Category Archives: EuroSun2008-5

Emulated water supply mains

The energy balance of the storage tank is drawn a number of times within the course of the efficiency test of SDHW systems. This is achieved by means of highly accurate temperature sensors in the inlet and the outlet of the storage tank.

Doing this more than the entire volume of water of the storage tank is exchanged. This needs a large amount of fresh water.

The new testing laboratory is independent from the water supply mains. Those are emulated by a cold-water-buffer-tank in combination with a process thermostat having an adequate and sufficient cooling power.

This setup provides advantages to carry out the necessary measurements and experimental investigations.

It is possible to adjust the inlet temperature into the storage tank. That way, the cold water inlet temperature will be exactly the same between two tests. This enhances the reproducibility of the tests. Especially regarding the test of the “ability of the solar plus supplementary system to cover the load” mentioned above. This test is sensible to the cold water inlet temperature.

The adjustment of the cold water inlet temperature is possible with a very high accuracy (0.1 K). That is a basic requirement for the testing of heat storages according prEN 12977-3 [2]. Thus it is possible to not only perform the testing of SDHW systems but also of heat storages.

Measuring errors due to a fluctuating water inlet temperature are reduced. The public water main supply is not always at a constant temperature.

The closed circuit can b

e vented. Measuring errors due to air bubbles in the water mains supply are decreased.

Classification of thermal solar systems

As can be seen from the title of the standards, the thermal solar systems have been divided into two groups: “factory made systems” and “custom built systems”. This division was necessary in order to be able to include the whole spectrum of thermal solar systems in Europe, which ranges from small compact systems (thermo-siphon and integrated collector-storage-systems) to very large systems individually designed by engineers. The classification of a system “as factory” made or “custom built” is a choice of the final supplier in accordance to the following definitions:

Factory made solar heating systems are batch products with one trade name, sold as complete and ready to install kits, with fixed configuration. Systems of this class are considered as a single product and assessed as a whole. For the determination of its thermal performance, such a system is tested as one complete unit. If a factory made solar heating system is modified by changing its configuration

or by changing one or more of its components, the modified system is considered as a new system for which a new test report is necessary.

Custom built solar heating systems are either uniquely built, or assembled by choosing from an assortment of components. Systems of this category are regarded as a set of components. The components are separately tested and test results are integrated to an assessment of the whole system.

Custom built solar heating systems are subdivided into two categories:

Large custom built systems are uniquely designed for a specific situation. In general HVAC engineers, manufacturers or other experts design them (HVAC: heating, ventilation, air­conditioning).

Small custom built systems offered by a company are described in a so called assortment file, in which all components and possible system configurations, marketed by the company, are specified. Each possible combination of a system configuration with components from the assortment is considered as one custom built system.

Table 2 summarises the different types of thermal solar systems. As a consequence of this way of classification, forced circulation systems can be considered either as factory made or as custom built, depending on the market approach chosen by the final supplier. Hence it is essential that the performance of these systems is determined for the same set of reference conditions as specified in Annex B of EN 12976-2 and Annex A of ENV 12977-2.

Table 2: Division criteria for factory made and custom built thermal solar systems

Factory Made Solar Heating Systems

Custom Built Solar Heating Systems

Integral collector-storage systems for domestic hot water preparation

Forced-circulation systems for hot water preparation and/or space heating, assembled using components and configurations described in a documentation file (mostly small systems)

Thermosiphon systems for domestic hot water preparation

Forced-circulation systems as batch product with fixed configuration for domestic hot water preparation

Uniquely designed and assembled systems for hot water preparation and/or space heating (mostly large systems)

During the past four years the standards listed above were revised and updated. This procedure resulted in the publication of the following revised version or new parts of standards respectively (see Table 3). The most important changes and highlights resulting from the revision will be described separately for each of the three standard series in the following chapters.

Experimental setup

The experiments are carried out in a domestic hot water tank and a space heating tank. Both tanks are of steel and have a volume of 400 litres with an internal height of 1.4 metres.

In the domestic hot water tank, fresh domestic water with high natural lime content, usual for Danish conditions, is led into the tank during cooling of the tank. During heating the water is circulated from the bottom of the tank through an external heat exchanger where it is heated and then led into the fabric pipe through the bottom of the tank. In this way domestic hot water is led into the fabric stratifier through the bottom of the tank. The inner surfaces of the domestic hot water tank are enamelled.

In the space heating tank, the same “dead” water is circulated. During heating the water is circulated from the bottom of the tank through an external heat exchanger where it is heated and then led into the fabric pipe through the bottom of the tank. In this way “dead” water is led into the fabric stratifier through the bottom of the tank. The inner surfaces of the space heating tank are not enamelled, no anode preventing corrosion is used and no additives preventing algae growth are added to the water.

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Fig. 1. The space heating tank (left) and the domestic hot water tank (right) used for the accelerated durability tests of the fabric inlet stratification pipes. In the front of the picture, a 27 kW heating element and two plate heat exchangers used for heating the water that circulates through the inlet stratifiers can be seen.

Подпись: Fig. 2. Fabric inlet stratifiers mounted in a circle at the cap in the bottom of the tank.

The fabric inlet stratifiers consist of two concentric fabric pipes, with diameters of 40 mm and 70 mm and the pipes are closed at the top. The pipes are mounted in a circle as shown in Fig. 2. The fabric inlet stratification pipes are secured at the cap in the bottom of the tanks, which is the only opening in the tank and spread over 93% of the tank height. Heating tests where cold tanks are heated with hot water through one fabric stratifier at the time, then cooled down again/heated again and so on are carried out during the test period. Tank temperatures, inlet and outlet temperatures and the volume flow rate through the inlet stratification pipes are measured during the whole test period.

2. Results

The results of the investigations show that several of the tested fabric pipes build up thermal stratification in exactly the same way after being in operation for a long time in the space heating tank. The investigations also show that this is not the case with any of the fabric pipes in the domestic hot water tank.

Table 2 shows the investigated fabric styles and the main results. Most likely there is a problem with deposits of lime attached to all pipes in the domestic hot water tank resulting in a strongly decreased ability to build up thermal stratification for all the fabric pipes tested.

For the space heating tank with “dead” water five of the tested fabric inlet stratifiers work at the end of the test period without decreased ability to build up thermal stratification, while two fabric inlet stratifiers have decreased ability to build up thermal stratification.

In order to eliminate small differences in the start temperature and inlet temperature from one experiment to the next in tests conducted with the same operation conditions, the normalized temperatures are used when comparing the thermal stratification profiles in the following figures. The normalized temperature is defined as:

(T — Ttank, start)/(Tinlet-Ttank, start ) (1)

In Fig. 3 — Fig. 5 normalized temperatures as functions of the height in the tanks obtained during heating periods are shown in the middle and at the end of the test period. For example, the heating curves for the fabric inlet stratification pipes style 769, 700-12 and 981 are shown for tests with a volume flow rate of 6 l/min, inlet temperatures of 44°C — 46°C over a time period of five months.

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image071

Curves after 10, 20, 30 and 40 minutes of heating are shown. From the figures it is clear that capability to build up thermal stratification is strongly decreased in the domestic hot water tank during the five-month period for the three shown fabric pipes. For the fabric pipes in the space heating tank, the capability of building up thermal stratification is slightly decreased for the fabric pipe style 981 while the capability of building up thermal stratification for the fabric pipes style 769 and 700-12 is unchanged during the five month-period.

Table 2. The tested fabric styles and main results.

Fabric Style #

Domestic hot water tank

Space heating tank

Style 361

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is decreased within the test period.

Style 769

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is unchanged within the test period.

Style 700-3

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is unchanged within the test period.

Style 700-12

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is unchanged within the test period.

Style 864

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is unchanged within the test period.

Style 867

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is unchanged within the test period.

Style 981

The fabric inlet stratifier fails to build up thermal stratification with time.

The performance of the fabric inlet stratifier is decreased within the test period.

-0.2 0 0.2 0.4 0.6 0.8 1 -0.2 0 0.2 0.4 0.6 0.8 1

(T_Ttank, start)/(TinleirTtank, start) [-] (T-T tank, start)/(TmlefTtank, start) [-]

Fig. 3. Temperature profiles for heating tests with the fabric inlet stratification pipe style 769 in the domestic
hot water tank (left) and the space heating tank (right). The volume flow rate is 6 l/min.

Fig. 6 shows the fresh fabric styles 700-12 (left) and 981 (right) before the tests. Fig. 7 and Fig. 8 show the fabric styles after the test period in the domestic hot water tank and in the space heating tank, respectively. The pictures are of the inside of the top of the inner fabrics. The fabric style 700-12 is a knit fabric with a dense structure while fabric style 981 is a woven fabric with relatively large holes in the structure. All the dark areas in the pictures are holes in the fabric structure. The pictures in Fig. 7 clearly show the lime deposits along the fabric fibres on both fabric styles. The pictures in Fig. 8 show smaller fractions of deposits, presumably from dirt and algae.

In the pictures, it can be clearly seen, that the fabrics are still permeable after the tests, especially the fabric style 981. However, deposits may result in stiffness of the fabric and hence prevent the fabric from contracting in order to equalize the pressure difference between the fabric pipe and the water in the tank in levels where the temperature in the pipe is higher than the temperature in the tank. This will result in the fabric starting to behave as a rigid pipe with holes where the pressure causes water to enter the fabric pipe at lower levels and thereby reducing the temperature in the pipe. Such a pipe is a mixing device rather than a stratification device [4].

Fig. 6. Pictures of two fabric styles before being tested. Left: Fabric style 700-12. Right: Fabric style 981.

 

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Fig. 7. Pictures of two fabric styles after being tested in the domestic hot water tank. Left: Fabric style 700­12. Right: Fabric style 981.

 

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Fig. 8. Pictures of two fabric styles after being tested in the space heating tank. Left: Fabric style 700-12.

Right: Fabric style 981.

 

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In order to quantify the mass of the deposits attached to the fabric pipes, the pipes were taken out of the tanks and weighted. Figure 9 shows the gained weight of each fabric pipe.

6

 

Style 700-12

■ Style 769

■ Style 700-3

■ Style 867 Style 361

■ Style 864 Style 981

 

Domestic hot water Domestic hot water Space heating tank — Space heating tank — tank — Inner pipe tank — Outer pipe Inner pipe Outer pipe

 

Fig. 9. Additional weight of the fabric inlet stratification pipes after the test period of one year.

For most fabrics, the deposit amounts are greater for the domestic hot water tank than for the space heating tank. However, for style 867 it is the other way around. For this fabric the ability to build up thermal stratification is not decreased in the space heating tank while the ability is strongly decreased in the domestic hot water tank in spite of the small deposited amounts. This indicates that it is the structure of the deposits that is important. Most likely the deposits result in rigid inflexible pipes while dirt and algae deposits at least for a long period of time do not destroy the flexibility of the fabric pipes.

 

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5. Conclusion and outlook

The long time durability of seven different fabric inlet stratification pipes is investigated experimentally in a domestic hot water tank and in a space heating tank. The results show that the lime contained in the domestic water is deposited in the fabric pipes in the domestic hot water tank and that this destroys the capability of building up thermal stratification for the fabric pipe. The results also show that although dirt, algae etc. are deposited in the fabric pipe in the space heating tank, the capability of the fabric inlet stratifiers to build up thermal stratification is unchanged for five of the seven fabric pipes within an operation period corresponding to operation of a solar heating system with a solar collector area of 10 m2 with a volume flow rate of 0.2 l/min per m2 solar collector area in 2/3 year.

Most likely the deposits result in rigid inflexible pipes while dirt and algae deposits, at least for a long period, do not destroy the flexibility of the fabric pipes.

The investigations have also shown that there is a need for further research on:

• Durability tests for much longer period of time of fabric inlet stratification pipes in a space heating tank

• The influence on the amount of deposits of dirt, algae etc. in the fabric pipe by adding e. g. an anode for corrosion protection and additives to prevent algae growth in the space heating tank used for the durability tests

• The durability of fabric inlet stratification pipes at high temperatures (90-95°C)

• How the mounting of the fabric inlet stratification pipe influences the capability of building up thermal stratification

Nomenclature

T Measured temperature in the tank during the experiment [°C]

Ttank, start Measured temperature in the tank at the beginning of the experiment [°C]

Tinlet Measured inlet temperature [°C]

References

[1] E. Andersen, S. Furbo, J. Fan, (2007). Multilayer fabric stratification pipes for solar tanks, Solar Energy, Vol. 81, pp. 1219-1226.

[2] E. Andersen, S. Furbo, M. Hampel, W. Heidemann, H. Muller-Steinhagen, (2007). Investigations on stratification devices for hot water heat stores, International Journal of Energy Research, May 2007.

[3] E. Andersen, S. Furbo, (2006). Fabric inlet stratifiers for solar tanks with different volume flow rates, in proceedings of EuroSun 2006 Congress, Glasgow, Scotland

[4] L. J Shah, E. Andersen, S. Furbo, (2005). Theoretical and experimental investigations of inlet stratifiers for solar storage tanks. Applied Thermal Engineering 25, pp. 2086-2099.

PET and PVC

The PET samples became brittle and degenerated already after 10 years of exposure. In the case of PVC high losses in transmittance were observed, but mechanical destruction occurred only after 20 years. These samples showed a colour change over yellow and brown to a non-transparent black. This effect was accelerated when exposed under a protective glazing with high transmittance, indicating that temperature and not radiation dose is the driving parameter.

5. Conclusion

PMMA showed the lowest soiling of the investigated polymers and no significant degradation, which resulted in a better overall weathering performance than the tested glasses. Some PMMA — types showed a persistent UV-blocking over the whole 20 years of exposure. They can be recommended to serve as weather resistant UV-protection coating for other materials such as PC for example. The fluorinated polymer films suffered from surprisingly high total losses mainly caused by soiling (FEP and PVF). For the ETFE samples high losses remained even after cleaning with ethanol such that material degradation can’t be excluded. The tested PC types showed yellowing effects and material erosion already after some years of exposure. The UV-protection additives of the tested PC-types were not able to prevent material degradation at the surface. The tested PET, PVC and UP products are unsuitable for the use as collector glazing because of high losses in transmittance or fast mechanical destruction.

1

High losses in solar transmittance due to soiling were observed (especially in Rapperswil). Structured glass-surfaces for reflex reduction had no effect on soil accumulation. Soiling leads to elevated losses in the solar transmittance of the collector glazing which can be assigned to the collector efficiency within wide limits. For that reason a regular cleaning of solar collectors is recommended, especially for polluted sites or glazing composed of FEP or PVF. PMMA, FEP and PVF have a better cleaning capability than glasses.

Acknowledgements

The work presented has been supported by the Swiss Federal Office of Energy SFOE. Some results could have been contributed to the IEA SHC Task 39. Many thanks go to Ueli Frei who initiated this project and to Thomas Hauselmann for many hours of sample preparation and measurements.

References

[1] Gary Jorgensen, Adoption of General Methodology to Durability Assessment of Polymeric Glazing Materials, IEA SHC Task 27.

[2] J. Vitko, Jr, J. E. Shelby, Solarisation of Heliosat Glasses, Solar Energy Materials 3 (1980) 69-80.

[3] Colom X., Garcia T., Sunol J. J, Saurina J., Carrasco F., Properties of PMMA artificially aged, Journal of Non-Crystalline Solids 28 (2001) 308-312.

[4] G. F. Tjandraatmadja, L. S. Burn, M. C. Jollands, Evaluation of commercial polycarbonate optical properties after QUV-A radiation—the role of humidity in photodegradation, Polymer Degradation and Stability 78 (2002) 435-448.

[5] Ram A., Zilber O., Kenig S., Life expectation of polycarbonate. Polymer Engineering & Science. 25 (1985) 535-540.

[6] A. Davis, D. Sims, (1983). Weathering of Polymers, Applied Science Publishers LTD, Essex, England.

Normative requirements of „Impact Resistance Tests“

Table 2 shows a comparison of the present requirements of the methods of impact resistance tests of the transparent cover of solar thermal collectors and pv-modules which directly influence the energy transmitted during the impact and thus also the damage potential. Only requirements concerning tests with ice balls and no steal ball tests are listed.

Table 2. Normative requirements to the diameter, the mass and the velocity of the ice balls.

Durchmesser In mm

Masse In g

Geschwindigkeit in m/s

Kinetische Energie in J

EN12975-1,2:2006

25,0

7,53

23,0

1,99 ± 0,10

AS/NZS 2712:2007

25,0

7,50

23,0

1,98 ± 0,10

IEC61215: 2005-4

12,5

0,94

16,0

0,12 ± 0,01

15,0

1,63

17,8

0,26 ± 0,01

25,0

7,53

23,0

1,99 ± 0,10

35,0

20,70

27,2

7,66 ± 0,38

45,0

43,90

30,7

20,69 ± 1,04

55,0

80,20

33,9

46,08 ± 2,31

65,0

132,00

36,7

88,89 ± 4,45

75,0

203,00

39,5

158,37 ± 7,93

ASTM E 1038 — 5

15,0

1,60

17,2

0,24 ± 0,01

25,0

7,50

22,2

1,85 ± 0,09

35,0

20,60

26,3

7,11 ± 0,36

45,0

43,90

29,8

19,47 ± 0,98

55,0

80,10

32,9

43,42 ± 2,18

65,0

132,20

35,8

84,70 ± 4,24

75,0

203,00

38,5

150,07 ± 7,51

85,0

296,00

40,9

248,00 ± 12,41

The allowanced deviation of the diameter, the mass and the velocity of the ice balls, in all listed standards are ± 5% of the required values with exception of the Australian standard AS/NZS 2712:2007. The accepted deviations defined within the Australian standard are ± 1 mm in the diameter, ± 1 g in the mass of the ice ball and ± 1 m/s concerning the velocity of the ice ball. The given tolerances for the resulting kinetic energy are determined from these deviations according to the Gaussian error propagation. Unlike to the other listed standards the American standard ASTM E 1038 — 5 demands the calculation of the resultant velocity according to equation 1 and equation 2 against a given wind speed.

^ = vf + vl (1)

vt = 4.4^Jd (2)

where d is the diameter, vr is the resulting velocity, vt is the velocity of the ice ball and vw is the wind

speed (0 m/s, 15 m/s, 20 m/s or 30 m/s) chosen by the applicant of the test or the testing institution. However, for better comparison the wind speed is neglected in this consideration. Further requirements regarding the production, the handling and the quality of the ice balls as well as requirements concerning the test assembly, the framing conditions and the test procedures are quite similar in the discussed standards. The differences are:

• AS/NZS 2712:2007 defines a higher storage temperature of the ice balls than the other standards (0°C in comparison to -4°C ± 2°C).

• The maximum time between the removal of the ice ball from the storage container and the launching of the ice ball is not specified in AS/NZS 2712:2007 and ASTM E 1038 — 5. Both other standards specify a maximum time of 60 seconds.

Reflectivity Measurement

image025 image026

The device shown in Fig. 15 consists of a laser and detector mounted on a support structure that can be positioned to measure reflectance of mirror surface samples from the ICPC. Using this device, a map of reflector performance for the ICPC array has been generated.

Fig. 18. Third Level Reflectance Degradation. Fig. 19. Fourth Level Reflectance Degradation.

Four levels of reflectance degradation are identified for the Sacramento site. At level 1 degradation, shown in Fig. 16, the reflector still performs well with just a minor change in the reflector appearance. In level 2 degradation, shown in Fig. 17, there is some whitening of the reflector. In level 3 degradation, shown in Fig.18, there is a substantial amount of degradation of
the reflector. In level 4 degradation, shown in Fig. 19, most of reflector is gone and you can easily see through it.

At the site, all 336 tubes were categorized, one-by-one, by their reflectivity levels, existence of a glass crack, surface temperature, water leakage, and fin orientation. Each tube was divided into ten sections along its length. Degradation levels were identified and marked for each of the ten sections. Fig. 20 shows a color mapping of tube degradation information for a portion of the array.

Подпись:

Подпись: 3. Conclusions A detailed ray trace analysis for characterizing the optical performance of ICPC evacuated tubes has been described and its results illustrated. As a consequence of the ray tracing, it was found that reflectivity degradation will play a significant role in the reduction of array efficiency. The nature of reflectivity degradation depends on the type of failure, such as water leakage from the heat transport tube or cracks in the cover glass. Overall performance is also degraded by the loss of vacuum in the tube. An analysis of the performance consequences of reflector degradation and loss of vacuum degradation will be incorporated into the reliability study.

Reflector samples representative of the four different degradation levels were taken from the Sacramento site for measurements in the laser laboratory at Colorado State University, as in Fig. 21. The samples for the four levels of degradation and undegraded reflector samples were measured for their reflectivity by the laser and detector device. Using this device, a map of reflector performance for the ICPC array is being generated. The reflectance results are shown in Table 1 for each level of degradation.

References

[1] Garrison, J. D., Optimization of Fixed Solar Thermal Collectors, Solar Energy, v23, 1979

[2] Snail, J. J., O’Gallagher and R. Winston, A Stationary Evacuated Collector with Integrated Concentrator, Solar Energy, v33, 1983

[3] Подпись: Fig. 21: Laser and Sensor Assembly in the Colorado State University Laser Laboratory. Winston, R, O’Gallagher, J., Mahoney, A. R., Dudley, V. E. and Hoffman, R., “Initial Performance Measurements from a Low Concentration Version of an Integrated Compound Parabolic Concentrator (ICPC)”, Proceedings of the 1999 ASES Annual Conference, Albuquerque NM, June, 1998 [5] [6]

O’Gallagher, Tom Henkel and Jim Bergquam, “Performance of the Sacramento Demonstration ICPC Collector and Double Effect Chiller in 2000 and 2001”, Solar Energy, vol. 76, pages 175-180, January 2004.

[6] Duff, William, Jirachote Daosukho, Klaus Vanoli, Roland Winston, Joseph O’Gallagher, Tom Henkel and Jim Bergquam, “Comparisons of the Performance of Three Different Types of Evacuated Tubular Solar

Collectors”, American Solar Energy

Table 1: Measurement of Reflectivity S°ciety 2006 Denvei;

Colorado, July 2006.

[7] Подпись: Degradation Level Percent Reflectivity Good 93.48 1st 79.66 2nd 38.46 3rd 22.93 4th 1.24 Duff, William S. and Jirachote Daosukho, “A Performance and Reliability Study of a Novel ICPC Solar Collector Installation”, American Solar Energy Society 2007 Congress, Cleveland, Ohio, July 2007.

The building design project documents and organization

It would be important to ensure that the homeowner or the condominium could have an operating and instructions manual, identifying equipment schemes, safety procedures, conservations and maintenance information about the solar collector system. It is fundamental to implement some control and management measures during the life-cycle time of these equipments, especially in summer, to guarantee durability, efficiency and therefore turning this investment cost-effective. The obligatory for solar collector brings to discussion the implementation of a repair and maintenance design project for residential buildings, with a wider scope then solar collector’s subject. Residential building design is today facing fundamental changes and energy efficiency seems to be a start step to new design and property management approaches. The intelligent residential buildings concept, slightly inspired in a facility management concept in service buildings, is been slowly implemented in buildings. Monitoring and supervising devices as well as controlling and regulating systems in buildings appealed to the development of building automation. Other new building regulations are been enacted forward to get sustainable buildings, are examples: measures to better water supply and waste water management; more rigorous fire safety rules and security. A repair and maintenance design project turns to be essential and it is almost obvious that the obligatory use of solar collectors is going to accelerate this demand by

local government authorities. Also, the health and safety design project must be adapted to this new reality. A care should be taken to new risks, for example, the potential for excessive temperature and pressure in heat transfer fluids and stored water, the risk of Legionnaires’ disease, working at height and electrical safety.

Conclusion, discussion and outlook

An overview of methods for monitoring and failure detection has been presented in this paper. Several differences are highlighted by means of a partial multi-criteria analysis. The results are presented in a performance matrix, in which the methods are qualitatively evaluated with certain criteria. Quite a few methods are in an (advanced) stage of research and development, this complicates the analysis of the functioning of the different approaches. The Input/Output Controller, Guaranteed Solar Results and Manual monitoring can already be applied in commercially built solar thermal systems. Of those, the Input/Output Controller is the only one that analyses the measurement data automatically and provides an automatic failure indication.

However, none of the approaches include the auxiliary heating system. Several approaches, e. g. the method from Kassel University, are being developed further to increase the ability of detection and identification of failures. Furthermore practical experience has to be gained for a better evaluation of the performance of several approaches.

Acknowledgement

The authors gratefully acknowledge the financial support provided by the Marie Curie early stage Research Training Network ‘Advanced solar heating and cooling for buildings — SOLNET’ that is funded by the European Commission under contract MEST-CT-2005-020498 of the Sixth Framework Programme.

References

[1] Dodgson, J., Spackman, M., Pearman, A. D., Phillips, L. D., 2000. Multi-criteria Analysis: a Manual. Department of the Environment, Transport and Regions, London.

[2] Fink, C., Riva, R., Pertl, M., Wagner, W., 2006. OPTISOL — Messtechnisch begleitete Demonstrationsprojekte fur optimierte und standardisierte Solarsysteme im Mehrfamilienwohnbau. AEE — Institut fur Nachhaltige Technologien, Gleisdorf, Austria.

[3] Altgeld, H., Mahler, M., 1999. Funktionskontrolle bei kleinen thermischen Solaranlagen ohne Warmemengenmessung. Testzentrum Saarbrucken, Saarbrucken, Germany.

[4] Altgeld, H., 1999. Funktionskontrollen bei kleinen thermischen Solaranlagen ohne Warmemengenmessung. Hochschule fur Technik und Wirtschaft des Saarlandes, Saarbruecken, Germany.

[5] Grossenbacher, U., 2003. Qualitatssicherungssystem fur Solaranlagen; Methode zur permanenten Funktionskontrolle thermischer Solaranlagen. EnergieBuro Grossenbacher, Murten, Switzerland.

[6] Synetrum AG, 1998. Qualitatssicherung bei Solaranlagen: Permanente Funktionskontrolle. Synetrum AG, Murten, Switzerland.

[7] Kalogirou, S. A., Panteliou, S., Dentsoras, A., 1999. Modeling of solar domestic water heating systems using artificial neural networks. Solar Energy 65, pp. 335-342.

[8] Kalogirou, S., Lalot, S., Florides, G., Desmet, B., 2008. Development of a neural network-based fault diagnostic system for solar thermal applications. Solar Energy 82, pp. 164-172.

[9] Parisch, P., Vanoli, K., 2007. Quality assurance with the ISFH-Input/Output-Procedure 6-year-experience with 14 solar thermal systems. Proceedings of ESTEC 2007, Freiburg, Germany, pp. 315-320.

[10] Parisch, P., Vanoli, K., 2007. Wissenschaftlicher Schlussbericht Kapitel 1-6; Forschungsvorhaben: Wissenschaftlich-technische Untersuchung des ISFH-Input/Output-Verfahrens zur Ertragskontrolle solarthermischer Systeme sowie Entwicklung und Erprobung von Input/Output-Controllern. Institut fur Solarenergieforschung GmbH, Hameln/Emmerthal, Germany.

[11] Wiese, F., 2006. Langzeituberwachung grofler solarintegrierter Warmeversorgungsanlagen. Ph. D. Thesis, Kassel University, Kassel, Germany.

[12] Wiese, F., Vajen, K., Krause, M., Knoch, A., 2007. Automatic fault detection for big solar heating systems. Proceedings of ISES Solar World Congress, Beijing, China, pp. 759-763.

[13] Luboschik, U., Schalajda, P., Halagic, N., Heinzelmann, P. J., Backes, J., 1997. Garantierte Resultate von thermischen Solaranlagen; Ein Projekt zur Markteinfuhrung solarthermischer Anlagen. ASEW, Schluflbericht Projekt SE/475/93/DE/FR, EU project.

[14] Peuser, F., Remmers, K., Schnauss, M., 2002. Solar Thermal Systems. Solar Praxis AG, Germany.

Steady State (SS) versus Quasi-dynamic (QD) test methodology

1.2. Testing limits for both test methodologies

For determination of thermal performance of solar collectors, measurement of the environmental and of working conditions relevant for the collector behaviour is needed. The test methodologies for this determination, steady state (SS) and quasi-dynamic (QD), considered in EN 12975 [1] have different requirements for test.

Table 1 summarizes the main requirements set out in the standard EN 12975-2 [1].

The less stringent limits on the validation of test periods for the QD test method mean that this method can be used to gather useful information during almost the whole daylight period throughout the year.

Considering a fix stand for installation of the collector to be tested, to perform a SS test, the period useful for test is reduced to a couple of hours on a day with clear sky conditions. This period of time to test according to SS test method can be larger if a tracking stand is used. But cloudy days can not be used for SS test method, independent of the type of stand used.

For QD test method, a clear day corresponds to almost 8 hours useful for test and cloudy days also give useful information for QD test method.

Table 1: Test conditions and allowable deviations in relation to the mean values for a test period.

SS Method

QD Method

Value

Allowable deviation *

Value

Allowable deviation *

Global irradiance on collector aperture (G)

> 700 W. m-2

± 50 W. m-2

300 < G < 1100 W. m-2

Incidence angle (0)

< 20 °

Diffused fraction (Gd/G)

< 30 %

Air speed (u)

3 m. s-1 ± 1 m. s-1

1 < v < 4 m. s-1

Collector inlet temperature (te)

± 0,1 K

± 1 K

Ambient temperature (ta)

± 1,5 K

Mass flow rate (m )

± 1 %, 10 %*

± 0.02 kg. s-1.m-2

± 1 %; ± 10 %**

Regarding the mean values for a stable test period (Steady-State test) or for the total test period (Quasi-Dynamic test).

If there is no indication to the contrary, fluid flow rate should be approximately 0.2 kg. s-1 per square metre of collector reference area (A). Flow should be kept stable at ± 1% of the value determined during each test period, and should vary by no more than ± 10% compared to the other test periods._________________________________________________

Strip angle and strip width

Calculations are carried out with different strip angles for the curved absorbers and different strip widths for the flat absorbers. The interval for the strip angle investigated is from 150° to 179°. The investigated strip width for Seido 1-8 is in the interval from 0.075 m to 0.095 m. For Seido 10-20 with

Подпись:flat absorber the investigated interval is from 0.045 m to 0.065 m. The optimum strip angle and width of the absorbers are the values resulting in the largest absorber area. The optimum angles and widths for the solar collectors can be seen in Table 5.

A change of the strip angle and strip width from the values in Table 1 to 179° and 0.095m / 0.065 m will result in a change in the optimum tilt of the collectors. The largest change in the optimum tilt is again seen in Nuussuaq where the tilt is increased with 6° for Seido 5-8 and 1-8. For Seido 10-20 the increase in the tilt is
slightly less, around 2°. In Sisimiut and Copenhagen only a slight change is seen as a result of a change in the absorber area. The optimum orientation is also found for the optimum strip angle and width. Here the optimum orientation changes for Nuussuaq so that the solar collectors should be turned even more towards east so that they are turned between 55° and 60° from south towards east. For Sisimiut Seido 5-8 and 1-8 should be turned back towards south so that the solar collectors are only turned 6° and 4° degrees from south to west where they in the original optimum orientation were turned 12° and 10°. In Copenhagen the collectors should all be turned slightly more towards west, about 1°. The improvement of the thermal performance as a function of the mean collector fluid temperature is shown for Nuussuaq in Fig 4. The improvement is largest for Seido 10-20 with flat absorber where the improvement is about 17 % as an average for mean collector fluid temperatures from 20 °C to 100 °C. For Seido 5-8 Seido 1-8 the thermal performance decreases for high mean collector fluid temperatures.

Подпись: Fig 4. Improvement of the thermal performance as a result of a larger absorber area. This is caused by an increasing heat loss from the increase in absorber area. The same tendency is seen for Sisimiut and Copenhagen. The improvement in thermal performance for the four collectors at a mean collector fluid temperature of 60 °C is for Seido 5-8 about 1.5 %, for Seido 1-8 about 2 %, for Seido 10-20 with curved absorber about 12 % and for Seido 10­20 with flat absorber about 16%.