Optimal Control in Thermal Engineering by Viorel Badescu

Author:Viorel Badescu
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

14.2.6.2 Model Validation

One of the most popular and tested renewable energy software packages in the public domain is Retscreen International . Many experts have contributed to the development, testing and validation of the RETScreen Solar Water Heating Project Model (RSWHM) (Retscreen 2001–2004).

Results obtained by using the present model were compared with results predicted by RSWHM. The same input data were used for both models, when possible. Mean monthly average values were computed for global solar irradiance and ambient air temperature in Bucharest by using the METEORAR database. The RETScreen database was used to provide the input data for the monthly averaged values of wind speed.

A South-oriented collector was considered. The collector slope angle was 45° which is close to the optimum angle for a yearly operation. The RETScreen application type was Service Hot Water and system configuration was: No Storage. The hot water use was 400 L/day. This entry is needed by RETScreen software for proper operation.

RSWHM uses constant (i.e. time and temperature-independent) entries for and . The following values were used in computations: and . The present method was slightly changed to use the same temperature-independent entries. The yearly average air temperature computed by the RETScreen package is and this value was adopted to evaluated the quantity .

Input (constant) values for RETScreen software are cold water temperature (i.e. ) and desired water temperature (i.e. ). Computations were performed for six set of values (in degrees Celsius).

Results are given for the ratio in Fig. 14.4 where the bars indicating the ±2.5% deviation are also included. There is good concordance between the two models, with slight overestimation by the present model. Also, both methods predict that the solar fraction f decreases from 0.52 to 0.42 when T increases from 10 to 60 °C. This is in agreement with the current practice of sizing the solar collector area in such a way that overproduction of solar heat in the warm season is avoided (Lund 2005).

Fig. 14.4Ratio [Ks3/kg] predicted by the present model and Retscreen International Software (Retscreen 2001–2004), respectively. ±2.5% deviation bars are also shown

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.