difference between calulated design load and user design load

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The calculated design load is the load calculated by EnergyPlus based on your thermostat setpoint, your design day and your Sizing:Zone parameters.

The user design load is simply the calculated design load multiplied by your Sizing:Zone "Zone Heating Sizing Factor" or "Zone Cooling Sizing Factor"

From the Output Details and Example documentation, Zone Sizing Information (eio output file - same information goes to both the eio output and table output):

Field: Calc Des Load {W} The unaltered zone load resulting from the zone sizing calculations, using the design weather and schedules specified in the input.

Field: User Des Load {W} User Des Load is the load after user specified adjustments and is the load actually used for sizing components. Following the calculations (as in the previous field) various adjustments can be made based on user input - the most obvious is a sizing factor; but it could also be something like cooling min air flow per zone area or just a user input design flow rate.

Field: Calc Des Air Flow Rate {m3/s} This is the calculated design air flow rate in m3/s. The calculated design air flow rate is the "non-adjusted" air flow rate. It is the air flow rate sufficient to meet the zone loads from the design day simulation.

Field: User Des Air Flow Rate {m3/s} User Des Air Flow Rate is the flow rate after user specified adjustments and is the flow rate actually used for sizing components. Following the calculations (as in the previous field) various adjustments can be made based on user input - the most obvious is a sizing factor; but it could also be something like cooling min air flow per zone area or just a user input design flow rate.