How to Fix Pressure Gradient Errors in IESVE
The program gives a pressure loss of 247 Pa/m for a pipe, whereas the pressure loss tables in the CIBSE Guide for an equivalent pipe (Copper with water at 75°C), a pressure gradient of around 160 Pa/m is stated. The values are for pipes with roughness 0.0015 as per PiscesPro. So the pressure gradients appear to be wrong. I have also checked this for steel pipes with similar variations.
The calculations have been checked thoroughly and no problems have been found. However, there is a problem with the default value for water viscosity.
When you create a project the default value is 0.004 Pa s but it should be 0.0004 Pa s. Because it is a default, users should rightly expect that the value does not need checking. This will result in the numbers which are ten times too small and therefore pressure drops that are roughly 50% too large. If you amend this you will find that the results are in much closer agreement with the CIBSE tables.
This is now fixed and it will go into the next service pack or into version 5.3.
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