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.     

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.     

水幕空调的应用分析

某五星级酒店利用人造瀑布形成的水池来改善室内热环境,分析比较了在热压通风、夜间风机运行、空调运行三种工况下水池中采用10～16℃不同温度的冷水改善室内热环境的效果。结果显示,利用风机和水池的低温冷水可以使酒店部分区域在不开启空调的情况下满足人体热舒适要求。建议设置水池温度为10℃,白天运行空调,夜间部分区域运行风机,部分区域运行空调,可以达到一定的节能效果。     

套室内人体热舒适的研究

借助于通用流场计算软件PHOENICS，在考虑了外界气温、太阳的热辐射条件，家具以及人员等室内微气候影响的情况下，预测了两室一厅套室内气流三维流场和温度场。得到了套室内气流的速度、温度和人体热舒适指数等参数的分布，并经过评定，该套室内的热环境达到了人体的舒适性要求。模拟计算结果对套室的设计及其空调系统的配置具有重要的参考价值，并为套室内人体热舒适的进一步研究和室内空气品质问题的研究奠定了基础。     

Multicriteria analysis of ventilation in summer period

This paper presents a multicriteria analysis of ventilation during summertime in Europe. Multicriteria analysis theories are used to determine the most suitable ventilation strategy on a university building, that is to say to ensure the best possible indoor air quality, thermal comfort of the occupants and the lower energy consumption in case of accelerated diurnal or nocturnal ventilation and/or air conditioning. After defining the possible actions, the criteria of quality regarding thermal comfort, indoor air quality and energy consumption are defined. The possible actions are then assessed relative to each of these three criteria and ranked from the best to the worst ones using two different multicriteria analysis methods.     

A global approach of indoor environment in an air-conditioned office room

This study presents a multi-criteria method used for analysing the quality of an air-conditioned indoor environment. Indoor air flow induced by an actual Heating Ventilation and Air Conditioning system was experimentally studied under various conditions. The attention was focused on thermal comfort, acoustical comfort and indoor air distribution by considering spatial statistic studies of comfort indices. The compounded electric power of fan, compressor and pumps was measured in order to get information about energy consumption. A first analysis of these parameters showed that indoor comfort cannot be described by a general law. Thus, to reach the objective of a global approach of comfort by a spatial statistical study of the various discomforts, a multi-criteria analysis based on ELECTRE II method adapted to the comfort of air-conditioned indoor environment was applied. In this way the operating rules for coherent air conditioning systems can be defined, with a requirement for quality of indoor environment.     

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.     

Personal heating: effectiveness and energy use

Buildings use approximately 40% of primary energy with most energy expended on the provision of a comfortable indoor climate. An extended range of indoor temperatures can significantly reduce the energy load. However, lower temperature set points for heating can cause thermal discomfort. Giving building occupants the option to warm themselves (e.g. a local source at their desk or workstation) can mitigate this discomfort by the provision of a personalized conditioning system. A model is presented to assess the performance of personalized heating and its impact on the whole building energy load. Researchers, designers and facility managers can use this model to compare performance and analyse energy savings. The total energy use of personalized heating is estimated by scaling its settings to the actual level of discomfort resulting from a lowered heating set point. This model is used to assess seven different personalized heating systems. Assessments reveal that personalized heating brings a remarkable energy-saving potential, while maintaining or even improving individually perceived thermal comfort. Assessments are based on an assumed linear relation between the power and level of increased thermal sensation. Future research in personalized conditioning systems should be directed towards the development of the full characteristics and specific settings.     

A field study of the thermal comfort in residential buildings in Harbin

This field study was performed during the winter of 2000–2001 in order to investigate the thermal environment and thermal comfort in residential buildings in Harbin, northeast of China. A total of 120 participants provided 120 sets of physical data and subjective questionnaires. An indoor climate analyzer and a thermal comfort meter made in Denmark were used to collect the measured parameters of the indoor environment, the predicted mean vote (PMV), and predicted percentage of dissatisfied (PPD). The conclusions are as follows: males are less sensitive to temperature variations than females; the neutral operative temperature of males is 1 °C lower than that of females; Harbin subjects are as sensitive to temperature variations as the Beijing and Tianjin subjects; the minimum value of PPD (7.5%) is similar to the Tianjin occupants; both the sensitivity and the minimum value of PPD are lower than those of the foreign field studies.     

Bayesian adaptive comfort temperature (BACT) of air-conditioning system in subtropical climate

Indoor thermal climate is an important issue affecting the health and productivity of building occupants. In the designing of commercial air-conditioning systems, it is believed that the conventional fixed temperature set point concept is limited because indoor comfort temperature depends on the business culture, such as the nature of activities and dress code of occupants, etc. Researchers have been interested in investigating adaptive temperature control for a realistic in-situ control of comfort. Unfortunately, those studies put great emphasis on energy saving opportunities and sometimes might result in thermal discomfort to individuals. This study argues that complaints of thermal discomfort from individuals, despite representing only a small portion of the population, should not be ignored and can be used to determine the temperature setting for a population in air-conditioned environment. In particular, findings of a new notion of Bayesian adaptive comfort temperature (BACT) in air-conditioned buildings in a humid and subtropical climate like Hong Kong are reported, and the adaptive interface relationship between occupants’ complaints of thermal discomfort and indoor air temperature is determined. This BACT algorithm is intended to optimise the acceptance of thermal comfort, as determined by physical measurements and subjective surveys.     

空调室内气流组织与建筑节能

论述了室内环境热舒适性的重要性,以及空调气流组织对室内环境热舒适性和建筑节能的影响。空调室内气流组织不合理不仅会导致人员热舒适性降低,而且还会影响工作效率和身心健康,同时,还会导致设备初投资和运行费用的增加。室内空调气流组织优化不仅要考虑室内人员环境的热舒适性,同时,要考虑降低空调运行能耗以实现建筑节能。     

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。     

KTV中央空调优化设计研究

应用Fluent对成都某KTV中央空调工程中包间1的室内气流组织进行数值模拟,并分析其速度场、温度场、PMV、PPD和空气龄,通过与传统KTV中央空调设计方案的对比,从节能、室内空气品质、热舒适度等方面指出本设计方案的合理性与经济性,从而为此类建筑的中央空调设计提供一定的参考依据。     

个体化微环境调节研究进展

指出由于室内人员在生理和心理反应、衣着量、活动强度和对室内温湿度与气流速度方面的偏好的差异，全空间空调方式不能同时为所有人提供可接受的热感觉和室内空气品质，而个体化调节方式可以在更大程度上满足人员的不同需要。综述了在人体周围空气流动、人体反应、个体调节系统方面的研究进展，讨论了个体化调节在减少能耗和提高生产率方面的优势。     

Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

空调系统运行性能ELECTRE多属性评价

提出了空调系统运行性能ELECTRE评价模型.性能评价准则考虑了运行能耗、热舒适性PMV和PPD、室内空气品质指标CO2浓度和TVOC浓度等5个指标.在TRNSYS(Transient system)空调系统仿真平台上,以7种不同运行工况为例,对空调系统运行性能进行多属性优劣排序.采用3种不同权重方案分别计算各方案的级别优先得分.结果表明,评价模型能够对不同运行工况下的性能进行多属性优劣排序,以选择出最优方案.不同的权重赋值对研究中的性能优劣排序结果影响不大.以后的研究应考虑诸如控制系统执行性能等更多指标的空调系统运行性能综合评价.     

A literatu rereview on the improvement strategies of passive design for the roofing system of the modern house in a hot and humid climate region

Increase of indoor temperature compared with outdoor temperature is amajor concern in modern house design. Occupants suffer from this uncomfortable condition because of over-heating indoor temperature. Poor passive design causes heat to be trapped, which influences the rise in indoor temperature. The upper part, which covers the area of the roof, is the most critical part of the house that is exposed to heat caused by high solar radiation and high emissivity levels. During daytime, the roof accumulates heat, which increases the indoor temperature and affects the comfort level of the occupants. To maintain the indoor temperature within the comfort level, most house designs usually depend on mechanical means by using fans or air conditioning systems. The dependence on amechanical ventilation system could lead to additional costs for itsinstallation, operation, and maintenance. Thus, this study concentrates on reviews on passive design and suggests recommendations for future developments. New proposals or strategies are proposed to improve the current passive design through ventilated and cool roof systems. It is possible to achieve the comfort level inside a house throughout the day by reducing the transmitted heat into the indoor environment and eliminating the internal hot air. These recommendations could become attractive strategies in providing a comfortable indoor temperature to the occupants as well as inminimizing energy consumption.     

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.     

空调房间的温度控制与节能

介绍了空调房间室内温度控制的途径和方法，分析了空调房间内空气计算参数温度对热舒适性和建筑能耗的影响，指出在一定温度和湿度的范围内，通过提高室内温度的途径来减少空调系统能耗的方法。