[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

subject: [EnergyPlus_Support]] Unmet Load Hours Linked to NightCycle Cycling Run Time?





Hi All -

I'm investigating the inability of my EnergyPlus model to maintain setpoint during unoccupied hours.

The short story:

For my centralized VAV system (modeled through template objects), it appears that the AvailabilityManager:NightCycle control (cycleonany) is working properly for the time input into the "Cycling Run Time" field (currently set for 3,600 seconds - 1 hour). However, at the end of the cycle, the equipment drops to zero for one timestep, before cycling back on for an hour. Thus, running the model with 6 timesteps, the cooling coil energy will have values for 6 timesteps, then a zero, then values again for 6 timesteps, then zero, etc. This causes a drop in the VAV damper position and an increase supply air temperature (cooling) for said timestep, which allows the zone temp to float above the setback. I have no idea why it is doing this.

Image of a Sunday and Monday - notice the cycling of the AHU-2 cooling coil energy and VAV terminal damper temperature (https://drive.google.com/file/d/0B6aA8ZsOIiibNGh5VWFSNjh0MFE/view?usp=sharing)

The long story:

100+ zone, 2-story school. I used the HVACTemplateSystem:VAV, HVACTemplateZone:VAV, and constituent plant objects to model 6 air handling units for the various thermal zones of the building.

The zone I'm analyzing is an office zone, and I double checked all internal loads to make sure nothing was out of whack.

I've looked at the chilled water temperature leaving the plant and entering the air handling units, and the water temperatures look good. Its only the air temperatures leaving the coil that oscillate with the cycling behavior.

I've tried to change the "Cycling Run Time field: in the AvailabilityManager:NightCycle, but the mysterious zero values still happen at the end. It's as if it takes a timestep for the system to realized it needs to come back on. I'm running the model at 6 timesteps, which is the only reason I saw the mysterious zero values in the first place.

Also, looking at the other 5 air handlers, they all exhibit the same cycling behavior - EXCEPT the gym zone. It is the only one that doesn't, but I'm fairly certain everything is modeled the same. Here's an image of all 8 air handling unit cooling coil energies, notice the cycling during the unoccupied times (https://drive.google.com/file/d/0B6aA8ZsOIiibZW80QUlaQXl3VWM/view?usp=sharing)

Link to the expanded .idf file - set up to run for 1 week in June, 6 timesteps (https://drive.google.com/file/d/0B6aA8ZsOIiibaV9hbUtvYTFQMU0/view?usp=sharing)

Link Hourly CSV File (https://drive.google.com/file/d/0B6aA8ZsOIiibbl9aQ3JVNTA3RHc/view?usp=sharing)

Cheers and thanks for any help!



Jacob Dunn - LEED AP


"Building services today are essentially mechanical compensations for the fact that buildings are bad for what they are designed for--human life"  - Bjarke Ingels


__._,_.___

Posted by: Jacob Dunn <arch.dunn@xxxxxxxxx>


Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.




Visit Your Group
Yahoo! Groups
PrivacyUnsubscribeTerms of Use

__,_._,___