Component 513:  Mixing Dampers and Merge by HVACSIM+

General Description
	Component 513 represents a pair of mixing dampers, mechanically linked 
so that one damper opens as the other closes.  The first inlet is closed when 
the input control signal, C, is zero, and open when C is one.  The reverse is 
true for the second inlet.  Hysteresis effects and an actuator time constant 
are not included in the model.
	Flow resistances are calculated in the same manner as in the Component 
506 damper or valve model.  For a discussion of damper characteristics and 
recommended parameter values, see section 4.5 of reference [1].
	Component 513 takes three pressures as inputs and calculates three flow
rates.  In this respect, it is similar to Component 510 flow split and 
Component 511 inlet conduit, both of which also compute an inlet flow rate 
rather than an inlet pressure.

Nomenclature
	C - control signal (0 <= C <= 1)
	Ko - flow resistance coefficient when damper is open
	P - pressure
	R - flow resistance as a function of damper position
	T - temperature
	w - mass flow rate
	Wf - weighting factor for linear term of flow resistance

Subscripts
	1 - first inlet
	2 - second inlet
	3 - outlet

Mathematical Description
	R1 and R2 are the flow resistances of the two inlets:
	R1 = {(Wf*Ko) / [(1 - y)*C + y]^2} + (1 - Wf)*Ko*y^(-2*(1 - C))
	R2 = {(Wf*Ko) / [(1 - y)*(1 - C) + y]^2} + (1 - Wf)*Ko*y^(-2*C)
These equations model linear damper characteristics when Wf is one, exponential
characteristics when Wf is zero, and intermediate characteristics for 
intermediate values of Wf.  These flow resistances are used to find two of the
three flow rates:
	w1 = sign(P1 - P3)*[|P1 - P3| / R1]^0.5
	w2 = sign(P2 - P3)*[|P2 - P3| / R2]^0.5
The third flow rate is the sum of the first two:
	w3 = w1 + w2
The outlet temperature is a weighted average of the two inlet temperatures:
	T3 = (w1*T1 + w2*T2) / w3

Component 513 Configuration
	Inputs		Description
	1	P1	- pressure at first inlet
	2	P2	- pressure at second inlet
	3	P3	- pressure at outlet
	4	T1	- temperature at first inlet
	5	T2	- temperature at second inlet
	6	C	- input control signal
	Outputs		Description
	1	w1	- flow rate at first inlet
	2	w2	- flow rate at second inlet
	3	w3	- flow rate at outlet
	4	T3	- temperature at outlet
	Parameters	Description
	1	Ko	- full open resistance (0.001/(kg-m))
	2	y	- leakage parameter ( - )
	3	Wf	- weighting factor for linear term of 
			  flow resistance ( - )

Reference:
1.	HVACSIM+ Building Systems and Equipment Simulation Program Reference 
	Manual (NBSIR 84-2996)
	Daniel R. Clark
	United States Department of Commerce
	National Institute of Standards and Technology
	Gaithersburg, Maryland  20899-0001