I am working on modeling a multistory apartment building with a Water Source Heat Pump system. I am modeling the system with a heat pump loop connected to separate heating and cooling loops with heat exchangers as shown in the picture below. The heating loop has a natural gas boiler and the cooling loop has a cooling tower.
When I run the model in this configuration, I get a very low gas heating consumption. In contrast, when I run the model with the Boiler and Cooling tower directly in the heat pump loop, I get a much higher natural gas consumption. It appears to me that Openstudio is not counting the gas consumption of the boiler when it is in the heating loop. I ran a test by removing the heat exchanger between the heat pump loop and the heating loop, and compared the system node temps of the heat pump loop with and without the heat exchanger for the heating loop connected. As you can see from the graphs below, the boiler does appear to be maintaining the loop temps at the setpoint when connected through the heat exchanger, however, there is no difference in the natural gas consumption between these two scenarios.
Thanks in advance for any insight you may have into what is occurring!
Primary Heat Pump Loop
With Boiler connected through heat exchanger, heat pump loop system node temp
Without Boiler connected through heat exchanger, heat pump loop system node temp
