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Reliability of hot water solar systems in Greece
So/at Energy VoL 44, No. 6, pp. 305-313, 1990 Printed in the U.S.A.
0038-092X/90 $3.00 + .00 Copyright © 1990 Pergamon Pnm ptc
RELIABILITY OF HOT WATER SOLAR SYSTEMS IN GREECE S. PANTEHOU, T. CHONDROS, G. BOUZIOTIS,and A. D. D1MAROGONAS* Machine Design Laboratory, University of Patras, Greece, and *Washington University, St. Louis, U.S.A. Abstract--Ten thousand domestic hot water solar systems were surveyed in Greece to assess component and system reliability. Data concerning the functioning condition of the systems was collected, a computerized data base was established and statistical analysis was performed. This work is part of a solar system evaluation program within the European Community. Greece was selected due to the high concentration of solar collector systems and the fact that these systems have reached maturity, the average lifespan being five years. !. INTRODUCTION
Prompted by the energy crisis in the early 1970s the Greek Governments have developed incentives for the installation of solar domestic hot water systems. The result has been a very substantial number of systems installed in the past 15 years. It is estimated that more than 200,000 systems and half m~llion square meters of collector surface have been installed. Since the majority of these systems are ageing, an extensive effort was undertaken to assess the reliability of such systems. This work was carried out by the Machine Design Laboratory of the University of Patras under contracts with the European Community (Joint Research Center of Ispra) and the Greek Ministry of Industry, Research and Technology[ 1]-[2]. Selected mechanical engineering students were trained to fill out an appropriate statistical questionnaire for each solar installation. They inspected nearly 10,000 systems in Greece, which is the 5% of the total existing sample. The analysis performed was based on approximately 6000 questionnaires. The inspection was mainly visual, but dismantled systems were also considered.
2. GENERAL CHARACTERISTICS OF INSPECTED SYSTEMS The geographical distribution of most of the inspected installations during the period July 1986-August 1988 can be seen in Fig. 1. Also the distribution of the installed systems as a function of the location, is presented in Table 1. It is evident that most are in urban areas. It should be noted here that despite the small percentage of inspected systems installed in an industrial environment, there was one sample which consisted mainly of solarsystems near chemical works. This sample is discussed in Section 7.I. The age distributionofthe systems isshown in Fig2. Systems installedprior to 1978 were excluded because they represented a negligiblepercentage of the total number of installations.It is observed from Fig2 that there is in general an upwards trend of new installationsbetween years 1978 and 1985. Between 1978 and 1980 the number of new systems nearly quadrupled. During the next two years (1980-1982), 305
the number of systems installed remained almost constant. From 1982 a continuous increase is observed until 1985 since when there is a steady decline up to 1988. Concerning the orientation of collectors the majority of them (75%) are south oriented. A small percentage are oriented E, SE, SW, (3.4%, 18.1%, 1.8%, respectively) due to particular site problems, e.g., a block of flats near a lower building. The tilt angle varies between 30 ° and 60 ° , the majority being between 40 ° and 4 5 ° . The installation mode distributions of the system and water tank are shown in Table 2. It can be seen that the main installation mode is integrated modules with a horizontal tank. The storage tank volume is 140 lit and the absorbing surface aperture is 2.65 m 2 on average. The average absorbing surface area as a function ofthe location can be seen in Fig. 3, where letters A to O stand for different geographical locations demonstrated in Fig- 1. It should be mentioned that the number of inspected systems in each location is, respectively, A-160, B-100, C-100, D98, E-100, F-99, G-83, H-100, 1-101, J-98, K-101, L158, M-103, N-100, 0-82. The observed deviations above the average can be explained by the fact that some locations are mainly summer resorts, where larger residential units can be found, accommodating more people than usual. The most widely used working fluid (99%) is water. Concerning the design of the circulation system, 23.7% are open (direct) systems and 74.3% are closed (indirect). It was also found that in 54% of the closed systems alcohol additives were used for antifreeze purposes. The increase in the use of additives in the circuit according to the severity of the climate is demonstrated in Fig- 4. Letters A~, to K--- stand for locations with decreasing severity of climate conditions and are presented in Fig. 1. The number of inspected systems is also reported for each site (A~-.-100, B,~--217, C ~ 121, D~-100, E ~ - I 0 0 , F~-116, G~,-85, H'-,,-41, I ~-104, K ~ - 4 5 ) . There is a safety valve in the cold water inlet in about 68% of the systems. This depends on the manufacturer, due to lack o f enforceable national standards. About 87% of the systems are accompanied by a reliability warranty.
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3. COLLECTOR
3.1 Absorbing surface This section examines the characteristics, malfunctions and problems observed on the absorbing surface. In 88% of the inspected collectors, the absorber was black, while only 12% had a selective surface. The variety of materials used in the construction of the absorbing surface is listed below. Fe Other Cu lnox Plastic Unknown
24.4 20.2 19.7 5.6 2.8 27.2
It should be explained here that the term "Other" includes certain materials different from Fe, Cu, Inox,
Table 1. Systems distribution by location Type of Location Urban Rural Seashore Industrial Else
Installed Syst~s 49.1 27.0 13.4 6.3 4.Z
Plastic, while "unknown" indicates the inability of the inspectors to identify the materials used. The level of degradation of the absorbing surface is summarized in Fig. 5. Concerning the definition of the criteria: Low, Medium, Significant, Severe, indicated in Fig. 5, the following meaning should be given • Low means the initiation of any kind of degradation • Medium means a heavier level of degradation than Low, but there is no need for repairs yet • Significant means heavily degradated but not destroyed absorber. Repairs should be recommended
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Reliability of hot water solar systems in Greece
21 2O 19 18 17 16 15 14 13 1211 109 8 7 6 5 4 3 2 1 78
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79
80
81
82
83
84
85
86
87
Y E A R OF I N S T A L L A T I O N
Fig. 2. Installation year of systems.
• Severe means destroyed absorber. Parts must be replaced. Although a large percentage of the collectors was observed to exhibit a low level of degradation, relatively few of them seem to face a more serious problem. The frequency of peeling and distortion of the absorbing surface was observed to be 9% and 7%, respectively. Dust (40.5%) and dirt (19%) seem to be more serious problems affecting the efficiency of the collectors. Very often the system is integrated on parts of the buildings very difficult to access in order to maintain it. By the term dust only dust is meant while under the term dirt any other product (i.e., mud, dungs of birds, rubbish, etc.) is included. Deposits on the absorbing surface were found in 20% of the collectors, condensation in 12.7%, while leaking connections in the collector were found in about 3.5% of the systems.
Table 2. Installation mode System
3.3 Frame The percentages of damages in this part of the system were found to be mechanical damage distortion oxidation
4.5
Vertical tanks
24.90
Site-built collector
0.0
Horizontal tanks
68.75
88.S
3.0% 2.0% 12.5%
3.4 Sealants--Insulation The frequency of sealants degradation and ageing were found to be 21% and 13%, respectively. By the term degradation, any kind of deterioration due to external factors is meant (i.e., humidity condensation and deposits) while ageing is supposed to be due to pure natural ageing (i.e., material powdering). The insulation was made of
Y e t e r Tank
Modules on roof
Integrated modules
3.2 Transparent cover The cover is made of glass (83%) or plastic (17%). Dust is high (62%) as in the absorbing surface. Condensation and deposits below the cover were found in 17.5% and 15.6% of the systems respectively. The frequency of broken covers, ageing, and distortion were negligible (2.5%, 1%, 0.9%, respectively).
glass-wool polyurethane other unknown
46% 32% 6% 16%
S. PANTELIOU et al.
308
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Fig. 3. Absorbing surface aperture by location.
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Reliability of hot water solar systems in Greece
309
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LOW
SEVERE
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Fig. 5. Degradation of absorbing surface.
The comparatively large percentage of unknown material is due to the difficulty of inspection. Once again the term "other" refers to materials other than glasswool or polyurethane.
4. WATER TANK
The materials of which the water tank (container and internal tank) are made, are shown in Fig. 6. Although it is known from manufacturers data, that the frequency of damage in this part of the system is relatively high, this survey could not assess this factor because a detailed inspection of the inside of the water tank was not feasible. Nevertheless the most common problems that were observed are Internal tank degradation mechanical damage Container distortion mechanical damage rust Insulation degradation ageing humidity accumulation
By the term "Internal tank degradation" any type of deterioration is meant once again, while in the case of insulation, degradation is due to external factors and ageing is due to natural ageing. Concerning the electrical components of the tank Thermostat functioning Electric heating element not existing existing functioning
79% 3% 97% 86%
5. PIPING SYSTEM The most common malfunctions/damages observed in this part of the system are
2% 2.25% 3% 4% 1 I% 9% 6% 5%
Insulation degradation Leaking connections Distortion Air locks
26.0% 9.6% 6.9% 5.12%
The percentage of air locks is only an estimate, since most of the owners may not be aware of this problem and its consequences.
310
S. PANTELIOU et al.
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Fig. 7. Absorbing surface degradation in an industrial area.
SEVERE
Reliability of hot water solar systems in Greece 6. SYSTEM PERFORMANCE It was found that repairs had been necessary on about 11% of the collectors and 5% of the water tanks. Systems are able to retain heat during the night in about 90% of the cases, which coincides with the percentage of positive answers for the systems reliability. It is interesting to notice though that a larger percentage, i.e., 93%, of the owners are satisfied with their investment in a solar system, while only 88% would recommend to invest in a D H W solar installation. However 72% of them noticed a difference in the electricity bill, which represents 15% of the total bill, on average. Each unit serves on average 4 people and is used throughout the year (92%), except for a few that are used only during the summer. 7. PARTS OF SPECIAL INTEREST
7.1 Installations near industrial site These results refer to systems installed in the neighbourhood of a large-heavy industrial site resulting in severely polluted atmosphere. The first interesting feature is the heavy degradation of the Absorbing Surface (see Fig. 7). Comparing this figure with Fig. 5, which indicates the average degradation of absorbing surface of the total sample, it can be easily seen that the collectors are greatly affected by the hostile environment. Generally, these systems seem to suffer the greatest degradation (Table 3).
311
Table 3. Deterioration of systems installed in industrial areas compared with the corresponding averages of the total sample Type of DaNge
Total Sample S
Deposits on A.S. Condensation of A.S. Deposits below the transparent cover Condensation below the transparent cover Sealant degradation Oxidation of the cover |nterna] corrosion of water tank Insulation degradation of water tank
2O.O 12.7
81 23
15.6
4]
17.5 Zl.0 4.6
Z3 43 lZ
Z.9
13
$.4
14
A.$. - absorbing surface
7.2 Comparison of installations in different climatic conditions The influence of climate on the degradation of absorbing surface seems to be important. The relevant results for two areas (ALEXAND R O U P O L I - - K A L A M A T A ) the first of which has a continental climate (high level of humidity, large temperature differences, snow, etc.) in contrast ~5th the second which has mild climate are presented in Fig. 8. 7.3 Influence of age on the degradation of absorbing surface The interesting feature is that some level of degradation of the absorbing surface appears after the first
80
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30
UJ a. m Z
MEDIUM
LOW
DEGRADATION LEVEL AkEXANDROUPOLI
Industrial Sample
rT~
KALA MATA
Fig. 8. Absorbing surface degradation with climate.
S. PANTELIOUet al
312
year of installation, and from then on it depends on specific local conditions (e.g., Sections 7.1, 7.2) as can be seen in Fig. 9. This diagram shows the percentage of installations which exhibited low and medium degradation of absorbing surface as a function of age for various areas.
8. CONCLUSIONS
Table 4. More important problems (%) affecting the inspected DHW solar systems Absorbing Surface Dust Dirt Deposits Condensation Peeling Distortion Leakages Repairs
Frame
Dirt/Dust 62.0 Deposits 15.6 Condensation 17.5 Ageing 1.O Distortion 0.9 Broken Cover 2,5
Oxidation 12.5 Distortion Z.O 14echantcal Damage 3.0
ll.O
Piping System
Sealants
Collector
The Greek profile of a typical solar system is • Installed in urban area • Average age 5 years • South oriented • Tilt angle 400-45 ° • Black absorbing surface • Average absorbing surface aperture 2.6 m 2 • Average tank volume 140 lit • Horizontal water tank • Water is the beat transfer medium • Closed (indirect) circuit • Antifreeze in the circuit • Thermosyphonic circulation • Has a reliability warranty • Installation mode is integrated modules • Functioning electrical parts. As far as the absorbing surface is concerned, more than half of the inspected collectors exhibited low and medium degradation, while very few of them had serious degradation problems.
40.5 19.0 ZO.O 12.7 9.0 7.0 3.5
Transparent Cover
Ageing Degradation
Insulation Degradation Leaking Connections
13.0 ZI.O
Air Locks
Distortion
26.0 9.5
5.1
6.9
System
Water Tank
Water Tank Degradation 2.0 Water Tank Mechanical Damage Z.3 Container Distortion 3.0 Container Oxidation 11.0 Container Mechanical Oamage 4.0 Repairs 5.0 Insulation Degradation g.O Humidity Accumulation 5.0 [lectrlcal Resistance not functioning l l , 3
Retain Heat During Night Reliable Owners Satisfied Savings in Electricity
90.0 9O.O 93.0 72.0
The frame-cover block does not seem to face serious problems, however, the percentages of systems with ageing and degradation of sealants and insulating materials cannot be overlooked. In addition the number of repaired systems (absorbing surface-water tank) cannot be neglected. Fi-
0.9
0.8 -
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om
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0.6
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I 8O YEAR
(:3 A ' R q E N $
+
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OF
I
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85
86
87
INSTALLATION ~
IOANNINA
Fig. 9. Absorbing surface degradation with age.
m DRAMA
Refiability of hot water solar systems in Greece nally dust-dirt as well as lack of maintenance seem to be important. A general conclusion is that most of the owners have not been adequately informed about how to maintain their systems in the best working order. A complete picture of the more interesting results can be found in Table 4. The combined influence of these results in the reliability of the systems cannot be examined without detailed experimentation which is out of the scope of this work. This is due to the combined action of various environmental factors (i.e. ambient temperature, humidity, pollution, etc.), whose individual effects cannot be examined separately. A general conclusion is that the owners should learn how to maintain their systems and call the authorized team to service them at regular intervals. They must
313
also be able to recognize some elementary problems in order to cure them as soon as possible.
Acknowledgment--Supportof this work by the Joint Research Center, lspra, Italy, Commission of the European Community and Greek Ministry of Industry, Research and Technology is gratefully acknowledged. REFERENCES
!. J. L. Chevalier, Fiabilite et Durabilite des Capteurs Solaires Termiques, Cahiers du Centre Scientifique et Technique du Batiment CSTB, Livrnison 269, Cahier 2077, (1986). 2. S. Panteliou, T. Chondms, G. Bouziotis, and A. Dimarogonas, Reliability Analysis of Solar DHW Systems, Directorate General For Science Research and Development, Joint Research Center, 6th meeting, Copenhagen, Denmark, (1987).
0038-092X/90 $3.00 + .00 Copyright © 1990 Pergamon Pnm ptc
RELIABILITY OF HOT WATER SOLAR SYSTEMS IN GREECE S. PANTEHOU, T. CHONDROS, G. BOUZIOTIS,and A. D. D1MAROGONAS* Machine Design Laboratory, University of Patras, Greece, and *Washington University, St. Louis, U.S.A. Abstract--Ten thousand domestic hot water solar systems were surveyed in Greece to assess component and system reliability. Data concerning the functioning condition of the systems was collected, a computerized data base was established and statistical analysis was performed. This work is part of a solar system evaluation program within the European Community. Greece was selected due to the high concentration of solar collector systems and the fact that these systems have reached maturity, the average lifespan being five years. !. INTRODUCTION
Prompted by the energy crisis in the early 1970s the Greek Governments have developed incentives for the installation of solar domestic hot water systems. The result has been a very substantial number of systems installed in the past 15 years. It is estimated that more than 200,000 systems and half m~llion square meters of collector surface have been installed. Since the majority of these systems are ageing, an extensive effort was undertaken to assess the reliability of such systems. This work was carried out by the Machine Design Laboratory of the University of Patras under contracts with the European Community (Joint Research Center of Ispra) and the Greek Ministry of Industry, Research and Technology[ 1]-[2]. Selected mechanical engineering students were trained to fill out an appropriate statistical questionnaire for each solar installation. They inspected nearly 10,000 systems in Greece, which is the 5% of the total existing sample. The analysis performed was based on approximately 6000 questionnaires. The inspection was mainly visual, but dismantled systems were also considered.
2. GENERAL CHARACTERISTICS OF INSPECTED SYSTEMS The geographical distribution of most of the inspected installations during the period July 1986-August 1988 can be seen in Fig. 1. Also the distribution of the installed systems as a function of the location, is presented in Table 1. It is evident that most are in urban areas. It should be noted here that despite the small percentage of inspected systems installed in an industrial environment, there was one sample which consisted mainly of solarsystems near chemical works. This sample is discussed in Section 7.I. The age distributionofthe systems isshown in Fig2. Systems installedprior to 1978 were excluded because they represented a negligiblepercentage of the total number of installations.It is observed from Fig2 that there is in general an upwards trend of new installationsbetween years 1978 and 1985. Between 1978 and 1980 the number of new systems nearly quadrupled. During the next two years (1980-1982), 305
the number of systems installed remained almost constant. From 1982 a continuous increase is observed until 1985 since when there is a steady decline up to 1988. Concerning the orientation of collectors the majority of them (75%) are south oriented. A small percentage are oriented E, SE, SW, (3.4%, 18.1%, 1.8%, respectively) due to particular site problems, e.g., a block of flats near a lower building. The tilt angle varies between 30 ° and 60 ° , the majority being between 40 ° and 4 5 ° . The installation mode distributions of the system and water tank are shown in Table 2. It can be seen that the main installation mode is integrated modules with a horizontal tank. The storage tank volume is 140 lit and the absorbing surface aperture is 2.65 m 2 on average. The average absorbing surface area as a function ofthe location can be seen in Fig. 3, where letters A to O stand for different geographical locations demonstrated in Fig- 1. It should be mentioned that the number of inspected systems in each location is, respectively, A-160, B-100, C-100, D98, E-100, F-99, G-83, H-100, 1-101, J-98, K-101, L158, M-103, N-100, 0-82. The observed deviations above the average can be explained by the fact that some locations are mainly summer resorts, where larger residential units can be found, accommodating more people than usual. The most widely used working fluid (99%) is water. Concerning the design of the circulation system, 23.7% are open (direct) systems and 74.3% are closed (indirect). It was also found that in 54% of the closed systems alcohol additives were used for antifreeze purposes. The increase in the use of additives in the circuit according to the severity of the climate is demonstrated in Fig- 4. Letters A~, to K--- stand for locations with decreasing severity of climate conditions and are presented in Fig. 1. The number of inspected systems is also reported for each site (A~-.-100, B,~--217, C ~ 121, D~-100, E ~ - I 0 0 , F~-116, G~,-85, H'-,,-41, I ~-104, K ~ - 4 5 ) . There is a safety valve in the cold water inlet in about 68% of the systems. This depends on the manufacturer, due to lack o f enforceable national standards. About 87% of the systems are accompanied by a reliability warranty.
S. PANTELIOUet al.
306
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Fig. 1. Geographical distribution of the inspected systems.
3. COLLECTOR
3.1 Absorbing surface This section examines the characteristics, malfunctions and problems observed on the absorbing surface. In 88% of the inspected collectors, the absorber was black, while only 12% had a selective surface. The variety of materials used in the construction of the absorbing surface is listed below. Fe Other Cu lnox Plastic Unknown
24.4 20.2 19.7 5.6 2.8 27.2
It should be explained here that the term "Other" includes certain materials different from Fe, Cu, Inox,
Table 1. Systems distribution by location Type of Location Urban Rural Seashore Industrial Else
Installed Syst~s 49.1 27.0 13.4 6.3 4.Z
Plastic, while "unknown" indicates the inability of the inspectors to identify the materials used. The level of degradation of the absorbing surface is summarized in Fig. 5. Concerning the definition of the criteria: Low, Medium, Significant, Severe, indicated in Fig. 5, the following meaning should be given • Low means the initiation of any kind of degradation • Medium means a heavier level of degradation than Low, but there is no need for repairs yet • Significant means heavily degradated but not destroyed absorber. Repairs should be recommended
22!
Q iu
.4 .J < I(n Z (n IM. hU) ). U)
Reliability of hot water solar systems in Greece
21 2O 19 18 17 16 15 14 13 1211 109 8 7 6 5 4 3 2 1 78
307
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79
80
81
82
83
84
85
86
87
Y E A R OF I N S T A L L A T I O N
Fig. 2. Installation year of systems.
• Severe means destroyed absorber. Parts must be replaced. Although a large percentage of the collectors was observed to exhibit a low level of degradation, relatively few of them seem to face a more serious problem. The frequency of peeling and distortion of the absorbing surface was observed to be 9% and 7%, respectively. Dust (40.5%) and dirt (19%) seem to be more serious problems affecting the efficiency of the collectors. Very often the system is integrated on parts of the buildings very difficult to access in order to maintain it. By the term dust only dust is meant while under the term dirt any other product (i.e., mud, dungs of birds, rubbish, etc.) is included. Deposits on the absorbing surface were found in 20% of the collectors, condensation in 12.7%, while leaking connections in the collector were found in about 3.5% of the systems.
Table 2. Installation mode System
3.3 Frame The percentages of damages in this part of the system were found to be mechanical damage distortion oxidation
4.5
Vertical tanks
24.90
Site-built collector
0.0
Horizontal tanks
68.75
88.S
3.0% 2.0% 12.5%
3.4 Sealants--Insulation The frequency of sealants degradation and ageing were found to be 21% and 13%, respectively. By the term degradation, any kind of deterioration due to external factors is meant (i.e., humidity condensation and deposits) while ageing is supposed to be due to pure natural ageing (i.e., material powdering). The insulation was made of
Y e t e r Tank
Modules on roof
Integrated modules
3.2 Transparent cover The cover is made of glass (83%) or plastic (17%). Dust is high (62%) as in the absorbing surface. Condensation and deposits below the cover were found in 17.5% and 15.6% of the systems respectively. The frequency of broken covers, ageing, and distortion were negligible (2.5%, 1%, 0.9%, respectively).
glass-wool polyurethane other unknown
46% 32% 6% 16%
S. PANTELIOU et al.
308
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B
C
D
E
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K
L
M
N
0
LOCATIONS
Fig. 3. Absorbing surface aperture by location.
100
\
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LOCATIONS
Fig. 4. Additives in collector circuit.
' [~'--]
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I
J
r"--"
K
Reliability of hot water solar systems in Greece
309
50
40
:i
30
i.m tl
cI MJ
20
om a~
10
0
\ MEDII.RA
LOW
SEVERE
sIGNIFICANT
DEGRADATION
LEVEL
Fig. 5. Degradation of absorbing surface.
The comparatively large percentage of unknown material is due to the difficulty of inspection. Once again the term "other" refers to materials other than glasswool or polyurethane.
4. WATER TANK
The materials of which the water tank (container and internal tank) are made, are shown in Fig. 6. Although it is known from manufacturers data, that the frequency of damage in this part of the system is relatively high, this survey could not assess this factor because a detailed inspection of the inside of the water tank was not feasible. Nevertheless the most common problems that were observed are Internal tank degradation mechanical damage Container distortion mechanical damage rust Insulation degradation ageing humidity accumulation
By the term "Internal tank degradation" any type of deterioration is meant once again, while in the case of insulation, degradation is due to external factors and ageing is due to natural ageing. Concerning the electrical components of the tank Thermostat functioning Electric heating element not existing existing functioning
79% 3% 97% 86%
5. PIPING SYSTEM The most common malfunctions/damages observed in this part of the system are
2% 2.25% 3% 4% 1 I% 9% 6% 5%
Insulation degradation Leaking connections Distortion Air locks
26.0% 9.6% 6.9% 5.12%
The percentage of air locks is only an estimate, since most of the owners may not be aware of this problem and its consequences.
310
S. PANTELIOU et al.
35
30
25 v
20
w I-
~
,~
r~ w I-
~
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Fe
INTERNAL TANK
PLASTIC
OTHER
/ INOX
\ GLASE ENAMELING
CONTAINER
Fig. 6. Water tank material.
45
40
\\ \~,~
30
m I! w g,. m lb a w
le
I
I
I
II
I
1. ~ \ )
'i o
,",\'~ LOW
MEDIUM
DEGRADATION
SIGNIFICANT
LEVEL
Fig. 7. Absorbing surface degradation in an industrial area.
SEVERE
Reliability of hot water solar systems in Greece 6. SYSTEM PERFORMANCE It was found that repairs had been necessary on about 11% of the collectors and 5% of the water tanks. Systems are able to retain heat during the night in about 90% of the cases, which coincides with the percentage of positive answers for the systems reliability. It is interesting to notice though that a larger percentage, i.e., 93%, of the owners are satisfied with their investment in a solar system, while only 88% would recommend to invest in a D H W solar installation. However 72% of them noticed a difference in the electricity bill, which represents 15% of the total bill, on average. Each unit serves on average 4 people and is used throughout the year (92%), except for a few that are used only during the summer. 7. PARTS OF SPECIAL INTEREST
7.1 Installations near industrial site These results refer to systems installed in the neighbourhood of a large-heavy industrial site resulting in severely polluted atmosphere. The first interesting feature is the heavy degradation of the Absorbing Surface (see Fig. 7). Comparing this figure with Fig. 5, which indicates the average degradation of absorbing surface of the total sample, it can be easily seen that the collectors are greatly affected by the hostile environment. Generally, these systems seem to suffer the greatest degradation (Table 3).
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Table 3. Deterioration of systems installed in industrial areas compared with the corresponding averages of the total sample Type of DaNge
Total Sample S
Deposits on A.S. Condensation of A.S. Deposits below the transparent cover Condensation below the transparent cover Sealant degradation Oxidation of the cover |nterna] corrosion of water tank Insulation degradation of water tank
2O.O 12.7
81 23
15.6
4]
17.5 Zl.0 4.6
Z3 43 lZ
Z.9
13
$.4
14
A.$. - absorbing surface
7.2 Comparison of installations in different climatic conditions The influence of climate on the degradation of absorbing surface seems to be important. The relevant results for two areas (ALEXAND R O U P O L I - - K A L A M A T A ) the first of which has a continental climate (high level of humidity, large temperature differences, snow, etc.) in contrast ~5th the second which has mild climate are presented in Fig. 8. 7.3 Influence of age on the degradation of absorbing surface The interesting feature is that some level of degradation of the absorbing surface appears after the first
80
70 ! \ \ ~
60
w
50
\\
4o O
UJ
FU
30
UJ a. m Z
MEDIUM
LOW
DEGRADATION LEVEL AkEXANDROUPOLI
Industrial Sample
rT~
KALA MATA
Fig. 8. Absorbing surface degradation with climate.
S. PANTELIOUet al
312
year of installation, and from then on it depends on specific local conditions (e.g., Sections 7.1, 7.2) as can be seen in Fig. 9. This diagram shows the percentage of installations which exhibited low and medium degradation of absorbing surface as a function of age for various areas.
8. CONCLUSIONS
Table 4. More important problems (%) affecting the inspected DHW solar systems Absorbing Surface Dust Dirt Deposits Condensation Peeling Distortion Leakages Repairs
Frame
Dirt/Dust 62.0 Deposits 15.6 Condensation 17.5 Ageing 1.O Distortion 0.9 Broken Cover 2,5
Oxidation 12.5 Distortion Z.O 14echantcal Damage 3.0
ll.O
Piping System
Sealants
Collector
The Greek profile of a typical solar system is • Installed in urban area • Average age 5 years • South oriented • Tilt angle 400-45 ° • Black absorbing surface • Average absorbing surface aperture 2.6 m 2 • Average tank volume 140 lit • Horizontal water tank • Water is the beat transfer medium • Closed (indirect) circuit • Antifreeze in the circuit • Thermosyphonic circulation • Has a reliability warranty • Installation mode is integrated modules • Functioning electrical parts. As far as the absorbing surface is concerned, more than half of the inspected collectors exhibited low and medium degradation, while very few of them had serious degradation problems.
40.5 19.0 ZO.O 12.7 9.0 7.0 3.5
Transparent Cover
Ageing Degradation
Insulation Degradation Leaking Connections
13.0 ZI.O
Air Locks
Distortion
26.0 9.5
5.1
6.9
System
Water Tank
Water Tank Degradation 2.0 Water Tank Mechanical Damage Z.3 Container Distortion 3.0 Container Oxidation 11.0 Container Mechanical Oamage 4.0 Repairs 5.0 Insulation Degradation g.O Humidity Accumulation 5.0 [lectrlcal Resistance not functioning l l , 3
Retain Heat During Night Reliable Owners Satisfied Savings in Electricity
90.0 9O.O 93.0 72.0
The frame-cover block does not seem to face serious problems, however, the percentages of systems with ageing and degradation of sealants and insulating materials cannot be overlooked. In addition the number of repaired systems (absorbing surface-water tank) cannot be neglected. Fi-
0.9
0.8 -
I< Q < a,
om
0.7
0.6
0.5
Q
0.4 0.3
I 8O YEAR
(:3 A ' R q E N $
+
ISLANDS
OF
I
I
I
85
86
87
INSTALLATION ~
IOANNINA
Fig. 9. Absorbing surface degradation with age.
m DRAMA
Refiability of hot water solar systems in Greece nally dust-dirt as well as lack of maintenance seem to be important. A general conclusion is that most of the owners have not been adequately informed about how to maintain their systems in the best working order. A complete picture of the more interesting results can be found in Table 4. The combined influence of these results in the reliability of the systems cannot be examined without detailed experimentation which is out of the scope of this work. This is due to the combined action of various environmental factors (i.e. ambient temperature, humidity, pollution, etc.), whose individual effects cannot be examined separately. A general conclusion is that the owners should learn how to maintain their systems and call the authorized team to service them at regular intervals. They must
313
also be able to recognize some elementary problems in order to cure them as soon as possible.
Acknowledgment--Supportof this work by the Joint Research Center, lspra, Italy, Commission of the European Community and Greek Ministry of Industry, Research and Technology is gratefully acknowledged. REFERENCES
!. J. L. Chevalier, Fiabilite et Durabilite des Capteurs Solaires Termiques, Cahiers du Centre Scientifique et Technique du Batiment CSTB, Livrnison 269, Cahier 2077, (1986). 2. S. Panteliou, T. Chondms, G. Bouziotis, and A. Dimarogonas, Reliability Analysis of Solar DHW Systems, Directorate General For Science Research and Development, Joint Research Center, 6th meeting, Copenhagen, Denmark, (1987).