AgsMyDude
Mechanical
- Jul 28, 2021
- 24
We are in the final stages of a study and are currently estimating the resources it would take to bring the project from budgetary level of definition to IFC. I am looking for some information on hydraulically modelling ductwork systems to size large fans (approx. 500,000 cfm @ 20” H2O).
For the purposes of the budgetary study design, we used loss factors for specific ductwork fittings(area changes, tees, and bends) from the ASHRAE Duct Fitting Database and input into AFT Arrow. I guess my concern with the ASHRAE database is that it is clearly geared towards smaller HVAC system. Our ductwork will be up to 15'x15' in some places. I confirmed that the loss factors provided by ASHRAE do not change with scale (i.e. loss factor for a 4"x4" bend was same for 8"x8", given the same velocity for the two cases) but I am wondering if there is a better methodology for estimating ductwork dP at this scale. We do have CFD capability but have not typically used CFD to size fans (although we could if that is typical).
My ultimate goal is to scope the effort necessary to build on what we have at present and produce a calculation that could be used to support purchase were the project to proceed.
For the purposes of the budgetary study design, we used loss factors for specific ductwork fittings(area changes, tees, and bends) from the ASHRAE Duct Fitting Database and input into AFT Arrow. I guess my concern with the ASHRAE database is that it is clearly geared towards smaller HVAC system. Our ductwork will be up to 15'x15' in some places. I confirmed that the loss factors provided by ASHRAE do not change with scale (i.e. loss factor for a 4"x4" bend was same for 8"x8", given the same velocity for the two cases) but I am wondering if there is a better methodology for estimating ductwork dP at this scale. We do have CFD capability but have not typically used CFD to size fans (although we could if that is typical).
My ultimate goal is to scope the effort necessary to build on what we have at present and produce a calculation that could be used to support purchase were the project to proceed.
