Heat storage for solar heating systems Department of Civil - - PowerPoint PPT Presentation

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Heat storage for solar heating systems Department of Civil - - PowerPoint PPT Presentation

Dec 29, 2022 23 likes •274 views

Heat storage for solar heating systems Department of Civil Engineering Now and in the future Simon Furbo Department of Civil Engineering Technical University of Denmark Brovej building 118 DK-2800 Kgs. Lyngby, Denmark Tel.: +45 45 25 18

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Department of Civil Engineering

Heat storage for solar heating systems Now and in the future

Simon Furbo Department of Civil Engineering Technical University of Denmark Brovej – building 118 DK-2800 Kgs. Lyngby, Denmark Tel.: +45 45 25 18 57, Fax: +45 45 93 17 55 E-mail: sf@byg.dtu.dk

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BYG DTU BYG DTU

Department of Civil Engineering

Solar tanks for

  • Solar Domestic Hot water Systems
  • Solar Combi Systems
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BYG DTU BYG DTU

Department of Civil Engineering

Small Solar Domestic Hot Water Systems

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BYG DTU BYG DTU

Department of Civil Engineering

China

Thermo syphon systems

Southern Europe

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BYG DTU BYG DTU

Department of Civil Engineering

Central & northern Europe

Pumped systems

Solar collector Auxiliary energy supply Mantle tank Hot water Cold water

Low flow Mantle tank

Solar collector Auxiliary energy supply Spiral tank Hot water Cold water

High flow Spiral tank

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BYG DTU BYG DTU

Department of Civil Engineering

Advantages by low flow mantle tank systems compared to high flow spiral tank systems

  • Extra thermal performance: 10-25%
  • Improved performance/cost ratio: 39%
  • Reduced lime deposits: 2.5 times

Lime in tank after 3 years of operation Spiral tank Mantle tank

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BYG DTU BYG DTU

Department of Civil Engineering

Marketed mantle tanks can be strongly improved by simple design changes

500 600 700 800 900 1000 1100 1200 Danlager 1000 Large H/D-ratio Large H/D-ratio, Smaller mantle Large H/D-ratio, Smaller mantle, More insulation Large H/D-ratio, Smaller mantle, More insulation, Stainless steel (3mm) Large H/D-ratio, Smaller mantle, More insulation, Stainless steel (2mm) Net utilised solar energy [kWh/year] 0,1 0,2 0,3 0,4 0,5 0,6 0,7 Solar fraction [-] Net utilised solar energy Solar fraction

20% extra thermal performance by:

  • Increased height/diameter ratio
  • Reduced mantle height
  • Lowering the position of the mantle inlet
  • Increased insulation thickness on the sides of the tank

Further improvements by use of tank material with low thermal conductivity

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BYG DTU BYG DTU

Department of Civil Engineering

Control

Improved cold water inlet design

Standard cold water inlet Cold water inlet with reduced mixing during draw-offs

Extra thermal performance: 5%

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BYG DTU BYG DTU

Department of Civil Engineering

Hot water tank with hot water draw-off from two levels Extra thermal performance: 5%

RAVI valve Electric heating element PEX pipe PEX pipe Mantle Three way valve Electric heating element

Marketed tank Tank with two draw-off levels

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BYG DTU BYG DTU

Department of Civil Engineering

Boiler/hot water tank unit

Potential advantages:

  • Increased efficiency of natural gas

boiler/oil boiler

  • Increased thermal performance of

solar heating system

  • Increased energy savings
  • Reduced space demand
  • Easy to install
  • Easy to sell
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BYG DTU BYG DTU

Department of Civil Engineering

Smart hot water tank

Marketed solar tank Smart solar tank

Tank heated from the top Individual variable auxiliary volume Auxiliary energy supply fitted to heat demand

Extra thermal performance: Up to 35% Cost/performance improvement: Up to 25%

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BYG DTU BYG DTU

Department of Civil Engineering

Large Solar Domestic Hot water Systems

Collector area: 336 m², partly facing east, partly facing west Collector tilt: 15° Tank volume: 10000 l Measured net utilized solar energy (2001-2002): 455 kWh/m² year; solar fraction: 21% (10%) Utilization of solar radiation: 46%

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BYG DTU BYG DTU

Department of Civil Engineering

Solar combi systems

CONTROL

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BYG DTU BYG DTU

Department of Civil Engineering

Solar tanks for solar combi systems

A huge variety of designs exist: and so on …………………………………………………

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BYG DTU BYG DTU

Department of Civil Engineering

Important for a well performing system

  • Good interplay between solar collector and

auxiliary energy supply system

  • Small auxiliary volume in top of tank
  • Low temperature level of auxiliary volume
  • Low heat loss from heat storage
  • Good thermal stratification in heat storage
  • Independent of operation/installation conditions

Vacuum panel

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BYG DTU BYG DTU

Department of Civil Engineering

Increased thermal performance due to increased thermal stratification. Why?

  • Low temperature in lower part of tank results in

longer operation periods for the solar collector and thus increased collector performance

  • High temperature in upper part of tank will meet the

heat demand and/or turn off the auxiliary energy supply system

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BYG DTU BYG DTU

Department of Civil Engineering

SH

Solar DHW Solar Solar DHW Solar Solar DHW SH DHW = Domestic Hot Water SH = Space Heating Inlet stratifiers for thermal stratification

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BYG DTU BYG DTU

Department of Civil Engineering

Solvis inlet stratifier

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BYG DTU BYG DTU

Department of Civil Engineering

New fabric inlet stratifier – stratifier of the future?

Status

  • Excellent thermal performance
  • Water inlet in all levels
  • Inexpensive
  • Easy to transport and store
  • Optimal diameter influenced by

flow rate Future investigations

  • Long time durability
  • Experience from practice

Stratifier with two fabric layers

70 mm 40 mm

Fabric

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BYG DTU BYG DTU

Department of Civil Engineering

SH: Space heating DHW: Domestic hot water AUX: Auxiliary energy SOLAR: Solar energy

AUX SOLAR SH DHW

Theoretical investigations of solar combi system with different solar tanks Collector area: 20 m² Solar tank volumne: 1000 l Danish weather data

1.1 1.2 1.3 1.4

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BYG DTU BYG DTU

Department of Civil Engineering

Reference system

2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 5000 10000 15000 20000 Space heating consumption [kWh/year] Annual net utilized solar energy [kWh/year]

spiralHX/fixSH strsolar/fixSH spiralHX/strSH strsolar/strSH DHW 200 l/day DHW 100 l/day 1.1 1.2 1.3 1.4

1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 5000 10000 15000 20000 Space heating consumption [kWh/year] Performance ratio [-]

strsolar/fixSH-DHW100 strsolar/fixSH-DHW200 spiralHX/strSH-DHW100 spiralHX/strSH-DHW200 strsolar/strSH-DHW100 strsolar/strSH-DHW200

1.1 1.2 1.3 1.4 1.1 1.2 1.3 1.4 1.2 1.3 1.4

Step by step improvement

Optimal position

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BYG DTU BYG DTU

Department of Civil Engineering

1.1 1.2 1.3 1.4 3.2 3.3 3.4 2.2 2.1 3.1

Reference systems Stratifier in solar collector loop Stratifier in space heating loop Stratifier in solar collector loop and in space heating loop Theoretical investigations

Heat storage with side-arm Hot water tank with heat exchanger spiral for space heating

AUX AUX AUX SOLAR SOLAR SOLAR DHW DHW DHW SH SH SH

Tank in tank

Best tank ☺

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BYG DTU BYG DTU

Department of Civil Engineering

General:

  • Tank/auxiliary energy supply system unit
  • Smart tanks/smart control systems
  • Solar/electric heating systems based on heat from wind turbines in windy

periods; advanced control based on weather forecast Tank types:

  • Tank in tank storage with inlet stratifiers
  • Bikini mantle tanks
  • Seasonal PCM heat storage based on material with stable super cooling

Future heat stores for solar combi systems

Condensing natural gas boiler
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BYG DTU BYG DTU

Department of Civil Engineering

Conclusions

  • Possiblities for huge improvements of marketed solar tanks!

Future solar tanks General

  • Solar tank/auxiliary energy supply system units
  • Low tank heat loss
  • No thermal bridges/pipe connections in upper part of tanks
  • Variable auxiliary volume fitted to heating demand
  • Smart control of auxiliary energy supply system
  • Highly stratified solar tank: Limited mixing, low downwards heat conduction,

stratified charge and discharge SDHW systems

  • Mantle tanks
  • Hot water tanks with inlet stratifier(s)

Solar combi systems

  • Tank in tank heat storage with inlet stratifiers
  • Bikini tanks
  • Seasonal PCM stores
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BYG DTU BYG DTU

Department of Civil Engineering

Ph.D. Course Thermal stratification in solar storage tanks September 27 – October 17, 2007

  • Kgs. Lyngby, Denmark: October 10-17, 2007

Organized by: Department of Civil Engineering Technical University of Denmark, DTU SUPPORTED BY SOLNET

Thermal stratification in solar storage tanks Department of Civil Engineering at the Technical University of Denmark, DTU, is hosting this Ph.D. course

  • n Thermal stratification in solar storage tanks.

For small solar heating systems the heat storage is the most important component, both from a thermal and economical point of view. The thermal performance of solar heating systems is strongly influenced by the thermal stratification in the heat

  • storage. The better thermal stratification in the solar tank

is built up and maintained the higher the thermal performance of the solar heating system. Consequently, it is very important that solar tanks are designed in such a way that thermal stratification is built up in the best possible way. Further, in order to develop optimum designed solar tanks and evaluate differently designed solar storage tanks it is important to be able to model, measure and characterize thermal stratification in solar storage tanks. The course is focused on all aspects of thermal stratification in solar storage tanks