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.     

地板辐射与置换通风空调系统运行参数

建立了基于EnergyPlus的地板辐射供冷加置换通风空调系统模型,模拟得到的室内温度和辐射地板所承担冷量与实验结果的误差小于±7%。在此模型基础上,改变送风参数和供水参数,得到置换通风供冷量、辐射地板供冷量、地板表面温度、室内空气平均温度、AUST温度等参数的变化规律。结合热舒适性模型,得到满足室内热舒适性(-0.5≤PMV≤0.5)条件下,置换通风的送风参数和辐射地板的供水参数范围,为复合系统设计和应用提供依据。     

一种适用于长江流域冬季的新型空调方式--辐射板+自然通风

在我国长江流域,冬季具有室外气温高,空气相对湿度极大的特点。在这种空调负荷较小的情况下,笔者认为完全可以采用一种新型的空调方式-“辐射 自然通风”,辐射方式的采用,降低了室内的空气温度,这样,使用自然通风也不会增加很多负荷,而自然通风的采用,会大大改善室内的空气品质。笔者从热负荷,舒适度,通风量,气流组织四个方面简单地论证了其可行性,并举例说明一个具体的系统方式及系统计算,分析了这种方式的优缺点及具体的适用范围,指出它对于城市建筑物中占很大比例的两类建筑-普通住宅及办公建筑是适用的。     

Thermal comfort assessment and application of radiant cooling: A case study

A field assessment of thermal comfort was conducted at Mehran University of Engineering and Technology, situated in the subtropical region of Pakistan. The results show that people of the area were feeling thermally comfortable at effective temperature of 29.85 °C (operative temperature 29.3 °C). A comparison of this neutral effective temperature was made with the neutral effective temperature determined from adaptive models. It is found that the neutral effective temperature determined during this study closely match that of the adaptive model based on either indoor temperature or both indoor and outdoor temperatures. The results of thermal acceptability assessment show that more than 80% of occupants were satisfied at an effective temperature of 32.5 °C, which is 6.5 °C above the upper boundary of ASHRAE thermal comfort zone. Naturally ventilated classrooms and air-conditioned offices of the University were simulated using TRNSYS system simulation program for two cases, once when conventional air-conditioning is used for providing thermal comfort, and when comfort is achieved through radiant cooling. In the simulation, cooling tower was used to regenerate cooling water for the radiant cooling system. Energy consumption was estimated from simulation of both cases. The results show that it is possible to achieve thermal comfort for most of the time of the year through the use of radiant cooling without a risk of condensation of moisture from air on the radiant cooling surfaces. A comparison of the energy consumption estimates show that savings of 80% is possible in case thermal comfort is achieved through radiant cooling instead of conventional air-conditioning.     

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.     

车站高大空间空调系统气流组织与热舒适性分析

兼顾人体热舒适和建筑节能的要求,对目前车站高大空间空调气流组织的数值模拟研究报道进行对比分析。分析结果显示,人们对高大空间建筑室内热舒适要求高于居住建筑和办公建筑;从满足人体热舒适角度出发,空调送风加地板辐射供冷方案适于夏季满员工况,地板辐射供热加空调加湿方案适用于冬季满员工况;高大空间的空调系统适宜采用上送上回的送风方式,其温度场和速度场均优于上送下回的空调送风方式;在高大空间内设置分层空调系统将在一定程度上降低空调能耗,且分层空调中送风速度对分层界面的位置影响较大,送风温差对高大空间分层空调的温度分布和流场分布有较大影响。     

Application of radiant cooling as a passive cooling option in hot humid climate

In hot and humid region, air-conditioning is increasingly used to attain thermal comfort. Air-conditioning is highly energy intensive and it is desirable to develop alternative low-energy means to achieve comfort. In a previous experimental investigation using a room equipped with radiant cooling panel, it was found that cooling water kept to 25 °C could be used to attain thermal comfort under some situations, while water at such temperature would not cause condensation of moisture from air on the panel. This paper reports results of a series of whole-year simulations using TRNSYS computer code on applications of radiant cooling to a room model that represents the actual experimental room. Admitting the inability of radiant cooling to accept latent load, chilled water at 10 °C was supplied to cooling coil to precool ventilation air while water cooled by cooling tower was used for radiant cooling in daytime application. For night-time, cooling water from cooling tower supplied for radiant cooling was found to be sufficient to achieve thermal comfort. Such applications are considered to be more amenable to residential houses.     

浅析太原市地板辐射供冷的应用

通过对太原市夏季室内空气温度和相对湿度的调查,结合地板辐射供冷系统的节能、舒适等特点,对太原市采用地板辐射供冷的可行性进行了分析,得出了地板辐射供冷用于太原市居住建筑夏季降温理论上可行的结论。     

办公建筑中吊顶辐射空调系统夏季工况性能测试研究

以办公建筑中实际使用的一套金属吊顶辐射板+新风的空调系统为研究对象,对夏季运行工况进行了测试研究。分别对比分析了高温和高湿气象条件下办公建筑室内的温湿度分布,比较了不同高度和不同位置处的温湿度场,在测试条件下,室内有良好的热舒适性。     

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.     

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.     

太阳辐射对多孔地板辐射采暖热舒适性的影响

本文针对含多孔型地板的室内低温地板辐射采暖的传热问题进行研究,采用有限元法求解控制方程,分析了太阳辐射对整个室内空间温度场和速度场的影响,探讨了不同时刻太阳辐射对室内温度场和速度场的影响规律。在保证室内空气温度和速度均达到规范中冬季供暖的舒适性设计值的前提下,再根据温度和速度计算出PMV和PPD的数值,获得不同时刻下所需求的地板辐射热流密度最佳范围。     

Application of the control methods for radiant floor cooling system in residential buildings

In applying radiant floor cooling, its control system must prevent the floor surface condensation in hot and humid weather conditions. With no additional dehumidification system, only the radiant floor cooling system prevents floor condensation. In this case, the effects of the control of the cooling system on the indoor conditions can be changed because of the thermal inertia of the systems. Also different types of control system can be composed according to the control methods, which can affect the construction cost in the design stage. Therefore, the control methods for the radiant cooling system with respect to floor surface condensation must be studied. Furthermore, because Korean people's lifestyle involves sitting on the floor, it is necessary to evaluate if a floor cooling system will influence the thermal comfort of the occupants. This study intends to clarify the control methods of the radiant floor cooling system and to analyze the control performance and applicability of each control method with regard to the floor surface condensation and comfort by computer simulations and experiments on the control methods of the radiant floor cooling system. The results of computer simulations and experiments show that water temperature control is better than water flow control with respect to temperature fluctuations in controlling room air temperature. To prevent floor surface condensation, the supply water temperature could be manipulated according to the dew point temperature in the most humid room, and in individual rooms, the water flow rate (on/off control) can be controlled. Also, the results of radiant cooling experiments show that the floor surface temperature remained above 21 °C, the temperature difference among surfaces remained below 6 °C, and the vertical air temperature difference remained below 1.9 °C, conforming well to comfort standards.     

Analysis on the impact of mean radiant temperature for the thermal comfort of underfloor air distribution systems

Despite the potentially significant advantages of underfloor air distribution (UFAD) systems, the shortcomings in fundamental understanding have impeded the use of UFAD systems. A study has been carried out on the thermal stratification which is crucial to system design, energy efficient operation and comfort performance of UFAD systems with an aim of examining impact of mean radiant temperature (MRT) on thermal comfort. Clear elucidation of the benefit of UFAD systems has been shown by comparing it to the traditional overhead air distribution systems. Keeping the same level of comfortable environment in the occupied zone, UFAD systems require much higher temperature of supply air, which represents significant energy savings. The benefit of UFAD systems is more pronounced at the condition of high ceiling height building. Considerable discrepancies in thermal comfort are found on the assumption that air temperature rather than MRT is used for the evaluation of PMV. However, more rigorous analysis including the full radiation simulation does not show any significant difference in PMV distribution. The result of the full radiation simulations requires much longer simulation time but gives similar air temperature distribution and only slightly higher averaged temperature than present approaches.     

日较差对居住建筑夜间通风室内热环境的影响

为了研究不同日较差情况下,夜间通风对室内热环境的影响,采用Energyplus软件对西安地区某公寓室内空气温度、平均辐射温度进行了模拟研究。结果表明,与无夜间通风相比,夜间通风时室内最高气温、最高平均辐射温度分别降低了0.32℃、0.34℃。室内空气温度、平均辐射温度随日较差的增大而降低,且机械通风时段比渗透通风时段降低显著。当日较差为4℃、6℃、8℃、10℃、12℃时,室内处于热舒适时段的比例分别为0,16.11%,28.06%,32.01%和34.86%。     

Effect of MRT variation on the energy consumption in a PMV-controlled office

This paper investigates the energy-saving potential of a thermal comfort-controlled office building. A comparative simulation study between the thermal comfort control and conventional thermostatic control is conducted on a building with glass façades where changes in the outdoor temperature and solar radiation over the course of a day affect radiant temperature and thus thermal comfort. To evaluate the thermal performance in the comfort-controlled space, a PMV-based thermal comfort controller, which adjusts the set-point room temperature of the existing thermostatic controller according to the changes of environmental variables, is assumed. The results demonstrate that thermal comfort competes with energy saving in a conventional thermostatic-controlled space. However, it is suggested that thermal comfort control provides consistent thermal comfort as well as energy-saving effect. The results show that energy consumption in a thermal comfort-controlled space is more affected by a change in the mean radiant temperature than in the conventional thermostatic-controlled space. The energy-saving potential in the thermal comfort-controlled space increases with low mean radiant temperature conditions. Although the energy-saving potential is reduced under high mean radiant temperature conditions, it is suggested that thermal comfort control is still a reasonable strategy to achieve both thermal comfort and energy savings simultaneously.     

冬冷夏热地区地板辐射采暖的现场测试和模拟研究

本文首先对地板辐射采暖房间进行现场测试,得到房间布点位置的温度和湿度,为数值模拟边界条件的设置提供依据.利用CFD对房间进行了数值模拟,得出了房间的温湿度分布、气流的运动状态和房间热舒适性评价指标（PMV-PPD）等,对房间的热舒适性进行了总体分析评价.     

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。     

Comfort and airflow evaluation in spaces equipped with mixing ventilation and cold radiant floor

In this work the comfort and airflow were evaluated for spaces equipped with mixing ventilation and cold radiant floor. In this study the coupling of an integral multi-nodal human thermal comfort model with a computational fluid dynamics model is developed. The coupling incorporates the predicted mean vote (PMV) index, for the heat exchange between the body and the environment, with the ventilation effectiveness to obtain the air distribution index (ADI) for the occupied spaces with non-uniform environments. The integral multi-nodal human thermal comfort model predicts the external skin and clothing surfaces temperatures and the thermal comfort level, while the computational fluid dynamics model evaluates the airflow around the occupants. The air distribution index, that was developed in the last years for uniform environments, has been extended and implemented for non-uniform thermal environments. The airflow inside a virtual chamber equipped with two occupants seated in a classroom desk, is promoted by a mixing ventilation system with supply air of 28 °C and by a cold radiant floor with a surface temperature of 19 °C. The mechanical mixing ventilation system uses a supply and an exhaust diffusers located above the head level on adjacent walls.     

A full-scale experimental set-up for assessing the energy performance of radiant wall and active chilled beam for cooling buildings

Full-scale experiments under both steady-state and dynamic conditions have been performed to compare the energy performance of a radiant wall and an active chilled beam. From these experiments, it has been observed that the radiant wall is a more secure and efficient way of removing heat from the test room than the active chilled beam. The energy saving, which can be estimated to around 10%, is due to increased ventilation losses. The asymmetry between air and radiant temperature, the air temperature gradient and the possible short-circuit between inlet and outlet play an equally important role in decreasing the cooling need of the radiant wall compared to the active chilled beam. It has also been observed that the type and repartition of heat load have an influence on the cooling demand. Regarding the comfort level, both terminals met the general requirements, except at high solar heat gains: overheating has been observed due to the absence of solar shading and the limited cooling capacity of the terminals. No local discomfort has been observed although some segments of the thermal manikin were slightly colder.