PartialFlow

Water ports as arrays, one element per connection: the inlets mix, every outlet leaves at TOut; with pressure-driven flows, the inlets meet in a pressure node of small compliance

FastSmoothBuildings.Hydronics.PartialFlow, partial model (source)

Purpose

Base class of the water components with one inlet and one outlet. Each port is an array with one element per connection (nPorts_a, nPorts_b): the inlets mix, every outlet leaves at TOut, and all inlets share the pressure pIn of the inlet node.

Equations

Flow through the component, from the inlets: ṁ = ∑_i ṁ_a,i (m_flow).

Mixed inlet temperature, with δ = m_flow_small and T̄_a the mean of the inlet temperatures:

T_in = (∑_i w_i T_a,i + δ T̄_a) / (∑_i w_i + δ),

where w_i = ṁ_a,i with set flows and w_i = positivePart(ṁ_a,i, δ) with pressure-driven flows. At zero flow the inlet takes the mean inlet temperature, and TIn stays defined.

The flow that carries the inlet water through the component, used by the energy balances of the extending classes, is mTra = ṁ with set flows and positivePart(ṁ, δ) with pressure-driven flows, so that a flow reversing while the pressures settle carries no water backwards through the balance.

Set flows and pressure-driven flows

• Set flows (pressureDriven = false): pIn = 0.
• Pressure-driven flows: the inlet node is a pressure state of small compliance, τ_hyd G_hyd dp_in/dt = ṁ + ∑_j ṁ_b,j, with τ_hyd = tauHyd and G_hyd = GHyd. When GHyd is the conductance of the outlets, as the extending classes set it, the pressure of the node settles with the time constant tauHyd.

Extending classes

An extending class gives TOut and, with pressure-driven flows, the flow of every outlet port_b[j].m_flow from pIn and the pressure port_b[j].p of the node downstream. With set flows it adds the mass balance (PartialConserving), or leaves it to the circuit when the component is the reference of its circuit (Boiler, HeatPump).

Parameters

Parameter	Type	Unit	Default	Description
nPorts_a	Integer		1	Number of connections of the inlet
nPorts_b	Integer		1	Number of connections of the outlet
m_flow_small	Real	kg/s	1e-6	Flow below which the inlet takes the mean inlet temperature
pressureDriven	Boolean		false	true: flows from the pressures of the circuit (closed loop); false: flows set by the valves (optimal control)
tauHyd	Real	s	5	Time constant of the pressure of the inlet node (pressure-driven flows)
GHyd	Real	kg/(s.Pa)	1e-4	Conductance scaling the compliance of the inlet node

Revisions

• October 2026: moved from trano's FastModel.Hydronics.