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Cooling Only (Design) Schedules and LEED Energy Modeling

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I am working on an energy model for a LEED project using Trace, it's my
first one, and I was going through the error comments Trace generates and I
saw a warning about using the Cooling Only (Design) schedule. Essentially
the warning was that ASHRAE requires schedules to be reflective of actual
occupant uses, and cooling only schedules wouldn't be realistic.

I use this schedule all the time when using Trace for HVAC loads but I'm
nervous now using it from energy modeling. Will this get me a review comment
if a reviewer see's that I used this schedule, or is this schedule pretty
typically used in an energy model?

Thanks.

Ben Hollon, EIT, LEEDR AP BD+C, MBA

Sep 16, 2013
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Ben,

I don't think there is necessarily a problem using this schedule as far as LEED goes, but I think you are hurting yourself by doing so. By making all loads 100% 24/7 you will drive energy consumption way up and dilute potential savings with high annual costs. LEED requires that systems cycle with occupancy and using this schedule indicates that all spaces are occupied all the time, therefore systems will run all the time. This schedule is ideal for load calculations as it presents you with a worst case scenario... 100% of loads for cooling and 0% for heating, however this will likely never be the case during actual operation. Personally, I like to create my own schedules that still include 100% 24/7 for cooling design, but weekday/weekend schedules that reflect actual occupancy. Keep in mind that heating design should always be zero, as you don't want people/light/receptacle loads to help heat the space when designing for worst case scenario. Ventilation schedules however should be set to 100% for heating design however, as this needs to be factored in for your heating worst case scenario.

Hope that helps!

Best,
Jay

Sep 16, 2013
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Ben, Reasonable schedules are extremely important for an energy model. They are one of the defining differences between an energy model and a design simulation. The Cooling Only schedule will make it so that whatever it is applied to will be 100% on 100% of the time, except during the heating design calculation. So if it is applied to lighting, then all of your lights will be on all of the time, day and night. So, it will be important for you to learn and understand how schedules are done in TRACE. To see the details of any schedule, go to the library/template editors. You can get to it under Actions-Edit Library/Templates. Once there, click on the clock. The schedule type is 'Utilization'. You can find the Cooling Only schedule there, along with many others. This is also where you can create your own schedules, which is often necessary. Chances are good that using the 'Cooling Only' schedule throughout your model will raise a red flag for the reviewer, and will give very distorted results. Good luck, and I hope this helps! Christian
Sep 16, 2013
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One more point - there are good "example" schedules at the end of the ASHRAE 90.1-2007 User's Manual.
We often use these as starting points, especially for speculative buildings.

Aaron

Aaron Dahlstrom, PE, LEED(r) AP

Sep 16, 2013
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I believe the cooling only schedules are meant to be for heating/cooling loads only.  This is why you should have separate files for your loads and model.

It wouldn't surprise me at all if LEED came back with a comment on it.  I usually use the built in schedules that are closest to what room conditions I have or I'll create my own.  Whatever you use - they have to match in both the base and proposed.

Sep 26, 2013
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