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EnergyPlus Peak Gain Components Report - Timestamp

asked 2019-08-29 16:06:40 -0500

updated 2019-10-12 18:35:49 -0500

I have one simple and another potentially less simple question related to the Peak Cooling Sensible Heat Gain Components report (and its Peaking Heating counterpart). I'll keep the two questions separate for good housekeeping.

Question: How should I read these timestamp values? 02-SEP-06:02 26-JUL-08:01 07-SEP-08:01

I would expect 02-Sep would be Sep 2nd.. Then I'd infer that 06:02 means 5:02 or 6:02am, which doesn't make sense to me. First of all, I wouldn't expect a timestep to fall on 01 and 02 after the hour. I also wouldn't expect all my zones to have cooling peaks early in the morning.

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answered 2019-10-11 09:27:02 -0500

The Sensible Heat Gain Components report operates at the HVAC system timestep. When a zone temperature is changing quickly, EnergyPlus shortens the HVAC system simulation timestep. This typically occurs during morning recovery from setback. So, yes, the peak HVAC system sensible heating and cooling are happening during morning recovery on September 6 at 6:02 am and Jul 26 at 8:01 am standard time, which is likely 7:01 am clock time if daylight savings time is active. (All EnergyPlus timestamps are in standard time, DST simply shifts the schedules.)

To see this with the 5ZoneAirCooled example file, replace "hourly;" with "detailed;" and look at the csv variables output. The maximum value for "SPACE1-1:Zone Air System Sensible Heating Rate W" occurs at timestamp 02/25 06:01:52 and peak cooling is at 09/27 16:00:00. (Run with v9.2 and Chicago O'Hare TMY3 weather.)

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Thanks for the thorough response. Makes total sense now.. For load sizing, I'd prefer to have temp setpoints constant in "occupied" condition during all hours.. That way, systems aren't oversized when operations could use Optimum Start or a similar warm-up/cool-down sequence. But that's a completely different issue.

Greg Collins gravatar imageGreg Collins ( 2019-10-11 13:37:58 -0500 )edit

Can't you control this by setting the cooling and heating design day profiles for the temperature setpoint schedules constant in "occupied" condition during all hours?

anchapin gravatar imageanchapin ( 2019-10-11 13:42:32 -0500 )edit
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In theory, yes, but we are typically using E+ for CA code compliance with CBECC-COM which is super locked down.

Greg Collins gravatar imageGreg Collins ( 2019-10-11 13:48:57 -0500 )edit

Sizing is a separate issue from the Sensible Heat Gain Summary report which is populated during the actual simulation. There is also the Sizing:Parameters "Timesteps in Averaging Window" which helps to reduce oversizing due to setback recovery with a default of a 1hour sliding window for the peak load.

MJWitte gravatar imageMJWitte ( 2019-10-15 17:25:27 -0500 )edit

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Asked: 2019-08-29 16:06:40 -0500

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Last updated: Oct 11