Solar Combisystems A state of the art report

1
Solar CombisystemsA state of the art report
By Frank Fiedler and Helena Gajbert Ph.D. Course
SOLAR HEATING Department of Civil
Engineering Technical University of Denmark (DTU)
1
2
Table of contents

• general aspects of solar combisystems
• Task 26
• work, results, testing methods etc.
• improvment of the components
• (tanks, materials, storage medium, insulation,
  controllers, collectors)
• system concepts
• (compact systems, integrated auxiliary heaters,
  advanced control strategies )
• conclusions

2
3
Solar combisystems in general

• European Commision market share renewable 6 -
  12 , 2010.
• Energy consumption in building sector - 40 of
  tot. energy cons. in EU - 75 for HW SH.
• Until 2000 - ca 0.11 of the total requirement
  for HW SH covered by solar thermal systems in
  residential buildings.
• According to the EU White Paper - target the
  share of solar thermal energy sources within the
  residential building sector in EU should increase
  to 1.18 until 2010. ca 100 million m2
  collector area.
• Today the installed collector area in the EU is
  ca 28 million m2 ( ca. 7 million m2 combisystems)
  - that would mean 100 million m2 (20 million m2
  combisystems) by the year 2010 - an increase of
  20 increased collector area per year.

3
4
Solar combisystems - objective increase in EU
4
5
Solar combisystems in European countries
5
6
Installed collector area in the EU per capita

• Best developed markets in the EU- Greece and
  Austria are the country with the largest
  installed collector area per capita

6
7
Hot water - Space heating

• Hot water
• Small seasonal variations
• Great daily variations
• Large temperature differences
• - high hot water temperatures
• (45-60?C)
• - low inlet (grid) temperatures
• (4-20?C).

• Space heating
• Great seasonal variation
• Small daily variations
• Small temperature differences in the heating loop
• - low delivery temperature
• (30-50?C)
• - high return temperature
• (25-45?C)

7
8
Combined HW /SH

• Difficulties of combisystem -achieve a good
  balance between..
• ...requirements of the SHsystem
• ...hot water system
• ...the consumers interests
• The DHW heat demand is usually 10 - 40 of the
  total heating demand for space heating and hot
  water together.

• The two heat loops require liquids of different
  temperatures,
• - two different tanks
• - combined tank
• Combined tank need a high level of stratification
  
• minimize mixing of temperatures and aviod
  lowered efficiency of the system.

8
9
Task 26 - Solar Combisystems

• investigation and optimisation of solar
  combisystems from several countries in Europe
  with different system concepts
• For these systems, standardised classification
  and evaluation processes are developed
• Reference conditions established
• (loads, energy sources, thermal losses,
  heat
• transfer, pipe length etc.)
• 8 representative system have been chosen and
  modelled with TRNSYS

• Results
• Parametric studies to optimize the chosen
  combisystems
• New test methods for combisystems
• Fractional energy savings/fractional solar
  consumption (FSC) as a measure compare different
  system concepts
• Systems performance strongly related to the
  boiler efficiency
• Cost performance indicator CPI

9
10
Task 26 - Testing methods

• New test methods have been developed within Task
  26 Subtask B
• WHY?
• Existing CTTSS (component testing/system
  simulation) test precedure according ENV 12977-2
• Time consuming parameter for all components
  have to be identified seperately
• Good for costumer built systems
• Results are very precise
• ? Easy test method for factory made systems is
  required

10
11
Task 26 - Testing methods

• New developed test methods
• DC (direct comparison) method
• CCT (concise cycle test) method - a twelve day
  system test

11
12
Task 26 - DC method

• Based on thermal store test precedure called
  combitest
• Indoor tests - system has to be setup
• Solar input by sun simulator or emulated by a
  heater
• Load is emulated for specific climate conditions
  and heat distribution system
• Core phase of test consist of 6 days with
  representative weathe and load conditions for one
  year
• Auxilliary energy is the performance indicator
  for the system
• With this method also the function of the control
  system is evaluated interplay between solar and
  auxilliary

12
13
Task 26 - DC method

• Limited to system size up to 20 m2 collector area
  and 2000 liter storage
• For larger systems the prediction error is too
  large
• Results are only valid for simular climate and
  load conditions
• ? three climate zones and three load profiles
  are defined to simplify comparisons

13
14
Task 26 - CCT method

• Similar to the DC method
• Core phase of 12 days
• Building load is simulated online, system decides
  by its controller how the heat is supplied
• Allows to characterise systems with the building
  mass as heat storage
• No predictable energy use for space heating
  complicates characterisation
• Both test method are still need validation and
  more practical experience!

14
15
Improved components for combisystems

• Storage Tanks
• Smart tanks and mantel heat exchangers
• PCM Phase change materials
• Improved stratification units
• Better insulation material
• Other components
• Collector
• Controller

15
16
Improved insulation for the storage

• 5-10 heat losses from the storage even for well
  insulated storages
• Space demand for thicker insulation is limited
• Better insulation material are required
• Vacuum insulation already used for other
  applications
• 5 to 10 times smaller heat conductivity
• silicic acid with a very small pore size
• produced in under low pressure and packet in
  panels and covered with an gas-tight foil

16
17
Improved components for combisystemscollectors

• Load mismatch
• Over heating

17
18
Improved components for combisystemsCollectors

• MaReCo- spring-/fall collector
• Designed and developed at Vattenfall Utveckling
  AB
• Parabolic reflector, bifacial absorber
• Optimised for low solar altitude angles
• The summer production will be lowered, thus
  preventing overheating and stagnation

18
19
Improved components for combisystemsCollectors
19
20
Improved components for combisystemsCollectors

• MaReCo Spring-/Fall Collector
• The concentrated irradiation increases the energy
  output - it will be sufficient to use less
  absorber area
• less over heating
• Cheep reflector -compensates for larger area
• cost reductions for the whole system.
• It was shown that the energy output decreased in
  the summer, preventing over heating, still giving
  an annual output of 222 kWh/m2

20
21
Load adapted collector

• Simple geometry with internal reflector
• Low optical efficiency in the summer (prevents
  overheating)
• High optical efficiency in spring and autumn
• Improved thermal performance (small absorber
  area)
• Potential for price reduction

21
22
Advanced Control Strategy

• predictive control using weather forecast
• Dynamic model of the combisystem and the building
• Automatic parameter identification of the
  building
• Auxiliary energy savings up to 13
• Lower mean temperature for the advanced control
  strategy
• Better regulation performance

22
23
Compact systems

• From a complex design with many seperate
  components to a compact system with the one
  combined storage as the main component
• Advantages - less control and hydraulik problems
• - easier and faster installation
• - less connections, shorter pipes ? less
  losses
• - cheaper less material and space demand
• But storage has to be carefull designed and
  allow a good stratification,
• connections to the storage have to be placed at
  the right temperature layer

23
24
Compact systems store integrated pellet burner

• Pellets Integral developed at SERC
• Compact design 50 cm long, diamater 25cm
• Can be mount in any store
• Automatical ash removal and cleaning of the heat
  exchanger
• Low flue gas temperature long path through the
  spiral heat exchanger
• So far only two prototypes exist

24
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
Conclusions

• Combisystem have made a big step forward from
  complicated costumer made systems towards compact
  factory made systems
• Within Task 26 this systems have been
  systematically investigated and optimized
• There is still a large potential for improvements
  of components and concepts

32