Thermal Loads - Design Day vs. 3 Months run

@chris and team,

When I get the load calculations I’m trying to get the worst day of summer per room (one room will different than the other) . I’m trying to get the worst time for cooling per each room to size my equipment.

For example:
Apartment 1 will have a max solar gain different day than apartment 2 but the model is based in one design day. I tried to upload the ddy but still get my sizing base in one day.

Can I make a ddy that ranges 3 months and chooses a peak design day depending on the max load per room?


Hi @casasola8877 ,

I am not completely clear about your question but maybe it helps to know that design days are only ever one day and not 3 months. Still, you can specify as many design days as you want in a .ddy file so you could plug in a .ddy with 90 design days and E+ will run all of them and use the one with the highest heating/cooling demand to size the system.

You can build your own design days and .ddy files using the components under the Dragonfly Alternate Weather tab, specifically the DF Construct Design Day and DF Write DDY components.

But there’s a reason why design days are the way that they are and there’s no solid evidence that you’ll get a better result by picking 3 months of a TMY EPW to size your system rather than using the TMY .ddy files, which are also derived from statistical analysis of several years of observed weather data.