Dear all
I am comparing the epuipment sizing of a day time and a 24 hr office
building on EnergyPlus. When I simulate the two while autosizing the hvac
equipment, the Nominal Cooling Capacity (W) of the 24 hr building comes less
than the day time building. Though the total energy consumption, as
expected, of the 24 hr building is more than the 12 hr building, why
the cooling capacity (equipment size) of the 24 hr building is lower than
the 12 hr building. In my particular case, for a conditioned area of around
1600 m2, the cooling capacity for day time and 24 hr building is coming
around 146 kW and 128 kW, respectively.
What could be the possible reasons for such behaviour?
Thanks
Sandeep Kachhawa
My best guess would be the pull-down cooling load. If you're modeling the 12-hr building as 12 hours occupied and 12 hours unoccupied. The software may let the building temperature float way up outside of setpoint during the unoccupied hours. Then, when your occupied hours start, the equipment needs extra capacity to pull down the thermal lag of the building to meet setpoint in a reasonable timeframe. Make sense? Are you modeling it that way?
Michael
yes the thermal mass of the building may lead to this sort of behavior, but
is it a general phenomenon? Further to my previous mail, there is no night
setback in my model and I am taking the same building for both the cases by
just changing the schedules accordingly
Regards
Sandeep Kachhawa