Simultaneous Heating and Cooling and Unmet Load Hours

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Hi all,

I've spent countless hours trying to troubleshoot unmet heating hours, as well as determine why I have simultaneous heating and cooling. I suspect that it's a controls issue, but I cannot figure out what the issue is. The unmet load hours isn't crazy significant--around 450 hours--however, the simultaneous heating and cooling is what is bothering me the most. I want to make sure that I'm modeling the building as accurately as possible, as opposed to building it with questionable "workarounds" to get rid of unmet hours.

Some background on the model:

  1. I'm using eQuest 3-64 for LEED-IDC v4. The model in question is the proposed model.
  2. Some spaces in the building aren't in scope. For the model these thermal zones were moved to two thermal zone groups I made: "Not Conditioned" (not owned by tenant) or "Whiteboxed" (owned by tenant, but aren't being developed as part of the LEED scope). These spaces were specified to be unconditioned in the internal loads section and in the air-side HVAC section. The "Surface Type" of the floors and ceilings of the in-scope spaces that were adjacent to non-scope spaces were specified to be adiabatic. All system equipment capacities have been downsized based on in-scope area per the LEED guidelines.
  3. The building has IDF/MDF rooms, which are cooled via CRAC units (I'm assuming this means that there will be cooling all year round, but not to the extent at which it is). There is also a commercial kitchen and I have accounted for the resulting sensible heat load to the space.
  4. Most of the ventilation is provided by three VAV AHUs. For the model I combined these into one AHU because they serve one medium pressure loop. All of my thermal zones with unmet hours are served by this main AHU.
  5. The AHUs have HW heating in the winter to temper the air, but most of the heating should be provided at the zone level, which have HW FPBs/VAVs with HW reheat, as well as HW baseboard heating.
  6. Spaces with a roof heating load should be served by FPBs, while most other spaces are served by VAVs. Right now the air-side system type is modeled as "Variable Air Volume" with VAV boxes only and baseboard heating.
  7. The design space temperature is 75F in cooling and 70F in heating. The main AHU is scheduled to be off at night and the zone fans are to cycle during this time.

Things I've tried:

  1. Changing "HMax Flow Ratio" from default of 0.5 to 1.0. I did this incrementally in steps of 0.1, but ultimately found that 1.0 was the best solution.
  2. Specifying a capacity for the perimeter baseboard heating and changing the control setting from "Outdoor Reset" to "Thermostatic." This reduced unmet hours, but the only way to optimize the model was to only do this in zones with unmet hours. When I did this to all perimeter zones, the consumption skyrocketed, as well as the simultaneous heating and cooling.
  3. Varying the system level "Hot Deck Max Leaving Temp" and the "Reheat Delta T". This did not significantly reduce unmet load hours unless it was 120F and reheat was 70F. Realistically, this should be 55F and 40F reheat (at most), which is where it's at right now.
  4. Right now I have values for "Hot Deck Max Leaving Temp" and "Reheat Delta T". I tried to restore the "Hot Deck Max Leaving Temp" to default values, but eQuest was terminating the simulations when I did this, even if I entered in a value for "Zone Entering Max Supply Temp."
  5. Changing the throttling range from 2F to 4F, which helped with the unmet load hours, but this is not my preferred way to address the unmet load hours (see reasoning below in question section).
  6. Messed with schedules. So many schedules. Temperature, occupancy, equipment, etc.

Things I've noticed:

  1. I have unmet heating hours during June, when heating shouldn't be available. This makes me think that I'm having a controls issue, where both heating and cooling are fighting to serve these spaces.
  2. The baseboard heating isn't turning on unless I specify a capacity and change the control setting from "Outdoor Reset" to "Thermostatic"
  3. When the hot deck leaving temp was set to be the same as the minimum cold supply air temp (and therefore less than the max cooling supply air temp), the program crashed.

Questions I have:

  1. What is the best way to model a VAV AHU which serves a mix of FPBs and VAV units? When I chose "Variable Air Volume" as the system type, eQuest won't let me simulate a mix of FPBs and VAVs (it was terminating the simulation). I tried selecting "Powered Induction Unit," which did let me simulate a mix, but this was resulting in even more unmet hours.
  2. I tried changing the throttling range from the default of 2F to 4F, which helped with the unmet hours, but is this allowable? I'm not sure if this would be considered finagling with the model. I would prefer to get rid of these unmet hours by addressing the simultaneous heating and cooling.
  3. I just realized this--some of the spaces that aren't in scope are adjacent to in-scope spaces, and the interior wall partitions between the two have not been specified as adiabatic. Could this be a source of my issue? I should note that I was having issues with simultaneous heating and cooling prior to addressing these not-in-scope spaces.
  4. Does anyone have any leads as to what the main source of my issue is, given the provided information? I've been browsing forums and can't pinpoint a parallel project.

I would really appreciate any input or leads that anyone can provide! Thanks!

June Unmet Heating Hours
Electric and Gas Consumption
Waterside HVAC
Main AHU
System Level Heating Control
System Level Cooling Control
System Level Fan Power and Control
Zone Level Basic Specs
Zone Level Fan Control
Zone Level Heating Control
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