Unmet Hours

Energy-plus report - peak load and design load

asked 2018-02-27 08:33:15 -0600

D.l22
51 ●3

updated 2018-03-02 02:25:18 -0600

Hi, I'm new in using energy-plus simulation and i have some questions about cooling/heating peak conditions. In the summary i got a "Difference" (difference between peak design load and sensible-instant and sensible-delayed) very high and i don't understand why. How does Energy-plus get the "peak design load" value?

ps. i use Energy-plus with Sefaira plug-in for Revit and coils loads between Sefaira report and Energy plus report don't match...

Thank you $C:\fakepath\SEF.PNG$

Comments

Which outputs specifically are you looking at? Zone loads or system loads? Maybe it would be useful if you could post a screenshot or something of what you are looking at.

bbrannon4 ( 2018-03-01 23:40:27 -0600 )edit

I attached a screenshot, thank you

D.l22 ( 2018-03-02 02:25:30 -0600 )edit

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answered 2018-03-06 15:38:54 -0600

mdahlhausen

9499 ●19 ●11 http://openstudio.net/

The Peak Design Sensible Load [W] comes from the heat balance algorithm, and the Estimated Instant + Delayed Sensible Load [W] comes from an estimation of contributions to the sensible load from the zone components load summary.

Read through the Zone Component Loads Summary section in the EnergyPlus Engineering reference to get more of an idea of how the software is calculating the component loads:

"The Estimated Cooling Peak Load Components and Estimated Heating Peak Load Components subtables of the Zone Component Loads Summary report contain values that are estimated and are not part of the normal heat balance algorithms used in the rest of EnergyPlus. In particular, the column described as Sensible-Delayed represents an estimate of the sensible load contributed at the peak time based on radiant contributions from various load components that have radiant portions in previous timesteps. The focus of this section will be on the Sensible-Delayed column."

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Comments

Agreed. Ideally these total values would come out as (near) equal. Personally, if the 'estimated instant + delayed sensible load' varies from the 'peak design sensible load' by more than a few %, I don't trust the results from the zone component load breakdown. This usually means the decay curves from the estimation procedure aren't producing results that are well aligned with the heat balance algorithm for that particular zone/run.