Partner und Internationale Organisationen
(Englisch)
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TNO Building and construction research (NL), DTI Solar Energy Laboratory (DK), ITW-Universität Stuttgart (D), FHG-ISE (D), Infa-Solar (D), LECS-ITE/INETI (P), NCSR ‚Demokritos' (UK), University of Wales College of Cardiff (UK), SP Energy Technology (S), CSTB (F)
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Abstract
(Englisch)
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Background
European quality standards for Solar Domestic Hot Water (SDHW) systems are being prepared by the CEN committee TC 312. The Dynamic System Testing (DST) method is one of the methods chosen there to measure the energetic performance of these systems. It is proposed that an outdoor DST test on a SDHW system suffices to give predictions of the energetic performance for a whole year under various climates and circumstances.
Objectives
The project objectives are:
- · Comparison of the DST method to the CSTG method, which is also used in the CEN, leading to correspondence factors which enable comparison of DST results with CSTG results.
- · Fine-tuning of the present description of the procedure to an expected reproducibility of 5 to 10 %, with predictions for different climates and hot water consumption.
- · Clear demarcation, definition and widening of the scope of the test method, to allow for as many systems and conditions as possible
- · Experimental validation of the DST method by means of inter-comparison tests in a number of recognised laboratories throughout Europe
Work programme
Work Package 1:
Definition of scope. Investigations were conducted on weaknesses, boundaries and limits of the DST performance test method. This was done by means of simulation of a large number of DST tests using a detailed computer model instead of a physical SDHW system. Furthermore, different climates and cold water temperatures were analysed and a suitable measure for the accuracy was defined.
Work package 2:
Comparison to the CSTG method. In three laboratories, parallel tests have taken place on five SDHW systems using the DST and the CSTG method.
Work package 3:
Experimental validation programme. SDHW systems of all relevant different system types are to be tested at eight European laboratories. This will yield validation results on repeatability, comparability, climate or season dependency and possible ambiguities in the procedure.
Results and achievements
Applicability
Combining the results of the calculation study and the experimental validation programme, the conclusion upon the applicability of the DST test method is:
The DST test method will produce precise predictions of the thermal performances of 'preheat' as well as 'solar-plus-supplementary' SDHW systems (±5% - Solar Fraction or ±3% - Load ), taking into consideration the aspects that define the applicability range, mentioned below.
For more critical cases the precision of the DST test method can lead up to ±10% (Solar Fraction or ±5% - Load). This applicability holds for different testing and prediction climates, different hot water demands and for the system types common on the European market.
Comparison CSTG vs. DST
Considering the claimed uncertainty of the performance predictions for both methods:
· CSTG: ±5% for clear climates and ±10% for cloudy climates
· DST: ±5% for most cases and ±10% for extreme cases
Differences in the order of maximum ±14% (=10Ö2 ) can be expected. The results obtained are within this limit. Conversion factors have been defined.
Aspects that demarcate the applicability range
· DST is sensitive to systematic errors in sensor readings.
DST is not sensitive to random sensor errors in sensor readings
· Systems with an integrated electrical heater might show a bad performance due to the fact that almost the whole storage is heated. The DST test method reveals this behaviour by finding a large value for the faux - parameter. The resulting poor solar energy gain is however not predicted in a reproducible way.
· In the case of a strong Incident Angle Dependency of the SDHW system (collector), a correction with respect to this Incident Angle Dependency must be carried out.
· When the overheating protection mechanisms of a SDHW system are activated during the test, the precision of the test will be destroyed. This must be avoided.
· When a significant reverse flow (a heat flow from the store to the collector) is present, the DST performance prediction cannot be trusted.
· With respect to the treatment of the wind around the collector, the option Wforce (of the DST software) for SDHW systems with glazed collectors must be used.
· A SDHW system with a load side heat exchanger in combination with the temperature dependent pump control on the (load side) pump, cannot be dealt with by the DST test method.
· There is a very promising agreement in the predicted annual thermal performance under reference conditions between the Component Test method (CTSS) and the DST test method.
· In general the parameters identified from a DST test characterise a SDHW system. However, this does not necessarily mean that from two DST tests performed the same individual parameter set result.
· In many tested SDHW systems, both SC and DL parameters are small or statistically insignificant. In case a parameter is not significant in the parameter set, a parameter set without this parameter can be identified and can be used for long term performance predictions; omitting this parameter(s) has no significant influence on the final prediction result.
· The parameter identification of a DST test on an ICS system, fixing the collector heat loss parameter (uC*) to zero, shows promising results in performance predictions.
A list of recommendations for CEN, ISO and also for further research has been formulated.
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