Detailed Three-Way Mixing Valve - Calculates Pressure
By M. Brandemuehl
Revised for TRNSYS by N. Blair and R. Schwarz

      	This model was adapted strictly for use with the TRNSYS Program by
the Solar Energy Laboratory.

	This algorithm determines the pressure for a 3-way mixing valve or
damper as a function of the mass flow rates and the valve or damper position
for given physical characteristics.  The algorithm calculates the inlet
pressure at each port from the outlet pressure, flow rates, and valve position
given the nominal flow resistance through the open valve, a parameter that 
describes the valve characteristics, and a leakage parameter for each port.
The algorothm nominally calculates inlet pressures for a mixing valve given 
outlet pressure and the leaving flow rates.  The algorithm will describe a 
diverting valve by using negative values of the flow rates and substituting the
entering pressure as the subroutine input pressure. The resulting subroutine 
output pressures will be the pressures leaving the valve.  Component 1212 
calculates the pressure for a two way valve.  Component 1213 calculates the
flow rate for a two way valve.  Component 1215 calculates the flow rate for a 
three-way mixing valve or damper.  Sample input and output are included in the
source code.

REF: A Toolkit for Secondary HVAC System Energy Calculations  May 25, 1992
     Joint Center for Energy Management  University of Colorado at Boulder