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Abstract: A dynamic flat-plate collector model for parametric sensitivity studies on polymer-based collector designs was developed. Validation using experimental results of conventional flat-plate collectors showed satisfying results especially regarding the calculation of individual part temperatures of a collector. The model was used to predict system efficiency as well as individual part temperatures in order to analyse a polymeric collector approach in comparison to a conventional collector. The simulation results showed that the fractional energy savings of systems with conventional flat-plate collectors cannot be reached with the analysed polymeric collector approach. Also the stagnation temperatures of more efficient approaches are too high for low-cost polymeric materials. The exemplary analysis of annual temperature loads of the backside insulation for different approaches proved the necessity of careful collector design aiming at temperature reduction for all individual collector parts. [Copyright &y& Elsevier]

Abstract: The incidence angle modifier (IAM) of a solar thermal collector for diffuse irradiance is usually determined under the simplifying assumption of isotropic sky and ground radiance. It is applied as one constant collector parameter, independent from slope or weather conditions. The simulation model introduced here considers the varying anisotropy of sky radiance. To create realistic distributions, the approach of Brunger and Hooper is used. Three modes are possible: Mode 1 calculates separate IAMs for anisotropic sky (for every time step) and isotropic ground. Mode 2 calculates separate IAMs for isotropic sky and isotropic ground (once per simulation). Mode 3 uses a user-specified isotropic IAM-value for the collector hemisphere. The model is applied to a stationary, double-covered process heat flat-plate collector with one-sided CPC booster reflector (RefleC). This collector shows a biaxial and asymmetric IAM for direct irradiance. It is found that, compared to anisotropic modeling, the simplified isotropic model is undervaluing the annual output of this collector by 13.7% for a constant inlet temperature of 120°C in Würzburg, Germany. At 40°C inlet temperature the undervaluation is 9.3%. For the basis flat-plate without reflector the undervaluation is 7.5% at 120°C and 3.3% at 40°C. An annual irradiation distribution diagram shows that this is due to an underestimation of diffuse irradiation from directions with high direct irradiation. Detailed results reveal that for RefleC the IAM for anisotropic diffuse sky radiance can vary by up to approx. 25 percentage points during one day. It is concluded that isotropic modeling of diffuse irradiance can be expected to significantly undervalue the annual output of all non-focusing solar thermal collectors. Highest relevance is found for high collector slopes, complex IAMs and at low-efficiency operation. The optimal collector slope is almost not affected. Accuracy of existing models can be increased by applying Mode 2. [Copyright &y& Elsevier]

Abstract: This paper described the development of regression models which are able to predict office building annual heating, cooling and auxiliary energy requirements for different HVAC systems as a function of office building heating and cooling demands. In order to represent the office building stock, a large number of building parameters were explored such as built forms, fabrics, glazing levels and orientation. Selected parameters were combined into a large set of office building models (3840 in total). As different HVAC systems have different energy requirements when responding to same building demands, each of the 3840 models were further coupled with five HVAC systems: VAV, CAV, fan-coil system with dedicated air (FC), and two chilled ceiling systems with dedicated air, radiator heating and either embedded pipes (EMB) or exposed aluminium panels (ALU). In total 23,040 possible scenarios were created and simulated using EnergyPlus software. The annual heating and cooling demands and their HVAC system''s heating, cooling and auxiliary energy requirements were normalised per floor area and fitted to two groups of statistical models. Outputs from the regression analysis were evaluated by inspecting models best fit parameter values and goodness of fit. Based on the described analysis, the specific regression models were recommended. [Copyright &y& Elsevier]