juneau's profile - activity

The availability schedules are the same (always on) and the supply fan mode schedule is "0" (cycles with load) for both. Zonal setpoints are the same, and no economizer for either building since it is multi-family residential. COP is 4 and 3.82 for the VRF and DX split, respectively. I also have heat pump waste heat recovery set to "yes". Neither system has unmet hours. I'm curious how you determined the changes to the VRF performance curves. How do you determine what are correct coefficients? Perhaps the DX curves in my model are too efficient for a 14 SEER unit? Is there a way I can check?

Thanks. I was able to load both measures (OS VRF & yours) and run them separately using apply measure now. I took out the DOAS from the OS version and also changed the supply fan operating mode schedule to onoff to cycle with the demand. Your curves do result in less cooling/heating/fan energy use compared to the default VRF measure, but it still uses twice the cooling energy of the system composed of individual split systems. I wonder if the issue is with the split system definition? It's from the DOE prototype building (14 SEER, AC gas heat). I've not found another one on the BCL.

Someone else had a similar issue with the weather file on Unmet Hours. Deleting the project folder and moving the .osm file to a different location before opening seemed to clear the problem.

I can now run the OS VRF measure but I am unclear on how to replace it with the altered the VRF measure. Do I just replace the files in the scripts folder and re-run?

Thanks.

I tried to add the OS VRF measure to my run for the base building and I get the following error: "Weather Simulation requested, but no weather file attached" I confirmed that I have a weather file selected in the Site tab and the model runs fine when the OS VRF measure is not selected in the Measure tab.

I don't understand why adding a measure would affect the weather file.

Thanks for your response. Yes, there is an annual energy use difference between the two systems and it's good to learn that the default VRF curves in the OpenStudio are not ideal. However, I am noticing a difference in what I believe to be the total heat gains and losses in the two buildings. I'm basing that assumption on the "Monthly Load Profiles" table in the results summary report for OpenStudio where the monthly cooling and heating load totals are reported in MBtu. The two buildings should be the same so I'm not sure why one building would have nearly twice the cooling load of the other.

I created two copies of a midrise multifamily residential building in OpenStudio 1.13 and applied split AC with gas furnace to one and LG VRF measures from BCL to the other. Looking at the HVAC Load Profile tables in the OpenStudio output report shows that the VRF building has significantly higher monthly cooling and heating loads compared to the split AC building.

I checked the weather files between the two models (same), I compared the sensible heat gain components (same values, other than VRF shows air cooling and heating occurring with the zone equipment and the split systems show air cooling and heating in the terminal unit columns). From reading these boards, I understand that there is no way to dis-aggregate the load components in Open Studio, but I tried running the zone component loads report in EnergyPlus and did not see any differences there either. As far as I can tell, neither system is doing mechanical ventilation and the infiltration rates are the same. In July, the VRF building has a cooling load of 23.11 MBtu compared to 12.96 MBtu for the split AC building.

Any suggestions for diagnosing this issue would be greatly appreciated.