Junction¶
Split valve: its inlets (port_1) mix, its outlets (port_2, port_3) leave at the mixed temperature; with pressure-driven flows the resistance of Buildings' Junction (dp_nominal[1] at m_flow_nominal[1], linearized) is placed on each outlet
FastSmoothBuildings.Hydronics.Junction, model (source)
Purpose
Split of a circuit into an outlet port_2 and a second outlet port_3 (e.g. the bypass of
a ThreeWayValve). The connections of the
inlet port_1 mix, and both outlets leave at the mixed temperature T.
Equations
Mixed temperature, with δ = m_flow_small and T̄1 the mean of the
inlet temperatures:
T = (∑i wi T1,i + δ T̄1) / (∑i wi + δ),
where wi is the inlet flow with set flows and its positive part with pressure-driven flows.
Set flows and pressure-driven flows
With set flows, the junction conserves mass, ∑ port_1.m_flow + ∑ port_2.m_flow +
∑ port_3.m_flow = 0, and the split between the outlets is set by the rest of the circuit.
With pressure-driven flows, the inlet is a pressure node of small compliance and each outlet connection has the
linear conductance G = |m_flow_nominal[1]| / max(dp_nominal[1],
dpLink):
port_k[j].m_flow = −G (pin − pk,j),
τhyd G (n2 + n3)
dpin/dt = sum of the flows of all ports.
Only dp_nominal[1] and m_flow_nominal[1] enter the equations; when
dp_nominal[1] is not positive, the conductance takes dpLink.
Relation to Buildings
The resistance of Buildings.Fluid.FixedResistances.Junction on its first port,
dp_nominal[1] at m_flow_nominal[1], linearized and placed on each outlet.
Use
The return of Examples.BoilerCircuit: to the boiler and to the bypass of the three-way valve. Junction2 is the same without the second outlet.
Parameters¶
| Parameter | Type | Unit | Default | Description |
|---|---|---|---|---|
| nPorts_1 | Integer | 1 | Number of connections of the inlet | |
| nPorts_2 | Integer | 1 | Number of connections of the outlet | |
| nPorts_3 | Integer | 1 | Number of connections of the second outlet | |
| m_flow_small | Real | kg/s | 1e-6 | |
| pressureDriven | Boolean | false | true: flows from the pressures of the circuit | |
| tauHyd | Real | s | 5 | Time constant of the pressure of the inlet node |
| dp_nominal | Real | Pa | {5000, -1, -1} | Pressure drops of Buildings' Junction |
| m_flow_nominal | Real | kg/s | 0.15*{1, -1, -1} | Nominal flows of Buildings' Junction |
| dpLink | Real | Pa | 1000 | Pressure drop at the nominal flow when dp_nominal[1] is not positive |
| G | Real | kg/(s.Pa) | abs(m_flow_nominal[1])/max(dp_nominal[1], dpLink) | Conductance of each outlet (dp_nominal[1], at least dpLink) |
Revisions¶
- October 2026: moved from trano's
FastModel.Hydronics.