Transient Performance of Fixed-Bed Regenerators for Energy Recovery in HVAC Applications 

Hadi Ramin^\*^, Easwaran Krishnan, Gurubalan Annadurai, Carey Simonson

Department of Mechanical Engineering, University of Saskatchewan

57 Campus Drive, Saskatoon, Saskatchewan, Canada, S7N 0W5

^\*^Corresponding author email:  hadi.remin@usask.ca

The building sector accounts for a significant portion of the total energy consumption and CO~2~ emission globally. Ventilation is an essential task for the heating, ventilation, and air conditioning (HVAC) systems to provide fresh outdoor air and remove the contaminated indoor air. The ventilation maintain the indoor air quality which is known to be of great importance for occupants’ health and productivity. The conditioning of outdoor air is energy-intensive especially for the cold climate such as Canada, yet the occupants’ health and productivity cannot be compromised for the sake of energy consumption. Therefore, HVAC engineers incorporate air-to-air energy exchangers (AAEEs) to reduce the energy consumption for conditioning the outdoor air. Among the different types of AAEEs, fixed-bed regenerators (FBRs) have a higher ratio of heat transfer area to the volume which results in high sensible effectiveness. Unlike the steady-state operation of conventional heat exchangers in which the outlet temperature of the streams reaches a constant value, FBRs reach a quasi-steady state condition at which the outlet temperature profiles of air vary with time but repeat itself cyclically. This quasi-steady state temperature profile is used to determine the sensible effectiveness of FBRs. FBRs undergo several cycles to reach the quasi-steady state operation.

Canadian Standards Association recommends to operate FBR for at least one hour to achieve a quasi-steady state condition. The duration of initial transient cycles is essential for the performance testing of FBRs, as the effectiveness changes significantly during this period. It depends on the cycle period of FBR, airflow rate, and the thermal condition of the exchanger at the beginning of the test. The heat transfer behavior of FBRs during their transient operation is not studied so far, and therefore, the present study addresses this research gap. A small-scale test facility is developed to determine the sensible effectiveness of FBRs, and the results are used to validate a numerical model. The numerical and experimental results for quasi-steady state condition are in good agreement within the experimental uncertainty bounds.  The effects of the mass flow rate of air and the cycle duration on the transient period of FBR are investigated. The results shows that FBR reaches a quasi-steady state operation in less than 30 minutes. The results will be useful for understanding the time required for performance testing, which will reduce the cost and time per each test. 

Keywords: Transient operation, Fixed-bed regenerators (FBRs), Sensible effectiveness, Performance testing. 


Transient Performance of Fixed-Bed Regenerators for Energy Recovery in Hvac Applications

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.