ASHRAE Baseline system 3 - High Fan Energy
I am working on LEED modeling for a project that the design has 1 rooftop, DX cooling, HW heating unit with VAV HW reheat at the zone level. The size and number of floors dictate the use of App G System 3 (packaged rooftop air conditioner) with constant volume fans, DX cooling and gas heating coils for ALL the thermal zones.
Our calculations for the baseline fan pressure drops based on App G formulas show relatively higher pressure drops compared to the ones for the design case. Even compared to the formulas for the System 1 and 2, the fan pressure drops are more than 2 times higher in the 4-5 inch water range compared to AHU fan pressure drops around 3 inch water. I think the questions below are more on clarification on 90.1 intent behind fan pressure drop calcs for these single zine units. This is probably the only time that a single zone system is dominating the baseline I am modeling and I am not sure if the results I am seeing make sense compared to the design case.
The design case rooftop AHU has a return fan. Does this mean that every single System 3 rooftop unit for the baseline need to have a return fan? This means a lot more fan energy for the baseline!
Given that the design case only has a few fans (2 AHU fans+few low pressure drop FCUs+ exhaust fans), the number of fans and the total energy consumption of baseline fans totals to a huge percentage of the baseline energy consumption. More than 50%! Has anyone else had a similar issue with single zone baseline systems comparison to a design case?
Thanks.
