Boiler

Boiler (Buildings BoilerPolynomial): water and metal heated by the part load ratio y; with set flows, the reference of its circuit (no mass balance)

FastSmoothBuildings.Hydronics.Boiler, model (source)

Extends PartialFlow.

Purpose

Boiler fired at the part load ratio y: a single node of water and metal at the temperature T, heated by the fuel and losing heat to the boiler room. The water leaves at T.

Equations

Fuel power and efficiency, the coefficients a padded with zeros to six:

Q_fue = y Q_flow_nominal / η_nom,

effCur	η	ηnom
QuadraticLinear	a1 + a2 y + a3 y2 + (a4 + a5 y + a6 y2) T	η at y = 1 and T = T_nominal
Constant, Polynomial	a1 + a2 y + … + a6 y5	η at y = 1

Energy balance of the water and metal, with the heat capacity C = ρ VWat c_p + 500 J/(kg K) mDry:

Q_wat = η Q_fue + UA (TAmb − T),   C dT/dt = mTra c_p (TIn − T) + Q_wat.

The fuel meter EFue integrates Q_fue in kWh: a state, exact whatever the output interval.

Set flows and pressure-driven flows

With set flows, the boiler is the reference of its circuit: it has no mass balance, the circuit closes it, and its flows are set by the valves. With pressure-driven flows, each of the n_b outlets passes the flow of a quadratic resistance, port_b[j].m_flow = −quadraticFlow(p_in − p_b,j, m_flow_nominal/n_b, dp_nominal, deltaM), regularized below deltaM times the nominal flow.

Parameters

• UA: heat loss conductance to the boiler room, twice 10⁻⁴ Q_flow_nominal by default, because BoilerPolynomial of Buildings 13 counts its loss twice.
• m_flow_nominal: by default the flow that carries Q_flow_nominal with a 20 K temperature difference; used with pressure-driven flows only.
• VWat, mDry: water volume and dry mass, by default proportional to Q_flow_nominal.

Relation to Buildings

Buildings.Fluid.Boilers.BoilerPolynomial, with the efficiency curves of Types.EfficiencyCurves. Buildings 13 injects η Q_fue and the heat flow of its loss conductance into the water, then conducts that loss out of the water again: the loss counts twice, which the doubled UA reproduces.

Use

Fired by Controls.BoilerTemperatureControl in Examples.BoilerCircuit.

Parameters

Parameter	Type	Unit	Default	Description
m_flow_nominal	Real	kg/s	Q_flow_nominal/cpWat/20	Nominal flow (pressure-driven flows)
dp_nominal	Real	Pa	5000	Pressure drop at the nominal flow (pressure-driven flows)
deltaM	Real		0.1	Regularization of the quadratic flow law below deltaM*m_flow_nominal
Q_flow_nominal	Real	W		Nominal heating power
effCur	Integer		Types.EfficiencyCurves.Constant	Efficiency curve
a	Real		{0.9}	Coefficients of the efficiency curve (Buildings)
T_nominal	Real	K	353.15	Temperature used to compute the nominal efficiency
VWat	Real	m3	1.5e-6*Q_flow_nominal	Water volume
mDry	Real	kg	1.5e-3*Q_flow_nominal	Dry mass
UA	Real	W/K	21e-4Q_flow_nominal	Heat loss conductance to the boiler room (Buildings 13 BoilerPolynomial counts its UA loss twice)
TAmb	Real	K	288.15	Temperature of the boiler room
T_start	Real	K	293.15	Initial water temperature
C	Real	J/K	rhoWatVWatcpWat + 500*mDry	Heat capacity of the water and of the dry mass

Revisions

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