Side-by-side comparison of a pressurized and a nonpressurized solar water heating thermosiphon system

Abstract

Two commercially available domestic size hot water heating systems, in which the natural convection maintained the flow of water from the collector to the tank, were studied experimentally under identical meteorological conditions. One of the systems was a pressurized type of system and the other was a nonpressurized type. The measurements have been validated by numerical calculations performed using a simplified theory. An explicit expression has been derived for the mass flow rate of water due to thermosiphon effect in terms of known physical parameters. The measurements show that for an incident solar energy of 6.75 kWh/m 2 of collector area, the useful energy available from the pressurized and nonpressurized system is 3.06 kWh and 3.83 kWh per unit collector area respectively yielding a daily average efficiency of 41% and 47%. The system's performance has also been evaluated for typical water consumptions in the domestic sector.