Why do we need 7 design days ?

asked 2018-09-19 01:03:10 -0500

Siv's avatar

Whenever I import a DDY file into OpenStudio, I am able to see 7 design days. 4 for summer and 3 for winter. Why do we need 7 design days ? what is the significance of this? Isnt one design day for summer and one for winter sufficient ?

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To me that's duplicated from https://unmethours.com/question/17053... see my answer there, I explain the design days and when you need each. If you only have simple equipment, and no cooling towers, you could get away with using only 2 design days. I suggest closing this thread

Julien Marrec's avatar Julien Marrec  ( 2018-09-19 02:26:12 -0500 )edit

Thank you, I just have a small doubt, suppose I add cooling towers to my model and cooling is the only objective, should I include Condns WB=> MDB in addition to DB=>MWB or just Condns WB=> MDB will suffice.

Siv's avatar Siv  ( 2018-09-19 04:00:50 -0500 )edit

Try both, look at your peak cooling and sizing values, and decide for yourself. My advice is that when articulating the model or debugging, it's fine to use only two sizing design days to speed things up. Worst case you just add it in the final run.

Julien Marrec's avatar Julien Marrec  ( 2018-09-19 06:36:03 -0500 )edit


Siv's avatar Siv  ( 2018-09-19 07:05:21 -0500 )edit

I personally tend to use both Condns WB=> MDB and DB=>MWB whenever I have cooling towers, regardless or whether I have other cooling eq., but I don't have any hard evidence that it's warranted.

Julien Marrec's avatar Julien Marrec  ( 2018-09-20 04:46:23 -0500 )edit