Question-and-Answer Resource for the Building Energy Modeling Community
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I couldn't find anything specific in the reference either, but I ran a test and I believe that for ZoneHVAC:LowTemperatureRadiant:VariableFlow objects, the 'Maximum Hot/Cold Water Flow' inputs are maximum for the whole system, regardless of number of circuits.
For the test I had one model with hard-sized radiant system coil flow rates, and 'Number of Circuits' set to OnePerSurface, and Autosized Hydronic Tubing Length. The comparison model was identical, but with 'Number of Circuits' = CalculateFromCircuitLength, and various combinations of 'Circuit Length' and 'Hydronic Tubing Length'. For each model I output the System Node Standard Density Volume Flow Rate at the outlet node of the radiant system coils. Each run showed that the maximum flow rate at the coil outlet nodes equals the input maximum flow rate. Thus if the system has multiple circuits, the maximum flow is indeed split among those circuits.
