Design of a Heat Exchanger Performance Model for Chillers

Photo of John Greenwood, Evan Mueller, Matt Novogoratz (Team Leader) Students: John Greenwood, Evan Mueller, Matt Novogoratz (Team Leader)

Sponsor: University of Texas Utilities and Energy Management

Date: Spring 2010

Requirements:
The performance model must be developed in Microsoft Excel, and designed to be applicable to other heat exchangers around campus. In addition, the model must be equipped to analyze the most current chiller operating data available from the UT Utilities database. The model must operate using instrumentation that is already installed in the chilling station. Once the data has been analyzed, the model must recommend to the user whether or not maintenance is cost beneficial.

Problem:
The University of Texas Utilities and Energy Management requested a performance model be developed for the heat exchangers of one of the chilling stations (Chilling Station #6) used to cool water for use in campus climate control. The model willbe used for the optimization of maintenance on the chillers, which must be periodically shut down for cleaning as a result of performance declines caused by fouling buildup (as seen below).

Solution:
Analysis of chiller performance was based on the effectiveness of the heat exchangers - a ratio of the heat removed from the chilled water to the theoretical maximum amount of heat that can be removed based on current operating conditions. After analyzing the performance decline over time of the chiller heat exchangers, the decline was extrapolated into the future for use in an economic model of maintenance costs. Based on this analysis and the rate at which the chiller performance drops, we concluded that maintenance becomes cost beneficial about 8 times in a 5 year operating period. This takes into account the cost of electricity produced from market priced natural gas, as well as the cost of maintenance and system downtime.

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