Advantages using inlet stratification devices in solar domestic hot water storage tanks

The thermal performance of a domestic hot water system is strongly affected by whether the storage tank is stratified or not. Thermal stratification can be built up in a solar storage tank if the heated water from the solar collectors enters the tank through an inlet stratifier.Measured thermal performances of two solar domestic hot water systems are presented.

One system is a traditional high flow system with a heat exchanger spiral in the tank. The other system is a low flow system with an external heat exchanger and a newly developed inlet stratifier from EyeCular Technologies ApS installed in the tank. The two systems are otherwise identical which makes it possible to compare the thermal performance and the thermal stratification built up in each tank.Based on a measuring period of 140 days in the period from April 26, 2016 to September 25, 2016, the investigation shows, that the system with the stratification device has a higher thermal performance compared to the system with the heat exchanger spiral inside the tank.The relative performance (defined as the ratio between the net utilized solar energy of the low flow system and the net utilized solar energy of the high flow system), is a function of the solar fraction.

The lower the solar fraction is, the higher the relative performance will be. Weekly relative performances up to about 1.10 are measured. That is, weekly extra thermal performances of up to 10% arc measured for the system with the inlet stratifier.