Elsevier

Building and Environment

Volume 84, January 2015, Pages 10-21
Building and Environment

Energy-efficient comfort with a heated/cooled chair: Results from human subject tests

https://doi.org/10.1016/j.buildenv.2014.10.026Get rights and content

Highlights

  • The PCS (personal comfort system) chair modifies subjects' thermal sensation.

  • The PCS chair improves comfort between 16 °C and 29 °C.

  • PCSs that require at most 16 W provide comfortable conditions between 18 °C and 29 °C.

  • PCSs are a good strategy to improve building resilience to future climate change.

  • Using fans to provide room-temperature cooling prevents uncomfortable overcooling.

Abstract

A novel heated/cooled chair was evaluated for its effect on thermal sensation and comfort. The chair is exceptionally efficient, allowing standalone battery operation over long periods. Its capabilities at providing comfort needed to be established.

Twenty-three college students participated in 69 2.25-h tests. Four heated/cooled chairs were placed in an environmental chamber resembling an office environment. The chamber temperatures were 16 °C, 18 °C and 29 °C. During the tests the subjects had full control of the chair power through a knob located on the chair. The heated/cooled-chair results could be compared to those of conventional mesh and cushion chairs tested in the same three environmental conditions in a previous study, as well as to a thermoelectrically heated and cooled chair.

Subjective responses for thermal sensation and comfort were obtained at 15-min intervals. The results show that the heated/cooled chair strongly influences the subjects’ thermal sensation and improves thermal comfort and perceived air quality. No significant differences were found between men and women. The chair provided comfortable conditions for 92% of the subjects in a range of temperatures from 18 °C to 29 °C.

Introduction

Buildings currently account for 40% of primary energy consumption in many countries, and are a significant source of carbon dioxide emissions [1]. Roughly half of this is for heating and cooling. The floor area of commercial and institutional buildings is expected to grow by almost 195% by year 2050 [2], so reducing building energy consumption is a priority.

Despite the significant energy used to serve the demand for thermal comfort, poor thermal comfort is one of the most common complaints from building users. Although buildings are designed to have at least 80% of occupants satisfied with their thermal environment [3], a survey of 215 buildings shows that only 11% of them met this criterion [4].

Personal comfort systems (PCS) are a promising technology for both improving occupants' thermal comfort and simultaneously reducing buildings' heating and cooling energy. They provide comfort by targeting a relatively small amount of energy directly onto occupants. Several authors have reported that the use of PCS decreases occupants’ dissatisfaction.

PCS saves energy by enabling the ambient air temperature to be less controlled. In U.S. commercial buildings, a typical temperature range between setpoints for heating and cooling systems (setpoint deadband) is between 21.5 °C and 24.5 °C. Each 1 °C broadening of this deadband reduces annual HVAC energy use by approximately 10% [5], [6]. This is a very significant amount. At the same time, several laboratory studies [7], [8], [9], [10], [11], [12] have established that PCS can produce comfort across ambient temperature ranges in the vicinity of 18–30 °C. This implies that a building can be controlled with an extended thermostat deadband while still maintaining occupants’ thermal comfort. A recent field study has demonstrated this for the winter season, using a foot-warming PCS at 19 °C [13].

By widening the comfortable ambient deadband, personal comfort systems allow energy to be rather easily saved in new and existing buildings, improve buildings’ resilience to future climate change, and serve to deepen demand response during peak temperatures. PCS can be deployed to assist existing air conditioning (AC) systems or, in climates characterized by moderate temperatures, to enable low-energy conditioning strategies or the avoidance of AC altogether.

A heated/cooled chair is a type of PCS that has been found to provide improved comfort. Watanabe at al [14]. studied the influence of a ventilated chair incorporating two fans in the back and seat to provide isothermal forced airflow for cooling. The authors concluded, based on survey's results, that the chair provided an acceptable ambient temperature at 30 °C. Kogawa et al. [15] tested ventilated chairs in an office. The chair had two air nozzles installed on both armrests. Results showed that the ventilated chair could keep occupants comfortable at 27 °C, cooling the occupant up to one unit on the seven-point thermal sensation scale. Brooks and Parsons [16] tested in cool environments a car seat heated with encapsulated carbon fabric. They reported improved overall thermal comfort at ambient temperatures below 20 °C. Zhang et al. [17] tested a car seat whose surfaces were both heated and cooled by water tubes, extending the drivers' range of acceptable ambient temperatures 9.3 °C downwards and 6.4 °C upwards.

Pasut et al. [10] tested a chair with thermo-electric devices providing heating and cooling in the surface of the seat. The chair improved subjects' thermal comfort and thermal sensation in a range of temperatures from 16 °C to 29 °C. Some subjects reported an unpleasant sensation at 29 °C coming from contact with the cold surfaces of the chair's back and seat.

The Center for the Built Environment (CBE) at UC Berkeley has developed a new type of heated and cooled PCS chair with highly optimized energy efficiency. The goal of this study is to quantify its comfort performance and determine the range of ambient temperatures within which its users are comfortable.

Section snippets

Description of test chair

The CBE heated/cooled office chair (here referred to as ‘PCS chair’) uses a maximum of 16 W for heating and 3.6 W for cooling. With such low energy consumption the chair can operate for multi-day periods on a battery that is recharged at night when the chair is not in use. The chair is made from a conventional mesh chair into which three fans are integrated into the seat and back, and two electrical heating elements are sewn into the mesh (Fig. 1). The fans are positioned within plenums, lined

Subjects and test conditions

Human subjects using the PCS chair had their comfort evaluated under three different room air temperatures: 16 °C, 18 °C and 29 °C. The relative humidity of the chamber was kept at 50% ± 1%. The air velocity was less than 0.1 m/s. Twenty-three subjects (12 females and 11 males) participated in each of the three test conditions, for a total of 69 tests. The subjects were selected with a normal (healthy weight) body mass index (BMI). The BMI of the sample ranged from 19.4 to 24.8, and the age

Whole body thermal sensation and comfort

The authors had previously tested a thermoelectrically heated and cooled chair against two conventional office chairs, in the identical environmental conditions as this study. The two conventional chairs, one meshed and one cushioned, produced almost identical thermal comfort responses in the occupants [10]. As the current study followed the same test procedures and conditions as the earlier study, the earlier study's results for the conventional chairs are used in this paper as reference

Whole-body thermal comfort and thermal sensation

The PCS chair has a strong effect on subjects' overall thermal sensation (Fig. 5) and thermal comfort (Fig. 6). Zhang [24] defined the “most influential group” of body parts affecting thermal comfort as the back, chest, and pelvis. She showed that sensation from these body parts has a dominant impact on overall sensation. The PCS chair affects two of these three influential body parts. This may explain the strong influence that it had on subjects’ whole-body thermal sensation.

The small

Conclusions

The PCS chair plus the small desk fan is seen to provide comfortable conditions for more than 90% of the subjects in a range of temperatures from 18 °C to 29 °C, and around 75% at 16 °C. The potential energy consequences in real buildings are large: an 11 °C setpoint deadband — under which 90% of PCS chair users are seen to be comfortable — yields an energy saving of more than 50% in many climates [5], [6]. The energy saving is not significantly offset by the chair energy consumption, which is

Acknowledgment

The authors thank the Center for the Built Environment (CBE) and its industry partners for financial support of this research (www.cbe.berkeley.edu). This work was also partially supported by the California Energy Commission (CEC) Public Interest Energy Research (PIER) Buildings Program under contract 500-08-044 and PIR-12-026.

References (25)

  • C. Huizenga et al.
    (2006)
  • T. Hoyt et al.

    Energy savings from extended air temperature setpoints and reductions in room air mixing

    (2009)
  • Cited by (167)

    View all citing articles on Scopus
    View full text