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Open Access Publications from the University of California
Cover page of Predicting thermal pleasure experienced in dynamic environments from simulated cutaneous thermoreceptor activity

Predicting thermal pleasure experienced in dynamic environments from simulated cutaneous thermoreceptor activity


Research into human thermal perception indoors has focused on ‘neutrality’ under steady-state conditions. Recent interest in thermal alliesthesia has highlighted the hedonic dimension of our thermal world that has been largely overlooked by science. Here, we show the activity of sensory neurons can predict thermal pleasure under dynamic exposures. A numerical model of cutaneous thermoreceptors was applied to skin temperature measurements from 12 human subjects. A random forest model trained on simulated thermoreceptor impulses could classify pleasure responses (F1-score of 67%) with low false positives/negatives (4%). Accuracy increased (83%) when excluding the few extreme (dis)pleasure responses. Validation on an independent dataset confirmed model reliability. This is the first empirical demonstration of the relationship between thermoreceptors and pleasure arising from thermal stimuli. Insights into the neurophysiology of thermal perception can enhance the experience of built environments through designs that promote sensory excitation instead of neutrality.

Cover page of Detailed measured air speed distribution in four commercial buildings with ceiling fans

Detailed measured air speed distribution in four commercial buildings with ceiling fans


The layout of ceiling fans in buildings is challenging because of the need to co-ordinate with other elements in the ceiling space, and because the resulting airflows within the occupied space interact with furniture. This study conducted detailed air speed measurements in four buildings with different room sizes, furniture configurations, ceiling fan types, and ceiling-fan-to-floor-area ratios. We measured air speeds across the occupied spaces at four heights while varying ceiling fan operation modes such as fan rotational speed, operating direction, and the number of operating fans. In total, we collected 207,080 air speed samples at 343 sites under 20 test conditions. This paper presents the magnitude and distribution of air speeds, cooling effects, and their influencing factors. The Airspeed Coverage Index (ACI= (Fan air speed (SF)× Fan diameter (D))/√(Average area served per ceiling fan (A))) describes the combined effects of multiple influencing factors on the magnitude of air speed. ACI is employed to predict the average air speed and occupant cooling effect, yielding regression confidences higher than 0.95. When designing a space to a target airspeed or cooling effect, the ACI can help to determine parameters such as fan density required for fan choices. The measured data are compared with predictions from the CBE fan tool that had been developed from laboratory tests under simplified conditions. The comparison displays the blocking effects of the furniture, lowering the average air movement in the space, as well as reducing the air movement at the ankle level while increasing it at higher heights. The blocking effect increases with the density of the furniture. We also visually present fan interactions in which triplets of fans are arranged linearly or diagonally, showing that the diagonal layout of ceiling fans increases average air speed and improves its uniformity.

Cover page of Field evaluation of thermal and acoustical comfort in eight North-American buildings using embedded radiant systems

Field evaluation of thermal and acoustical comfort in eight North-American buildings using embedded radiant systems


We performed a post-occupancy assessment based on 500 occupant surveys in eight buildings using embedded radiant heating and cooling systems. This study follows-up on a quantitative assessment of 60 office buildings that found radiant and all-air buildings have equal temperature and acoustic satisfaction with a tendency for increased temperature satisfaction in radiant buildings. Our objective was to investigate reasons of comfort and discomfort in the radiant buildings, and to relate these to building characteristics and operations strategies. The primary sources of thermal discomfort are lack of control over the thermal environment (both temperature and air movement) and slow system response, both of which were seen to be alleviated with fast-response adaptive opportunities such as operable windows and personal fans. There was no optimal radiant design or operation that maximized thermal comfort, and building operators were pleased with reduced repair and maintenance associated with radiant systems compared to all-air systems. Occupants reported low satisfaction with acoustics. This was primarily due to sound privacy issues in open-plan offices which may be exacerbated by highly reflective surfaces common in radiant spaces.

Cover page of Occupant satisfaction with the indoor environment in seven commercial buildings in Singapore

Occupant satisfaction with the indoor environment in seven commercial buildings in Singapore


Understanding occupants’ satisfaction with their environment is an important step to improve indoor environmental quality (IEQ). These satisfaction data are limited to Singaporean commercial buildings. We surveyed (N = 666) occupant satisfaction with 18 IEQ parameters in seven Green Mark certified air-conditioned commercial buildings in Singapore. About 78 % of the participants expressed satisfaction with their overall workspace environment. Occupants were most satisfied with flexibility of dress code (86 % satisfaction), electrical lighting (84 %) and cleanliness (82 %), and most dissatisfied with sound privacy (42 % dissatisfaction), personal control (32 %) and temperature (30 %). We found that satisfaction with cleanliness has the highest impact to overall workspace environment satisfaction. Our results suggest achieving high occupant satisfaction for some IEQ factors is harder than others, which suggests the premise of singular satisfaction rating (e.g., 80 %) that applies to all IEQ parameters may not be reliable and representative. We determined that the major contributors to thermal dissatisfaction were insufficient air movement and overcooled workspaces. Occupants in open plan office were unhappy with the noise produced by their nearby colleagues. We also found that several IEQ variables (odors, air movement, available space, overall privacy, sound privacy and temperature) which are not statistically significant to the overall workspace satisfaction on their own, but their impacts becomes substantial when these IEQ variables are merged into larger environmental factors (i.e., Perceived Air Quality, Acoustics, Layout and Thermal). These results can support the development of an IEQ benchmarks for commercial buildings in Singapore.

Cover page of Modeling solar radiation on a human body indoors by a novel mathematical model

Modeling solar radiation on a human body indoors by a novel mathematical model


Solar radiation affects occupant comfort and building energy consumption in ways that have received relatively little attention in environmental design and energy simulation. Direct, diffuse, and reflected irradiation on the body have warming effects that can be equated to increases in the mean radiant temperature (MRT) of the occupant’s surroundings. A simplified occupant-centered model (SolarCal Model, i.e., SC Model) has recently been adopted in ASHRAE Standard 55, followed by a comprehensive simulation procedure combining detailed room- and manikin geometries using the Daylight Coefficient Model (DC Model). This paper presents an intermediate-level mathematical model (the HNU Solar Model) capable of rapid annual calculations of the MRT increases. Both the room and occupant geometries are simplified but consistent with those of the SC Model. Novel strategies of the calculation include a sky-annulus fraction, virtual body shadow, and equivalent window. Modeled results are compared with those simulated by the DC Model using Radiance software, which is assumed to be accurate. The differences in the Delta MRT by diffuse, direct, and reflected solar radiation are usually less than 1, 2, and 0.5°C between the DC and HNU Solar Models, respectively. For a given occupant position indoors, the HNU Solar Model only needs five seconds to obtain the annual Delta MRT, while the DC Model needs about seven minutes. The HNU Solar Model provides a simple and practical way to evaluate indoor environments at the room scale, to design fenestration, and to predict set-point changes in annual energy simulation of HVAC systems.

Cover page of Skin Temperature Sampling Period for Longitudinal Thermal Comfort Studies

Skin Temperature Sampling Period for Longitudinal Thermal Comfort Studies


There is limited scientific evidence on what is the optimal sampling period to measure skin temperature in longitudinal thermal comfort studies, and how this sampling period selection affects the results. iButtons® are among the most widely used wireless sensors in field and lab studies to measure skin temperature, since they are accurate, reliable, and cause minimal discomfort. However, their use is significantly limited by their memory capacity. We aimed to determine what is the optimal sampling period of skin temperature in studies which use iButtons®. We measured wrist skin temperature of 14 participants at 60 s intervals for a period of 1 month and wrist temperature of 5 participants at 20 s intervals for a week. Results showed that the selection of a 300 s sampling period would provide reasonably accurate results while limiting the number of times data needs to be downloaded.

Cover page of Targeted occupant surveys: A novel method to effectively relate occupant feedback with environmental conditions

Targeted occupant surveys: A novel method to effectively relate occupant feedback with environmental conditions


Occupant satisfaction surveys are widely used in laboratory and field research studies of indoor environmental quality. Field studies pose several challenges because researchers usually have no control over the indoor environments experienced by building occupants, it is difficult to recruit and retain participants, and data collection methods can be cumbersome. With this in mind, we developed a survey platform that uses real-time feedback to send targeted occupant surveys (TOS) at specific indoor environmental conditions and stops sending survey requests when collected responses reach the maximum surveys required. We performed a pilot study of the TOS platform with occupants of a radiant heated and cooled building to target survey responses at 16 radiant slab surface (infrared) temperatures evenly distributed from 15 to 30 °C. We developed metrics and ideal datasets to compare the TOS platform against other occupant survey distribution methods. The results show that this novel method has a higher approximation to characteristics of an ideal dataset; 41% compared to 23%, 19%, and 12% of other datasets in previous field studies. Our TOS method minimizes the number of times occupants are surveyed and ensures a more complete and balanced dataset. This allows researchers to more efficiently and reliably collect subjective data for occupant satisfaction studies.

Cover page of Air-conditioning use behaviors when elevated air movement is available

Air-conditioning use behaviors when elevated air movement is available


Many experimental studies demonstrated that elevating indoor temperatures to 28 or 30°C is comfortable if fans are used, while this elevation often is not applied in practice. This study aims to investigate AC thermostat use behaviors when elevated air movement is available, as well as to provide insights at guiding occupants to select warmer environments without reducing their comfort. 20 subjects participated in a series of tests at three initial ambient temperatures (26, 28, and 30°C) with different settings of an AC thermostat and a ceiling fan: (1) a free-controlled thermostat without a fan, (2) a free-controlled thermostat with a free-controlled fan, (3) a free-controlled thermostat with an always-on fan (controllable but not allowed to turn off), (4) a limited thermostat (no lower than 28°C) with a free-controlled fan, and (5) a limited thermostat with an always-on fan. The results show that without the ceiling fan, subjects used AC to lower indoor temperatures to 25.7°C. When the fan was available (free-controlled), they did not only rely on lowering the AC set-point alone but also turned on the fan immediately when starting using AC. This behavior ended a final ambient temperature up to 27.4°C. Under always-on fan conditions, the fan was running at a high speed at the beginning of using AC. Although subjects turned down the fan speed, the final fan speeds were about doubled the speeds as compared with free-controlled fan conditions. This higher initial speed by the always-on fan made subjects select higher indoor temperatures: at the 28°C initial temperature, there was no further lowering of ambient temperatures; at the 30°C initial temperature, the final temperatures were 28.6 and 28.9°C for the free-controlled and limited AC test conditions, about a 3-K set-points extension compared with the no-fan condition. Further, despite different conditions, more than 90% of subjects had comfortable feelings, which indicates that people with adjustable AC prefer a constant thermal perception rather than a constant ambient temperature. Therefore, the strategy of using fans before AC should be adopted to guide people actively to select higher AC set-point temperatures.

Cover page of Improved long-term thermal comfort indices for continuous monitoring

Improved long-term thermal comfort indices for continuous monitoring


Thermal comfort standards have suggested a number of physical indices which can be calculated from either building simulations or in situ physical monitoring to assess the long-term thermal comfort of a space. However, the prohibitively high cost of sensor technologies has limited the applications of these physical indices, and their usefulness has never been established using data collected in real buildings. This paper is the first assessment of the six types of existing indices (23 total) found in standards and five types of new indices (36 total) and their correlation with the long-term thermal satisfaction of building occupants. Correlation analyses were based on continuous thermal comfort measurements and post-occupancy evaluation surveys from four air-conditioned office buildings in Sydney, Australia. We found that the majority of existing indices, especially those based on predicted mean vote (PMV) and predicted percentage dissatisfied (PPD) metrics, have a weak correlation with thermal satisfaction. The percentage of time outside a temperature range was the best-performing index from the standards (r=-0.63). A new index based on the percentage of time that daily temperature range is greater than a threshold reported the strongest correlation (r=-0.8) with thermal satisfaction for this dataset. The results suggest that occupants’ long-term thermal comfort is influenced more by pronounced excursions beyond some acceptable temperature range and large variations in daily temperature than the average experience over time. These findings support the use of continuous monitoring technologies for long-term thermal comfort evaluation and inform potential amendments of international thermal comfort standards.

Cover page of Prototyping Solutions to Improve Comfort and Enable HVAC Energy Savings

Prototyping Solutions to Improve Comfort and Enable HVAC Energy Savings


Digital and physical prototypes are commonly used across a broad range of industries for product development and user experience testing. Prototyping processes are also used in scientific research to generate ideas and test hypotheses. However, these creative activities receive less attention in research papers than the quantitative methods and findings. This paper describes a resourceful and iterative process of building, refining and testing a variety of ‘personal comfort devices’ that were used in a series of research studies in labs and in occupied non-residential buildings. The studies demonstrated that when building users have the ability to individualize their thermal environments, they can accept wider temperature ranges, potentially leading to reductions in HVAC energy consumption while also improving comfort. The devices tested include office chairs with battery-powered heating and cooling, IoT-connected desk fans and low-energy heating devices. This paper describes the ‘scrappy’ prototyping work that enabled this research, placing it within a context of prototyping theory. Without the highly developed prototypes created by the researchers, it would not have been possible to make the quantitative changes to building standards that are needed to influence practice.