This is a model of a boiler whose efficiency is described by a polynomial. The heat input into the medium is

Q̇ = y Q̇0 η ⁄ η0

where y ∈ [0, 1] is the control signal, 0 is the nominal power, η is the efficiency at the current operating point, and η0 is the efficiency at y=1 and nominal temperature T=T0 as specified by the parameter T_nominal.

The parameter effCur determines what polynomial is used to compute the efficiency, which is defined as

η = Q̇ ⁄ Q̇f,

where is the heat transferred to the working fluid (typically water or air), and f is the heat of combustion released by the fuel.

The following polynomials can be selected to compute the efficiency:

Parameter effCur Efficiency curve
Buildings.Fluid.Types.EfficiencyCurves.Constant η = a1
Buildings.Fluid.Types.EfficiencyCurves.Polynomial η = a1 + a2 y + a3 y2 + ...
Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear η = a1 + a2 y + a3 y2 + (a4 + a5 y + a6 y2) T

where T is the boiler outlet temperature in Kelvin. For effCur = Buildings.Fluid.Types.EfficiencyCurves.Polynomial, an arbitrary number of polynomial coefficients can be specified.

The parameter Q_flow_nominal is the power transferred to the fluid for y=1 and, if the efficiency depends on temperature, for T=T0.

The fuel mass flow rate and volume flow rate are computed as

f = Q̇f ⁄ hf


f = ṁf ⁄ ρf,

where the fuel heating value hf and the fuel mass density ρf are obtained from the parameter fue. Note that if η is the efficiency relative to the lower heating value, then the fuel properties also need to be used for the lower heating value.

Optionally, the port heatPort can be connected to a heat port outside of this model to impose a boundary condition in order to model heat losses to the ambient. When using this heatPort, make sure that the efficiency curve effCur does not already account for this heat loss.

On the Assumptions tag, the model can be parameterized to compute a transient or steady-state response. The transient response of the boiler is computed using a first order differential equation to compute the boiler's water and metal temperature, which are lumped into one state. The boiler outlet temperature is equal to this water temperature.


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