A novel personalized thermal comfort control, responding to user sensation feedbacks

This paper presents a novel heating, ventilation, and air conditioning (HVAC) control architecture for office buildings, which uses the predicted mean vote (PMV) index of each occupant as feedback and offers them the opportunity to act on their own comfort level by signalling a possible thermal uncomfortable sensation to a personal user interface. A co-simulation EnergyPlus/Simulink has been used to test this new personalized and adaptive thermal comfort control in an office building for different seasons, up to two employees per office. Simulation results show that such a comfort control algorithm leads to sizeable energy savings as well as comfort improvement for each occupant. Moreover, after processing the order given by the user interface, the control algorithm makes the simulated thermal sensation match the actual thermal sensation of the occupant with a high accuracy, leading to a better consideration of his thermal comfort.     

Predictive controllers for thermal comfort optimization and energy savings

The present work is focused on the study of indoor thermal comfort control problem in buildings equipped with HVAC (heating, ventilation and air conditioning) systems. The occupants’ thermal comfort sensation is addressed here by the well-known comfort index known as PMV (predicted mean vote) and by a comfort zone defined in a psychrometric chart. In this context, different strategies for the control algorithms are proposed by using an only-one-actuator system that can be associated to a cooling and/or heating system. The first set of strategies is related to the thermal comfort optimization and the second one includes energy consumption minimization, while maintaining the indoor thermal comfort criterion at an adequate level. The methods are based on the model predictive control scheme and simulation results are presented for two case studies. The results validate the proposed methodology in terms of both thermal comfort and energy savings.     

Numerical investigation of local thermal discomfort in offices with displacement ventilation

Local thermal discomfort in offices with displacement ventilation is investigated using computational fluid dynamics. The standard κ-ϵ turbulence model is used for the prediction of indoor air flow patterns, temperature and moisture distributions, taking account of heat transfer by conduction, convection and radiation. The thermal comfort level and draught risk are predicted by incorporating Fanger's comfort equations in the airflow model. It has been found that for sedentary occupants with summer clothing common complaints of discomfort in offices ventilated with displacement systems result more often from an unsatisfactory thermal sensation level than from draught alone. It is shown that thermal discomfort in the displacement-ventilated offices can be avoided by optimizing the supply air velocity and temperature. It is also shown that optimal supply air conditions of a displacement system depend on the distance between the occupant and air diffuser.     

Thermal comfort analysis of a low temperature waste energy recovery system: SIECHP

The use of a recovery device is justified in terms of energy savings and environmental concerns. But it is clear that the use of a recovery system also has to lead to controlling indoor environmental quality, nowadays a priority concern. In this article, experimental research has been carried out whose aim is to study the thermal comfort provided by a combined recovery equipment (SIECHP), consisting of a ceramic semi-indirect evaporative cooler (SIEC) and a heat pipe device (HP) to recover energy at low temperature in air-conditioning systems. To characterize this device empirically in terms of thermal comfort (TC), Fanger's predicted mean vote (PMV), draught rate, and vertical air temperature difference were used in this study as the TC criteria.     

Coupled simulation of convicton,radiation, and HVAC control for attaining a given PMV value

A new computational fluid dynamics (CFD) simulation for designing indoor climates is presented in this study. It is coupled with a radiative heat transfer simulation and heating, ventilating, and air-conditioning (HVAC) control system in a room. This new method can feed back the outputs of the CFD to the input conditions for controlling the HVAC system, and includes a human model to evaluate the thermal environment. It can be used to analyze the conditions of the HVAC system (e.g. temperature of supply air, surface temperature of radiation panel, etc.) and the heating/cooling loads of different HVAC systems under the condition of the same human thermal sensation (e.g. PMV, operative temperature, etc.) To examine the performance of the new method, a thermal environment within a semi-enclosed space which opens into an atrium space is analyzed under steady-state conditions in the summer season. Using this method, the most energy efficient HVAC system can be chosen under the same PMV value. In this paper, two types of HVAC system are compared: one is a radiation-panel system and the other is an all-air cooling system. The radiation-panel cooling is found to be more energy efficient for cooling the semi-enclosed space in this study.     

Advanced fuzzy logic controllers design and evaluation for buildings’ occupants thermal–visual comfort and indoor air quality satisfaction

The aim of this paper is to present and evaluate control strategies for adjustment and preservation of air quality, thermal and visual comfort for buildings’ occupants while, simultaneously, energy consumption reduction is achieved. Fuzzy PID, fuzzy PD and adaptive fuzzy PD control methods are applied. The inputs to any controller are: the PMV index affecting thermal comfort, the CO₂ concentration affecting indoor air quality and the illuminance level affecting visual comfort. The adaptive fuzzy PD controller adapts the inputs and outputs scaling factors and is based on a second order reference model. More specifically, the scaling factors are modified according to a sigmoid type function, in such a way that the measured variable to be as closer as possible to the reference model. The adaptive fuzzy PD controller is compared to a non-adaptive fuzzy PD and to an ON–OFF one. The comparison criteria are the energy required and the controlled variables response. Both, energy consumption and variables responses are improved if the adaptive fuzzy PD type controller is used. The buildings’ response to the control signals has been simulated using MATLAB/SIMULINK.     

Indoor thermal environment evaluations and parametric analyses in naturally ventilated buildings in dry season using a field survey and PMVe-PPDe model

The PMV model predicts thermal sensation well in HVAC buildings while it predicts a warmer thermal sensation than the occupants actually feel in naturally ventilated buildings. For using PMV model to predict thermal sensation well in a naturally ventilated building, the extended PMV model (PMVe) including an expectancy factor (e) and PMV was proposed by Fanger. Besides, calculations of PMV are too complex to be applied in practice. To obtain simple and applicable correlations, taking Qujing of Yunnan province, China, as example, a dry season (6-month) field measurement was conducted in a naturally ventilated residential room. Based on the collected data, PMVe values were calculated by using Newton’s iterative method. It is shown that the PMVe values approximately vary from −1.3 to 0.20 and the indoor thermal environment is somewhat discomfortable on some cloudy or rainy days. Parameters relationships and indoor air temperature gradients (vertical and horizontal) were also studied by using linear regression technique and quadratic polynomial fit technique. Numerous correlations with high relativities have been developed. It is convenient to use these results to evaluate the indoor thermal environment in naturally ventilated buildings under similar climatic conditions.     

Field study of human thermal comfort and thermal adaptability during the summer and winter in Beijing

This study was conducted during the summer and winter in Beijing. Classrooms and offices in a university were used to conduct the survey. The respondents’ thermal sensation and thermal adaptability in both seasons were analyzed. During the study, indoor environmental parameters including air temperature, mean radiant temperature, relative humidity, and air velocity were measured. The respondents’ thermal sensation was determined by questionnaire.A relationship between indoor temperature and thermal sensation was found. In the summer study, the “scissors difference” between TSV and PMV was observed in the air-conditioned environments if the temperature was out of the neutral zone. People had higher tolerance in the hot environment than PMV predicted. During winter, the outdoor temperature had a prominent influence on thermal adaptability. The low outdoor temperature made people adapt to the cold environment. When the indoor temperature was heated to a high temperature by space heating facilities, respondents felt uncomfortable since their adaptability to the cold environment was nullified.Furthermore, the differences in thermal responses between respondents from North and South China showed that the different climates of people's native regions also affected their thermal comfort and adaptability.     

Draught,Radiant Temperature Asymmetry and Air Temperature – a Comparison between Measured and Estimated Thermal Parameters

Thermal comfort measurements were taken in 17 enterprises at 129 work sites in shops, stores and offices. The measurements included air temperature, air velocity, relative humidity and radiant temperature asymmetry according to ISO 7726 and ISO 7730 standards. The workers also answered a questionnaire dealing with thermal comfort. Predicted mean vote (PMV) and the percentages of workers complaining of draught (“percentage dissatisfied”, PD) were determined and compared with the workers' assessments of thermal conditions. The estimations of air temperature were always too low, and the estimated PMV indicated that the thermal environment was too warm. The calculated PMVs were usually lower than the estimated ones. Most of the workers complained of draught, even though, according to the PD index, fewer than 17% of the workers should have felt discomfort due to draught. The radiant temperature asymmetry was always small and did not explain complaints of draught on the basis of the reference value. Judged by the present reference values, and the measurement of the thermal environment, the workers overestimated the sensation of thermal discomfort.     

A simplified model of thermal comfort

The purpose of conditioning the air in a building is to provide a safe and comfortable environment for its occupants. Satisfaction with the environment is composed of many components, the most important of which is thermal comfort. The principal environmental factors that affect human comfort are air temperature, mean radiant temperature, humidity, and air speed; virtually all heating, ventilating and air-conditioning (HVAC) systems, however, are usually controlled only by an air-temperature set-point. Significant efficiency improvements could be achieved if HVAC systems responded to comfort levels rather than air-temperature levels. The purpose of this report is to present a simplified model of thermal comfort based on the original work of Fanger, who related thermal comfort to total thermal stress on the body. The simplified solutions allow the calculation of predicted mean vote (PMV) and effective temperature which (in the comfort zone) are linear in the air temperature and mean radiant temperature, and quadratic in the dew point, and which can be calculated without any iteration. In addition to the mathematical expressions, graphical solutions are presented.     

自然通风环境下的热舒适分析

鉴于自然通风环境下的PMV实际热舒适调查结果有较明显的偏差，热舒适研究领域提出了两种新的模型：PMV修正模型和适应模型。对这两种模型进行了分析，认为应对自然通风环境和空调稳态环境参数进行更细致的分析，以建立一种适用于自然通风环境的集总参数模型或评价指标。     

Extended predicted mean vote of thermal adaptations reinforced around thermal neutrality

Predicted mean vote (PMV) is a prevailing thermal comfort model adopted by thermal comfort standards. To extend its ability in explaining thermal adaptations, the PMV is multiplied by an extension factor. However, the original extended PMV (ePMV) cannot account for thermal adaptations around thermal neutrality, resulting in deviation around thermal neutrality, therefore, is unable to predict thermal sensation around thermal neutrality accurately. Given the unusual importance of thermal sensation around thermal neutrality for energy-efficient provision of indoor thermal comfort, this study modifies the ePMV to reinforce thermal adaptations around thermal neutrality by adding a thermal neutrality factor. The modified ePMV is quantified by explicitly expressing the extension factor and the thermal neutrality factor as functions of field datasets of the PMV, thermal sensation vote (TSV), and ambient temperature. The modified ePMV is validated to improve thermal sensation prediction effectively (by up to 73%), particularly for prediction around thermal neutrality with the TSV between −0.5 and 0.5, by mitigating deviation around thermal neutrality for different types of buildings under various climate conditions around the world. Moreover, the modified ePMV is explicitly formulated and, therefore, convenient for practical applications.     

不同气流组织下夏季空调室内热舒适环境模拟

基于模型和Fanger提出的热舒适性PMV评价指标,对三种不同气流组织条件下夏季室内热舒适环境进行了数值模拟,模拟结果给出了室内的速度、温度及舒适度PMV指标分布情况。研究结论为改善室内热舒适环境,舒适性空调系统的设计及节能控制提供了参考依据。     

Predictions of thermal comfort in stratified room environment

Studies of thermal comfort of occupants started in the early part of the 20th century to describe the comfort level in terms of environmental variables. Field studies have indicated that many of the complaints about unsatisfactory indoor environment can be attributed to the thermal environment. Hence, heating, ventilation, and air conditioning (HVAC) systems are used in buildings to create thermal environments that are capable of providing comfort to the occupants. Among different ventilation systems, displacement ventilation (DV) systems have become popular as more energy efficient room air distribution systems compared with the other more common forms of air distribution systems, such as mixing ventilation. However, local cold discomfort at the lower extremities due to vertical temperature gradient is often reported with DV systems. Although many studies are reported in the literature that compare the performance of the DV systems with the other more conventional types of ventilation systems, the performance of different displacement ventilation types in providing thermal comfort need further investigation. The aim of the current work is to compare the ventilation performance, as predicted by an advanced thermal comfort model, of three commonly used DV air terminal devices (ATDs) for room ventilation: a flat wall diffuser (ATD1), semi-cylindrical wall diffuser (ATD2) and floor swirl diffusers (ATD3). The CBE (Center for the Built Environment at Berkeley) comfort model has been implemented in this study to compare the thermal comfort provided by the three ATDs due to its good performance in non-uniform thermal environments. Based on the test conditions and the results obtained from the comfort model, the predicted occupant’s local sensations for the case of ATD2 were better than those for ATD1 and ATD3 and it showed better overall thermal sensation. Since the local comfort of the CBE model is a function of both local and overall thermal sensations, the predicted occupant’s local comfort values for ATD2 were better than those for ATD1 and ATD3 and consequently it provided better overall thermal comfort.     

Dynamic evaluation of thermal comfort environment of air-conditioned buildings

In this paper, based upon Fanger's thermal comfort concept, several concepts, which utilize computing results obtained from the large eddy simulation (LES), are put forward, such as thermal comfort index based on time-averaged parameters, instantaneous thermal index, time-averaged thermal comfort index and time-averaged thermal comfort index along walking routes. Also their discrepancies and calculation methods are discussed in the paper. Apart from these, we have calculated PD value as an example, whose results indicate that the distributions of four indices are obviously different. Therefore, it is suggested to distinguish different cases and select correspondingly thermal comfort evaluation indices while considering the question of thermal comfort.     

Real-time determination of optimal indoor-air condition for thermal comfort,air quality and efficient energy usage

For building, “surroundings” that effect on indoor-air condition change with respect to the time. Without proper determination of the desired indoor-air condition to heating, ventilating and air-conditioning (HVAC) system, it may not be feasible to provide simultaneously occupants with thermal comfort and acceptable air quality with efficient energy consumption all the time. This paper presents an alternative methodology of real-time determination of optimal indoor-air condition for HVAC system in order to achieve such total requirements. Predicted mean vote (PMV), CO₂ concentration and cooling/heating load are used as parameter indices for thermal comfort, indoor-air quality and energy consumption respectively. The performance index of the HVAC system is then defined by summation in terms of square errors between those actual parameter indices and their desired values. This performance index is to be systematically minimized by a gradient-based technique in order to yield optimal indoor-air condition for HVAC system. A case study was chosen in 24 h operating HVAC system of a single-storey building by determining indoor-air temperature, indoor-air humidity, indoor-air velocity, and air-ventilation rate. The experiment results show that the proposed methodology can be efficiently implemented in the real-time determination of indoor-air condition to HVAC system that maintains PMV and CO₂ concentration close to the desired levels with less energy consumption when compared to those from the conventional approach.     

Thermal comfort in residential buildings – Failure to predict by Standard model

A field study, conducted in 189 dwellings in winter and 205 dwellings in summer, included measurement of hygro-thermal conditions and documentation of occupant responses and behavior patterns. Both samples included both passive and actively space-conditioned dwellings. Predicted mean votes (PMV) computed using Fanger's model yielded significantly lower-than-reported thermal sensation (TS) values, especially for the winter heated and summer air-conditioned groups. The basic model assumption of a proportional relationship between thermal response and thermal load proved to be inadequate, with actual thermal comfort achieved at substantially lower loads than predicted. Survey results also refuted the model's second assumption that symmetrical responses in the negative and positive directions of the scale represent similar comfort levels. Results showed that the model's curve of predicted percentage of dissatisfied (PPD) substantially overestimated the actual percentage of dissatisfied within the partial group of respondents who voted TS > 0 in winter as well as within the partial group of respondents who voted TS < 0 in summer. Analyses of sensitivity to possible survey-related inaccuracy factors (metabolic rate, clothing thermal resistance) did not explain the systematic discrepancies. These discrepancies highlight the role of contextual variables (local climate, expectations, available control) in thermal adaptation in actual settings. Collected data was analyzed statistically to establish baseline data for local standardized thermal and energy calculations. A 90% satisfaction criterion yielded 19.5 °C and 26 °C as limit values for passive winter and summer design conditions, respectively, while during active conditioning periods, set-point temperatures of 21.5 °C and 23 °C should be assumed for winter and summer, respectively.     

室内气流组织和空气品质的数值研究

分析了气流分布性能的评价指标、热舒适性评价指标和室内空气品质的评价指标。将通风方式分为置换通风和混合通风,利用暖通空调专用模拟软件Airpak对室内气流进行模拟。模拟某小型会议室的温度、速度、CO2浓度、平均空气龄、PMV值和PPD值,并依据模拟结果分析不同气流组织下的室内空气品质、人体热舒适性和空调能耗情况。指出不同气流组织对室内空气品质、人体热舒适性和空调能耗的影响不同,置换通风和上侧送上回送风方式能得到较好的空气品质和有效的能量利用。     

A study on the thermal comfort in sleeping environments in the subtropics—Developing a thermal comfort model for sleeping environments

In the subtropics, air conditioning serves to maintain an appropriate indoor thermal environment not only in workplaces during daytime, but also at night for sleeping in bedrooms in residences or guestrooms in hotels. However, current practices in air conditioning, as well as the thermal comfort theories on which these practices are based, are primarily concerned with situations in which people are awake in workplaces at daytime. Therefore, these may not be directly applicable to air conditioning for sleeping environments. This paper, reports on a theoretical study on a thermal comfort model in sleeping environments. A comfort equation applicable to sleeping thermal environments was derived by introducing appropriate modifications to Fanger's comfort model. Comfort charts which were established by solving the comfort equation, and can be used for determining thermally neutral environmental conditions under a given bedding system have been developed. A related paper reports on an experimental study on measuring the total thermal insulation values of a wide range of bedding systems commonly used in the subtropics, which are an essential input to the comfort equation developed and reported in this paper.     

An experimental technique for thermal comfort comparison in a transient pull down

Various types of spaces are controlled for maintaining a desired comfort-condition level. Examples include buildings, automobiles, airplanes, and trains. The steady-state or longer-duration HVAC control is well established. However, situations are encountered where a rapid march towards a thermal space comfort level is required such as in the parked automobiles or in buildings where thermal mass is utilized for conserving energy. Many times design changes are proposed to improve the transient pull down in one zone but that could significantly affect the transient pull down in another zone. Further, in addition to the temperature, other parameters such as air velocity, mean radiant temperature, humidity need to be considered for assessing space comfort level. In our work we have developed an experimental technique for the multi-zone or comparative assessment of thermal comfort in a transient pull-down situations. First, the fan and system curves were developed for the competing designs. The predicted mean vote (PMV) methodology was employed for determining perceived comfort level. PMV is an ideal technique since it accounts for all of the above-mentioned parameters that are needed to assess space comfort level. Using an indoor climate analyzer, the transient PMV response at various locations was obtained. Conclusions are drawn to illustrate how this technique can be utilized for the simultaneous assessment of thermal comfort level in multiple zones, especially when transient pull downs are encountered.