modelHotWaterStorage_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.

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

L4: Storage is diveded in layered volumes. Each volume is ideally stirred. Between the fluid volumes heat conduction 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 modelled.

4. Interfaces

Heat

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

heatPorts(optinal): temperature of connected fluid volume and heat flow to or from the fluid volume

Fluid

inletCHP: fluid connection from CHP, fluid flows to the storage

outletCHP: fluid connection to CHP, fluid flows from the storage

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

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

inletSolar (optional): fluid connection from solar thermie, fluid flows depending on the temperature to different storage layers

outletSolar (optional): fluid connection to Solar thermie system, fluid flows from solar thermie to the storage

addPorts (optional): a various number of fluid connections to other components for example chiler.

5. Nomenclature

Just parameters and of the main model are described. Further explanations are in the sub models. medium: medium in the hot water storage. Has to be one phase fluid from the TILMedia library

nSeg: number of vertical layered fluid segments

maxTemperature_allowed: maximum allowed temperatur inside the storage

minTemperature_allowed: minimum allowed temperatur inside the storage

Use_Solar(Boolean): if true the ports inletSolar and outletSolar are active

Use_HeatPorts(Boolean): if true heatPorts is active

nHeatPorts: number of heat ports

nAdditionalFluidPorts: number of additional fluid ports

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.

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 installted at TUHH for research purposes. The model is validated against measurements and simulations from Harmsen. Parts of the Validation are shown in the figures below. The temperatures in the storage have been measured in four different heights (red: 1.592m, blue: 1.044m, green: 0.618m, black: 0.293m). The dotted lines show the measured temperatures, the dashed lines the temperatures from a reference simulation and the solid lines the temperatures of this model. The following picture shows the overnight cooling while no fluid flows entered or left the storage. The simulation was done with disretizing the storage in ten segemnts.

9. References

(no remarks)

10. Version History

Model created by Tobias Ramm (tobias.ramm@tuhh.de), Mar 2015

Revised and edited by Lisa Andresen (andresen@tuhh.de), Jun 2015

Parameters

Connectors

Components

Contents

Name	Description
CostVariables