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Basic Envelope Change results in opposite EUI results of those expected

asked 2019-04-03 10:20:05 -0500

Mark's avatar

updated 2019-04-03 16:30:14 -0500

This is a very basic question. I have two OpenStudio files. The only difference is one wall construction with a higher R value between the two. After running the simulation, the file with the higher R value in an exterior wall has returned a higher EUI. I can't find the issue. Any ideas?

I have a link to Dropbox below. The Alt file has the improved Envelope.

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what climate? what causes the EUI increase - heating, cooling, or both? what kind of system? You need to include much more detail on your model for the forum to be able to help.

mdahlhausen's avatar mdahlhausen  ( 2019-04-03 10:32:10 -0500 )edit

It is in a Western Canadian Climate. Heating is increasing, no cooling system is installed. Am I able to upload the files somehow? Just change the extension?

Mark's avatar Mark  ( 2019-04-03 10:35:16 -0500 )edit

upload it to google drive or other service and then post the link above.

mdahlhausen's avatar mdahlhausen  ( 2019-04-03 10:44:04 -0500 )edit

Added link above in question.

Mark's avatar Mark  ( 2019-04-03 10:51:38 -0500 )edit

1 Answer

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answered 2019-04-06 14:59:17 -0500

Running the models and looking at the OpenStudio Results, I noticed some suspicious things:

  • The heating and cooling design load is zero.

image description

  • This is because there is no heating and cooling setpoint schedule assigned to the ThermalZone in the model

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Once you add thermostat setpoint schedules to both models you'll get results that make sense. Picture below shows where these schedules get added on the Thermal Zones tab.

image description

With more complex system types missing thermostats usually result in failing simulations, but with very simple system types like this single-zone furnace, sometimes the simulation will succeed but you'll see nonsensical results.

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It CAN occur just as you describe with a properly created HVAC system. When the building is cooling-dominated and in a moderate climate like climate zone 5, the envelope ihelps remove heat that otherwise needs to be removed by the cooling system. That, in turn reduces cooling energy. If you increase wall insulation, cooling energy and overall energy increases in that situation. My colleague Javed Iqbal presented on this topic at last fall's ASHRAE Building Performance analysis conference as it affected energy codes in Hungary. [link text](

Jim Dirkes's avatar Jim Dirkes  ( 2019-04-08 07:17:34 -0500 )edit

Thanks very much! I'm not sure how I missed that. Appreciate the help.

Mark's avatar Mark  ( 2019-04-09 09:48:13 -0500 )edit

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Asked: 2019-04-03 10:20:05 -0500

Seen: 225 times

Last updated: Apr 06 '19