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Why doesn't my HVAC energy demand reduce when I change the U-value of my windows?

asked 2019-11-21 12:29:18 -0600

SG's avatar

updated 2020-01-13 16:40:34 -0600

My building is an office building essentially made of glass, but when I increase the U-value of all the windows the total energy consumed (in GJ) doesn't change - for lighting or for heating/cooling.

Can anyone advise why this is? Thanks.

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we need more information to answer the questions. Specify which software you are using. My guess is the windows you are changing aren't assigned in the model. If you are using a default construction set, make sure there aren't any hard-coded constructions at the space or building story level.

mdahlhausen's avatar mdahlhausen  ( 2019-11-21 13:34:57 -0600 )edit

Hi thanks for responding! Sorry for not specifying but I made my model in google sketchup and am now running Openstudio. I have double checked that I'm changing the assigned windows so that can't be it :( How would I check if there are hard-coded constructions?

SG's avatar SG  ( 2019-11-21 14:43:09 -0600 )edit

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answered 2019-11-21 18:32:51 -0600

@SG, did you confirm the proper construction is assigned to the windows in the input file, or looking at the envelope section of the EnergyPlus HTML file. I would recommend the second option. The next thing to check is to confirm that the zone that contains has a thermostat and also equipment serving it. Also, to clarify the question, are you saying the peak demand didn't change or the energy consumption annually didn't change? In either case are the values exactly the same or off by a very small fraction?

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@David Goldwasser I confirmed by checking my construction set in OpenStudios and what materials were associated with each construction. Annual energy consumption was exactly the same despite window material. I see now that I hadn't applied the set points - oops!

SG's avatar SG  ( 2019-11-21 21:14:32 -0600 )edit

another unmet hours questions solved in the karma-less comments ;)

mdahlhausen's avatar mdahlhausen  ( 2019-11-22 10:35:47 -0600 )edit

Sorry I'm new to this forum and unsure how to mark the comment as an answer!

SG's avatar SG  ( 2019-11-22 13:29:40 -0600 )edit

we need to respond to your question as an answer, not a comment. it's on us.

mdahlhausen's avatar mdahlhausen  ( 2019-11-22 16:15:32 -0600 )edit

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Asked: 2019-11-21 12:29:18 -0600

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Last updated: Nov 21 '19