HWSIM: Development and Validation of a Residential Hot Water Distribution System Model

Panel: Residential Buildings: Technologies, Design, Performance Analysis, and Building Industry Trends

Authors:
David Springer, Davis Energy Group, Inc.
Leo Rainer, Davis Energy Group, Inc.
Marc Hoeschele, Davis Energy Group, Inc.
Robert Scott, RASENT Solutions

Abstract

The performance characteristics of storage water heaters (the predominant water heater type in the U.S.) are well documented. The performance of the distribution system is not well understood as once the hot water leaves the water heater a wide range of factors come into play. Hot water usage patterns and quantities, piping materials and pipe locations, environmental temperatures surrounding the piping, and presence of insulation are just a few of these factors. A detailed event-based simulation model (HWSIM) was developed to better evaluate hot water distribution system performance. The program tracks the flow and heat transfer of a volume element of hot water as it flows from the water heater to the end use point. The program is based on engineering first principles and allows the user to input the hot water distribution layout (pipe material, location, diameter, surrounding environment), temperature conditions of the surrounding environments (varying monthly and hourly, if desired), cold water inlet temperatures by month, hot water draw characterization (time of day, day of week, duration, flow rate, end use fixture, minimum useful temperature), and water heater performance parameters. Model output includes energy tabulations, hot and cold water wasted and used, and overall distribution efficiencies.

The paper describes model development, validation against laboratory data, and presents results from a set of runs evaluating the effect of insulation and hot water usage pattern on overall energy and water use.