eQUEST Proposed Model Design Supply Airflows
Hello! I'm modeling an existing office building in eQUEST. The proposed model system type is Variable Air Volume, fan power is entered as kW/cfm, and I am using the part-load fan performance curve from 90.1-2010 Table G3.1.3.15. I originally let eQUEST autosize the proposed model airflows and am now entering them per the actual design. The AHU design airflows are about 50% larger than eQUEST's autosized flows so I expected to see a fan power savings due to the fans hitting lower on the part-load fan power curve. However, when I entered the design fan airflows in eQUEST, with no other edits to the model, the fan power and cooling energy actually increased. Upon further inspection, I see that the eQUEST supply airflows are now about 15% higher during summer months. Also, the zones are now being maintained at a slightly cooler temperature compared with the autosized airflow model. (The cooling setpoint is 75F, and the zones are maintained around 76F in the autosized airflow model and around 75F in the design airflow model.) I'm not sure why this is happening because I made no changes to the model except for entering design supply airflow.
I've looked at the following so far and haven't found an explanation: disabled air-side economizer, set the fan min turndown very low, looked at design supply air temperatures and reset for heating and cooling (these haven't changed between the models), looked at zone throttling range (this is 4F in both models). Also, unmet load hours are very similar in both models.
I couldn't figure out how to upload an image to this post but graphs of the two scenarios can be found here: http://tinypic.com/r/zkhe28/8
Any ideas of what could be happening or other things to check? Thanks in advance!
Holly
It's hard without seeing the INP file... It would at least be very helpful if you could explain what type of equest system do you have, if you have outside air being brought in, and what is the actual eQuest keywords you've changed (look into the inp file or do a right click on the field to bring up the dict)
The system type is variable air volume (VAVS). It is serving interior zones only, which are modeled using floor multipliers. The zone exhaust airflow is setting the outdoor air rate for the system (64,000 cfm during occupied hours as shown in the system airflow graphs). The keywords I used to hard-code system airflows are SUPPLY-FLOW and RETURN-FLOW. (Note: I also tried entering design cfm at zone level but got the same results.) Other relevant inputs: OA-Control=OA-Temp, cooling control=warmest, heating control=coldest, max-humidity=60. Please let me know if any other info would be helpful.
Yes, the actual .inp file (or at least one VAVS and a couple of zones) and a potential .prd where you made the actual changes would do a lot towards understanding what's going on really... If you could host them somewhere and share a link that'd be great
@Holly Stevenson: In the meatime I started an "answer" with where I would start... I hope it's helpful. Try that and if it doesn't work, I think the next step would be to have someone look at your actual file.