Can you advise how the software calculates the Pressure Drop for bend and tees.
Are the K values from CIBSE GUIDE C edition 2007 for tee and bends.
You can find the list of K value of the tee and bends from here.
The software collects the values from CIBSE GUIDE C of 2007.
Does it collect values from CIBSE GUIDE C of 2007 for tee and bends. The table shared does not include K value for bends or tees. How does the software calculated a bend k value.
Just to clarify the above - the calculations are based on CIBSE Guide C 2001 rather than 2007 - please note that you can find detailed information on the calculation methods used in the manual (accessed as shown here), eg as below:
In regard to calculation methods in Netsys for bends and tees; individual K values and pressures due to bends/tees are not provided in the results, as ductwork sections and bends are not calculated separately, eg as with CIBSE based calculations, and the K value's are determined according to ratio's of velocity, flow rate, or cross sectional area. Standard data is based on that available in CIBSE Guide C and other data is provided by manufacturers but is still selected on the above criteria based on the data provided.
Thus, a breakdown of separate pressure drops across ductwork/bends is not given by the software, as these are computed hand-in-hand. If the K-value these are required then you would need to take the pressure drop results across the section in question, inclusive of the fittings, and work these out using manual hand calc's.
Please note that development is occurring right now on updating the Netsys capabilities in OpenBuildings - this is planned for completion in update 10 - you can find further details on this here.
Shane Regan | Principle Building Performance Support Engineer