Louise Jivan Shah & Simon Furbo
Department of Civil Engineering, Technical University of Denmark

Building 118
DK-2800 Kgs. Lyngby
Denmark

E-mail: lis@bvg. dtu. dk

Introduction

A new collector design based on parallel-connected double glass evacuated tubes has previously been investigated theoretically and experimentally (Shah, L. J.

& Furbo, S. (2004)). The tubes were annuluses with closed ends and the outside of the inner glass wall was treated with a selective coating. The collector fluid was floating inside the inner tube where also another closed tube was inserted so less collector fluid was needed.

The collector design made utilization of solar radiations from all directions possible. Fig. 1 shows the design of the evacuated tubes and the principle of the tube connection.

The investigations resulted in a validated collector model that could calculate the yearly thermal performance of the collector based on hourly weather data. The advantages of the model were that shadows, the solar radiation and the incidence angle modifier for Fig. 1: Design of the each tube were precisely determined for all solar evacuated tubes (top)and positions, including solar positions on the “back” of the the tubes connected to a collector. However, the model could be improved solar panel (bottom). further as the model was only valid for vertically tilted

pipes and as the model was not developed for a commonly used simulation program.

In the present paper, the theory is further developed so it can simulate solar collector panels of any tilt and based on the theory a new TRNSYS (Klein, S. A. et al. (1996). ) collector type is developed. This model is validated with the measurements from outdoor experiments.

TRNSYS simulations of the yearly thermal performance of a solar heating plant based on the evacuated solar collectors are carried out and among other things it is investigated how the distance between tubes and the collector tilt influences the yearly thermal performance. The calculations are carried out for two locations: Copenhagen, Denmark, lat. 56°N, and Uummannaq. Greenland, lat. 71°N.

Further, the results are compared to the calculated thermal performance of the solar heating plant based on traditional flat plate collectors.