Aaron P. Wemhoff

Aaron P. Wemhoff

Villanova University

H-index: 21

North America-United States

About Aaron P. Wemhoff

Aaron P. Wemhoff, With an exceptional h-index of 21 and a recent h-index of 14 (since 2020), a distinguished researcher at Villanova University, specializes in the field of Comptuational Heat Transfer, Microscale Heat Transfer, Energy, Sustainability, Data Centers.

His recent articles reflect a diverse array of research interests and contributions to the field:

Characterization of a Rack-Level Thermosyphon-Based Cooling System

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Data Center Environmental Burden Reduction Through On-Site Renewable Power Generation

The sustainability benefits of economization in data centers containing chilled water systems

The Difference in Blue Water Usage of Meals Prepared at Home Versus Meals Prepared Away From Home

Using Network Modeling to Test for ASHRAE 90.4 Standard Compliance

Characterizing Data Center Cooling System Water Stress in the United States

Assessing the impact of electricity consumption on water resources in the US

Aaron P. Wemhoff Information

University

Villanova University

Position

Associate Professor of Mechanical Engineering

Citations(all)

1279

Citations(since 2020)

605

Cited By

891

hIndex(all)

21

hIndex(since 2020)

14

i10Index(all)

40

i10Index(since 2020)

21

Email

University Profile Page

Villanova University

Aaron P. Wemhoff Skills & Research Interests

Comptuational Heat Transfer

Microscale Heat Transfer

Energy

Sustainability

Data Centers

Top articles of Aaron P. Wemhoff

Characterization of a Rack-Level Thermosyphon-Based Cooling System

Authors

Rehan Khalid,Steven Schon,Luca Amalfi,Alfonso Ortega,Aaron P Wemhoff

Journal

Journal of Electronic Packaging

Published Date

2024/9/1

This study aims to improve the combined energy efficiency of data center cooling systems and heating/cooling systems in surrounding premises by implementing a modular cooling approach on a 42U IT rack. The cooling solution uses a close-coupled technique where the servers are air-cooled, and the air in turn is cooled within the rack enclosure using an air-to-refrigerant heat exchanger. The refrigerant passively circulates in a loop as a thermosyphon, making the system self-sustaining during startup and shutdown, self-regulating under varying heat loads, and virtually maintenance-free by eliminating mechanical parts (other than the cabinet fans). A heat load range of 2 kW-7.5 kW is tested on a prototype system. Experimental results reveal stable thermosyphon operation using R1233zd (E) as the working fluid, a maximum evaporator pressure drop of 21.5 kPa at the highest heat load and a minimum …

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Authors

R Khalid,E Youssef,RL Amalfi,A Ortega,AP Wemhoff

Journal

Journal of Electronic Packaging

Published Date

2024/6/1

A thermosyphon-based modular cooling approach offers an energy efficient cooling solution with an increased potential for waste heat recovery. Central to the cooling system is an air-refrigerant finned tube heat exchanger (HX), where air is cooled by evaporating refrigerant. This work builds on a previously published two-dimensional (2D) model for the finned-tube HX by updating and validating the model using in-house experimental data collected from the proposed system using R1233zd (E) as the working fluid. The results show that key system variables such as refrigerant outlet quality, air and refrigerant outlet temperatures, and exchanger duty agree within 20% of their experimental counterparts. The validated model is then used to predict the mean heat transfer coefficient on the refrigerant side for each tube in the direction of airflow, indicating a maximum heat transfer coefficient of nearly 1200 W/(m 2 K) for a …

Data Center Environmental Burden Reduction Through On-Site Renewable Power Generation

Authors

Matt McMullen,Aaron P Wemhoff

Journal

ASME Journal of Engineering for Sustainable Buildings and Cities

Published Date

2024/5/1

The energy demands from data centers contribute greatly to water scarcity footprint and carbon emissions. Understanding the use of on-site renewable power generation is an important step to gain insight into making data centers more sustainable. This novel study examines the impact of on-site solar or wind energy on data center water scarcity usage effectiveness (WSUE) and carbon usage effectiveness (CUE) at a US county scale for a given data center size, water consumption level, and energy efficiency. The analysis uncovers combinations of specific metrics associated with grid-based carbon emissions and water scarcity footprint that enable predictions of the improvements anticipated when implementing on-site solar or wind energy. The implementation of on-site renewables has the most benefit in reducing carbon footprint in areas with high existing grid-based emissions such as the western side of the …

The sustainability benefits of economization in data centers containing chilled water systems

Authors

Li Chen,Aaron P Wemhoff

Journal

Resources, Conservation and Recycling

Published Date

2023/9/1

This study provides the first known conservative estimates of reductions in carbon and water scarcity footprints when employing economization technologies in chilled water-based data centers (DCs) in the U.S. Specifically, a generic DC that employs a Computer Room Air Handling (CRAH)-based cooling system with a total IT load of 400 kW is computationally modeled at 925 locations in the U.S. with airside and/or water-side economization. The energy savings and environmental benefits are presented in terms of key DC performance metric reductions, including Carbon Usage Effectiveness (CUE) and Water Scarcity Usage Effectiveness (WSUE). The results suggest that implementing both water-side and airside economization schemes under conditions within the ASHRAE A1 Allowable envelope reduces the mean state-averaged PUE, WUE, CUE, and WSUE by 11%, 22%, 11%, and 15%, respectively. These …

The Difference in Blue Water Usage of Meals Prepared at Home Versus Meals Prepared Away From Home

Authors

Schuyler Sices,Aaron P Wemhoff

Published Date

2023/7/10

The global trend of increasing consumption of food prepared away from home (FAFH) versus food prepared at home (FAH) can have environmental consequences such as blue water footprint. This study therefore estimates the difference in blue water usage of FAFH versus FAH. Blue water footprints of individual food items and consumer survey data were combined to obtain overall values for FAFH and FAH consumption. The data suggest that FAFH consumes approximately 258 L per kilogram of food, which is approximately 15% higher than FAH. The difference in water footprint is largely due to an increased consumption protein-based meals in FAFH compared to FAH. However, the gap in water footprint is mitigated by the increased consumption of high water-consuming snacks at home such as nuts and dried fruits, as well as meal ingredients like processed oils. The calculations suggest a much higher …

Using Network Modeling to Test for ASHRAE 90.4 Standard Compliance

Authors

A Wemhoff,Russ Tipton,Mark Seymour

Journal

Proceedings of the 2023 ASHRAE Winter Conference

Published Date

2023/1

The ASHRAE 90.4 Standard provides important guidelines to justify data center design standards to meet energy efficiency criteria. As a building, a data center heat load due to the contained IT equipment far overshadows thermal gains and losses of traditional buildings that house people. In addition, one approach to being energy efficient is to evaporate water to achieve latent cooling, which can consume significant quantities of water, creating another potential environmental issue. Also, importantly, energy modelling tools assume mixing for thermal comfort, whereas data centers operate better with segregation of cold supply and warm return air. Thus, traditional energy modeling tools for general buildings are not ideally designed for evaluating data center performance. Designers therefore often resort to ad-hoc assessment approaches using the like of spreadsheets or other bespoke calculation approaches. The risk is that calculations are not very standardized and so methods and outcomes may not be very consistent, which is a disincentive for states to adopt the Standard. Therefore, general computational tools for design justification to the Standard are needed. The most useful tools contain a broad capability to model a variety of cooling and power systems and an underlying framework to calculate the corresponding MLC and ELC metrics associated with the Standard. One approach that accomplishes this task is to use network modeling to connect various cooling system component models into a system-wide framework, with a similar approach for the electrical system. Both systems are modeled under a single umbrella to account for …

Characterizing Data Center Cooling System Water Stress in the United States

Authors

Li Chen,Aaron P. Wemhoff

Published Date

2022/1/29

Massive data center (DC) energy demands lead to water consumption concerns. This study quantifies on-site and off-site DC water consumption and its holistic impact on regional water availability. This study proposes a new DC sustainability metrics, Water Scarcity Usage Effectiveness (WSUE), that captures the holistic impacts of water consumption on regional water availability by considering electricity and water source locations and their associated water scarcity. We examine the water consumption of various DC cooling systems by tracking on-site water consumption along with the direct and indirect water transfers associated with electricity transmission at the contiguous U.S. balancing authority (BA) level. This study then applies the WSUE metric for different DC cooling systems and locations to compare the holistic water stress impact by large on-site water consuming systems (e.g., via cooling towers) versus systems with higher electrical consumption and lower on-site water consumption such as the conventional use of computer room air conditioner (CRAC) units. Results suggest that WSUE is strongly dependent on location, and a water-intensive cooling solution could result in a lower WSUE than a solution requiring no or less on-site water consumption. The use of the WSUE metric aids in DC siting decisions and DC cooling system design from a sustainability point of view.

Assessing the impact of electricity consumption on water resources in the US

Authors

Li Chen,Aaron P. Wemhoff

Journal

Resources, Conservation and Recycling

Published Date

2022/3

Electricity generation heavily relies on water. Growing electricity demand globally inevitably leads to water availability concerns. This study proposes a means to quantify the indirect water usage embodied in electricity and assesses the holistic impact of water consumption on available water resources. First, the energy water intensity factor (EWIF), which quantifies the amount of water used to produce energy, is updated at the contiguous U.S. balancing authority (BA) level and on an end user basis to account for electricity trades using an input-output model. Further, the scarce water index (SWI), or volume of scarce water embodied per kWh electricity consumed, is proposed to predict electricity consuming facility water stress impact as the water scarcity footprint (WSF). A case study of U.S. data centers is presented to demonstrate the use of these metrics. Results show that WSF is region-dependent, and the burden …

Gaussian process regression as a replicable, streamlined approach to inventory and uncertainty analysis in life cycle assessment

Authors

Tao Dai,Sarah M Jordaan,Aaron P Wemhoff

Journal

Environmental Science & Technology

Published Date

2022/2/24

Life cycle assessment plays a critical role in quantifying environmental impacts, but its credibility remains challenged when data and uncertainty analysis are lacking. In this study, we propose a data compilation framework to address these two issues. The framework first quantifies the correlations of production activities among existing data in temporal, geographical, and taxonomic dimensions. The framework then introduces covariance functions to convert these correlations to a similarity matrix, and the Gaussian process regression model is adopted to predict new data based on these covariance functions. The associated uncertainty is automatically characterized using the posterior distribution of predictions. The framework is demonstrated on the nitrogen fertilizer application rate for food production─an activity recognized for its environmental burden─with results capable of reflecting temporal and geographical …

Coupled Calculations of Data Center Cooling and Power Distribution Systems

Authors

Aaron P Wemhoff,Faisal Ahmed

Journal

Journal of Electronic Packaging

Published Date

2022/12/1

Physics-based modeling aids in designing efficient data center power and cooling systems. These systems have traditionally been modeled independently under the assumption that the inherent coupling of effects between the systems has negligible impact. This study tests the assumption through uncertainty quantification of models for a typical 300 kW data center supplied through either an alternating current (AC)-based or direct current (DC)-based power distribution system. A novel calculation scheme is introduced that couples the calculations of these two systems to estimate the resultant impact on predicted power usage effectiveness (PUE), computer room air conditioning (CRAC) return temperature, total system power requirement, and system power loss values. A two-sample z-test for comparing means is used to test for statistical significance with 95% confidence. The power distribution component …

Predictions of Airside Economization-Based Air-Cooled Data Center Environmental Burden Reduction

Authors

Li Chen,Aaron P. Wemhoff

Published Date

2022/10

Modern data centers, which consume roughly 3% of global electricity, continue to experience increased demand. Therefore, green data centers that consume less energy and have minimal environmental impact are desirable. This study examines the potential energy savings and environmental benefits of applying airside economization with evaporative cooling in air-cooled data centers in the continental U.S. A generic data center that employs a Computer Room Air Conditioning (CRAC)-based cooling system with a total IT load of 400 kW is modeled at 925 locations using the National Renewable Energy Laboratory’s (NREL’s) TMY3 database. The energy savings and environmental benefits are evaluated in terms of key data center performance metrics: Power Usage Effectiveness (PUE), Carbon Usage Effectiveness (CUE), and the recently proposed Water Scarcity Usage Effectiveness (WSUE) metric …

Predicting embodied carbon emissions from purchased electricity for United States counties (vol 292, 116898, 2021)

Authors

Li Chen,Aaron P. Wemhoff

Journal

Applied Energy

Published Date

2021/6/1

Predicting the embodied scope 3 carbon dioxide equivalent (CO2e) emissions from purchased electricity for end users in the United States is challenging due to electricity transmission within interconnected power grids. Existing methods only focus on large aggregation areas, thereby ignoring potentially significant emission factor (EF) variations, so this study proposes a novel method to translate the CO2e emissions from the balancing authority (BA)-level to the county-level by utilizing explicit finite-difference theory for electricity flow predictions, and then employing economic input–output theory to evaluate the scope 3 embodied lifecycle CO2e emissions. Results show that the generation-based EFs at the BA-level range from 0.007 to 0.905 MT-CO2e/MWh with a mean value of 0.400 MT-CO2e/MWh and a standard deviation of 0.229 MT-CO2e/MWh. The consumption-based EFs at the BA-level range from 0.008 to …

Corrigendum to" Predicting embodied carbon emissions from purchased electricity for United States counties"[Appl. Energy 292 (2021) 116898]

Authors

Li Chen,Aaron P Wemhoff

Journal

Applied Energy

Published Date

2021/10

The authors regret that the supporting information of this article was not included in the previous publication.

Modeling the thermal energy storage capability of a phase change material confined in a rectangular cavity

Authors

Xuewei Zhang,Sylvie Lorente,Aaron P Wemhoff

Journal

International Communications in Heat and Mass Transfer

Published Date

2021/7/1

Phase change materials (PCM) may be used as a thermal energy barrier for applications requiring insulation. This project explores the behavior of pure PCM within a two-dimensional rectangular cavity as a thermal barrier using a new thermal barrier efficiency metric. The dimensionless parameters are determined that dictate the efficiency for one-dimensional transport with cyclical heat flux loading on one side and a convective boundary condition on the opposite side. Two limiting conditions for the PCM behavior (No Phase Change and Full Phase Change) are studied analytically, and numerical models show that the predicted thermal barrier efficiency exceeds these limits, suggesting that the limiting conditions provide useful conservative estimates of PCM performance in designing PCM thermal barriers. Results show that both the No Phase Change limit and Full Phase Change efficiencies decrease with …

Study of a lab-scale organic rankine cycle for the ultra-low-temperature waste heat recovery associated with data centers

Authors

Sebastian Araya,Aaron P Wemhoff,Gerard F Jones,Amy S Fleischer

Journal

Journal of Electronic Packaging

Published Date

2021/6/1

The ongoing growth in data center rack power density leads to an increased capability for waste heat recovery. Recent studies revealed the organic Rankine cycle (ORC) as a viable means for data center waste heat recovery since the ORC uses waste heat to generate on-site, low-cost electricity, which can produce economic benefits by reducing the overall data center power consumption. This paper describes the first experimental and theoretical study of a lab-scale ORC designed for ultralow grade (40–85 °C) waste heat conditions typical of a data center server rack, and it outlines the implementation of a similar ORC system for a data center. The experimental results show thermal efficiencies ranging from 1.9% at 43 °C to 4.6% at 81 °C. The largest contributors to ORC exergy destruction are the evaporator and condenser due to large fluid temperature differences in the heat exchangers. The average …

Rack-Level Thermosyphon Cooling and Vapor-Compression Driven Heat Recovery: Compressor Model

Authors

Rehan Khalid,Raffaele Luca Amalfi,Aaron P Wemhoff

Published Date

2021/10/26

This paper introduces a novel thermal management solution coupling in-rack cooling and heat recovery system. System-level modeling capabilities are the key to design and analyze thermal performance for different applications. In this study, a semi-empirical model for a hermetically sealed scroll compressor is developed and applied to different scroll geometries. The model parameters are tuned and validated such that the model is applicable to a variety of working fluids. The identified parameters are split into two groups: one group is dependent on the compressor geometry and independent of working fluid, whereas the other group is fluid dependent. By modifying the fluid-dependent parameters using the specific heat ratios of two refrigerants, the model shows promise in predicting the refrigerant mass flow rate, discharge temperature and compressor shaft power of a third refrigerant. Here, the approach has …

Restructuring a Pedagogical Course to Benefit Engineering Ph. D. Students and Faculty

Authors

Aaron P Wemhoff

Published Date

2021/4/9

___, an introductory course in engineering pedagogy for engineering PhD students, was restructured to increase student engagement and to create a mechanism for engineering faculty to improve their own teaching. This restructuring enables more active learning in class, makes course materials available online for current engineering faculty and enables faculty development workshops, and improves the students’ ability to improve their own teaching. These goals were accomplished through flipping the course and developing an assessment hierarchy: self/partner assessment prior to class-wide assessment. Collaboration with experts in diversity, equity and inclusion enabled additional materials in this area to promote the growth of underrepresented groups in engineering. Successes and lessons learned in the restructuring are outlined.

Measuring the Thermal Contact Resistance Between Cu Foams and Substrates for On-Chip Cooling Applications in Data Centers

Authors

Lucas Arrivo,Steven Schon,Aaron P Wemhoff

Published Date

2021/10/26

Data centers housing high performance computing equipment have large and growing rack densities, which pushes the limits of traditional air cooling technologies because of limited heat transfer coefficients. Therefore, on-chip cooling using so-called cold plates is emerging as a necessary cooling option for high-density electronics. The use of mini-channels or pins fins to enhance internal heat transfer area inside cold plates requires extensive micro-machining that is relatively time consuming and expensive for mass production. As an alternative approach, inserting and bonding pre-manufactured metal foams into hollow bodies are explored as a potentially inexpensive means to enhance the interior heat transfer area of cold plates. One key aspect of the performance of metal foams in cold plates is the thermal contact resistance in the bonding between the foam and the substrate. This project predicts the contact …

An experimental study of an Organic Rankine Cycle utilizing HCFO-1233zd (E) as a drop-in replacement for HFC-245fa for ultra-low-grade waste heat recovery

Authors

Sebastian Araya,Aaron P Wemhoff,Gerard F Jones,Amy S Fleischer

Journal

Applied Thermal Engineering

Published Date

2020/11/5

The use of Organic Rankine Cycles (ORCs) for waste heat recovery can reduce energy consumption in data centers, which in turn benefits the environment through the reduction of carbon-based fuels. However, data center applications exist in the ultra-low temperature range (40 − 80℃), making efficient and economical operation challenging. The operating fluids that are viable in this temperature range are limited, so it can be a challenge to identify a suitable drop-in replacement for a proven fluid. In this study, the use of HCFO-1233zd(E) is explored to determine its suitability as a low Global Warming Potential and zero Ozone Depletion Potential alternative to the more common HFC-245fa in ultra-low temperature data center applications. This study features the first known comprehensive comparison between the alternative working fluid HCFO-1233zd(E) and HFC-245fa in a lab-scale experimental ORC under …

Life cycle inventory regionalization and uncertainty characterization: a multilevel modeling approach

Authors

Tao Dai,Amy S Fleischer,Ross Lee,Aaron P Wemhoff

Journal

Journal of cleaner production

Published Date

2020/1/1

Life cycle inventory (LCI) databases are essential to evaluate the environmental burden of a product or service using life cycle assessment (LCA). The demand for improved accuracy and credibility of LCA results has increased the need for LCI containing higher data granularity and quantified uncertainty. In this study, a novel data processing method is proposed to facilitate regionalized LCI database compilation and uncertainty characterization. The key step in the proposed method is to retain variations within the datasets by building a relationship between the geographical and temporal quantified characteristics and material/energy input amounts using multilevel modeling (MLM) rather than losing the variations via a traditional aggregation method. The uncertainty is objectively characterized by the model prediction interval. An example case study is conducted on nitrogen fertilizer application for corn production …

See List of Professors in Aaron P. Wemhoff University(Villanova University)

Aaron P. Wemhoff FAQs

What is Aaron P. Wemhoff's h-index at Villanova University?

The h-index of Aaron P. Wemhoff has been 14 since 2020 and 21 in total.

What are Aaron P. Wemhoff's top articles?

The articles with the titles of

Characterization of a Rack-Level Thermosyphon-Based Cooling System

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Data Center Environmental Burden Reduction Through On-Site Renewable Power Generation

The sustainability benefits of economization in data centers containing chilled water systems

The Difference in Blue Water Usage of Meals Prepared at Home Versus Meals Prepared Away From Home

Using Network Modeling to Test for ASHRAE 90.4 Standard Compliance

Characterizing Data Center Cooling System Water Stress in the United States

Assessing the impact of electricity consumption on water resources in the US

...

are the top articles of Aaron P. Wemhoff at Villanova University.

What are Aaron P. Wemhoff's research interests?

The research interests of Aaron P. Wemhoff are: Comptuational Heat Transfer, Microscale Heat Transfer, Energy, Sustainability, Data Centers

What is Aaron P. Wemhoff's total number of citations?

Aaron P. Wemhoff has 1,279 citations in total.

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