From the test sequences obtained for QD test method, test periods according to SS test method conditions were selected and the parameters of efficiency curve determined (equation (3)). The values determined are listed in Table 2.
Table 2: Parameters of efficiency curve according to SS test method
Comparison of results between the QD and SS methods is presented in the form of an efficiency curve with respect to Tm* = (tm-ta)/G*, where G* is the global irradiance incident on the collector. The following values were considered:
G* = 1000 W/ m2; Gd = 150 W/ m2; 0: = 15°
according to the standard’s recommendations for the presentation of results.
The above figure shows good agreement between the two test methods for the flat ...Read More
The solar system considered in this work is a large hot water production system suitable for a small hotel, blocks of flats, offices or similar applications. Although the FDS system developed can be applied to small systems as well it is thought that the expenditure required would not balance the extra benefits incurred in such cases and in domestic applications the users are usually more sensitive to the maintenance of their own system in comparison with the maintenance staff of a hotel for example or the tenants of a multi building installation where everybody but really nobody is responsible. The system schematic is shown in Fig. 1. The system consists of 40 m2 of collectors, a differential thermostat (not shown in Fig. 1) and a 2000 L storage tank...Read More
The power of the collectors during the day is studied to investigate the transient thermal performance of the ETCs. Figure 2 shows the collector power in an autumn day. In the morning, the direct flow ETC 7 starts up first, followed by the heat pipe ETC 4, ETC 2 and the double glass ETC with heat pipe. There is a sharp increase of the power of the heat pipe ETCs which is most likely caused by the late start-up of evaporation in the heat pipe causing “overheated” absorber temperatures. A possible explanation is that the upper part of the collector is heated up first, but the heat pipe will not be able to work until the bottom part of the heat pipe is heated up to the evaporation temperature...Read More
In addition to the equipment required for thermal performance testing, the test facility is delivered with the complete equipment required for durability and reliability testing of solar thermal collectors according to EN 12975-2. This comprises test facilities for outdoor exposure, external and internal thermal shock, rain penetration, mechanical load test and internal pressure test.
Like for thermal performance testing, it is also possible to combine test facilities required for several durability and reliability tests into a single test facility. Figure 5 shows the test facility for the rain penetration which can also be used for performing external thermal shock tests.
For carrying out exposure tests, high-temperature resistance tests and internal thermal shock tests, the same test fac...Read More
The first stage of the calculations was to compute the main evaluation indexes (Nic, Nvc, Nac and Ntc) for the buildings with their base-case envelope, as described in section 2. Table 5 and Table 6 show the results of the heating and cooling needs for each of the 7 analysed locations. The results show that, with the base-case envelope, the heating needs are above the allowed limit if the buildings are located in the coldest regions – Bragan? a, Guarda, Penhas Douradas and Viana do Castelo (this later one only in the case of the dwelling). The cooling needs pose no problem in any of the studied locations.
Table 5: Results for the apartment with the base-case envelope – heating and cooling needs
William S. Duff* and Jirachote Daosukho
Department of Mechanical Engineering, Colorado State University, Ft. Collins CO 80523
* Corresponding Author, bill@engr. colostate. edu
A novel integral compound parabolic concentrator evacuated solar collector (ICPC) array has been in continuous operation at a demonstration project in Sacramento California since 1998. An ongoing study addresses the impact of optical, thermal, degradation and component failure factors on array performance over the ten years of operation. This paper reports on the ray trace modeling for the vertical and horizontally oriented fined absorber tubes and the degradation of the reflector in the tubes of the array...Read More
Based on the project results Fraunhofer ISE together with the partners DLR and PSE performed a technology comparison between Linear Fresnel-Collector (LFC) and Parabolic Trough (PT) for a 50 MW solar power station. Due to the lower collector efficiency (cosine, shading and blocking losses) of the LFC a larger aperture area is needed than for the PT. For optimized optical and thermal performance it seems completely feasible that due to lower investment costs per aperture area the levelised electricity costs (LEC) for the LFC are appreciably lower than for the PT.
relative change of parameters
Figure 8: Break-even-costs for LFC compared to PT (assumed specific costs 275 €/m2) Starting point for LFC design is the prototype collector performance – 25% thermal loss would require vacuum tube...
In this paper a partial multi-criteria analysis (MCA) is used to evaluate and compare methods that can be used for detection and identification of failures or malfunctions during the operation of solar thermal systems. A multi-criteria analysis is often applied to support policy decisions and evaluate different alternatives . One of the advantages of MCA is that the criteria, on basis of which the comparison is made, are explicit. There are several MCA methods; a relatively simple one without weighting the different scores and combining these to a result score will be used here. Since the weights would depend on the application of the method, this will not be carried out here.
The MCA conducted in this paper consists of four steps.
1. Identification of aims and decision makers