PVVT Heating Airflow modulation

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Have an eQuest model where the PVVT systems will not increase the heating airflow up above the minimum flow ratio causing significant unmet hours (1,000s).

This occurs with both auto-sized and hard sized airflows & capacities, so its not a capacity issue. If the min-flow-ratio is set to 30% (as per design) and reverse acting t-stat the heating airflow does not increase. I can ‘force’ the heating airflow increase by specifying the heating-min-flow ratio, but that’s not really the design. Checking with wizard, the default min-flow-ratio is 0.67.

I can’t see or think of anything that would prevent the system from increasing its airflow and heating output to increase to meet the load. Hourly report for the ‘amount of heating needed to hold setpoint’ show the need heating capacity is less than the system capacity and that the model recognizes there is a heating need – but will not allow airflow & heating output to increase.

Initially thought this was a custom schedule or other ‘junk’ in the model, but this is occurring even with a dummy wizard model. The PVVT system(s) wont increase airflows from the min-flow-ratio in heating even with reverse acting t-stats.

What could be causing the model to not increase airflow in heating when the capacities are sufficient?