Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
I did review the code for each of these terminal units but it is difficult to say if there is an actual difference. The original intent was to allow the HeatAndCool model to modulate air flow AND coil capacity at the same time but after this review I don't see that operation. It may be that the original intent has change over time, not necessarily in the model inputs but in the model code, or that these terminal units were not really that different from the start. The one thing to remember about these terminal units is they are used with different systems, one that will usually hold a constant inlet temperature (VAV systems) and one that will vary the inlet temperature based on all zone loads (CBVAV). This will make the analysis below more difficult.
The best way to see the performance is to compare the results by creating the plot shown above for each terminal type. Use a full annual simulation to report terminal unit outlet temp and air flow rate. Then scatter plot these data on a single plot versus Zone Predicted Sensible Load to Setpoint Heat Transfer Rate. The result will be a mirror image of the figure above on the x-axis unless the Zone Predicted Sensible Load to Setpoint Heat Transfer Rate magnitude is multiplied by -1. Quite frankly I would not be able to tell the difference in performance without this type of plot. Also, this is the type of analysis I use during bug investigations.
