Long time durability tests of fabric inlet stratification pipes
E. Andersen* and S. Furbo
Department of Civil Engineering, Technical University of Denmark, Brovej, Building 118, DK-2800 Kgs.
* Corresponding Author, 5an@byg. dtu. dk
The long time durability of seven different two layer fabric inlet stratification pipes for enhancing thermal stratification in hot water stores is investigated experimentally. Accelerated durability tests are carried out with the inlet stratification pipes both in a domestic hot water tank and in a space heating tank. Heating/cooling cycles are carried out with different operation conditions including different temperature levels and volume flow rates.
The results show that that lime contained in the domestic water is deposited in the fabric pipes in the domestic hot water tank and that this destroys the capability of building up thermal stratification for the fabric inlet stratification pipe. The results also show that although dirt, algae etc. are deposited in the fabric pipes in the space heating tank, the capability of the fabric inlet stratifiers to build up thermal stratification is unchanged for five out of seven fabric pipes within the test period.
Keywords: Hot water tanks, thermal stratification, fabric inlet stratifiers, long time durability of fabric inlet stratifiers
Previous investigations have shown that thermal stratification in hot water stores can be built up in a very good way with inlet stratification pipes made of two fabric layers [1, 2, 3]. This is true even with volume flow rates through the pipes as high as 10 l/min. Many different fabric styles have been investigated including both stretchable and non-stretchable fabrics but the investigation did not result in one superior fabric being pointed out. On the contrary, several of the tested fabrics show similar good behaviour.
Based on these promising results, accelerated long time durability tests are carried out with two fabric layers inlet stratification pipes made of seven different fabric styles, see Table 2.
Table 1. Investigated fabric styles.
The long time durability tests consisting of continuous heating/cooling periods of hot water stores with built in inlet stratification pipes have been going on for one year and the fabric pipes have been inside the tanks during this time. Hot water is pumped into the tanks through the inlet stratification pipes during all heating periods. In average each fabric pipe has been in operation in 480 hours. During this period the inlet temperatures have varied in the range 30°C - 70°C. The volume flow rates have varied in the range 2 l/min - 10 l/min. The applied operation conditions correspond to operation of a solar heating system with a solar collector area of 10 m2 with a volume flow rate in the solar collector loop of 0.2 l/min per m2 solar collector area in 2/3 year. Solar heating systems with flat plate solar collectors are typically in operation 1800 hours per year in Denmark.