Research Papers

Horizontal Inlets of Water Storage Tanks With Low Disturbance of Stratification

[+] Author and Article Information
Corsin Gwerder, Lukas Lötscher, Jason Podhradsky, Matthias Kaufmann, Andreas Huggenberger, Igor Mojic

Institute for Solar Technology SPF,
University of Applied Sciences (HSR),
Rapperswil CH-8640, Switzerland

Simon Boller, Boris Meier

Institute for Energy Technology IET,
University of Applied Sciences (HSR),
Rapperswil CH-8640, Switzerland

Michel Y. Haller

Institute for Solar Technology SPF,
University of Applied Sciences (HSR),
Rapperswil CH-8640, Switzerland
e-mail: michel.haller@spf.ch

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received May 22, 2015; final manuscript received July 1, 2016; published online August 15, 2016. Assoc. Editor: Jorge E. Gonzalez.

J. Sol. Energy Eng 138(5), 051011 (Aug 15, 2016) (9 pages) Paper No: SOL-15-1154; doi: 10.1115/1.4034228 History: Received May 22, 2015; Revised July 01, 2016

Solar combi-storages are used in many countries for storing solar heat for space heating and domestic hot water (DHW) in one device. When a combi-storage is used in combination with a heat pump, the temperature stratification efficiency of the storage is a decisive factor for the overall efficiency and thus, for the consumed end-energy of the system. In particular, fluid that is entering the storage with a high velocity may cause considerable mixing, thus, destroying stratification and leading to poor system performance. This work presents computational fluid dynamics (CFD) simulations of direct horizontal inlets at midheight of a typical solar combi-storage of about 800 L volume. Different inlet diffusor designs were simulated, and laboratory measurements were used to validate CFD experiments. For the given tank geometry, mass flow rates, and inlet position, it is found for a fluid inlet temperature of 30 °C that fluid velocities should be below 0.1 m/s and Reynolds numbers below 3000–5000 at the outlet of the diffusor in order to avoid the disturbance of a hotter 50 °C zone above the inlet. Furthermore, the fluid path within the diffusor must exceed a minimum length that corresponds to three to four times the hydraulic diameter of the diffusor.

Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.


Sharp, M. K. , and Loehrke, R. I. , 1979, “ Stratified Thermal Storage in Residential Solar Energy Applications,” J. Energy, 3(2), pp. 106–113. [CrossRef]
Phillips, W. F. , and Dave, R. N. , 1982, “ Effects of Stratification on the Performance of Liquid-Based Solar Heating-Systems,” Sol. Energy, 29(2), pp. 111–120. [CrossRef]
Andersen, E. , and Furbo, S. , 2007, “ Theoretical Comparison of Solar Water/Space-Heating Combi Systems and Stratification Design Options,” ASME J. Sol. Energy Eng., 129(4), pp. 438–448. [CrossRef]
Haller, M. Y. , Haberl, R. , Mojic, I. , and Frank, E. , 2014, “ Hydraulic Integration and Control of Heat Pump and Combi-Storage: Same Components, Big Differences,” Energy Proc., 48, pp. 571–580. [CrossRef]
Hollands, K. G. T. , and Lightstone, M. F. , 1989, “ A Review of Low-Flow, Stratified-Tank Solar Water Heating Systems,” Sol. Energy, 43(2), pp. 97–105. [CrossRef]
Haberl, R. , Haller, M. Y. , Reber, A. , and Frank, E. , 2014, “ Combining Heat Pumps With Combistores: Detailed Measurements Reveal Demand for Optimization,” Energy Proc., 48, pp. 361–369. [CrossRef]
Haller, M. Y. , Haberl, R. , Carbonell, D. , Philippen, D. , and Frank, E. , 2014, “ SOL-HEAP—Solar and Heat Pump Combisystems,” Institut für Solartechnik SPF, Hochschule für Technik HSR, Rapperswil, Switzerland, Report Contract No. SI/500494-02.
Zurigat, Y. H. , Liche, P. R. , and Ghajar, A. J. , 1991, “ Influence of Inlet Geometry on Mixing in Thermocline Thermal Energy Storage,” Int. J. Heat Mass Transfer, 34(1), pp. 115–125. [CrossRef]
Hahne, E. , and Chen, Y. , 1998, “ Numerical Study of Flow and Heat Transfer Characteristics in Hot Water Stores,” Sol. Energy, 64(1–3), pp. 9–18. [CrossRef]
van Berkel, J. , Rindt, C. C. M. , and van Steenhoven, A. A. , 2002, “ Thermocline Dynamics in a Thermally Stratified Store,” Int. J. Heat Mass Transfer, 45(2), pp. 343–356. [CrossRef]
Shah, L. J. , and Furbo, S. , 2003, “ Entrance Effects in Solar Storage Tanks,” Sol. Energy, 75(4), pp. 337–348. [CrossRef]
Shin, M.-S. , Kim, H.-S. , Jang, D.-S. , Lee, S.-N. , Lee, Y.-S. , and Yoon, H.-G. , 2004, “ Numerical and Experimental Study on the Design of a Stratified Thermal Storage System,” Appl. Therm. Eng., 24(1), pp. 17–27. [CrossRef]
Andersen, E. , Furbo, S. , and Fan, J. , 2007, “ Multilayer Fabric Stratification Pipes for Solar Tanks,” Sol. Energy, 81(10), pp. 1219–1226. [CrossRef]
Vogelsanger, P. , Marty, H. , and Cinelli, M. , 2007, “ Experiments With Vertical Pates for Temperature Stratification in a Heat Storage Tank,” Institut für Solartechnik SPF, Rapperswil, Switzerland, Project Report D2 of Subtask D.
Chung, J. D. , Cho, S. H. , Tae, C. S. , and Yoo, H. , 2008, “ The Effect of Diffuser Configuration on Thermal Stratification in a Rectangular Storage Tank,” Renewable Energy, 33(10), pp. 2236–2245. [CrossRef]
Aviv, A. , Blyakhman, Y. , Beeri, O. , Ziskind, G. , and Letan, R. , 2009, “ Experimental and Numerical Study of Mixing in a Hot-Water Storage Tank,” ASME J. Sol. Energy Eng., 131(1), p. 011011. [CrossRef]
Lohse, R. , 2010, “ Einfluss von Beladeeinrichtungen auf die Thermische Schichtung in Warmwasserspeichern,” Fakultät für Maschinenbau der Technischen Universität Chemnitz, Chemnitz, Germany.
Steinert, P. , Göppert, S. , and Platzer, B. , 2013, “ Transient Calculation of Charge and Discharge Cycles in Thermally Stratified Energy Storages,” Sol. Energy, 97, pp. 505–516. [CrossRef]
Eames, P. C. , and Norton, B. , 1998, “ The Effect of Tank Geometry on Thermally Stratified Sensible Heat Storage Subject to Low Reynolds Number Flows,” Int. J. Heat Mass Transfer, 41(14), pp. 2131–2142. [CrossRef]
Carlsson, P. F. , 1993, “ Heat Storage for Large Low Flow Solar Heating Systems,” ISES Solar World Congress, Budapest, Hungary, Aug. 23–27, Vol. 5, pp. 441–445.
Jenni, J. , 2000, “ Speicher in Theorie und Praxis,” Jenni Energietechnik AG, Oberburg, Switzerland.
Huhn, R. , 2007, “ Beitrag zur Thermodynamischen Analyse und Bewertung von Wasserwärmespeichern in Energieumwandlungsketten,” Ph.D. thesis, Fakultät für Maschinenwesen der Technischen Universität Dresden, Dresden, Germany.
Drück, H. , 2007, “ Mathematische Modellierung und Experimentelle Prüfung von Warmwasserspeichern für Solaranlagen,” Ph.D. thesis, Institut für Thermodynamik und Wärmetechnik (ITW) der Universität Stuttgart, Shaker Verlag, Aachen, Germany.
Huggenberger, A. , 2013, “ Schichtung in Thermischen Speichern—Konstruktive Massnahmen am Einlass zum Erhalt der Schichtung,” Bachelor thesis, Institut für Solartechnik SPF, University of Applied Sciences HSR, Rapperswil, Switzerland.
Kaufmann, M. , 2013, “ Optimierung der Wärmeschichtung in Kombiwärmespeicher—Numerische Simulationen von Verschiedenen Einströmgeometrien,” SPF Institut für Solartechnik, Hochschule für Technik HSR, Rapperswil, Switzerland.
Lötscher, L. , and Podhradsky, J. , 2014, “ Analyse der Temperaturschichtung bei direkter Beladung von Kombi-Wärmespeichern,” Bachelor thesis, Institut für Solartechnik SPF, University of Applied Sciences HSR, Rapperswil, Switzerland.
Haller, M. Y. , Mojic, I. , Kaufman, M. , and Meier, B. , 2014, “ Disturbance of Stratification Caused by Direct Horizontal Inlets Into a Water Storage Tank,” EuroSun 2014 Conference, ISES Europe, Aix-les-Bains, France, Sept. 16–19, pp. 1277–1385.


Grahic Jump Location
Fig. 3

Geometries of inlet diffusors and connecting pipes before the inlet

Grahic Jump Location
Fig. 2

The analyzed vertical cylinder combi-storage in the initial state

Grahic Jump Location
Fig. 1

Simplified scheme of a combi-storage in combination with a solar thermal system and a heat pump

Grahic Jump Location
Fig. 4

Hydraulic scheme for the laboratory measurements

Grahic Jump Location
Fig. 5

Results of the mesh-study, with measured points at 1200 s of the experiment

Grahic Jump Location
Fig. 9

Temperature profiles for an inlet with a diffusor plate in simulation and experiment for mass flow rates of 0.125 kg/s, 0.25 kg/s, and 0.5 kg/s. Simulated with the SST-SAS model.

Grahic Jump Location
Fig. 6

Root mean square errors of temperatures and simulation time for different mesh sizes

Grahic Jump Location
Fig. 7

Comparison between full and simplified simulation

Grahic Jump Location
Fig. 8

Temperature profiles for a 1 in. horizontal inlet in simulation and experiment for different mass flow rates and different turbulence models used for the CFD simulations, full simulation without simplifications

Grahic Jump Location
Fig. 14

Displacement of the thermocline for different hydraulic diameters and mass flow rates

Grahic Jump Location
Fig. 10

Selected temperature profiles after 1 h of simulation with mass flow rates of 0.25 kg/s (top) and 0.5 kg/s (bottom row) for the inlet at midheight of the storage

Grahic Jump Location
Fig. 11

Temperature profiles for various diffusor geometries and mass flow rates colored by the Reynolds number for the flow in the diffusor or inlet

Grahic Jump Location
Fig. 12

The same temperature profiles as in Fig. 10, colored by the velocity of the flow at the entrance

Grahic Jump Location
Fig. 13

Influence of the length of the mitigation zone on the effectiveness of the diffusor




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In