A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

Comparative study of room temperature control in buildings with and without the use of PCM in walls

The concept of thermal energy storage in building gains a specific importance in the present energy scenario related to energy consumption and indoor thermal comfort. The material used to store the thermal energy which undergoes a phase change referred as PCM and it is considered as a possible solution for reducing energy consumption in the building by storing and releasing heat within a certain temperature range; it raises the building inertia and also stabilizes indoor air temperature fluctuations. The room temperature is controlled by imposing PCM inside the walls. An attempt has been made to compare room air temperature with and without the use of PCM inside the walls of constructed modular building unit. The PCM imposed modular building shows the reduced temperature fluctuations in room, the PCM absorbs and liberates excess heat which is gained from the outer side of the room and maintains constant inner room temperature. The PCM imposed walls of modular building unit have an ability to reduce 10–30% of heat load in comparison with the plain wall. The results showed that reduction in room temperature is about 2–4°C and it has been concluded that the PCM imposed modular building unit has more energy saving opportunities than normal modular building unit.     

Numerical model of a building with transparent insulation

An explicit finite difference simulation model is developed to study the thermal performance of an outdoor test-room with one transparently insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device and for air flow through the TI wall to the room. Simulation results indicate significant energy savings with practically no auxiliary heating required on cold sunny days in Montreal. However, appropriate control strategies are required to prevent overheating of the room and discomfort. Air flow through the TI wall and then into the room succeeds in lowering its room surface temperature to less than 31°C and reducing to zero the auxiliary heating required on any clear day. Blind control is based on several criteria, including outside temperature, room-facing surface temperature of TI wall (not to exceed 29°C) and room air temperature not to exceed a certain maximum.     

Performance evaluation of a radiant floor cooling system integrated with dehumidified ventilation

The radiant floor cooling system can be used as an alternative to all-air cooling systems, using the existing Ondol system (a radiant floor heating system) in Korea to save energy and maintain indoor thermal comfort. Unfortunately, a radiant floor cooling system may cause condensation on the floor surface under hot and humid conditions during the cooling season. In addition, the radiant floor system does not respond quickly to internal load changes due to the thermal storage effect of the concrete mass, which is usually present in radiant floor cooling systems.This study proposes a radiant floor cooling system integrated with dehumidified ventilation, which cools and dehumidifies the outdoor air entering through the cooling coil in the ventilator by lowering the dew-point temperature to prevent condensation on the floor surface. Furthermore, outdoor reset control was used to modulate the temperature of chilled water supplied to the radiant floor, and indoor temperature feedback control was then used to respond to the internal load changes.To evaluate the performance of the radiant floor cooling system integrated with dehumidified ventilation, both a physical experiment in a laboratory setting and TRNSYS simulation for an apartment in Korea have been conducted. As a result, it was found that the proposed system was not only able to solve the problem of condensation on a floor surface but also to control the indoor thermal environment within the acceptable range of comfort. Furthermore, the proposed system improved the responsiveness to internal load changes.     

On the non-periodic unsteady heat transfer through walls

Existing calculation methods of the transient heat flow through walls for air-conditioning applications, assume periodic outdoor conditions. Therefore, the effect of a temporary temperature rise on the indoor heat flow is usually neglected. In the present work an attempt is being made to model the related non-periodic transient problem. The method of approach is based on a finite-difference solution of the transient heat conduction equation within the wall. Outdoor air temperature deviation parameters are introduced, which characterize any temporary deviation of the outdoor air-temperature from periodicity. Indoor heat flow deviation characteristics are defined, which describe the deviation of the indoor heat flow from periodicity, provoked by the corresponding outdoor air temperature deviation. A parametric study is conducted, where the effects of the temperature deviation parameters on the indoor heat flow deviation characteristics are examined. It has been found that (a) the maximum heat flow deviation varies linearly with the mean temperature difference, (b) the restoration ratio is practically independent of the temperature amplitude difference, and (c) an increase in the wall thermal diffusivity results in a decrease of the maximum heat flow deviation. The practical importance of the present analysis is that it helps towards the estimation of peak loads under non-periodic outdoor conditions.     

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。     

A Two-Dimensional Numerical Analysis for Thermal Performance of an Intermittently Operated Radiant Floor Heating System in a Transient External Climatic Condition

Abstract

Building thermal inertia and operation control strategies have impacted on the thermal performance of a radiant floor heating system. This study conducts a two-dimensional numerical analysis of an intermittently operated radiant floor heating system using the Re-Normalization Group model with Discrete Ordinates Radiation model. A detailed numerical simulation setups and various analyses are provided, including grid independency analysis, initial condition, time step sizes and external boundary conditions. Three different weekend day intermittent operation strategies are investigated. The results showed that Case 3 designed with pre-heating of 20?h has better performance compared to Case 1 designed with pre-heating of 8?h and Case 2 designed with pre-heating of 14?h. The average indoor air temperature differences of approximate 2.1, 1.6 and 1.2 K are observed for Case 1, Case 2 and Case 3, respectively, when comparing two-time slot at 8:00am on Friday morning and Monday morning. This significantly highlights the effect of thermal inertia and the potential of energy saving due to the utilization of intermittent operation. Therefore, the current study presents numerical simulation potential in evaluating the radiant floor heating effects on indoor thermal environment, taking into account building thermal inertia and transient external climatic conditions.     

Investigation of thermal performance of a passive solar building with floor radiant heating

This paper presents a theoretical study of an integrated radiant floor heating–direct gain passive solar system. Thermal mass is utilized both for storage of auxiliary heating energy and direct solar gains incident on the floor. An explicit finite difference model is developed to accurately model nonlinear effects and auxiliary heating control. The numerical simulation model is employed to study the performance of a passive solar outdoor test-room with different amounts of thermal mass under various control strategies with constant and sinusoidal room thermostat setpoints. A satisfactory thermal mass is determined based on energy savings, reduction of room temperature swings, and prevention of floor surface overheating. Control of auxiliary heating based on a room effective (operative) temperature is shown to result in improved thermal comfort and higher utilization of passive solar gains as compared to room air temperature control.     

Energy efficiency and indoor thermal perception: a comparative study between radiant panel and portable convective heaters

This study investigates experimentally the thermal perception of indoor environment for evaluating the ability of radiant panel heaters to produce thermal comfort for space occupants as well as the energy consumption in comparison with conventional portable natural convective heaters. The thermal perception results show that, compared with conventional convection heater, a radiantly heated office room maintains a lower ambient air temperature while providing equal levels of thermal perception on the thermal dummy head as the convective heater and saves up to 39.1% of the energy consumption per day. However, for human subjects’ vote experiments, the results show that for an environmentally controlled test room at outdoor environment temperatures of 0°C and 5°C, using two radiant panel heaters with a total capacity of 580 W leads to a better comfort sensation than the conventional portable natural convective heater with a 670 W capacity, with an energy saving of about 13.4%. In addition, for an outdoor environment temperature of 10°C, using one radiant panel heater with a capacity of 290 W leads to a better comfort sensation than the conventional convection heater with a 670 W capacity, with an energy saving of about 56.7%. From the analytical results, it is found that distributing the radiant panel heater inside the office room, one on the wall facing the window and the other on the wall close to the window, provides the best operative temperature distribution within the room.     

Thermal analysis of a direct-gain room with shape-stabilized PCM plates

The thermal performance of a south-facing direct-gain room with shape-stabilized phase change material (SSPCM) plates has been analysed using an enthalpy model. Effects of the following factors on room air temperature are investigated: the thermophysical properties of the SSPCM (melting temperature, heat of fusion and thermal conductivity), inner surface convective heat transfer coefficient, location and thickness of the SSPCM plate, wall structure (external thermal insulation and wallboard material) etc. The results show that: (1) for the present conditions, the optimal melting temperature is about 20 °C and the heat of fusion should not be less than 90 kJ kg⁻¹; (2) it is the inner surface convection, rather than the internal conduction resistance of SSPCM, that limits the latent thermal storage; (3) the effect of PCM plates located at the inner surface of interior wall is superior to that of exterior wall (the south wall); (4) external thermal insulation of the exterior wall obviously influences the operating effect and period of the SSPCM plates and the indoor temperature in winter; (5) the SSPCM plates create a heavyweight response to lightweight constructions with an increase of the minimum room temperature at night by up to 3 °C for the case studied; (6) the SSPCM plates really absorb and store the solar energy during the daytime and discharge it later and improve the indoor thermal comfort degree at nighttime.     

Experimental and numerical study of unsteady non-periodic wall heat transfer under step,ramp and cosine temperature perturbations

An experimental and numerical study of the transient non-periodic wall heat transfer problem is presented. A computer-controlled indoor/outdoor environment simulation system produces any desired variation of the air temperature, thus allowing measurement of the dynamic thermal behaviour of any test wall under the desired boundary conditions. Measurements of the temperature field within the wall, of the heat flow and of the convection coefficients at the wall surfaces are performed during step, ramp and cosine perturbations of the outdoor air temperature. The measurements are in very good agreement with the numerical predictions obtained by a developed finite difference solution procedure. The results showed that in building heat transfer applications, for example in air conditioning, the usual assumption of periodic outdoor conditions may lead to considerable errors in case of a significant temporary deviation of the temperature from periodicity.     

多孔太阳墙式太阳能房间与普通房间热舒适性分析

通过对某多孔太阳墙式太阳能房间和普通房间的数值模拟,分析太阳墙板内空气的受热过程及流动情况,同时系统地比较两种建筑在工作区范围内的热舒适性。与普通采暖房间相比,在有多孔太阳墙送风的情况下,可将室外空气由-3℃加热到21℃,空气流动速度由0.1m/s提高到0.31m/s,提供44.6m3/h的新风量,一定程度上解决了冬季开窗换气所引起的室内热负荷及采暖负荷,论证了多孔太阳墙可使室内热舒适性明显增强的结论。     

A Comprehensive Evaluation on Energy,Economic and Environmental Performance of the Trombe Wall during the Heating Season

Trombe wall is a passive building energy saving technology that uses solar energy to reduce buildings' heating load and adjust indoor thermal environment. In recent years, much research has been done to increase the thermal efficiency of Trombe wall, but little is focused on the evaluation of Trombe wall from energy, economic and environmental aspects comprehensively. Based on the thermal performance calculation method in ISO 52016-2:2017(E), the authors proposed a concise method to evaluate the energy, economic and environmental performance of ventilated and non-ventilated Trombe walls during a heating season. Firstly, non-iteration calculation methods were introduced for the energy evaluation of Trombe wall and conventional wall during the heating season. Then the economic and environmental evaluation models were brought out according to the energy performance of Trombe wall. After that, a residential building was presented as the case building to evaluate Trombe walls' performance in five building climate zones of China. The calculation results showed that both heating degree days and solar radiation had significant impact on the energy saving effect of Trombe walls. In comparison with non-ventilated Trombe walls, ventilated ones displayed more obvious energy saving potential in all five climate regions, which can provide averagely 62% more heating for the room in the case study. Though the heating degree days of Guangzhou(hot-summer and warm-winter zone) was the smallest in the five zones, ventilated Trombe wall in the zone had the poorest economic performance due to the scarcest solar radiation during the heating season.     

冬季特朗贝墙内置卷帘对墙体热性能的影响

对大连地区某被动式太阳实验房进行实验研究,通过对玻璃幕墙内壁面温度、夹层内空气温度、特朗贝墙墙体温度等相关参数及室外气象参数等的实测,定量地分析了冬季夜间特朗贝墙采用卷帘保温的效果。并且通过有限空间自然对流换热理论计算分析,提出了更为合理的卷帘安装位置,最后根据围护结构响应因子BER指标,讨论了使用卷帘对提高室内热舒适性的影响。     

热系统内表面温度对空间有效温度场的影响

通过将平均辐射温度引入到建筑热舒适性传热计算中的方法简化建筑热舒适性和能耗的相互关系及其计算公式 ,进行平均辐射温度和房间的有效温度分布情况对热舒适性的影响分析。用这种方法来比较在不同热辐射换热和对流换热工况下变墙面温度时建筑内的热舒适性。理论分析和辐射、对流换热及其结合工况的热舒适性测试数据结果分析表明 ,热舒适性可以用平均辐射温度和有效温度来表征。用平均辐射温度和有效温度分析计算热建筑舒适性的方法 ,在优化建筑热系统的设计时 ,也有非常重要的参考价值。     

Heating and cooling of a building by double hollow concrete slab

This paper presents the thermal performance, in the heating and cooling of a building, of a double hollow concrete slab, one of whose faces is exposed to solar radiation and ambient air while the other is in contact with room air at constant temperature. A blackwened network of pipes is laid on the top surface and glazed sutiably. the flow rate of water / air through pipes is kept constant. It is seen that there is a time difference of 10-12 h between the maximum/ minimum of the thermal flux extering the room and the solair temperature for any flow rate. the heat flux inside the room is reduced appreciably for higher infiltration when there is no water flow to heat the building. the effect of a water film on the performance of the wall/roof has also been discussed and found to be more effective for the reduction of the heat flux coming into the building.     

Thermal and energy analysis of a Chinese kang

About 67 million Chinese kangs are still used by about 175 million people in China today. The kang utilizes biomass burning for space heating and hence reduces the use of commercial energy. However, the existing design of kangs is largely based on the accumulated experience of craftsmen, for lack of scientific studies and engineering design guidelines. Poor construction of kangs also leads to serious indoor air pollution. In this paper, a macroscopic smoke flow and heat transfer model of an elevated kang is integrated in a widely-used building energy analysis software in China-DeST, and the integrated software can be used for the thermal performance analysis of kang-integrated houses. A typical house with kangs in various villages of northern China is chosen as a case study. The annual performance of the kang under different insulations of building envelope and climatic conditions are discussed. Based on the simulation results, it is found that the thermal comfort requirement of the outside surface of the upper kang plate can be met by a proper construction of the kang and selection of the appropriate firing pattern. The better the insulation of the building envelope is or the better the room air tightness is, the greater the indoor air temperature rise and the greater the building heating load contribution of the kang. In the eight selected cities in northern China, the use of kang can meet 50%–80% of the house heating load.     

Effect of solar absorptivity and emissivity of exterior surfaces on the thermal performance of a building

The effects of the solar absorptivity and the thermal emissivity of exterior building surfaces on the indoor air temperature of a one room building are evaluated in terms of the discomfort index. The thermal performance of the building has been investigated for four different climates prevalent in India, namely, composite (New Delhi), hot and dry (Jodhpur), cold and humid (Srinagar), and cold and dry (Leh). The results confirm the common-sense view that the building surface should have low solar absorptivity and high thermal emissivity in hot climates and high solar absorptivity and low thermal emissivity in cold climates for indoor thermal comfort conditions.     

Properties and performance of advanced reflective paints to reduce the cooling loads in buildings and mitigate the heat island effect in urban areas

High reflective coatings and paints spread on the roof and walls can be very useful to reduce the cooling loads in buildings to ensure thermal comfort in the built environment. The solar reflectance of construction and cooling materials was measured with a spectrophotometer. A surface temperature monitoring campaign compared the thermal profiles of typical Italian construction materials with an innovative sustainable white paint, obtained with a special mixture of milk and vinegar of very high solar reflectance. Two building-integration cool-roof campaigns were run in the experimental building, Casa Intelligente of ENEA, in which indoor and outdoor air temperature and roof surface temperatures were monitored. This campaign, run in the summer of 2005 and 2006, allowed us to verify the influence of cool roofs to mitigate indoor air temperatures and to compare the behaviour of different cool-roof technologies.