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Development of a Simplified Model for Cooling and Dehumidifying Coils
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Precise understanding of the cooling coil in air handler units is vital to assure the proper temperature and humidity in conditioned space while minimizing the associated costs of operating the air conditioning system. Several models have been developed in the past to characterize the overall heat transfer coefficient of this component. However, these models require specific details about the coil construction which make them impractical for in-situ applications. A simplified engineering model suitable for application to existing coils in the field is therefore needed in the heating, ventilating, and air conditioning (HVAC) industry. The objective of this study is to develop a simplified model suitable for use with field measured data to characterize the overall heat transfer coefficient of in-situ water-to-air cooling coils. This model uses the electrical resistance analogy to treat the heat transfer process in the coil. Field measured data combined with a theoretical analysis are the basis for the development of the model. Non-linear regressions are applied to the data to trace the heat transfer behavior of the coil. The coefficients obtained from the regressions account for the physical characteristics of the coil under study as well as for the properties of the fluids involved (air and water). The calibration of these parameters to data generated by a coil manufacturer's simulation program allows the application of the resulting model to different types of cooling coils with different characteristics. Correlations are developed to predict the coefficients of the model and make it suitable for application to water cooling coils with a range of physical characteristics. The resulting model is validated by testing it on data from two different buildings at Texas excellent in both cases, predicting the thermal resistance of the coils and the return water temperature with an average deviation of 3.5% and 1.2 'F, respectively. Finally, the model is used to develop algorithms to simulate the two most common chilled water loops in buildings: the two-way valve and the blending station arrangement. These algorithms are incorporated in software developed at the Energy Systems Laboratory at Texas A&M University, College Station, which is used to simulate building heating, cooling and energy consumption based on a simplified air-side model. This addition enhances the capability of the software to simulate the response of the water-side to changes occurring in the space conditioning area, providing, in this way, a clear picture of the heat transfer phenomena that occurs in the cooling coil. The upgraded software was tested on a campus building and there was good agreement between the conditions.
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Includes bibliographical references: p. 74-76.
Issued also on microfiche from Lange Micrographics.
Maldonado, Eliezer (1997). Development of a Simplified Model for Cooling and Dehumidifying Coils. Master's thesis, Texas A&M University. Available electronically from
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