Date of Award

Spring 1-1-2012

Document Type

Thesis

Degree Name

Master of Engineering (ME)

Department

Civil, Environmental & Architectural Engineering

First Advisor

Gregor Henze

Second Advisor

Marc Thuillard

Third Advisor

Michael Brandenmuehl

Abstract

Computer modeling is quickly becoming a more accessible method to evaluate the performance of complex building systems, due in part to the recent advance in computing power over the last decade. Rising energy costs, stricter building codes, the threat of global climate change and governmental pressure have all influenced building owners, architects, engineers and system operators to design and operate the world's building stock in a more energy efficient manner. Particularly important in large buildings and campuses are the hydronic flow networks that deliver chilled water to the cooling coils in air handling units for the purpose of regulating temperature and humidity in occupied spaces. Large buildings are especially dominated by cooling loads, thus making it a priority for many to evaluate such hydronic systems for their energy performance characteristics. The design and operation of these hydronic systems are being optimized with the help of computers, in both new building stock and retrofits in order to reduce energy consumption.

A common problem that has been well documented over the last few decades is that of delta-T degradation, the decrease in the temperature difference between the supply and return flow of water from the design value over time. Most central plants are designed to deliver chilled water to respective buildings or air handling units at a relatively constant temperature. Typically chilled water is delivered to each branch circuit, which for this example will consist of piping, a cooling coil and a control valve. Coils are selected based on the cooling power needed and a design delta-T value. The flow rate of water through each cooling coil is adjusted to meet demand; therefore with a constant delta-T, an increase in cooling demand would necessitate a proportional increase in the flow rate of water.

There is a slight disconnect between manufacturer data on cooling coils and what actually happens in real systems. Coils are selected based on design values and assumed supply conditions, although installed characteristics of the coil can be quite different from that of the manufacturer specification sheet. For instance, a coil may be selected based on a specific supply water temperature, but if the supply water temperature rises, due to an overloaded central plant, the amount of cooling power delivered will be considerably less then design value. Coil performance can also degrade over time due to coil fouling on either the waterside or airside. Many causes of these parameter fluctuations are well known, however the consequences of such fluctuations are not fully documented. In order to better design and optimize intelligent control devices, a better understanding of the performance of cooling coils is needed. This documentation attempts to combine experimental data with computer simulation to provide a visual guide to how fluctuations in supply water flow rate, supply water temperature, supply air temperature, supply air flow rate and supply air humidity affect cooling power achieved from various cooling coils in operation. Experimental data is used in conjunction with computer simulation to investigate how performances of these coils are affected.

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