Very low temperature radiant heating/cooling indoor end system for efficient use of renewable energies

Solar or solar-assisted space heating systems are becoming more and more popular. The solar energy utilization efficiency is high when the collector is coupled with indoor radiant heating suppliers, since in principle, lower supply temperature means lower demand temperature and then the system heat loss is less. A new type radiant end system is put forward for even lower supply temperature compared to the conventional radiant floor heating systems. A three dimensional model was established to investigate its energy supply capacities. Simulation results show that 50 W per meter length tube can be achieved with the medium temperature of 30 °C for heating and 15 °C for cooling. The predicted results agree well with the actual data from a demonstration building. Furthermore, it is demonstrated that a supply temperature of 22 °C in winter and of 17 °C in summer already met the indoor requirements. The new end system has good prospects for effective use of local renewable resources.     

地板辐射供冷系统热舒适性的分析与研究

通过对采用地板辐射供冷系统建筑中竖直方向温度分布的均匀性、水平方向温度分布的均匀性、室内空气相对湿度、室内平均辐射温度等影响人体舒适度的因素进行理论分析并用实验进行验证,得出各个影响因素的变化规律以及影响舒适度的本质所在。如果整个系统设计合理,地板辐射系统在夏季供冷是完全可以满足人体热舒适度的要求,尤其在气候干燥的北方、西北地区能很好地发挥其舒适、节能的巨大优势。     

Ceiling radiant cooling panel capacity enhanced by mixed convection in mechanically ventilated spaces

The main thrust of this research is to estimate the impact of the mixed convection effect on the cooling capacity of a ceiling radiant panel in mechanically ventilated spaces. To estimate panel cooling capacity enhancement caused by mixed convection, a verified analytical panel model was used. The simplified correlation for mixed convection heat transfer coefficient which can be easily adopted in panel cooling capacity estimation was derived from established mixed convection and natural convection correlations. It was found that the total cooling capacity of radiant panels can be enhanced in mixed convection situations by 5–35% under normal operating panel surface temperatures.     

基于辐射供冷的太阳能吸收式空调试验研究

对基于辐射供冷的太阳能吸收式空调系统进行了试验。该系统采用96 m2的U型管式真空管太阳能集热器驱动额定制冷量为8 kW的吸收式制冷机组,吸收式制冷机产生的冷冻水被输送到辐射吊顶中,为50 m2的实验室提供夏季空调。吸收式制冷机运行在夏季晴朗天气时,平均制冷量为4.5 kW。辅助独立除湿机组与辐射吊顶联合运行。试验房间的热舒适指标PMV为-0.29~0.32,可满足热舒适要求。     

Free cooling of a building using PCM heat storage integrated into the ventilation system

This article presents a study of the free cooling of a low-energy building using a latent-heat thermal energy storage (LHTES) device integrated into a mechanical ventilation system. The cylindrical LHTES device was filled with spheres of encapsulated RT20 paraffin, a phase-change material (PCM). A numerical model of the LHTES was developed to identify the parameters that have an influence on the LHTES’s thermal response, to determine the optimum phase-change temperature and to form the LHTES’s temperature-response function. The last of these defines the LHTES’s outlet-air temperature for a periodic variation of the inlet ambient-air temperature and the defined operating conditions. The temperature-response function was then integrated into the TRNSYS building thermal response model. Numerical simulations showed that a PCM with a melting temperature between 20 and 22 °C is the most suitable for free cooling in the case of a continental climate. The analyses of the temperatures in a low-energy building showed that free cooling with an LHTES is an effective cooling technique. Suitable thermal comfort conditions in the presented case-study building could be achieved using an LHTES with 6.4 kg of PCM per square metre of floor area.     

辐射供冷系统末端形式对比及发展研究

介绍几种辐射供冷空调的末端形式,比较冷吊顶、楼板辐射供冷、毛细管席的供冷能力、热舒适性、能耗及投资等方面的不同,并建议完善辐射供冷系统试验研究方法,着重进行拥有自主产权产品的制造工艺的研究。     

地板辐射与下送风复合式供冷系统运行特性实验研究

测量地板辐射与下送风复合式供冷系统运行过程中的室内空气温湿度、围护结构表面温度等室内环境参数,分析室内温湿度、热舒适性、系统换热量的变化规律,并对室内空气环境进行影响因素分析。实验结果表明:室内空气绝对湿度较室内空气温度达到稳定需要的时间更短;MRT(mean radian temperature)、OT(operation temperature)和PMV-PPD值在系统开启后第1.0 h减小速率最大,1.5 h后逐渐趋于稳定,此时,PMV约为0.49,PPD约为10%,在热舒适范围内;地板净辐射换热量、对流换热量和总换热量在系统开启后的1.5 h内递增,然后趋于稳定,此时,地板辐射换热量约为37 W/m~2,占总换热量的47%;室内空气温度和作用温度均随室外综合温度、室内发热量、供回水平均温度和送风温度的增加而增加,当室外综合温度较低或较高,或室内发热量较低,或供回水平均温度较低时,室内空气温度和作用温度变化梯度较小,室内空气温度和作用温度随送风温度增加而增加的速率近似呈线性。     

地板辐射式供暖的能耗分析

依据辐射供热室内辐射与对流综合作用的传热规律,计算和分析了地板辐射式采暖房间能耗的构成及影响因素,给出在相同舒适度条件下,几种常见的围护结构地板辐射式供暖房间的能耗随地表面加热温度的变化关系,并与相应的对流式采暧进行了对比。     

地板辐射采暖和风机盘管采暖室内热环境及能耗比较

对地板辐射和风机盘管两种采暖方式进行了实验研究和理论分析，提出了围护结构临界热阻临的概念，推导出了两个采暖系统的热舒适性随围护结构热阻和冷风渗透量波动的变化关系。实验验证了地板辐射采暖既改善了室内热环境又显示较好的节能效果。     

EnergyPlus软件在置换通风设计中的应用研究

介绍了EnergyPlus软件中的置换通风模型,采用EnergyPlus辅助某办公室置换通风系统设计,并采用CFD软件模拟了室内温度分布,结果表明,EnergyPlus可以精确地预测置换通风系统负荷,系统设计能满足热舒适要求。     

Heat transfer prediction for radiant floor heating/cooling systems using artificial neural network (ANN)

Radiant floor cooling and heating systems (RHC) are gaining popularity as compared with conventional space conditioning systems. An understanding of the heat transfer capacity of the radiant system is desirable to design a space conditioning system using RHC technology. In the present work, a simplified heat flux model for RHC is developed for both cooling and heating modes of operation. The Artificial Neural Network (ANN) technique is used for the development of the simplified model. Experimental data from literature covering a wide operating range of the RHC is considered for model development and validation. Operating parameters such as mass flow rate (m_f), heat resistance (R_s), mean temperature of water flowing through the pipe (T_m), and operative temperature (T_op) are considered independent variables influencing the heat flux (q_t). The neural network consists of four input layers, one output layer, and one hidden layer with a feed-forward-back-propagation algorithm. A study on the selection of the optimum number of neurons in the range of 1–9 for the hidden layer is also performed. On the basis of the performance parameters, namely, average-absolute-relative-deviation (AARD = 0.11283) percentage, mean-square-error (MSE = 0.00055), and the coefficient of determination (R² = 0.9984), a hidden layer is modeled with five neurons.     

顶板冷辐射加置换通风空调系统评价分析

介绍了顶板冷辐射与置换通风相结合的空调系统特点,分析了该系统在改善室内空气品质和满足人体的热舒适性方面的特点,评价了该系统的节能效果和经济性。     

Performance analysis on a building-integrated solar heating and cooling panel

The solar heating and nocturnal radiant cooling techniques are combined aiming at a novel solar heating and cooling panel (termed as SHCP) to be easily assembled as construction components for building roofing or envelope and also compatible with surroundings for its versatile coating colors, which can remove the double-skin mode from conventional solar equipment. SHCP has two functions for heating and cooling collecting. In this paper, the heating and cooling performances were analyzed in detail based on a small scale experimental system and effects of air gap and coatings were investigated. The results show that in sunny day of extreme cold January in Tianjin, China, the daily average heat-collecting efficiency is 39% with the maximum of 65%, while in sunny night during hot seasons the average cooling capacity can reach 87 W/m². When two different coatings were sprayed on SHCP without air gap, its heating and cooling performances were all analyzed, the daily average heat-collecting efficiency was 39% and 27% with the maximum points of 65% and 49%, respectively, and the cooling capacity was almost the same of 30 W/m² in January.     

吊顶辐射冷却塔供冷系统试验研究与性能分析

通过供冷试验及TRNSYS软件模拟研究了吊顶辐射冷却塔供冷系统的运行效果,分析了气象参数、部件结构等因素对系统供冷效果的影响,并与常规供冷系统全年的运行能耗进行对比。试验与理论分析结果表明,吊顶辐射冷却塔供冷系统的有效供冷量能够满足用户供冷需要,供冷房间温度稳定且分布均匀。冷却塔供冷效果与大气湿球温度、建筑内部负荷、热交换器结构等因素有关。辐射顶板末端与冷却塔供冷匹配性高,系统全年运行时数增加,应用于需全年供冷的建筑节能效果显著。     

Experimental performance of a thermoelectric ceiling cooling panel

An experiment has been performed to investigate the cooling performance of a thermoelectric ceiling cooling panel (TE‐CCP). The TE‐CCP was composed of 36 TE modules. The cold side of the TE modules was fixed to an aluminum ceiling panel to cool a test chamber of 4.5 m³ volume, while a copper heat exchanger with circulating cooling water at the hot side of the TE modules was used for heat release. Tests were conducted using various system parameters. It was found that the cooling performance of the system depended on the electrical supply, cooling water temperature and flow rate through the heat exchanger. A suitable condition occurred at 1.5 A of current flow with a corresponding cooling capacity of 289.4 W which gives the coefficient of performance (COP) of 0.75 with an average indoor temperature of 27°C. Using thermal comfort test data in literature for small air movements under radiant cooling ceilings, results from the experiments show that thermal comfort could be obtained with the TE‐CCP system. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance analysis of phase-change material storage unit for both heating and cooling of buildings

Utilisation of solar energy and the night ambient (cool) temperatures are the passive ways of heating and cooling of buildings. Intermittent and time-dependent nature of these sources makes thermal energy storage vital for efficient and continuous operation of these heating and cooling techniques. Latent heat thermal energy storage by phase-change materials (PCMs) is preferred over other storage techniques due to its high-energy storage density and isothermal storage process. The current study was aimed to evaluate the performance of the air-based PCM storage unit utilising solar energy and cool ambient night temperatures for comfort heating and cooling of a building in dry-cold and dry-hot climates. The performance of the studied PCM storage unit was maximised when the melting point of the PCM was ～29°C in summer and 21°C during winter season. The appropriate melting point was ～27.5°C for all-the-year-round performance. At lower melting points than 27.5°C, declination in the cooling capacity of the storage unit was more profound as compared to the improvement in the heating capacity. Also, it was concluded that the melting point of the PCM that provided maximum cooling during summer season could be used for winter heating also but not vice versa.     

Performance evaluation of a novel CCHP system integrated with MCFC,ISCC and LiBr refrigeration system

This paper proposes a novel combined cooling, heating, and power (CCHP) system integrated with molten carbonate fuel cell (MCFC), integrated solar gas-steam combined cycle (ISCC), and double-effect absorption lithium bromide refrigeration (DEALBR) system. According to the principle of energy cascade utilization, part of the high-temperature waste gas discharged by MCFC is led to the heat recovery steam generator (HRSG) for further waste heat utilization, and the other part of the high-temperature waste gas is led to the MCFC cathode to produce CO₃^2?, and solar energy is used to replace part of the heating load of a high-pressure economizer in HRSG. Aspen Plus software is used for modeling, and the effects of key factors on the system performances are analyzed and evaluated by using the exergy analysis method. The results show that the new CCHP system can produce 494.1 MW of electric power, 7557.09 kW of cooling load and 57,956.25 kW of heating load. Both the exergy efficiency and the energy efficiency of the new system are 61.69% and 61.64%, respectively. Comparing the research results of new system with similar systems, it is found that the new CCHP system has better ability to do work, lower CO₂ emission, and can meet the cooling load, heating load and electric power requirements of the user side at the same time.     

实用太阳能低温热水地板辐射采暖系统设计

针对我国能源消耗结构带来的环境问题,在现有太阳能资源和低温地板辐射采暖理论基础上,设计了家用小型太阳能低温热水地板辐射采暖系统。介绍了系统结构和工作原理,并以云南香格里拉气象条件为例对所设计的系统进行了实例计算,在采暖代表日,集热器与采暖房间的面积之比约为2:5。此系统具有较好的经济、节能、环保效益,具有良好的推广应用价值。     

A thermal analysis of a radiant floor heating system using SERI‐RES

Both intermittent and continuous heating are widely used for radiant floor heating systems in Korea, Intermittent heating circulates hot water according to a predefined schedule while the continuous heating controls water flow using thermostat control units. The standard version of SERI‐RES has been modified for the numerical simulation of the problem. Results show relatively large temperature swings in the case of intermittent heating with solar availability, although it costs less to implement due to its simplicity in design. On the other hand, the case of continuous heating would avoid such undesirable temperature fluctuations. These results are also verified by experimental evaluations. Copyright © 1999 John Wiley & Sons, Ltd.