Using Pipe-Flo and HYSM flow analysis modeling tools, we have built and managed computer models for large and complex hydronic systems, which have included multiple pumps, cross-ties, tanks, chillers, and boilers. The key to accurate modeling is obtaining accurate field test data. Without the accurate test data, you never know if you have a good model. Once verified, systems can be optimized for upgrades, including resizing pumps, replacing pipe sections that are too small, or identifying system coils that are undersized or not working properly. The customized data loggers have proven to be a very useful tool when developing models for complex projects.