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.