This package contains models for boilers. The main equations are computed in the base class Buildings.Fluid.Boilers.BaseClasses.PartialBoiler and the efficiency is described in the extended models using different methods.
The heat of combustion released by the fuel is computed as
Q̇f = y ⋅ Q̇0 ⁄ η0
where y ∈ [0, 1] is the control signal or firing rate, Q̇0 is the nominal heating power and η0 is the nominal efficiency. The nominal values correspond to the operating condition at y = 1 and, when applicable, at the nominal temperature T = T0 or Tinlet = Tinlet,0, depending on the choice of model.
The heat transferred to the working fluid (typically water or air) is
Q̇ = η ⋅ Q̇f - Q̇amb
where η is the efficiency at the current operating point and Q̇amb > 0 is the heat loss from the boiler to the ambient.
Q̇amb is considered only when the port heatPort
is 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 does not already account for this heat loss.
Also note that in
Buildings.Fluid.Boilers.BaseClasses.PartialBoiler,
the equation
QWat_flow = eta * QFue_flow + UAOve.Q_flow
uses a summation instead of a subtraction because the direction
of UAOve.Q_flow is from the ambient to the boiler.
The fuel is specified in Buildings.Fluid.Data.Fuels via
ṁf = Q̇f ⁄ hf
V̇f = ṁf ⁄ ρf
where ṁ is the mass flow rate of the fuel, hf is the heating value of the fuel, V̇f is the volumetric flow rate of the fuel, and ρf is the density of the fuel. Care must be taken to choose the higher or lower heating value correctly that corresponds to the efficiency η. (E.g., the efficiency of a condensing boiler may be computed on the higher heating value to avoid efficiencies higher than 1, whereas a non-condesing boiler's efficiency is typically on the lower heating value.)
There are two ways to specify the efficiency η.
Specifying the performance using a table as implemtend in Buildings.Fluid.Boilers.BoilerTable is generally easier for representing condensing boilers because the change in efficiency near the condensation point can be described conveniently.
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.