Constant volume system, design temperature influence.
I have a very simple single zone model served by a heating only constant volume system. There is no outdoor air and the fan pressure drop is zeroed out to reduce fan heat influence.
I run the model with zone sizing of 85 F heating supply and then with zone sizing of 95 F. I anticipated the heating results to be identical as the only impact this would have would be on the fan volume and fan power. However we see a 7% change in the heating energy. Could someone hint what could be causing this.
I energyplus V8.5 idf files I used: C:\fakepath\85.idf.jpg C:\fakepath\95.idf.jpg
Here are the HTML output files: C:\fakepath\85Table.html.jpg C:\fakepath\95Table.html.jpg
Sizing:Zone calculates the zone design air flow rate which assumes a variable amount of supply air at a fixed temperature and humidity. As you set different supply air temperatures, it results different zone design air flow rate with a different fan energy consumption.
@Tian, As I indicated I zeroed out the fan energy. the outputs attached indicate no fan energy consumed. For some reason there is a 7% change in the heating subcategory.
Are you hitting the thermostat setpoint in the 85F case? Did you make absolutely sure that there is no OA being brought in by your Outdoor Air System?