Category Archives: EuroSun2008-5

Manual monitoring with analysis by an expert (MM, e. g. Optisol)

In most cases in which solar thermal systems were monitored, the failure detection consisted of analysis of measurement data by an expert. An expert with enough experience can recognize if a system is performing as expected based on analysis of data. A state-of-the art example is provided in the Austrian demonstration project Optisol (OPT), in which 10 large solar thermal systems were built and monitored for ca. 1 year [2].

In the Optisol project an integrated approach was used for designing, building and monitoring the systems. The monitoring part consisted of a so called optimization phase of two months and a consecutive routine supervision of one year. During the optimization phase many weaknesses of the solar supported heating system were recognized by analysing the temperature profiles of the systems. 35 faults in installation, design or operation were detected in 9 systems, several of these faults were related to the auxiliary heating system. In the routine supervision monthly energy balances and yearly

[13] Introduction

The characterization of collector efficiency is the fundamental tool for long term thermal performance calculation, i. e. collector yield, and for design of solar thermal systems. It is, thus, one of the most important inputs in software tools aiming at the design of solar thermal systems.

1

[15] Introduction

Solar air collectors systems may have a number of advantages compared to solar collectors using a liquid heat transfer fluid. Just to mention some of them: solar air collectors are safe with respect to stagnation, because air as the heat transfer medium is not affected or destroyed by high temperatures. Air also does not boil or evaporate and no vapour pressure is built up in the solar loop under stagnation conditions. There is no need for membrane expansion vessels in the solar loop. Air as heat transfer fluid does not cost anything and does not need to be exchanged.

But also disadvantages exist, such as the necessity of larger heat exchanging areas, more voluminous air ducts compared to water pipes and (depending on system applications) a possibly higher auxiliary energy demand for the transport of energy by air.

With respect to system aspects, it may be mentioned that solar heated air can directly be used to heat residential — and office-buildings or industrial factory halls. The solar heat can also be stored, using suitable air-to-water heat exchangers together with water storage tanks or directly in other storages such as pebble bed storages.

[16] The specific heat capacity of air does not only depend on temperature, but also on the humidity of the air, see figure 3. The steep decreases at low temperatures denote the range in which the air is saturated and the water vapour condenses. In the range of the normal operating conditions, the value of cp increases at a given temperature by 1.6% when the absolute humidity is decreased from 1g/m3 to 20 g/m3.

Description of the fault diagnostic method

Подпись: Fig. 2 Schematic diagram of the FDS

Figure 2 shows the overall procedure used in this work, and each block is described hereafter. But before the description of the method, it is necessary to show that neural networks are able to accurately model the components of the solar system. In fact three parts of the system are monitored: the collector array, the connecting pipe from the tank to the collectors, and the return connecting pipe. As two components are similar, only two networks will be presented here.

Heat pipe ETCs

The thermal performances of four heat pipe ETCs are measured. They are ETC 1, 2, 3 and 4. ETC 1 and 2 have 8 tubes of tube diameter 100 mm. ETC 3 and 4 have 20 tubes of tube diameter 70 mm. The difference between ETC 1, 3 and ETC 2, 4 is that ETC 1 and 3 have a curved/semi-cylindrical fin while ETC 2 and 4 have a flat fin. As shown in Fig.4, the performance ratio of ETC 3/ETC 4 is in the range of 0.73-0.94 meaning that the ETC with a flat fin performs better than the ETC with a curved fin. For a mean collector fluid temperature of 63°C, the ETC with a flat fin has a thermal performance 12% higher than the ETC with a curved fin. With an increase of the mean collector fluid temperature to 75°C, the thermal performance of the ETC with a flat fin is increased to be 15% higher than the thermal performance of the ETC with the curved fin. The comparison of a collector with a curved fin and a flat fin with a tube diameter of 100 mm is given by the ratio of ETC 1/ETC 2. The advantage of the ETC with a flat fin tends to weaken with an increase of the tube diameter. However, the ETC with a flat fin is better than the ETC with a curved fin for most of the test period.

Fig. 4. Performance ratio of the differently designed ETCs.

Thermal performance of the ETCs in phase 1 is summarized in Fig. 5. The measurements were carried out half a year from winter to summer with the aim to get a better estimation of the yearly collector performance. The result shows that the collectors with flat fins perform relatively better than the collectors with curved fins. For a collector with a tube diameter of 70 mm, types 3 and 4, there is an

Подпись: Fig. 5: Collector performance in Phase 1.

increase of 13% of collector performance if a flat fin is used instead of a curved fin, while for a collector with a tube diameter of 100 mm, the extra thermal performance of the collector with a flat fin compared to the collector

curved fin absorbs 15.9% more solar energy annually than the flat fin. The explanation is the larger heat loss from the curved fin compared to that of the flat fin. The surface area of the curved fin is approx. 40% larger than the surface area of the flat fin, resulting in a higher heat loss from the curved fin and a lower thermal performance. It shall be noted that the location of the collector and the fact that He’s investigations only considered solar radiation from the front side might influence the conclusion as well. The measurement presented in this paper was carried out for a latitude of 56°, while in He’s investigations [3], a latitude of 40° was used.

The performance ratio between the ETC 2 and ETC 4 is less varying throughout the measuring period. This can be explained by the similarity of the fin design. The mean solar collector fluid temperature has a slight influence on the ratio of the thermal performance. There is an increase of the performance ratio with a decrease of mean solar collector fluid temperature, indicating that ETC 2 has a higher heat loss coefficient than that of ETC 4.

Experiences gained to-date

Up to now (August 2008) three mobile test facilities have been completed. The test facilities were delivery by SWT as complete, ready to use turn-key products. One of the facilities was sold to the South African Bureau of Standards (SABS) located in Pretoria, South Africa. This test facility is shown in Figure 9.

This test facility is the key component of a solar thermal test centre that was established, co­financed by the United Nations Development Program (UNDP), at the South African Bureau of Standards (SABS). The test facility shown in Figure 9 allows for testing of solar collectors and thermal solar systems according to ISO 9459-2 (CSTG-method).

Due to the installation of the above mentioned test facility the SABS is able to carry out thermal performance tests and durability tests of solar thermal systems and collectors according to the relevant standards. This is one important basis for the formal accreditation of the test laboratory according to ISO 17025.

Another test facility which allows testing of solar collectors according to EN 12975-2 (and solar thermal systems according to EN 12976 or ISO 9459-2 and ISO 9459-5 respectively is installed at the Research and Test Centre for Thermal Soar Systems (TZS) at the Institute for Thermodynamics and Thermal Engineering (ITW) at the University of Stuttgart.

Подпись: Fig. 9: The mobile, stand-alone test facility at SABS, South Africa Подпись: Fig. 10: The mobile, stand-alone test facility at Skopje, Republic of Macedonia

A further all-in-one test facility was delivered to the Hydrometeorological Service located in Skopje, Republic of Macedonia where if forms the basis for a solar thermal test and competence centre (see Figure 10)

Changes to achieve class A+

The results of table 9 show that, with a proper selection of energy supply equipments and vectors, it is possible to fulfil the regulation and to achieve class A in all locations and even class A+ in some locations. It is however important to clarify if class A+ can be achieved in all the studied locations. In order to assess this, a new round of improvements was implemented for the locations where class A+ had not yet been achieved. The improvements consisted on the adoption of a better solar collector and on several improvements to the building envelope. Table 10 shows a detailed list of the improvements made at each of the locations where the A+ had not yet been achieved.

Table 10: Changes implemented to try to achieve class A+.

Braganja

Apartment

— Better solar collector (h0=79%, ai=4.7)

Dwelling

— Better solar collector (h0=76%, a1=2.8)+ Wall insulation increased to 8 cm (U=0.37 at walls and 0.41 at plan. therm. brdg.) + Insulation of interior envelope walls increased to 8 cm (U=0.39) + Roof slab insulation increased to 8 cm (U=0.32) + Windows with low-e glazing and plastic frame (U=2.0) + Window frame class 3, resulting in air change rate = 0.90 ach-1.

Guarda

Apartment

— Better solar collector (h0=76%, a1=2.8) + Wall insulation increased to 8 cm XPS (U= 0.31)

+ Insulation at planar thermal bridges increased to 8 cm XPS (U=0.39) + Floor slab insulation increased to 8 cm (U=0.39) + Window frames with thermal break + night occl. dev. low-e glazing, resulting in U=2.7 W/m2.°C.

Dwelling

— Better solar collector (h0=76%, a1=2.8) + Wall insulation increased to 8 cm (U=0.32) + Insulation of interior envelope walls increased to 8 cm (U=0.32) + Windows with low-e glazing and plastic frame (U=2.0) + Mech. Vent. 0.6 ach-1 + heat recovery 50%

Penhas

Douradas

Apartment

— Better solar collector (h0=76%, a1=2.8) + Wall insulation increased to 8 cm XPS (U= 0.31+ Insulation at planar thermal bridges increased to 8 cm XPS (U=0.39 ) + Floor slab insulation increased to 8 cm (U=0.37) + Window frames with thermal break + night occl. dev.+ low-e glazing, resulting in U=2.7 W/m2.°C.

Dwelling

— Better solar collector (h0=76%, a1=2.8) + Wall insulation increased to 8 cm (U=0.32) + Insulation of interior envelope walls increased to 8 cm (U=0.32) + Windows with low-e glazing and plastic frame (U=2.0) + Floor slab insulation increased to 8 cm (U=0.32) + Mech. Vent. 0.6 ach-1 + heat recovery 70%

Viana do Castelo

Apartment

Dwelling

— Better solar collector (h0=76%, aj=2.8) + Wall insulation increased to 6 cm (U=0.45)

Lisbon, Faro, Evora: No changes required

Table 11 and Table 12 show the results after this new round of improvements. The results confirm that class A+ is reachable in all locations both for the apartment and for the dwelling. The level of constructive and technological sophistication differs according to the building and location. For the dwelling in Guarda and in Penhas Douradas, reaching class A+ implied adopting mechanical ventilation with heat recovery, a solution not common in Portugal so far.

Table 11: Results for the apartment after the changes to try to achieve class A+

Lisboa

Braganga

Faro

Ёvora

Guarda

P. Dourad.

Viana C. lo

Nic /Ni

92%

91%

95%

97%

87%

83%

76%

Nvc /Nv

46%

33%

46%

45%

14%

16%

44%

Eqpt. 1

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

52% [B]

56% [B]

52% [B]

53% [B]

55% [B]

55% [B]

51% [B]

Eqpt. 2

Nac / Na

22%

19%

21%

21%

21%

21%

28%

Ntc /Nt

23% [A+]

29% [A]

21% [A+]

23% [A+]

28% [A]

29% [A]

25% [A+]

Eqpt. 3

Nac / Na

68%

68%

68%

68%

68%

68%

68%

Ntc /Nt

136% [NC]

131% [NC]

137% [NC]

136% [NC]

130% [NC]

128% [NC]

136% [NC]

Eqpt. 4

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

50% [A]

51% [B]

50% [A]

51% [B]

51% [A]

51% [B]

49% [A]

Eqpt. 5

Nac / Na

16%

15%

14%

11%

15%

15%

16%

Ntc /Nt

30% [A]

40% [A]

35% [A]

36% [A]

38% [A]

38% [A]

38% [A]

Eqpt. 6

Nac / Na

22%

21%

21%

21%

20%

21%

28%

Ntc /Nt

21% [A+]

24% [A+]

19% [A+]

21% [A+]

23% [A+]

24% [A+]

23% [A+]

NC. = Not Compliant

Table 12: Results for the dwelling after the changes to try to achieve class A+

Lisboa

Braganga

Faro

Evora

Guarda

P. Dourad.

Viana C. lo

Nic /Ni

87%

56%

91%

93%

62%

59%

49%

Nvc /Nv

44%

43%

44%

43%

84%

81%

50%

Eqpt. 1

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

53% [B]

56% [B]

53% [B]

54% [B]

53% [B]

53% [B]

55% [B]

Eqpt. 2

Nac / Na

26%

23%

24%

24%

22%

22%

24%

Ntc /Nt

24% [A+]

32% [A]

22% [A+]

25% [A+]

29% [A]

29% [A]

29% [A]

Eqpt. 3

Nac / Na

68%

68%

68%

68%

68%

68%

68%

Ntc /Nt

132% [NC]

124% [NC]

133% [NC]

132% [NC]

122% [NC]

119% [NC]

132% [NC]

Eqpt. 4

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

50% [A]

51% [B]

50% [A]

51% [B]

49% [A]

49% [A]

51% [B]

Eqpt. 5

Nac / Na

19%

17%

18%

18%

16%

16%

18%

Ntc /Nt

34% [A]

48% [A]

31% [A]

32% [A]

40% [A]

40% [A]

44% [A]

1st International Congress on Heating, Cooling, and Buildings, 7th to 10th October, Lisbon — Portugal /

Eqpt. 6

Nac / Na

26%

23%

24%

18%

22%

22%

24%

Ntc /Nt

24% [A+]

22% [A+]

23% [A+]

24% [A+]

25% [A+]

25% [A+]

20% [A+]

NC. = Not Compliant

4. Conclusions

This study analysed the compliance of different sets of constructive and technological solutions of two residential buildings with the thermal regulations in different places in Portugal, as well as the corresponding energy class.

The first major conclusion form the results is that it is possible to comply with the regulation and to achieve the best energy classes (A and A+). Since the studied locations included extreme cold and extreme hot locations of Portugal, it is possible to infer that this holds true for the whole country.

The second major conclusion is that the requirements for the envelope are determined essentially by the need to comply with the heating requirements. It was found that the thermal quality level of the envelope needed to comply with the regulations is substantially different between the mildest and the coldest regions of the country. While 3 to 4 cm of insulation seem to be enough in the locations close to the coast, the interior mountains regions it may require about 6 to 8 cm. Nevertheless, compliance seems to be possible without interfering significantly the architectural appearance of the buildings (glazed area, solar orientation).

Regarding the energy class, it was found that is determined essentially by the equipment choices for heating, cooling and domestic hot water, with a decisive influence of this later one, due to the weighting factors 0.1 / 0.1 / 1.0 used in equation 1. In this aspect it was confirmed that a solution of domestic hot water heated exclusively with an electrical resistance seems to be incompatible with the regulation. Nevertheless, optimization of the envelope seems to be also needed to make difference for class A+ in the coldest regions, and in some cases even mechanical ventilation with heat recovery may be required to reach that energy class.

Regarding the importance of solar collectors, apart of the issues of its obligation and of the reasons that allow to drop that obligation, it is clearly demonstrated by the fact that they were part of all the sets of solutions that achieved class A+ and of most of those that achieved class A. Naturally, since Ntc is evaluated in primary energy, solutions of solar collectors complemented with gas boilers lead to better results than those complemented with electric resistances. In the coldest regions where class A+ is more difficult to achieve, a high quality solar collector (or a collector area higher that strictly required by the regulation) is one of the most effective elements in finding solutions towards class A+.

5. References

[1] Regulamento das Caracteristicas de Comportamento Termico dos Edificios — RCCTE, Decree-Law 80/2006 in Portuguese).

[2] Sistema Nacional de Certificagao Energetica e da Qualidade do Ar interior dos Edificios, Decree-law 78/2006,

[3] CAMELO, S. Camelo, P dos Santos et al.: Regulamento das Caracteristicas de Comportamento Termico dos Edificios (RCCTE). Manual de apoio a aplicagao do RCCTE (in Portuguese).

ICPC Performance Testing at Sandia

Prior to the start of the 1998 Sacramento demonstration, individual fourteen tube modules were tested on Sandia National Laboratory’s two-axis tracking (AZTRAK) platform. See Winston et al [3]. These tests measured losses from the new ICPC collector operating at about 150C on a 35C summer day of only 120w/m2 of collector aperture.

1.2 Sacramento Demonstration

A 100 m2 336 Novel ICPC evacuated tube solar collector array has been in continuous operation at a demonstration project in Sacramento California since 1998. The evacuated collector tubes are based on a novel ICPC design that was developed by researchers at the University of Chicago and Colorado State University in 1993. The evacuated collector tubes were hand-fabricated from NEG Sun Tube components by a Chicago area manufacturer of glass vacuum products.

From 1998 through 2002 demonstration project ICPC solar collectors supplied heated pressurized 150C water to a double effect (2E) absorption chiller. The ICPC collector design operates as efficiently at 2E chiller temperatures (150C) as do more conventional collectors at much lower temperatures. This new collector made it possible to produce cooling with a 2E chiller using a collector field that is about half the size of that required for a single effect (1E) absorption chiller with the same cooling output. Data collection and analysis has continued to the present [5, 6, 7]

Fig. 1: 1998 Daily Collection Performance for Fig. 2: 1998 Daily Collection Performance for

Operation at 90 to 110C Collector to Ambient Operation at 110 to 130C Collector to Ambient

Temperature Differences. Temperature Differences.

As can be seen in Fig. 1 and 2, the non­tracking ICPC evacuated solar collector array provided daily solar collection efficiencies (based on the total solar energy falling on the collector) approaching fifty percent and instantaneous collection efficiencies of

Подпись:about 60 percent at the 140C to 160C collector operating temperature range. Daily chiller COPs of about 1.1 were achieved. The ICPC array has recently been operating at the lower temperatures to drive a single effect absorption chiller. The ICPC array has provided daily solar collection efficiencies approaching

fifty-five percent at the 80C to 100C collector operating temperature range.

The implementation of the regulations on Solar collectors in Buildings

Maria Isabel Abreu1* and Rui Oliveira2

1 Polytechnic Institute of Bragan^a, Campus de Sta Apolonia, Apartado 1134, 5301-875 Bragan^a, Portugal
* Corresponding Author, isabreu@ipb. pt

Abstract

The use of solar energy constitutes a great concern of national and international bodies, as a result of a strategic policy towards green energy consumption. The Portuguese regulations on building thermal behaviour and energy efficiency, recently enacted by the Portuguese Government, in line with the European Union Directive 2002/91/CE, have introduced the obligatory use of solar collector technology for hot water production applied to new building projects and to some important retrofit works. To cope with the prescriptions of these regulations, the solar technology market is been growing and the Portuguese project designers and construction professionals are founding new challenges. The purpose of this study is to identify and analyse the major problems and initial impacts of the obligatory implementation of solar collector technology in buildings and provide contributions to improve solar energy use in the future. The results show that, as almost all new technology implementation, some obstacles have always to be faced initially.

Keywords: Solar Collector, Solar DWH, Building Thermal Regulations, Portugal.

1. Introduction

In residential buildings the energy for hot water production (DHW) contributes strongly to the final building consumptions of useful energy [1,2]. In the beginning of this decade, the Portuguese Program E4 — Energy Efficiency and Endogenous Energies have proposed an ambitious goal of 1 million m2 of solar collector area in Portugal until 2010. To cope with this, it was implemented in 2001 by Portuguese Government the National Program Solar Hot Water for Portugal (IP-AQSpP) [3]. A more recent government effort is The National Plan for de Energy Efficiency (PNAEE), approved some months ago, that include important measures for buildings, ambitioning an improvement of 1% per year on energy efficiency [4]. The Portuguese new Thermal Regulations (RCCTE) opens to all constructions partners a new opportunity for implementing more strongly renewable energy technologies in buildings. Using solar hot water systems it can represent a saving of 20% on the total energy consume of a family in electricity and gas [3].

2. Methodology

The methodology used on this study consisted of a literature review on government and institutions publications and information, statistics and also interviews to professionals. Secondly, to complement the analysis, it was made simulations with the regulations methodology and with the official software for solar collectors, Solterm, with the consequent discussion of results.

Criteria to Analyse Performance (Step 3)

The criteria are used to measure the performance of the different failure detection approaches. The selection is very important, since the result will be different, if not all relevant criteria are included.

As most of the methods are still in development, a qualitative evaluation is applied. The criteria are as follows:

• Automatic Failure detection included?

• Accuracy/effectiveness of failure detection

• Automatic Failure identification included?

• Accuracy/effectiveness of failure identification

• Costs (operational and hardware)

3. Overview of Failure Detection Methods

The methods for failure detection will be described in the next sections. Table 3.1 lists some characteristics of the different methods, like what time scale and for what type of systems they are applied to.

Table 3.1 Overview of several Characteristics of Methods

Characteristics

MM

OPT

FUKS

SPM

IOC

ANN

GRS

KU

Time scale of data logging1

Var

15 min

<1 min

1 sec

min

Hour?

var

1 min

Time scale of analysis

Var

?

sec

day

hour

Mon or yr

10 min and day

Simulation?

No

No

No

No

Yes

Yes

Yes

Yes

Scale of the system (tested) (collector area in m2)

Var

30-250

5

7-16

2-455

402

Very

large

88-400

Type of system

Var

DHW

Combi

DHW

DHW

(simpl)

DHW

DHW

Stage of development[11]

++

++

++

++

++

+-

Level of automation[12]

++

++

++

++

+-

++

1 Time scale: var = variable, sec = second, min = minute, hour, day = day, mon = month, yr = year

2 TRNSYS simulation

key figures were studied. These are compared to the values determined in the planning phase, which are based on the irradiation and temperature profile of a typical reference year [2].

The optimisation phase was very effective regarding failure detection, however, it is time-consuming and therefore costly. The routine supervision phase is not that time-consuming, but does not deliver a quick feedback if the system is working properly and it does not locate failures.

Indoor / Outdoor Test Stand for Solar Thermal Collectors

The idea is to mount a tracker, the thermostat and the complete data acquisition equipment on a carriage on tracks, which allows the collectors on the testing surface to be tested outdoors under natural conditions as well as indoors under the solar simulator. The tracker’s testing surface is 2.5 x 5 m: space enough for four standard solar collectors.

image170

Figure 1: Schematic illustration of the test stand

The hydraulic system and the data acquisition equipment are such that all four collectors can be tested simultaneously outdoors. However, as the indoor testing surface is limited to 2 x 2.2 m, collectors under the solar simulator can only be tested consecutively.

The thermostat for parallel testing of up to four collectors, on a movable frame, was specially developed by TUV Immissionsschutz und Energiesysteme GmbH and Lauda GmbH for this application. In this unique design, the cold production, tempering and data acquisition are combined in one unit, which means that only the electrical connection and one network cable need to be disconnected for a change of position. To function smoothly under the Libyan climate conditions, both the control cabinet with the data acquisition equipment and controls and the tempering unit cabinet are air-conditioned.

The moveable frame is a modification of a trolley such as is used in the cement industry to move heavy loads. measX used the measurement system Almemo® by Ahlborn for the data acquisition. This system controls the thermostat as well as the data acquisition and can, for example, set the temperature test values.

To prevent the collector tests from being distorted by the heat radiation between the collector and the solar simulator’s hot metal halide lamps, a cold artificial sky is used. For the first time, this artificial sky, which consists of two parallel non-reflective, low-iron panes of glass, between which chilled air is circulated, was mounted directly on the lamp field.

The CSES test facilities conform to all current international testing standards in the field of solar thermal and PV modules. For solar thermal, this includes the ISO 9806 set of norms for collectors as well as the ISO 9459 set of norms for systems. There is also a testing facility for solar storage according to the European Technical Specification EN TS 12977-3 (there is currently no corresponding international norm).

In addition, the design includes all necessary test facilities to fulfill the requirements of ISO 9806-2 for serviceability tests of solar thermal liquid collectors. Besides smaller testing equipment, this includes a stand for testing performance in rain, shock and exposure conditions.

For long-term management of the operation with local personnel, BEG makes sure that the necessary know-how is communicated and offers training workshops in Germany and Libya. Other project partners are also involved in these training sessions.

The complete facility was installed in Libya at the end of 2007.

Determination of Daily System Performance

As for determination of daily system performance, the system shall be allowed to operate for 12 h, from 6 h before solar noon until 6 h after solar noon. At 6 h after solar noon the collector shall be shielded, and water drawn off from the store at a constant flow rate of 600 lit/hr. The cold make-up water shall be at the temperature tmain defined during the preconditioning of the system. The temperature of the water being drawn off (td) shall be measured at least every 15 s and an average value recorded at least every time a tenth of the tank volume is drawn off. A volume of water equal to three times the tank volume shall be drawn off. If the temperature difference between the water drawn off and the cold water entering the store is greater than 1 K after three tank volumes, then the draw-off shall be continued until the temperature difference is less than 1K. And especially during the draw-off,

the temperature of the cold water entering the storage tank shall not fluctuate by more than ±0.25 K

and shall not drift by more than 0.2 K during the draw-off period. The flow rate during the draw-off of hot water from the store is very important, and can greatly influence the draw-off temperature profile. The flow controller must therefore maintain a constant flow rate through the storage vessel at 600lit/hr

±50lit/hr.

Figs. 5-7 present the main experimental results gained by the automatic system. Daily draw-off performance, inlet temperature and flow rate profiles can be seen in Fig. 5. And the Fig. 6 shows that the temperature difference between outlet temperature and inlet temperature of system is suitable to the requirements of the standard. From Fig. 7 the fluctuation and drift of the temperature of the entering the storage tank during the preconditioning period and drawn-off period separately can be seen.

image035

Fig.5. Daily draw-off temperature and flow rate profiles

image036

Fig.6 Preconditioning temperature profiles

image037

Fig.7 Drift and fluctuation temperature profiles