辐射顶板供冷性能测试方法及计算方法

辐射顶板供冷以其节能、良好的热舒适度、无吹风感、改善室内空气品质、降低峰值能耗、节省建筑空间等优点,已经被越来越多地选作空调末端。辐射顶板供冷市场需求不断增大同时对辐射顶板制冷量的测试提出了更高的要求。本文对两种顶板辐射供冷性能实验测试方法(DIN EN 14240标准和ANSI/ASHRAE 138标准)和两种辐射顶板制冷量的计算方法(ASHRAE手册和BS EN 1264标准)做了介绍,并对辐射板供冷量的两种实验测试方法和两种计算方法分别做了比较;在按EN 14240标准搭建的实验台中对金属辐射顶板进行了测试,将辐射板单位面积供冷量两种计算值与实验测试值进行了比较并分析了误差原因。     

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.     

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.     

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.     

Development of a radiant heating and cooling model for building energy simulation software

Efficient radiant heating and cooling systems are promising technologies in slashing energy bills and improving occupant thermal comfort in buildings with low-energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modeling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit-tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.     

Effect of humidity and small air movement on thermal comfort under a radiant cooling ceiling by subjective experiments

Radiant air-conditioning systems are expected to be more comfortable and superior energy-saving systems than convective air conditioning ones generally used. There are some studies on radiant cooling systems. However, they were seldom put to practical use because of dew point problem in Japan. The objective of this study is to investigate the thermal comfort of local parts of the body and the whole body, in particular, including the effects of humidity (45% rh, 65% rh, 85% rh) and small air movements, by subjective experiments under a radiant cooling system. The experiments have been performed by using radiant cooling panels in a climate chamber. Subjects were seated on a chair under the radiant cooling panels, and voted their thermal sensation and comfortable sensation. The following results were obtained. Even in the radiant cooling system, the influence of humidity and small air movement on thermal sensation votes of the whole body could be correctly estimated by using a standard new effective temperature (SET*) within one scale error of thermal sensation. Small air movement with the radiant cooling system had a possibility of improving the comfortable sensation votes in the radiant cooling.     

轻型电热地垫用于间歇采暖建筑适宜性研究

通过实验的方法研究了轻型电加热地面辐射采暖应用于间歇采暖建筑的适宜性,从舒适性、响应时间、能耗三方面对比了空调送风和电热地垫的特点：电热地垫加热房间下部所需时间更短,响应时间上更占优势;稳定后电热地垫采暖房间下部操作温度较上部高,空调送风采暖时情况则相反;定义用能有效性参数e衡量不同采暖方式对房间下部加热的效果,电热地垫采暖的e约为0．5左右且受加热功率的影响较小,而空调送风采暖的e比电热地垫低且随加热功率增大而减小。研究结果表明,电热地垫采暖房间垂直温度梯度小,对房间下部加热效果较空调送风要好,在一定程度上补偿了其制热效率低的不足。在室内环境控制18℃左右的情况下,权衡了COP和加热有效性,使用两种采暖方式用电量相近。     

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。     

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.     

Evaluation of thermal comfort using combined CFD and experimentation study in a test room equipped with a cooling ceiling

This paper reports a full-scale experimental campaign and a computational fluid dynamics (CFD) study of a radiant cooling ceiling installed in a test room, under controlled conditions. This research aims to use the results obtained from the two studies to analyze the indoor thermal comfort using the predicted mean vote (PMV). During the whole experimental tests the indoor humidity was kept at a level where the condensation risk was minimized and no condensation was detected on the chilled surface of the ceiling. Detailed experimental measurements on the air temperature distribution, surface temperature and globe temperature were realized for different cases where the cooling ceiling temperature varied from 16.9 to 18.9 °C. The boundary conditions necessary for the CFD study were obtained from the experimental data measurements. The results of the simulations were first validated with the data from the experiments and then the air velocity fields were investigated. It was found that in the ankle/feet zone the air velocity could pass 0.2 m/s but for the rest of the zones it took values less than 0.1 m/s. The obtained experimental results for different chilled ceiling temperatures showed that with a cooling ceiling the vertical temperature gradient is less than 1 °C/m, which corresponds to the standard recommendations. A comparison between globe temperature and the indoor air temperature showed a maximum difference of 0.8 °C being noticed. This paper also presents the radiosity method that was used to calculate the mean radiant temperature for different positions along different axes. The method was based on the calculation of the view factors and on the surface temperatures obtained from the experiments. PMV plots showed that the thermal comfort is achieved and is uniformly distributed within the test room.     

辐射吊顶的实验研究

描述了在实验小室内对辐射吊顶夏季供冷和冬季供暖的热工性能进行的测试,根据实验数据,计算了对流和辐射的综合效果。表明了在我国应用辐射吊顶可以满足供暖的要求,而且具有适宜的室内温度分布和人体舒适感。     

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。     

Hydronic radiant cooling — preliminary assessment

A significant amount of the electrical energy used to cool non-residential buildings equipped with all-air systems is drawn by the fans that transport the cool air through the thermal distribution system. Hydronic systems reduce the amount of air transported through the building by separating the tasks of ventilation and thermal conditioning. Due to the physical properties of water, hydronic systems can transport a given amount of thermal energy and use less than 5% of the otherwise necessary fan energy. This improvement alone significantly reduces the energy consumption and peak-power requirement of the air conditioning system. Radiant cooling has never penetrated the US markets significantly. The scope of this survey is to show the advantages of radiant cooling in combination with hydronic thermal distribution systems, as compared to the commonly-used all-air systems. The report describes the development, thermal comfort issues, and cooling performance of the hydronic systems. The peak-power requirement is also compared for hydronic systems and conventional all-air systems.     

Numerical and experimental study on the characteristics of radiant ceiling systems

ABSTRACT

Insufficient knowledge about characteristics of radiant systems has caused problems in the wider application of the radiant system, such as water condensation, bad thermal comfort, etc. In this study, key characteristics of a radiant system in terms of an inherent relationship between total heat flux and surface temperature were analysed. General models for describing such the relationship were developed and validated by elaborate experimental data. Operation limit region of the radiant system was identified and proposed by plotting key parameters in one surface, including supply water temperature, operative temperature panel surface temperature as well as total heat flux density. It was found that not all of the points within the operation limit region were suitable for practical application in order to avoid water condensation risk in cooling mode and large temperature differences in a vertical direction in heating mode. Evolved forms of operation limit regions for cooling and heating applications were put forward and their characteristics were addressed. The results reported in this paper could help manufacturers as well as engineers to better design, configure and regulate radiant systems for better product development and improved indoor thermal comfort.     

Review of modelling approaches for passive ceiling cooling systems

Passive ceiling cooling systems can lead to reduced cooling requirements, less fan energy and downsized ductwork, compared to conventional all-air systems. Additionally, radiant cooling of occupants allows for improved comfort while allowing for higher operating temperature, improving chiller efficiency. This paper presents a comprehensive review of current modelling approaches for passive ceiling cooling systems in order to document the state of the art and identify current research gaps and modelling development needs. Modelling methods are separated in three main categories, based on the domain of interest: component or “passive ceiling cooler” models, “indoor environment” models and “integrated” models. Simplified, detailed and empirical models are presented for each category. Different modelling approaches may be appropriate for different purposes (design vs. control analysis, and system simulation vs. whole building performance). The study summarizes useful findings, modelling limitations and applications, and presents needs for further modelling and simulation research, including passive chilled beams.     

冷却顶板空调系统中热环境分析

采用CFD软件,探讨了某通透大型玻璃幕墙建筑顶板冷辐射空调系统中的空调方案对室内热环境的影响,并进行了热舒适评价,研究表明：在不能安装辐射换热管系统的部分空间内,可以采用安装地板辐射管,并采取适当的通风方式带走室内余热以达到设计要求。     

Experimental investigation of a solar cooling absorption system operating without any backup system under tropical climate

In the last few years, thermal comfort research in summer has significantly increased the electricity consumption in buildings. This is mainly due to the use of conventional air conditioning systems operating with mechanical vapor compression. Solar cooling systems appear to be an interesting solution to solve this problem. But the understanding of this technology has to be refined through fundamental studies by developing numerical simulations. Moreover, the study of pilot plants is a practical method to gain experience by analyzing all the processes behind solar cooling technology. This paper presents an experimental study of a solar cooling absorption system implemented in Reunion Island, located in the southern hemisphere near the Capricorn Tropic. The particularity of this project is to achieve an effective cooling of classrooms, by a solar cooling system without any backup systems (hot or cold). The aim of this experimental study is to define the limits of the use of such system under tropical climate conditions without setting a set point temperature. Indoor thermal comfort is achieved by a self-stabilizing operating system that maintains the indoor temperature 6 °C below the outdoor temperature. During some critical periods of the year, when the outdoor temperature is very high and when the solar cooling system cannot provide enough refrigerating production, thermal comfort inside the building is achieved by using ceiling fans. Firstly we will present the installation and the choices we made in the control and design process. In the second part, an analysis of the experimental results will be presented.     

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。     

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。     

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.