Elsa Andersen

Thermal performance of Danish solar combi systems in practice and in theory

An overview of measured thermal performances of Danish solar combi systems in practice is given. The thermal performance varies greatly from system to system. Measured and calculated thermal performances of different solar combi systems are compared and the main reasons for the different thermal performances are given. Further, a parametric study on two solar combi system types is performed. Based on the investigation it can be concluded that the thermal performance first of all is influenced by the space heating consumption during the summer period and that the systems in practice perform as theoretically expected.

Heat Losses from Pipes Connected to Hot Water Storage Tanks

The heat loss from pipe connections at the top of hot water storage tanks with and without a heat trap is investigated theoretically and compared to similar experimental investigations. Computational Fluid Dynamics (CFD) is used for the theoretical analysis. The investigations show that the heat loss from an ideally insulated pipe connected to the top of a hot water tank is mainly due to a natural convection flow in the pipe, that the heat loss coefficient of pipes connected to the top of a hot water tank is high, and that a heat trap can reduce the heat loss coefficient significantly. Further, calculations show that the yearly thermal performance of solar domestic hot water systems is strongly reduced if the hot water tank has a thermal bridge located at the top of the tank.

MEASURED REFLECTION FROM SNOW

This paper presents an investigation of reflection from snow. Based on measurements of the reflected radiation and global radiation from a test facility in Sisimiut, Greenland, the effective albedo for the ground is determined. The influence of snow on the effective albedo is presented, and a high contribution from the specular reflection is seen. The effective albedo from snow-covered ground is compared with the effective albedo on a summer day without snow. The effective albedo is much higher for the snow-covered ground than the effective albedo for the ground without snow. In the summer the reflection happens as diffuse reflection and as backward reflection, because of the uneven terrain. There is no specular reflection.