Up until now we've been talking about the TRACE 700 simulation as if it was calculating every day of the year separately. While TRACE can do that, that is not what happens by default. Using default TRACE data, you are actually calculating using a reduced year sequence of day types.

In order to understand a reduced year sequence, it's best to start with an actual sequence for simplicity. If we take a small subsection of the year, we're going to take Wednesday-Friday, July 12-14. If we look at the data from those days, July 12 has a pretty standard profile, July 13’s profile is slightly different and July 14th is a bit more different but without any substantial differences. The question is, “Why waste all this time calculating days that are nearly identical, especially if you're familiar with the time it takes to calculate some TRACE 700 files?”

Reduced Weather Schedules

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As a result, TRACE defaults to reduced year calculations, and there are only a four day types: weekdays, Saturday, Sunday and Monday. Holidays are treated as Sundays. The question is, “How can we calculate the energy in a 31 day month using only 4 day types?” If we look at July in the reduced year calendar, we notice there are 18 weekdays, 5 Saturdays, 5 Sundays, plus one holiday, or 6 Sundays, and 5 Mondays.

Now let’s do a sample calculation and say that TRACE ran through four days. On a weekday it calculated 100 kilowatt hours, on a Saturday it calculated 40 kilowatt hours, 30 kilowatt hours on Sunday, and 110 kilowatt hours on Monday because it had to make up for the drift points that it fell to over the course of the weekend. That is why Monday is calculated separately from weekdays. In a typical building, especially an office building or a school, we see a reduction in temperature in the weekend in heating mode and an increase in temperature in the weekend in cooling mode, which means Mondays have to work a little bit harder. If we stick to this example, you've seen the calendar on the previous slide, we can cross multiply the energy by the number of days. If we multiply each day type by the subsequent number of days, calculate the kilowatt hours total, we end up with 2730 kilowatt hours. While this may not be as accurate as a full year weather simulation, it's usually pretty close. The advantage here is that the program can calculate in one-sixth the time, and the other advantage is that all default TRACE weather files are actually reduced year weather. If we want to calculate in full year weather, we actually have to go and import a weather file, which we'll see in the next example.