Buildings.Fluid.Storage.Ice

Ice tank model

Information

Package with ice thermal storage models.

Extends from Modelica.Icons.Package (Icon for standard packages).

Package Content

Name	Description
ControlledTank	Ice tank with performance based on performance curves and built-in control for outlet temperature
Tank	Ice tank with performance based on performance curves
Data	Performance data for ice thermal tank
Validation	Package that validates the ice tank model
BaseClasses	Base classes for ice tank models

Buildings.Fluid.Storage.Ice.ControlledTank

Ice tank with performance based on performance curves and built-in control for outlet temperature

Information

This model implements an ice tank model with built-in idealized control that tracks the set point TSet for the temperature of the working fluid that leaves the tank, as shown in the figure below.

The model is identical to Buildings.Fluid.Storage.Ice.Tank, except that it takes as an input the set point for the temperature of the leaving working fluid. This temperature is maintained if the flow rate and temperatures allow sufficient heat flow rate between the tank and the working fluid.

The built-in control is an idealization of a tank that has a controller that bypasses some of the working fluid in order to meet the set point for the temperature of the leaving working fluid. The fluid from port_a to port_b has by default a first order response. If the tank has sufficient capacity for the given inlet temperature and flow rate, then the idealized control has no steady-state error. During transients, the set point may not be met exactly due to the first order response that approximates the dynamics of the heat exchanger.

Note that the setpoint is also tracked during charging mode. If the full flow rate should go through the tank during charging, which is generally desired, then set TSet to a high temperature, such as 20°C.

Usage

This model requires the fluid to flow from port_a to port_b. Otherwise, the simulation stops with an error.

Extends from Buildings.Fluid.Storage.Ice.Tank (Ice tank with performance based on performance curves).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Storage.Ice.Tank

Ice tank with performance based on performance curves

Information

This model implements an ice tank model whose performance is computed based on performance curves.

The model is based on the implementation of Guowen et al., 2020 and similar to the detailed EnergyPlus ice tank model ThermalStorage:Ice:Detailed.

The governing equations are as follows:

The mass of ice in the storage m_ice is calculated as

d SOC/dt = Q̇/(H_f   m_ice,max)

m_ice = SOC   m_ice,max

where SOC is state of charge, Q̇ is the heat transfer rate of the ice tank, positive for charging and negative for discharging, Hf is the fusion of heat of ice and m_ice,max is the nominal mass of ice in the storage tank.

The heat transfer rate of the ice tank Q̇ is computed using

Q̇ = Q_sto,nom   q^*,

where Q_sto,nom is the storage capacity and q^* is a normalized heat flow rate. The storage capacity is

Q_sto,nom = Hf   m_ice,max,

where Hf is the latent heat of fusion of ice and m_ice,max is the maximum ice storage capacity.

The normalized heat flow rate is computed using performance curves for charging (freezing) or discharging (melting). For charging, the heat transfer rate q* between the chilled water and the ice in the thermal storage tank is calculated using

q^* Δt = C₁ + C₂x + C₃ x² + [C₄ + C₅x + C₆ x²]ΔT_lmtd^*

where Δt is the time step of the data samples used for the curve fitting, C_1-6 are the curve fit coefficients, x is the fraction of charging, also known as the state-of-charge, and T_lmtd^* is the normalized LMTD calculated using Buildings.Fluid.Storage.Ice.BaseClasses.calculateLMTDStar. Similarly, for discharging, the heat transfer rate q* between the chilled water and the ice in the thermal storage tank is

- q^* Δt = D₁ + D₂(1-x) + D₃ (1-x)² + [D₄ + D₅(1-x) + D₆ (1-x)²]ΔT_lmtd^*

where Δt is the time step of the data samples used for the curve fitting, D_1-6 are the curve fit coefficients.

The normalized LMTD ΔT_lmtd^* uses a nominal temperature difference of 10 Kelvin. This value must be used when obtaining the curve fit coefficients.

The log mean temperature difference is calculated using

ΔT_lmtd^* = ΔT_lmtd/T_nom

ΔT_lmtd = (T_in - T_out)/ln((T_in - T_fre)/(T_out - T_fre))

where T_in is the inlet temperature, T_out is the outlet temperature, T_fre is the freezing temperature and T_nom is a nominal temperature difference of 10 Kelvin.

Usage

This model requires the fluid to flow from port_a to port_b. Otherwise, the simulation stops with an error.

Reference

Strand, R.K. 1992. “Indirect Ice Storage System Simulation,” M.S. Thesis, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign.

Guowen Li, Yangyang Fu, Amanda Pertzborn, Jin Wen and Zheng O'Neill. An Ice Storage Tank Modelica Model: Implementation and Validation. Modelica Conferences. 2021. doi:10.3384/ecp21181177.

Extends from Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

Parameters

Connectors

Modelica definition