How can I use sprinkler K factor information in Pipe Flow Expert?
Pipe Flow Expert allows the modelling of a sprinkler through the generic Component object, through the definition of the performance characteristic, either by specifying a Sprinkler K factor, or by specifying a set of flow rate versus pressure-loss performance points.
The following discussion explains how Sprinkler K factors relate to flow versus pressure loss performance data.
PRESSURE LOSSES for SPRINKLERS
Many sprinklers are rated with a K factor that describes their performance. This is defined as:
Q = K √(P)
Where: Q = Flow rate (US gpm or l/min, K has units of US gpm/psi0.5 or l/min/(bar)0.5 depending on the published literature.
The K factor for sprinklers is NOT the same as a fitting K factor (which is used with a velocity2 element to calculate head loss).
Typical sprinkler Discharge Coefficients might be:
K=5.6 (where the units are in US gpm/psi0.5)
This equates to a metric K of 80.6 (units are in (l/min)/bar0.5)
K=8.0 (where the units are in US gpm/psi0.5)
which equates to a metric K of 115.2 (in units of (l/min)/bar0.5)
An illustrative example: A sprinkler with an imperial K factor of 5.6 would give a flow rate of 15.0 US gpm with a pressure drop of 7.2 psi.
The flow rate is calculated from: 7.2 psi0.5 x 5.6 = 15.0 US gpm
A component could be used to model the flow and pressure loss through this sprinkler. For a given pressure drop across the sprinkler component, the flow rate is determined using a sprinkler K value of 5.6. The following are pressure drop / flow rate data points for such a sprinkler:
1.0 psi drop gives √(1.0) x 5.6 = 5.6 US gpm flow
4.0 psi drop gives √(4.0) x 5.6 = 11.2 US gpm flow
9.0 psi drop gives √(9.0) x 5.6 = 16.8 US gpm flow
16.0 psi drop gives √(16.0) x 5.6 = 22.4 US gpm flow
Alternatively, for a given flow rate through the sprinkler, the pressure loss can be calculated from the K value.
Note: Imperial & Metric sprinkler K factors are different. To convert from an Imperial sprinkler K factor to a Metric sprinkler K factor multiply by 14.4 approximately.
For standard type sprinkler heads the many design standards specify K-factors and minimum pressure requirements, which can be used for different Hazard classifications and design densities.
For information on how to apply the performance curve of the sprinkler using a Pipe Flow Expert Component object, please see 'How do I model a sprinkler system with Pipe Flow Expert?'
NOTE: In Pipe Flow Expert version 7 and later, the Spinkler K factor can be specified directly in the Component object and this one value can then be used to determine the flow versus pressure loss performance characteristic for the sprinkler nozzle.