Air-conditioned Office Buildings Research Articles

Development of a rapid assessment tool for integrating thermal comfort in early design stage of energy-efficient office buildings

Comprehending and predicting energy performance of existing buildings and new constructions is crucial towards decarbonization. Instead of utilizing simulation software, multiple regression models are utilized to predict building energy consumption while ensuring indoor thermal comfort to speed up this process. However, previous predictive models prioritize reducing energy demand, with limited focus on thermal comfort. This study aims to support decision-making during retrofitting and new construction planning though developing a prediction model. An air-conditioned office building served as a reference building for simulation. 21 design parameters were analyzed, including aspects of weather, building envelope, internal loads, ventilation, and temperature settings. Stepwise regression results unveiled the crucial variables in the final model, with 8, 9, 13, and 6 variables remaining for peak cooling load, annual cooling load, overheating hours (WE), and Environmental Quality Index for thermal comfort (EQITC) in the perimeter zones, and 5, 6, 8, and 5 variables for the core zones, respectively. Furthermore, insights into the important variables regarding cooling load and thermal comfort were respectively provided. Weather- and envelope-related variables, such as cooling degree-days, global solar radiation, solar heat gain coefficient (SHGC), and U-value, have the highest impacts on cooling load. For thermal comfort, variables including temperature setpoint, occupant activity level, and factors related to window sunlight transmission performance, such as SHGC, window area ratio, and overhang projection ratio, proved to be influential. Overall, this study provided accurate models for assessing optimal strategies for energy efficiency and thermal comfort during the early design phases, advancing building performance practices.

A Review on Adaptive Thermal Comfort of Office Building for Energy-Saving Building Design

The thermal environment quality of office buildings has an important role because thermal comfort is directly related to human productivity. Thermal comfort conditions are influenced by climate, location, and the built environment; hence, comfort standards are required to assist building designers in creating a comfortable indoor environment for building occupants. In this context, the present study analyzes the adaptive thermal comfort studies conducted in office buildings from various countries. A large number of research articles selected from the Scopus database were considered for this study. Based on the analysis, outdoor climatic conditions have a greater influence on indoor thermal conditions in naturally ventilated than in air-conditioned office buildings. The temperature required for comfort is as low as 17.6 °C and as high as 31.2 °C in naturally ventilated buildings. An adaptive comfort equation for naturally ventilated and air-conditioned office buildings has also been proposed to predict the indoor comfort temperature. Various studies show that a substantial amount of energy can be saved by changing the set point and natural ventilation. Furthermore, this study successfully provides hearty evidence that there is a need for climate-specific standards on thermal comfort for energy-efficient design development because existing comfort standards might not be applicable to all climates.

Numerical study on the thermal performance of water flow window fed with air-conditioning condensate

A water flow window (WFW) fed with potable water is deemed as an effective system for absorbing incoming heat energy through the glazing area of a window. In this study, condensate formed in an air-conditioning (A/C) system is applied in a WFW for reducing heat gain and electricity consumption of a building. There is no need to consume any potable water. Through building energy simulations and numerical computation, this study unveils that a fully air-conditioned office building operating under a subtropical climate can produce condensate of sufficient flow rate to absorb heat energy from the glazing panes of an A/C condensate fed WFW system. The surface temperature of an outer glazing pane in an A/C condensate fed WFW system can be dropped by 16.3 °C when compared to a Low-e glass window. Moreover, an A/C condensate fed WFW can offer better thermal performance than a conventional WFW. When comparing to a Low-e glass case, an A/C condensate fed WFW facing four different orientations (N, E, S & W) can give reduction percentages of transmitted heat gain ranging from 57.2% to 63.5%. This A/C condensate fed WFW system shows a promising performance and has good potential for real application in commercial buildings.

Thermal adaptation of different set point temperature modes and energy saving potential in split air-conditioned office buildings during summer

The Chinese government issued a regulation that the cooling set point temperature (SPT) in office buildings cannot be lower than 26 °C. Therefore, SPTs were divided into different modes: SPT≥26 °C and SPT<26 °C. To study the human thermal adaptation of different SPT modes and determine the comfort and energy saving of the policy, a field test and subjective questionnaires were conducted in 21 split air-conditioned (SAC) office buildings during the warm season in the cold zone of China. We measured the environmental parameters and subjects' skin temperatures, and the subjective thermal responses were also investigated. The results showed that 45% of the air conditioner SPTs were less than 26 °C. In the high SPT mode, people's physiological adaptability to the warm environment was stronger, and subjects were more active in reducing clothes and increasing air velocity to improve thermal discomfort. Because the two modes had similar thermal histories and the same perceptual control, in the same SET ranges, no significant differences were found in thermal sensation, acceptability and comfort between the two SPT modes. The effects of long-term indoor thermal history on human thermal adaptation varied with the thermal exposure type, mode and intensity. From the analysis of thermal adaptation, the rationality of the policy was fully proved, and it was determined that SAC office buildings could save 26.4–35.2% of power energy consumption by reasonably increasing SPT in the cold zone. The results can enrich the thermal adaptation theory and provide a theoretical basis for the government's energy-saving policies in SAC office buildings.

Investigation on typical occupant behavior in air-conditioned office buildings for South China’s Pearl River Delta

The excessive simplification of occupant behavior is considered as the most important factor that affects the uncertainty of building performance simulation, thus affects the reliability and generalizability of simulation-based design and forecast. In this paper, occupant behavior in air-conditioned office buildings of the Pearl River Delta (PRD) region was investigated and defined. Copies of 873 questionnaires about the occupant behavior in air-conditioned office buildings in the PRD region were collected to study the relationship between indoor environment quality and adaptive behaviors. Eight typical office occupant schedules were defined via K-means clustering method. A probability prediction model of cooling temperature set-point was established by using the Ordinal Logistic Regression method. According to the different control modes of air conditioning, window, blind and lighting equipment, four types of typical behavior patterns were proposed using the K-prototype clustering method, which could be developed into 20 typical occupant behavior styles of office buildings in the PRD region.

Effectiveness of phase change material in improving the summer thermal performance of an office building under future climate conditions: An investigation study for the Moroccan Mediterranean climate zone

The rise in global temperature due to the climate change phenomenon would increase the severity of summer season in the future. The integration of phase change materials (PCM) into the building envelope has been considered as one of the most promising measures to improve the thermal performance of buildings. This paper aims at investigating the effectiveness of the PCM in improving summer thermal performance of buildings under the climate conditions of the next three decades. The moderate scenario RCP4.5 of the Intergovernmental Panel on Climate Change was used to simulate future climate conditions. The present study was conducted for two building case studies: free-running and air-conditioned office buildings located in the north of Morocco (Mediterranean climate with hot summer). The findings have disclosed that an appropriate selection of the PCM melting temperature could enhance the thermal performance by 9.87 % for the free-running building and by 20.5 % for the air-conditioned building case over the whole building lifespan (30 years). A decade-by-decade analysis showed that the effectiveness of the optimum selected PCM would slightly decline over time. The research involved an economic analysis of the air-conditioned building case study. The latter led to calculating the maximum allowable cost of the PCM installation to achieve a payback period within the lifespan of the building. The findings of the present work can be used as guidelines to design office buildings integrated with PCM in the Mediterranean region.

Hybrid Ventilation in an Air-Conditioned Office Building with a Multistory Atrium for Thermal Comfort: A Practical Case Study

This study involved a series of computational fluid dynamics simulations to evaluate the effectiveness of stack and displacement ventilation in providing better thermal comfort in an air-conditioned office building. To reduce energy consumption, the public area of the studied building is cooled by air from air-conditioned rooms with lower temperatures. The air, which is driven by buoyancy, then, flows outside through the multistory atrium. The simulation results indicated that displacement ventilation provides superior thermal comfort performance relative to stack ventilation. A design with a higher ceiling, a higher heat source and a lower inlet with cold air can substantially enhance the efficiency of displacement ventilation. Furthermore, handrails near the atrium play a crucial role because they help to retain cold air in the public space for a longer period, thereby contributing to a better predicted mean vote value.

Effect of spring grass fires on indoor air quality in air-conditioned office building

Open biomass burning (OBB) is a significant air pollution source, but it is still not clear to what extent OBB events affect indoor air quality [1]. Outdoor and indoor measurements of submicron particulate matter (PM1) were conducted on 25–29 April (2019) in the capital city Vilnius (Lithuania). Fires from neighbouring countries (Belarus, Ukraine and Russia) and in the vicinity of Vilnius broke out during the measurement campaign. The temporal evolution and transport of OBB plume were investigated by combining the air mass backward trajectory analysis and fire satellite observation (MODIS) database. Measurements of the PM1 chemical composition in real-time were performed using an aerosol chemical speciation monitor (ACSM) and an aethalometer. Organic matter was the clearly dominant component, accounting for &gt;70%, in both indoor and outdoor PM1. The air filtering system of the office building removed approximately up to 55% of PM1. Despite a significantly lower PM1 pollution level in the office, highly acidic indoor PM1 could have harmful effects on the human health. Source apportionment of particulate carbonaceous matter revealed a significant importance of OBB-related particles (average 56%) to indoor air.

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.

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.

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.

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.

The effectiveness of phase change materials in relation to summer thermal comfort in air-conditioned office buildings

The incorporation of Phase Change Materials (PCMs) into the opaque envelope of lightweight buildings is a good solution to compensate for the small thermal inertia, which usually entails pronounced overheating and high space cooling load in summer. However, the position and the thickness of the PCMs, as well as their thermal properties, must be attentively selected in order to ensure their effective operation. This paper shows a comprehensive investigation about the effectiveness of a commercial PCM, available in the form of mats, when installed within drywall partition systems in air-conditioned lightweight office buildings. The study is based on dynamic simulations carried out with EnergyPlus on a typical office building, with the aim to calculate the indoor operative temperature and the cooling load under thermostatic control. The performance for the base case (without PCM) is then compared with the case where PCM mats with various thickness and melting temperature are applied. The analysis is repeated in three different locations, ranging from Southern Europe (Rome, Italy), Continental Europe (Wien, Austria) and Northern Europe (London, UK). The results of the simulations highlight that in lightweight air-conditioned office buildings PCMs contribute to attenuate the inside surface temperature peak by around 0.5 °C, while also reducing the peak cooling load by 10% or even 15%, depending on the PCM thickness and on the outdoor climate. The conclusions may help designers to make the correct choices in terms of thickness of the PCMs, scheduled rate of nighttime ventilation and value of the peak melting temperature.

A Comprehensive Case Study of Climate Change Impacts on the Cooling Load in an Air-Conditioned Office Building in Malaysia

In an earlier paper [1], the authors had comprehensively reviewed the climate change impacts for commercial buildings and their technical services in the tropics, and it revealed that numerous studies have been conducted to assess the climate change impacts in terms of energy consumption of a building. However, only few studies were carried out in the tropical region. This study aims to project the future cooling load needed for the years of 2000, 2020, 2050 and 2080 in the tropics using the TRNSYS simulation. Based on the simulation results, the total cooling load increases as the temperature changes. The total maximum cooling loads required in the years of 2000, 2020, 2050 and 2080 are 297000 kJ/hr, 305000 kJ/hr, 321000 kJ/hr and 332000 kJ/hr, respectively. When compared with the year 2000, the maximum cooling load needed in the years of 2020, 2050 and 2080 increases by 2.96%, 8.08% and 11.7% respectively. Based on the simulation results, in the next 70 years, the efficiency and durability of the existing system is predicted to decrease.

Determining key variables influencing energy consumption in office buildings through cluster analysis of pre- and post-retrofit building data

This study aims to determine key building variables influencing energy consumption in air-conditioned office buildings. The study is based in Singapore which entails tropical climatic conditions. The analysis is based on assessment of several energy audit reports concerning pre- and post-retrofit data from 56 office buildings. A list of 14 building variables, extracted from these reports form the superset. These are systematically analyzed further to derive key variables influencing energy consumption and retrofitting decisions. For this purpose, a robust iterative process is developed utilizing k-means clustering. This process tests all combinations of the 14 variables against change in energy use intensity (EUI, measured as kWh/m2.year) for pre- and post-retrofit conditions. The results indicate that the best set of variables consists of: 1) gross floor area (GFA), 2) non-air-conditioning energy consumption, 3) average chiller plant efficiency, and 4) installed capacity of chillers. This information can be utilized to explore energy saving potential of office buildings that need to be retrofitted. The resultant clusters can also be used to benchmark buildings based on pre-retrofit conditions and energy saving potential.