Pipe internal recirculation in storage connections - Characteristics and influencing parameters

Pipe internal recirculation (PIR) is an undesired phenomenon which may lead to significant additional heat losses. Although different research institutes already measured singular PIR effects, there is still a lack of wide-ranging evaluations and practical solutions. This paper describes a test and evaluation method and reports on results regarding the influence of the pipe's slope, the material (copper, stainless steel) and diameter on the PIR caused heat loss coefficient. For combined pipe path arrangements a new method is presented, which allows to calculate the heat losses from basic investigations on horizontal and vertical pipe orientations. This method has been experimentally validated. Finally, the effectiveness of different measures for the reduction of PIR induced heat losses is presented

Development of an insulated glass solar thermal collector

Insulated glass solar thermal collectors result from the insertion of a solar absorber into the outer gap of a multiple glazed unit. Taking advantages from the manufacturing technology of the glass and window industry, a flexible and highly automated production as well as an easier and architecturally more appealing integration into the building envelope is expected. Ensuring long-term functionality, on the other hand, represents a very challenging development task due to high temperatures and to the thermally induced deformations of the solar absorber. The paper analyzes the behavior of this new kind of collector by means of theoretical calculations and experiments, focusing on both the performance and the reliability aspects. Efficiency measurements according to EN 12975 on prototypes with a slim design report specific values comparable to those of standard flat plate collectors (η0 = 0.78, a1 = 3.77 W/m2K, a2 = 0.011 W/m2K2 for a 50 mm thick, argon-filled prototype). Prolonged exposure to stagnation temperature and internal thermal shock-tests attest the durability of collector configurations featuring temperatureresistant components and suitable constructions, able to reduce and compensate the absorber deformation

Pipe internal recirculation in storage connections - An unseen efficiency barrier

Basically, pipe internal recirculation (PIR) at storage connections is a known phenomenon. However, it is not sufficiently considered by storage manufacturers and installers. There is still a lack of awareness and quantification of the PIR effect in typical installations and practice-oriented solutions. Within this paper, the final results of a research project aiming at the detailed qualitative description and quantification of the effect including extrapolation of the results regarding the PIR impact on storage heat losses are presented. This includes the results regarding the influence of the pipe's material (copper, stainless steel, plastic), diameter, insulation and connection type (direct to storage, indirect via immersed or external heat exchanger) on PIR including their effects on the overall heat losses of ready installed storage tanks. Derived from generalized measurements, a calculation method has been developed, which enables to determine the annual heat losses caused by PIR in domestic hot water storages using dynamic system simulations (TRNSYS). In conclusion, different measures for the reduction of PIR induced heat losses and their effectiveness may be presented. © 2015 The Authors