Center for the Built Environment

Far-UVC (222 nm) irradiation effectively inactivates airborne pathogens, but photolyzes oxygen to generate ozone, potentially initiating indoor chemistry that may form secondary pollutants. To evaluate these impacts in a realistic setting, we conducted experiments in a full-scale (158 m3) office chamber. The study involved 13 sessions with human subjects (n=4–8) under typical mechanical ventilation (0.7–0.8 h⁻¹). We monitored ozone, ultrafine particles, and nitrogen oxides, and took time-integrated volatile organic compounds (VOCs) samples before and after the lamps on. We found that while far-UVC operation increased ozone concentrations, the elevation in the occupied room was modest (median increase 1.44 ppb). We didn’t observe discernible secondary aerosol and VOCs formation. Participant surveys indicated that air quality remained acceptable throughout the experiments. These results suggest that in ventilated, occupied offices, far-UVC can be deployed with minimal impact on chemical indoor air quality.

This poster, presented at the 2026 CEC EPRI Electrification Summit, details an ongoing project (Grant Award #: EPC-23-033) aimed at mainstreaming Personal Comfort Devices (PCDs) to provide targeted occupant comfort and reduce HVAC energy and emissions in large commercial buildings. The research focuses on developing a "Personal Control Ecosystem" centered on a Personal Control Hub (PC Hub), an open-source hub built on an ESP32 microcontroller with integrated sensors for occupancy, temperature, humidity, PM2.5, CO2, and VOCs. Novel PCDs developed include a nanofabric handwarmer using nanotube material and a heated/cooled desktop pad for wrist comfort. Integration strategies with Building Management Systems (BMS) utilize networking (BACnet) and semantic layers (Brick or ASHRAE 223) to facilitate load shifting and widened temperature deadbands. Field study results indicate that using PCDs can maintain equivalent comfort while achieving over 30% savings in heating energy by lowering setpoints. The project includes the creation of a web-based PCD Design Guidebook for HVAC engineers and real estate managers to specify PCDs for diverse use cases, ranging from "Rogue Zones" to demand response signals.

This study examines how personal comfort systems (PCS) support thermal adaptation among adults with intellectual disabilities living in energy-poor households in Chile. Participants (n = 8) in two identical social-housing units completed two in-home field campaigns: winter (June–August 2023; 10 weeks) and summer (December 2023–March 2024; 14 weeks). The study combined an adapted daily point-in-time thermal comfort questionnaire, continuous indoor dry-bulb temperature monitoring (15 min), and pre-/post-season interviews. Indoor conditions frequently fell outside reference comfort thresholds (92.6% of winter temperatures < 21.5°C; 64.1% of summer temperatures > 26°C). Using participant-level paired comparisons with thermal preference ‘No change’ as a comfort proxy, PCS use showed no systematic winter increase (median Δ = –0.014; p = 0.944) but a consistent summer increase (median Δ = 0.126; p = 0.014). Interview accounts indicated that PCS supported everyday adaptation, while operability and access constraints sometimes limited independent use. Findings highlight the potential of inclusive PCS to improve perceived comfort under summer heat stress, alongside the need for complementary building-level measures to reduce thermal exposure in vulnerable housing.

Air mixing and movement are often driven by the design and operating conditions of the heating, ventilation, and air conditioning (HVAC) system, and are influenced by occupants and thermal gradients at windows and walls. Air mixing affects the indoor-generated pollutants dispersion and thus influences the effectiveness of ventilation and within-room air cleaning systems, including upper-room germicidal ultraviolet disinfection (GUV). In rooms with a ceiling exhaust and/or upper-room GUV, upward airflow from occupants can enable faster pollutant removal compared to well-mixed conditions. We used pulsed ethanol as a tracer and measured concentration at 2 s time resolution using fast-response metal oxide sensors at three levels: near the floor at 0.1–0.4 m, mid-height at 1.1–1.4 m, and at 2.4 m, 0.3 m from the 2.74 m ceiling. Forty experiments were conducted under the following conditions: HVAC off; supply air at ~380 (low) or ~1200 m3 h-1 (high) at neutral, cooling, or heating temperatures with 20% or 100% outdoor air; and added mixing fans. Air mixing times were determined from the start of ethanol release until the relative standard deviation of the concentrations fell below 20%, indicating an approximately well-mixed condition. We found that the air mixing time was longest with the HVAC off (15.1–15.4 min), followed by conditions with a low total supply airflow rate at all temperatures (6.6–11.4 min under heating; 5.6–10.1 min under neutral/cooling), and was fastest under high airflow at neutral/cooling temperatures (2.9–5.6 min) or when mixing fans were added (1.9–4.8 min). The outdoor airflow rate (20% or 100%) did not significantly affect spatial heterogeneity or air mixing time. Long air mixing times resulted in high spatial variability of absolute integrated concentrations and relative exposures. Under slow mixing conditions (HVAC off or low airflow rate) and with releases associated with heaters simulating occupants, several upper or mid-level sensors peaked after the release, and mixing into the upper room and occupied space was slow. Under fast mixing conditions (high airflow rate with neutral/cooling settings or added fan), air reached and mixed in the upper room more quickly and spread faster in the occupied zone.

The quality of window views influences building occupants’ well-being, yet little is known about what constitutes high view quality. We investigated eight factors: number of layers visible, presence of nature, object-to-glazing distance, observer proxy, window-to-wall ratio, horizontal and vertical view angles, and blind position. We conducted a human subject experiment in which 69 participants each evaluated 15 window views and rated their satisfaction. Views with equal to or more than 35% greenery or sky and unobstructed clear glazing were strongly associated with higher satisfaction. Blind position emerged as a key moderator, shaping how other factors influenced view quality. Under clear glazing, increasing the proportion of nature elements and extending the distance of visible objects from the glazing significantly improved satisfaction. However, when blinds were lowered, these changes offered no benefit. We also found that compliance with the LEED Quality Views guideline meaningfully increased satisfaction, particularly the requirement for unobstructed glazing. Based on these findings, we propose revisions to strengthen the current guidelines by establishing a baseline condition using the ratio of nature in the view and the horizontal and vertical view angles, along with threshold combinations involving the distance between outside objects and the glazing, the observer’s distance to the window, and the blind condition.

Intermittent cooling, characterized by the on-off cycling of air-conditioning systems, generates a non-steady-state indoor thermal environment. While widely adopted for energy conservation, its impact on human thermophysiological and perceptual dynamics remains insufficiently understood. To investigate this, we conducted chamber experiments in a simulated residential/office space using three cooling set-points (thermostat target temperature: 28 °C, 26 °C, and 20 °C). Each trial involved 70 minutes of active cooling followed by 50 minutes of shutdown. We continuously monitored indoor air temperature, skin temperature, blood pressure, heart rate, and subjective thermal responses from 12 participants throughout each cycle. Results show that cold exposure intensity significantly shaped the temporal dynamics of human thermal response. Under strong cooling (20 °C), skin temperature declined continuously without stabilization over 70 minutes, thermal sensation and acceptability remained unstable until 35 - 40 minutes, and cardiovascular responses (e.g., DBP, HR) were only activated after prolonged exposure, stabilizing after > 50  minutes. In contrast, moderate and weak cooling (26 - 28 °C) enabled most physiological and perceptual responses to stabilize within 15 - 25 minutes. Asynchronous was observed among systems: skin temperature stabilized earliest, followed by perceptual responses, while cardiovascular regulation remained notably delayed under stronger cooling. After AC shutdown, overall recovery occurred within 35  minutes transitional timeframe, during which the effects of residual cold exposure continued to influence thermal perception and physiology. Based on these findings, we propose a theoretical framework for a “Cumulative Thermal Stimulus (CTSI)” index that integrates thermal deviation and exposure duration, offering a quantitative tool for adaptive cooling strategies that optimize comfort, health, and energy efficiency.

This case study summarizes our efforts to optimize speech intelligibility in a medium-sized lecture hall. In addition to describing the acoustical design, we also interpret the results of our acoustical measurements. Speech intelligibility in the hall was assessed both subjectively and objectively using natural as well as amplified speech. We determined that natural speech could be clearly understood at the rear of the hall (about 50 feet from the speaker) without electronic amplification. Thus, one of our design goals was achieved. Adding sound-absorbing materials on the ceiling and selected walls reduced the reverberation time to 0.4 seconds, thereby meeting a project design goal. Due to the distributed sound absorption and low background noise level, exceptional speech intelligibility has been achieved in the room.

Radiant cooling panels are an energy-efficient heating, ventilation, and air conditioning (HVAC) alternative to conventional all-air systems, as they operate with higher chilled water temperatures and rely on water as the primary heat transfer medium. However, their wider adoption has been constrained by the risk of surface condensation, which limits allowable surface temperatures and reduces cooling capacity. Elevated air movement, such as that induced by ceiling fans, has been proposed as a strategy to enhance cooling capacity and maintain thermal comfort, yet its impact on condensation behavior remains insufficiently understood, particularly under conditions where panel surfaces operate below the dew point. This study employs transient computational fluid dynamics (CFD) simulations using the interThermalPhaseChangeFoam solver in OpenFOAM to investigate the effects of air speed on condensation phenomena over a uniformly cooled radiant panel. A simplified numerical wind tunnel containing a small-scale radiant panel element is simulated to isolate airflow effects on phase change behavior with air temperatures of 22-27 °C, relative humidity levels of 50-60%, air velocities ranging from 0-3 m/s, and panel surface temperatures set 0.5-2.0 °C below the dew point. The analysis focuses on steady-state phase change heat flux and equivalent water thickness on the panel surface. Results show that increasing subcooling temperature (defined as the difference between the panel surface temperature and the dew-point temperature of the surrounding air) consistently increases both phase change heat and equivalent water thickness. In contrast, the influence of air speed on phase change heat is strongly dependent on subcooling level, exhibiting non-monotonic behavior at higher subcooling conditions. Meanwhile, the equivalent water thickness decreases monotonically with increasing air velocity across all cases, indicating enhanced removal of condensed water by airflow. These findings demonstrate that condensation risk cannot be assessed using a single metric alone and highlight the importance of jointly considering latent heat transfer and surface water retention. The results further suggest that, under appropriate subcooling and airflow conditions, elevated air movement may enable increased cooling capacity while mitigating practical condensation risks in radiant cooling applications.

Industrial workers in hot and humid environments are vulnerable to heat stress, especially in facilities where mechanical cooling can be expensive and/or impractical to install and operate. We assessed whether air movement from fans can effectively reduce heat strain and improve thermal comfort in an un-airconditioned manufacturing facility in Baton Rouge, (Louisiana, USA). Over six weeks, thirty workers were monitored under alternating fan-on and fan-off conditions. Physiological, environmental, and survey data were collected to evaluate comfort, perceived performance, thermal stress and physiological strain. Results show that fans significantly reduced discomfort and the level of perceived effort equivalent to a 5°C reduction in temperature. All the workers stated that having fans in the workplace was important to them and 79% felt that they were more effective at their job with the fans running. Sublingual temperature, heart rate and sweat rate increased with ambient temperature, but did not differ with or without the electric fans. These findings show that air movement offers a low-cost, energy-efficient and effective strategy to mitigate worker discomfort and perceived level of effort and it does not worsen physiological indicators of heat stress in hot manufacturing environments.

The recently completed IEA Annex 69 (Strategy and Practice of Adaptive Thermal Comfort in Low Energy Buildings) identified mixed-mode (MM) building design and operation as key strategies for the buildings sector in its transition towards a low-carbon mode. Mixed-mode is short-hand for naturally ventilated designs with supplemental air-conditioning that can be called upon whenever and wherever external climatic loads and/or internal loads dictate. Success of the MM strategy requires shifting the sector’s concept of thermal comfort away from a static comfort zone towards an adaptive approach in which the indoor comfort zone drifts in the same direction as external weather and seasonal trends. The potential for mixed-mode design arises from its applicability in both new construction and existing building stock. The objective of this paper is to elevate awareness of the mixed-mode design concept within the building sector and related research communities. Furthermore, it aspires to influence international thermal comfort standards and guidelines, advocating for a more explicit endorsement of adaptive thermal comfort in mixed-mode applications. Towards this end, we address ten critical questions concerning the application of adaptive thermal comfort in mixed-mode buildings. The questions elucidate the fundamental aspects of MM buildings, the role of adaptive thermal comfort, and the broader implications for building design and operation.