Evaluation and comparison of thermal comfort of convective and radiant heating terminals in office buildings

Radiant heating systems are increasingly widely utilized in buildings for its energy conservation potential and enhanced thermal comfort. This paper presented an experiment to compare the thermal comfort performance of radiant heating system with convective heating system through objective measurement and subjective survey. Six physical parameters which might influence occupants' thermal satisfaction, including the Mean Radiant Temperature(MRT), humidity, air movement, A-weighted sound level,temperature fluctuation and vertical temperature difference, were measured. In addition, 97 subjects participated in the subjective survey part of this experiment, experiencing all the three environments heated by air source heat pump, radiator and floor heating.And they were asked to vote in six thermal comfort related aspects, i.e. thermal sensation, humidity, draught, local discomfort,overall thermal satisfaction and overall preferences, plus the acoustic environment, since the operation noise of heating system might lead to complains of the occupants. It was found that in continuous heating, no significant difference between radiant and convective heating system was observed in the Mean Radiant Temperature(MRT), indoor humidity and noise issue. Though radiant heating systems resulted in lower draught risk and less local discomfort complains in the feet region due to the less significant temperature fluctuations and vertical temperature gradients, radiant heating did not have significantly higher overall thermal satisfaction votes and was not significantly more preferred by occupants.     

Evaluating the low exergy of chilled water in a radiant cooling system

In this paper, in order to make guidelines for designing a low-energy radiant cooling system with an air-handling unit (AHU) for dehumidification, we investigated the impact of various air-conditioning parameters on the exergies of chilled water supplied to radiant panels and a cooling coil. The cooling load, thermal comfort index PMV, relative humidity, area of radiant panels, sensible heat factor (SHF), temperature and air-flow rate of supply air of the AHU, and presence/absence of total heat exchanger were considered. We used computational fluid dynamics (CFD) code in order to analyze the indoor air-flow and thermal environments, and added models for the calculation of thermal transfer to radiant panels and a cooling coil. Furthermore, a feedback control algorithm was introduced to calculate the surface radiant panel temperature, targeting the average PMV of the task area in an office room. As a result, the impact of various air-conditioning parameters on the exergies of chilled water were demonstrated quantitatively. As an example, by reducing the cooling load rate from 100% to 57% and 27%, the exergy of chilled water decreased by 47% and 67%, respectively.     

Thermal comfort and energy consumption of the radiant ceiling panel system.: Comparison with the conventional all-air system

The purpose of this study is to investigate the various characteristics of a radiant ceiling panel system and their practical application to office buildings. The radiant ceiling panel system and conventional air-conditioning system were compared in terms of thermal comfort, energy consumption, and cost. Thermal environment, along with human response, was tested by using a small meeting room equipped with radiant ceiling panels. The responses were collected by questionnaires given to the male subjects in the room. The experiment for the female subjects was conducted separately. Results show that the radiant ceiling panel system is capable of creating smaller vertical variation of air temperature and a more comfortable environment than conventional systems. When using a cooled ceiling, a small volume of supplied air creates a less draught environment, which reduced the discomfort of feeling cold in the lower part of the body. Numerical simulation of yearly energy consumption and cost estimation were conducted. Typical office rooms located on the 3rd, 4th, and 5th floor of a six-floor building in the Tokyo area were simulated. Since part of the sensible heat load is handled by radiant ceiling panels, the volume of supplied air can be reduced, leading to lower energy consumption for air transport. By using the radiant ceiling panel system in one of the three floors of the simulated building, energy consumption can be reduced by 10%. Estimated pay back time was from 1 to 17 years depending on the market price of the radiant ceiling panel.     

热湿工况下工位辐射空调的热舒适实验研究

为研究热湿工况下使用工位辐射空调的人体热舒适情况,在人工环境实验室内,通过改变环境背景温度来影响人体的热感觉,并采用热感觉投票(TSV)作为评价标准,重点研究了人体头部、躯干、上肢、下肢以及整体热感觉情况。实验结果表明,尽管背景环境参数超出舒适范围,但使用工位辐射空调能维持受试者的舒适状态,即背景温度稳定在28℃时,平均整体热感觉投票值低于+0.2;背景温度为30℃时,受试者热感觉仍能满足ASHRAE规范中规定的80%可接受范围要求。     

动态条件下人体对个体送风的热反应研究

实验研究了动态条件下不同背景温度、送风温差和送风速度时的人体热反应,并与稳态条件下的结果进行了比较;给出了动态条件下整体热感觉的预测公式.研究结果表明,动态送风可以显著降低使用者的整体热感觉,提高使用者对个体送风的评价和感知空气质量;但TSV与TCV不一致,发生了偏离.     

Predicted and reported thermal sensation in climate chambers,offices and homes

Past thermal comfort research has shown differences in the thermal sensation votes given in field and laboratory settings. However, such research tends to compare the votes of different groups of people in different environments rather than comparing the same people in each environment. Therefore, a two-phase study was conducted of the thermal comfort of 30 BRE employees in their home, in their office, and in a climate chamber. In the first phase each subject spent two 3 h sessions in each environment and the temperature was adjusted between sessions within the range 18–26°C. Data loggers were used to record the air and mean radiant temperature, air velocity and relative humidity; subjective ratings of thermal sensation were obtained using questionnaires. The subjects wore the same clothing in each session and were allowed to conduct only sedentary activities. The reported thermal sensation votes were compared with those predicted using ISO 7730. The observed neutral temperatures for each of the three environments differed by up to 2°C and were up to 1°C different to those predicted. This finding has implications for energy use. In the second phase, the subjects were studied in their home and office only. No restrictions were imposed on clothing, previous or current activities, or environmental conditions. The observed thermal sensation votes were very poorly correlated with those predicted and with operative temperature.     

Effects of turbulent air on human thermal sensations in a warm isothermal environment

Air movement can provide desirable cooling in "warm" conditions, but it can also cause discomfort. This study focuses on the effects of turbulent air movements on human thermal sensations through investigating the preferred air velocity within the temperature range of 26 degrees C and 30.5 degrees C at two relative humidity levels of 35% and 65%. Subjects in an environmental chamber were allowed to adjust air movement as they liked while answering a series of questions about their thermal comfort and draft sensation. The results show that operative temperature, turbulent intensity and relative humidity have significant effects on preferred velocities, and that there is a wide variation among subjects in their thermal comfort votes. Most subjects can achieve thermal comfort under the experimental conditions after adjusting the air velocity as they like, except at the relative high temperature of 30.5 degrees C. The results also indicate that turbulence may reduce draft risk in neutral-to-warm conditions. The annoying effect caused by the air pressure and its drying effect at higher velocities should not be ignored. A new model of Percentage Dissatisfied at Preferred Velocities (PDV) is presented to predict the percentage of feeling draft in warm isothermal conditions.     

地板辐射供冷-置换通风的实验研究

为了研究地板辐射供冷的热工性能,测试了北京地区不同室外气温下地板辐射供冷系统的运行工况,得到了该系统的制冷量,地板表面温度,室内温度场分布等参数,并且把单独地板辐射供冷系统的运行参数与地板辐射供冷-置换通风复合式系统进行了对比,提出了将地板辐射供冷与置换通风配合用于夏季空调室内供冷除湿的新型空调方式,置换通风系统在近地面处形成干燥空气层,可有效防止夏季热湿天气在地板表面出现结露现象,并且使这种新型空调系统条件下地面与室内的换热得到强化.通过理论分析和实验研究指出这是一种舒适、节能的空调方式.     

辐射供冷空调结露问题的研究现状及其对策

辐射供冷空调具有良好的热舒适度、改善室内空气品质、节能等优点。但在热湿地区,由于辐射板表面容易结露,使得它在市场上的应用受到极大限制。本文通过对辐射供冷空调系统结露问题研究现状的总结,提出了一种"疏导结露"的辐射板模型,为辐射供冷空调系统结露问题的研究提供了新思路。     

Combined comfort model of thermal comfort and air quality on buses in Hong Kong

Air-conditioning settings are important factors in controlling the comfort of passengers on buses. The local bus operators control in-bus air quality and thermal environment by conforming to the prescribed levels stated in published standards. As a result, the settings are merely adjusted to fulfill the standards, rather than to satisfy the passengers' thermal comfort and air quality. Such "standard-oriented" practices are not appropriate; the passengers' preferences and satisfaction should be emphasized instead. Thus a "comfort-oriented" philosophy should be implemented to achieve a comfortable in-bus commuting environment. In this study, the achievement of a comfortable in-bus environment was examined with emphasis on thermal comfort and air quality. Both the measurement of physical parameters and subjective questionnaire surveys were conducted to collect practical in-bus thermal and air parameters data, as well as subjective satisfaction and sensation votes from the passengers. By analyzing the correlation between the objective and subjective data, a combined comfort models were developed. The models helped in evaluating the percentage of dissatisfaction under various combinations of passengers' sensation votes towards thermal comfort and air quality. An effective approach integrated the combined comfort model, hardware and software systems and the bus air-conditioning system could effectively control the transient in-bus environment. By processing and analyzing the data from the continuous monitoring system with the combined comfort model, air-conditioning setting adjustment commands could be determined and delivered to the hardware. This system adjusted air-conditioning settings depending on real-time commands along the bus journey. Therefore, a comfortable in-bus air quality and thermal environment could be achieved and efficiently maintained along the bus journey despite dynamic outdoor influences. Moreover, this model can help optimize air-conditioning control by striking a beneficial balance between energy conservation and passengers' satisfaction level.     

Experimental and numerical analysis of air and radiant cooling systems in offices

This paper analyses office cooling systems based on all air mixing ventilation systems alone or coupled with radiant ceiling panels. This last solution may be effectively applied to retrofit all air systems that are no longer able to maintain a suitable thermal comfort in the indoor environment, for example in offices with high thermal loads.     

The moisture content distribution of a room with radiant ceiling cooling and wall-attached jet system

Radiant ceiling cooling is a comfortable and energy saving air conditioning system, but condensation on the panels limits its application. The moisture distribution of a radiant cooling room is one of the key factors affecting the condensation of radiant panels. This paper uses a simulation model validated by experimental data to investigate the influence of wall-attached jets on the moisture content distribution of a room with radiant cooling. The influence of diffuser types and air velocities on the moisture content distribution is analyzed in the pre-dehumidification stage. This paper also studies the moisture content distribution and dew point temperature variation of the attached air layer with the cooling system operating with and without pre-dehumidification. The results show that a linear diffuser has a better attach effect, and the moisture content distribution is more uniform. The time it takes to reduce the moisture content to the design value of different diffusers is similar, approximately 25 min. With increasing air velocity and decreasing linear diffuser length, the non-uniformity coefficient (NUC) of the moisture content distribution increases and the pre-dehumidification time becomes longer. When the radiant cooling system operates without pre-dehumidification, the attached layer moisture content is high at the beginning, which may cause condensation in the first 7 min. Pre-dehumidification can decrease the moisture content and dew point temperature and effectively prevent condensation.     

A field study of occupant thermal comfort and thermal environments with radiant slab cooling

This paper presents the findings of a field study of occupant thermal comfort and thermal environments with a radiant slab cooling system. The study combined field measurements and questionnaires based on the ASHRAE RP-921 project protocol. A total of 116 sets of data from 82 participants were collected in summer and winter. The results reveal that occupant whole-body thermal sensations with radiant cooling were consistent with the PMV model. The main advantage of radiant cooling for thermal comfort was found to be reduced local thermal discomfort with reduced vertical air temperature difference as well as reduced draft rate. The survey results revealed that 14–22% of participants in the study reported local cold discomfort in the arm–hand and the leg–foot regions. The results indicated that there may be lower limits on air speeds acceptable to occupants. Statistical analysis indicated that occupant thermal votes were free of significant correlation with personal, contextual and psychological factors. Suggestions to improve the questionnaire and the field survey process are offered.     

Thermal comfort, skin temperature distribution, and sensible heat loss distribution in the sitting posture in various asymmetric radiant fields

This study aimed at investigating the thermal comfort for the whole body as well as for certain local areas, skin temperatures, and sensible heat losses in various asymmetric radiant fields. Human subject experiments were conducted to assess the overall comfort sensation and local discomfort, and local skin temperatures were measured. Through thermal manikin experiments, we discovered a new method for the precise measurement of the local sensible heat loss in nonuniform thermal environments. The local sensible heat losses were measured by the use of a thermal manikin that had the same local skin temperatures as the human subjects. The experimental conditions consisted of the anterior–posterior, right–left, and up–down asymmetric thermal environments created by radiation panels. A total of 35 thermal environmental conditions were created ranging from 25.5 to 30.5 °C for air temperature, from 11.5 to 44.5 °C for surface temperature of radiation panels, from 40% RH to 50% RH for humidity, and less than 0.05 m/s for inlet air velocity to the climatic chamber. The local skin temperature changed depending on the environmental thermal nonuniformity, even if the mean skin temperature remained almost the same. It is essential to use the skin temperature distribution as well as mean skin temperature for expressing thermal comfort in nonuniform environments. The local sensible heat loss changed depending on the environmental thermal nonuniformity, even if the mean sensible heat loss remained almost the same. The relationship between the local skin temperature and local sensible heat loss cannot be depicted by a simple line; instead, it varies depending on the environmental thermal nonuniformity. The local heat discomfort in the head area was dependent on both the local skin temperature and local sensible heat loss. However, the local cold discomfort in the foot area was related only to the local skin temperature.     

新风除湿辅助毛细管辐射供冷房间流场模拟

建立毛细管辐射供冷系统传热模型。对分别采用单纯毛细管辐射供冷系统、新风除湿辅助毛细管辐射供冷系统的空调房间内的温度场、速度场进行模拟。采用新风除湿辅助毛细管辐射供冷系统,室内可达到更为舒适的温度范围,在工作区内无吹风感。     

均匀和不均匀热环境下热感觉、热可接受度和热舒适的关系

对30名受试者采用问卷调查的方式,研究了均匀热环境和不均匀热环境下人体全身热感觉、热可接受度和热舒适的关系。结果显示,在均匀热环境下,全身热感觉、热可接受度和热舒适具有较强的线性相关关系,可接受范围涵盖了(0,1.5)的热感觉投票和"舒适"与"稍有不适"标度范围内的热舒适投票;在不均匀热环境下,全身热可接受度与热舒适密切相关,而全身热感觉与热可接受度和热舒适出现分离,热感觉不均匀度是其原因。综合考虑全身热感觉和热感觉不均匀度的影响,提出了综合评价模型。经验证,该模型适用于全身热状态为中性偏热的均匀和不均匀热环境。     

Overall thermal sensation,acceptability and comfort

The relationships between overall thermal sensation, acceptability and comfort were studied experimentally under uniform and non-uniform conditions separately. Thirty subjects participated in the experiment and reported their local thermal sensation of each body part, overall thermal sensation, acceptability and comfort simultaneously. Sensation, acceptability and comfort were found to be correlated closely under uniform conditions and acceptable range ran from neutral to 1.5 (midpoint between ‘Slightly Warm’ and ‘Warm’) on thermal sensation scale and contained all comfortable and slightly uncomfortable votes on thermal comfort scale. Under non-uniform conditions overall thermal acceptability and comfort were correlated closely. However, overall thermal sensation was apart from the other two responses and non-uniformity of thermal sensation was found to be the reason for the breakage. Combining the effects of overall thermal sensation and non-uniformity of thermal sensation, a new thermal acceptability model was proposed and the model was testified to be applicable to uniform and non-uniform conditions over a wide range of whole body thermal state from neutral to warm.     

Experimentally-determined characteristics of radiant systems for office buildings

Radiant heating and cooling systems have significant energy-saving potential and are gaining popularity in commercial buildings. The main aim of the experimental study reported here was to characterize the behavior of radiant cooling systems in a typical office environment,including the effect of ceiling fans on stratification,the variation in comfort conditions from perimeter to core,control on operative temperature vs. air temperature and the effect of carpet on cooling capacity. The goal was to limit both the first cost and the perceived risk associated with such systems. Two types of radiant systems,the radiant ceiling panel( RCP) system and the radiant slab( RS) system,were investigated. The experiments were carried out in one of the test cells that constitute the FLEXLAB test facility at the Law rence Berkeley National Laboratory in March and April 2016. In total,tentest cases( five for RCP and five for RS) were performed,covering a range of operational conditions. In cooling mode,the air temperature stratification is relatively small in the RCP,with a maximum value of 1. 6 K. The observed stratification effect was significantly greater in the RS,tw ice as much as that in the RCP.The maximum increase in dry bulb temperature in the perimeter zone due to solar radiation was 1. 2 K for RCP and 0. 9 K for RS-too small to have a significant impact on thermal comfort. The use of ceiling fans was able to reduce any excess stratification and provide better indoor comfort,if required. The use of thin carpet requires a 1 K low er supply chilled water temperature to compensate for the added thermal resistance,somew hat reducing the opportunities for water-side free cooling and increasing the risk of condensation. In both systems,the difference betw een the room operative temperature and the room air temperature is small when the cooling loads are met by the radiant systems. This makes it possible to use the air temperature to control the radiant systems in lieu of the operative temperature,reducing both first cost and maintenance costs.     

Numerical Method for a Full Assessment of Indoor Thermal Comfort

Heat, mass and momentum transfer takes place simultaneously in ventilated rooms. For accurate predictions of the indoor environment, all the environmental parameters that influence these transport phenomena should be taken into consideration. This paper introduces a method for a full assessment of indoor thermal comfort using computational fluid dynamics in conjunction with comfort models. A computer program has been developed which can be used for predicting thermal comfort indices such as thermal sensation and draught risk. The sensitivity of predicted comfort indices to environmental parameters is analysed for a mechanically ventilated office. It was found that when the mean radiant temperature was considered uniform in the office, the error in the predicted percentage of dissatisfied (PPD) could be as high as 7.5%. The prediction became worse when the mean radiant temperature was taken to be the same as air temperature point by point in the space. Moreover, disregarding the variation of vapour pressure in the space resulted in an error in PPD of abour 4% near the source of moisture generation. The importance of evaluating both thermal sensation and draught risk is also examined. It is concluded that in spaces with little air movement only the thermal sensation is needed for evaluation of indoor thermal comfort whereas in spaces with air movement induced by mechanical vantilation or air-conditioning systems both thermal sensation and draught risk should be evaluated.     

Thermal performance of a personalized ventilation air terminal device at two different turbulence intensities

The performance of a circular perforated panel (CPP) air terminal device for a personalized ventilation (PV) system operating under two levels of turbulent intensity (Tu) was examined. The impact of Tu on spatial distribution of the cooling effect on the facial region and whole body were studied through experiments carried out in an indoor environment chamber using a breathing thermal manikin and 24 tropically acclimatized subjects. The PV system was adjusted to deliver treated outdoor air over a range of conditions, which were presented blind to the subjects in a balanced order. Over a 15-min exposure, subjects voted their thermal sensation experienced at the facial region and whole body. At each of the conditions, the near body flow field characteristics and heat loss rate on each of the 26 body segments of the manikin were measured. The results indicate that over the range of PV air supply volume studied, by controlling the temperature and velocity of PV air supply at 15 cm from the face, PV air supplied at lower Tu, when compared against that supplied at higher Tu:

• Achieved a larger range of velocities at the face.

• Achieved a greater cooling effect on the head region.

• Achieved a lower facial thermal sensation, which has potential draft risks (when facial_thermal sensation vote <−1).