This paper presents the major findings and summary of ASHRAE Research Project 852. The objective of the research was to provide a firmer rational basis for the selection of a public domain computer modeling software that can be used to simulate the complex behavior of ducted air distribution systems used for space conditioning in residential and small commercial buildings. Three distinct stages were used to accomplish the research project. The first stage was to identify candidate duct computer models based on the criteria required by the project. Five public domain models were preliminarily selected: HOUSE II, HVACSIM+, ESP-r, FSEC 3.0, and a model developed at a national laboratory in California that will be referred to as the Berkeley model. The second stage was to determine the accuracy of the pertinent numerical solutions and algorithms employed by each model using a series of problems with known, exact analytical or benchmark solutions. The evaluation results showed that the HOUSE II and HVACSIM+ models did not meet the minimum criteria of the project. The third stage was to investigate the three remaining models by comparing results from a group of parametric simulations where the problems consisted of a series of interconnected pressure vessels (building spaces) interacting with a leaking forced-air distribution system and the outdoor atmospheric environment. General conclusions were drawn from the analysis of simulation results. The ESP-r model showed acceptable agreement for all the analytical test cases; however, simulation results were not always consistent with expected results for whole building simulations. The Berkeley model did not provide acceptable solutions for all the analytical test cases and sometimes predicted unrealistic distribution efficiencies for the whole building simulations. The FSEC 3.0 model showed excellent agreement for all the analytical test cases, and whole building predictions were consistent with expected results. The recommendation from the present research is to select the FSEC 3.0 model as the simulation tool of choice for air distribution system analysis used by Standard Project Committee 152P.

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