How is the energy consumption of air distribution fans decided in ApacheHVAC?

[iggleton]

The sum of the design power of all my fans is about 90Kw but when I run an apache simulation the energy consumption for air distribution fans equals around 500Kw. Why is it so much more?

[farahghanem]

design power and fan consumption are two different things. Your fan power rating is in kW while your consumption would be in kwh. And yes it should be higher than the input power. In fact if it is only showing at 500kWh over the entire year then something is wrong with your hvac system.

If you want put some more details such as screenshots of your inputs and results maybe it would help me better understand your question.

[NebK22]

Farahghanem,

On the topic of fan design power, I've been playing with the fan in the out of the box DOAS w/ 4 pipe FCU and changing it's motor efficiency / efficiency at design airflow in order to reach 0.25 W/cfm to represent ECM motors. Additionally, I've made the proportional bandwidth for the fan controllers 2 to represent VSD, but there's no change in my fan energy consumption.

Any thoughts?

[farahghanem]

I believe you would need to check that the fan is set as a variable volume to properly account for performance.

[NebK22]

Farahghanem,

Thank you! I swear I have tunnel vision when I'm going through this software, didn't even realize that check box existed. It's interesting though that changing the proportional bandwidth of the fan controller has no affect on the fan energy consumption, even after checking the Variable volume and setting a VSD fan curve. Have you found this to be true?

[farahghanem]

Generally it should work, just make sure that when you have applied the change in the FCU fans, the system got saved properly (i had to "save as" the system after changing the fans with a different name and use that in the apache sim).