# .Buildings.Fluid.Boilers.BoilerPolynomial

## Information

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

and

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.

## Revisions

• May 27, 2016, by Michael Wetter:
Corrected size of input argument to `Buildings.Utilities.Math.Functions.quadraticLinear` for JModelica compliance check.
• May 30, 2014, by Michael Wetter:
Removed undesirable annotation `Evaluate=true`.
• October 9, 2013 by Michael Wetter:
Removed conditional declaration of `mDry` as the use of a conditional parameter in an instance declaration is not correct Modelica syntax.
• December 14, 2012 by Michael Wetter:
Renamed protected parameters for consistency with the naming conventions.
• December 22, 2011 by Michael Wetter:
Added computation of fuel usage and improved the documentation.
• May 25, 2011 by Michael Wetter:
• Removed parameter `dT_nominal`, and require instead the parameter `m_flow_nominal` to be set by the user. This was needed to avoid a non-literal value for the nominal attribute of the pressure drop model.
• Changed assignment of parameters in model instantiation, and updated model for the new base class that does not have a temperature sensor.
• January 29, 2009 by Michael Wetter:
First implementation.

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