modelHotWaterStorage_constProp_L4

Information

1. Purpose of model

One dimensional fluid storage model with stratification. Intention of the model is to represent a hot water storage in a bigger system with more accurate outflow temperatures compared to a zero dimensional storage model. Several ports on the producer and grid side can be added as well as electric heating rods.

2. Level of detail, physical effects considered, and physical insight

L4: Storage is divided in layered volumes. Each volume is ideally stirred. Between the fluid volumes, heat conduction, heat diffusion, heat losses and boyancy are considered.

Heat losses to the ambient are simplified as heat conduction through top, side wall and bottom.

3. Limits of validity

- The storage model includes just a vertical temperature distribution. No horizontal temperature distribution is modeled. Mixing effects due to the velocity of the fluid at inlets an outlets are not modeled.

- Losses to the ambient are modeled as linear dependent from temperature difference (no radiation or convection modeled)

- Thermodynamic properties of fluid are constant (no temperature dependency modeled)

- No pressure losses or levels modeled

- No change of gaseous state modeled

- Geometry is cylindric

- arbitrary fluid port numbers with individual heigths

4. Interfaces

Heat

heatLosses: ambient temperature and the collected heat flow to the ambient through top, side wall and bottom

port: heat port connected to each layer of the storage tank if fluid ports are disabled.

Fluid

waterPortIn_prod: fluid connection from producer, fluid flows to the storage

waterPortOut_prod: fluid connection to producer, fluid flows from the storage

waterPortIn_grid: fluid connection from heating grid, fluid flows to the storage

waterPortOut_grid: fluid connection to heating Grid, fluid flows from the storage

5. Nomenclature

(no remarks)

6. Governing Equations

Energy and mass or volume balance inside every volume segment. Heat losses due to one dimensional thermal conductance through top, bottom and side wall. Thermal conductance between volume segments. Modeled boyancy introducing heat flow from lower to higher segment if the lower segemnt has a higher temperature. Direct fluid connection between the volumes.

7. Remarks for Usage

The allowed minimum number of volume segements is two. The higher the number of segments the higher the number of equations.

If FluidPorts are disabled, the amount of heat that is transferred to each layer needs to be specified via the heat port 'port'.

8. Validation

The model is validated with hot water storage Vitocell 160E. The storage tank has a capacity of 1000 liters and an inner height of 1.88 metres (without insulation). The tank has multiple fluid inflow and outflow connections. The storage is used for climatisation and is installed at TUHH for research purposes. The model is validated against measurements and simulations from Harmsen.

9. References

(no remarks)

10. Version History

Model created by Tobias Ramm (tobias.ramm@tuhh.de) on Fri Mar 20 2015

Model revised by Lisa Andresen (andresen@tuhh.de), Jun 2015

Model revised and redesigned by Pascal Dubucq (dubucq@tuhh.de) on Wed August 24, 2016

- Switched order of control volumes to more intuitive counting (1=bottom, then counting up until N_cv=top)

- Renamed variables to Transient / ClaRa code conventions

- Changed diffusion modeling to second order finite difference approximation

- Removed TIL Media object that was used to calculate *some* of the thermodynamic properties (but not all of them). Now all properties are constant which reduces model complexity. Relevant properties (density, thermal conductivity, heat cacpacity) are mainly temperature dependent and storage operates in fairly narrow temperature range.

Added cost statistics on March 30, 2017

Model expanded to include several producer and grid ports on different heights and electric heating rods by Carsten Bode (c.bode@tuhh.de), Nov 2018

Modification by Anne Hagemeier (anne.hagemeier@umsicht.fraunhofer.de) in August 2021 (Enabled the model to be used without fluid ports)

Parameters

Connectors

Components

Contents

Name	Description
ProducerCosts_elHeater
CostStatisticsModel
ElectricPowerPort
PowerBoundary