modelTank

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.

Parameters

Components

Revisions

• January 26, 2022, by Michael Wetter:
  Refactored model to new architecture. Changed model to allow idealized control. Avoided SOC to be outside [0, 1].
• December 14, 2021, by Yangyang Fu:
  First implementation.