Date of Award

Spring 1-1-2010

Document Type


Degree Name

Master of Science (MS)

First Advisor

Moncef Krarti

Second Advisor

Michael Brandemuehl

Third Advisor

Jay Burch


Tankless water heaters (TWHs) are generally thought of as an efficient method of producing hot water, and receive incentives in various federal, state, and utility programs. However, it has up to now been impossible to know the actual efficiency for any specific draw pattern. In addition, TWHs have been used in conjunction with solar systems, and it is uncertain what the impact of pre-heated water will be on THW operation. To address these questions experiments have been performed to fully understand and characterize behavior of TWHs, and a new TRNSYS component has been developed embodying that understanding. The model is multi-node in the heat exchanger, with ad-hoc control features mimicking observed behaviors. The TRNSYS model was calibrated to several hours of data, yielding burn efficiency of 80.2%, capacitance of 8.36 ± 0.6 kJ/C, and total loss coefficient of 12.99 ± 4 kJ/hr-K. The model was validated against several draw profiles, and used to carry out analyses of performance with different draw profiles used in the Building America Program. Efficiency depends on the draw, varying from 77% for low use to 65% for high use.