Air-conditioned Office Research Articles

Simulation and optimization of night cooling with diffuse ceiling ventilation and mixing ventilation in a cold climate

Accurate convective heat transfer coefficient (CHTC) is crucial to assess the night ventilation performance accurately. Previous experimental studies proposed CHTC correlations tailored for night cooling with diffuse ceiling ventilation (DCV) and mixing ventilation (MV). A holistic approach integrating the building energy simulation and optimization method was put forward to validate the experimentally proposed correlations, simulate and optimize the performance of night cooling with DCV and MV. The validation results demonstrated that the proposed correlations predicted the surface temperatures accurately with a maximum mean absolute error of 1.9 °C. For a typical air-conditioned office room, night cooling with DCV saved about 0.2 kWh/m2 total cooling energy per unit floor area (TCEC) more and provided a lower average predicted percentage of dissatisfied during the working hours (aPPD) by up to 3.1% than that with MV. Compared with the validated correlations, the empirical ceiling diffuser convection algorithm overestimated the night energy-saving potential by up to 0.5 kWh/m2 (13.8%) and yielded a maximum difference in the aPPD of 1.5%. Optimization significantly saved TCEC by 1.1 kWh/m2 (29.0%) for DCV and 0.9 kWh/m2 (25.7%) for MV while maintaining the aPPD within 10%, compared to respective base cases.

Impacts of Air-Conditioning Equipment Sizing on Energy Performance of US Office Buildings

Abstract The paper summarizes the results of systematic and comprehensive analysis to investigate the impacts of inadequate sizing air-conditioning (AC) systems on the overall energy consumption of medium and large office buildings located in representative US cities. The effects of proper sizing on the overall and disaggregated AC systems are evaluated in terms of energy consumption, peak demand, equipment run-time, and indoor thermal comfort. The presented analysis covers the performance of a wide range of AC equipment components that serve US office buildings including packaged rooftop units as well as central cooling plants. The analysis results indicate that oversizing penalties can be significant on the annual energy consumption and electrical peak demand as well as capital costs for both medium and large office buildings. In particular, the reliance on simplified calculation methods and rules-of-thumb to determine equipment capacities can lead to significantly oversizing AC systems for office buildings in the vast majority of US climates. The analysis results indicate that 50% oversizing of AC systems can result in increases in annual energy consumption of up to 91% for large offices and 39% for medium office. Moreover, oversizing increases capital costs required for air-conditioning office buildings and extends cycling periods and associated structural stresses and failures of AC equipment.

Simple method to improve the TCXDVN 306:2004 indoor climate standard for closed office workplaces in Vietnam

Thermal comfort is an important parameter of indoor climate, which affects office worker health and productivity, and also aids planning for energy efficient building design and operation. To provide satisfactory thermal comfort in office workplaces under hot and humid outdoor conditions, most contemporary office buildings in Vietnam are fitted with ducted air-conditioning systems. The current Vietnamese standard TCXDVN 306:2004 for indoor climate was derived from thermal comfort research conducted between the 1960s and 1980s. This standard is limited by various drawbacks, including no distinction between natural or artificial environments. In response, this 2018 research provides physical measurements and opinion surveys of current indoor climatic conditions in representative office workplaces in three regions of Vietnam: North, Central and South. The measurement results have been transformed into ET, PMV and PPD indicators, which value demonstrate the shortcomings of the TCXDVN 306:2004 standard, while providing a baseline input for updating this standard to meet the thermal comfort needs of air-conditioned office workplaces, based on the concept of probability comfort, which are integral with the ISO and the ASHRAE standard.

Field study on occupants’ subjective symptoms attributed to overcooled environments in air-conditioned offices in hot and humid climates of Asia

Indoor thermal environments in various offices in hot and humid climate regions of Asia are overcooled by air conditioning (AC) systems. Overcooled environments affect the occupants’ health and lead to excessive energy consumption. This study aims to clarify the association of occupants’ subjective symptoms with indoor thermal environments through field surveys conducted in Thailand, Indonesia, and Singapore. Indoor thermal measurement and thermal comfort surveys, including a questionnaire about thermal sensation and subjective symptoms, were conducted, targeting 599 occupants in 11 offices. The results showed that the mean indoor operative temperatures (Top) for all cities were lower than 24°C. More than half of the occupants wore light clothing ensembles (0.30–0.59 clo). Therefore, 42.6% of the occupants’ calculated predicted mean vote (PMV) was less than −0.5. The correlation between indoor temperatures and the actual percentage of occupants who reported subjective symptoms (APSS) was analyzed. The lower Top and standard new effective temperature (SET*), the more APSS was increased. In each temperature category of below 24.5°C, more than 30% of occupants reported subjective symptoms related to coldness. Therefore, the findings from this study suggest that raising Top higher than 24.5°C is a first step to minimize the harmful effects of the cooling environments on the occupants’ health in this region. As the number of samples in the higher temperature range was insufficient in this study, further experiments in actual offices are necessary to verify the reduction of occupants who report subjective symptoms while raising the setpoint temperature.

Assessment of Thermal Comfort and Building-Related Symptoms in Air-Conditioned Offices in Tropical Regions: A Case Study in Singapore and Thailand

Indoor thermal environment is important for maintaining comfort and health. In a tropical region, it becomes more critical when the air-conditioning system consumes excessive energy for a whole year. This study aims to clarify the impact of thermal environment on human comfort and building-related symptoms in air-conditioned offices. A field study was conducted in office spaces in Singapore and Thailand from 2017 to 2019 by installing data loggers to measure thermal variables together with a questionnaire survey. As a result, the psychometric charts of ASHRAE 55 show that most of the measured thermal environments were fitted to the 1.0 clo comfort zone, which was not recommended for people in this region. Overcooling determined the cause of high discomfort when people felt cold and preferred a warmer temperature. Based on Griffith’s method, average comfort temperatures were 24.8 °C (Singapore) and 24.0 °C (Thailand). The probit analysis illustrated that the comfort temperature range for a dissatisfaction of 20% was 23.6–26.4 °C (Singapore) and 22.9–25.6 °C (Thailand). These comfort temperature ranges which were higher than the measured values reflected the clothing adaptation and the personal complaints. Symptoms were reported in the coldest temperature group (21–22 °C), with the highest odds ratio of symptom occurrence. The thermal sensation vote defined that the higher rate of symptoms belonged to the colder-than-neutral side, whereas the thermal comfort vote could not well predict the symptom occurrence. The intention of enhancing comfort and promoting better health conditions in the offices of these regions was discussed, while considering warmer indoor temperatures.

Evaluation of thermal comfort in an office building in the humid tropical climate of Benin

Benin, like most West African countries, is confronted with the lack of indoor thermal comfort standards adapted to the realities of the region. This situation leads to the adoption of Western comfort standards, the consequences of which can be seen in the discomfort of building occupants and above all in significant energy losses. This justifies the need to identify, among the many comfort models developed in the literature, those that are better adapted to the evaluation of thermal comfort in buildings in Benin. Thus, after a literature review on the subject, two comfort models were found to be relevant for the assessment of thermal comfort in air-conditioned buildings in hot and humid regions. These are the adaptive models of López-Pérez and al. and Indraganti and al. The application of these two models on an air-conditioned office building located in the city of Cotonou in southern Benin, resulted in comfort temperatures of 26.1°Cand 26°Crespectively. These values, very close to the average neutral temperature of the occupants (26.1°C), reveal the effectiveness of these adaptive models in assessing thermal comfort in the said building. Moreover, the application of Fanger's static model (PMV) and hybrid models (aPMV and PMVnew) has shown that the PMVand aPMVof Yao and al. underestimate the adaptability of the occupants to relatively high comfort temperatures while the PMVnewof Olissan and al. overestimates this adaptability.

Impact assessment of window to wall ratio on energy consumption of an office building of subtropical monsoon climatic country Bangladesh

Building’s window-to-wall ratio (WWR) plays a significant role for predicting energy consumption in tropical climate because huge amount of solar heat gain occurs through the exterior windows for having high solar radiation intensity and annual average temperature in tropical climatic regions. This study investigates the impact of WWR on energy consumption of air-conditioned office buildings in subtropical monsoon climatic country Bangladesh. This research was conducted through rigorous energy simulation perspective by developing a two storey prototype office building in a validated energy simulation tool eQUEST. Around 216 design alternatives were developed for simulation considering eight major cities of Bangladesh, WWR percentage from 10% to 80%, wall thickness, thermal insulation thickness, shading height and window orientations. A comprehensive data analysis was performed to predict the optimum range of WWR percentage for the air-conditioned office buildings. This research suggests a range of WWR that 30% to 40% is the optimum range for the air-conditioned office buildings in Bangladesh. An existing office building was able to save about 9.40% percent of electricity by incorporating optimum percentage of WWR. The output of this work can be incorporated into Bangladesh National Building Code as energy efficient strategies for designing an air-conditioned office building.

An integrated approach to evaluate thermal comfort in air-conditioned large-space office

With the continuous promotion of urbanization, numerous large-scale public buildings appear in cities. With the characteristics of large floor area and high personnel density, creating a thermally comfortable environment is a significant task for large-scale buildings. However, an uneven thermal environment is usually detected in large-scale spaces, indicating that some areas are overcooled while some lack cooling. Meanwhile, this nonuniform environment causes discomfort to occupants. This study proposes an integrated approach to investigating the thermal status of a large-space office based on the PMV-PPD thermal comfort model. This combined method not only provides an insight into the spatial distributions of indoor environmental parameters, such as air temperature, air velocity, and mean radiant temperature, but calculates the spatial distribution of PMV index. The spatial profiles of thermal comfort index reveal that PMV values are lower than −0.5 in the middle area and higher than 0.5 in the side areas. Such spatial distributions of PMV values mean that occupants feel either cold or warm within the target space. Thus, the integrated method offers a comprehensive evaluation approach for the indoor environment of a large-space office. Furthermore, for ways to avoid a nonuniform thermal environment, possible causes of the uneven thermal environment and feasible suggestions are discussed, providing useful guidance for design and operation of HVAC in large-space buildings.

Application of phase change materials, thermal insulation, and external shading for thermal comfort improvement and cooling energy demand reduction in an office building under different coastal tropical climates

Architectural techniques have evolved over the century. Presently, climatic conditions require architecture that is more adaptable to the environment. Coastal regions have been recognised to be the most vulnerable to the effects of climate change. Thus far, limited research has offered some strategies to mitigate the solar effect on thermal comfort and energy demand in coastal tropical regions. To address this problem, this study was conducted with the aim of evaluating, analysing, comparing, and discussing the impacts of passive strategies on thermal comfort and energy consumption (as well as the introduction of photovoltaic panels) in coastal tropical climate regions. All simulations were conducted for a period of one year using the Design Builder software. The results demonstrate that phase change materials (PCMs) have a significant effect on thermal comfort and energy consumption in an office under different coastal tropical climates. The combination of PCMs with thermal insulation has the ability to increase the comfort rate by up to 3% while decreasing the cooling energy consumption by approximately 12% in three studied climate zones. In a naturally ventilated building, the most significant increase in the comfort rate is observed with the introduction of PCMs in combination with thermal insulation, whereas thermal insulation, along with external shading, results in the most significant reduction in the cooling energy consumption of an air-conditioned office building (approximately 19%) in three studied climates. Furthermore, the introduction of photovoltaic panels enables us to generate 43–79% of the total energy consumption of the studied office building.

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.

Experimental Study on Thermal Comfort Towards Increasing Temperature Set-Points in Air-Conditioned Office Spaces in a Tropical Region: A Case Study in Thailand

Many countries propose indoor temperature set-points of air-conditioned offices to be comfortably sustainable and to reduce energy consumption. Even though there are recommendations for the optimum temperatureset-points, it is questionable how those values could be applied to the actual situation in a tropical region. This study aims to survey thermal performance and estimate thermal comfort in different set-points. In 2019, two air-conditioned office buildings were tested by increasing set-points from the actual value between 23 °C and 25 °C. Data loggers measuring thermal variables were installed in the offices and the questionnaire was distributed to evaluate human response. Considering the ASHRAE psychometric chart, thermal environments of both cases on the day of a normal set-point were low; falling inside in the 1.0 clo zone. Thermal environments gradually moved from the 1.0 clo zone to the 0.5 clo zone, however, some of them were out of both comfort zones due to high absolute humidity. The predicted mean vote (PMV) and the thermal sensation vote (TSV) show that the votes changed from the cold side to the neutral side, and the higher acceptance rate was at warmer temperatures. The comfort temperature calculated from Griffith’s method was found to be 23.6–25.1 °C which was lower than the measured operative temperature. Adaptive clothing behavior is described to confirm a better condition at warmer temperatures. A possibility of increasing cooling set-points at 24–25 °C is applicable to office buildings in the tropics to remain comfortable.

Integration of Energy Efficiency measures and Renewable Energy technologies as an Approach to Sustainable development in Egypt

Energy demand has been increasing worldwide and the building sector represents a large percentage of global Energy consumption. This is directly related to increasing global warming. In Egypt, electricity consumption is increasing rapidly due to the rapid population growth, urbanization, economical development and increase in comfort levels. To solve the Energy problems, efforts need to be concentrated on the supply side, and the demand side as well. Energy efficiency is becoming an integral and important part of solving the Energy problem at the demand side. On the other hand, Renewable Energy technologies are promising as a solution at the supply side. Thus there is a need for integrated, adaptive, approach to reach the optimal combination of applying energy efficiency measures and Renewable Energy sources. In this paper the energy related policies of Egypt have been presented. The present status of renewable energy utilization in Egypt has been discussed as well. The research introduces and examines the effect of combining Energy Efficiency measures with photovoltaic rooftop application in an air-conditioned office building in Egypt. Annual Energy reductions and Annual energy production due to the PV roof top installation was calculated by means of Energy Plus, a reliable Energy simulation software.The energy requirements for cooling, and lighting was evaluated as well. It was proven that Reductions in Annual Energy Consumption reached about 48 % due to applying Energy Effeciency measures.The Annual electricity production due to the installation of 900 m2 PV Panels on the building roof coverd about 40% from the building Energy consumption. This demonstrates that it is technically possible to meet more than 60% reductions in building Energy consumption with the proper combination between Energy Efficiency measures and RE sources.

PM2.5 exposure of various microenvironments in a community: Characteristics and applications

While the measurement of particulate matter (PM) with a diameter of less than 2.5 μm (PM2.5) has been conducted for personal exposure assessment, it remains unclear how models that integrate microenvironmental levels with resolved activity and location information predict personal exposure to PM. We comprehensively investigated PM2.5 concentrations in various microenvironments and estimated personal exposure stratified by the microenvironment. A variety of microenvironments (>200 places and locations, divided into 23 components according to indoor, outdoor, and transit modes) in a community were selected to characterize PM2.5 concentrations. Infiltration factors calculated from microenvironmental/central-site station (M/S) monitoring campaigns with time-activity patterns were used to estimate time-weighted exposure to PM2.5 for university students. We evaluated exposures using a four-stage modeling approach and quantified the performance of each component. It was found that the SidePak monitor overestimated the concentration by 3.5 times as compared with the filter-based measurements. Higher mean concentrations of PM2.5 were observed in the Taoist temple and night market microenvironments; in contrast, lower concentrations were observed in air-conditioned offices and car microenvironments. While the exposure model incorporating detailed time-location information and infiltration factors achieved the highest prediction (R2 = 0.49) of personal exposure to PM2.5, the use of indoor, outdoor, and transit components for modeling also generated a consistent result (R2 = 0.44).

Association between microenvironment air quality and cardiovascular health outcomes.

Exposure to fine particulate matter (PM2.5) is associated with cardiovascular disease risk. To date, there are few studies on short-term PM2.5 exposure in different microenvironments and its impact on immediate health effects, particularly in the Southeast Asia region. This study assessed PM2.5 concentrations in different microenvironments in a densely populated city in the tropics using low-cost personal PM2.5 sensors as well as their associations with acute cardiovascular health outcomes. A total of 49 adult participants affiliated with the National University of Singapore (NUS) community were recruited. Personal low-cost sensors were used to measure PM2.5 concentrations between September 2017 and March 2019. Demographic information and time-activity patterns were collected using questionnaires. Wilcoxon pairwise comparisons were used to determine statistical differences between PM2.5 exposures at 18 different microenvironments. Generalized Estimating Equations (GEE) models were used to assess the association between PM2.5 exposure and blood pressure as well as heart rate. All models were adjusted for age, sex, body mass index, physical activity, temperature, duration of exposure, and baseline cardiovascular parameters. Significant differences in PM2.5 concentrations were observed across different microenvironments. Air-conditioned offices and tertiary teaching spaces had the lowest (median=13.1μg/m3) and hawker centres had the highest (median=32.0μg/m3) PM2.5 concentrations. Significant positive associations between PM2.5 exposure and heart rate (β=0.40, p=4.6×10-5) as well as diastolic blood pressure (β=0.16, p=0.0077) were also observed. Short-term exposure to PM2.5 was significantly associated with higher heart rate and blood pressure. Further work is needed to investigate the variations within each type of microenvironment and expand the study to other sub-populations such as the elderly and children.

Exploiting the Advantages of Molecular Tools for the Monitoring of Fungal Indoor Air Contamination: First Detection of Exophiala jeanselmei in Indoor Air of Air-Conditioned Offices.

Today, indoor air pollution is considered a public health issue. Among the impacting pollutants, indoor airborne fungi are increasingly highlighted. Most of the monitoring protocols are culture-based, but these are unable to detect the uncultivable and/or dead fraction or species suppressed by fast-growing fungi, even though this fraction could impact health. Among the contaminants suspected to be part of this fraction, Exophiala jeanselmei is an interesting case study. Known to be pathogenic, this black yeast grows in humid environments such as air-conditioning systems, where it has been previously detected using classical culture-based methods. However, until now, this fungus was never detected in indoor air in contact with these air-conditioning systems. This study shows the first detection of E. jeanselmei in indoor air collected from offices in contact with contaminated air-conditioning reservoirs. While its presence in indoor air could not be demonstrated with culture-based methods, it was found by real-time PCR and massive parallel sequencing. The latter also allowed obtaining a broader view on the fungal diversity in the tested samples. Similar approaches were applied on water samples collected from the conditioning reservoirs to trace the source of contamination. The comparison of results obtained with both methods confirmed that the molecular tools could improve indoor air monitoring, especially of dead and/or uncultivable contaminants or when competition between species could occur.

Analysis of indoor environment condition towards thermal comfort level in an air-conditioning office building

Office workers spend most of their time indoor with average of eight hours spent inside the office buildings. Therefore, the indoor environment condition will be one of the factors contributing to comfort level inside the building. Since air conditioning system is commonly used to maintain the indoor condition, the selection of appropriate and right capacity of the system is crucial. The purpose of this work is to conduct an analysis of the indoor environment condition towards the thermal comfort level inside office building. The case study building for this study is the Chancellery Building of Universiti Teknikal Malaysia Melaka (UTeM) which is installed with the central air-conditioning system. The thermal condition was measured by using the thermal microclimate instrument. The parameters involved in this study include air temperature and humidity. Based on the data measurement, the temperatures were range between 25.7 °C to 26.2 °C while the humidity recorded is between 68.1% to 70%. Comparing with ASHRAE Standards 55 and ASHRAE Standards 62.1 the thermal and humidity condition fall outside of the comfort range.

Formaldehyde monitoring in office buildings located in tropical climates of India

Indoor air pollution is a result of complex phenomenon that occurs due to constantly changing interaction of various indoor and outdoor environmental factors. Volatile Organic Compounds (VOCs) are the major pollutants in air conditioned indoors, perhaps having a large subset of hazardous compounds. In this study, formaldehyde (HCHO) was monitored at 30 minute interval using portable photoelectric absorptiometric sensors along with comfort parameters like air temperature, relative humidity and air flow rate at six newly constructed or renovated office buildings located in composite, temperate and warm-humid climatic zones (in various parts of India). Results show that formaldehyde emissions exceeded the limits suggested by LEED guidelines (27 ppb) in all the buildings except in the ones where low emitting green interiors were used. Furniture and interior decorative work were found to be the primary sources of formaldehyde emission than other parameters. A logarithmic relationship (R2=0.65) was established between HCHO and respective age of the building/refurbished time. The analysis also presents that in a scenario of green interiors (low HCHO concentration) and the humidity levels above 60%, the trend of HCHO concentration with indoor moisture exhibits certain time delays in reaching equilibrium due to slow conditioning of HCHO molecules and indoor moisture. The study provides a rational analysis on HCHO emissions in Indian office buildings, which is important to understand possible sources and their effects on HCHO concentration in office indoors. The study data helps to implement required measures to control indoor humidity levels or necessary HCHO mitigation strategies during design and operation process of the air-conditioned office buildings.

Occupant perceptions on the thermal comfort guidelines in air-conditioned offices in Colombo, Sri Lanka

ASHRAE Standard 55 sets the minimum requirements for thermal comfort in built environments. However, this standard is more appropriate to cold climates of the western countries than to hot climates of the tropical countries like Sri Lanka. This research was conducted to investigate the thermal comfort perceptions of the occupants of air-conditioned office environments located in hot and humid regions using a case study conducted in office environments in Colombo in Sri Lanka. A mixed research approach was used in two phases to collect the required data. Phase 1 which had ten expert interviews was followed by Phase 2 which had a questionnaire survey conducted among 144 individuals working in 36 air conditioned offices. The data collected were analysed using NVivo and SPSS software. Six parameters, namely temperature, humidity, air velocity, mean radiant temperature, average metabolic rate and average clothing level of each of the 36 office environments considered were examined for their compliance with ASHRAE Standard 55. Six of the environments did not comply with the thermal comfort range specified in the ASHRAE Standard.

Thermal Adaptive Behavior of Occupants in Air-conditioned Office Buildings in Thailand

Thermal adaptive behaviors are the actions people take to adjust to the indoor environment. This study aims to clarify occupants’ perception of thermal environments and how they adapt themselves into those environments of air-conditioned offices in the tropical region. Six offices in Bangkok, Thailand, were investigated during April to September 2018. Indoor environment quality measuring devices were installed inside the offices to evaluate factors such as indoor temperature, humidity, and air velocity. Questionnaires following the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 55 standard were distributed to occupants during working hours. Thermal comfort votes were analyzed together with behavioral adaptation votes. When we plotted thermal environment values on a psychrometric chart, they were inside 1.0 clo rather than 0.5 clo. Out of 2, 028 samples, 50.2 % of occupants voted neutral. However, they felt colder than neutral rather than feeling warmer than neutral (36 %:14 %). Occupants who felt comfortable were 45% of total occupants, and 59.7% of them preferred “no change”. Considering adaptive behavior, the highest activity was changing of clothes (50%). Those who wore more clothing (68.9 %) voted for feeling slightly cool to cold. Of those, 34% changed clothing during the day. The median of clothing increased from 0.56 clo to 0.61 clo to reduce the feeling-cold sensation and increase thermal neutrality. Other adaptive behaviors were drinking hot or cold water (31.3%), doing nothing (26.2%), moving around (24.5%), wearing a scarf (14.7%), using a pedestal fan (11.8%), taking a rest (8.6%), washing hands or face (8%), and opening or closing window blinds (7.7%). These adaptive behaviors were strongly relevant to thermal sensation votes and maintaining thermal comfort. These adaptive actions were adopted by both the feeling-hot persons and the feeling-cold persons. This study would be applicable to offices in Thailand in terms of both thermal satisfaction and human behavior.

Field study on thermal comfort and energy saving potential in 11 split air-conditioned office buildings in Changsha, China

All existing thermal comfort standards are applicable to naturally ventilated buildings and air-conditioned buildings, except mixed-mode buildings. Split air-conditioned buildings, as a type of mixed-mode buildings, account for a large proportion of current buildings. It is urgent to explore the applicability of thermal comfort standards and determine the energy saving potential in split air-conditioned buildings. In this research, the authors conducted a field study in Changsha, China. Eleven split air-conditioned office buildings were investigated from July to September 2016. 442 valid data sets were obtained. The results indicated that occupants preferred a “cooler” temperature of 26 °C, 0.6°Clower than neutral temperature of 26.7 °C. Occupants have adapted to thermal environment and accepted higher temperature than that predicted by PPD. 95% of occupants were satisfied with the thermal environment. Compared to PMV model, the adaptive model was more applicable to split air-conditioned buildings. 8.6% of cooling energy could be conserved during summer in split air-conditioned buildings.