Flow patterns and thermal comfort in a room with panel,floor and wall heating

Thermal comfort aspects in a room vary with different space heating methods. The main focus in this study was how different heating systems and their position affect the indoor climate in an exhaust-ventilated office under Swedish winter conditions. The heat emitters used were a high and a medium–high temperature radiator, a floor heating system and large wall heating surfaces at low temperature. Computational fluid dynamics (CFD) simulations were used to investigate possible cold draught problems, differences in vertical temperature gradients, air speed levels and energy consumption. Two office rooms with different ventilation systems and heating needs were evaluated. Both systems had high air exchange rates and cold infiltration air.     

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.     

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.     

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.     

哈尔滨地区既有住宅冬季室内热环境研究及其优化设计

2013年对哈尔滨地区部分既有住宅室内温度测试发现:典型起居室室内平均温度16.2℃,点测90%室内不足18℃;遂采用正交实验法和全因素实验法对哈尔滨地区既有住宅就围护结构及采暖方式进行优化。对比Fluent模拟结果发现,当使用壁挂式采暖器时,采暖温度起主要影响作用,以EPS保温板为例:370 mm外墙选用90 mm厚保温层、PVC三玻窗、采暖器表面温度65℃。当采用表面温度23℃低温辐射供暖时,保温层对其影响较大,370 mm外墙选用100 mm厚保温层、20 mm双玻塑钢窗,当墙体厚度为490 mm时将保温层减少5 mm。     

燃气辐射采暖与热风采暖方式能耗的比较

采用CFD模拟软件,对应用传统的热风采暖方式的工业厂房进行模拟,得出厂房内的温度场分布、围护结构内表面温度及厂房的采暖能耗。分别对比应用对流采暖和辐射采暖的工业厂房,在工作区温度相同时的采暖能耗,以及在相同舒适度条件下,厂房的采暖能耗,并对结果进行分析。     

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.     

Vertical Temperature Profiles in Rooms Ventilated by Displacement: Full-Scale Measurement and Nodal Modelling

The vertical temperature profiles have been measured in a full-scale office room ventilated by displacement. Different wall radiative emissivities have been employed to study the effect of thermal radiation. The change of the vertical locations of the heat source does not affect the stationary front, but modifies the temperature profile. Two new nodal models, i.e. a four-node model and a multi-node model, are developed for predicting the temperature profile based on the flow and thermal characterization in the room. Agreement between the models and the experiments are very good. The calculated results are applied to show that the temperature profile is influenced considerably by the heat conduction through the walls and the thermal radiation between the wall surfaces. The models developed can be used for design purposes, as well as to supply the thermal boundary conditions in a CFD code.     

Heat emission from thermal skirting boards

The performance of three hydronic skirting heating systems was investigated. The main focus of the study was to ascertain whether thermal skirting boards served by low-temperature supply flow were able to suppress strong downdraught. The evaluation was made for a two-person office room with mechanical ventilation. Computational Fluid Dynamics (CFD) simulations and three different draught rating models were employed to predict the level of thermal discomfort inside the room. CFD results were validated against several analytical calculations and four sets of experimental data presented in previous studies. Numerical simulations showed that all three skirting heating arrangements were able to cover transmission and ventilation thermal losses of the office room. Horizontal and vertical heat distribution inside the room was uniform for all heating systems. CFD simulations also showed that thermal skirting boards served by 40 and 45 °C supply flow had difficulty in reducing the velocity of the downdraught at ankle level. Consequently the draught rating in this region was around or slightly above 15% for these cases. In contrast, heat-emitting skirting boards supplied by 55 °C hot water showed a better ability to suppress downdraught, and the proportion of people sensing draught at 0.1 m above the floor was low. The conclusion of this study was that thermal performance of hydronic skirting heaters with low-temperature water supply must be improved in order to counter strong downdraughts, in particular where such systems may be combined with heat pumps of other low-valued sustainable energy sources.     

Analysis of thermal comfort in an office room by varying the dimensions of the windows on adjacent walls using CFD: A case study based on numerical simulation

Ventilation provides a more comfortable thermal environment for occupants inside of buildings. The growing demand for electricity has encouraged research focused on natural ventilation. In this study, we analyze the thermal comfort in an office room with varied window opening dimensions using the computational fluid dynamics (CFD) technique. We created a 3-dimensional model room with windows on adjacent walls and an atmospheric zone. The flow equations were solved using the control volume method. Steady k-ɛ turbulence model and incompressible fluid flow of constant property have been considered, neglecting the variation due to temperature. We examined the effects of the window openings’ area and aspect ratio on thermal comfort. The CFD code was compared with the network model and its discrepancy value was less than 8%. Air temperatures along the various midlines of the room were predicted and compared for a range of window sizes. We identified the room areas occupied by the low temperature zone at various planes. Finally, we determined the predicted mean vote (PMV) contours at the midplane to identify the comfort zone. Areas other than the room corners and the areas nearest to the windowless walls are identified as the most comfort zone. Results from this study indicate the optimum window opening area and aspect ratio for maintaining thermal comfort in an office room.     

不同外部热源及气压对软包装锂离子电池热失控影响

开展不同低压环境(90、70、50 kPa)下的锂离子电池热失控实验,分别使用加热板、辐射环和辐射板搭建3个锂离子电池热失控实验平台.改变加热条件,观察软包装锂离子电池在低压下热失控火行为、温度变化、热释放速率、总释热量、耗氧量和CO2生成量的变化情况.压力的降低会使得锂离子电池在燃烧阶段氧气不充足,电池内部可燃物质与...     

Influence of the ventilation system on thermal comfort of the chilled panel system in heating mode

In heating mode, fresh air is still essential for a chilled panel system in order to ensure the indoor air quality. In this paper, a chilled ceiling panel system was designed and built in a typical office room. The thermal environment and thermal comfort in the room were fully measured and evaluated by using the Fanger's PMV-PPD model and the standard of ISO 7730 respectively, when room was heated in two modes, one of which is the chilled panel heating mode and the other of which is the combined heating mode of chilled panel and supply air. The research results indicate that in the combined mode, ceiling ventilation improves the general thermal comfort and reduces the risk of local discomfort. Under the condition of same general thermal comfort, the heating supply upper limit of chilled panel can be increased by 12.3% because of air mixing effect caused by introduction of air ventilation.     

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。     

Study on indoor thermal environment of office space controlled by cooling panel system using field measurement and the numerical simulation

The purpose of this study was to analyze the performance of a cooling panel system installed in the vertical plane with condensation (hereinafter a cooling panel system) using field measurement and coupled simulation of convection and radiation (CFD). Unlike an all-air cooling system, the cooling panel system could remove the cooling load by convection and radiation. Since the surface temperature of the cooling panel analyzed in this study can be controlled under the dew point, this system is expected to be energy-saving and dehumidifying. In the first step of this study, the indoor thermal environment of the office space, which is air-conditioned by a cooling panel system, was analyzed by field measurement and CFD. By comparing both results, the expected precision of CFD for an indoor space with a cooling panel was examined and the CFD method verified from a practical point of view. In the next step, the thermal environment of the model office space, which is cooled by three types of HVAC system (cooling panel system, all-air cooling system, and hybrid air cooling system composed of cooling panel and natural ventilation), was analyzed using CFD. Installing a human model in the office, the characteristics of heat transportation from the human model were also analyzed. The analysis deals with only sensible heat in this study. The operative temperature in the cooling panel system was lower than that in the all-air cooling system when each of the sensible cooling loads of all types of HVAC system was the same. In conclusion, the cooling panel system was found to be very energy-efficient.     

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.     

热水地板辐射供暖系统的设计与数值模拟

介绍了热水地板辐射供暖系统的设计。对采用热水地板辐射供暖系统的办公室的速度场、温度场进行了数值模拟,室内气流分布比较均匀,没有吹风感觉,竖直方向温度梯度较小,热舒适度较好。     

碰撞射流通风供暖房间热环境特征的研究

采用数值模拟方法研究了碰撞射流通风系统的供热特性,对供热房间内热环境特征以及热舒适性的分析结果表明：在典型送风参数工况下,碰撞射流供热房间内靠近送风口附近位置处存在垂直温度分层,空气温度随房间高度增加而降低,工作区热舒适情况良好。     

Design considerations with ventilation-radiators: Comparisons to traditional two-panel radiators

Performance of heat emitters in a room is affected by their interaction with the ventilation system. A radiator gives more heat output with increased air flow along its heat transferring surface, and with increased thermal difference to surrounding air. Radiator heat output and comfort temperatures in a small one-person office were studied using different positions for the ventilation air inlet. In two of the four test cases the air inlet was placed between radiator panels to form ventilation-radiator systems. Investigations were made by CFD (Computational Fluid Dynamics) simulations, and included visualisation of thermal comfort conditions, as well as radiator heat output comparisons. The room model was exhaust-ventilated, with an air exchange rate equal to what is recommended for Swedish offices (7 l s⁻¹ per person) and cold infiltration air (−5 °C) typical of a winter day in Stockholm.Results showed that under these conditions ventilation-radiators were able to create a more stable thermal climate than the traditional radiator ventilation arrangements. In addition, when using ventilation-radiators the desired thermal climate could be achieved with a radiator surface temperature as much as 7.8 °C lower. It was concluded that in exhaust-ventilated office rooms, ventilation-radiators can provide energy and environmental savings.     

电热膜供暖的热舒适性分析

通过对低温辐射电热膜供暖系统的温度场和热舒适性的分析，指出目前在我国住宅中采用的单片功率为20W的电热膜，会导致室内PMV过大，造成温度过高而使人感到不舒适。建议开发单片功率较小的电热膜用于顶棚敷设。     

Personalized ventilation: evaluation of different air terminal devices

Personalized ventilation (PV) aims to provide clean air to the breathing zone of occupants. Its performance depends to a large extent on the supply air terminal device (ATD). Five different ATDs were developed, tested and compared. A typical office workplace consisting of a desk with mounted ATDs was simulated in a climate chamber. A breathing thermal manikin was used to simulate a human being. Experiments at room air temperatures of 26 and 20 °C and personalized air temperatures of 20 °C supplied from the ATDs were performed. The flow rate of personalized air was changed from less than 5 up to 23 l/s. Tracer gas was used to identify the amount of personalized air inhaled by the manikin as well as the amount of exhaled air re-inhaled. The heat loss from the body segments of the thermal manikin was measured and used to calculate the equivalent temperature for the whole body as well as segments of the body. An index, personal exposure effectiveness, was used to assess the performance of ATDs in regard to quality of the air inhaled by the manikin. The personal exposure effectiveness increased with the increase of the airflow rate from the ATD to a constant maximum value. A further increase of the airflow rate had no impact on the personal exposure effectiveness. Under both isothermal and non-isothermal conditions the highest personal exposure effectiveness of 0.6 was achieved by a vertical desk grill followed by an ATD designed as a movable panel. The ATDs tested performed differently in regard to the inhaled air temperature used as another air quality indicator, as well as in regard to the equivalent temperature. The results suggest that PV may decrease significantly the number of occupants dissatisfied with the air quality. However, an ATD that will ensure more efficient distribution and less mixing of the personalized air with the polluted room air needs to be developed.