NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Annual Energy Savings and 

Thermal Comfort of 

Autonomously Heated and 

Cooled Office Chairs

Scott Carmichael, Chuck Booten, 

Joseph Robertson, Justin Chin, 

Dane Christensen, Jacquelyn Pless, and

Doug Arent

National Renewable Energy Laboratory (NREL)

Technical Report

NREL/TP-6A80-66431

July 2016
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Annual Energy Savings and 

Thermal Comfort of 

Autonomously Heated and 

Cooled Office Chairs

Scott Carmichael, Chuck Booten, 

Joseph Robertson, Justin Chin, 

Dane Christensen, Jacquelyn Pless, and 

Doug Arent

National Renewable Energy Laboratory (NREL)

Prepared under Task No. BE4R.3071

Technical Report

NREL/TP-6A80-66431

July 2016
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Available electronically at SciTech Connect http:/www.osti.gov/scitech

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

OSTI http://www.osti.gov

Phone: 865.576.8401

Fax: 865.576.5728

Email: reports@osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

NTIS http://www.ntis.gov

Phone: 800.553.6847 or 703.605.6000

Fax: 703.605.6900

Email: orders@ntis.gov

Cover Photos by Dennis Schroeder: (left to right) NREL 26173, NREL 18302, NREL 19758, NREL 29642, NREL 19795.

NREL prints on paper that contains recycled content.
iii

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Acknowledgments

This work was funded by the National Renewable Energy Laboratory’s Laboratory-Directed 

Research and Development (LDRD) fund. We wish to thank Stuart Macmillan for his continued 

support and insights. A special thanks to the team members of the Human-Centered Energy 

Service LDRD, Steven Isley and Karun Joseph, for their invaluable input. We also wish to thank 

Bob Fogoros and Tempronics, Inc., for supplying the heated and cooled smart-chairs used in our 

experiments. We would also like to thank Lucas Phillips and Tom Bethel for their efforts in 

constructing the environmental test chamber that enabled this research. 
iv

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

List of Acronyms

BEMS Building Energy Management System

HVAC Heating, Ventilation, and Air Conditioning

ML Machine Learning

NREL National Renewable Energy Laboratory

PEC Personal Environmental Climate

PMP Predicted Mean Vote

PPD Predicted Percent Dissatisfied

PTP Personal Thermal Profile
v

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Executive Summary

Although reducing energy use is widely accepted as a critical component of energy and climate 

change policy in the United States, solutions are non-trivial at least partially because human 

behavior and decision making related to energy use are extremely complex. For example, U.S. 

office building energy use is largely driven by air-conditioning demands. However, the optimal 

temperature setting for each building is not homogenous for all building occupants, leading to 

the proverbial thermostat war where individuals prefer different temperature settings. Many 

occupants independently overcome building comfort challenges by using their own space heaters 

or fans, but these devices create additional energy use and may even compound the issue. These 

realities about human behavior and preferences contribute to the challenge of reducing energy 

use in commercial buildings.

The National Renewable Energy Laboratory (NREL) set out to study one component of this

problem. Broadly, the building comfort and energy-use reduction challenge can be broken into 

multiple phases. First, today’s understanding of human comfort needs is oversimplified and 

applied to a general population rather than considering individual preferences. Thus, we

developed an experimental process to measure the statistical variability of individuals’ comfort 

requirements. Second, we reviewed personal comfort technologies and found that existing 

technologies have insufficient controls, lacking the ability, for example, to be controlled 

remotely by a building’s energy management system. On the other hand, automation could help 

to achieve these products’ potential. We established an innovative control system to automate 

personal comfort products so that they could deliver each occupant’s comfort needs. Next, 

individual devices operating autonomously may satisfy comfort, but to achieve whole-building 

energy savings, they should be coordinated with the building automation equipment and heating, 

ventilation, and air conditioning (HVAC) systems. Finally, the localized economic viability of 

this packaged solution should be confirmed. This report documents NREL’s completion of work 

that addresses phases 1 and 2 using a single personal comfort technology as well as initial work 

addressing phase 4.

The first personal comfort product NREL tested is a customized office chair that automatically 

heats and cools the occupant along the seat and chair back according to his or her personal 

preferences. This product is shown to deliver markedly better comfort at room temperatures well 

above typical office cooling set points. Experimental subjects reported satisfaction in these 

elevated air temperatures (27 to 30°C, or 80 to 86°F) at least partly because the chair’s cooling 

effect was tuned to each individual’s needs. 

Simulation of the chair in office buildings around the United States shows that energy can be 

saved everywhere, with impacts varying due to the climate. In NREL’s study, total building 

HVAC energy savings for HVAC set point dead-band widening combined with the operation of 

autonomously operated heated and cooled office chairs exceeds 10% in hot-dry climate zones.

The potential HVAC energy savings increases to >17% when hypothetical low-power (5 W)

comfort devices are considered. Due to the high-end nature of the chair considered in this study, 

the simple payback period for purchasing this product is higher than the expected chair life (eight 

years) when energy usage alone is considered as opposed to also considering co-benefits such as 

enhanced productivity of the occupant due to greater comfort. Productivity co-benefits associated 
vi

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

with enhanced comfort may lower the payback period. However, a productivity study was not 

conducted as part of this research.

This work led us to establish cost-performance targets for comfort delivery packages. From the 

population-weighted energy consumption of the tested product, NREL derived several 

hypothetical energy/cost/comfort targets for personal comfort product systems. In some U.S. 

climate regions, these show the potential for office building HVAC energy savings in excess of 

20% when the peak power requirements for a thermal comfort delivery package falls below 5 W. 

This report documents this research and provides an overview of the methods, results, and areas 

for future research.
vii

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table of Contents

1 Introduction........................................................................................................................................... 1

2 Background........................................................................................................................................... 3

2.1 Early work and the Fanger Model................................................................................................. 3

2.1.1 Predicted Mean Vote and Predicted Percent Dissatisfied ................................................ 3

2.1.2 Shortcomings of Static Models........................................................................................ 4

2.1.3 Dynamic Environmental Conditions................................................................................ 5

2.1.4 Personal Environmental Control Devices ........................................................................ 5

3 Experimental Method ........................................................................................................................... 7

3.1 Hardware, Software, and Experimental Test Facility ................................................................... 7

3.1.1 PEC Device ...................................................................................................................... 7

3.1.2 Smart Chair and Automated Microcontroller................................................................... 7

3.1.3 Smartphone to Smart-Chair Interface............................................................................... 7

3.1.4 Environmentally Controlled Chamber (Comfort-Suite)................................................... 9

3.1.5 Cloud-Based data Acquisition and Control Server ........................................................ 10

3.2 Experimental Protocol................................................................................................................. 11

3.2.1 Objective ........................................................................................................................ 11

3.2.2 Clothing Insulation Values............................................................................................. 11

3.2.3 Experimental Phases ...................................................................................................... 12

4 Experimental Results ......................................................................................................................... 15

4.1 Thermal Comfort Survey Results................................................................................................ 15

4.2 Personalized Thermal Profile Results ......................................................................................... 16

4.3 Averaged Thermal Profile Results.............................................................................................. 17

4.4 Smart-Chair Power Profiles......................................................................................................... 17

5 Opportunity and Impact Assessment............................................................................................... 20

5.1 Energy Simulation....................................................................................................................... 20

5.1.1 PEC Power Profiles........................................................................................................ 20

5.1.2 Hypothetical Design Alternatives .................................................................................. 21

5.2 Energy Savings Results............................................................................................................... 21

5.3 Criteria for Economic Viability................................................................................................... 23

6 Discussion........................................................................................................................................... 25

6.1 Individualization of Comfort and Enabling Technologies.......................................................... 25

6.2 Striking a Balance Between Comfort and Energy Efficiency..................................................... 25

6.3 Co-Benefits of Improved Comfort .............................................................................................. 25

6.4 Expanded Opportunities Beyond Built Environments................................................................ 25

7 Conclusion .......................................................................................................................................... 27

References................................................................................................................................................. 28
viii

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

List of Figures

Figure 1. The percentage of people dissatisfied according to Fanger's models...................................... 4

Figure 2. The smartphone application.................................................................................................... 9

Figure 3. An image of the Comfort-Suite climate-controlled chamber configured as a simulated office 

environment; the positions of various sensors are annotated ...................................................... 10

Figure 4. A histogram of the clo values for experimental participants ................................................ 12

Figure 5. Results from Experiments A, B, and C................................................................................. 13

Figure 6. Thermal sensation (upper panel) and thermal comfort (lower panel) survey responses for 32 

individuals showed statistically significant improvement in the comfort evaluation and PMV at 

dry-bulb temperatures above 27°C.............................................................................................. 16

Figure 7. Personal thermal profiles for experimental participants ....................................................... 17

Figure 8. An example chair power profile............................................................................................ 18

Figure 9. The average chair power profile (blue line) is calculated according to Eq. (1) by projecting 

the individual PTPs (Figure 7) onto the corresponding chair power surfaces (Figure 8) to arrive 

at individual power profiles (gray lines) ..................................................................................... 19

Figure 10. Personal comfort system power profile............................................................................... 21

Figure 11. Annual HVAC energy savings by climate and building thermostat offset for different 

PEC power profiles (hypothetical 5W, hypothetical 20W, and as-measured PEC devices 

[“Actual”])................................................................................................................................... 22

Figure 12. HVAC-related energy consumption for the 20-W max PEC power for all climates.......... 23

Figure 13. Energy cost savings due to the personal comfort system.................................................... 24

List of Tables

Table 1. Predicted mean vote Scale ..............................................................................................................4

Table 2. Parametric Analysis Details..........................................................................................................20
1

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

1 Introduction

The global energy landscape is changing, characterized by increasing penetration of low-carbon 

resources such as renewable energy and natural gas, along with a simultaneous shift in business 

and policy objectives that aim to build a more resilient, low-carbon energy future. Reducing 

energy use is one potential solution contributing toward these goals. As such, understanding the 

dynamics and determinants of energy use has emerged as an important topic for researchers, 

practitioners, and policymakers around the world, but it is vastly complex and requires a deep 

understanding of human preferences and behavior. 

Thermal comfort—the condition of mind that expresses satisfaction with the thermal 

environment and is assessed by subjective evaluation1

—is relative, governed by personal factors 

such as metabolic rate, clothing insulation value, body mass index, activity level, gender, and 

societal norms. These factors vary widely among individuals and even within individuals as they 

move through space and time, which makes it difficult to make shared spaces comfortable for all 

occupants. For example, recent research demonstrated that because men have faster metabolisms

on average, women prefer temperatures to be at least a few degrees warmer than men, which 

biases the standard practice of office air conditioning toward men’s comfort today.

2 Furthermore, 

humidity, temperature, airflow, radiant temperature, and even its non-uniformity each affect 

thermal comfort level. Comfort often affects the productivity of individuals, which adds an 

additional cost or benefit to a firm or household beyond the value of the energy costs accrued. 

This is especially true in an office environment. As such, there is a tension between achieving 

reduced energy consumption and maintaining acceptable comfort conditions for building 

occupants.

In the United States today, office building air-conditioning systems are mostly operated by static 

controls or schedule-driven building automation systems, and homogenous levels of temperature 

and lighting are generally applied across space rather than applied heterogeneously to meet 

differing preferences across occupants. This makes it difficult to achieve universal occupant 

satisfaction while also achieving energy reductions. In other words, buildings lack real-time 

feedback on the presence of individual environmental preferences of occupants, limiting the 

savings potential of energy efficiency measures and creating operational challenges. 

Furthermore, operations managers often lack detailed information about actual occupancy and 

comfort responses, which leads to wasted energy. Not only is this operationally inefficient, but 

employee complaints of discomfort are widespread, and multiple surveys show that even LEEDcertified buildings generally fail to deliver 80% or higher occupant satisfaction.

3 Workers in 

every climate have been seen to bring in personal comfort devices—space heaters, blankets, fans, 

etc.—to overcome office comfort dissatisfaction, which ultimately increases building energy use. 

Building heating, ventilating, and air conditioning (HVAC) accounts for 15% of primary energy 

demand in the United States, and in most climates, it is a major contributor to electric grid peak 

load.4 Recent work indicates that thermostat control in commercial buildings can result in up to 

6% HVAC energy savings per degree Celsius of set point widening (3.3 %/°F).

5 At the same 

time, while these improvements are feasible from a technical and engineering perspective, the 

ways in which humans interact with these systems cannot be ignored. Comfort is a basic human 

need and is essential for productivity and satisfaction. As the widening of thermostat set points 
2

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

can have drastically different impacts on occupants, it can potentially create adverse impacts on

comfort if other environmental changes are not also implemented.

1, 5–7

Recent work has aimed to address these challenges. Seeking to improve thermal comfort in 

buildings, some researchers have developed personal environmental control (PEC) systems that 

allow occupants individual control of their own local environment through a variety of usercentric devices such as desk fans, leg warmers, wrist warmers, and heated and cooled office 

chairs. PEC systems also may enable energy use reduction as the provision of comfort at the 

individual level allows the widening of thermostat set points without adversely affecting comfort 

levels. 

In this research, we perform human subject experiments and building energy simulations to 

assess the comfort and energy impacts of a heated and cooled office chair with the goal of

delivering personalized comfort and maintaining comfort satisfaction when thermostat set points

are widened. Personalized environmental control systems offer a unique solution to addressing 

variations in occupant comfort, especially when dead-band widening scenarios are considered. 

Through the use of heated and cooled office chairs, desk fans, foot and leg warmers, and other 

emerging personal comfort technologies, the energy demands that must be met to satisfy

personal comfort can be offloaded from a building’s HVAC system onto localized comfort 

devices. The comfort impacts of PEC systems have been investigated in a wide body of previous 

work,

8–12 but these studies do not include system-level coordination using devices with two-way 

communication to enable a) dynamic control and b) coordination between HVAC and PEC 

operations. This technical report details a technology that NREL has developed and tested to 

provide localized comfort in office spaces in a way that is amenable to the integration of more 

advanced control techniques that incorporate information for HVAC and PEC operations as well 

as human factors. Two-way communication is a requirement for such a system to operate;

otherwise, the “right hand” will not know what the “left hand” is doing.

We examine the efficacy of a fully automated and network-enabled PEC system consisting of 

heated and cooled office chairs for maintaining personal thermal comfort. We also present 

preliminary analysis of economic and energy impacts this technology can have in different 

climate regions. While we focus on a single PEC system here, we lay the groundwork for the 

development of optimization and control algorithms (and human-in-the-loop evaluation thereof)

for the entire ensemble of PEC devices that may be incorporated into a building energy 

management system (BEMS). 

Automated control of PEC is one part of the overall energy conservation equation; the other part 

is reducing total building HVAC energy use. A key component for an effective energyconserving comfort system is its incorporation into an overall building energy management 

strategy such that energy demands related to comfort can be balanced with HVAC and overall 

building energy usage. In the past, BEMS had relatively few levers to enhance comfort or reduce 

costs. However, new PEC systems could result in an enhanced level of control and expand 

opportunities to include cost savings and comfort improvements. The integration of PEC into a 

BEMS affords additional options for meeting thermal comfort needs without relying on the 

HVAC system alone. As such, we use building simulations to analyze the national energy 

implications of deploying automated PEC in commercial buildings in several climate zones. 
3 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2 Background

2.1 Early work and the Fanger Model

Since the 1950s, research related to thermal comfort generally has focused on designing indoor 

environments suitable for a general population. For example, in P.O. Fanger’s thermal comfort 

experiments, surveys assessed the thermal comfort of a large sample group of human subjects in 

climate-controlled chambers.

6, 12–18 Fanger’s early work laid the foundation for thermal comfort 

research, including development of the Predicted Mean Vote (PMV) and Predicted Percentage of 

Dissatisfied (PPD) measures. These equations predict human thermal comfort in buildings given 

a set of parameters that define the indoor environmental conditions as well as human factors. The 

PMV equation predicts how a group of people perceives the thermal comfort of a room;

however, it does not address individual preferences, and it has been argued that unintended 

biases may have been introduced in the model due to the demographics of the original study 

group participants upon which the model is based.

2

2.1.1 Predicted Mean Vote and Predicted Percent Dissatisfied

The PMV is an evaluation or “vote” of a room’s thermal sensation based on a scale of +3, which 

represents feeling hot, to -3, which represents feeling cold. The PDD predicts the percentage of 

dissatisfied occupants in a room and is a function of a PMV using the following measured 

parameters related to the room conditions and occupants:

Air Temperature (Room Condition)

Clothing Insulation (Occupant Parameter)

Metabolic Rate (Occupant Parameter)

Radiant Temperatures (Room Condition)

Relative Humidity (Room Condition)

Room Air Speed (Room Condition).

Table 1 shows the PMV scale values and the sensation descriptor associated with each vote. As 

the PMV moves away from zero (neutral thermal sensation), the percentage of dissatisfied (PPD) 

occupants increases.
4

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 1. Predicted mean vote Scale

Predicted mean 

vote Sensation

+3 hot

+2 warm

+1 slightly warm

0 neutral

-1 slightly cool

-2 cool

-3 cold

2.1.2 Shortcomings of Static Models

The PMV and PPD have become the standard thermal comfort models to assess thermal comfort 

for building design. Building thermal comfort design guidelines such as ASHRAE Standard 55 

and ISO 7730 recommend buildings remain below a PPD of 20%, which equates to PMV 

between -0.5 and +0.5.

1, 19 In other words, thermal environments that feel slightly cool, neutral, 

or slightly warm are considered acceptable for occupant thermal comfort. It is important to note, 

however, that a building with environmental parameters that yield a PMV of zero will still have a 

percentage of occupants who are dissatisfied with the thermal conditions (Figure 1) because the 

PMV is an average assessment of a group of occupants. This average is part of a distribution that 

includes both individuals that are too hot and too cold in the same space, and these tails are 

partly attributable to gender and other individual human differences as well as personal well

being, mindset, and personal thermal history.

Figure 1. The percentage of people dissatisfied according to Fanger's models 

It should be noted that there exists a finite percentage of individuals who are not thermally satisfied at PMV of zero.
5

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Modeling and predicting thermal comfort can be improved by categorizing occupants based on 

physiological factors that influence thermal comfort. For instance, consider differences in

metabolism between genders, on average, and how this affects preferences for room temperature 

and differences in thermal perception. Although there is not a significant difference between 

comfortable “neutral” temperature ranges for males and females, females tend to be more 

sensitive to temperature deviations from this neutral comfort temperature and more likely to 

express thermal dissatisfaction.20 Furthermore, skin temperatures are linearly correlated with 

thermal comfort vote, which contributes to predictive models for thermal comfort.

21 However,

improving thermal comfort prediction accuracy of the model is possible by clustering individuals 

based on personal thermal preferences.

21 This research demonstrates the importance of 

integrating individual preference-based environment changes into modeling thermal comfort and 

its potential for generating energy use savings.

2.1.3 Dynamic Environmental Conditions

Building occupants frequently experience changes in room temperatures, or transient thermal 

conditions, as they travel throughout or enter into buildings during the course of a day. In 

response, building occupants may modify their thermal environments when they feel discomfort 

by taking actions such as putting on additional clothing or opening windows. Dynamic thermal 

conditions and adaptive human behaviors are especially prevalent when building designs 

incorporate natural ventilation which, in some cases, rely on occupants to adjust windows for 

cooling comfort. To account for the dynamic thermal nature of buildings and adaptations of 

occupants, Brager and de Dear (1998) developed the Adaptive Comfort Models.

22, 23 The 

Adaptive Thermal Comfort Model, developed through analysis of thermal comfort studies, is 

based on the premise that occupants will naturally adjust or adapt to their environment to 

maintain thermal comfort.

23

The array of thermal comfort technologies available to building occupants is expanding rapidly. 

Further, advances in computational power, wireless communication, and sensing capabilities 

now allow for real-time analysis, prediction, and modeling of thermal comfort conditions at very 

fine levels of granularity.

24–28 The combination of more advanced thermal comfort-enhancing 

technologies as well as the ability to control them dynamically has opened up new avenues for

research about how to intelligibly and efficiently control and model building occupant comfort 

and building operations.

2.1.4 Personal Environmental Control Devices

PEC devices allow individuals to augment their local ambient conditions (i.e., optical, thermal,

humidity, ventilation, air movement, and acoustic conditions) to fit their preferences. The 

concept of fine-grained control of local thermal environments, such as that provided by PECs, is 

not new (e.g., space heating). However, the ability to integrate and coordinate the operation of 

numerous localized comfort devices with larger-scale building facilities is a recent development. 

As such, early research on PEC systems has explored the design principles that are required to 

maintain human thermal comfort. For example, the University of California - Berkeley’s Center 

for the Built Environment pioneered this area of research with an extensive body of work 

examining the efficacy of a wide array of PEC systems. Several PEC technologies have been 

studied including ventilated desk systems, personal table fans, foot warmers, radiant thermal 

panels, and more recently, heated and cooled office chairs.

10, 11, 29–31 PEC systems such as these 
6 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

have been shown to improve thermal comfort across room temperatures spanning 16°C to 29°C

(60.8 to 84.2°F). 

In light of this, modeling thermal responsiveness and sensitivity of different regions of the 

human body has proven to be useful for developing effective PEC systems. In a series of papers, 

Zhang et al. (2009) detail the Berkeley Thermal Comfort Model that predicts the thermal 

sensation and comfort of individual body parts and their influence on the overall body’s thermal 

sensation and comfort.

32–34 They found that different areas of the human body can be classified 

into two groups based on their influence on overall thermal sensation: 

Dominant body: The back, chest, and pelvis, which are thermally sensitive locations that 

can significantly affect the overall body’s perception of thermal sensation and comfort. 

Minor body parts: The remaining body parts individually that are thermally less sensitive 

as compared to the dominant body part. Individually, they may not significantly 

contribute to the overall body’s perception of thermal sensation and comfort. However, a 

group of minor body parts experiencing thermal discomfort can affect the overall body’s 

perception of thermal sensation and comfort. 

The Berkeley model has helped to inform the design of effective PEC systems by identifying the 

most thermally sensitive body parts. In the case of a heated and cooled office chair, the heat 

transfer is applied to the back (if reclined) and pelvis while the remaining body parts are exposed 

to the ambient conditions. The Opposite Sensation Model proposed by Zhang and co-workers

(2010) accounts for situations where two or more minor body parts experience the opposite 

thermal sensation than the dominant body parts.34 In these situations, minor body parts can 

dominate overall thermal sensation. As such, it may be necessary to provide auxiliary thermal 

conditioning to the hands, face, and legs in order to provide acceptable overall thermal comfort 

when these minor body parts experience thermally opposite sensations from the dominant body 

parts. 
7 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

3 Experimental Method

Leveraging previous research in the field of thermal comfort, we focused on one PEC device that 

holds promise for being both an effective comfort-enhancing device as well as potentially saving 

overall building energy use if integrated properly with a BEMS. Experiments were performed 

with human subjects to assess the efficacy of PEC control for maintaining occupant thermal 

comfort at elevated and suppressed ambient dry-bulb temperatures. In order to facilitate the 

experiments discussed in detail below, an array of hardware and software solutions as well as an

experimental facility were developed. 

3.1 Hardware, Software, and Experimental Test Facility

3.1.1 PEC Device

The PEC device used in this study was a heated and cooled office chair (manufactured by 

Tempronics Inc.). The chair had a string of thermoelectric Peltier junctions woven into the seat 

and back cushions. The direction of current flow through the thermoelectric string determined 

whether the chair surface provided heating or cooling to the user. The polarity of electricity 

flowing through the thermoelectric string was controllable. As sold by the manufacturer, a dial

allowed the user to manually modulate the chair between full heating to full cooling. 

3.1.2 Smart Chair and Automated Microcontroller 

The chair’s manual control was removed and, in its place, a prototype Bluetooth-enabled 

microcontroller was used. The microcontroller managed local control of the active heating and 

cooling, collected data, and managed communications with a networked server. Digital 

temperature sensors for both the seat cushion and underside of the chair were located relatively 

far from chair cooling fans (for sensing ambient air temperatures). The magnitude of chair 

heating or cooling was controlled by a pulse-width modulation signal from the microcontroller. 

As a safety measure, an analog over-temperature shutoff circuit was incorporated to cut power to 

the smart-chair if the seat temperature exceeded 41°C (105.8 °F). Additionally, there was a lower 

threshold which triggered if the analog temperature signal was lost. Two temperature sensors 

(low-power linear active thermistor ICs MCP9700) were installed on each smart-chair. One 

sensor, located on the seat cushion, was utilized as a reference for proportional integral control. 

The sensor was affixed to the seat cushion upholstery and was positioned immediately above a

thermoelectric Peltier junction. Body weight ensured that adequate thermal contact between the 

sensor and the junction was maintained. The second sensor, located on the underside of the seat, 

measured the ambient air temperature. Temperature data were collected at a frequency of 2 Hz 

and streamed over Bluetooth to an Android smartphone application and finally, forwarded to a

data-logging server.

3.1.3 Smartphone to Smart-Chair Interface

During the experiments described in Section 3.2, smartphones were provided to participants to 

facilitate experimental data gathering. The smartphones ran a custom application (Figure 2) that 

served several purposes:

Sensor data from the chair were gathered for display and analyzed and forwarded to a 

central server for logging and analysis. 
8 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

The application received commands from the central server to perform thermal comfort 

surveys. 

The application sent set point update commands to the smart-chair microcontroller in 

either of two modes:

o Users updated the smart-chair set point through a slider bar on the smartphone 

touchscreen (Figure 2, top segment). 

o The set point of the chair was automatically updated according to a personal 

thermal profile (PTP) that was constructed during a self-learning protocol. 

3.1.3.1 Personal Thermal Profile

The smart-chair’s self-learning protocol provided a data array of ambient air-temperature and 

smart-chair set point pairs. The temperature/set point pairs defined knot points of a piecewise 

linear interpolating function. When the smart-chair was operated in autonomous mode, set point

temperatures were determined via interpolation within the PTP function. Interpolation was 

performed on this function using the current ambient air temperature (as reported by the smartchair itself) as the independent variable to arrive at the smart-chair set point temperature. The set

point temperature range of the smart-chair spans 25°C to 40°C (77 to 104 °F).
9

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 2. The smartphone application 

Slider bars allowed a user to indicate desired smart-chair set point temperature, level of thermal sensation, comfort

vote, and thermal preferences for the room and the chair. An input field allowed entry of a current estimate of the

room temperature. 

3.1.4 Environmentally Controlled Chamber (Comfort-Suite)

An occupied environmental test chamber (Comfort-Suite) was constructed to support comfort 

testing with human subjects (Figure 3). The space measured 4.9m (length) x 2.45m (width) x 

2.45m (height) and was configured as a simulated office environment. Four 100-cm-x-60-cm 

desks were situated along the long walls of the test chamber with two on each side of the room 

arranged in a staggered configuration. The walls, floor, and ceiling were wood-framed

construction with internal fiberglass insulation and 1.27-cm extruded polystyrene foam. The 

walls and ceiling were covered with drywall and the flooring was finished with laminate. A 

once-through cooling and reheating HVAC system with supply registers and vents situated on 

the floor and ceiling created a uniform flow field within the space (average air velocity at the 

registers was 2.56 m/s and 0.14 ± 0.03 m/s standard deviation on average at the desk locations).

While objects and people in the space certainly affected local airflows, the room’s high air 

exchange rate (2.3 min/air-exchange), coupled with the relatively low average air velocity, are 

designed to minimize these effects.
10

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Temperature within the space was controllable to within ±1°C (±2°F). T-type thermocouples 

housed in aspirated radiative shields had an error of ±0.5°C (±0.9°F) and were positioned at five 

locations (the four work stations and the center of the ceiling) with aspirated thermocouples.

35 

Analysis of temperature sensor data showed a high degree of temperature uniformity throughout 

the space (0.6°C mean variance). During the experiments, the relative humidity was bounded 

between 20% – 55%. 

Figure 3. An image of the Comfort-Suite climate-controlled chamber configured 

as a simulated office environment; the positions of various sensors are annotated

3.1.4.1 Comfort-Suite Data Acquisition System

A data acquisition system (DAQ) controlled the operation of the Comfort-Suite HVAC system. 

Air dry-bulb temperature, relative humidity, and CO2 concentration data were logged by the 

DAQ and uploaded to the server at a frequency of 2 Hz.

3.1.5 Cloud-Based data Acquisition and Control Server

To orchestrate Comfort-Suite HVAC system operation, the smart-chair operation, and comfort 

survey administration, a server infrastructure was created to provide a bi-directional data link

that allowed for communication to any number of different endpoint devices. These included the 
11

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

smartphone application, microcomputers that transmitted imagery data, a Microsoft Kinect 

device that transmitted human posture data,

36 and a website information and control dashboard.

3.1.5.1 Infrared and Visible Imagery

At each workstation, infrared (IR) and visible images were taken throughout the experiment. A 

FLIR Lepton long-ware IR camera module and a four-megapixel camera module was integrated 

with a Raspberry Pi microcomputer. Images were collected once every three seconds and synced

with the server over a Wi-Fi Internet connection. While we did not analyze the imagery in this 

work, future investigations may examine the accuracy of thermal comfort assessment based on 

imagery data and potential applications thereof in PEC control system.

37, 38

3.1.5.2 Microsoft Kinect

One Microsoft Kinect device was located high in a corner of the Comfort-Suite. The Kinect was

a game system peripheral that allowed players to control a game with their bodies. It utilized an

infrared camera and an infrared dot projector to create detailed three-dimensional maps (dotfields) of an environment. The resulting 640-x-480 pixel resolution depth images had 1-mm dot 

sensitivity. Additionally, the software that powers the Kinect device could produce skeletal 

tracking data in near-real time for all occupants within the field of view of the device.

36 These 

data were uploaded to the server at a frequency of 1 Hz. We also did not analyze the dot-field or 

skeletal data in this work, but future investigations may focus on predicting occupant discomfort 

via biomechanical signatures of thermal discomfort (e.g., rubbing forearms, hunching, etc.).

Further, recent work by Gao et al. (2013) demonstrated the integration of the Kinect into an 

occupancy-aware HVAC control system.

39

3.1.5.3 Data Visualization

Sensor data streams and imagery data were published to a secure website by the server. The 

website continuously updated a data visualization framework, allowing for experimental data 

integrity to be verified while experiments are in progress. Additional input fields on the website 

allowed the temperature set points of both the Comfort-Suite and the smart-chairs to be 

controlled remotely.

3.2 Experimental Protocol

3.2.1 Objective

The objectives of the following experiments were threefold. First, we aimed to assess the thermal 

comfort impact of automated heated and cooled smart-chair operation on individuals in a 

simulated office environment. Second, we sought to understand how variations in individual 

thermal preferences affected the energy usage of the smart-chairs. Finally, analysis provided a 

basis data set for quantifying the opportunities for integrating PECs and energy systems across 

the national building stock.

3.2.2 Clothing Insulation Values 

Participants were asked to arrive at the experiment facility dressed in business casual attire. As a 

result, there was some variation in participant clothing choices. Clothing insulation values (clo, a 

measure of the thermal insulating properties of the clothing) were estimated using a standardized

garment checklist. Participant clo values fell within the range 0.35 – 0.65 clo with a mode of 

0.55 clo, as shown in Figure 4. One aim of these experiments was to measure the comfort 
12

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

impacts of the smart-chair in an office setting, so no corrective actions were undertaken to 

account for differences in clo values among individuals. The distribution of clo values we 

observed in these experiments was consistent with typical summertime office worker clo values 

found in the global thermal comfort database.

40 A study that examines the combined impacts of 

seasonal clothing ensembles and PEC operations was not part of the scope of this research.

Figure 4. A histogram of the clo values for experimental participants

3.2.3 Experimental Phases

Three experiments were conducted with each group of participants. Group sizes varied between 

two and four people. The temperature within the Comfort-Suite was varied in accordance with 

the schedule shown in Figure 5. The purposes of each experimental phase are described in the 

sections below. 
13

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 5. Results from Experiments A, B, and C 

The dry-bulb temperature (black line) is ramped at a rate of 0.18°C/min (0.32°F/min) from 16°C to 30°C (60.8 to 

86°F) during Experiment A (green zone). The dry-bulb temperature is held at five discrete temperatures—30, 27, 23, 

19, and 16°C (86, 80.6, 73.4, 66.2, and 60.8 °F) during the course of Experiment B (blue zones). The dry-bulb 

temperature is ramped at a rate of 0.18°C/min from 16°C to 30°C during Experiment C (red zone). Comfort surveys 

(green dots) were conducted every 5 minutes during Experiments A and C, and every 3 minutes during Experiment 

B.

3.2.3.1 Experiment A (Baseline)

To gather control data for comfort survey responses, a baseline experiment (A) was performed 

with the smart-chairs deactivated. Participants were situated at workstations within the ComfortSuite. The space was pre-conditioned to a temperature of 16°C (60.8°F). A fifteen-minute 

thermal adaptation period was observed to allow participants to become accustomed to this

starting temperature. During Experiment A, the dry-bulb temperature in the climate chamber was 

gradually ramped from 16°C to 30°C (60.8° to 86°F) (0.32°F/min) over a 75-minute period at a 

rate of to 0.18°C per minute. Comfort surveys (Figure 2) were given every five minutes to

quantify each participant’s thermal sensations, thermal comfort, thermal preference, and bestguess estimate of the current ambient temperature. These surveys served as a baseline with 

which to compare the comfort surveys in later experiments.

3.2.3.2 Experiment B (Tuning)

A second experiment (B) was performed to allow the smart-chairs to self-learn the thermal 

preference profile of the occupant. The smart-chairs were activated and the temperature set point

control was given to participants via the smartphone application. The temperature within the 

climate chamber was held at 16, 19, 23, 27, and 30°C (86, 80.6, 73.4, 66.2, and 60.8 °F) for 22 

minutes each period. Comfort surveys were given every three minutes for the final 15 minutes of 

each hold period (i.e., there was a seven-minute thermal adaptation period). The smart-chair set

point temperature and ambient air temperature at the end of each hold period were stored in the

smartphone application as a knot point in each participant’s PTP.
14

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

3.2.3.3 Experiment C (Automated Control)

A final experiment (C) was performed to assess the smart-chair’s ability to autonomously 

provide individualized thermal comfort. As in Experiment A, the ambient temperature of the 

climate chamber was ramped from 16°C to 30°C (60.8 to 86°F) over a 75-minute period. The set

point of each chair was automatically adjusted by the smart-chair’s microcontroller in response 

to the locally measured ambient room temperature. The set point was determined by referencing

each individual’s PTP and interpolating between knot points from Experiment B. The smartchair set points were automatically updated at a frequency of 2 Hz. Comfort surveys were

administered every five minutes.
15

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

4 Experimental Results

In total, 32 individuals participated in these experiments. The ages of participants ranged 

between 19 and 30 years old (13 female and 19 male). Participants were recruited from 

universities near the Denver, Colorado metro area. Experiments were conducted between August 

10th, 2015 and September 20th, 2015 at NREL’s South Table Mountain Campus. 

4.1 Thermal Comfort Survey Results

The efficacy of the automated thermoelectric heated and cooled chair affecting individual 

thermal sensation and comfort was evaluated based on participant responses to the thermal 

comfort surveys (Figure 2). Figure 6 show that a statistically significant (paired t-test, p-values < 

0.05) difference in both thermal sensation (top panel, Figure 6) and thermal comfort (bottom 

panel, Figure 6) was observed at dry-bulb temperatures above 26°C (78.8°F) between the 

deactivated smart-chair experimental data (gray data) and the autonomously controlled smartchair data (green data). At these elevated temperatures, a 0.5 thermal sensation point shift toward 

the thermal neutral zone was observed. Similarly, an increase of thermal comfort (by 0.5 PMV) 

was observed at these temperatures. 

Interestingly, smart chair-induced thermal comfort enhancements were not observed at low 

ambient temperatures. This result differs substantially from previous work by Pasut and 

colleagues (2012) that found a significant enhancement of thermal comfort at 16°C using an 

identical model thermoelectric chair (albeit with manual temperature controls).

41 The 

disagreement likely stems from differences in experimental implementation, the small sample 

sizes inherent to climate chamber studies, and differences in experimental protocols between the 

two studies. We do not offer these results as conclusive evidence of no comfort-enhancing effect 

of the thermoelectric heated and cooled chair at low ambient temperatures, but instead, these 

results suggest an opportunity for further investigation.
16

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 6. Thermal sensation (upper panel) and thermal comfort (lower panel) 

survey responses for 32 individuals showed statistically significant improvement 

in the comfort evaluation and PMV at dry-bulb temperatures above 27°C 

The size of semi-circles for the chair-deactivated (gray) and activated (green) corresponds to the fraction of votes 

normalized by the total number of votes for a given dry-bulb temperature. The colored bands represent the 95% 

confidence interval of the mean votes. 

4.2 Personalized Thermal Profile Results

PTPs for each participant were created during Experiment B (Figure 7). A participant’s PTP 

informed the smart-chair set point temperature during autonomous operation modes (i.e.,

Experiment C). Variance in the shape of different individuals’ PTPs reflected remarkable

differences in thermal preferences among individuals. While several participants preferred for 

the smart-chair to be relatively warm under all ambient temperatures studied, others preferred 

that it remain cold. On average, the PTPs monotonically decrease from a set point of 36°C at an 

ambient temperature of 16°C to a set point of 28°C at an ambient temperature of 30°C. 
17

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 7. Personal thermal profiles for experimental participants 

The individual thermal profiles (gray lines) indicate the participants desired smart-chair temperature set point for a 

given ambient room temperature. The average thermal profile (blue line) with associated standard deviation margins 

(blue shaded region) show that, as expected, participants preferred the smart-chair to be relatively warmer at low 

ambient room temperatures and cooler at relatively high ambient temperatures.

4.3 Averaged Thermal Profile Results

The functional shape of an individual’s PTP had a direct link to the total energy use of that 

individual’s smart-chair. Smart-chair power depended upon the set point temperature of the chair 

as well as the ambient temperature of the building (discussed in Section 4.4). When the chair was

operated in an autonomous mode, the set point of the chair was determined by local air 

temperature according to an individual’s PTP. As such, if a building’s indoor temperature varies 

throughout the course of a day, so will the power usage of its occupants’ smart-chairs. 

4.4 Smart-Chair Power Profiles

The power required for a smart-chair to maintain a given set point temperature (when occupied 

by a human body) depended upon the ambient temperature of the room. This relationship was 

measured for each smart-chair by performing a calibration experiment where the ambient room 

temperature was varied between 16°C and 30°C (60.8 and 86°F) and the smart-chair set point

temperature was varied between 25°C and 40°C (77 and 104°F). An 8x8 grid of ambient 

temperature/smart-chair set point temperature pairs was explored. At each set of experimental 

conditions the smart-chairs were occupied and the temperature of the chair was allowed to 

equilibrate. Power measurements were collected over a period of 3 minutes at a frequency of 

1 Hz. These data were time-averaged and assembled to form a chair power surface (Figure 8) for 

each chair. 

Individual smart-chair power surfaces were collected during a calibration study. An example 

smart-chair power profile (Figure 8) shows how there was a trough of relatively low power usage 
18

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

that spanned from low ambient/low set point conditions to high ambient/high set point

conditions. Generally, at the extreme smart-chair set point temperatures of 25°C and 40°C (77 

and 104°F), the power required to maintain a given set point was 70W and 40W respectively, 

while at mid-range chair set point temperatures (34°C / 93.2°F) the power reached a minimum 

near 0W. 

Figure 8. An example chair power profile 

Chair power profiles were measured for each of the four smart-chairs used in the experiment. As the ambient 

temperature decreased, the smart-chair uses less power to maintain the same set point temperature. These data were 

measured with the smart-chair occupied as the set point temperature and ambient temperature were varied. 

The smart-chair power calibration surfaces were useful for modeling the power usage when an 

individual’s PTP determined the chair set point temperature for a given ambient temperature 

condition. For example, projecting a single PTP (one of the gray lines in Figure 7) onto the 

calibration surface yielded an individualized power curve (smart-chair power vs. ambient 

temperature, as shown in Figure 9). 

To arrive at the average power usage profile for many individuals (each with a unique PTP),

each PTP was projected onto the calibration surface and the average power was calculated 

according to the following equation:

(1)

where maps an individual to the smart-chair that he or she occupied, is the calibration 

power surface (see Figure 8) corresponding to the smart-chair that the participant occupied, 

is the ambient temperature of the room, and is the PTP for the 

individual, and is the total number of individuals considered in the average. This aggregation 
19

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

and mapping operation takes a collection of PTPs and produces an average power profile (as 

shown by the blue line in Figure 9) that can be integrated into office building energy usage 

simulations.

Figure 9. The average chair power profile (blue line) is calculated according to Eq.

(1) by projecting the individual PTPs (Figure 7) onto the corresponding chair 

power surfaces (Figure 8) to arrive at individual power profiles (gray lines)

The aggregate power profile constructed using the actual PTPs measured during the course of the 

experiments was a monotonically increasing function. This result was counterintuitive, as one 

would expect the average chair power to reach a minimum that was near “room temperature” (22

- 24°C, 71.6 – 75.2°F). Indeed, the majority of individual power profiles did show a minimum 

near moderate ambient temperatures, but the asymmetry of the chair power profiles 

(approximately 70W when cooling and 40W when heating) coupled with the large variance in 

PTPs resulted in a monotonically increasing average chair power with increasing ambient room 

temperatures.

The average power analysis presented above was useful for predicting the building-level energy 

impact of a deployed smart-chair-based PEC system. A generalizable approach to analyzing the 

impacts of PEC systems on energy systems is desirable not only for informing system-scale 

impacts but also for outlining viable design envelopes for future PEC systems. For example, the 

heated and cooled smart-chair investigated here was selected from a growing array of existing 

and emerging PEC technologies, and different technologies could vary substantially in the 

amount of power they use and the reported comfort levels which they are able to support as 

ambient room temperatures change.
20

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

5 Opportunity and Impact Assessment

5.1 Energy Simulation

DOE’s OpenStudio software platform, based on EnergyPlus, was used to perform an initial

impact analysis of deploying automated PECs in a commercial building in different United 

States climates.42 The parameters for the energy usage profiles of the PEC systems came directly 

from the experiments performed in the climate chamber. The buildings were DOE small office 

commercial prototype buildings.

43 The thermal preference profiles for experiment participants 

were incorporated into EnergyPlus simulations of a DOE reference small office building for 

expanded HVAC set points across four representative U.S. climate zones.44 These climates span 

the majority of the commercial buildings in the United States. Parametric analysis was performed 

by creating a baseline commercial building model and by applying design alternatives to that 

baseline model. 

Table 2. Parametric Analysis Details

Parameter Values Simulated

Building Type DOE prototype small office

Cooling Set point 75°F - 81°F in 1°F increments

Heating Set point 64°F - 70°F in 1°F increments

Maximum PEC Power Experimental profile

20 W

5 W

Climate Phoenix, AZ

Memphis, TN

Baltimore, MD

Chicago, IL

Vintage 1980-2004

5.1.1 PEC Power Profiles

Although the thermoelectric chairs were effectively Peltier heat pumps, we modeled the smartchairs as resistive heaters dissipating an amount of heat that was equal to the average power 

usage of the smart-chairs, as measured experimentally. This was appropriate for building energyuse calculations since the chairs move heat from people into the indoor air or vice versa, but do 

not move heat across the thermal enclosure. The only change in the conditioned space was 

addition of the electrical energy supplied to the chair, which was dissipated as heat within the 

building. This variable heat load was modeled as a function of indoor temperature based on the 

population-weighted energy consumption of the PECs in use. The simulated PEC power profiles 

are shown in Figure 10. 
21

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 10. Personal comfort system power profile 

Note that this is the average profile over the collection of all systems in the building.

5.1.2 Hypothetical Design Alternatives

The parameters considered in this analysis were the power profiles of the PEC, the thermostat set

points in the building, and the climate zone. The building details and the range of parameter 

values are given in Table 2. The thermostat set points were adjusted in 1°F (0.55°C) increments 

based on nominal heating and cooling set points of 70°F (21.1°C) and 75°F (23.9°C),

respectively. Three power profiles were analyzed as shown in Figure 10. The first profile was the 

experimentally derived profile from the Tempronics chair. The second two were hypothetical 

profiles representative of the type of optimized profile averaged across a collection of PECs that 

could potentially exist within a given building. Below 64°F (17.8°C) and above 80°F (26.7°C), 

the average system was assumed to be at full power, providing either heating or cooling,

respectively. Near 72°F (22.2°C), the average system was assumed to be at minimum power. 

Note that any individual PEC will go to zero power at some temperature where the occupant is 

comfortable at that ambient temperature. However, that temperature is expected to vary across a 

population of occupants such that at any given temperature near where people are comfortable 

(assumed to be 72°F) some systems will be heating, some will be cooling, and some will be off. 

Therefore, the average power across the population of PECs will never be zero.

5.2 Energy Savings Results

Figure 11 shows a simulated annual HVAC energy savings percentage for each climate, PEC 

maximum power level, and thermostat set point offset in the parametric study. Negative set point 

offsets correspond to lowering the building set point during the heating season and positive

offsets correspond to increasing the set point during the cooling season. These offsets were 

calculated relative to the assumed set points of 70°F (21.1°C) for heating and 75°F (23.9 C) for 

cooling. Energy savings were calculated as the reduction in HVAC energy consumption, 

deriving from lower HVAC load due to thermostat offsets, less the energy use by PECs, which 

also adds heat to the building air, thus changing HVAC load. Potential for energy savings was 

found to be quite large even at relatively modest temperature offsets. 
22

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

At and near zero offset the average power draw of the collection of as-measured “Actual” PECs 

was found to be non-zero, so this power draw was added to the building load resulting in 

negative energy savings. This effect was most pronounced when the smart-chairs were used in 

cooling mode; however, this effect was still present in heating mode because the PECs were less 

efficient at heating the building than the primary HVAC system. The experimental, or “Actual,”

power profile exhibited a more pronounced effect in this regard due to higher power demand

than the hypothetical profiles. Even so, simulations using the smart-chair profile showed positive 

energy savings for all climates if the PEC was able to support occupant comfort when the

building thermostat was offset by greater than +3°F (+1.7°C) for cooling or -1°F (-0.55°C) for 

heating.

Figure 11. Annual HVAC energy savings by climate and building thermostat offset 

for different PEC power profiles (hypothetical 5W, hypothetical 20W, and asmeasured PEC devices [“Actual”]) 

Note that negative energy savings can occur at zero offset because, on average, the collection of PECs never have 

zero power draw; some people will be cooling at nominal building temperatures while others might turn the PEC off 

or be heating. Note that benefits derived from increases in individual comfort attained in these situations are not 

reflected in these charts.

Figure 12 shows a simulated building’s energy usage for each climate for the 20-W maximum 

PEC power profile and a ±4°F (±2.2°C) thermostat offset. The energy use of the PEC was seen 

to be a weak function of climate and was small relative to total HVAC energy use. However, the 

energy savings potential of the combined system was found to be sizeable.
23

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Standard building controls and set points in the DOE Reference Building Model43 were used for 

this work, except thermostat set point offsets as noted. It should be noted that in some climates 

there may be a need for alternative HVAC system controls to manage indoor humidity levels for 

comfort, indoor air quality, and building durability. At set point offsets proposed in this work, it 

is possible that such dehumidifying equipment could result in additional energy consumption. 

We leave this as an opportunity for future research.

Figure 12. HVAC-related energy consumption for the 20-W max PEC power for all 

climates 

This shows that a relatively small amount of additional energy for the PEC has potential to dramatically reduce 

HVAC energy use.

5.3 Criteria for Economic Viability

Any new technology must be cost-effective to gain market traction. Therefore, the breakeven 

first cost for each PEC (5W and 20W and the experimental profiles) was estimated across 

climates assuming an 8-year lifespan. The results are shown in Figure 13. This graph may serve

as a guide to developers of new personal comfort systems and to policymakers looking to 

incentivize market development. For example, if a new system could deliver comfort at a +4°F 

(+2.2°C) offset during the cooling season only, the breakeven cost should be between $50 and 

$200, depending on climate and power draw. If that device also provides comfort with a -4°F

(-2.2°C) offset during the heating season, the breakeven cost would increase by up to $45,

depending on climate and power draw. Note that although the energy savings were greater 

during the heating season, the major economic impact was during the cooling season, thus

allowing for a higher cost for the PECs that provide cooling.
24

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 13. Energy cost savings due to the personal comfort system

Cost savings are dependent upon the device’s energy use profile (Figure 10). This provides an estimate of the costs 

that can be justified for the PEC given the expected cost savings. The black dotted line marks the breakeven point. 

For clarity, the scale on the lower panel is shifted relative to the two upper panels.
25

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

6 Discussion

6.1 Individualization of Comfort and Enabling Technologies

In order to deliver improved comfort while enabling reduced energy usage relative to a

traditional HVAC approach, a personal comfort system framework must address two key issues. 

First, the PEC system should enhance thermal comfort when the ambient temperature is 

operating within a widened margin relative to current standards. Second, the PEC system should 

deliver such a comfort service while using a low enough amount of power that it becomes 

economically viable to operate. The automated smart-chair system explored in this work cannot 

address the thermal comfort of extremities which, in cool ambient conditions, can dominate 

overall thermal comfort.

34 The incorporation of auxiliary thermal comfort devices such as hand, 

wrist, foot, and leg warmers have been shown effective at improving overall thermal comfort.

31

Incorporation of such auxiliary devices into the automated personal-preference-profile-based 

comfort system described in this work may lead to greater comfort-energy benefits.

6.2 Striking a Balance Between Comfort and Energy Efficiency

Predictive thermo-physiological models such as the IESD-Fiala could provide a means of linking 

individualized comfort preferences to HVAC and PEC controls.45 Models that are incorporated 

into predictive control schemes that balance thermal comfort requirements with building energy 

usage allow for a comfort system to anticipate thermal comfort deficiencies or high-energy use 

events before they occur and minimize the occurrence and magnitude of such events. For 

example, an intelligent BEMS could anticipate peak load events and choose to pre-heat or -cool 

an office space beyond the typical dead-band range to save energy. As buildings are often on 

pricing programs where their peak energy usage determines the electricity rate that they pay to a 

utility, this strategy could result in monetary savings beyond those gained by consuming less 

energy. Leveraging thermo-physiological models to predict the comfort impacts of changes due 

to HVAC set point modifications will allow a BEMS to better utilize automated PEC systems to 

maintain thermal comfort of building occupants. 

6.3 Co-Benefits of Improved Comfort

Ambient office temperatures affect worker productivity and performance. For instance, field 

studies show that, as ambient temperatures exceed 24°C (~75°F) or fall below 20°C (68°C), a 

decrease in office worker performance is observed.

46–50 Productivity co-benefits associated with 

thermal comfort-enhancing PEC systems could further incentivize businesses to deploy them. 

For example, a 2002 study estimated the potential productivity gains of the office worker 

populations to be between $37B and $208B annually.

47 Productivity co-benefits associated with 

thermal comfort create incentives that extend beyond the economic gains associated with a lower 

overall building energy usage, which is estimated to be 1% of operating expenses for a nonindustrial workplace.

46

6.4 Expanded Opportunities Beyond Built Environments

The operationalization of personal preference profiles has comfort and energy applications 

outside of the office as well. Automobiles, buses, airplanes, restaurants, hotels, theaters, and 

classrooms are all examples of environments that have potential interface points for automated 

PEC systems. The integration of personal preference profile data, occupancy detection and 
26

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

prediction capabilities, and real-time feedback on the energy usage and performance of these 

disparate energy consuming systems could facilitate more efficient delivery of energy services to 

individuals.
27

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

7 Conclusion

Historically, a lack of information about actual occupancy and comfort responses that reflect 

individual heterogeneous consumer preferences has led to inefficient energy system operations, 

yielding significant waste. This creates a tremendous opportunity for energy use reductions 

through improved occupancy-based controls that achieve significant consumer lighting and 

HVAC improvements across residential and commercial business types. With the emergence of 

the so-called “internet of things,” devices now have the capability of instantaneous

communication with people, buildings, and infrastructure, which open up new research areas in 

personal comfort and BEMS. “Things” can now collaborate in real-time to provide better 

quality-of-life services to people while potentially reducing the overall energy and environmental 

impact of them. In other words, today’s technology enables the achievement of multi-objective 

optimization in the context of reducing energy use while enhancing quality of life by satisfying 

real-time individual comfort preferences, and it was the objective of this study to explore one 

such application.

In this work, we investigate the potential for smart-chairs in an office environment to reduce 

building-wide energy use by meeting individual thermal comfort preferences in real time. This 

research aimed to demonstrate the value of collecting individual-level data on occupant presence 

and adaptive behavior for reducing energy use and ultimately, to contribute to the growing need 

for improved representation of occupants in building energy simulation tools. While this study 

provides a pilot and demonstrates the potential for gaining a greater understanding of behaviorrelated model inputs, the scope of opportunity is much larger and provides significant room for 

growth toward developing novel occupant-centered building software and hardware that can be 

integrated cost effectively with building control schemes. Personal preference profiles that 

follow people through space and time can be an enormous benefit not only to the people that 

they are associated with, but also to the intelligent operation of large scale energy systems.

Here we have outlined an integrated approach for evaluating comfort and energy impacts of PEC

technologies. Human subject tests were carried out in an environmental test chamber that mimics 

an office environment. An automated PEC system consisting of a heated and cooled office chair 

that is automated via a smartphone was evaluated for its ability to enhance personal comfort at 

ambient temperatures outside of typical HVAC set point ranges. PTPs were measured for each of 

32 experimental participants and these profiles were integrated into a series of building energy 

simulations to assess the energy impacts of such a PEC system deployed in a small office 

building in the United States. Our results (Figure 6) indicate the autonomously controlled smartchairs are capable of maintaining personal comfort at temperatures as high as 30°C (86°F), 

which could result in up to a 10% HVAC energy reduction in hot-dry climates (Figure 11, 

bottom panel magenta line for Phoenix).

While we focused on a single PEC device, the groundwork has been laid for the characterization 

of a variety of emerging PEC technologies as well as the design and optimization of building 

integrated control systems that operate them. The research approach followed in this work sets 

the stage for further advances in human-informed design of energy-efficient PEC systems and 

human-in-the-loop development of the algorithms that control them. 
28 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

References 

1. ASHRAE Standard 55. 2013. “Thermal environmental conditions for human occupancy.”

Atlanta. Am. Soc. Heat. Refrig. Air-Cond. Eng. Inc 55. 

2. Kingma, B., and W. van Marken Lichtenbelt. 2015. “Energy consumption in buildings and 

female thermal demand.” Nat. Clim. Change advance online publication, (2015). 

3. Walker, K. 2015. Indoor environment quality in LEED buildings: Understanding conditions 

affecting performance. eScholarship. Accessed March 2016, 

http://escholarship.org/uc/item/13p0k3sx. 

4. DOE. 2009. Buildings Energy Data Book. Washington, D.C.: DOE. 

5. Hoyt, T., K. Lee, H. Zhang, E. Arens, and T. Webster. 2009. “Energy savings from extended 

air temperature setpoints and reductions in room air mixing.” Int. Conf. Environ. Ergon. 

Accessed January 2016, http://escholarship.org/uc/item/28x9d7xj. 

6. Fanger, P.O. 1970. “Thermal comfort” and “Prediction of human heat tolerance.” In 

Goldman R.F. 1970. Environmental Stress: Individual Human Adaptations. New York, NY: 

Academic Press.

7. Hoyt, T., E. Arens, and H. Zhang. 2015. “Extending air temperature setpoints: Simulated 

energy savings and design considerations for new and retrofit buildings.” Build. Environ.

(88); 89–96. 

8. Arens, E., H. Zhang, and W. Pasut. 2011. “Thermal comfort and perceived air quality of a

PEC system.” Proc. Indoor Air 2011. Accessed February 2016, 

http://escholarship.org/uc/item/3sv803jx. 

9. Bauman, F., G. Carter, A. Baughman, and E. Arens. 1997. “A Field Study of PEM (Personal 

Environmental Module) Performance in Bank of America’s San Francisco Office 

Buildings.” Cent. Built Environ. Accessed December 2015, 

http://escholarship.org/uc/item/717760bz. 

10. Taub, M., H. Zhang, E. Arens, F. Bauman, D. Dickerhoff, M. Fountain, W. Pasut, D. 

Fannon, Y. Zhai, and M. Pigman. 2015. “The use of footwarmers in offices for thermal 

comfort and energy savings in winter.” eScholarship. Accessed January 2016, 

http://escholarship.org/uc/item/7vc2q28k. 

11. Pasut, W., H. Zhang, E. Arens, and Y. Zhai. 2015. “Energy-efficient comfort with a 

heated/cooled chair: Results from human subject tests.” Build. Environ. 84, 10–21. 

12. Fanger, P.O. 2001. “Human requirements in future air-conditioned environments.” Int. J. 

Refrig. 24, 148–153. 

13. Fanger, P. 1982. . 

R.E. Krieger Pub. Co. Accessed April 2016, http://www.worldcat.org/isbn/0898744466. 
29

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

14. Fanger, P. O., A.K. Melikov, H. Hanzawa, and J. Ring. 1988. “Air turbulence and sensation 

of draught.” Energy Build 12, 21–39.

15. Fang, L., G. Clausen, and P.O. Fanger. 1988. “Impact of Temperature and Humidity on 

Perception of Indoor Air Quality During Immediate and Longer Whole-Body Exposures.”

Indoor Air 8, 276–284.

16. Fang, L., G. Clausen, and P.O. Fanger. 1998. “Impact of Temperature and Humidity on the 

Perception of Indoor Air Quality.” Indoor Air 8, 80–90.

17. Ole Fanger, P. & Toftum, J. Extension of the PMV model to non-air-conditioned buildings in 

warm climates. Energy Build. 34, 533–536 (2002).

18. Fang, L., Wyon, D. P., Clausen, G. & Fanger, P. O. Impact of indoor air temperature and 

humidity in an office on perceived air quality, SBS symptoms and performance. Indoor Air

14, 74–81 (2004).

19. ISO 7730: Moderate Thermal Environments - Determination of the PMV and PPD Indices 

and Specification of the Conditions for Thermal Comfort. (ISO, 1994).

20. Jacquot, C.M.C., L. Schellen, B.R. Kingma, M.A. van Baak, and W.D. van Marken 

Lichtenbelt. 2014. Influence of thermophysiology on thermal behavior: the essentials of 

categorization. Physiol. Behav. 128, 180–187.

21. Schellen, L., Loomans, M. G. L. C., de Wit, M. H., Olesen, B. W. & van Marken 

Lichtenbelt, W. D. The influence of local effects on thermal sensation under non-uniform 

environmental conditions--gender differences in thermophysiology, thermal comfort and 

productivity during convective and radiant cooling. Physiol. Behav. 107, 252–261 (2012).

22. Brager, G. S. & de Dear, R. J. Thermal adaptation in the built environment: a literature 

review. Energy Build. 27, 83–96 (1998).

23. de Dear, R. & Brager, G. S. Developing an adaptive model of thermal comfort and 

preference. Cent. Built Environ. (1998). at <http://escholarship.org/uc/item/4qq2p9c6>

24. Shaikh, P. H., Nor, N. B. M., Nallagownden, P., Elamvazuthi, I. & Ibrahim, T. A review on 

optimized control systems for building energy and comfort management of smart sustainable 

buildings. Renew. Sustain. Energy Rev. 34, 409–429 (2014).

25. Castilla, M. et al. A comparison of thermal comfort predictive control strategies. Energy 

Build. 43, 2737–2746 (2011).

26. Castilla, M., Álvarez, J. D., Normey-Rico, J. E. & Rodríguez, F. Thermal comfort control 

using a non-linear MPC strategy: A real case of study in a bioclimatic building. J. Process 

Control 24, 703–713 (2014).

27. Dong, B., Lam, K. P. & Neuman, C. Integrated building control based on occupant behavior 

pattern detection and local weather forecasting. (2011).
30

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

28. Ferreira, P. M., Ruano, A. E., Silva, S. & Conceição, E. Z. E. Neural networks based 

predictive control for thermal comfort and energy savings in public buildings. Energy Build.

55, 238–251 (2012).

29. Bauman, F., Carter, T. & Baughman, A. Field study of the impact of a desktop task/ambient 

conditioning system in office buildings. Cent. Built Environ. (1998). at 

<http://escholarship.org/uc/item/8x98n5hj>

30. Tham, K. W. & Pantelic, J. Performance evaluation of the coupling of a desktop personalized 

ventilation air terminal device and desk mounted fans. Build. Environ. 45, 1941–1950 

(2010).

31. Zhang, H., Arens, E. & Zhai, Y. A review of the corrective power of personal comfort 

systems in non-neutral ambient environments. Build. Environ. 91, 15–41 (2015).

32. Zhang, H., Arens, E., Huizenga, C. & Han, T. Thermal sensation and comfort models for 

non-uniform and transient environments: Part I: local sensation of individual body parts. 

Cent. Built Environ. (2009). at <http://escholarship.org/uc/item/3sw061xh>

33. Zhang, H., Arens, E., Huizenga, C. & Han, T. Thermal sensation and comfort models for 

non-uniform and transient environments, part II: Local comfort of individual body parts. 

Build. Environ. 45, 389–398 (2010).

34. Zhang, H., E. Arens, C. Huizenga, and T. Han. “Thermal sensation and comfort models for 

non-uniform and transient environments, part III: Whole-body sensation and comfort.”

Build. Environ. 45, 399–410 (2010).

35. Indoor Aspirated Shield. (2013). at 

<https://buildingsfieldtest.nrel.gov/indoor_aspirated_shield>

36. Shotton, J. et al. Real-time Human Pose Recognition in Parts from Single Depth Images. 

Commun ACM 56, 116–124 (2013).

37. De Oliveira, F., S. Moreau, C. Gehin, and A. Dittmar. 2007. Infrared imaging analysis for 

thermal comfort assessment. Conf. Proc. Annu. Int. Conf. IEEE Eng. Med. Biol. Soc. IEEE 

Eng. Med. Biol. Soc. Annu. Conf. 2007, 3373–3376.

38. Burzo, M. et al. Using Infrared Thermography and Biosensors to Detect Thermal Discomfort 

in a Building’s Inhabitants. V06BT07A015 (2014). doi:10.1115/IMECE2014-40269

39. Gao, P. X. & Keshav, S. SPOT: A Smart Personalized Office Thermal Control System. in 

Proceedings of the Fourth International Conference on Future Energy Systems 237–246 

(ACM, 2013). doi:10.1145/2487166.2487193

40. A global database of thermal comfort field experiments. at 

<http://www.academia.edu/9529843/A_global_database_of_thermal_comfort_field_experim

ents>
31

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

41. Pasut, W. et al. Effect of a heated and cooled office chair on thermal comfort. Proc. 2nd Int. 

Conf. Build. Energy Environ. (2012). at <http://escholarship.org/uc/item/7dt6v6hn>

42. OpenStudio. (Alliance for Sustainable Energy, LLC., 2015).

43. DOE Reference Buildings. (U.S. Department of Energy’s Building Technologies Office). at 

<http://energy.gov/eere/buildings/existing-commercial-reference-buildings-constructed-orafter-1980>

44. EnergyPlus. (U.S. Department of Energy’s Building Technologies Office, 2015). at 

<https://energyplus.net/>

45. Rugh, J. P. et al. Predicting human thermal comfort in a transient nonuniform thermal 

environment. Eur. J. Appl. Physiol. 92, 721–727 (2004).

46. Fisk, W. J. Health and Productivity Gains from Better Indoor Environments and Their 

Relationship with Building Energy Efficiency. Annu. Rev. Energy Environ. 25, 537–566 

(2000).

47. Seppanen, O., Fisk, W. J. & Lei, Q. H. Effect of temperature on task performance in office 

environment. Lawrence Berkeley Natl. Lab. (2006). at 

<http://escholarship.org/uc/item/45g4n3rv>

48. Tanabe, S., Iwahashi, Y., Tsushima, S. & Nishihara, N. Thermal comfort and productivity in 

offices under mandatory electricity savings after the Great East Japan earthquake. Archit. 

Sci. Rev. 56, 4–13 (2013).

49. Clements-Croome, D. J. in Innovative Developments in Architecture, Engineering and 

Contruction (ed. Anumba, C. J.) 335–341 (Millpress Science Publishers, 2003). at 

<http://centaur.reading.ac.uk/11878/>

50. Relationships between the indoor environment and productivity: A literature review -

ProQuest. at 

<http://search.proquest.com/openview/297438cd9725b868fbfa68423df67add/1?pqorigsite=gscholar>