Rigid pipe with openings

A rigid pipe with openings is the most common stratification concept seen on the market, and can be experienced in many different shapes and forms. The rigid pipe with openings can be very cheap and durable, and is relatively easy to produce. The concept is simple to most and only few are aware of the fact that the concept offers very low thermal efficiency.

The lack of “one-way” valves, results in cold water from the bottom of the tank to be sucked into the flow of hot water in the inlet pipe. The cold and the hot water mixes, and the inlet flow temperature drops with a low level of thermal stratification as a consequence. As experts within the solar energy at The Technical University of Denmarks states: “It is a mixing device rather than a stratification device!”

In the two videos shown, the (low) efficiency of the rigid pipe with openings is demonstrated.

The first video demonstrates a simulation of solar charging through an afternoon after the system has been fully discharged. The different inlet temperatures illustrated by different colors are not placed in the ideal thermal layers, but is placed in thermal intervals with a lower average temperature than the inlet water. 

The second video at the bottom of  the page is a CFD (Computer Fluid Dynamics) simulation that clearly demonstrates how the rigid pipe with openings sucks in the cold water from the bottom of the tank and simply mix it with the water inside the inlet pipe, causing the inlet water temperature to drop dramatically.