For a recent study, we were asked to calculate peak hourly cooling and heating loads for each of the 272 ASHRAE 90.1 2007 reference files (download from here). Peak cooling load square feet/Ton values reported by E+ were significantly higher than ASHRAE prescribed limits.
The three different approaches which were attempted were as follows:
a) First, the following output variable was added to each of the 272 files.
Output:Variable,*,Zone Predicted Sensible Load to Setpoint Heat Transfer Rate,hourly; !- HVAC Average [W]
Then based on whether the above output variable was positive or negative in eplusout.csv file for each zone, they were added accordingly to calculate total cooling load and total heating load. This gave peak cooling SF/Ton values which very off from ASHRAE limits. In the attachment, E+ reported values are in yellow cells. C:\fakepath\BuilsingEngChecks.png
b) Then the following two variables were considered but they also did not make much of difference and didn’t bring the results closer to ASHRAE limits.
Output:Variable,*,Zone List Sensible Heating Rate,hourly; !- HVAC Average [W]
Output:Variable,*,Zone List Sensible Cooling Rate,hourly; !- HVAC Average [W]
c) Third and final approach was to report the following variables for and add them.
Output:Variable,*,Cooling Coil Total Cooling Rate,hourly; !- HVAC Average [W]
Output:Variable,*,Heating Coil Air Heating Rate,hourly; !- HVAC Average [W]
Output:Variable,*,Heating Coil Heating Rate,hourly; !- HVAC Average [W]
This significantly improved the results but still not all the files were within ASHRAE limits.
Also, we tried to add IdealLoad HVAC in a few files which made some more improvement to approach c) above but then decided not to take this route as this takes away the reference nature of the files. Since these were ASHRAE 90.1 reference files, it is puzzling as to why the results are off? Are we missing something here ?
