K VALUE FOR DEFAULT BENDS AND TEES

RE: K VALUE FOR DEFAULT BENDS AND TEES

Carmen Lau — Wed, 29 May 2019 10:58:48 GMT

Hi Shane,

The key issue is if software cannot tell the K values breakdown, we wouldn't be able to adjust the design to reduce pressure drop to where required.

I encountered design software that gives the C-value (similar to K factor) however they are not CIBSE or DW144.

Sounds like we probably have to go back to hand calculations or source other tools, until Hevacomp updates the software.

Thanks for your response.

Regards,

Carmen

RE: K VALUE FOR DEFAULT BENDS AND TEES

Shane Regan — Tue, 28 May 2019 15:42:24 GMT

Hi Carmen,

The options you mention are the only ones available. As Steve mentioned above, we do not have a breakdown of K-values for each bend in the software, as the software calculation method involves iteratively calculating the loss of section inclusive of all fittings in that section - a breakdown showing the contribution of each bend is not possible. However simple fittings losses can be found here.

If you wish to compare your hand calculations to the software then I would firstly advise inspecting all the fittings results for each section eg as in image below. An explanation of what is what can be found here.

RE: K VALUE FOR DEFAULT BENDS AND TEES

Carmen Lau — Tue, 28 May 2019 12:07:38 GMT

Hi Shane, thanks for your swift response. Yes, sorry we noticed that vanes can be selected for the mitre bends. However, there is only one option for the short radius bend with single vane. Does the software have more options of vanes as in the following figure in CIBSE. Without the k factor allowance for the bends from the software we cannot tell if the bend we want to use is equivalent to what simulates in Hevacomp model. Can you help how we can dictate the k factor?

Regards,

Carmen

RE: K VALUE FOR DEFAULT BENDS AND TEES

Shane Regan — Tue, 28 May 2019 10:07:59 GMT

Hi Carmen, there are many bend types with vanes available in the software - if you go to Fittings > Default bends/tees you can find them as follows:

Alternatively, you can go to Fittings > Fix bend/tee:

RE: K VALUE FOR DEFAULT BENDS AND TEES

Carmen Lau — Tue, 28 May 2019 09:07:19 GMT

Hi Steve, display the K-value in the output is important for ducting design. We are currently looking to apply different type of bends trying to reduce the system pressure loss for varies large ducting system. Without knowing what the K-value for fittings (short bend, long bend, mitre bend.. etc.) used in the calculation, it is not possible for us to optimise the pressure loss and design the ducting system. Also, it appears that Hevacomp does not have bends with vanes for us to choose. I've probably missed something. Is it possible to apply bends with vanes in Hevacomp calculation?

Thanks in advance for helping.

Regards,

Carmen

RE: K VALUE FOR DEFAULT BENDS AND TEES

Stephen Brown — Tue, 16 Apr 2019 10:11:31 GMT

Hi,

I'm afraid we don't have this data in a digestible form at present. For many fittings there isn't a single K-value but a range which can be based on diameter and in some cases selected by velocity, direction of flow etc. This makes the data complex and difficult to display in a meaningful way. For future software we re looking to display the K-value used directly in the software so every section can be evaluated.

Best Regards
Steve