Multizone air infiltration and ventilation simulation software
COMIS is a multizone air infiltration and ventilation simulation program, developed by an international group of experts at the Lawrence Berkeley Laboratory. It is based on a nodal model, in which each space, assumed to be homogeneous, is modelled by a node characterised by its temperature and pressure, and possibly contaminant concentrations. The nodes are linked by non linear conductances, modelling the air paths (cracks, openings, ducts, etc.). Pressure coefficients, relating wind velocity to wind pressure can be attributed to external nodes. Not only wind effect, but also buoyancy resulting from temperature and air composition differences, as well as fans, are taken into account. Using air mass conservation, a system of non linear equations is built and solved, providing air flow rates through all conductances.
Within the International Energy Agency Energy – Conservation in Buildings and Community Systems – Annex 23 research program, this code was greatly improved and completed, and a careful evaluation of the multizone nodal air flow simulation code COMIS was performed under the responsibility of the LESO. The purpose of the evaluation of a computer code is to assess its limits of validity (i.e. to verify its validity within some limits) and to improve its useability. Several tasks are required for this purpose: code check, sensitivity analysis, inter-model comparison, experimental comparisons and user tests.
Code was first checked by the authors of each module, then run on several benchmarks.
Sensitivity analysis is an unavoidable step before inter-model or experimental comparison. Such a study provides the variations of the outputs related to variations (or uncertainties) in the inputs. New in this research programme was the use of the theory of experimental planning to perform the sensitivity analysis. This allowed us to obtain a large amount of information with a minimum of work.
A large experimental validation was performed, using comparisons with many experiments in several countries. For each comparison, a sensitivity study was performed. This showed that the sensitivity itself depends on the case studied. Therefore, in order to know the confidence interval of the results of a simulation, a sensitivity analysis should be performed in each case. A module was hence added to the user-friendly version of the code to allow for such studies.
For the user test, the code was distributed together with a problem to several users, asking them to solve the problem. Resulting input and output files were collected together with the comments of the users. Comparisons of the results showed misunderstandings of the user guide, which was then greatly improved.
References:
- Feustel, H.-E. and Raynor-Hoosen, A. (Editors) (1990): Fundamental of the Multizone Air Flow Model COMIS. AIVC Technical note 29, Air Infiltration and Ventilation Centre, Coventry.
- Fürbringer J.-M., Roulet C.-A., Borchiellini R. (Editors) (1995): Evaluation of COMIS, final report IEA.ECB&CS Annex 23 Multizone Air flow Modelling, LESO-PB, EPFL, 1015 Lausanne Switzerland.
- Fürbringer J.-M., Roulet C.-A., Borchiellini R.: (1996): An overview on the evaluation activi-ties of IEA ECB&CS Annex 23. Submitted to Energy and Buildings
- Fürbringer J.-M., Roulet C.-A. (1996): Confidence in simulation results: Put a SAM in your model. Submitted to Energy and Buildings.
- Roulet C.-A. and Cretton P. (1996): The Influence of the User on the Results of Multizone Air Flow Simulations with COMIS. Submitted to Energy and Buildings