NBERG Logo - State of Nebraska with NBERG and photo of team inside the state borders

September 7, 2020 - Yifeng Hu
Bio: Yifeng Hu, P.E. is a doctoral student in Architectural Engineering at UNL. He has a Master’s degree in HVAC from Tongji University, and a B.S. in Building Environment and Equipment Engineering from Southwestern University of Science and Technology in China. 
TitleDevelopment and Demonstration of a Method to Quantify Fault Prevalence in Residential Air-Conditioning Systems

Abstract: Vapor compression air conditioning systems have the potential to efficiently heat and cool buildings, but their effectiveness is limited by faults. Fault detection and diagnosis (FDD) methods are not widely adopted in residential buildings due to many challenges. Many methods are too complicated; specific to a particular system; or can only handle single faults rather than multiple simultaneous faults. In addition, prevalence of a given fault occurring is unknown, so whether the potential benefits of FDD outweigh the costs of maintenance service is still unclear to homeowners and decision-makers. In this presentation I’ll summarize potential FDD methods applicable to residential systems for each fault type, and compare them based on the tradeoffs between accuracy, difficulty and cost. In practice, faults tend to occur simultaneously instead of individually. Thus, four artificial faults were imposed both singly and collectively in a laboratory investigation of a split residential heat pump, to evaluate the impacts on the performance of the system and the FDD methods.

January 30, 2020 - Ian Bell
Bio: Dr. Bell is a Mechanical Engineer at NIST in Boulder, CO. Before starting at NIST in 2015, he created the popular software tools CoolProp and ACHP. Since 2008 he has published over 80 papers in the field of thermal science. He has PhD (Purdue) and BS (Cornell) degrees in mechanical engineering.
TitleA View of Thermophysics and Thermal Systems

Abstract: In this presentation, the last few years of my research activities are summarized, describing some common themes emerging from these studies, especially the development of open-access software libraries for thermal systems applications, the integral nature of thermophysical properties to all energy systems analysis, and new theoretical insights arising from probing the link between thermodynamics and transport (viscosity, thermal conductivity, diffusion) within the framework of entropy scaling. The discussion closes with speculation about future research directions and the evolution of the energy systems field.

December 19, 2019 - Amir Ebrahimifakhar
Bio: Amir is a Ph.D. candidate in Architectural Engineering. He has B.S. and M.S. degrees in Mechanical Engineering from Ferdowsi University of Mashad, and Buali Sina University, respectively. 
TitleData-driven fault detection and diagnosis for packaged air-conditioners using statistical machine learning classification methods

Abstract: In this presentation we propose a data-driven fault detection and diagnosis (FDD) strategy for packaged air-conditioners, using statistical machine learning classification methods. The FDD task is formulated as a multi-class classification problem. Seven typical rooftop unit faults are discriminated against one another as well as the normal condition. Since experimental data for rooftop units is rare and difficult to obtain, a library of simulated data for faulted and unfaulted systems is used for training and validating the classifications models. Support vector machine is found to be the best classifier (96% accuracy), and linear discriminant analysis the worst classifier (76% accuracy) from among the methods tested.

November 25, 2019 – Yifeng Hu
Bio: Yifeng Hu is a Ph.D. student in Architectural Engineering at the University of Nebraska - Lincoln. He has a BS in Building Environment and Equipment Engineering from Southwest University of Science and Technology (China), and an MS in HVAC Engineering from Tongji University (China). 
TitleFrost growth and heat transfer characteristics on a microchannel heat exchanger under clean and fouled surface conditions: an experimental study

Abstract: This presentation discusses frost formation and its resultant effects on a microchannel heat exchanger under both clean and fouled conditions. The input parameters varied in the testing are fouling level, initial air face velocity, and inlet air humidity. Frost formation rate is found to be closely tied to heat transfer rate. Increasing air relative humidity (humidity ratio) or initial air face velocity can enhance peak heat transfer rate and frost formation. A light level of fouling increases peak heat transfer rate and frost formation, while heavier fouling decreases each of these parameters.

November 19, 2019 – Moh’d-Eslam Dahdolan
Bio: Moh'd is a graduate student in the Architectural Engineering program at the University of Nebraska. He has a BSc in Mechanical Engineering (Thermal Power and Energy) from the Jordan University of Science and Technology. 
TitleAir Economizer Stuck Damper Faults in Rooftop Units: Economic Impacts, Fault Symptoms, and Fault Detection using Remote Mixed Air Temperature Measurements 

Abstract: An air economizer is a set of actuated dampers that are installed on the outdoor air and return air ducts. A controller and an actuator are used to modulate, close, or open dampers in order to minimize mechanical cooling. A feedback measurement of the outdoor air temperature or enthalpy (sometimes coupled with return air temperature or enthalpy measurements) is used by the controller. Air economizers are widely used in rooftop units and air handling units. ASHRAE Standard 90.1 (2016) list requirements for having economizers installed on "fan cooling units", a category that includes rooftop units. In this presentation, stuck damper fault impact on the Net Present Value of the air economizer is discussed, and the factors that affect this impact such as unit size and climate region. Furthermore, economizer fault symptoms and fault detection are discussed. A remote Cellular data Logger (CelLo) is developed to take mixed air temperature measurements and perform fault detection using a simple rule based algorithm.

November 29, 2018 - Xiaoyue (Zoe) Cheng, Ph.D. 
Bio: Dr. Cheng is Assistant Professor of Mathematics at the University of Nebraska - Omaha. She earned a Ph.D. in Statistics at Iowa State University. Her research focuses on: Data Visualization and Interactive Graphics, Data Exploratory Analysis, Data Mining, and Statistical Classification 
TitleAn Appetizer to the Machine Learning Banquet
Abstract: Whether we realize it or not, most of us live in an environment full of machine learning applications. What is machine learning? How is it used in engineering and other industry? What are the typical and popular techniques in machine learning? This talk will give a brief overview on machine learning, from simple regression to deep learning, from supervised to unsupervised methods, from basic ideas to complex models, from theory to examples.

October 18, 2018 - Iason Konstantzos, Ph.D.
Iason Konstantzos
Bio: Dr. Konstantzos joined the Durham School as an Assistant Professor of Architectural Engineering in August 2018. Before that, he was a post-doctoral researcher at Purdue University, where he also earned a PhD in Civil Engineering. .   
TitleA human – centered approach for the design of perimeter office spaces based on visual environment criteria
Abstract: A human-centered design perspective is a necessity for the visual environment, given its hybrid nature of impacting human satisfaction and energy performance. So far, knowledge gaps with respect to visual comfort and connection to the outside, as well as their effects on energy performance, prevented from achieving efficient building design and operation, compatible with the human element. This work implements three different research directions, advancing sensing and controls, conducting human factors experiments and developing new simulation models, in order to develop new metrics that fill in the gaps towards proposing a framework for a holistic human-centered visual environment.

September 27, 2018 - Adel KabiriKopaei
Adel KabiriKopaei
Bio: Adel is a Ph.D. student in Architectural Engineering, advised by Dr. Josephine Lau. 
TitleUncertainty analysis of various CO2-based methods for estimating ventilation rates in occupied and unoccupied classrooms
Abstract: Indoor air quality (IAQ) data of 220 classrooms in the Midwest region of the United States were measured during 2015-2017. To calculate ventilation rates from the collected CO2 data, there are three main methods derived from the mass balance equation: (1) steady-state; (2) decay rate; and (3) build-up methods. Since the uncertainty of the individual measurement parameter would affect the accuracy or the reliability of the calculated ventilation rate, an uncertainty analysis was performed for all three methods. R programming was used to relate the uncertainty of the calculated ventilation rates to the volume of the classroom, indoor and outdoor CO2 levels, and estimated student CO2 emission rates. The study shows that the steady-state method has the minimum uncertainty when calculating ventilation rates while decay and build-up methods have the lowest and highest values for ventilation rates, respectively.

July 13, 2018 - Alireza Behfar, Mehdi Mehrabi, and David Yuill
In this session, Alireza, Mehdi, and David will each give their presentations that they will be giving at the International Air-Conditioning and Refrigeration Conference or the High Performance Buildings Conference next week at Purdue University. 
Presentation 1: Alireza Behfar - Numerical Simulation of Fault Impacts for Commercial Walk-in Freezers

Presentation 2: Mehdi Mehrabi - Evaluation of the Effect of Washing on the Heat Transfer Capacity and Air-Side Flow Resistance of Air Cooled Condensers

Presentation 3: David Yuill - Method for Radon Measurement in Residential Sewer Connections

June 21, 2018 - Alireza Behfar
Bio: Alireza Behfar, P.E., will defend his doctoral dissertation in summer of 2018. 
TitleFault Detection and Diagnostic (FDD) Methods for Supermarkets
Abstract: Supermarket systems can undergo various operating faults that may cause energy waste, equipment damage, and risk of food waste. Several Fault Detection and Diagnostic (FDD) methods have been developed and tested, as described in the literature and patents, and showed great potential to provide an early warning of a fault. This presentation describes some methods, our tests of the methods using real-world data, and insights into the potential and the requirements for FDD application in these systems.

February 16, 2018 - Craig Bradshaw
Bio: Dr. Bradshaw is an Assistant Professor of Mechanical and Aerospace Engineering at Oklahoma State University.  He was previously the Manager of Research and Development at TORAD Engineering from August 2012 until July 2016. He received his Ph.D. in 2012 and B.S. in Mechanical Engineering from Purdue University. His research interests include modeling and development of positive-displacement compressors/expanders, heat exchangers, and waste-heat recovery systems. Dr. Bradshaw has authored/co-authored 1 book chapter, 28 journal and conference publications and is a named inventor on 6 patents. 
TitleHow compressor development can be accelerated using comprehensive modeling tools: A case study on the development of the spool compressor

Abstract: Heating/cooling systems in buildings and their compressors account for about 9% and 5% of total primary energy usage in the U.S., respectively. Rapid development of new compressor technologies or a rapid re-design effort on current compressor technologies must be performed to avoid an increase in building energy use during the transition to low-GWP refrigerant equipment. This talk will examine the development of a new compressor technology, the spool compressor, in this context. The comprehensive modeling tools required for the development of a new technology will be presented. The use of these tools to rapidly accelerate the development of the spool compressor will be shown.  Finally, a motivation for the development of more rapidly deployed modeling tools for rapid technology development will be discussed.

January 12, 2018 - Mehdi Mehrabi

Bio: Mehdi Mehrabi, P.E., is a doctoral candidate in Architectural Engineering at University of Nebraska - Lincoln. He anticipates completion of his Ph.D. in 2018.
TitleDevelopment of a method for testing air-side fouling effects on outdoor heat exchangers

Abstract: Deposition of airside fouling on condensers degrades performance of air conditioners. Several researchers have studied airside fouling effects on performance of heat exchangers, but much of the work focuses on evaporators. ASHRAE RP-1705, currently in progress, is intended to study condenser air-side fouling, and to characterize fouling material so that realistic fouling could be applied in laboratory measurements. Nine field-fouled split system condensers have been collected, and fouling samples from two US locations have been collected and analyzed. A test apparatus was designed and built to study the heat transfer and air-side pressure drop through different coils before and after cleaning the condenser. A test method is proposed that will be used with this apparatus to characterize air-side fouling effects for a given heat exchanger design, independent of the condenser fan’s performance. One potential outcome of this work is that it will facilitate design of heat exchangers that are less prone or less sensitive to air-side fouling.

November 10, 2017 - Melanie Derby
Bio: Dr. Melanie Derby graduated from Rensselaer Polytechnic Institute with a Ph.D. in Mechanical Engineering in 2013, and joined Kansas State University where she is an Assistant Professor of Mechanical Engineering, College of Engineering Keystone Research Faculty Scholar, and director of the Cooling and Heating Innovation Lab. She received a 2017 NSF CAREER Award, 2017 KSU College of Engineering Outstanding Assistant Professor Award, and 2017 ASME ICNMM Outstanding Early Career Award.
TitleUpdating Scientific Evidence about the Effects of Low Humidity on People 

Abstract: This work considers the impacts of low humidity on building occupants. Nearly 600 articles were located in citation and keyword searches regarding the effects of humidity on comfort, health, and indoor environmental quality. Of these, around 70 articles reported the effects of low humidity (relative humidity ≤ 40%) and were analyzed in detail. Information in some categories was well chronicled, while other categories had significant knowledge gaps. Low humidity decreased house dust mite allergens. Due to different envelopes, generalizations could not be made for all bacteria and viruses. However, lower humidity increased virus survival for influenza. For comfort, low humidity had little effect on thermal comfort, but skin dryness, eye irritation, and static electricity increased as humidity decreased. For indoor environmental quality, low humidity had nonuniform effects on volatile organic compound emissions and perceived indoor air quality. Across many low humidity studies, ventilation rates and exposure times were noted as confounding variables. A majority of studies that used human subjects utilized exposure times of three hours or less with adult subjects; few studies used children, adolescents, or elderly subjects. 

October 27, 2017 - Adam Thompson
Bio: Dr. Adam R. Thompson is Assistant Director of the Kutak Center for the Teaching and Study of Applied Ethics at the University of Nebraska-Lincoln.
TitleEthics in Engineering

Abstract: Applied ethics is often approached from a theory-laden perspective.  The main problem with that approach is that it tends to leave the impression that applied ethics is like applied mathematics—types of cases, issues, or puzzles correspond to types of theories.  Alternatively, some approach applied ethics from an issues-first perspective.  The main difficulty with that approach is that it often leaves us simply raising questions and concerns or highlighting moral considerations.  A third approach attempts to walk that line between both of those approaches.  This third way (a) first distinguishes results-based reasoning from non-results-based moral reasoning, (b) illuminates morally thick concepts and the central role they tend to play in our practical lives, and (c) leans on each of the previous points to elucidate a method for coming to and supporting conclusions about what to do across a variety of contexts and problems.  In this talk, I will discuss (a) – (c) and show how to apply it to the context of academia generally and engineering in particular.

October 20, 2017 - Christian Bach
Bio: Christian Bach is an Assistant Professor at the Building and Environmental Thermal Systems Research Group (BETSRG) in Mechcanical and Aerospace Engineering at Oklahoma State University ( He received his Ph.D. from Purdue University and his Dipl.-Ing.(FH) from Karlsruhe University of Applied Sciences.
Title: Efficiency Improvement of Vapor Compression Systems

Abstract: Evaporators in air conditioning and cooling systems typically have multiple parallel circuits.  Maldistribution between refrigerant and air side flow leads to a less effective evaporator, visible in a reduction of the evaporation temperature.  This in turn leads to a reduction of system capacity and system efficiency.  To overcome this issue, a hybrid control scheme can be used, where the flow to the individual evaporator circuits is actively controlled. The experimental results of the application of such a control scheme are presented for several applications.  Further research to reduce the cost of the hybrid control scheme as well as results for additional evaporator and system modifications will be presented.

May 18, 2017 - Clayton Miller (Workshop)
Clayton Miller data workshop
Bio: Clayton Miller is an Assistant Professor at the National University of Singapore (NUS) and is Director of buds lab – building and urban data science He received his Ph.D. from ETH Zürich, masters degrees from NUS and UNL, and BS from UNL in Architectural Engineering.
Title:  Data Science and Reproducible Research Workshop

Scope: In this 3-hour workshop, participants will learn the basics of how to use a suite of open source data analytics languages, libraries, and platforms, including: Python, Pandas, Jupyter, R, and R-Studio. Several real-world research datasets, with a particular focus on building energy usage, will be introduced and workflows will be demonstrated and discussed. Participants will need to download the free Anaconda data science platform ( and can follow along on their machines.

April 21, 2017 - Haorong Li
HaorongBio: Dr. Li is an Associate Professor of Architectural Engineering at the University of Nebraska.
 Title:  Smart Support Network for Built Environment

 Abstract: Modern civilization is powered by energy in an unsustainable fashion. Built environment, where things start and converge and where people spend about 90% of their time, is the single largest sector in terms of energy, environment and economic impact. Information technology has revolutionized almost every aspect of our existence but hardly impacted the way how people operate and interact with the buildings. Consequently, the building industry becomes more and more old-fashioned, its economic potential could not be reached, and there is no winner in the marketplace. In this presentation, a paradigm-shift framework termed Smart Support Network will be proposed to transform the whole building industry and unleash the potential through empowering all the stakeholders, especially the innovators such as the researchers in the academic settings. 

March 10, 2017 - Moh'd Dahdolan
Mohd Dahdolan
Bio: Moh'd is a graduate student in Architectural Engineering at the University of Nebraska - Lincoln.
TitleModeling and analysis of a passive tubular concentrating solar collector for saltwater distillation and electricity production
Abstract: This presentation discusses a proposed concentrating solar system design and its merits and disadvantages. The proposed design includes a solar concentrator, porous evaporator, and an internal condenser, and is designed to achieve thermosyphonic flow and passive cooling for water in the condenser. Three configurations have been studied: a stand-alone solar still system, an integrated photovoltaic and thermal still system, and an integrated thermoelectric generator still system. Results show the dependency of efficiency, daily water yield, and power output on ambient temperature, condenser temperature, solar irradiance, and wind speed, in addition to other material specifications.

February 17, 2017 - Bianca Howard

Bianca Howard

Bio: Dr. Howard is currently a postdoctoral researcher in the Department of Civil and Environmental Engineering at Imperial College London. She received her PhD and MSc degrees in Mechanical Engineering from Columbia University where she was a NSF IGERT fellow. She received her BSc degree in Mechanical Engineering from the University of Nebraska- Lincoln.

TitleHarnessing Data for Energy Savings in Facilities Management

Abstract: Dr. Howard will be discussing on-going work for the UK EPSRC funded research project “Future Proofing Facilities Management”. The aim of the project is to develop methods to reduce energy consumption in buildings that leverage opportunistic data sets produced by today’s commercial buildings. The project is interdisciplinary and includes several industrial partners that range from construction management, building controls companies, and facilities managers. During the seminar, Dr. Howard will introduce works developed for two work packages. The first project evaluates the potential to measure, predict, and simulate occupancy from Information, Communication, and Technology (ICT) data sets. The second project aims to develop methods to access historical faults in building HVAC&R systems for better decision making.

January 20, 2017 - Mehdi Mehrabi

Bio: Mehdi is a Ph.D. candidate in Architectural Engineering at the University of Nebraska.

TitleGeneralized Models of Fault Effects on Air Conditioners in Heating and Cooling Mode

Abstract: This presentation will provide generalized relationships between the fault level and its effect on normalized capacity and efficiency of air conditioners, for seven of the most important and common faults. The relationships are based on existing results of laboratory experiments in the literature. The generalizations are provided separately for fixed orifice and thermostatic expansion valve equipped systems in both cooling and heating mode.
Mehdi Mehrabi

January 13, 2017 - Alireza Behfar

Alireza BehfarBio: Alireza is a Ph.D. candidate in Architectural Engineering at the University of Nebraska.

TitleModeling the Effect of Vapor Compression Cycle Faults Using Gray-Box Models

Abstract: The development of new fault detection and diagnostic (FDD) methods and the evaluation of the existing methods require system fault-free and faulty data for a set of important system faults. The generation of such a dataset via direct measurements is time-consuming and difficult. Therefore, there is a need to develop models that are capable of generating such system data without the necessity to do experimental measurements for every operating and fault conditions. This research simulates the fault impacts of two commercial refrigeration systems via semi-empirical modeling to facilitate the testing and development of FDD methods for such systems. The systems are a commercial walk-in freezer and a walk-in cooler. The simulated faults in these research consist of heat exchangers' fouling, liquid line restriction, compressor valve leakage, and undercharge faults.
December 9, 2016 - Krittima Santiwattana

Bio: Krittima recently defended her thesis and will receive her M.S. degree in Architectural Engineering at the University of Nebraska.

TitleAn investigation of DX cooling coil inherent characteristics
Abstract: DX cooling coil (DCC) systems are widely used in light commercial and residential applications for cooling purpose. However, improper installation, non-optimum design, and non-optimum control/operations incur faults in HVAC systems. These consequences are subject to inefficient equipment modelling developed from: (1) insufficient understanding in equipment characteristics, (2) uncertainties in testing environment and data, and (3) access and cost limitations. Hence, inherent characteristics are investigated to improve DX cooling coil (DCC) modelling procedures. Model based control/optimization of DCC methods are: white-box and black-box. In practice, physical geometries and laboratory testing data are not always available or not accurate enough to provide robust approximations and validations. A generic rating-data-based (GRDB) model generates cooling performance modelling from readily available manufacturing data, and employs inherent characteristics of cooling coils to separate wet and dry conditions. Accordingly, GRDB method will be re-examined by air principles and fundamentals of vapor compression cycle. DCC modelling procedures are proposed and illustrated by normalized capacity plots; the findings are validated using manufacturers’ data from various conditions and systems. In addition, the results show correlations in associated with proposed hypotheses. Profound understanding of DCC inherent characteristics could lead to better modelling procedures as it could lessen model complexity and computational processes, which could benefit low-cost sensing and fault. detection and diagnostics technologies.

November 11, 2016 - Shihan Deng

Shihan DengBio: Shihan is a doctoral candidate in Architectural Engineering at UNL, with an anticipated graduation in 2017.

TitleThe evidence-based associations between classroom indoor environmental quality and achievement/absenteeism of K-12 students

Abstract: Providing a safe, comfortable, healthy, and beneficial indoor environment is the ultimate goal for building designers. This project provides evidence-based data to answer the questions:
  1. How do indoor environmental factors, including thermal comfort and indoor air quality, correlate with student absenteeism.
  2. How does the relationship between indoor environmental factors and student absenteeism depend on seasons.
  3. How do the indoor environmental factors correlate with student achievement, taking absenteeism into account. 

This project will provide evidence-based data of indoor environmental factors to answer these questions. The proposed project has the ability to significantly benefit the school's decision-making processes to select the most successful factors to improve in order to reach higher student absenteeism and achievement.

October 14, 2016 - Fadi Alsaleem

FadiBio: Dr. Alsaleem is an Assistant Professor of Architectural Engineering at  the University of Nebraska - Lincoln. Previously he was a faculty member at Wichita State University (Mechanical Engineering), a lead algorithm engineer at Emerson Climate Technologies and a control engineer at MicrostaQ, Inc.

TitleCloud-based diagnostics for residential HVAC

Abstract: In this work we present a cloud based model for monitoring and diagnostics of residential HVAC systems. This model will provide continuous diagnostics capabilities that leverages the latest technology advancements. Using embedded sensors and monitoring modules for the indoor and outdoor HVAC units, various measurements are transmitted to a cloud sever utilizing the homeowner Wi-Fi network. On the cloud side, algorithms process the data and generate triggers that a problem exist. One algorithms example is the use of an enhanced version of Mann-Kendall trending analysis for detecting and diagnosing HVAC systems faults such as refrigerant leakage and dirty filters. Relevant information from these algorithms is then shared with homeowners and contractors via e-mail & portals.  In this presentation we explain the system in more detail by providing actual case studies which demonstrate the value in a proactive maintenance and repair model as supported by time-series data. This contrasts the reactive model that exists today..

September 30, 2016 - Yuchen Wang
Yuchen Wang

Bio: Yuchen Wang is a Master's of Science student in Architectural Engineering at the University of Nebraska - Lincoln, working under the advisement of Dr. Haorong Li.

TitleInvestigation of Heat Pump Design Model (HPDM)

AbstractMini-split heat pump systems are widely adopted in residential application in Asian countries. Since there is limited experimental research on mini-split heat pump systems in the U.S, we investigate the system deeply by simulation.  In order to simulate this system, an accurate modeling software is essential. The presenter would like to introduce the Heat Pump Design Model (HPDM) and show audiences its possibility of generalization.  The HPDM is an online-based modeling software available for engineers and researchers to accurately simulate refrigeration cycle devices, while there are some other software packages available to model the refrigeration cycle. The model is a physical model in which several inputs are required, i.e. heat exchanger configurations, compressor data and other detailed parameters of the heat pump system. Then several key outputs: mass flow rate, power consumption and capacity can be obtained. Comparing the important outputs between the lab data, manufacturing data and simulation results, the presenter could demonstrate the capability of generalizing the model. Case studies will be provided based on lab data and manufacturing data of one mini-split heat pump system unit to test the application of the proposed model generalization. Based on the simulation results, Heat Pump Design Model can predict those key outputs in a certain temperature range with relative error around 5%.

September 9, 2016 - Mohammad Hasan

Mohammad Hasan

Bio: Mohammad Hasan is a Ph.D. student in Mechanical and Materials Engineering at the University of Nebraska - Lincoln, working under the advisement of Dr. Fadi Alsaleem.

TitleSensitivity analysis of PMV model and the use of wearable devices to measure comfort

Abstract: The predicted mean vote (PMV) comfort model is the most commonly used for comfort applications. Two model inputs - clothing insulation and the metabolic rate - are impractical to measure in real time, so these are neglected in typical application in buildings, which can lead to reduced comfort levels. In this work, measurements from a wearable device are used to infer metabolic rate in real time. We show that the metabolic rate cannot be estimated and its estimation may result in high errors. We also show that the metabolic rate is the most impactful factor in comfort analysis by measuring the sensitivity of the PMV model to different parameters. Lastly, we propose a comfort model by incorporating environmental parameters with personal parameters and biometric parameters to create a comprehensive personal comfort model.

August 26, 2016 - Sungmin Yoon

Sungmin Yoon presentation

Bio: Sungmin Yoon is a Ph.D. student in Architectural Engineering at the Durham School of Architectural Engineering and Construction at the University of Nebraska - Lincoln.

TitleExtended virtual in-situ calibration in building systems using Bayesian inference

Abstract: The role of building sensor networks is increasingly significant in building industry in that advanced building energy management, health diagnostics, and analytical optimization (MDO) are increasingly conducted based on measured data to improve building systems’ performance. However, various random errors and systematic errors of working sensors occur in real working conditions over time. These sensor errors, which are not obvious at all, could greatly misguide the MDO and lead to actions that negatively impact the building performance and indoor environment quality. In order to reduce the sensor errors, we propose a sensor calibration method in building systems, termed extended virtual in-situ calibration (EVIC). This method is mathematically formulated as a constrained nonlinear optimization. Bayesian inference is used to derive statistically optimal solutions regarding the optimization-based calibration problem. A case study of a LiBr-H2O absorption refrigeration system demonstrates the application of the suggested calibration.

July 7, 2016 - Mehdi Mehrabi and David Yuill

David Yuill

Overview: In preparation for their presentations at the 2016 International Conference on Air-conditioning and Refrigeration at Purdue, Mehdi and David gave a practice presentation to N-BE³RG.

Bio: Mehdi Mehrabi is a Ph.D. candidate in Architectural Engineering at the Durham School of Architectural Engineering and Construction at the University of Nebraska - Lincoln. 

Title 1Normalized Effect of Condenser Fouling and Refrigerant Charge on Performance of Vapor Compression Air Conditioning Systems

Abstract 1 : This presentation shows the results of an analysis of existing laboratory data to determine the effects of charge faults and condenser fouling on several normalized variables of interest, such as capacity and COP. The values are presented as a function of normalized fault levels, and regression coefficients are provided to form a basis for predicting the impact of faults on performance for air-conditioners in general.

Bio: David Yuill is an Assistant Professor of Architectural Engineering at the Durham School of Architectural Engineering and Construction at the University of Nebraska - Lincoln. 

Title 2
: A Prediction Method for Overall Economic Value of Fault Detection and Diagnostic Tools for Rooftop and Split Systems

Abstract 2 : Previously Yuill and Braun have presented a method for evaluating the performance of FDD tools applied to unitary air conditioning systems. However, the output of their method is difficult for laypersons and equipment owners to understand. This new method proposes a system for taking into account the holistic economic value of a given FDD tool, based upon multiple likely scenarios that are assigned probabilities. A single-number figure of merit provides the value, in $/ton, of applying a given FDD tool, on average.

April 1, 2016 - ASHRAE Student Design Competition Winners

System Selection

Design Calculations

Jim Butler
Applied Engineering Challenge

: All of the presenters are currently Master of Architectural Engineering students, but were undergraduates in Architectural Engineering at the time of their design. The presenters were:

System Selection Team: Mary Kleinsasser and Rachel Obenland
Design Calculations Team: Kristin Hanna, Garrett Johnson and Mark Wilder
Applied Engineering Challenge Team: Jim Butler

Title: Designs from the ASHRAE Student Design Competition 2015/2016

Abstract: The three teams will present a summary and highlights of the designs that they produced as an entry to the ASHRAE Student Design Competition. The System Selection Team and Design Calculations Team each won 1st place in the competition, and the Applied Engineering Challenge Team won third place. The designs compete against the entries from universities all over the world.

March 11, 2016 - David Yuill

David Yuill

Bio: David Yuill is an Assistant Professor of Architectural Engineering at the Durham School of Architectural Engineering and Construction at the University of Nebraska - Lincoln. He has Ph.D. in Mechanical Engineering from Purdue University, and is a licensed Mechanical Engineer. 

TitleA Standard Method to Evaluate the Performance of AFDD for Rooftop Units and Split Systems 

Abstract: There are many automated fault detection and diagnosis (AFDD) tools available commercially. In making a decision whether to adopt one of them, or whether to use AFDD at all, one should ask how well the tool works. However, there was previously no method to measure performance, or even a way to describe or characterize performance of AFDD tools. This presentation will describe a new standardized method of measuring and characterizing the performance of AFDD tools intended for unitary air conditioning equipment, and show some case studies that demonstrate that many existing methods provide surprisingly poor results.

March 4, 2016 - Clayton Miller

Bio: Clayton is a Doctorate Fellow at the Institute of Technology in Architecture (ITA) at ETH Zürich, and is working with the Low Exergy group with a focus on monitoring building performance metrics. His research is based at the Chair of Architecture and Sustainable Building Technologies (SuAT) in Zürich. 

Title: Extracting Value from Large, Temporal Data Sets from Buildings: Progress on Two Case Studies

Abstract: This talk will focus on two real world examples of managing and extracting information from large, temporal  data sets from sensors in buildings. The first project is the 3for2 case study in Singapore in which over one thousand points are streamed, visualized and processed from the BMS/EMS systems of a building with innovative cooling technologies. The use of modern time-series databases and web-based visualization prototypes will be showcased. The second case study is the analysis of over one thousand buildings with one year of hourly, electrical data available. This study focuses on the use of temporal feature engineering to enhance the assessment of benchmarking and potential interventions in portfolios. 

February 19, 2016 - Mehdi Mehrabi

Mehdi Mehrabi

Bio: Mehdi Mehrabi is a doctoral candidate in Architectural Engineering at the Durham School. He has a B.S. degree in Mechanical Engineering from the Iran University of Science and Technology, and an M.S. in Energy Engineering from Islamic Azad University. Prior to his doctoral studies he had several years of experience as a research and development manager for an energy conservation company. 

Title: The effects of several common faults on the performance of air conditioners

Abstract: Many experiments have been conducted over the past 25 years to determine what the effects of operating faults are on air conditioner performance. This presentation will show the effects of seven of the most important and common faults on the performance of air conditioners, based upon aggregates of the results of experiments for all known sets of data and published results. The faults are: undercharge and overcharge of refrigerant, condenser fouling, evaporator fouling, liquid line restrictions, non-condensable gas, and compressor valve leakage. The results include key operating parameters, such as mass flow rate, superheat, and subcooling, as well as whole system performance (capacity and efficiency).

April 24, 2015 - Shihan Deng

Titles: Part 1: Energy Benefits of Different Dedicated Outdoor Air Systems in Various Climates; Part 2: Evidence based Interactions between Indoor Environmental Factors and Their Effects on k-12 Student Achievement

Abstracts: Part 1: This study presents simulations to evaluate various energy saving benefits of different Dedicated Outdoor Air System (DOASconfigurations in diverse climate zones for commercial buildings in the United StatesConclusions of this study include: (1supply conditioned OA directly to each occupied space with a DOAS in all simulated locationsand (2) consider active chilled beams as the local terminal HVAC unit in locations that experience hot summerssuch as Miami and Phoenix.

Part 2: Indoor environmental factorsincluding thermal comfortindoor air qualityacousticsand lighting conditionsimpact achievement of K-12 students in many waysQuantification of the impact of each factorinteraction between factors, and rank order of these factors in terms of impact on student achievement will be addressed in this researchData from this research will benefit schools’ decision-making processes to select the important factors to address in order to promote higher student achievement.
A new physical method to enhance heat and mass transfer through gas-liquid phase will be introduced. The presentation will include system design, lab construction, data analysis and some preliminary theorization.

April 10, 2015 - Ziqi Shen

TitlesPart 1: Mechanism motion enhanced gas-liquid heat and mass transfer (lithium bromide absorption chiller, ASHRAE RP-1462); Part 2: Active phase change material (PCM) system in construction wall

Abstracts: Part 1: A new physical method to enhance heat and mass transfer through gas-liquid phase will be introduced. The presentation will include system design, lab construction, data analysis and some preliminary theorization.

Part 2: A preliminary experiment using PCM to actively store and release thermal energy will be introduced. This project aim to solve traditional PCM do not work during environment temperature stay out of PCM melting temperature.

March 13, 2015 - 
Clayton Miller

Bio: Clayton is a Doctorate Fellow at the Institute of Technology in Architecture (ITA) at ETH Zürich and is working with the Low Exergy group with a focus on monitoring building performance metrics. His research is based at the Chair of Architecture and Sustainable Building Technologies (SuAT) in Zürich. He was formerly the CTO of a Singaporean startup company focused in building performance monitoring and has also worked as a Mechanical Systems Designer and Energy Engineer. Clayton holds a MSc. (Building) from the National University of Singapore (NUS) and a Masters of Architectural Engineering (MAE) and BSc. from the University of Nebraska - Lincoln (UNL). He is a former Fulbright Student Scholar to Singapore at NUS and a Walter Scott Jr. Scholar at UNL. More information about Clayton's research can be found at: Open-source ad-hoc BMS/EMS data analysis

Abstract: My research focuses on the development and testing of ad-hoc data analysis techniques for BMS/EMS datasets in order to bridge the gap between simplified analysis and continuous monitoring-based techniques. I will discuss implementation of various filtering and screening techniques on real-world datasets.

Details can be found at

February 20, 2015 - Ehsan Mousavi

Bio: Ehsan is a doctoral candidate in Construction Engineering in the Charles W. Durham School at the University of Nebraska.

TitleAirflow patterns due to door motion and pressurization in hospital isolation rooms

Abstract: Certain pathogens are transmitted through air by respiratory droplets that desiccate shortly after emission and form droplet nuclei. Droplet nuclei are sufficiently small (<5.0µm) to remain suspended in air indefinitely, and thus, create a pathway between an infected and susceptible person. This process is called ‘airborne transmission’. Patients with an airborne infectious disease (e.g. measles, SARS, tuberculosis, varicella, etc.) are isolated from the healthcare environment in an Airborne Infection Isolation Room (AIIR) to protect other patients and healthcare workers. AIIRs have special features to effectively contain and remove airborne pathogens. For example, a 2.5Pa negative pressure relationship with adjoining spaces is required for an AIIR to create directional airflow into the AIIR and prevent the transmission of airborne pathogens from the AIIR to adjacent healthcare spaces. Directional airflow, however, may be disrupted and even reversed by door opening motion and the movement of people and equipment into and out of the AIIR. This presentation highlights the results of both experimental and computation studies that explore air exchange and particle movement between an isolation room and anteroom relative to 3, 5 and 7 second door cycle speeds, and, neutral and negative air pressure relationships.

January 30, 2015 - Alireza Behfar

Titles: 1) Heat and mass transfer enhancement potential on falling film absorbers for water-LiBr mixtures; 2) CO2-based demand control ventilation as a demand side management technique in commercial buildings

Abstracts: Significant process intensification (PI) of heat and mass transfer is indispensable in building compact and energy efficient absorption refrigeration systems. High potentials exist to achieve the required PI through (1) development of active heat and mass transfer enhancement techniques and (2) combining the active enhancement mechanism with proven and widely used passive enhancement techniques in transport processes. There is limited research on the effect of active mechanisms, such as vibration, on heat and mass transfer coefficients in absorption systems with falling film horizontal-tube absorbers. In this general survey, with the aim to enlighten the path for active mechanisms development, recorded heat and mass transfer enhancements via active mechanisms were extracted from pertinent research works, and were summarized in tables suitable for evaluation and comparison. The potential for future research on enhancing heat and mass transfer in absorption chillers was identified.

ASHRAE Standard 62.1– Ventilation for acceptable indoor air quality – allows the use of demand-controlled ventilation (DCV) for occupied spaces when the actual occupancy level of the space is available. Mainly, the purpose is to prevent over-ventilation at part load occupancy condition to save the energy required to condition the excessive outdoor airflow to the system. CO2 sensors, installed in each zone, could be used to estimate the space occupancy level in an occupied space with a fairly high accuracy. However, currently there is no standardized control logic for CO2-based DCV. Therefore, there is a critical need to develop control sequences to run the HVAC systems efficiently and effectively. To develop control sequences, energy and CO2 concentration models are essential. Till present, energy model is completed in EnergyPlus and CO2 concentration model is being developed in Matlab software.

January 16, 2015 - Denchai Woradechjumroen 
Bio: Denchai is a doctoral candidate in Architectural Engineering at University of Nebraska-Lincoln, anticipating completion of the degree in 2015. He obtained his B. Eng and M. Eng in Mechanical Engineering in 2005 and 2009, respectively, from Chulalongkorn University, Thailand. His research interests are 1) low-cost, plug-n-play, non-invasive automated monitoring, control, diagnostics, optimization and soft-repair of building energy systems and 2) automatic control and modeling of robot and mechanical systems.

Title: Development of soft-repair algorithms for solving oversizing effect on multiple RTUs

Abstract: Rooftop packaged air-conditioning units (RTUs) have been intensively utilized in commercial buildings for providing space heating and cooling. They serve over 60% of the commercial building floor space in the U.S., contributing around 230 trillion Btus of annual energy consumption. Inefficient routine operations of multiple RTUs result in waste energy consumption. Specifically, oversizing is an inherent issue practically caused by over design of mechanical engineers. With field test studies, oversizing can be up to 100% leading to much energy penalty. Although there are locally advanced control technologies utilized to improve the overall efficiency performance of RTUs, they are invasive approaches to interrupt normal operations and require experienced service teams for preventative maintenance causing high first cost installation and service costs with returning on investment (ROI) being more than 3-5 years depending on the type of a building. To reduce ROI being less than one year and permanently reduce inherent oversizing issue without intervention of an original system, the article proposes a novel and non-invasive methodology for permanently reducing energy penalty caused by non-optimal design. The novel approach is called "soft-repair" that uses adaptive control strategies to minimize the fault impact until the receipt of actual physical repair or to ultimately eliminate the fault without any further physical intervention. Control algorithms are systematically developed to mainly eliminate oversizing effect. With these algorithm implementations, severe faults including fail compressor, fail heater and some control-related faults can be temporarily disabled until these faults are physically fixed and ready to use normally. The proposed method will be further conducted to temporarily minimize the fault impact caused by faulty operations and improper commissioning such as over-circulation, outdoor air damper leakage and indoor humidity problem in near future. 

November 14, 2014 - Chunxiao Su, Ph.D.

Chunxiao SuTitle: Evaluation of upper-room UVGI in elementary school by culturable method and real-time bioaerosol monitor

Abstract: Upper-room ultraviolet germicidal irradiation (UVGI) has been proved to inactivate specific bioaerosols. This study evaluates the effect of upper-room UVGI on general bioaerosols in highly occupied environment like elementary classrooms. Both traditional cultural method and real-time monitors were used.