Hi to all,
I have a bit of confusion between the fan power allowance (table 6.5.3.1.1 A-B in ASHRAE 90.1) and the baseline fan power (table G3.1.2.9). I am working on an energy model for a production plant with very high renovation rates and air recirculation. As per appendix G, the baseline fan motor power for systems 5-8 (my baseline is system 8) is calculated with the formula for variable volume kWi = Ls*0.0021+A, being A the pressure drop adjustment from Table 6.5.3.1.1 and Ls the supply fan airflow rate. As per G3.1.2.10 fan power for systems 3-8 is Pfan = input kWi/Fan Motor Efficiency from table 10.8B assuming a totally enclosed fan-cooled motor at 1800 rpm.
In this case, I am modeling the baseline building and I need to set the fan power, Design Builder accepts two inputs for this (pressure rise and fan total efficiency). I have a design supply airflow of 1.98 m3/s, then kWi = 1980l/s*0.0021+A, I have several filters which pressure drop (PD) add up to around 600pa using the table 6.5.3.1.1 B. A = Sum of (PD x L/SD/65000) = 600*1980/65000 = 1.827
Therefore kWi = 1980*0.0021 + 1.827 = 5.985, and P = kWi/ Fan motor efficiency = 5.985/0.917 = 6.7 kW.
From this fan power I can estimate my total pressure drop assuming a 60% total fan efficiency, that is 2015Pa, which assuming 2/3 for supply and 1/3 for extract, would be 1343Pa for supply and 671Pa for extract.
Are these inputs and assumptions correct for pressure rise in Design Builder? if not, how should I proceed?
I am very confused about these concepts so any insight regarding this issue is very welcome.
Thanks
