heather0638's profile - activity

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 ...