Software, for allocating time and resources to enable this work.

Additional information

Funding

This work was funded in part by an American Society of Heating Refrigeration and Air conditioning Engineers (ASHRAE) Graduate Student Grant-in-Aid award. This work utilized the Janus supercomputer, which is supported by the National Science Foundation [award number CNS-0821794] and the University of Colorado.