Thermal performance of solar hot water systems using a flat plate collector of accelerated risers

الملخص EN

This study focuses on a comparison of the performance of two similar locally-fabricated solar water heaters.

One of the collectors features a new design for accelerated absorber ; its risers are made of converging ducts whose exit area is half that of the entrance.

The other collector is a conventional absorber, with risers of the same cross sectional area along its length.

Each collector is the primary part of an indirect thermo syphon circulation solar hot water system.

Both collectors face south with a fixed tilt angle of 33.3 from the horizontal.

A side-by-side experiment was conducted on the two solar water heaters from January to April of 2009 for different water withdrawal profiles, continuous, interrupted and no load, as well as for horizontal and vertical storage tank orientations.

Two types of storage tanks were investigated, those with two concentric cylinders, and those with helically-coiled tubes in the cylinder.

Results show that a considerable enhancement of thermal performance (approximately 60 %) of absorbed heat (useful gain) at solar noon was obtained for the new design, in comparison with the conventional type.

The instantaneous efficiency was 31.5 % for the accelerated absorbed flat plate at solar noon, while that of conventional absorber was (16.5 %).

The longitudinal water temperature variations in the risers of accelerated absorber were larger than that of the conventional absorber.

The stratification in the storage tank was significantly improved for the solar hot water system, with the new absorber design in which the maximum temperature measured was 50 ˚C (vertical storage tank), while that for conventional absorber was 37 ˚C.

The stratification obtained for a coiled tube in a cylinder storage tank indicated a good thermal performance with less space requirements.

Also, the circulation rate in the accelerated absorber was higher when it was connected to a coiled tube than when it was connected to the concentric cylinders.