Simulation tab on Model Options dialog and Options tab on Simulation Options dialog.
This data allows you to specify global heating and cooling sizing ratio default settings. These ratios will be applied at the zone level to all of the zone heating and cooling loads and air flow rates. These adjusted loads and air flow rates are used to calculate the system level flow rates and capacities and are used in all component sizing calculations.
Note: In theory the zone heating and cooling sizing factors are applied where not overridden in HVAC zones, however there is no way in DesignBuilder HVAC to not override these values so in practice these settings will have no effect on the simulation. The Design averaging window period does have an effect though.
You can also specify the width of a moving average window which can be used to smooth the calculated zone design flow sequences.
See also Autosizing HVAC Components for more detailed information on how autosizing works in DesignBuilder EnergyPlus.
The global heating sizing ratio applied to all zone design heating loads and air flow rates.
The global cooling sizing ratio applied to all zone design cooling loads and air flow rates.
The number window period which is used to calculate the load timesteps in the zone design flow sequence averaging window. The
default is 1, in which case the calculated zone design flow rates are averaged over the hour.
The zone design air flow rate calculation is performed assuming a potentially infinite supply of heating or cooling air at a fixed temperature. Thus the calculated design air flow rate will always be able to meet any load or change in load no matter how large or abrupt. In reality air flow rates are limited by duct sizes and fan capacities. The idealized zone design flow calculation may result in unrealistically large flow rates, especially if the user is performing the sizing calculations using thermostat schedules with night setup or setback. The calculated zone design flow rates are always averaged over the load timestep. The user may want to perform a broader average to mitigate the effect of thermostat setup and setback and prevent the warm up or cool down flow rates from dominating the design flow rate calculation. Specifying the width of the averaging window allows you to do this.
For example, if the Design averaging window period is to be 1 hour and the number of timesteps per hour is 4, then the zone design air flows will be averaged over a time period of 1 hour or 4 timesteps. Specifying 2 would result in averaging over a 2 hour period and 8 timesteps.