TRANSIENT ANALYSIS AND OPTIMIZATION OF FIXED-BED REGENERATORS FOR HVAC APPLICATIONS
Date
2021-12-13
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
Air-to-air energy exchangers (AAEEs) recover energy from the exhaust airstream to precondition the supply airstream into buildings. In a fixed-bed regenerator (FBR), a type of AAEE, energy from the exhaust airstream is stored in the exchanger over a period; then, the energy is transferred to the supply airstream flowing through the same exchanger in the next period. Due to the storage and release of energy in consequent periods, the temperature and humidity of the airstreams at the outlet of the FBR vary with time. This variation poses difficulties for experimental testing and effectiveness evaluation of the FBR because of the slow response of sensors. The primary goal of this thesis is to develop and validate transient numerical models to accurately predict the transient characteristics of FBRs (sensible and desiccant-coated) and their sensors (temperature and humidity).
A numerical model consisting of an exchanger model and sensor models is developed to capture the transient characteristics of FBRs and their sensors. The developed model is validated using experimental results and can distinguish the actual FBR performance from the performance that is measured by the sensors in an experiment. The results show that the configuration of the FBR, and the sensors’ location influence the measurement of the outlet air properties and, thus, the calculated effectiveness (effectiveness error). In addition, for the desiccant-coated FBRs, the effectiveness error depends on the operating condition of an experiment. This thesis also provides recommendations to improve North American testing standards (ASHRAE 84 and CSA C439-18) for FBRs. The results show that measurement requirements in the testing standards are conservative and can be relaxed for many designs and operating conditions. Furthermore, this thesis provides insights on optimizing sensible FBRs considering their transient characteristics.
Description
Keywords
Transient numerical model, Temperature and humidity measurement, Performance testing, Sensible and latent effectivenesses, Energy recovery, Sensor transient response, Test standards (ASHRAE standard 84 and CSA C439–18 standard)
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Mechanical Engineering
Program
Mechanical Engineering