Integrated collector-storage solar water heater with helical coil heat exchanger for indirect potable water heating
摘要
This study investigates the thermal performance of a heat exchanger type integrated collector-storage solar water heater (ICS-HX) developed to provide hygienic and energy-efficient potable hot water under winter conditions in Raipur. Conventional integrated solar water heaters often suffer from thermal stratification, poor heat retention, and direct contact between stored and potable water, motivating the development of an indirect heating configuration using a submerged helical coil heat exchanger. It was hypothesized that the incorporation of a reflector cover, forced water agitation, and optimized storage geometry would improve heat transfer and hot water delivery performance. A transient thermal model was developed and validated to evaluate the effects of storage depth, heat exchanger length, agitation, and overall heat transfer coefficient on system behaviour. The results showed that lower storage depths produced faster heating and higher peak temperatures, whereas larger depths improved heat retention. For a hot water demand of 180 kg day−1, the optimum configuration comprising a 20-cm tank depth (300 kg water capacity) and 20 m helical coil-maintained water temperatures above 40 °C under different withdrawal patterns, with withdrawal efficiencies ranging from 39.7 to 42.8%. The estimated hot water production cost was ₹0.144 L−1 (US$ 0.0015L−1), demonstrating the economic feasibility of the system. Water agitation enhanced the heat transfer coefficient between the coil and stored water, leading to improved thermal performance. The proposed ICS-HX system therefore provides a hygienic, scalable, and cost-effective alternative for domestic solar water heating applications and can be integrated with auxiliary heating under low solar radiation conditions.