Long term durability of crosslinked polyethylene tubing used in chlorinated hot water systems

This paper reports on the results of a comparison between short-term indoor testing and long-term outdoor monitoring of solar domestic hot water systems. Five solar-preheat systems were monitored under side-by-side conditions of irradiance and load, for a period of two years. The systems were then tested according to a standard day test, using a solar simulator, and a load schedule identical to that imposed on each system during the monitoring. The systems were found to deliver 19.7 MJ–25.8 MJ daily in the test, compared to a two-year average of 19.1 MJ–26.0 MJ (1.5 to 2.0 GJ/m2 annually) outdoors. System rank was reasonably well preserved. Comparison of results on the basis of efficiency and solar fraction suggests that good correspondence exists between long-term outdoor results and those of indoor testing, at least for systems with stable controllers. Selected systems were also tested at different load schedules and radiation levels. Methods of predicting the performance of a solar-preheat system from the results of a standard day test are discussed, and the possibility of reducing testing time to a single day is explored.

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Stearic Acid/Inorganic Porous Matrix Phase Change Composite for Hot Water Systems

Molecules ◽

10.3390/molecules24081482 ◽

2019 ◽

Vol 24 (8) ◽

pp. 1482 ◽

Cited By ~ 4

Author(s):

Ling Xu ◽

Rui Yang

Keyword(s):

Dynamic Response ◽

Stearic Acid ◽

Phase Change ◽

Heat Storage ◽

Waste Heat ◽

Porous Matrix ◽

Water Systems ◽

Hot Water ◽

Cyclic Stability

The storage and utilization of waste heat in low and medium temperature ranges using phase change materials (PCMs) is an effective technology to improve energy utilization efficiency in combined cooling, heating, and power (CCHP) systems. In this paper, stearic acid/inorganic porous matrix phase change composites were developed to store waste heat for hot water systems. Among them, stearic acid/expanded graphite (EG) phase change composite was highlighted and the thermal physical properties, the dynamic response, and the long-term cyclic stability were evaluated. The stearic acid concentrations in the composites were over 95 wt%. The thermal diffusion coefficients were 3–5 times higher than pure stearic acid, independent of composite densities. Accordingly, the heat storage and release times were decreased by up to 41% and 55%, respectively. After 100 cycles, the composites maintained good dynamic response and long-term cyclic stability, with heat storage density of 122–152 MJ/m3. Hence, this stearic acid/EG phase change composite exhibits excellent comprehensive performances. It is also easy to be prepared and flexible for various types of heat exchangers.

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