Techno-Economic Evaluation and System Design of Evacuated Tube Collector Based Water Heating for Institutional Hostels

Abstract

Water heating is increasingly becoming one of the major energy-consuming activities in Kenya and globally. This trend is largely driven by significant efficiency improvements in other energy consuming sectors such as lighting and household appliances, while heating technologies have experienced relatively minimal advancements. Although electric water heaters are efficient, their adoption in institutions such as Multimedia University (MMU) has declined due to several challenges, including high electricity costs, high maintenance costs associated with elevated chlorine levels in water, carbon dioxide (CO<sub>2</sub>) emissions from grid electricity, and national trade imbalances linked to the importation of heavy fuel oil used in non-renewable electricity generation. This study evaluates the techno-economic feasibility of replacing electric immersion heaters with evacuated tube solar collectors (ETCs) for large-scale water heating at MMU’s executive hostel, serving over 300 users. Water consumption patterns were monitored over one week, revealing an average usage of 49.1 L per person per bath and a total daily demand of 15,529.6 L, corresponding to an energy demand of 400.48 kWh/day. RETScreen Expert software was used to simulate and optimize the solar thermal system using a site solar radiation of 5.32 kWh/m<sup>2</sup>/day and collector parameters Fr(τα)=0.68 and FrUL=1.33. The results indicate that immersion heaters currently consume 175,200 kWh annually at a cost of $31,658.51 and generate 8,628.7 kg of CO<sub>2</sub> emissions per year. The optimal ETC system achieves a 64% solar fraction with a collector capacity of 21,300 L, a tilt angle of 15°, and storage of 75 L/m<sup>2</sup>. Economic analysis at a nominal discount rate of 10.75% yields a net present value of $29,083.96, an internal rate of return of 24%, and a payback period of less than three years, demonstrating the strong economic viability of solar water heating for institutional applications.