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14 декабря, 2021
Several criteria can be considered for comparing storage technologies. Task 32 of IEA SHC prepared a detailed list. The first indicator concerns the energy performance of a combisystem with the storage technology. The value of Fsav the fractionnal energy saving has been selected as the best indicator and can be derived from the parameter FSC’.
FSC’ is a dimensionless quantity simultaneously taking into account the climate, the building (space heating and domestic hot water loads) and the size of the collector area, in a way that doesn’t depend on the studied combisystem. First developed within IEA SHC Task 26 [2], the FSC (Fractional Solar Consumption) has been improved in Task 32 to yield to FSC’ which takes into account a possible cooling load also, and the ability of a store to be seasonal.
This means that it has been possible to show that Fsav is a function of FSC’ even if FSC’ is greater than 1.
Energy performance indicators
NRJ1 Fractional energy savings Fsav as a function of FSC’
NRJ2 Comfort for heating and DHW load met without penalties
NRJ3 Comfort in cooling conditions
NRJ4.1 Heat storage material energy density kWh/m3
N RJ4.2 Bulk storage density kWh/m3
NRJ4.3 Storage efficiency
Economical indicators
ECON1 Investment cost per kWh stored
ECON2 Operational costs per kWh discharged
Market introduction
MKT 1 1 if on the market, 2 if within 3 years, 3 in more than 3 years
Environmental indicators
ENV1 Storage material risk (corrosion + toxicity + safety)
ENV2 CO2 saved by the system compared to a reference System integration
INT1 weight of material for the storage unit kg/kWh capacity
INT2 number of separate pieces
INT3 level of skills required to install the storage unit
INT4 need for technical maintenance
Table 1. Criteria considered for comparison of heat storage units within Task 32
In order to assess Fsav in comparable conditions it is necessary to set up a standard simulation framework that many different systems can use. Task 32 defined a complete set of parameters for TRNSYS simulations, for 3 different reference houses (a low energy house with only 30 kWh/m2 for
space heating, 60 and 100 kWh/m2) in 4 different climates (Stockholm ,Ztirich, Barcelona, Madrid). The entire deck of parameters is available through IEA SHC.
Storage technologies integrated into a solar combisystem can be compared using this new method.
Water is still the storage of choice for solar combisystems for the years to come. Some important findings for other materials have been discovered by Task 32. Models are now available for more optimisation analysis and for defining the best material a combisystem would need.
Several technologies for advanced storage concepts have been tested within Task 32. Table 2 summarizes them and their status at the end of 2007.
Future work on new materials for heat storage is important since we discover the limits of some promising components.
A new IEA Task will continue the work Task 32 has initiated, but will be more focused on material research.
Solar energy need a dense and long term storage solution if it is to used intensively for house heating.
References
[1] Hadorn J.-C. editor, (June 2005), Thermal energy storage for solar and low energy buildings — State of the Art, a IEA SHC Task 32 book, Printed by Servei de Publicacions Universidad Lleida, Spain, 170 pages ISBN 84-8409-877-X, available through Internet www. iea-shc. org Task32
[2] IEA SHC Task 26 (2004): Solar Heating Systems for Houses — A Design Handbook for Solar Combisystems, W. Weiss and al., James & James, 2004, 313 pages
[3] Task 32 reports are available at http://www. iea-shc. org/task32/publications/index. html
Principle |
Material |
Institute |
Status 2007 |
Chemical reactions |
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Closed 2 phase absorption |
Mg SO4 7H20 |
ECN The Netherlands |
Material investigation |
Sorption |
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Open adsorption |
Zeolite solid |
ITW Germany |
Laboratory unit |
Closed adsorption |
Silica gel particles in bed |
AEE Austria |
System in a house tested — stopped |
Closed adsorption |
Silica gel and Zeolite beds |
SPF Switzerland |
Material and bed tested — stopped |
Closed 2 phase absorption |
NaOH / H2O |
EMPA Switzerland |
Laboratory unit runing |
Closed 3 phase absorption |
LiCl |
SERC Sweden |
commercial |
PCM |
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PCM seasonal storage using subcooling |
Na(CH3COO)3 H2O |
DTU Denmark |
Simulation of concept — Prototype 135 liters |
Macroencapsulated PCM in storage tank |
Na(CH3COO)3 H2O + graphite |
Univ. Lleida, Spain |
Lab prototype |
Macroencapsulated PCM in storage tank with integrated burner |
Na(CH3COO)3 H2O + graphite |
HEIG-VD Switzerland |
Complete combisystem tested |
Microencapsluated PCM slurry |
Paraffin, |
IWT-TUGraz Austria |
Lab prototypes — Stopped for storage |
Macroencapsulated PCM in storage tank |
Paraffine, Na(CH3COO)3 H2O with/without graphite |
IWT-TUGraz Austria |
Lab prototypes |
Immersed heat exchanger in PCM |
Na(CH3COO)3 H2O without graphite |
IWT-TUGraz Austria |
Lab prototypes |
Water |
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Simplified combisystem Maxlan system |
Water |
SPF Switzerland |
Simulation proved |
Water Stratifier |
Fabrics immersed in water |
DTU Denmark |
Laboratory proved |
Table 2. Storage technologies that IEA Task 32 has investigated between 2003 and 2007 |