Modeling and Test-and-Rate Methods for Innovative Thermosiphon Solar Water Heaters

Simulation models for innovative thermosiphon solar systems (TS) have been generally unavailable, hindering innovative system design/optimization and system rating. A TRNSYS module is introduced that calculates the mass flow rate in general natural convection loops, allows use of any existing tank and heat-exchanger modules, and handles reverse flow in TS when used with a new pipe module. To achieve desired rating accuracy, it is proposed that the flow rate sub-model in the underlying rating simulation be calibrated via nonintrusive flow data from an assembled system. Three innovative TS are being tested to validate the new modeling and the proposed test-and-rate method: two unglazed systems and a glazed polymeric system. An ultrasonic meter and a calorimetric flow-rate method both showed that model friction was high by ∼3X. After calibration, the model showed good agreement on both long-term collected energy and tank temperatures.