Pressure Loss Calculations
All calculations use the D'Arcy-Weisbach equation for flow of fluids in pipes. These equations are those reproduced in CIBSE, ASHRAE and similar publications.
The Colebrook and White equation is used to solve the D'Arcy friction factor in the turbulent flow regime and the Poiseuille equation is used in the laminar flow regime.
Pipework Heat Transfer
For uninsulated pipes, equations using the Nusselt, Prandtl and Grashof numbers are used, which assume that the outside temperature of the pipe is the same as the fluid; for insulated pipes standard heat transfer equations derived from Q = U x A x dT are used. A discontinuity occurs between the heat transfer given by the two equations, ie between the heat transfer from an uninsulated pipe and one with a very thin layer of insulation. This is an unlikely situation to occur, however, if required, it should be modeled as a bare pipe.
For plastic pipe materials, the calculation treats the plastic as a layer of insulation.
If the pipe length is greater than 5m (16ft), the pipe is sub-divided into 5m (16ft) lengths and each section is calculated separately, using the final temperature of each section as the initial temperature of the next.